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Distribution and coalification patterns in Canadian bituminous and anthracite coals
International Journal of Coal Geology, 13 (1989) 207-260
207
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
D i s t r i b u t i o n and c o a l i f i c a t i o n p a t t e r n s in C a n a d i a n b i t u m i n o u s and a n t h r a c i t e coals* P E T E R A. HACQUEBARD1 and ALEXANDER R. CAMERON 2
'Atlantic Geoscience Centre, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, N.S. B2 Y 4A2, Canada 2Institute of Sedimentary and Petroleum Geology, 3303-33rd Street, IV. W., Calgary, Alta. T2L 2A7, Canada (Received April 28, 1988; revised and accepted November 22, 1988)
ABSTRACT Hacquebard, P.A. and Cameron, A.R., 1989. Distribution and coalification patterns in Canadian bituminous and anthracite coals. In: P.C. Lyons and B. Alpern (Editors), Coal: Classification, Coalification, Mineralogy, Trace-element Chemistry, and Oil and Gas Potential. Int. J. Coal Geol., 13: 207-260. Canadian resources of bituminous and anthracite coal occur in six of ten provinces and in the Yukon and Northwest Territories. These higher-rank coals are found in 12 of the 16 coal-bearing basins within Canada. For some of these basins, knowledge of rank and coalification patterns is limited; in others, it is extensive. Coalification patterns were examined in detail for two areas: the southern end of the Canadian Rocky Mountain coal belt which is underlain by the coal-bearing Kootenay Group and the Maritimes Basin which is underlain by several coal-bearing formations of Pennsylvanian (Late Carboniferous) age. In the southern Rockies, reflectances on coal range from 0.61 to 2.65% R . . . . . which represent high-volatile B bituminous coal to semianthracite. In general, there is an increase in rank from SE to NW and from NE to SW. Superimposed on this pattern are several anomalies. At several locations, ranks change rapidly over short distances. An example is in the Mount Allan syncline, where the reflectances in the Kootenay section on the SW vertical limb range from 0.68 to 0.94% R . . . . in contrast to a range of 1.30-2.49% R . . . . for a comparable section on the NE upright limb. This variation occurs over a distance of about 3 km. Multiple intersections of Kootenay strata in oil wells at the south end of the area show low reflectances (0.76% R . . . . ) at depths of about 3800 m with no change in the shallower Kootenay repeats, whereas wells farther north show higher reflectances and increase with depth. Different burial depths, the influence of thick thrust plates, different paleogeothermal gradients and ground-water movements, all likely have played a part in generating these coalification patterns. A significant part of the coalification in the Kootenay Group appears to have been postdeformational. The rank of the coals in the various subbasins of the Maritimes Basin is nearly all bituminous. Evidence indicates that most of the coalification is postdeformational. Rank within a given coal bed generally increases with increase in depth of present-day burial and the pattern seems to be generally true for most of the coal fields studied. The average postdeformational component of total coalification has been calculated to be 72%. The most important coal field in the Maritimes Basin is the Sydney coal field. Here ranks have been shown to increase from NW to SE and from * Geological Survey of Canada Contribution No. 17088. 0166-5162/89/$03.50
© 1989 Elsevier Science Publishers B.V.
208 SW to NE, the latter direction following the downdip structure of the field. Coalification gradients for the Sydney field range from 0.052 to 0.088 Ro maJ100 m, reflecting different paleogeothermal gradients. In New Brunswick, local rank increases to anthracite are believed to be related to igneous activities. Reflectance measurements have been used to interpret stratigraphy and structure in several fields and even to trace the origin of coaly fragments obtained from deep-sea drilling near Bermuda.
INTRODUCTION C a n a d i a n coals o f b i t u m i n o u s to a n t h r a c i t e r a n k s o c c u r in r o c k s u c c e s s i o n s r a n g i n g f r o m D e v o n i a n to T e r t i a r y in age. G e o g r a p h i c a l l y , t h e y are f o u n d in six of C a n a d a ' s t e n p r o v i n c e s plus t h e Y u k o n a n d N o r t h w e s t T e r r i t o r i e s . Figu r e I s h o w s t h e a r e a l d i s t r i b u t i o n of C a n a d a ' s c o a l - b e a r i n g b a s i n s , a n d in Figure 2 t h o s e b a s i n s c o n t a i n i n g b i t u m i n o u s a n d a n t h r a c i t e coal are identified. R a n k d i s t r i b u t i o n w i t h i n t h e b a s i n s s h o w n on Figure 2 will be d i s c u s s e d briefly, followed b y m o r e d e t a i l e d t r e a t m e n t of c o a l i f i c a t i o n p a t t e r n s in t w o of t h e s e PRINCIPAL COAL-BEARING BASINS 1 N A N A I M O BASIN 2 OUEEN C H A R L O T T E B A S I N 3 BOWSEB B A S I N 4 SKEENA BASIN S BOWRON RIVER B A S I N 6 TERTIARY INTERMONTANE BASINS 7 WESTERN C A N A D A S E D I M E N T A R Y BASIN 8 MOOSE RIVER BASIN 9 M A R I T I M E BASIN 10 ST. ELIAS TROUGH 1 1 WHITEHORSE TROUGH 12 T I N T I N A TRENCH 13 BONNET PLUME B A S I N 14 B B A C K E T T BASIN
16 ARCTIC OCEAN
\
i s NORTHERN YOKON lS ARCT,C BASIN PRECAMSRIAN ,.-.,-,-1
~
s.,E.o
S^S,N AREA
A T L A N TIC ocEAN
HUDSON BAY
STATE-c;
~
i . - -~ " ~ . ~ -
-
kilometers
O I
500 I
I
Fig. 1. The principal coal-bearing basins of Canada (modified from Smith, 1989).
209
Fig. 2. Geographic distribution of bituminous and anthracitic coal in Canada {see Fig. I for basin identification).
areas, namely the Atlantic Provinces and the southern part of the Canadian Rocky Mountains and Foothills belt. R a n k terminology used in this paper will be that of the A S T M classification [American Society for Testing and Materials ( A S T M ) , 1979 ]. The most abundant resources of bituminous and anthracitic coals in Canada are found in several sequences of Upper J u r a s s i c / L o w e r Cretaceous strata preserved in a long narrow belt within the Rocky Mountains and Foothills of Alberta and British Columbia. This belt is on the western edge of the Western Canada Basin. The next most abundant resources of coal of these ranks occur in a number of Pennsylvanian (Upper Carboniferous ) coal fields in the Atlantic provinces of Nova Scotia, New Brunswick and Newfoundland. Large resources of high-rank coal, particularly anthracite, are believed to be present in the Groundhog coal field within the Bowser Basin of northwestern British Columbia. Total coal resources for Canada are summarized in Table 1 and presented in more detail in Figure 3. Table 2 is a summary of rank, chemical and petrographic data, for those basins that contain bituminous and anthracite coal, together with identification of the coal-bearing formations. Basins 8, 10,
210 TABLE 1 Summary of Canada's coal resources. Rank ''2
SA/AN LV/AN~ LV MV/LV MV HV/MV HV HV/SUB SUB LIG/SUB LIG
Resources of immediate interest 3
Resources of future interest 4
Measured
Indicated
Inferred
300 420 200 2890 240 1460 710 12230 450 1500
600 300 110 4700 160 1400 370 5130 320 2710
8O 1470 , 1320 370 13310 660 3600 1250 17580 2320 3570
4590 4840 2110
156790 77730
1Data (in megatonnes) from Smith (1989). 2LIG-- lignite, SUB -- subbituminous, HV-- high-volatile bituminous coal, MV = medium-volatile bituminous coal, LV = low-volatile bituminous coal, SA = semianthracite, AN-- anthracite. 3,'Resources of immediate interest are contained in coal seams that, because of favorable combinations of thickness, depth, quality and location, are considered to be of immediate interest for possible exploitation" (Hughes et al., 1989). Measured, Indicated and Inferred refer to decreasing levels of assurance for quantities estimated (see Bielenstein et al., 1979). 4"Resources of future interest are contained in seams that, because of less favorable combinations of thickness, depth, quality and location, are not of immediate interest for possible exploitation, but which may become of interest in the foreseeable future with some changes in economics and/ or production technologies" (Hughes et al., 1989). ~Most of the coal quantities reported in this category pertain to the Groundhog coalfield where anthracite is the predominant rank. 13, 14 (Fig. 1) c o n t a i n o n l y lignite a n d s u b b i t u m i n o u s coal a n d will n o t be discussed f u r t h e r in t h e c o n t e x t of this paper. F o r an overall p i c t u r e of t h e geology of C a n a d a ' s coal b a s i n s a n d t h e i r cont a i n e d resources, a c o m p r e h e n s i v e v o l u m e b y S m i t h (1989) s h o u l d be consulted. A n earlier review v o l u m e edited b y P a t c h i n g (1985) is a n a d d i t i o n a l valuable reference in this regard. Finally, several review articles o n specific regions p r e p a r e d for t h e D e c a d e of N o r t h A m e r i c a n Geology ( D N A G ) v o l u m e s are o t h e r sources o f b a c k g r o u n d reference m a t e r i a l (Bustin, in press; B u s t i n a n d Miall, in press; C a m e r o n , in p r e s s ) . A t p r e s e n t , b i t u m i n o u s coals of v a r i o u s g r o u p s are b e i n g m i n e d in N o v a Scotia, N e w B r u n s w i c k , A l b e r t a a n d B r i t i s h Columbia. B a s i n s w h e r e m i n i n g is c u r r e n t l y b e i n g c a r r i e d o n are i n d i c a t e d o n T a b l e 2. A n t h r a c i t i c coals are n o t b e i n g m i n e d a t p r e s e n t e x c e p t for small q u a n t i t i e s for t e s t i n g at a d e v e l o p i n g m i n i n g site in t h e G r o u n d h o g coal field.
211 SUB/HV 200o
HV 2000
0 •
l
4000 |
HV/MV 0
I
MV coo@ 8000
2000 4000
o 1000
i
I
i
I
i
I
,
I
MV/LV 1°°° °
10000 •
I
o
LV 2000
o
LV/AN AN ''~ 2000 ° 1000
,
I
EOCENE PALEOCENE CRET'/TERT" ] 13 UPPERCRET. ~
16 ~
1.7C.7D,7E
LOWER CRET. JURA/CRET.
7A 11
2.16
3,11,7A
2, 7A
JURASSIC TRIAS./PERM. PENNSYL. ##
MISS.
7F AN
Includes
semlenthrsclte
and
anthracite
#~'Resources
not
estimated
Fig. 3. Canada's bituminous and anthracitic coal resources of immediate interest grouped by geological age, rank and basin of occurrence. Quantities expressed in megatonnes. Basins identified by numbers, e.g.6, 13, 7E, etc. (data from Smith, in press); S U B = subbituminous coal;H V = highvolatile bituminous coal; MV=medium-volatile bituminous coal; LV=low-volatile bituminous coal; A N = anthracite.
In some of the sedimentary basins (Fig. 1 ), a wide variety of ranks is found in stratigraphic sequences of different ages. The best example of such diversity is the Western Canada Basin (Fig. 1, Area 7). Within this basin, every rank group from lignite to semianthracite occurs in strata ranging in age from Late Jurassic to Paleocene. Another example is the Sverdrup Basin/Franklinian Geosyncline (Fig. 1, Area 16), covering a large area in the Arctic Archipelago; there an equally broad rank spectrum is present in rocks ranging in age from Devonian to Eocene. Since the early 1970's, coalification studies have aroused much interest because of their significance not only to the coal industry, but also for evaluating oil and gas possibilities (Hacquebard and Donaldson, 1970). Studies have shown that the processes affecting changes in the rank of coal also control the availability and properties of hydrocarbons. Of these processes, heating seems to be the most important and a knowledge of the resulting maturation of organic materials in prospective sediments is considered essential for oil-potential evaluation. Maturation levels are a function of the maximum paleotemperatures to which organic materials have been exposed, as well as the duration of such heating. Therefore, knowledge of these two factors of temperature and time can be obtained from the rank of coal, simply because the maturation process is irreversible. When a specific rank has been attained, it will remain at that level or
212 TABLE 2 Summary of geological and compositional data on Canadian coals of bituminous and anthracitic ranks, 1, 2, 3, etc. refer to basins and areas indicated on Figures 1 and 2. 6A and 6B refer to two small closely spaced basins in Area 6. Data from Bonnell and Janke (1986), Nicolls (1951 ), Stansfield and Lang (1944), Swartzman (1953), and Tibbetts and Montgomery (1960). Basin 1 Formation
Age
Rank parameters VM (dmmf) %2 CV (moistmmf) 3 Range
Extension/ Protection
1
I
Mean
38.5-48.6 44.2
(33.2-34.8) 14271-14974
(33.7) 14501
HV-A
32.5-40.5 35.4
(32.7-35.6) 14062-15319 -
(34.7) 14908
HV-A
(25.5-30.7) 10949-13208 (32.2-35.6) 13835-15324 {25.6-30.2) 11000-13000 (30.3-33.3) 13024-14335 (30.2-30.6) 12969-13148 (31.3-36.9) 13449-15841 (28.7-37.0) 12319-15926 (26.8-32.1) 11521-13802 (28.1-33.5) 12078-14404 {25.3-30.6) 10880-13134
(29.0) 12482 {34.0) 14609 (27.9) 12000 (31.6) 13577 (30.4) 13059 (35.2) 15130 (34.6) 14867 (28.8) 12399 (30.8) 13230 (27.7) 11909 -
L. Cret.
Comox
2
Mean Range
R. . . . ASTM 4 Range Rank
Haida Yakoun
L. Cret. M. Jura.
4.8-41.9 -
3
Currier
L. Jura.
3.9-15.7
4
Red Rose
E. Cret.
5
Bowron River
6A
Coldwater
Paleocene or Younger M. Eocene 36.8-44.4 41.3
6B
Allenby
M. Eocene
7A
Kootenay
7B 7C
Gething/ Gates Saunders
7D
Belly River
7E
Wapiti
7F
Mattson
9.3
28.2-35.7 31.4
40.0-42.1 41.0
*5 Jura./ Cret. * E. Cret.
17.3-33.5
*
Cret./ Paleo. Cret.
35.1-44.7 39.7
Cret./ Tert. Miss.
36.6-45.2 39.9
Pennsyl6.
32.0-47.2 36.5
Pennsyl.
39.9-44.1
Morien * (Sydney field) Morien (Inverness/Mabou)
Pictou/SteUarton * Pennsyl. (Pictou field) Pictou/Stellarton Pennsyl. (N.B. fields) Cumberland Pennsyl. (Springhill-Joggins)
8.2-40.3 24.9 24.8
40.8-46.2 42.9
-
42.6
27.2-35.1 30.7 30.4-40.7 3 5 . 1 33.0-42.9 39.5
HV to AN 1.705.80 0.650.70 0.612.65 0.762.55 0.620.74 0.590.81 -
(29.7-36.2) 12763-15574 (28.7-31.6) 12333-13569
(34.3) 14755 (30.8) 13252
0.791.14 0.711.24 0.520.68
(32.8-35.4) 14104-15214 (27.9-36.7) 11989-15777 (31.9-34.3) 13694-14734
(34.1) 14653 {34.5) 14815 (33.0) 14170
0.852.04 0.612.53 0.800.93
LV to M-AN HV to MV HV-C, -B HV-B, -A HV-C, -B HVto AN HVto LV HV-C to-B HV-C, -A SUB to HV-B HV to MV HV-C to A HV-C, -B HV-A to MV HV-C to -A HV-C to-A
213 T A B L E 2 (continued) Basin ~ Formation
Age
Rank parameters VM (dmmf) %2
CV ( m o i s t m m f ) 3
Range
Mean Range
Mean
Riversdale *~ Pennsyl. (Pt. Hood-St. Rose)
38.1-41.1
39.2
(29.4-32.2) 12633-13858
(30.9) 13282
Tantalus
Cret.
35.8-40.2
37.9
(31.3-32.6) 13467-14026
(36.7) 15759
Laberge
Jura.
46.3-46.8 46.6
~
R. . . . ASTM 4 Range Rank
0.600.69
HV-C
HV-B to -A
11
12
15
Unnamed
-
-
HV
* Tert.
24.6-36.3
34.3
(24.7-33.5) 10615-14392
(27.6) 11865
1.062.06
HV-A to MV
Reindeer
Tert.
39.2-51.6
44.7
(29.9-30.4) 12840-13080
Kamik
E. Cret.
10.6-37.7 -
(30.1) 12960 -
Kayak
Miss.
0.540.75 0.862.93 2.844.03
HV-C to -B HV to SA SA /AN
Eureka Sound
Cret./ Tert. Cret. Cret.
0.170.70
LIG/ HV
Hassel Isachsen
8.0-13.7
10.1
53.3
-
10.6-15.9
-
-
(29.8) 12814 (31.2-32.8) 13394-14085
-
LV to AN
-
LV
16 Heiberg E m m a Fiord Parry Island, Beverley Inlet, Hecla Bay
Trias /Jura Miss.
14.3-15.4 -
Dev.
50.3-52.0
(32.8-34.9) 14103-15006
-
(30.2-32.2) 12996-13820
-
0.505.49 0.610.92
HV to M-AN HV
'See Figures 1 and 2 for basin and area names. 2 d m m f = dry, mineral-matter free; m m f - - moist, mineral-matter free. 3Number in parentheses is M J / k g , other n u m b e r is Btu/lb. 4ASTM rank designations based on volatile matter (VM, d m m f ) and calorific value (CV, m m f ) values where available; see Table 1 for explanation of abbreviations; M-AN = meta-anthracite. 5Basins or coalfields with active mining at present. 6Upper Carboniferous.
show an increase, but it can never revert back to a lower level. For evaluating oil and gas potential in an area, analysis of maturation levels by themselves suffices to provide important information without attempting to interpret paleotemperatures and burial times. However, to broaden the predictive aspect of maturation studies various approaches to temperature/time modelling are often applied, which involve calculations of maximum paleotemperatures and
214
in this sense coal, whether in true seams or finely dispersed in clastic rocks, can be used as a geothermometer. The rank changes of coal are caused by geological conditions and find expression in the coalification series of peat to anthracite. These geological conditions vary between different regions. In the northern part of the Rocky Mountain region of western Canada (Fig. 2, Area 7B ) the coalification is predominantly predeformational, whereas in the southern part (Fig. 2, Area 7A) a significant, though variable proportion appears to be post-deformational. In the Atlantic region (Fig. 2, Basin 9), coalification is almost entirely postdeformational (Hacquebard, 1975). Area 7A and Basin 9 are the two regions for which coalification patterns will be discussed in detail in this paper. SOURCEAND T Y P E O F D A T A
Most of the rank data presented in this paper are petrographic, i.e., reflectance measured on vitrinite. Many of these data are from the Geological Survey of Canada, and some have been extracted from published literature out of other coal-research laboratories in Canada, principally from the British Columbia Ministry of Energy, Mines and Petroleum Resources, and the University of British Columbia. In all cases, maximum reflectance (Romax) values are reported. Sample preparation and measurement procedures at all these laboratories followed standard procedures suggested by the ASTM (1979) and the ICCP (International Committee for Coal Petrology, 1971 ). Reflectance data are related to ASTM rank classes according to threshold values proposed by Davis (1978). Samples for analyses have been obtained from several different venues, namely outcrop, mine workings, exploration adits and trenches, coal exploration boreholes and oil and gas wells. Chemical data on rank, i.e., volatile matter and calorific value, were obtained from published and unpublished reports of the Geological Survey of Canada as well as from CANMET (Canada Centre for Mineral and Energy Technology), British Columbia Ministry of Energy, Mines and Petroleum Resources and the Alberta Research Council. Most of these data have been determined according to ASTM analytical specifications, although some older data, such as those for the Queen Charlotte Islands, predate the establishment of modern ASTM standards. RANK DISTRIBUTION BY BASINS
Nanaimo Basin (Basin 1, Figs. I and 2)
On Vancouver Island, high-volatile bituminous coals occur in several fields of the Nanaimo Basin. The two most important of these in terms of mining history have been the Nanaimo and Comox coalfields. The coal beds occur in
215 two formations of the Nanaimo Group of Late Cretaceous age (Table 2). Rank data based on proximate analyses indicate a rank of high-volatile A bituminous coal. The beds in the older Comox Formation appear to have lower volatilematter contents than those of the overlying Extension/Protection Formation (Table 2 ). LocalJy in the Quinsam coalfield of this basin, intrusives have apparently increased the rank (Barnstable, 1980). There are no published reflectance data on these coals.
Queen Charlotte Islands (Basin 2, Figs. 1. and 2) On Graham Island in the Queen Charlotte Islands, the Yakoun Formation (Middle Jurassic ) and Haida Formation (Cretaceous) contain bituminous to anthracitic coals (Sutherland Brown, 1968). Data on rank of these coals are sparse, but the few recorded in the literature suggest a broad rank range (Table 2). The high level of coalification in some beds may be local and related to igneous intrusion. Structure in the coal-bearing units is characterized by extensive folding and faulting.
Groundhog coalfield, Bowser Basin (Basin 3, Figs. I and 2) In terms of resource potential, one of the most important fields in the interior of British Columbia is the Groundhog coal field in the northeast part of the Bowser Basin. Its stratigraphy and structure were described by Bustin and Moffat (1983). The coals occur within the Currier beds and the overlying McEvoy unit of the Bowser Lake Group and display ranks ranging from lowvolatile bituminous coal to meta-anthracite. Reflectance values range from 1.7 to 5.8% (Romax) (Bustin, 1984). These values are in rough agreement with volatile-matter data (Table 2 ), although the latter were obtained from outcrop samples. According to Bustin (1984), ranks appear to increase toward the eastern side of the field. Coalification gradients are variable and range from 0.8% to 3.0% Ro m~/km. Bustin (1984) suggested that the high ranks and gradients may be related to high pretectonic paleogeothermal gradients, possibly resulting from large intrusive bodies at depth which accompanied the collision of terrains on this part of the North American margin during Mesozoic time. The high ranks and coalification gradients seem slightly out of line with estimated maximum burial which is believed to have been 3500 m. The coal measures have been extensively deformed by folding and faulting, including some fairly large thrusts.
Skeena Basin (Basin 4, Figs. 1 and 2) Adjacent to the south end of the Bowser Basin lies the Skeena Basin with a number of coal fields, the most important of which is at Telkwa. Here in the
216
Lower Cretaceous Red Rose Formation of the Skeena Group, 17 coal beds occur in moderately deformed strata with ranks ranging from high-volatile to medium-volatile bituminous coal (Table 2). Intrusives cut the coal measures at one end of the field and dikes have been encountered in some of the mine workings (Koo, 1983). These have locally produced some drastic rank increases, including the formation of natural coke. Within the rest of the Skeena Basin there are at least six other coalfields, some of which contain anthracitic coals. Rank data for these fields are sparse.
Bowron River coalfield (Basin 5, Figs. i and 2) Southeast of the Bowser and Skeena Basins, the Bowron River coalfield contains high-volatile C and possibly high-volatile B bituminous coals. The coal-bearing strata are late Paleocene or younger in age and contain lenticular seams up to 3.5 m thick. Reflectances (Ro max) are of the order of 0.65-0.70% (British Columbia Ministry of Energy, Mines and Petroleum Resources 1986 ) and calorific values range from 25.6 to 30.2 M J / k g (11,000 to 13,000 Btu/lb ). The Bowron River field is the most northern of a series of relatively small basins aligned in a roughly north-south direction in the interior of British Columbia. They contain coal of various ages ranging from Paleocene to Oligocene and in rank from lignite to bituminous.
South central British Columbia (Area 6, Figs. I and 2) A closely spaced group of small basins of south central British Columbia are a continuation of a belt of Tertiary coal-bearing troughs mentioned in the last section (Bowron River coalfield). Two of them, the Merritt and Princeton/ Tulameen basins, contain bituminous coal. In the Merritt coalfield, coal occurs in the Coldwater beds of Middle Eocene age. The coal is bituminous with volatile-matter contents (dmmf) ranging from 37 to 44% and calorific values (moist, mmf basis ) varying from approximately 25.6 to 33.3 M J / k g (13,000 to 14,300 Btu/lb). These data indicate mainly high-volatile'B bituminous coal with some high-volatile A bituminous coal present as well (Table 2). These coal measures have been moderately to severely deformed. The Princeton/Tulameen coalfield consists of two presently separated subbasins, each containing coal beds in the Middle Eocene Allenby Formation. The Princeton subbasin appears to contain only subbituminous coal (Rice, 1947; Shaw, 1952 ). The coal in the Tulameen part of the field is higher in rank with heat values averaging 25.6 M J / k g (13,000 Btu/lb) and with reflectance values that range from 0.62 to 0.86% R . . . . (Donaldson, 1973; Williams and Ross, 1979). The chemical analyses and reflectance data indicate ranks of highvolatile C to high-volatile B bituminous coal for the Tulameen coals. Both the Tulameen and Princeton coals have been severely affected by folding and
217
faulting, particularly at Tulameen where locally the coal has been greatly thickened tectonically. The higher ranks at Tulameen as compared to Princeton and the variability within the Tulameen field are thought to be due to igneous activity complicated by folding and tilting before some of the volcanism took place (Williams and Ross, 1979). Western Canada Basin (Basin 7, Figs. 1 and 2)
The bulk of Canada's presently known coal resources, including the major part of its high-rank coals, occurs within this very large basin. Because the basin is large and complex in terms of the number of coal-bearing formations and the ranks of coals contained within them, it has been divided, for the purpose of the present discussion, into six regions (Fig. 2, 7A-7F ). Of these areas, rank distribution in 7A will be examined in detail later. Areas 7A and 7B (Fig. 2) The bulk of Canada's resources of bituminous coal plus a substantial quantity of anthracitic coal occurs in areas 7A and 7B in the Rocky Mountains and Foothills of Alberta and British Columbia. These two areas together form a narrow belt some 1200 km long and stretching northwest from the U.S. border to the Peace River in British Columbia. The belt consists in detail of a number of structurally separated areas underlain by coal-bearing rocks of Late Jurassic to Early Cretaceous age. Regions 7A and 7B are separable stratigraphically. The former is underlain by the Jurassic/Cretaceous Kootenay Group, whereas the coal-bearing strata in the latter are represented by the younger Bullhead and Fort St. John Groups (Early Cretaceous) and their equivalents. The remarkably persistent conglomerates of the Cadomin Formation serve to fix the stratigraphic relationship of these various sequences. In area 7A, the Cadomin overlies the Kootenay, whereas in area 7B the Cadomin forms the basal noncoal-bearing member of the Bullhead Group which, in turn, is overlain by the Fort St. John Group. Figure 4 shows schematically the relationships of these major stratigraphic units. Underlying the Cadomin in area 7B is the Minnes Group, which is believed to be equivalent to the Kootenay Group (Stott, 1984 ). It contains some minor coal beds but the major coal-bearing sequences in area 7B are the Gething Formation (Bullhead Group) and the Gates Formation (Fort St. John Group), both above the Cadomin Formation. The equivalent stratigraphic sequence in the south (area 7A) is the Blairmore Group and it does not contain coal. Hacquebard and Donaldson (1974) published the first regional study of coal ranks for areas 7A and 7B. The results of their reflectance analyses (Fig. 5) show a variety of ranks and coalification gradients. Kilby (1988) studied reflectances of a number of samples from both areas 7A and 7B. He showed that many exhibit biaxial optical properties, which suggest a significant tectonic
218 /I U.S.A. //
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Fig.4. Schematic crosssectionshowing relationshipof Upper Jurassicto Lower Cretaceous strata in the Canadian Rocky Mountains and Foothills.Hatched areas indicatecoal-bearingbeds. Compiled in part from data by Stott (1974, 1984) and Gibson (1985).
influence on the orientation of reflectance parameters. Kalkreuth et al. (1989) have shown by a study of oriented blocks from area 7B that orientations of Ro maxand Ro raincan be related to fold axes orientation and direction of tectonic stress. Rank variations in area 7B will be examined in another paper (Kalkreuth et al., 1989) and only the general pattern will be summarized at this point. The geological framework of the coal-bearing Minnes Group and Gething and Gates Formations in area 7B has been well established by Stott (1974, 1984) and Gibson (in press). Hacquebard and Donaldson (1974), Karst and White (1980), Kalkreuth and McMechan (1984) and Kalkreuth and Langenberg (1986) have touched on various aspects of rank variation within the area and used reflectance as the organic maturity index. Steiner et al. (1972) included this area in their evaluation of coal-rank patterns in Alberta and utilized standard chemical data. The coals of the Gething and Gates Formations range in rank from highvolatile to low-volatile bituminous coal with a large proportion being mediumvolatile bituminous coal (Fig. 3). Coalification appears to have been largely pre-orogenic as indicated by some local studies where isorank lines seem to follow stratigraphic horizons in deformed beds (Kalkreuth and Langenberg,
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Fig. 5. Reflectance (R. . . . )-depth profiles for representative sections of Jurassic to Cretaceous coal-bearing strata in the Canadian Rocky Mountains and Foothills (from Hacquebard and Donaldson, 1974). Coalification gradients are represented on each section by two numbers. The first is actual gradient (To R . . . . change/100 m) for each section; e.g. for section 1, gradient is 0.071. The second number on each section is the ratio obtained when the gradient is divided by a reference gradient. Reference gradient used is from the Peel region in the Netherlands and has a value of 0.115/100 m. An example of the resultant ratio is 0.62 on section 1. VM= volatile-mattercontent.
1986). As the coal-bearing units are traced from the Plains southwestward toward the mountains, rank first increases and then decreases near the western edge of the Foothills. Kalkreuth and McMechan (1984, 1988) explained this seeming anomaly by reference to the timing of geological events in the area. Deposition of the coal-bearing sediments was at least partly synchronous with the uplift of the Cordillera to the west. As a consequence, the western part of the coal-bearing sequences was never buried as deeply or for as long a period of time as the eastward extension of these beds along the axis of the Alberta syncline. As a result, the coals in the Alberta syncline have the highest rank (Fig. 6). Kalkreuth and McMechan (1984) concluded from their studies that temperature and duration of heating with depth were sufficient to account for the achieved levels of maturity and only locally do abnormal levels of heat flow appear necessary.
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Area 7C (Fig. 2) In the Outer Foothills region of west-central Alberta, there is an area underlain by moderately deformed coal-bearing rocks of Late Cretaceous to Paleocene age. This sequence of strata is termed the Saunders Group and its
221
stratigraphy, sedimentology and age have been reported by Jerzykiewicz and McLean (1980), Jerzykiewicz (1985) and Jerzykiewicz and Sweet (1986). Two formations within the Saunders Group contain bituminous coals: the Brazeau Formation and the stratigraphically higher Coalspur Formation. The latter contains the more abundant coal resources. The Coalspur Formation straddles the Cretaceous/Tertiary boundary, and the important coal zones are in the Tertiary. There are at least six coal zones in the Coalspur Formation. The Coalspur Formation is coeval with the Scollard Formation that underlies an area farther east on the Alberta Plains. The coal beds of the Scollard Formation are subbituminous in rank, whereas those in the Coalspur are high-volatile C bituminous coal with volatile-matter contents, heating values and reflectance ranges as indicated in Table 2. The somewhat higher rank of the Coalspur coals is likely due to deeper burial as compared to the Scollard coals. Area 7D (Fig. 2) The area in southern Alberta designated as 7d is underlain by the Upper Cretaceous beds of the Belly River Group/Formation (Campbell, 1974). In the southeastern part of the province, the group is divisible into the Foremost and Oldman Formations, whereas comparable beds in the southwest are undivided and are referred to as the Belly River Formation. In the southeast and southcentral parts of the province, the Belly River contains three coal zones of which the rank, in part, is high-volatile C bituminous coal. Farther west in the Foothills, the Belly River contains two coal zones that are not as laterally extensive as the seams farther east. The rank of the Belly River coals in the Foothills is higher than that of Belly River coals farther east; in the Foothills there is highvolatile A bituminous coal. Area 7E (Fig. 2) A large area in west-central Alberta and adjacent parts of British Columbia is underlain by the Wapiti Group, a coal-bearing succession of Late Cretaceous/Tertiary age (Kramers and Mellon, 1972). It lies north of the area underlain by the Saunders Group. The Wapiti is thought to be correlative with the Saunders, Belly River and Edmonton Groups. Data on coal occurrences are scarce. In one area, Allan and Carr (1946) indicated the presence of 9 coal beds. Some of these coals have reached a rank of high-volatile C bituminous coal (Table 2). Area 7F (Fig. 2) An area at the northern end of the Western Canada Basin contains coal in the Late Cretaceous Wapiti Group and the Mississippian Mattson Formation. The area is close to the juncture of the boundaries of the Yukon Territory, the Northwest Territories and British Columbia. Some exploration in the 1970's
222 was carried out in this area, but detailed information on lateral persistence of coal beds is sparse. The Wapiti coals are subbituminous, whereas those in the Mattson are high-volatile A bituminous coal, according to reflectance data (Table 2). The Mattson contains at least two coal beds (Lord, 1983). Whitehorse Trough (Basin 11, Figs. I and 2) The Whitehorse Trough contains coal in sequences of two geological ages. These are the Laberge Group (Jurassic) and the Tantalus Formation (Cretaceous). For a number of years, a mine at Carmacks in the Yukon Territory produced coal from a bed in the Tantalus Formation. This coal is mainly of high-volatile B bituminous rank. A rather limited number of chemical analyses suggest that most of the coals in both the Laberge Group and Tantalus Formation are of the bituminous rank class. At least one locality near Whitehorse shows coal of anthracitic class although microscopic observations suggest that it may have been abnormally heat-affected (Goodarzi, 1983). Bustin (1984) suggested that the high heat flux that influenced rank in the Groundhog coalfield may have extended northward to affect coal rank in the Whitehorse Trough. Tintina Trench (Basin 12, Figs. I and 2) In the Tintina Trench, a number of coal occurrences are recorded within a narrow belt extending from the Yukon Territory/British Columbia border to the Yukon/Alaska boundary. Most of these appear to be lignite and subbituminous coal, but one deposit near Ross River in the Yukon Territory is medium-to low-volatile bituminous coal. Reflectances of coals in the Ross River area range widely from 1.06 to 2.03% (Ro m~). Such values are not totally consistent with the proximate analyses data on the same coals (Table 2 ), and may reflect that the samples analyzed were from outcrop and likely weathered to varying degrees. Hughes and Long (1980) suggested that the higher ranks at Ross River, compared to other parts of the Tintina Trench, were caused by igneous intrusions. Northern Yukon (Area 15, Figs. 1. and 2) A belt of Arctic Coastal Plain and adjacent fold complex in the northern Yukon Territory and extreme northwest part of the Northwest Territories is partly underlain by three coal-bearing sequences with high-volatile bituminous coal to anthracite ranks (Fig. 7). The oldest of these units is the Kayak Formation of Mississippian age which contains at least one thick ( > 5 m) bed of semianthracite to anthracite coal in the Hoidahl Dome area (Fig. 7, station
223
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Fig. 7. Distribution of coal-bearing rocks in northern Yukon Territory and adjacent District of Mackenzie, NWT, area 15, Fig. 1.
F, Cameron et al., 1988). The next oldest coal-bearing succession is the Kamik Formation of Early Cretaceous age which contains thin coal beds varying in rank from high-volatile A bituminous coal to semianthracite. Only a few analyses are available on the Kamik, and patterns of rank change cannot be delineated as yet. The third stratigraphic unit of area 15 is the Reindeer Formation of Paleocene/Eocene age. Reflectance and chemical data on the Reindeer coal beds indicate ranks of high-volatile C and B bituminous coal (Table 2). Reflectances on all three formations are summarized in Figure 8. In addition to the coals at Hoidahl Dome, other exposures of Kayak strata containing thin coal beds and carbonaceous shales were sampled at 4 other stations within the area (Fig. 7). Three of these (stations H, I and J) in the British Mountains showed reflectance significantly higher than stations F and G farther southeast. Values of 3.55-4.03% (Ro ~ ) , corresponding to anthracite, were obtained at stations H, I and J, as compared with 2.33-3.03% (Ro_ max), mainly or entirely semianthracite, at stations F and G (Cameron et al., 1986). This difference is not readily explained at present. There are granitic intrusions in the area but they are older than the Kayak. There was uplift and associated deformation in the area during the mid-Mesozoic and later during Late Cretaceous and early Tertiary time, and it is possible that some of the resulting uplifts were cored with younger intrusives (Cameron et al., 1986).
224 RomaX
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Fig. 8. Distribution of R . . . . a n d R . . . . aom values for sample sites shown in Fig. 7. Length of bar indicates range of reflectance values at each site.
There is an indication that this northwestward change in rank may not be confined only to the Kayak Formation. The coal beds of the Reindeer Formation, which were sampled at 3 sites (Fig. 7, stations A, B, C ), also show a subtle westward increase in rank based on reflectance (Fig. 8), whereas at stations D and E, from which Kamik Formation coals were analyzed, the more westward site (Fig. 7, station E) is of higher rank.
Sverdrup Basin/Franklinian Geosyncline (Basin 16, Figs. I and 2) Basin 16 encompasses a very large area in the Canadian Arctic Archipelago, mainly within the geologic provinces designated as the Arctic Platform, the Franklinian Geosyncline and the Sverdrup Basin (Thorsteinsson and Tozer, 1970). Figure 9 shows a more detailed map of this area. Coal is found in Devonian, lower Carboniferous (Mississippian), Triassic, Jurassic, Cretaceous and Tertiary strata. Of these, the Eureka Sound Group of Late Cretaceous to Eocene age is the most important in terms of known coal resources. Although the area is remote and the level of exploration for coal per se has been low, a rather large amount of information on coal occurrence and rank is accumulating because of hydrocarbon exploration and systematic regional mapping by the Geological Survey of Canada. There is no mining in the area at present and only small amounts of coal have been mined. Recent regional discussions of coal in the Arctic have been published by Ricketts and Embry (1984), Bustin (1986) and Bustin and Miall (in press). Much of the coal in the Arctic is lignite to subbituminous coal. However, there are substantial resources of bituminous coal and locally even some semianthracite (Ricketts and Embry, 1984 ). The Devonian coals occur in the Hecla
225 COAL-BEARING F O R M A T I O N S
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Bay, Beverly Inlet and Parry Islands Formations, all within the Franklinian Geosyncline, and appear to be no higher in rank than high-volatile B bituminous coal (Table 2). Some of these coals are cannel coal with high liptinite contents (F. Goodarzi, pers. commun., 1988). The Emma Fiord Formation contains a few coal beds up to 1 m thick (Thorsteinsson, 1974), but exposures are few. The Emma Fiord is interesting because it contains thick (70 m) beds of oil shale on northwest Devon Island (Fig. 9). Measured reflectances on vitrinite from this locality differ widely, as compared with those obtained on samples from another exposure of this formation on Ellesmere Island (Goodarzi et al., 1987 ). On the Devon Island samples, values ranged from 0.26 to 0.50% Ro max, whereas the Ellesmere samples gave values over 5.0% Ro . . . . corresponding to meta-anthracite. The Emma Fiord is Early Mississippian (Early Carboniferous) in age, more or less equivalent to the Kayak Formation in the northern Yukon. Coal occurrences have been recorded in the Triassic/Jurassic Heiberg Formation, the Early Cretaceous Isachsen Formation and the mid-Cretaceous Hassel Formation. These are mainly concentrated on Ellesmere and Axel Heiberg Islands. Rank data on coals of these formations are sparse but indicate variable degrees of coalification. Fortier et al. (1963) show data for Isachsen
226 Formation coals that vary from lignite to semianthracite and data for a few samples of Heiberg coals also show some high ranks. These higher ranks may be the result of localized increases due to igneous intrusion. More recent data by Goodarzi et al. (in press) show low reflectance values on Isachsen Formation coals from Melville Island; the values indicate ranks of lignite to subbituminous coal. The largest coal resources documented to date in the Canadian Arctic occur in the Eureka Sound Group of Late Cretaceous to Eocene age. Large areas of the Archipelago are underlain by strata of this group, particularly on Ellesmere, Axel Heiberg and Devon Islands (Fig. 9). Some sections include numerous seams with as many as 90 in a 3200-m-thick section in central Ellesmere Island (Bustin,1986). Although much is lignite to subbituminous coal, a substantial part of the resource is bituminous coal, especially in the eastern part of the Sverdrup Basin on Ellesmere and Axel Heiberg Islands. On the basis of a regional maturation study utilizing reflectance measurements, Bustin (1986) concluded that most of the coalification was pre-orogenic and related to depth of burial. His studies indicate that paleogeothermal gradients have varied from 55°C/km in the eastern end of the study area (Ellesmere Island) to about 15 ° C/km on Melville Island, approximately 1000 km to the west. This easterly to northeasterly increase in rank in the Eureka Sound Group parallels a similar pattern in older Carboniferous and Permian sequences. Utting et al. (in press) have evaluated organic maturity by three different methods: conodont alteration index (CAI), thermal alteration index based on spore coloration (TAI), and vitrinite reflectance. They showed a northeastward increase in maturity in the Carboniferous and Permian successions. Bustin (1986) suggested a possible relationship between the higher coalification at the northeastern end of the Sverdrup Basin and its tectonic history. Intermittent tectonic activity affected the area during the Phanerozoic up to the Miocene. Bustin (1986) suggested that higher heat flows associated with this activity and with evaporite diapirs may have influenced coalification. RANK DISTRIBUTIONIN KOOTENAYGROUP, SOUTHERNCANADIANROCKIES AND FOOTHILLS (Fig. 2, Area 7A) One of the most important coal-bearing successions in western Canada is the Late Jurassic to Early Cretaceous Kootenay Group. Its areal distribution in general terms has already been sketched (Fig. 2), and its importance in Canada's coal inventory is indicated by the magnitude of its contained resources of medium-volatile bituminous coal as shown on Figure 3. A map showing the distribution of the Kootenay Group in more detail is presented in Figure 10A.
227
Fig. 10. A. Distribution of KootenayGroup in British Columbiaand Alberta. B. samearea as A but showinglocation of major thrust faults. Section line 1-58 indicates location of oil wells in which Kootenayintersectionsweresampledin subsurface.
Geologyof Kootenay Group In order to better understand rank distribution in the Kootenay Group, it is necessary to briefly sketch the geology of the group. It is comprised of three formations which, in ascending order, are: Morrissey, Mist Mountain and Elk Formations. Norris (1959, 1964), Gibson (1979,1985), and Gibson et al. (1983) have discussed stratigraphic, structural and sedimentological aspects of the Kootenay, whereas Hacquebard and Donaldson (1974), Pearson and Grieve (1985), and England and Bustin (1986) have discussed various aspects of rank variations in the Kootenay coals. Hughes and Cameron (1985) discussed sedimentology and vertical rank variation in an important Kootenay section at Mount Allan, Alberta. The Mist Mountain Formation is mainly Jurassic. The important coal seams are in the Mist Mountain Formation. Only a few relatively thin and laterally impersistent seams are found in the Elk Formation. Gibson (1985) has proposed a delta prograding to the east as the paleoenvironmental setting for deposition of the Kootenay Group. The Kootenay conformably overlies beds of the Fernie Formation and is overlain unconformably
228
in part by the continental sequence of the Blairmore Group with the lowest Blairmore unit, belonging to the distinctive Cadomin Formation, in immediate contact. Locally, a conglomeratic unit, known as the Pocaterra Creek Member, is in immediate contact with the Kootenay. The thickest Kootenay section (1112 m) has been described by Gibson (1985) near Sparwood, British Columbia (Fig. 10A). The number of coal beds or coal zones varies from section to section. The maximum number appears to be in sections in the Upper Elk Valley of British Columbia where there are at least 20 coal beds or zones. In an eastward direction, the Kootenay thins rapidly. Its eastern limit in subcrop approximately parallels the Rocky Mountains and is not far distant from the edge of the disturbed belt (Fig. 10). An important aspect of the Kootenay is how its present-day distribution has been affected by regional tectonics. Strong compressional forces associated with the Laramide Orogeny moved thick sequences of strata ranging from Precambrian to Tertiary northeastward along westward-dipping thrusts. Figure 11 is a cross section through the mountains and foothills showing typical stacking of multiple thrust sheets. These thrusts resulted in multiple repeats of the Kootenay Group as observed in subsurface sections. A number of these repeats come to the surface and are reflected in the elongated, narrow and more or less parallel patches of Kootenay outcrop shown on Figure 10A. Surface traces of the most important of these faults are also shown on Figure 10B. The thrust faults and the lateral transport of thick slabs of strata along them are the most important structural characteristics affecting the Kootenay Group and these are prominent throughout the area underlain by Kootenay, from the U.S. border to the Clearwater River, a distance of some 370 km. The Kootenay is also folded and normally faulted and in many places coal beds are so intensely sheared as to obliterate original depositional laminae. W21 W23 Scale
on wells
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and reflectances
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Fig. 11. Cross section through southern end of Kootenay study area (section line A -A' ) in Figure 10B. Section shows major thrust faults and position of subsurface Kootenay intersections. Reflectance values (R. . . . ) for Kootenay coals shown for wells on or close to section line (modified from P.R. Fermor and R.A. Price, pers. commun., 1988).
229
Rank distribution in surface sections At the surface the Kootenay coals range from high-volatile B bituminous coal to semianthracite. There are several discernible patterns on a regional basis upon which are superimposed some rather surprisingly rapid changes within local areas. An important factor is the degree of preorogenic vs. postorogenic coalification, coupled with the influence of the thrust faulting. Thrust faulting exerts a two-fold effect: it has translated Kootenay sections that were once widely separated into close proximity to one another, and it has played a role not yet clearly defined in adding to normal burial depths on some Kootenay sections. Some Kootenay sections have been moved by thrusting as much as 140 km. Frictional heat generated by the thrusting process seems not to have been significant in promoting coalification (Hacquebard and Donaldson, 1974; Bustin, 1983). Initial studies on rank changes in the Kootenay Group by Hacquebard and Donaldson (1974) suggested that coalification was predeformational, that is, prethrusting. Later more detailed studies by Pearson and Grieve (1985) and England and Bustin (1986) indicated that a substantial proportion of the coalification was postdeformational, though the proportion varies from site to site. Pearson and Grieve (1985) estimated that this proportion of postorogenic coalification ranged from 25 to 75%. They based their conclusions regarding postorogenic coalification on sections through the coal measures such as shown on Figure 12. At this site (Coal Creek Mountain), reflectances (R . . . . ) determined on three beds increased progressively downdip. W
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Lu
COAL CREEK 9O0
KILOMETEN
Fig. 12. Cross-section of Coal Creek, Fernie Basin, showing stratigraphic position of three bituminous coal seams (indicated by thin black lines), and reflectance values (R . . . . ) obtained on these seams (from Pearson and Grieve, 1985).
Flathead/Sage Creek Lodgepole/Flathead Ridge Mount Taylor Coal Creek Grassy Mountain Sparwood Ridge Oldman Gap Line Creek Cabin Ridge Ridge Creek Wilkinson Creek Greenhills Fording River Weary Ridge Bleasdell Creek Mist Mountain Highwood Junction Bragg Creek EV-boreholes Canmore Mount Allan Barrier Mountain
A B C D E F G H I J K L M N 0 P Q R S T U V
82G/2 82G/7 82G/10 82G/10 82G/9 82G/10 82G/16 82G/15 82J/2 82J/1 82J/2 82J/2 82J/2 82J/7 82J/7 82J/10 82J/7 82J/15 82J/11 820/3 82J/14 820/12
NTS Map
E 678000-N 5441300 E 654000-N 5466400 E 663900-N 5489200 E 645000-N 5486700 E 686800-N 5506100 E 653500-N 5505200 E 692500-N 5528800 E 659300-N 5533700 E 677500-N 5545600 E 688500-N 5554100 E 670700-N 5565400 E 650600-N 5554500 E 653100-N 5561200 E 650700-N 5582200 E 646050-N 5581700 E 659000-N 5602400 E 666800-N 5585900 E 654000-N 5546500 E 636900-N 5604700 E 613000-N 5660000 E 627050-N 5649860 E 598500-N 5729250
U.T.M. coordinates, all in Zone 11
236 662 660 656 116 1082 81 648 198 120 308 665 790 + 1052 486 741 231 72 941 + 477 1038 659
Thickness of section (m)
186 340 138 528 111 595 52 308 161 44 194 665 451 463 481 659 99 39 875 477 873 589
(m)
Interval covered by R. . . . values
4 7 2 3 4 11 3 10 6 2 4 18 10 11 11 13 7 3 30_+ 12 38 10
Number of seams measured
Sources: Gibson ( 1985 ); Graham et al. ( 1977 ); Grieve ( 1985 ); Hacquebard and Donaldson (1974); Hughes and Cameron ( 1985 ).
Geographic name
Section (See Fig. 13 )
Location and thickness data for surface sections of Kootenay Group
TABLE 3
1.10-1.19 1.25-1.58 1.02-1.19 0.97-1.24 1.18-1.28 0.98-1.46 1.06-1.19 0.97-1.49 1.25-1.36 0.99-1.16 1.10-1.37 0.81-1.31 0.92-1.35 1.00-1.58 0.61-0.84 0.89-1.79 1.45-1.69 1.68-1.91 0.65-1.24 1.62-2.65 1.30-2.49 1.48-2.50
(Romax)
Reflectance range
t~ q.O
231 1.48-2.50
1.30-2.49
v
0.89-1.79
o
iiiiiili t .i:::::il .vB
mv,
PSOOm
/ I
0
__ ~R
~..~'~ I~'~.-.~ .~i!I :i:i:!:i:!:i:!:i: :i: ::ii::::::ii::ii0.:ii::::i B1~1.~31 l ~ L~097-149 ~
0.98- ]~iill w I~:~:~I
40 km
l~iii::i]
mS
R~
oX
C'-?\\
l.::~:i:i:i:~1.50-2.05 IvB _^_ SA
~ ~ t
0.8.'
~
I :i]
145169
1.16
ok,~, K~ " M • |~.:!:\i:.iil L~MZ\~r~ j 1.2~6 | \,~ ~' 'I~i!:] F~|
~E
1 06 i19
E
F~ l
0.97-1.24 t'~-~" ~
~.91-
1.02-1.19
~
1.10-1.19
1.25-1.58
Fig. 13. Summaryof rank data obtainedon coals of 22 surfacesectionsof KootenayGroup. Sections dividedinto ASTM ranks (1979) accordingto reflectance(R. . . . ) distributions obtained in section. Figure 13 shows the rank distribution for a number of surface sections of the Kootenay. Table 3 gives the location of these sections and the thickness of the Kootenay Group at that site. The overall range of the reflectance data (Fig. 13) is 0.61-2.65%, representing high-volatile B bituminous coal to semianthracite. The thicknesses of the intervals covered by reflectance measurement in the sections vary widely from 39 m at Bragg Creek {Fig. 13, Section R), to about 875 m in sections S and U (Fig. 13, Table 3). The thinner sections (E, G, J, Q and R) are all on the eastern side of the outcrop area, indicative of the eastward thinning character of the Kootenay. The overall pattern of rank distribution indicates that the highest levels of coalification are found to north and west and the lowest toward the south and east. Low reflectances are also encountered in other sections such as F, H, L, M, N, O and P (Fig. 13). Section O is somewhat anomalous and will be dis-
232 cussed later. The low reflectances in the other six sections mentioned above occur toward the top of thick successions of Kootenay strata, whereas the higher values, such as 1.58% in section N, occur in beds near or at the base of the Mist Mountain Formation, and these are the values that should be compared with the reflectances shown for sections A, C, E and G because they represent data on equivalent horizons. The Kootenay Group thins eastward by the disappearance, either by nondeposition and/or erosion, of the upper units of the group. Thus the lowest seam in sections A and C, having a reflectance at both sites of 1.19%, is possibly correlative with the basal seam at sections B and F, where reflectances of 1.58% and 1.46% respectively, have been measured. As the Kootenay Group is traced west, and particularly to the north, the overall reflectances shown by the surface sections increase and reach their maximum in sections T (Canmore), U (Mount Allan) and V (Barrier Mountain). In these three sections, much of the coal has reached ranks of low-volatile bituminous coal and semianthracite. The pattern of regional rank change is more clear from the reflectance values measured on the basal seam of the Mist Mountain Formation (Fig. 14). This seam is usually within 50 m of the Mist Mountain-Morrissey contact. Here, the low reflectances representative of high-volatile bituminous coal are quite evident in the southeastern part of the area with a more or less gradual increase northward to semianthracite (0.93-2.65 % ) at Canmore, Mount Allan and Barrier Mountain. However, within this pattern there are variations when examined in detail. In the Fernie Basin, described by Price (1962) as a doubly plunging fold (see Fig. 10A for location), Pearson and Grieve (1985) noted a progressive increase in rank from the northern to the southern end of the basin as represented by the reflectance increase from 1.46 to 1.85% in the basal seam (Fig. 14), corresponding to medium- and low-volatile bituminous coal. They suggested that the difference was due to increased depth of burial at the south end and they estimated this increase to be 600 m. In the Elk Valley coalfield north of the Fernie Basin, the Alexander Creek syncline (Fig. 14) appears to be continuous throughout the extent of the field (Pearson and Grieve, 1980 ). The plunge on this structure is slight and variable. Faults, both normal and thrust, complicate the rank pattern somewhat but in general, it appears that the seams on the west limb of the Alexander Creek structure are of lower reflectance than correlative beds on the east limb. There are some exceptions to this, e.g., a reflectance value of 1.38% was obtained on the basal seam on the west side of the syncline, as compared to 1.35% measured on the basal seam in the east limb. However, at other sites on the west limb, the basal seam gave values of 1.14% and 1.08%. The most striking difference in rank between east and west limbs of the Alexander Creek syncline is shown by sections N and O (Fig. 13 ), with O being on the west limb. A schematic cross-section of the syncline is shown in Figure 15A. The data indicate that the coals on the west limb are all high volatile
233
~~ 2.09
2~.65~ +L..
0
,
50
km
ALBERTA
eq
•
Calgary
.p
"'~16~ I,'4
BR,T,S. -~-~'~ ~ \ COLO.B,A
f S+
o.7et~ '.sl 1"1.69 ~-~+ 1.16 1.11 -) 1.49 ~.~
.
"
Fig. 14. Map showing distribution of reflectance (R . . . . ) values on basal seam of Mist Mountain Formation (Kootenay Group). Data mostly from Pearson and Grieve (1985). Map of Elk Valley coal field showing position of Alexander Creek syncline (lower left figure ).
bituminous coal, whereas correlative seams on the east limb vary from highto low-volatile bituminous coal. At section O, the beds are vertical to overturned and the sample material available was badly weathered in most cases. Nevertheless, even if the measured reflectances were adjusted as suggested by Marchioni (1983) to equate weathered to fresh-coal values, ranks on the west limb would still be much lower than those on the east. A similar situation occurs at M o u n t Allan (Fig. 15B ) where the seams on the overturned limb of the M o u n t Allan syncline show reflectances much lower than those on the upright limb. As was the case with section O at Bleasdell Creek, the coal beds in the overturned limb are badly weathered, b u t the differences in reflectance between the two limbs are too great to be explained by weathering alone. In both areas, there is little change in rank gradient across the stratigraphic interval in the vertical or overturned limbs, in contrast to the upright limbs where
234 7 5 0 ~ R-o-m a x R a n g e J .0"~1 - o.a.
o
Romax Range 1.00 - 1.5.
i
',
,,
0 ~
R o m a x Range 0.68 - 0.94 " ' "
Sw
I 1000 " ~
I
i
I\
i
I
"~
|
|
NE • o" ,~,, I ' ~ s ° ~ e f e" :,,'~t~u"
R o m a x Range 1.30 - 2.49 * ,
,'"
'
~
~r'~,.',
I
,
~
'
!
~ 500 •
~
,_ t:m.
/
PC : Pocaterra Cr.
0 I
0 . - ~ ~S
Approximate measured
-/
traces f o r Ro
1 k /m
!
of seams
Morrlusey Fm.
Fig. 15. Schematic cross-sections of asymmetrical synclinal structure at Elk Valley (A) and Mount Allan syncline (B). Diagram showsthe decrease in Romaxfrom the upright limbs ofboth structures to the vertical or overturned limbs. Dips only approximate. there is substantial change (Fig. 16). This suggests that a substantial component of the coalification is postfolding.
Rank distribution in subsurface sections Figure 17 shows reflectance values determined Dn samples from oil wells positioned on a northwest-trending section line roughly parallel to the Rocky Mountains. In all of these wells, a variable number of thrust slices were penetrated which resulted in multiple intersections of the Kootenay. The data presented in this figure allow some evaluation of rank change in the Kootenay when the dimension of variable depths of present-day burial is added to results from surface sections. A comparison with surface data shows some general similarities. The occurrence of lower reflectances toward the southeast and higher reflectances toward the northwest again appears, b u t this pattern is distorted by values at relatively shallow depths in some wells that are higher than values measured
235 BLEASDELL CREEK
WEARY
500
0.7 ,
,
400
300
1.00
1.0
,
•
,
L
500
0.5
2.00 ' ........
800
J
'
1.00
1,0
'
'
' ~
900
700
"
•
800
"
300
"
600
"
ee
7O0
'
600
500
•
•
3.00 I
•
400
-
"
500
•
~p
s.
g
I
O-
2.00 i
I
-
100'
•
0.7 '
400
e 100
ALLAN
(upright)
%
200-
200
MT.
ALLAN
(overturned)
Rolnnx
Romax 0.5
MT.
RIDGE
o
;
300
-
200
-
100
•
0
400
•
•
•
•
e~
300
"
200
•
100
-
0
ee~
•
Fig. 16. Reflectance(Ro.~,)-depth profiles for 4 sections plotted on Figure 15, e.g., Elk Valley upright (Fig. 13, section N, Weary Ridge) and vertical (Fig. 13, section O, Bleasdell Creek); Mount Allan upright (Fig. 13, section U) and vertical (not shown on Fig. 13).
at greater depths in wells to the north, e.g., comparison of well 48 with wells 50 and 51. The distribution of reflectances shown in Figure 17 is distorted by the fact that different thrust slices are involved in different wells. It is quite conceivable that within a given thrust slice a consistent pattern of reflectance is present, but it is very difficult to correlate with certainty individual thrusts from well to well. The distribution of reflectance values on Figure 17 does suggest something about the influence on rank of deeper burial by multiple thrusts. In nearly all the wells where measurements were made on Kootenay "repeats", the deeper intersections show higher reflectances, e.g., wells 23, 37, 40 and 52. Similar variation also appears in some of the wells projected on the cross section of Figure 11. Although the progressive increase in rank of deeper Kootenay sections in most wells is probably a function of coalification after thrusting, there is a possibility that the deeper slices, which during thrusting were moved to the northeast a shorter distance than the higher slices, were coalified to a higher degree before movement. Thus, there would exist in the Kootenay a situation
236 NW
SE 57
58
37 56. 55
52 51 54 53
50
49 "T" 48
.
1.81
,.8~
.Oil .25
,~
1.( 1.(
•
~:I
.1.73
" =.oo
1.84" " 1.8g~ ~
1,26. 1.37
"2.0IB %61 •
, :1.16
1,3
~:~
1.70 -1.74
, 1.71 ~1.62 ,1.67
1
43
1.2'7 .
~.3.188
' "0.90
;;
l:~°
23
1.251"23:
f
1.27
1.03 -1.01
~
1 39 ~1.44 ~1.46
•
1,24" ~ 1.28
.1.81 1.72 1,90 2.27 2.32" "
:1.7! 1.71 .69
~
50 A
e
km
m
0,84
"1.12
.29 1.50
S ea Level
/o.8,
13,
1,61
2 1
r-
2.03
0
18
23
~" 34 1.48/ "F1.9~
"1.78
45
)9
48 1.8
1 . 8 5 :~ $
40 47
0.9] 0.94
1.52 "1.58
084
0.87" : 0,83 0.84'
0.78
0.79 ~ 0.76'
1,84 '1.06
8OO
f°
IOOO
Fig. 17. Reflectance (Romax)data measured on subsurface samples of Kootenaycoals intersected in oil wells on section line 1-58 (Fig. 10B). Kootenayintersectionsindicated by heavyhorizontal bars; thrust faultsby diagonallines. Welltops at groundlevel.ThicknessofKootenayintersections not drawn to scale; most are less than 100 m and most were selected for study because of an apparently normal contact with underlyingFernie Formation. comparable to t h a t described by Kalkreuth and McMechan (1984) for northeast British Columbia and adjacent Alberta where the higher ranks are not found near the western limit of those coal-bearing rocks, but farther east (Fig. 6). However, the previously discussed data on the K o o t e n a y surface sections suggest t h a t this is not the case. An exception to this trend is the pattern of reflectances for Kootenay repeats in wells 1, 2 and 18 at the southeastern end of the section line (Fig. 17). These wells show the lowest reflectances measured in the oil-well samples and also show little or no variation with depth. Some quite low reflectances were encountered at great depth, e.g., a value of 0.76 at a depth of about 3600 m in well 2. Clearly, in this area of southwestern Alberta the paleogeothermal gradient, at least since the inception of Laramide deformation, has been quite low. Here, extra burial by thrusting seems to have had little or no effect on coalification. Of possible relevance to rank in this southwestern corner of Alberta are the results of Majorowicz et al. (1985). T h e y found the lowest ( < 20 ° C / k m ) geothermal gradient in the province in this area and their belief is t h a t these gradients extend well back into the Tertiary. Variation in levels of coalification for Kootenay coals are not related to a single cause. Predeformational depth of burial undoubtedly contributed an imp o r t a n t component. Deep-seated intrusions may have influenced rank in some
237 areas (Hacquebard and Donaldson, 1974). Extra burial by thrust faulting should also be taken into account and is a complex factor involving rate of movement and thickness of the plates, rate of erosion and the disruption and re-establishment of thermal equilibrium. Yet another factor is the influence of ground-water movement on geothermal gradients. Studies by Hitchon (1984) and Majorowicz et al., (1985) have shown that geothermal gradients in the mountains and foothills are influenced by the recharge of cold meteoric water into the sedimentary column in topographically higher areas. They suggest this process has been operative since the early Tertiary with the effect of reducing geothermal gradients along the Mountain Front compared to farther out on the Plains. To further complicate the picture, there are variations in geothermal gradients parallel to the Mountain Front because lithological and structural variations inevitably result in variation in ground-water movement. ATLANTICPROVINCES
Geology o[ coal measures The coal measures of the Atlantic Provinces are Pennsylvanian (Late Carboniferous) in age. These strata were laid down in subbasins of the larger Maritimes Basin (Bradley, 1982) which, in turn, contain a number of coal fields as shown in Figure 18. Of these fields the most important in terms of resources and production is the Sydney coalfield. Other fields with past or present production are the three smaller fields 8, 9 and 10 on western Cape Breton Island, fields 5, 6 and 7 on the mainland of Nova Scotia and 1, 2 and 3 in New Brunswick. The coals in the different fields occur in different stratigraphic units which, in ascending order, are: Riversdale, Cumberland and Pictou/Stellarton Groups (Bell, 1944; Hacquebard, 1972). The Morien sequence in the Sydney field is equivalent to the Pictou/Stellarton Group. Deformation within these fields ranges from gentle to moderately severe. The most disturbed field structurally is probably Springhill (Fig. 18, Field 5 ). In the Sydney field, structure is characterized by broad, open folds superimposed on a gentle eastward dip toward the offshore. The deformation observed in the Atlantic Provinces coal basins resulted from the Appalachian orogeny at the close of Pennsylvanian (Carboniferous) time, which corresponds to the Caledonian phase of the Hercynian orogeny in Europe. Coal ranks in the Atlantic fields are virtually all bituminous, most of them high-volatile A bituminous coal. Some anthracite has been reported from the Debert-Kemptown field (Fig. 18, Field 6). As mentioned above, most of the coalification is believed to be postdeformational. The rationale for this conclusion will be discussed in detail.
238 COALFIELDS 1
~":i~
~9 Vhite
Bay
NEW- ~
GULF OF ST LAWRENCE
1. 2. 3. 4. 5. 6. 7. 8, 9.
10. 11, 12. 13,
MINTO LAKESTREAM BEERSVILLE JOGGINS-CHIGNECTO SPRINGHILL DFBERT-KEMPTOWN PICTOU PORT HOOD MABOU-INVERNESS ST. ROSE-CHIMNEY CORNE~[ SYDNEY ST GEORGES HOWLEYCOAL AREA
St. 6~orges~c~p12
B=y/
~
/~
Magdalen ~ : ~ Islands
~C
,S/'°-
11
1 ~:" ta:;
ATLANTIC ocEAN
Kilometers
ROCK GROUP
STAGE
<=
RIVERSDALE -
PERIOD
PICTOU/ STELLARTON
CUMBERLAND 1
MORIEN
PERMIAN
MINTOI
BEERSVILLE : OEBERTKEMPTOWN ~
D ~ ~
c B
PORTHOOD ST GEORGES ST ROSE/ CHIMNEY
NAMUREAN
JOGGINS- i i 1 ~ I CHIGNECTO SPRINGHILL
PICTOU MABOUINVERNESS
VISEAN TOURNAISIAN
j3~
SYDNEY [J B
PENNEYLVANIAN
MISSISSIPPIAN
~ Period o/ coat deposition
DEVONIAN
Fig. 18. Map showing distribution of coalfields in Atlantic Provinces of Canada. Diagram in lower part of figure shows coal-bearing stratigraphic units in each coal field (from Smith, 1989).
Fundamental aspects of coalification in Atlantic Canada Evidence for postdeformational coalification
In postdeformational coalification, the rank increases with the present depth
239 NAME OF SEAM 0-m
PT. ACONI BONAR STUBBART
200-
MEAN MAXIMUM REFLECTANCE, R o - % 0i70 0i7S 0.801 0i85 0ig0 •
I. "I
HARBOUR
9 uJ
400-- _ ~ B L A C K R O C K m COLLINS
0 0
m SPENCER
GREAT BRAS D'OR CLIFF SECTION
.'1" I.
Iw
6O0-
Z )-
g
I i I
800.
w ffJ 1000. m
"1a.
COALBROOK
•
_ TRACY
I
"I
MIRA BAY CLIFF SECTION
1200- w I-n,I,-
I I
1400_ SHOEMAKER 160n METRES
McAULAY
•
I I
Fig. 19. R variations of surface coals and stratigraphicposition,Sydney coal field (afterHacquebard and Donaldson, 1970). ....
below the surface, and does not follow stratigraphy in surface exposures (Hacquebard and Donaldson, 1970). Figure 19 illustrates that in a series of surface coals exposed in cliff sections of the Sydney coal field the rank (as measured by Rom~) does not increase with stratigraphic depth. The explanation for this is offered in Figure 20, which shows four inclined seams (A to D ) with a total stratigraphic separation of 300 m. At the surface (wavy line) these coals all have a rank of V7, i.e., they all have reflectances between 0.70% and 0.79%. However, in boreholes (at vertical right hand side of the diagram) the rank increases with depth from 0.75 to 0.80, 0.85 and 0.90% Ro max,respectively (or from V-7 to V-9 reflectance (rank) levels). The isograds (dashed lines) run horizontally and are not parallel to the seams as is the case in predeformational coalification. This means that the coal obtained its present rank from the maximum overburden that existed after deformation. In the example shown the eroded overburden was calculated at 3700 m, using the method employed by Suggate (1959).
Effect of stratigraphic separation In predeformational coalification, the stratigraphic separation between the coals and attendant higher temperatures and duration of heating were the con-
240
tlmmltl
tm l L lillTIILtli
,E,,~o?F?,' pVE,,R~U,R~N,
(3700 m. ACC. TO SUGGATE INDEX @31
%Ro
° o
'"P]UIIIIJJJII'"'IUIIIIU]II' " IIUI II"" 2001
0.80
0.85
kO0
(Sydney-N.S.)
~
,
0.90
m. Fig. 20. Diagnostic features of postdeformational coalification (after Hacquebard,1975). 0.8 I
0
0.9 I
I.o f
1.1 I
1.2 I
1.3 I
1.h I
1.5 l
(~)DOM. NO. 14
1.6 J
"]
X McBEAN
[ ) • SPRINGHILL NO. 2 |
\ ~ " Oi;:~-//O~'~,O~ ~
400
Ak DRUMMONDNO. l
!X
,2o0
~ ~"~..
]
~FO\ "~
;
ua
~.
- '~'~" ]
~ ~kPRE-FOLDING ~(Strat.
I
Separation)
"-..
COLLI ERY
J
~(Vertieal Sequences)
POST-FOLDING ~"..~{IndividualSeams)
I
"
I
1600
% R0
""-
I
"~'
~-
I
\ HV i
36
I
34
"'
%VM
I
~
I
I
MV
I
I
I#
32
30
28
I
26
I
LV
22
20
,
l
I
24
18
Fig. 21. Determination of predeformational coalification in Carboniferous of Maritime region {after Hacquebard, 1975).
trolling rank factors. In this case, maximum overburden was reached before folding. Although essentially postdeformational in origin, the coals of eastern Canada were affected to a minor degree by predeformational coalification also, as shown in Figure 21. In this figure, the middle curve (postfolding) shows the change in rank of individual seams with the present depth of mining. It is a
241 composite curve, put together from the rank changes observed in four slope mines, namely: Dominion No. 14 of Sydney field; McBean and Drummond No. 1 of Pictou field; and No. 2 Mine of Springhill field (see Fig. 18). As can be seen, the changes in rank are considerable. Over a depth of 500 m, for instance, the rank increases in Dominion No. 14 from a high-volatile bituminous (HV) coal with 36% volatile matter to a medium-volatile bituminous (MV) coal with 30% volatile matter. The coaliflcation gradient of this curve amounts to 0.044% R . . . . per 100 m of depth. As individual seams are involved, the 0.044 rate of increase is caused by post-deformational coalification only, because there is no stratigraphic separation. The upper curve of Figure 21 (resultant rank) shows the change in reflectance of successive seams cut in boreholes. It also is a composite curve that was derived from several wells that have been examined previously by Hacquebard and Donaldson (1970). Its coaliflcation gradient is 0.061/100 m. This is 0.017 higher than the gradient obtained on the middle curve, and this value represents the increase caused by the stratigraphic depth, or by predeformational coalification. It is shown separately in the lower curve. In the Maritime region, the postdeformational coalification greatly exceeds the predeformational coalification. A coal at position A in Figure 21 on the lower curve, with a rank of about 34% volatile matter before deformation, obtained the rank of B on the upper curve (equal to about 25% volatile matter), because of overburden that accumulated after deformation.
Effect of overburden and geothermal variations Regional changes in coalification are due mainly to differences in the original depth of overburden, but superimposed on these are changes in the paleogeothermal gradients. The effect of this is revealed by coal rank studies in the Sydney coalfield and in the Carboniferous basin of New Brunswick.
Rank changes in Sydney coalfield Rank~overburden relationship. The lateral changes in rank in the Sydney coalfield are shown on the isoreflectance map of Figure 22, which pertains to the Harbour seam (Hacquebard, 1983 ). Within this seam the rank increases from V-7 in the west to V-9 in the east of the field. This change occurs in coal that lies at about the same depth below the surface. It is also apparent by comparing readings obtained in the offshore area at greater depth. The Harbour seam intersected at - 9 1 4 m in borehole H-1A at Lingan has a rank of 1.11% R . . . . . whereas at - 707 m in borehole H-8 at Donkin it reached a reflectance of 1.13% Ro max. This means that it requires 207 m less depth of mining at Donkin than at Lingan to encounter coal of the same MV rank. Apart from the regional increase in rank from west to east, the map of Figure
242
ATLANTIC OCEAN ..........
.°
i,.....
" ............ 4000
~Sydney V-TYPE
% V.M'~
V7
38-41
eH'2 BOREHOLE
V8
36-38
...... CONTOURS
V9
33-36
- - ' - - OUTCROP
vlo VII
31-33 29-31
-__
EXTENT OF WORKINGS
0 ()
Km Mi,
5
i " ~
......
4 GSC
Fig. 22. Regional rank variations in the Harbour seam of the Sydney coalfield, plotted in increments of equal vitrinite reflectance (Ro max) (after Hacquebard, 1983). V.M.-- volatele-matter content.
22 also shows a distinct increase in the degree of coalification, as measured by Ro max,from southwest to northeast. This direction closely follows the downdip structure of the seam, and results in higher-rank coals being present at a greater depth of mining (and greater distance from shore). Noteworthy is the observation that lines of equal rank cross the structure contours, thus showing that the coal had obtained its present rank position after folding took place. In other words, postdeformational coalification is clearly indicated. As was mentioned previously, such coalification reflects the maximum amount of overburden that existed after the deformation. The observed regional increase in rank indicates that there existed less burial in the northwestern than in the southeastern parts of the coalfield. Calculations according to the method of Suggate (1959) gave 3700 m of eroded overburden in the western part of the field as compared to 4200 m at Donkin. This result is in agreement with the transgressive nature of the upper coal-bearing zone, which shows a thickening from west to east.
Rank/paleogeothermal relationship. The effect of variations in paleogeothermal conditions on the rank of coal can be deduced from changes in the coalification gradient of vertical seam successions. For the Sydney field, as shown
243
in Figure 23, rank-depth relationships of sixty-three coals intersected in ten boreholes are illustrated in four diagrams (Hacquebard, 1984a). Each diagram relates to an area in which the slope of the coalification curves in each of the four subfigures is subparallel, signifying almost identical coalification gradients, which are expressed in %R . . . . change per 100 m increase in depth. Different gradients were obtained in the four diagrams, from a low of 0.052% to a high of 0.088% Ro ~ J 1 0 0 m (underlined numbers). These considerable variations (the latter is 1.7 times the former) are likely the result of marked changes in the paleotemperatures at the different sites. These temperatures can be calculated from coal-rank data according to the method outlined by Bostick et al. (1979), and then can be used to determined the paleogeothermal gradient of each well. A variation of 2.5-6.7°C/100 m was obtained; with the majority of the wells in the central part of the field showing a gradient of 4.3 ° C/ 100 m, a value which compares with 4.0 and 4.3°C/100 m obtained in the Carboniferous coalfields of the Ruhr and Dutch Limburg (Hacquebard, 1984a). The detailed correlation between the two gradients in the Sydney coalfield is shown in Figure 24. It amounts to a change in paleogeothermal gradient of 1 °C per 0.01% change in the coalification gradient. This value is not constant, but varies between different coal areas because different rank relationships and different coalification times are represented. LEGEND
0.7 oo .
, .>.
,e~?, ,-,%
,
...... ~~ : < ~ ~
i
%Ro max '.,
'
'
'
1.2 '
1
Structure and well location map wilh contours on Harbour seam 0.8 1.3 500
IIOC
X
O.088=Coaliflcatlon Gradient in %Ro/lOOm de~rh • • :Samples of individual coal seams WELL AND SAMPLE IDENTIFICATION I: Murphy el al North Sydney P-05, " 2 : Shell el al North Sydney F 24; • 3: DEVCO C IlL • 4:NSDM GIace Buy H IA(1977), 5: H 2 (~978), 6= H-8A(1978), 7: H 8(1977); 8: H-SB(1977), 9: H 6 H977), I0: Birchgrove No I well, •
0.7 O 0.8 I O O i ~ '
1.2 '
,
,
0.072 "% ' ~ ' X 4 5 0.052 800
6
80C
Fig. 23. Coalification curves of ten wells in the Sydney Basin (after Hacquebard, 1984a).
244 0.100
/
CORR.COEE:0.9753 /
I
-
0.080
6 .5"4~ 0.060
.10
2 0.0401
2:0
" 3:0
4'o
5:o
6:o
7'o
°C/100rn
Fig. 24. Correlation of coalification gradients and paleogeothermal gradients in the Sydney coalfield (after Hacquebard, 1984a).
Rank changes in Carboniferous basin of New Brunswick Relationship with underlying igneous basement. The total Carboniferous cover in the central basin of New Brunswick is less than 2 km thick and rests with marked angular unconformity on a basement of earlier Paleozoic and Precambrian rocks. These earlier sediments were considerably metamorphosed by tectonism and intrusions of granite during the Acadian orogeny in Devonian time (Gussow, 1953 ). All igneous activity had ceased when the coal measures were laid down during Westphalian C and D and Stephanian times. The coals present in the central Carboniferous basin show a progressive increase in rank from HV-C bituminous coal to anthracite via HV-B, HV-A, MV, LV, and semianthracite, when proceeding from northeast to southwest (Fig. 25), (Hacquebard and Avery, 1984). As the coal-bearing sediments also become progressively older in the same direction, the rank changes can, in part, be related to an increase in the thickness of the original overburden, but only to the rank of HV-A bituminous coal. Beyond this rank, the amount of original overburden required to reach the anthracite stage probably never existed in the area (an additional 2200 m would be required, whereas the stratigraphy only provides 200 m). Therefore, as deduced from wells in eastern Prince Edward Island, a heat source other than that provided by greater depth of burial is required. This heat source may have originated from the igneous rocks that surround the southwest corner area and most likely underlie it. This is deduced from the
245 64 o
66° CHALEUR BAY
LEGEND %Ho MAX
L
Icl c
0.6 ~
OB ~
"4 fill Sil
I+8~;:: t 2.6~r~,~
HIGH VOLATILE
GULF OF G[ LAWRENCE
I~I
. . . . OL. . . . . SEMIAHTHRACITE
ANTHRACITE
i:"~
!~i.'~' ..... ii!ii~ i::i:i:i::.::i: i!
46°
fS
0
KILBMETRES,
50
64°
Fig. 25. Generalized coal rank map of the Carboniferous Basin of New Brunswick (after Hacquebard and Avery, 1984).
Bouguer gravity map (Fig. 26, Chandra et al., 1980) and shows the gravity variations in 20 milligal increments. Negative gravity values of - 20 milligals and more are interpreted as expressions of igneous rocks, whereas those less than - 20 milligals denote metamorphic and sedimentary sequences. The map indicates that the pre-Carboniferous igneous rocks that border the basin in the southwest corner of the area may continue past Fredericton in a northeast direction. Other igneous rocks of the pre-Carboniferous basement complex may occur near Bathurst in the north and in the extreme southeast at the border between New Brunswick and Nova Scotia. The possible effect of the igneous rocks on the variations in coal rank is indicated by the isoreflectance contours that have been superimposed on the gravity map (Fig. 26). Areas of higher rank appear to be underlain by igneous rocks or lie in close proximity to them. Because the latter predate the coal
246 64 °
66 °
GRAVITY IN MILLIGALS -60
~I~
-40
-20
0
+20
ISOPLETH Of VITRINITEREFLECTANCE (%Ro)
GULFOFETLAWRENCE Jpl
~-2o?" I
/
s
fl t,~
~'\\ !
",
] J
/
11
~
~l \\
/I
::
~ : .:::::;
~\
I
i
L--.+ ,o',
/
4!iii: : ?
/ /
..:::::::::::. *.: : : : -
i_
:::
/:
iI
J"
/---40~ /
E
/
i/I I//
/
-/
•
.,:.:.:. ~: : : : : :
E'---
;
)~
d6°
64 •
Fig. 26. Relationship between gravity variations and coal rank (after Hacquebard and Avery, 1984).
measures by a considerable amount of time [they are Devonian and Late Carboniferous (Mississippian) in age ], direct heating from intrusion or volcanism did not occur, but additional heat flow due to the high conductivity of igneous rocks likely did take place. This view is supported by present-day heat flow measurements in the area (Hyndman et al., 1979), which show the highest value (72 m Wm -2) at Mount Pleasant (in extreme southwest corner). This compares with values of 57 and 64 south of Bathurst, 45 in central Prince Edward Island, and 49 at Wallace, Nova Scotia. The progressive increase in heat flow towards the igneous masses appears to offer a better explanation for the occurrence of high-rank coals in the southwest corner of the central basin than the 2200 m of additional overburden from younger formations that was mentioned previously.
247
Some geological applications of coalification studies in A tlantic Canada Depth of burial determinations Subbituminous coals and lignites. The coalification process is caused by the actions of pressure, temperature, and duration of heat. As mentioned earlier, the process is irreversible; once a particular coalifica'tion level has been reached it cannot revert back to a lower level; therefore, rank data can provide information on the paleoburial conditions under which coal was formed. This includes the depth of the original overburden required to reach the rank position that has been attained, under existing paleogeothermal conditions. During the early stages of diagenesis it is mainly pressure that advances the degree of coalification. The pressure caused by the weight (or thickness) of the original overburden causes a loss of moisture content, until the rank of high-volatile C bituminous coal is reached. On the basis of a series of German data, Hacquebard (1977) found that an asymptotic relationship exists between "bed" (or equilibrium) moisture content and depth of burial. The German data were later augmented by moisture determinations on subbituminous coals of Alberta by Nurkowski ( 1985 ), as shown in Figure 27. The relationship found in Alberta coals can be expressed in the following formula: DOB = (1.865 - log. MEQ)/0.00046
DEPTHOF BURIALIN FEET 5000
0 i
i
L
i
J
i
L
10000 i
i
J
5O 70 3Ot 3
i
Ro
~
0.3
-0.4
2o
0
2 lO m_
U Z
a u.i
/4
- 0.5
~
o
~U
-0.6
Oz.~ ..r~V 'T"
1
I
o
I
1000 2000 DEPTHOF BURIALIN METRES
I
3000
Fig. 27. Modified moisture-depth of burial diagram (Hacquebard, 1977 ), including the coal ranks
as found in the plains of Alberta (after Nurkowski, 1985). Brown coal as used in this diagram corresponds roughly to the German soft brown coal (Weichbraunkohle) whereas lignite refers to part of the Mattbraunkohle of the German classification (Teichmtiller and Teichmtiller, 1982). Lignite as used here also roughly corresponds to the ASTM lignite A. Ro = mean maximum vitrinite reflectance.
248
in which D O B = m a x i m u m depth of coal burial and M E Q = equilibrium moisture content. W i t h the aid of this formula, the depths of burial of two Nova Scotia lignite deposits, with 30 and 35% equilibrium or "bed" moisture contents have been calculated at 760 and 780 m (Hacquebard, 1984b). As these deposits, which are of Early Cretaceous age, occur in close proximity to the surface it can be concluded that at least some 750 m of sediments have been removed by erosion. The lignite deposits form part of very limited and isolated Cretaceous deposits that occur on the mainland of Nova Scotia and Cape Breton Island. At one time they may have been much more extensive, as is still the case in the present offshore Cretaceous sediments on the Nova Scotia Shelf.
Bituminous coals. Once the coalification level of bituminous coal is reached, the equilibrium moisture content remains fairly constant and is generally below 5%. In bituminous coals, the volatile-matter content and vitrinite reflectance are the most sensitive rank parameters. Following Hilt's Law (1873), which states that in vertical sequences coalification increases regularly with depth, the amount of original overburden can be deduced from coal-rank determinations. In Atlantic Canada, the composite coalification curve of (Hacquebard (1974) can be used for rank determination. It is based on the changes in coal rank with depth of a series of Mesozoic and Carboniferous coals. The rank data were obtained from vitrinite reflectance (R . . . . ) measurements, which are indicated on the abscissa at the top of Figure 28; the corresponding volatile-matter contents (VM) and the A S T M (1979) rank classes are shown at the bottom. The composite curve (Fig. 28) was derived from Ro max determination of 29 Mesozoic coals (upper curve) intersected in boreholes of the Scotian Shelf, and 39 Carboniferous coals (lower curve) from onshore boreholes in Atlantic Canada. The two curves overlap in the rank range from 0.63 to 0.95% Ro max, where they have almost identical coalification gradients, namely 0.033/100 m and 0.036/100 m. Because of the identical gradients it is acceptable to consider the two curves as one general coalification curve for the Maritime region. The asymptotic relationship between rank and depth is clearly indicated and when plotted on semi-log grid a linear curve will result (Hacquebard and Avery, 1984 ). The Maritime coalification curve permits direct conversion of coal rank to original depth of overburden. The depth shown on the ordinate is thought to relate to the maximum sediment thickness that ever existed on the Scotia Shelf (McIver, 1972). Therefore, from the curve it is deduced that on Brion Island 2240 m of strata have been eroded (Fig. 28). The general coalification curve can be used to convert the rank of individual surface or near-surface coals to overburden thickness, when borehole sequences are not available, but it will give an average value only. However, when a vertical succession of coals is present, the coalification curve of that succes-
249 .2
.3
0
.4 1
I
.5 I
.7
.6 I
I
.8
.9
I
I
1.0
I.I
1.2
1.3
1.4
1.5
T
I
r
i
1
f
1.6 I
% Ro
o
OOO -
l o
:\o
000 -
WELL H (BRION I S . )
o
Xo
PERMIAN ?
V-5 2460 m
×o ~×
~000
STEPHANIAN
TOP MIC MAC m
m
• ~
000
WELL WELL WELL WELL WELL WELL WELL WELL WELL WELL
5000 BROWN METRES COAL % VM
800 m
D
WESTPHALIAN
A~ B o C x
MESOZOIC
D% E +" F m G A H • I
•
J
4-
LIG.
++
u+ L
• CARBONIFEROUS
SUB BT.
IIIGH C 45
B 40
VOLATILE A
MEDIUM VOLATILE
I LOW VOLATILE
I 31
22
i
13
Fig. 28. Composite coalification curve of Mesozoic and Carboniferous coal sequences in the Maritime region (after Hacquebard, 1975 ). Ro = mean maximum vitrinite reflectance; V M = volatilematter content (daf).
sion should be used. Its gradient may differ from the general curve and a more precise overburden determination will result. The maximum depth of burial is obtained by projecting the curve to the 0.2% Ro maxlevel, which is the reflectance of newly formed vitrinite (huminite) (Dow, 1977; Fig. 29). This level, therefore, may be regarded as the zero position of coalification, a conclusion supported by numerous east coast offshore wells that are believed to be at maximum burial depth at present (Vonk, 1986).
250 Ro/PERCENT LOG SCALE 0.4 0.6
0.2
0.8
1
1.4
0
PROJECTED: 0.2% R o = -1530m 0.44% Ro= 0m
.__1 I I.n
121
\
LEGEND x 2-
= COAL
S L O P E = 0.222 LOG R o / K m
Fig. 29. Coalification curve of the Bradelle L-49 well with projected original depth of overburden (after Vonk, 1986).
Rank as aid to structural interpretations
The Upper Carboniferous coals of Atlantic Canada have been only mildly affected by the Hercynian orogeny. Folding of the coal measures has been largely the result of initial dip, of differential compaction, and of variable uplift due to diapiric movements. Most of this deformation took place during the early stages of coalification, but this was followed later by the development of major faulting, particularly along the west coast of Cape Breton Island and in western
251 Newfoundland. A large fracture zone can be traced in this region and even may represent the pre-continental drift extension of the Great Glen Fault of Scotland (Hacquebard, 1972). Therefore, the faulting represent the major tectonic event that affected the coal measures in Atlantic Canada, but the age of this faulting and its relationship to the Hercynian orogeny has not been resolved. As will be shown here, the interpretation of coal-rank variations in the Mabou coalfield of western Cape Breton Island (Fig. 18) has thrown light on this problem. The rank:depth relationship of four coals intersected in four offshore wells drilled in the Gulf of St. Lawrence Basin is illustrated in Figure 30A (Hacquebard, 1986). In the diagram, the lines of equal rank, or isograds, run horizontally and correspond with specific depth positions, because postdeformational coalification is represented. These positions correspond with maximum depth of burial values shown in the ordinate on the right, which were obtained from the Maritime coalification curve previously discussed. The Maritime curve relates a rank of 0.5% Romax to an overburden of 2658 m (8720 ft), which is indicated at the upper end of the ordinate. The scale below this value corresponds to the present depth scale and therefore takes into account the gradient of the curve, which differs somewhat from the general Maritime curve. The curve shows a near-perfect linear correlation between depth and rank (plotted on logarithmic scale) when the Ro m a x data on the two Mabou coals of Borehole M-2A and the six surface coals are not included. The latter all have nearly the same rank of about 0.64% Ro maxand, therefore, should have plotted at a depth of 762 m (2500 ft), and the coals in Borehole M-2A at a depth of 1158 m (3800 ft). The present position of these coals is related to the faulting shown in Figure 30B. These faults are part of the major fracture zone that occurs along the west coast of Cape Breton Island, as previously described. Figure 30C shows that at Mabou Mines some 2286 m (7500 ft) of additional sediments must have been present to meet the rank-overburden requirements of the coals involved. These additional strata most likely accumulated during Permian time, as can be deduced from the fact that a few thousands of meters of red beds of Permian age are still present today in most wells drilled in the Gulf of St. Lawrence (Hacquebard, 1986). The rank of the surface coals also required additional overburden, and, therefore, the coals cannot have been placed in their present position until after the Permian red beds had been deposited. It is concluded from this analysis that the faulting took place in postPermian time, probably Early Triassic time. This event probably constituted the final phase of deformation of the Fundy epieugeosyncline. It led to the formation of a complex rift valley, which is bounded by high-angle faults (Hacquebard, 1972 ). Apart from determining the age of faulting, rank studies also can provide information on the displacement along various faults. At Mabou Mines the total displacement was of the order of 762 m (2500 ft), as this is the difference
u_
7 FT
o 13 FT
•
4%Ro
12
10
09
M-2A
~
o
I
i
L
RION IS. ~x~M-1
SURFACE C O A L S
i
10
Rank
• 15 FT
f(Vertlcal Depti])
INV EQ
ISOGRAD
L
12
--~
i
__
18000 (5486m)
14.000
-10000
-8.720
1 4 %Ro ( m a x )
%
MABOU
EAST PT.
M ' 2 A ~ o - ~ x ~
i
08
A. GULF OF ST. LAWRENCE C O A L I F I C A T I O N CURVE FROM B O R E H O L E Ro.-DATA, AND RANK POSITION OF SURFACE C O A L S IN UPTHROWN FAULT B L O C K S
10.000(3049m)
5000
08
07
06--
i
06
<
::]
7I-r, W ,'m
rn
n'-
L,L
W £3
I I--
Z
...I W
~"
5000 {1524m
2500-
0-
6000-1 (1829m)
4000"
2000\0~ 5
COAL SEAMS
4
M-2A o
.
.
.
.
.
.
.
I
M-,
~. ~-:./"-4-
. . .
15FTJ
-
]------
MABOU SHORE
7500 FT. OF P E R M I A N RED BEDS (NOW ERODED)
F A U L T I N G A N D UPLIFT IN POST P E R M I A N T I M E
-----
N
/064
"<\
~-...
12 000 !3658m)
~10 000
- 8 720
-8000
0
MINES
7 8 FT-I_ MABOU
065\
.. S / \ . - " "
C. C R O S S S E C T I O N AT M A B O U M I N E S AT T I M E OF M A X I M U M BURIAL, B E F O R E FAULTING AND UPLIFT
0 7 --
°71
..-:'~"
0 74~
O
M-I
r INVERNESS EQUIVALENT 7 FTJ
-- 13 F T ~
o75.q /
"
----
~
M-2A
Fig. 30. Coal-rank variations as indicator of time of faulting in mMbou coalfield, Nova Scotia (after Hacquebard, 1986 ).
I-o_ LU th
I
Z
_l J w
Go
0
t
04
0 FT
B. CROSS S E C T I O N AT M A B O U MINES WITH %Ro. D A T A (0.65)
X <
O. W C3
I
m
uv
l'O CJ1 bO
253 in depth between the Ro m,x of 0.6% of the surface coals and the R . . . . of 0.6% in Borehole M-2A (Fig. 30B). A displacement of this magnitude indicates a major tectonic event was involved. The M a b o u data also gave information on the duration of the coalification process. Because it was postfolding, but prefaulting, only the time span of the Permian, or about 40 million years, may have been involved (van Eysinga, 1975).
Rank as aid to provenance determinations of sedimentary rocks from contained detrital particles of coal Under certain conditions the rank of detrital particles of coal can be used to determine their source area. These conditions are as follows. The particles should be predominantly of one rank and derived from in situ coal seams (not from bark vitrain), because true coal seams might possess certain petrographic compositional features and a palynological assemblage that would help in identification and age dating. The coals of the possible source area should have limited rank variations, restricted geographic distribution of the rank level represented, and erosional possibilities of exposed coal seams. This set of conditions was encountered in a study of coal detritus present in samples of sand collected from below the ocean floor, in the Sohm Abyssal Plain, some 760 km east of Bermuda (Fig. 31; Hacquebard et al., 1981). The samples were from a piston core that intersected 13 m of unconsolidated Late Pleistocene to Holocene sediments at the ocean floor. Below 8 m they consisted of graded turbidite clays with basal laminae of silt and sand, which contained IO0o
o
Fig. 31. Physiographic regions of the northwest Atlantic Ocean with coal sample location and onshore areas with high-volatile bituminous coal (hatched areas) (after Hacquebard et al., 1981).
254 minute grains of coal. The latter were I mm or less in size, and the total amount of coal available for study was about 50 mg. Microscopic examinations of polished surfaces under reflected light revealed that a normal banded coal is represented. All coal maceral groups occur, i.e., the vitrinite, liptinite and inertinite maceral groups, as well as finely divided pyrite. This indicates origin from ancient peat accumulations that led to the formation of normal banded coal. Therefore, the detrital coal particles must have been derived from in-situ coal seams. The rank of the coaly fragments is HV-A bituminous, which was determined from vitrinite reflectance. An average Ro maxof 0.80% was obtained which correlates with 36% volatile matter (KStter, 1960). Because the reflectogram has a unimodal distribution, it can be assumed that coal from only one provenance is present. In eastern North America, surface or near-surface coals with a rank of HVA bituminous occur in the Appalachian and Interior coal provinces of the United States and in the Maritime Provinces of Canada (Fig. 31) (Moore, 1947). These coals are all of Carboniferous age and only those regions bordering the coast of the Atlantic Ocean, or possessing main drainage systems into this ocean (e.g., the Hudson and St. Lawrence rivers), need be considered as possible source areas for the Sohm Abyssal Plain coal occurrence. The main drainage system for the Interior and Appalachian coal provinces is into the Gulf of Mexico. Such source regions are present only in Nova Scotia, namely in the coalfields of Joggins on the Bay of Fundy and Sydney on the Laurentian Channel (Fig. 31). The petrographic composition of the detrital coal particles closely resembles that of the Sydney coals. Identical microlithotypes and similar forms of pyrite are present. Most interesting is the observation that the maceral sporinite is derived from plant spores and probably not from pollen. This indicates that the coal most likely is of Carboniferous age, because pollen-bearing plants did not exist until the late Mesozoic, when the flowering plants first appeared in geologic time. A study of isolated spores carried out by M.S. Barss of the Atlantic Geoscience Centre confirmed the above view: a Carboniferous coal is represented and it can be dated as Westphalian D, because the Thymospora zone is clearly indicated (M.S. Barss, pers. commun., 1988; also Barss and Hacquebard, 1967). This age strongly suggests a Sydney source for the detitral coal because only in this field do coals of Westphalian D age occur and are exposed at the surface, both onshore and in the nearshore submarine area (see fig. 4, Hacquebard et al., 1981). The spore dating rules out derivation from the Joggins coal field, because there the coals are Westphalian B in age. With the Sydney coalfield as provenance area the question may be asked: what was the mode of transport to move the detrital coal particles a distance of some 1800 km, from Sydney to the Sohm Abyssal Plain? Turbidity flow is
255 believed to be the answer. This view is supported by evidence obtained from the 1929 Grand Banks earthquake. This quake jarred the continental slope and shelf, setting submarine slumps in motion, which triggered a large turbidity current. This current moved from the Laurentian Cone southeast towards the west flank of the Mid-Atlantic Ridge and then south along the east side of the Sohm Abyssal Plain. How far the Grand Banks turbidite reached is not known, but the observation that at 740 km from its source the velocity was still 20 km per hour suggests that the area affected extended hundreds of kilometers farther south (Heezen and Ewing, 1952). It should be noted that the direction of flow of the Grand Banks turbidite of 1929 pointed directly at the coal location in the Sohm Abyssal Plain. The coal attests to the fact that a previous turbidity flow, which took place some 35,000 years ago, apparently followed nearly the same path, and reached a point that is some 1,500 km south of the continental rise. This result supports the view expressed by Heezen and Ewing (1952) that sediment can be transported far out into the oceanic basins through the medium of turbidity flow. The value of detrital coal in sediment transport analysis was shown also by Burgess (1987), who traced his "coffee grounds" particles of the Mississippi Delta to the Interior Coal Province, some 1600 km upstream from the site. Here too, coal-rank determinations and spore identifications provided the dual approach in reconstructing provenance, transport history, and origin of the detrital coal particles. ACKNOWLEDGEMENTS The authors deeply appreciate assistance in a variety of forms from a number of colleagues at The Atlantic Geoscience Centre (AGC) and the Institute of Sedimentary and Petroleum Geology (ISPG). Special thanks are due to Donna Smith at ISPG who typed the final draft of the manuscript, to Carol Boonstra at ISPG who assisted with typing and also drafted a number of the figures, Nelly Koziel (AGC) who typed the initial draft of the Maritimes portion of the manuscript and to Ken Pratt (ISPG) and Mike Avery (AGC) who carried out many of the reflectance determinations upon which the paper is based. The paper was reviewed by R.M. Bustin and N.H. Bostick.
REFERENCES Allan, J.A. and Carr, J.L., 1946. Geologyand coal occurrencesof Wapiti-Cutbank area, Alberta. Res. Counc.Alberta, Rep. 48, 43 pp. AmericanSocietyfor Testing and Materials (ASTM), 1979. AnnualBook of ASTM Standards, Part 26, GaseousFuels; Coal and Coke;AtmosphericAnalysis,938 pp. Barnstable, D., 1980. The Quinsamcoalproject. Bull. Can. Inst. Min. Metall., 73 (816): 89-97.
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260 Stott, D.F., 1974. Lower Cretaceous coal measures of the Foothills of west-central Alberta and northeastern British Columbia. Can. Inst. Min. Metall. Bull., 67: 87-101. Stott, D.F., 1984. Cretaceous sequences of the Foothills of the Canadian Rocky Mountains. In: D.F. Stott and D.J. Glass (Editors), The Mesozoic of North America. Can. Soc. Pet. Geol., Mere., 9: 85-107. Suggate, R.P., 1959. New Zealand coals; their geological setting and its influence on their properties. N. Z. Dep. Sci. Indust. Res., 134: 113. Sutherland Brown, A., 1968. Geology of the Queen Charlotte Islands, British Columbia. B. C., Minist. Energy Mines. Pet. Resour. Bull. 54, 226 pp. Swartzmann, E., 1953. Analysis directory of Canadian coals. Can. Dep. Mines, Tech. Surv., Mines Branch, Rep. 836, 204 pp. Teichmiiller, M. and Teichm~iller, R., 1982. The geological basis of coal formation. In: E. Stach, M.Th. Mackowsky, M. Teichmiiller, G.H. Taylor, D. Chandra and R. Teichmiiller (Editors), Coal Petrology. Borntraeger, Berlin-Stuttgart, pp. 5-86. Thorsteinsson, R., 1974. Carboniferous and Permian stratigraphy of Axel Heiberg Island and western EUesmere Island, Canadian Arctic Archipelago. Geol. Surv. Can., Bull., 224, 115 pp. Thorsteinsson, R. and Tozer, E.T., 1970. Geology of the Arctic Archipelago. In: R.J.W. Douglas, (Editor), Geology and Economic Minerals of Canada. Geol. Surv. Can., Econ. Geol. Rep., 1: 549-59O. Tibbetts, T.E. and Montgomery, W.J., 1960. Analysis directory of Canadian coals, Supplement No. 2. Can. Dep. Mines, Tech. Surv., Mines Branch, Monogr. No. 868, 56 pp. Utting, J., Goodarzi, F., Dougherty, J. and Henderson, C., in press. Thermal maturity of Carboniferous and Permian rocks of the Sverdrup Basin, Canadian Arctic Archipelago. Geol. Surv. Can. Paper. Van Eysinga, F.W.B. (compiler), 1975. Geological Time Table, 3rd ed. Elsevier, Amsterdam, The Netherlands. Vonk, A.M., 1986. Vitrinite reflectance (R . . . . ) of coal samples from Shell-Soquip-Amoco Bradelle L-49. Atlantic Geoscience Centre, Dartmouth, Nova Scotia, Canada. Report No. EPGSDOM. 9-86AMV, 26 pp. Williams, E.V. and Ross, C.A., 1979. Depositional setting and coal petrology of Tulameen Coalfield, south-central British Columbia. Bull., Am. Assoc. Pet. Geol., 63: 2058-2069.
207
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
D i s t r i b u t i o n and c o a l i f i c a t i o n p a t t e r n s in C a n a d i a n b i t u m i n o u s and a n t h r a c i t e coals* P E T E R A. HACQUEBARD1 and ALEXANDER R. CAMERON 2
'Atlantic Geoscience Centre, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, N.S. B2 Y 4A2, Canada 2Institute of Sedimentary and Petroleum Geology, 3303-33rd Street, IV. W., Calgary, Alta. T2L 2A7, Canada (Received April 28, 1988; revised and accepted November 22, 1988)
ABSTRACT Hacquebard, P.A. and Cameron, A.R., 1989. Distribution and coalification patterns in Canadian bituminous and anthracite coals. In: P.C. Lyons and B. Alpern (Editors), Coal: Classification, Coalification, Mineralogy, Trace-element Chemistry, and Oil and Gas Potential. Int. J. Coal Geol., 13: 207-260. Canadian resources of bituminous and anthracite coal occur in six of ten provinces and in the Yukon and Northwest Territories. These higher-rank coals are found in 12 of the 16 coal-bearing basins within Canada. For some of these basins, knowledge of rank and coalification patterns is limited; in others, it is extensive. Coalification patterns were examined in detail for two areas: the southern end of the Canadian Rocky Mountain coal belt which is underlain by the coal-bearing Kootenay Group and the Maritimes Basin which is underlain by several coal-bearing formations of Pennsylvanian (Late Carboniferous) age. In the southern Rockies, reflectances on coal range from 0.61 to 2.65% R . . . . . which represent high-volatile B bituminous coal to semianthracite. In general, there is an increase in rank from SE to NW and from NE to SW. Superimposed on this pattern are several anomalies. At several locations, ranks change rapidly over short distances. An example is in the Mount Allan syncline, where the reflectances in the Kootenay section on the SW vertical limb range from 0.68 to 0.94% R . . . . in contrast to a range of 1.30-2.49% R . . . . for a comparable section on the NE upright limb. This variation occurs over a distance of about 3 km. Multiple intersections of Kootenay strata in oil wells at the south end of the area show low reflectances (0.76% R . . . . ) at depths of about 3800 m with no change in the shallower Kootenay repeats, whereas wells farther north show higher reflectances and increase with depth. Different burial depths, the influence of thick thrust plates, different paleogeothermal gradients and ground-water movements, all likely have played a part in generating these coalification patterns. A significant part of the coalification in the Kootenay Group appears to have been postdeformational. The rank of the coals in the various subbasins of the Maritimes Basin is nearly all bituminous. Evidence indicates that most of the coalification is postdeformational. Rank within a given coal bed generally increases with increase in depth of present-day burial and the pattern seems to be generally true for most of the coal fields studied. The average postdeformational component of total coalification has been calculated to be 72%. The most important coal field in the Maritimes Basin is the Sydney coal field. Here ranks have been shown to increase from NW to SE and from * Geological Survey of Canada Contribution No. 17088. 0166-5162/89/$03.50
© 1989 Elsevier Science Publishers B.V.
208 SW to NE, the latter direction following the downdip structure of the field. Coalification gradients for the Sydney field range from 0.052 to 0.088 Ro maJ100 m, reflecting different paleogeothermal gradients. In New Brunswick, local rank increases to anthracite are believed to be related to igneous activities. Reflectance measurements have been used to interpret stratigraphy and structure in several fields and even to trace the origin of coaly fragments obtained from deep-sea drilling near Bermuda.
INTRODUCTION C a n a d i a n coals o f b i t u m i n o u s to a n t h r a c i t e r a n k s o c c u r in r o c k s u c c e s s i o n s r a n g i n g f r o m D e v o n i a n to T e r t i a r y in age. G e o g r a p h i c a l l y , t h e y are f o u n d in six of C a n a d a ' s t e n p r o v i n c e s plus t h e Y u k o n a n d N o r t h w e s t T e r r i t o r i e s . Figu r e I s h o w s t h e a r e a l d i s t r i b u t i o n of C a n a d a ' s c o a l - b e a r i n g b a s i n s , a n d in Figure 2 t h o s e b a s i n s c o n t a i n i n g b i t u m i n o u s a n d a n t h r a c i t e coal are identified. R a n k d i s t r i b u t i o n w i t h i n t h e b a s i n s s h o w n on Figure 2 will be d i s c u s s e d briefly, followed b y m o r e d e t a i l e d t r e a t m e n t of c o a l i f i c a t i o n p a t t e r n s in t w o of t h e s e PRINCIPAL COAL-BEARING BASINS 1 N A N A I M O BASIN 2 OUEEN C H A R L O T T E B A S I N 3 BOWSEB B A S I N 4 SKEENA BASIN S BOWRON RIVER B A S I N 6 TERTIARY INTERMONTANE BASINS 7 WESTERN C A N A D A S E D I M E N T A R Y BASIN 8 MOOSE RIVER BASIN 9 M A R I T I M E BASIN 10 ST. ELIAS TROUGH 1 1 WHITEHORSE TROUGH 12 T I N T I N A TRENCH 13 BONNET PLUME B A S I N 14 B B A C K E T T BASIN
16 ARCTIC OCEAN
\
i s NORTHERN YOKON lS ARCT,C BASIN PRECAMSRIAN ,.-.,-,-1
~
s.,E.o
S^S,N AREA
A T L A N TIC ocEAN
HUDSON BAY
STATE-c;
~
i . - -~ " ~ . ~ -
-
kilometers
O I
500 I
I
Fig. 1. The principal coal-bearing basins of Canada (modified from Smith, 1989).
209
Fig. 2. Geographic distribution of bituminous and anthracitic coal in Canada {see Fig. I for basin identification).
areas, namely the Atlantic Provinces and the southern part of the Canadian Rocky Mountains and Foothills belt. R a n k terminology used in this paper will be that of the A S T M classification [American Society for Testing and Materials ( A S T M ) , 1979 ]. The most abundant resources of bituminous and anthracitic coals in Canada are found in several sequences of Upper J u r a s s i c / L o w e r Cretaceous strata preserved in a long narrow belt within the Rocky Mountains and Foothills of Alberta and British Columbia. This belt is on the western edge of the Western Canada Basin. The next most abundant resources of coal of these ranks occur in a number of Pennsylvanian (Upper Carboniferous ) coal fields in the Atlantic provinces of Nova Scotia, New Brunswick and Newfoundland. Large resources of high-rank coal, particularly anthracite, are believed to be present in the Groundhog coal field within the Bowser Basin of northwestern British Columbia. Total coal resources for Canada are summarized in Table 1 and presented in more detail in Figure 3. Table 2 is a summary of rank, chemical and petrographic data, for those basins that contain bituminous and anthracite coal, together with identification of the coal-bearing formations. Basins 8, 10,
210 TABLE 1 Summary of Canada's coal resources. Rank ''2
SA/AN LV/AN~ LV MV/LV MV HV/MV HV HV/SUB SUB LIG/SUB LIG
Resources of immediate interest 3
Resources of future interest 4
Measured
Indicated
Inferred
300 420 200 2890 240 1460 710 12230 450 1500
600 300 110 4700 160 1400 370 5130 320 2710
8O 1470 , 1320 370 13310 660 3600 1250 17580 2320 3570
4590 4840 2110
156790 77730
1Data (in megatonnes) from Smith (1989). 2LIG-- lignite, SUB -- subbituminous, HV-- high-volatile bituminous coal, MV = medium-volatile bituminous coal, LV = low-volatile bituminous coal, SA = semianthracite, AN-- anthracite. 3,'Resources of immediate interest are contained in coal seams that, because of favorable combinations of thickness, depth, quality and location, are considered to be of immediate interest for possible exploitation" (Hughes et al., 1989). Measured, Indicated and Inferred refer to decreasing levels of assurance for quantities estimated (see Bielenstein et al., 1979). 4"Resources of future interest are contained in seams that, because of less favorable combinations of thickness, depth, quality and location, are not of immediate interest for possible exploitation, but which may become of interest in the foreseeable future with some changes in economics and/ or production technologies" (Hughes et al., 1989). ~Most of the coal quantities reported in this category pertain to the Groundhog coalfield where anthracite is the predominant rank. 13, 14 (Fig. 1) c o n t a i n o n l y lignite a n d s u b b i t u m i n o u s coal a n d will n o t be discussed f u r t h e r in t h e c o n t e x t of this paper. F o r an overall p i c t u r e of t h e geology of C a n a d a ' s coal b a s i n s a n d t h e i r cont a i n e d resources, a c o m p r e h e n s i v e v o l u m e b y S m i t h (1989) s h o u l d be consulted. A n earlier review v o l u m e edited b y P a t c h i n g (1985) is a n a d d i t i o n a l valuable reference in this regard. Finally, several review articles o n specific regions p r e p a r e d for t h e D e c a d e of N o r t h A m e r i c a n Geology ( D N A G ) v o l u m e s are o t h e r sources o f b a c k g r o u n d reference m a t e r i a l (Bustin, in press; B u s t i n a n d Miall, in press; C a m e r o n , in p r e s s ) . A t p r e s e n t , b i t u m i n o u s coals of v a r i o u s g r o u p s are b e i n g m i n e d in N o v a Scotia, N e w B r u n s w i c k , A l b e r t a a n d B r i t i s h Columbia. B a s i n s w h e r e m i n i n g is c u r r e n t l y b e i n g c a r r i e d o n are i n d i c a t e d o n T a b l e 2. A n t h r a c i t i c coals are n o t b e i n g m i n e d a t p r e s e n t e x c e p t for small q u a n t i t i e s for t e s t i n g at a d e v e l o p i n g m i n i n g site in t h e G r o u n d h o g coal field.
211 SUB/HV 200o
HV 2000
0 •
l
4000 |
HV/MV 0
I
MV coo@ 8000
2000 4000
o 1000
i
I
i
I
i
I
,
I
MV/LV 1°°° °
10000 •
I
o
LV 2000
o
LV/AN AN ''~ 2000 ° 1000
,
I
EOCENE PALEOCENE CRET'/TERT" ] 13 UPPERCRET. ~
16 ~
1.7C.7D,7E
LOWER CRET. JURA/CRET.
7A 11
2.16
3,11,7A
2, 7A
JURASSIC TRIAS./PERM. PENNSYL. ##
MISS.
7F AN
Includes
semlenthrsclte
and
anthracite
#~'Resources
not
estimated
Fig. 3. Canada's bituminous and anthracitic coal resources of immediate interest grouped by geological age, rank and basin of occurrence. Quantities expressed in megatonnes. Basins identified by numbers, e.g.6, 13, 7E, etc. (data from Smith, in press); S U B = subbituminous coal;H V = highvolatile bituminous coal; MV=medium-volatile bituminous coal; LV=low-volatile bituminous coal; A N = anthracite.
In some of the sedimentary basins (Fig. 1 ), a wide variety of ranks is found in stratigraphic sequences of different ages. The best example of such diversity is the Western Canada Basin (Fig. 1, Area 7). Within this basin, every rank group from lignite to semianthracite occurs in strata ranging in age from Late Jurassic to Paleocene. Another example is the Sverdrup Basin/Franklinian Geosyncline (Fig. 1, Area 16), covering a large area in the Arctic Archipelago; there an equally broad rank spectrum is present in rocks ranging in age from Devonian to Eocene. Since the early 1970's, coalification studies have aroused much interest because of their significance not only to the coal industry, but also for evaluating oil and gas possibilities (Hacquebard and Donaldson, 1970). Studies have shown that the processes affecting changes in the rank of coal also control the availability and properties of hydrocarbons. Of these processes, heating seems to be the most important and a knowledge of the resulting maturation of organic materials in prospective sediments is considered essential for oil-potential evaluation. Maturation levels are a function of the maximum paleotemperatures to which organic materials have been exposed, as well as the duration of such heating. Therefore, knowledge of these two factors of temperature and time can be obtained from the rank of coal, simply because the maturation process is irreversible. When a specific rank has been attained, it will remain at that level or
212 TABLE 2 Summary of geological and compositional data on Canadian coals of bituminous and anthracitic ranks, 1, 2, 3, etc. refer to basins and areas indicated on Figures 1 and 2. 6A and 6B refer to two small closely spaced basins in Area 6. Data from Bonnell and Janke (1986), Nicolls (1951 ), Stansfield and Lang (1944), Swartzman (1953), and Tibbetts and Montgomery (1960). Basin 1 Formation
Age
Rank parameters VM (dmmf) %2 CV (moistmmf) 3 Range
Extension/ Protection
1
I
Mean
38.5-48.6 44.2
(33.2-34.8) 14271-14974
(33.7) 14501
HV-A
32.5-40.5 35.4
(32.7-35.6) 14062-15319 -
(34.7) 14908
HV-A
(25.5-30.7) 10949-13208 (32.2-35.6) 13835-15324 {25.6-30.2) 11000-13000 (30.3-33.3) 13024-14335 (30.2-30.6) 12969-13148 (31.3-36.9) 13449-15841 (28.7-37.0) 12319-15926 (26.8-32.1) 11521-13802 (28.1-33.5) 12078-14404 {25.3-30.6) 10880-13134
(29.0) 12482 {34.0) 14609 (27.9) 12000 (31.6) 13577 (30.4) 13059 (35.2) 15130 (34.6) 14867 (28.8) 12399 (30.8) 13230 (27.7) 11909 -
L. Cret.
Comox
2
Mean Range
R. . . . ASTM 4 Range Rank
Haida Yakoun
L. Cret. M. Jura.
4.8-41.9 -
3
Currier
L. Jura.
3.9-15.7
4
Red Rose
E. Cret.
5
Bowron River
6A
Coldwater
Paleocene or Younger M. Eocene 36.8-44.4 41.3
6B
Allenby
M. Eocene
7A
Kootenay
7B 7C
Gething/ Gates Saunders
7D
Belly River
7E
Wapiti
7F
Mattson
9.3
28.2-35.7 31.4
40.0-42.1 41.0
*5 Jura./ Cret. * E. Cret.
17.3-33.5
*
Cret./ Paleo. Cret.
35.1-44.7 39.7
Cret./ Tert. Miss.
36.6-45.2 39.9
Pennsyl6.
32.0-47.2 36.5
Pennsyl.
39.9-44.1
Morien * (Sydney field) Morien (Inverness/Mabou)
Pictou/SteUarton * Pennsyl. (Pictou field) Pictou/Stellarton Pennsyl. (N.B. fields) Cumberland Pennsyl. (Springhill-Joggins)
8.2-40.3 24.9 24.8
40.8-46.2 42.9
-
42.6
27.2-35.1 30.7 30.4-40.7 3 5 . 1 33.0-42.9 39.5
HV to AN 1.705.80 0.650.70 0.612.65 0.762.55 0.620.74 0.590.81 -
(29.7-36.2) 12763-15574 (28.7-31.6) 12333-13569
(34.3) 14755 (30.8) 13252
0.791.14 0.711.24 0.520.68
(32.8-35.4) 14104-15214 (27.9-36.7) 11989-15777 (31.9-34.3) 13694-14734
(34.1) 14653 {34.5) 14815 (33.0) 14170
0.852.04 0.612.53 0.800.93
LV to M-AN HV to MV HV-C, -B HV-B, -A HV-C, -B HVto AN HVto LV HV-C to-B HV-C, -A SUB to HV-B HV to MV HV-C to A HV-C, -B HV-A to MV HV-C to -A HV-C to-A
213 T A B L E 2 (continued) Basin ~ Formation
Age
Rank parameters VM (dmmf) %2
CV ( m o i s t m m f ) 3
Range
Mean Range
Mean
Riversdale *~ Pennsyl. (Pt. Hood-St. Rose)
38.1-41.1
39.2
(29.4-32.2) 12633-13858
(30.9) 13282
Tantalus
Cret.
35.8-40.2
37.9
(31.3-32.6) 13467-14026
(36.7) 15759
Laberge
Jura.
46.3-46.8 46.6
~
R. . . . ASTM 4 Range Rank
0.600.69
HV-C
HV-B to -A
11
12
15
Unnamed
-
-
HV
* Tert.
24.6-36.3
34.3
(24.7-33.5) 10615-14392
(27.6) 11865
1.062.06
HV-A to MV
Reindeer
Tert.
39.2-51.6
44.7
(29.9-30.4) 12840-13080
Kamik
E. Cret.
10.6-37.7 -
(30.1) 12960 -
Kayak
Miss.
0.540.75 0.862.93 2.844.03
HV-C to -B HV to SA SA /AN
Eureka Sound
Cret./ Tert. Cret. Cret.
0.170.70
LIG/ HV
Hassel Isachsen
8.0-13.7
10.1
53.3
-
10.6-15.9
-
-
(29.8) 12814 (31.2-32.8) 13394-14085
-
LV to AN
-
LV
16 Heiberg E m m a Fiord Parry Island, Beverley Inlet, Hecla Bay
Trias /Jura Miss.
14.3-15.4 -
Dev.
50.3-52.0
(32.8-34.9) 14103-15006
-
(30.2-32.2) 12996-13820
-
0.505.49 0.610.92
HV to M-AN HV
'See Figures 1 and 2 for basin and area names. 2 d m m f = dry, mineral-matter free; m m f - - moist, mineral-matter free. 3Number in parentheses is M J / k g , other n u m b e r is Btu/lb. 4ASTM rank designations based on volatile matter (VM, d m m f ) and calorific value (CV, m m f ) values where available; see Table 1 for explanation of abbreviations; M-AN = meta-anthracite. 5Basins or coalfields with active mining at present. 6Upper Carboniferous.
show an increase, but it can never revert back to a lower level. For evaluating oil and gas potential in an area, analysis of maturation levels by themselves suffices to provide important information without attempting to interpret paleotemperatures and burial times. However, to broaden the predictive aspect of maturation studies various approaches to temperature/time modelling are often applied, which involve calculations of maximum paleotemperatures and
214
in this sense coal, whether in true seams or finely dispersed in clastic rocks, can be used as a geothermometer. The rank changes of coal are caused by geological conditions and find expression in the coalification series of peat to anthracite. These geological conditions vary between different regions. In the northern part of the Rocky Mountain region of western Canada (Fig. 2, Area 7B ) the coalification is predominantly predeformational, whereas in the southern part (Fig. 2, Area 7A) a significant, though variable proportion appears to be post-deformational. In the Atlantic region (Fig. 2, Basin 9), coalification is almost entirely postdeformational (Hacquebard, 1975). Area 7A and Basin 9 are the two regions for which coalification patterns will be discussed in detail in this paper. SOURCEAND T Y P E O F D A T A
Most of the rank data presented in this paper are petrographic, i.e., reflectance measured on vitrinite. Many of these data are from the Geological Survey of Canada, and some have been extracted from published literature out of other coal-research laboratories in Canada, principally from the British Columbia Ministry of Energy, Mines and Petroleum Resources, and the University of British Columbia. In all cases, maximum reflectance (Romax) values are reported. Sample preparation and measurement procedures at all these laboratories followed standard procedures suggested by the ASTM (1979) and the ICCP (International Committee for Coal Petrology, 1971 ). Reflectance data are related to ASTM rank classes according to threshold values proposed by Davis (1978). Samples for analyses have been obtained from several different venues, namely outcrop, mine workings, exploration adits and trenches, coal exploration boreholes and oil and gas wells. Chemical data on rank, i.e., volatile matter and calorific value, were obtained from published and unpublished reports of the Geological Survey of Canada as well as from CANMET (Canada Centre for Mineral and Energy Technology), British Columbia Ministry of Energy, Mines and Petroleum Resources and the Alberta Research Council. Most of these data have been determined according to ASTM analytical specifications, although some older data, such as those for the Queen Charlotte Islands, predate the establishment of modern ASTM standards. RANK DISTRIBUTION BY BASINS
Nanaimo Basin (Basin 1, Figs. I and 2)
On Vancouver Island, high-volatile bituminous coals occur in several fields of the Nanaimo Basin. The two most important of these in terms of mining history have been the Nanaimo and Comox coalfields. The coal beds occur in
215 two formations of the Nanaimo Group of Late Cretaceous age (Table 2). Rank data based on proximate analyses indicate a rank of high-volatile A bituminous coal. The beds in the older Comox Formation appear to have lower volatilematter contents than those of the overlying Extension/Protection Formation (Table 2 ). LocalJy in the Quinsam coalfield of this basin, intrusives have apparently increased the rank (Barnstable, 1980). There are no published reflectance data on these coals.
Queen Charlotte Islands (Basin 2, Figs. 1. and 2) On Graham Island in the Queen Charlotte Islands, the Yakoun Formation (Middle Jurassic ) and Haida Formation (Cretaceous) contain bituminous to anthracitic coals (Sutherland Brown, 1968). Data on rank of these coals are sparse, but the few recorded in the literature suggest a broad rank range (Table 2). The high level of coalification in some beds may be local and related to igneous intrusion. Structure in the coal-bearing units is characterized by extensive folding and faulting.
Groundhog coalfield, Bowser Basin (Basin 3, Figs. I and 2) In terms of resource potential, one of the most important fields in the interior of British Columbia is the Groundhog coal field in the northeast part of the Bowser Basin. Its stratigraphy and structure were described by Bustin and Moffat (1983). The coals occur within the Currier beds and the overlying McEvoy unit of the Bowser Lake Group and display ranks ranging from lowvolatile bituminous coal to meta-anthracite. Reflectance values range from 1.7 to 5.8% (Romax) (Bustin, 1984). These values are in rough agreement with volatile-matter data (Table 2 ), although the latter were obtained from outcrop samples. According to Bustin (1984), ranks appear to increase toward the eastern side of the field. Coalification gradients are variable and range from 0.8% to 3.0% Ro m~/km. Bustin (1984) suggested that the high ranks and gradients may be related to high pretectonic paleogeothermal gradients, possibly resulting from large intrusive bodies at depth which accompanied the collision of terrains on this part of the North American margin during Mesozoic time. The high ranks and coalification gradients seem slightly out of line with estimated maximum burial which is believed to have been 3500 m. The coal measures have been extensively deformed by folding and faulting, including some fairly large thrusts.
Skeena Basin (Basin 4, Figs. 1 and 2) Adjacent to the south end of the Bowser Basin lies the Skeena Basin with a number of coal fields, the most important of which is at Telkwa. Here in the
216
Lower Cretaceous Red Rose Formation of the Skeena Group, 17 coal beds occur in moderately deformed strata with ranks ranging from high-volatile to medium-volatile bituminous coal (Table 2). Intrusives cut the coal measures at one end of the field and dikes have been encountered in some of the mine workings (Koo, 1983). These have locally produced some drastic rank increases, including the formation of natural coke. Within the rest of the Skeena Basin there are at least six other coalfields, some of which contain anthracitic coals. Rank data for these fields are sparse.
Bowron River coalfield (Basin 5, Figs. i and 2) Southeast of the Bowser and Skeena Basins, the Bowron River coalfield contains high-volatile C and possibly high-volatile B bituminous coals. The coal-bearing strata are late Paleocene or younger in age and contain lenticular seams up to 3.5 m thick. Reflectances (Ro max) are of the order of 0.65-0.70% (British Columbia Ministry of Energy, Mines and Petroleum Resources 1986 ) and calorific values range from 25.6 to 30.2 M J / k g (11,000 to 13,000 Btu/lb ). The Bowron River field is the most northern of a series of relatively small basins aligned in a roughly north-south direction in the interior of British Columbia. They contain coal of various ages ranging from Paleocene to Oligocene and in rank from lignite to bituminous.
South central British Columbia (Area 6, Figs. I and 2) A closely spaced group of small basins of south central British Columbia are a continuation of a belt of Tertiary coal-bearing troughs mentioned in the last section (Bowron River coalfield). Two of them, the Merritt and Princeton/ Tulameen basins, contain bituminous coal. In the Merritt coalfield, coal occurs in the Coldwater beds of Middle Eocene age. The coal is bituminous with volatile-matter contents (dmmf) ranging from 37 to 44% and calorific values (moist, mmf basis ) varying from approximately 25.6 to 33.3 M J / k g (13,000 to 14,300 Btu/lb). These data indicate mainly high-volatile'B bituminous coal with some high-volatile A bituminous coal present as well (Table 2). These coal measures have been moderately to severely deformed. The Princeton/Tulameen coalfield consists of two presently separated subbasins, each containing coal beds in the Middle Eocene Allenby Formation. The Princeton subbasin appears to contain only subbituminous coal (Rice, 1947; Shaw, 1952 ). The coal in the Tulameen part of the field is higher in rank with heat values averaging 25.6 M J / k g (13,000 Btu/lb) and with reflectance values that range from 0.62 to 0.86% R . . . . (Donaldson, 1973; Williams and Ross, 1979). The chemical analyses and reflectance data indicate ranks of highvolatile C to high-volatile B bituminous coal for the Tulameen coals. Both the Tulameen and Princeton coals have been severely affected by folding and
217
faulting, particularly at Tulameen where locally the coal has been greatly thickened tectonically. The higher ranks at Tulameen as compared to Princeton and the variability within the Tulameen field are thought to be due to igneous activity complicated by folding and tilting before some of the volcanism took place (Williams and Ross, 1979). Western Canada Basin (Basin 7, Figs. 1 and 2)
The bulk of Canada's presently known coal resources, including the major part of its high-rank coals, occurs within this very large basin. Because the basin is large and complex in terms of the number of coal-bearing formations and the ranks of coals contained within them, it has been divided, for the purpose of the present discussion, into six regions (Fig. 2, 7A-7F ). Of these areas, rank distribution in 7A will be examined in detail later. Areas 7A and 7B (Fig. 2) The bulk of Canada's resources of bituminous coal plus a substantial quantity of anthracitic coal occurs in areas 7A and 7B in the Rocky Mountains and Foothills of Alberta and British Columbia. These two areas together form a narrow belt some 1200 km long and stretching northwest from the U.S. border to the Peace River in British Columbia. The belt consists in detail of a number of structurally separated areas underlain by coal-bearing rocks of Late Jurassic to Early Cretaceous age. Regions 7A and 7B are separable stratigraphically. The former is underlain by the Jurassic/Cretaceous Kootenay Group, whereas the coal-bearing strata in the latter are represented by the younger Bullhead and Fort St. John Groups (Early Cretaceous) and their equivalents. The remarkably persistent conglomerates of the Cadomin Formation serve to fix the stratigraphic relationship of these various sequences. In area 7A, the Cadomin overlies the Kootenay, whereas in area 7B the Cadomin forms the basal noncoal-bearing member of the Bullhead Group which, in turn, is overlain by the Fort St. John Group. Figure 4 shows schematically the relationships of these major stratigraphic units. Underlying the Cadomin in area 7B is the Minnes Group, which is believed to be equivalent to the Kootenay Group (Stott, 1984 ). It contains some minor coal beds but the major coal-bearing sequences in area 7B are the Gething Formation (Bullhead Group) and the Gates Formation (Fort St. John Group), both above the Cadomin Formation. The equivalent stratigraphic sequence in the south (area 7A) is the Blairmore Group and it does not contain coal. Hacquebard and Donaldson (1974) published the first regional study of coal ranks for areas 7A and 7B. The results of their reflectance analyses (Fig. 5) show a variety of ranks and coalification gradients. Kilby (1988) studied reflectances of a number of samples from both areas 7A and 7B. He showed that many exhibit biaxial optical properties, which suggest a significant tectonic
218 /I U.S.A. //
0
/
/
200 |
• km
/i
~
Kootenay
t /~1~1)2 Gr
~ . . %..['-x.,~ ,.~ "
/
Luscar, Minnas, Bullhead and Fort St. John Groups
6
~
010
3000 2000 1000
0
Cabin Cr. (1) ~Fernie
"
~
Smoky River
3
)
Mt
Allan
N. S e e k .
~
(4) R
Peace River (8) ~'
Athabasca
River (5) i I
v e S.C./AIt
r
Sikannl Chief River
Muakwa River
:[......... ....... (1 i :::
o
E
1000
~
2000 m 3000
~
?
km
2?0
Blairmore Gp, Kootenay Gp.
~ ~
Fort St. John Gp.
Fernle Gp.
~
Minnes Gp.
Bullhead Gp. 'o' Datum= CadominFro.
Fig.4. Schematic crosssectionshowing relationshipof Upper Jurassicto Lower Cretaceous strata in the Canadian Rocky Mountains and Foothills.Hatched areas indicatecoal-bearingbeds. Compiled in part from data by Stott (1974, 1984) and Gibson (1985).
influence on the orientation of reflectance parameters. Kalkreuth et al. (1989) have shown by a study of oriented blocks from area 7B that orientations of Ro maxand Ro raincan be related to fold axes orientation and direction of tectonic stress. Rank variations in area 7B will be examined in another paper (Kalkreuth et al., 1989) and only the general pattern will be summarized at this point. The geological framework of the coal-bearing Minnes Group and Gething and Gates Formations in area 7B has been well established by Stott (1974, 1984) and Gibson (in press). Hacquebard and Donaldson (1974), Karst and White (1980), Kalkreuth and McMechan (1984) and Kalkreuth and Langenberg (1986) have touched on various aspects of rank variation within the area and used reflectance as the organic maturity index. Steiner et al. (1972) included this area in their evaluation of coal-rank patterns in Alberta and utilized standard chemical data. The coals of the Gething and Gates Formations range in rank from highvolatile to low-volatile bituminous coal with a large proportion being mediumvolatile bituminous coal (Fig. 3). Coalification appears to have been largely pre-orogenic as indicated by some local studies where isorank lines seem to follow stratigraphic horizons in deformed beds (Kalkreuth and Langenberg,
219 l%Ro I ,I;0,
1;4
, ,I;4,
s,.m.h.O~.,~_.
,OJ 0.62 O_t.
"
'
i
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Ri0.62 ~on o.63,
'
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,
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'
Fig. 5. Reflectance (R. . . . )-depth profiles for representative sections of Jurassic to Cretaceous coal-bearing strata in the Canadian Rocky Mountains and Foothills (from Hacquebard and Donaldson, 1974). Coalification gradients are represented on each section by two numbers. The first is actual gradient (To R . . . . change/100 m) for each section; e.g. for section 1, gradient is 0.071. The second number on each section is the ratio obtained when the gradient is divided by a reference gradient. Reference gradient used is from the Peel region in the Netherlands and has a value of 0.115/100 m. An example of the resultant ratio is 0.62 on section 1. VM= volatile-mattercontent.
1986). As the coal-bearing units are traced from the Plains southwestward toward the mountains, rank first increases and then decreases near the western edge of the Foothills. Kalkreuth and McMechan (1984, 1988) explained this seeming anomaly by reference to the timing of geological events in the area. Deposition of the coal-bearing sediments was at least partly synchronous with the uplift of the Cordillera to the west. As a consequence, the western part of the coal-bearing sequences was never buried as deeply or for as long a period of time as the eastward extension of these beds along the axis of the Alberta syncline. As a result, the coals in the Alberta syncline have the highest rank (Fig. 6). Kalkreuth and McMechan (1984) concluded from their studies that temperature and duration of heating with depth were sufficient to account for the achieved levels of maturity and only locally do abnormal levels of heat flow appear necessary.
220 \
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ISOREFLECTANCE % Romax
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Fig. 6. Rank distribution at base of Bluesky-Gething Formation (Fort St. John Group) in eastcentral British Columbia and adjacent Alberta. Area of study centred approximately on locations 6,7 and 8 of Figure 4. (From Kalkreuth and McMechan, 1988).
Area 7C (Fig. 2) In the Outer Foothills region of west-central Alberta, there is an area underlain by moderately deformed coal-bearing rocks of Late Cretaceous to Paleocene age. This sequence of strata is termed the Saunders Group and its
221
stratigraphy, sedimentology and age have been reported by Jerzykiewicz and McLean (1980), Jerzykiewicz (1985) and Jerzykiewicz and Sweet (1986). Two formations within the Saunders Group contain bituminous coals: the Brazeau Formation and the stratigraphically higher Coalspur Formation. The latter contains the more abundant coal resources. The Coalspur Formation straddles the Cretaceous/Tertiary boundary, and the important coal zones are in the Tertiary. There are at least six coal zones in the Coalspur Formation. The Coalspur Formation is coeval with the Scollard Formation that underlies an area farther east on the Alberta Plains. The coal beds of the Scollard Formation are subbituminous in rank, whereas those in the Coalspur are high-volatile C bituminous coal with volatile-matter contents, heating values and reflectance ranges as indicated in Table 2. The somewhat higher rank of the Coalspur coals is likely due to deeper burial as compared to the Scollard coals. Area 7D (Fig. 2) The area in southern Alberta designated as 7d is underlain by the Upper Cretaceous beds of the Belly River Group/Formation (Campbell, 1974). In the southeastern part of the province, the group is divisible into the Foremost and Oldman Formations, whereas comparable beds in the southwest are undivided and are referred to as the Belly River Formation. In the southeast and southcentral parts of the province, the Belly River contains three coal zones of which the rank, in part, is high-volatile C bituminous coal. Farther west in the Foothills, the Belly River contains two coal zones that are not as laterally extensive as the seams farther east. The rank of the Belly River coals in the Foothills is higher than that of Belly River coals farther east; in the Foothills there is highvolatile A bituminous coal. Area 7E (Fig. 2) A large area in west-central Alberta and adjacent parts of British Columbia is underlain by the Wapiti Group, a coal-bearing succession of Late Cretaceous/Tertiary age (Kramers and Mellon, 1972). It lies north of the area underlain by the Saunders Group. The Wapiti is thought to be correlative with the Saunders, Belly River and Edmonton Groups. Data on coal occurrences are scarce. In one area, Allan and Carr (1946) indicated the presence of 9 coal beds. Some of these coals have reached a rank of high-volatile C bituminous coal (Table 2). Area 7F (Fig. 2) An area at the northern end of the Western Canada Basin contains coal in the Late Cretaceous Wapiti Group and the Mississippian Mattson Formation. The area is close to the juncture of the boundaries of the Yukon Territory, the Northwest Territories and British Columbia. Some exploration in the 1970's
222 was carried out in this area, but detailed information on lateral persistence of coal beds is sparse. The Wapiti coals are subbituminous, whereas those in the Mattson are high-volatile A bituminous coal, according to reflectance data (Table 2). The Mattson contains at least two coal beds (Lord, 1983). Whitehorse Trough (Basin 11, Figs. I and 2) The Whitehorse Trough contains coal in sequences of two geological ages. These are the Laberge Group (Jurassic) and the Tantalus Formation (Cretaceous). For a number of years, a mine at Carmacks in the Yukon Territory produced coal from a bed in the Tantalus Formation. This coal is mainly of high-volatile B bituminous rank. A rather limited number of chemical analyses suggest that most of the coals in both the Laberge Group and Tantalus Formation are of the bituminous rank class. At least one locality near Whitehorse shows coal of anthracitic class although microscopic observations suggest that it may have been abnormally heat-affected (Goodarzi, 1983). Bustin (1984) suggested that the high heat flux that influenced rank in the Groundhog coalfield may have extended northward to affect coal rank in the Whitehorse Trough. Tintina Trench (Basin 12, Figs. I and 2) In the Tintina Trench, a number of coal occurrences are recorded within a narrow belt extending from the Yukon Territory/British Columbia border to the Yukon/Alaska boundary. Most of these appear to be lignite and subbituminous coal, but one deposit near Ross River in the Yukon Territory is medium-to low-volatile bituminous coal. Reflectances of coals in the Ross River area range widely from 1.06 to 2.03% (Ro m~). Such values are not totally consistent with the proximate analyses data on the same coals (Table 2 ), and may reflect that the samples analyzed were from outcrop and likely weathered to varying degrees. Hughes and Long (1980) suggested that the higher ranks at Ross River, compared to other parts of the Tintina Trench, were caused by igneous intrusions. Northern Yukon (Area 15, Figs. 1. and 2) A belt of Arctic Coastal Plain and adjacent fold complex in the northern Yukon Territory and extreme northwest part of the Northwest Territories is partly underlain by three coal-bearing sequences with high-volatile bituminous coal to anthracite ranks (Fig. 7). The oldest of these units is the Kayak Formation of Mississippian age which contains at least one thick ( > 5 m) bed of semianthracite to anthracite coal in the Hoidahl Dome area (Fig. 7, station
223
~
~
~
~
Reindeer Frn.
OCEAN
/~
_
~! . . ~ - ~
I
i
~.~
.
"~
e) "''''v''
Fig. 7. Distribution of coal-bearing rocks in northern Yukon Territory and adjacent District of Mackenzie, NWT, area 15, Fig. 1.
F, Cameron et al., 1988). The next oldest coal-bearing succession is the Kamik Formation of Early Cretaceous age which contains thin coal beds varying in rank from high-volatile A bituminous coal to semianthracite. Only a few analyses are available on the Kamik, and patterns of rank change cannot be delineated as yet. The third stratigraphic unit of area 15 is the Reindeer Formation of Paleocene/Eocene age. Reflectance and chemical data on the Reindeer coal beds indicate ranks of high-volatile C and B bituminous coal (Table 2). Reflectances on all three formations are summarized in Figure 8. In addition to the coals at Hoidahl Dome, other exposures of Kayak strata containing thin coal beds and carbonaceous shales were sampled at 4 other stations within the area (Fig. 7). Three of these (stations H, I and J) in the British Mountains showed reflectance significantly higher than stations F and G farther southeast. Values of 3.55-4.03% (Ro ~ ) , corresponding to anthracite, were obtained at stations H, I and J, as compared with 2.33-3.03% (Ro_ max), mainly or entirely semianthracite, at stations F and G (Cameron et al., 1986). This difference is not readily explained at present. There are granitic intrusions in the area but they are older than the Kayak. There was uplift and associated deformation in the area during the mid-Mesozoic and later during Late Cretaceous and early Tertiary time, and it is possible that some of the resulting uplifts were cored with younger intrusives (Cameron et al., 1986).
224 RomaX
Rorandom 0.60
1.00
2.60
3.00 i I I I
, g
I I i~
SITE
["-] [~
A
I
I I
SITE B SITE
I
I
SAIA
,
i
!
I
3.50 I
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,
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B I T = Bltumlnous S A = Semlanthraclte A = Anthracite
C !
D
SITE D SITE E [
I
~
BIT
I SA
I I
I
I
I
SITE
F
'1 S I T E G I
I
I i
,
J'i S I T E H ~
SITE I SITE J I~[
Fig. 8. Distribution of R . . . . a n d R . . . . aom values for sample sites shown in Fig. 7. Length of bar indicates range of reflectance values at each site.
There is an indication that this northwestward change in rank may not be confined only to the Kayak Formation. The coal beds of the Reindeer Formation, which were sampled at 3 sites (Fig. 7, stations A, B, C ), also show a subtle westward increase in rank based on reflectance (Fig. 8), whereas at stations D and E, from which Kamik Formation coals were analyzed, the more westward site (Fig. 7, station E) is of higher rank.
Sverdrup Basin/Franklinian Geosyncline (Basin 16, Figs. I and 2) Basin 16 encompasses a very large area in the Canadian Arctic Archipelago, mainly within the geologic provinces designated as the Arctic Platform, the Franklinian Geosyncline and the Sverdrup Basin (Thorsteinsson and Tozer, 1970). Figure 9 shows a more detailed map of this area. Coal is found in Devonian, lower Carboniferous (Mississippian), Triassic, Jurassic, Cretaceous and Tertiary strata. Of these, the Eureka Sound Group of Late Cretaceous to Eocene age is the most important in terms of known coal resources. Although the area is remote and the level of exploration for coal per se has been low, a rather large amount of information on coal occurrence and rank is accumulating because of hydrocarbon exploration and systematic regional mapping by the Geological Survey of Canada. There is no mining in the area at present and only small amounts of coal have been mined. Recent regional discussions of coal in the Arctic have been published by Ricketts and Embry (1984), Bustin (1986) and Bustin and Miall (in press). Much of the coal in the Arctic is lignite to subbituminous coal. However, there are substantial resources of bituminous coal and locally even some semianthracite (Ricketts and Embry, 1984 ). The Devonian coals occur in the Hecla
225 COAL-BEARING F O R M A T I O N S
KILOMETERS o
EUREKA SOUND GROUP m
OceaR HASBELFORMATION ISACHSEN FORMATION HEIBERGFORMATION DEVONIANCOAL-BEARINGSTRATA
~
3oo
GEOLOGICALPROVINCES ARCTICCOASTALPLAIN B SVERDRUPBASIN C FRANKLINIANGEOSYNCLINE D ARCTICPLATFORM E BOOTHIAUPLIFT F PRECAMBRIANSHIELD
• ~
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VICTORI A 18LAND °°*°o,,.,
""*"
/:[://V~
,°•*'o•. *'% ~4 ~ *°
•"
.
'sz~,o
...........
Fig. 9. Map of Arctic Archipelago showing geological provinces and occurrence of coal-bearing formations (from Smith, 1989); area 16, Fig. 1.
Bay, Beverly Inlet and Parry Islands Formations, all within the Franklinian Geosyncline, and appear to be no higher in rank than high-volatile B bituminous coal (Table 2). Some of these coals are cannel coal with high liptinite contents (F. Goodarzi, pers. commun., 1988). The Emma Fiord Formation contains a few coal beds up to 1 m thick (Thorsteinsson, 1974), but exposures are few. The Emma Fiord is interesting because it contains thick (70 m) beds of oil shale on northwest Devon Island (Fig. 9). Measured reflectances on vitrinite from this locality differ widely, as compared with those obtained on samples from another exposure of this formation on Ellesmere Island (Goodarzi et al., 1987 ). On the Devon Island samples, values ranged from 0.26 to 0.50% Ro max, whereas the Ellesmere samples gave values over 5.0% Ro . . . . corresponding to meta-anthracite. The Emma Fiord is Early Mississippian (Early Carboniferous) in age, more or less equivalent to the Kayak Formation in the northern Yukon. Coal occurrences have been recorded in the Triassic/Jurassic Heiberg Formation, the Early Cretaceous Isachsen Formation and the mid-Cretaceous Hassel Formation. These are mainly concentrated on Ellesmere and Axel Heiberg Islands. Rank data on coals of these formations are sparse but indicate variable degrees of coalification. Fortier et al. (1963) show data for Isachsen
226 Formation coals that vary from lignite to semianthracite and data for a few samples of Heiberg coals also show some high ranks. These higher ranks may be the result of localized increases due to igneous intrusion. More recent data by Goodarzi et al. (in press) show low reflectance values on Isachsen Formation coals from Melville Island; the values indicate ranks of lignite to subbituminous coal. The largest coal resources documented to date in the Canadian Arctic occur in the Eureka Sound Group of Late Cretaceous to Eocene age. Large areas of the Archipelago are underlain by strata of this group, particularly on Ellesmere, Axel Heiberg and Devon Islands (Fig. 9). Some sections include numerous seams with as many as 90 in a 3200-m-thick section in central Ellesmere Island (Bustin,1986). Although much is lignite to subbituminous coal, a substantial part of the resource is bituminous coal, especially in the eastern part of the Sverdrup Basin on Ellesmere and Axel Heiberg Islands. On the basis of a regional maturation study utilizing reflectance measurements, Bustin (1986) concluded that most of the coalification was pre-orogenic and related to depth of burial. His studies indicate that paleogeothermal gradients have varied from 55°C/km in the eastern end of the study area (Ellesmere Island) to about 15 ° C/km on Melville Island, approximately 1000 km to the west. This easterly to northeasterly increase in rank in the Eureka Sound Group parallels a similar pattern in older Carboniferous and Permian sequences. Utting et al. (in press) have evaluated organic maturity by three different methods: conodont alteration index (CAI), thermal alteration index based on spore coloration (TAI), and vitrinite reflectance. They showed a northeastward increase in maturity in the Carboniferous and Permian successions. Bustin (1986) suggested a possible relationship between the higher coalification at the northeastern end of the Sverdrup Basin and its tectonic history. Intermittent tectonic activity affected the area during the Phanerozoic up to the Miocene. Bustin (1986) suggested that higher heat flows associated with this activity and with evaporite diapirs may have influenced coalification. RANK DISTRIBUTIONIN KOOTENAYGROUP, SOUTHERNCANADIANROCKIES AND FOOTHILLS (Fig. 2, Area 7A) One of the most important coal-bearing successions in western Canada is the Late Jurassic to Early Cretaceous Kootenay Group. Its areal distribution in general terms has already been sketched (Fig. 2), and its importance in Canada's coal inventory is indicated by the magnitude of its contained resources of medium-volatile bituminous coal as shown on Figure 3. A map showing the distribution of the Kootenay Group in more detail is presented in Figure 10A.
227
Fig. 10. A. Distribution of KootenayGroup in British Columbiaand Alberta. B. samearea as A but showinglocation of major thrust faults. Section line 1-58 indicates location of oil wells in which Kootenayintersectionsweresampledin subsurface.
Geologyof Kootenay Group In order to better understand rank distribution in the Kootenay Group, it is necessary to briefly sketch the geology of the group. It is comprised of three formations which, in ascending order, are: Morrissey, Mist Mountain and Elk Formations. Norris (1959, 1964), Gibson (1979,1985), and Gibson et al. (1983) have discussed stratigraphic, structural and sedimentological aspects of the Kootenay, whereas Hacquebard and Donaldson (1974), Pearson and Grieve (1985), and England and Bustin (1986) have discussed various aspects of rank variations in the Kootenay coals. Hughes and Cameron (1985) discussed sedimentology and vertical rank variation in an important Kootenay section at Mount Allan, Alberta. The Mist Mountain Formation is mainly Jurassic. The important coal seams are in the Mist Mountain Formation. Only a few relatively thin and laterally impersistent seams are found in the Elk Formation. Gibson (1985) has proposed a delta prograding to the east as the paleoenvironmental setting for deposition of the Kootenay Group. The Kootenay conformably overlies beds of the Fernie Formation and is overlain unconformably
228
in part by the continental sequence of the Blairmore Group with the lowest Blairmore unit, belonging to the distinctive Cadomin Formation, in immediate contact. Locally, a conglomeratic unit, known as the Pocaterra Creek Member, is in immediate contact with the Kootenay. The thickest Kootenay section (1112 m) has been described by Gibson (1985) near Sparwood, British Columbia (Fig. 10A). The number of coal beds or coal zones varies from section to section. The maximum number appears to be in sections in the Upper Elk Valley of British Columbia where there are at least 20 coal beds or zones. In an eastward direction, the Kootenay thins rapidly. Its eastern limit in subcrop approximately parallels the Rocky Mountains and is not far distant from the edge of the disturbed belt (Fig. 10). An important aspect of the Kootenay is how its present-day distribution has been affected by regional tectonics. Strong compressional forces associated with the Laramide Orogeny moved thick sequences of strata ranging from Precambrian to Tertiary northeastward along westward-dipping thrusts. Figure 11 is a cross section through the mountains and foothills showing typical stacking of multiple thrust sheets. These thrusts resulted in multiple repeats of the Kootenay Group as observed in subsurface sections. A number of these repeats come to the surface and are reflected in the elongated, narrow and more or less parallel patches of Kootenay outcrop shown on Figure 10A. Surface traces of the most important of these faults are also shown on Figure 10B. The thrust faults and the lateral transport of thick slabs of strata along them are the most important structural characteristics affecting the Kootenay Group and these are prominent throughout the area underlain by Kootenay, from the U.S. border to the Clearwater River, a distance of some 370 km. The Kootenay is also folded and normally faulted and in many places coal beds are so intensely sheared as to obliterate original depositional laminae. W21 W23 Scale
on wells
2 1 , 2 3 &24 e x p a n d e d ~---
and reflectances
0.88 1.09
w
A Wll
W24
0.90
W12
W21
1.03 1.12 1.24 .38 • W23
/
E -1.00 1.15
~.~11 0. 036 W24
A'
W28
i--
f
o
i
4000
0
12
~
Kootenay Group
km
Fig. 11. Cross section through southern end of Kootenay study area (section line A -A' ) in Figure 10B. Section shows major thrust faults and position of subsurface Kootenay intersections. Reflectance values (R. . . . ) for Kootenay coals shown for wells on or close to section line (modified from P.R. Fermor and R.A. Price, pers. commun., 1988).
229
Rank distribution in surface sections At the surface the Kootenay coals range from high-volatile B bituminous coal to semianthracite. There are several discernible patterns on a regional basis upon which are superimposed some rather surprisingly rapid changes within local areas. An important factor is the degree of preorogenic vs. postorogenic coalification, coupled with the influence of the thrust faulting. Thrust faulting exerts a two-fold effect: it has translated Kootenay sections that were once widely separated into close proximity to one another, and it has played a role not yet clearly defined in adding to normal burial depths on some Kootenay sections. Some Kootenay sections have been moved by thrusting as much as 140 km. Frictional heat generated by the thrusting process seems not to have been significant in promoting coalification (Hacquebard and Donaldson, 1974; Bustin, 1983). Initial studies on rank changes in the Kootenay Group by Hacquebard and Donaldson (1974) suggested that coalification was predeformational, that is, prethrusting. Later more detailed studies by Pearson and Grieve (1985) and England and Bustin (1986) indicated that a substantial proportion of the coalification was postdeformational, though the proportion varies from site to site. Pearson and Grieve (1985) estimated that this proportion of postorogenic coalification ranged from 25 to 75%. They based their conclusions regarding postorogenic coalification on sections through the coal measures such as shown on Figure 12. At this site (Coal Creek Mountain), reflectances (R . . . . ) determined on three beds increased progressively downdip. W
E
COAL CREEK MOUNTAIN 0.90L ~ 8 2
~
--
FERNIEI~<:. ~~¢,~,
21oo
~¢.,: ....
::::::::::::::::::::::::::::::::::::::::::::::: ~
.(-1.12 YoRo
1~oo
Lu
COAL CREEK 9O0
KILOMETEN
Fig. 12. Cross-section of Coal Creek, Fernie Basin, showing stratigraphic position of three bituminous coal seams (indicated by thin black lines), and reflectance values (R . . . . ) obtained on these seams (from Pearson and Grieve, 1985).
Flathead/Sage Creek Lodgepole/Flathead Ridge Mount Taylor Coal Creek Grassy Mountain Sparwood Ridge Oldman Gap Line Creek Cabin Ridge Ridge Creek Wilkinson Creek Greenhills Fording River Weary Ridge Bleasdell Creek Mist Mountain Highwood Junction Bragg Creek EV-boreholes Canmore Mount Allan Barrier Mountain
A B C D E F G H I J K L M N 0 P Q R S T U V
82G/2 82G/7 82G/10 82G/10 82G/9 82G/10 82G/16 82G/15 82J/2 82J/1 82J/2 82J/2 82J/2 82J/7 82J/7 82J/10 82J/7 82J/15 82J/11 820/3 82J/14 820/12
NTS Map
E 678000-N 5441300 E 654000-N 5466400 E 663900-N 5489200 E 645000-N 5486700 E 686800-N 5506100 E 653500-N 5505200 E 692500-N 5528800 E 659300-N 5533700 E 677500-N 5545600 E 688500-N 5554100 E 670700-N 5565400 E 650600-N 5554500 E 653100-N 5561200 E 650700-N 5582200 E 646050-N 5581700 E 659000-N 5602400 E 666800-N 5585900 E 654000-N 5546500 E 636900-N 5604700 E 613000-N 5660000 E 627050-N 5649860 E 598500-N 5729250
U.T.M. coordinates, all in Zone 11
236 662 660 656 116 1082 81 648 198 120 308 665 790 + 1052 486 741 231 72 941 + 477 1038 659
Thickness of section (m)
186 340 138 528 111 595 52 308 161 44 194 665 451 463 481 659 99 39 875 477 873 589
(m)
Interval covered by R. . . . values
4 7 2 3 4 11 3 10 6 2 4 18 10 11 11 13 7 3 30_+ 12 38 10
Number of seams measured
Sources: Gibson ( 1985 ); Graham et al. ( 1977 ); Grieve ( 1985 ); Hacquebard and Donaldson (1974); Hughes and Cameron ( 1985 ).
Geographic name
Section (See Fig. 13 )
Location and thickness data for surface sections of Kootenay Group
TABLE 3
1.10-1.19 1.25-1.58 1.02-1.19 0.97-1.24 1.18-1.28 0.98-1.46 1.06-1.19 0.97-1.49 1.25-1.36 0.99-1.16 1.10-1.37 0.81-1.31 0.92-1.35 1.00-1.58 0.61-0.84 0.89-1.79 1.45-1.69 1.68-1.91 0.65-1.24 1.62-2.65 1.30-2.49 1.48-2.50
(Romax)
Reflectance range
t~ q.O
231 1.48-2.50
1.30-2.49
v
0.89-1.79
o
iiiiiili t .i:::::il .vB
mv,
PSOOm
/ I
0
__ ~R
~..~'~ I~'~.-.~ .~i!I :i:i:!:i:!:i:!:i: :i: ::ii::::::ii::ii0.:ii::::i B1~1.~31 l ~ L~097-149 ~
0.98- ]~iill w I~:~:~I
40 km
l~iii::i]
mS
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oX
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l.::~:i:i:i:~1.50-2.05 IvB _^_ SA
~ ~ t
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~
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145169
1.16
ok,~, K~ " M • |~.:!:\i:.iil L~MZ\~r~ j 1.2~6 | \,~ ~' 'I~i!:] F~|
~E
1 06 i19
E
F~ l
0.97-1.24 t'~-~" ~
~.91-
1.02-1.19
~
1.10-1.19
1.25-1.58
Fig. 13. Summaryof rank data obtainedon coals of 22 surfacesectionsof KootenayGroup. Sections dividedinto ASTM ranks (1979) accordingto reflectance(R. . . . ) distributions obtained in section. Figure 13 shows the rank distribution for a number of surface sections of the Kootenay. Table 3 gives the location of these sections and the thickness of the Kootenay Group at that site. The overall range of the reflectance data (Fig. 13) is 0.61-2.65%, representing high-volatile B bituminous coal to semianthracite. The thicknesses of the intervals covered by reflectance measurement in the sections vary widely from 39 m at Bragg Creek {Fig. 13, Section R), to about 875 m in sections S and U (Fig. 13, Table 3). The thinner sections (E, G, J, Q and R) are all on the eastern side of the outcrop area, indicative of the eastward thinning character of the Kootenay. The overall pattern of rank distribution indicates that the highest levels of coalification are found to north and west and the lowest toward the south and east. Low reflectances are also encountered in other sections such as F, H, L, M, N, O and P (Fig. 13). Section O is somewhat anomalous and will be dis-
232 cussed later. The low reflectances in the other six sections mentioned above occur toward the top of thick successions of Kootenay strata, whereas the higher values, such as 1.58% in section N, occur in beds near or at the base of the Mist Mountain Formation, and these are the values that should be compared with the reflectances shown for sections A, C, E and G because they represent data on equivalent horizons. The Kootenay Group thins eastward by the disappearance, either by nondeposition and/or erosion, of the upper units of the group. Thus the lowest seam in sections A and C, having a reflectance at both sites of 1.19%, is possibly correlative with the basal seam at sections B and F, where reflectances of 1.58% and 1.46% respectively, have been measured. As the Kootenay Group is traced west, and particularly to the north, the overall reflectances shown by the surface sections increase and reach their maximum in sections T (Canmore), U (Mount Allan) and V (Barrier Mountain). In these three sections, much of the coal has reached ranks of low-volatile bituminous coal and semianthracite. The pattern of regional rank change is more clear from the reflectance values measured on the basal seam of the Mist Mountain Formation (Fig. 14). This seam is usually within 50 m of the Mist Mountain-Morrissey contact. Here, the low reflectances representative of high-volatile bituminous coal are quite evident in the southeastern part of the area with a more or less gradual increase northward to semianthracite (0.93-2.65 % ) at Canmore, Mount Allan and Barrier Mountain. However, within this pattern there are variations when examined in detail. In the Fernie Basin, described by Price (1962) as a doubly plunging fold (see Fig. 10A for location), Pearson and Grieve (1985) noted a progressive increase in rank from the northern to the southern end of the basin as represented by the reflectance increase from 1.46 to 1.85% in the basal seam (Fig. 14), corresponding to medium- and low-volatile bituminous coal. They suggested that the difference was due to increased depth of burial at the south end and they estimated this increase to be 600 m. In the Elk Valley coalfield north of the Fernie Basin, the Alexander Creek syncline (Fig. 14) appears to be continuous throughout the extent of the field (Pearson and Grieve, 1980 ). The plunge on this structure is slight and variable. Faults, both normal and thrust, complicate the rank pattern somewhat but in general, it appears that the seams on the west limb of the Alexander Creek structure are of lower reflectance than correlative beds on the east limb. There are some exceptions to this, e.g., a reflectance value of 1.38% was obtained on the basal seam on the west side of the syncline, as compared to 1.35% measured on the basal seam in the east limb. However, at other sites on the west limb, the basal seam gave values of 1.14% and 1.08%. The most striking difference in rank between east and west limbs of the Alexander Creek syncline is shown by sections N and O (Fig. 13 ), with O being on the west limb. A schematic cross-section of the syncline is shown in Figure 15A. The data indicate that the coals on the west limb are all high volatile
233
~~ 2.09
2~.65~ +L..
0
,
50
km
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.
"
Fig. 14. Map showing distribution of reflectance (R . . . . ) values on basal seam of Mist Mountain Formation (Kootenay Group). Data mostly from Pearson and Grieve (1985). Map of Elk Valley coal field showing position of Alexander Creek syncline (lower left figure ).
bituminous coal, whereas correlative seams on the east limb vary from highto low-volatile bituminous coal. At section O, the beds are vertical to overturned and the sample material available was badly weathered in most cases. Nevertheless, even if the measured reflectances were adjusted as suggested by Marchioni (1983) to equate weathered to fresh-coal values, ranks on the west limb would still be much lower than those on the east. A similar situation occurs at M o u n t Allan (Fig. 15B ) where the seams on the overturned limb of the M o u n t Allan syncline show reflectances much lower than those on the upright limb. As was the case with section O at Bleasdell Creek, the coal beds in the overturned limb are badly weathered, b u t the differences in reflectance between the two limbs are too great to be explained by weathering alone. In both areas, there is little change in rank gradient across the stratigraphic interval in the vertical or overturned limbs, in contrast to the upright limbs where
234 7 5 0 ~ R-o-m a x R a n g e J .0"~1 - o.a.
o
Romax Range 1.00 - 1.5.
i
',
,,
0 ~
R o m a x Range 0.68 - 0.94 " ' "
Sw
I 1000 " ~
I
i
I\
i
I
"~
|
|
NE • o" ,~,, I ' ~ s ° ~ e f e" :,,'~t~u"
R o m a x Range 1.30 - 2.49 * ,
,'"
'
~
~r'~,.',
I
,
~
'
!
~ 500 •
~
,_ t:m.
/
PC : Pocaterra Cr.
0 I
0 . - ~ ~S
Approximate measured
-/
traces f o r Ro
1 k /m
!
of seams
Morrlusey Fm.
Fig. 15. Schematic cross-sections of asymmetrical synclinal structure at Elk Valley (A) and Mount Allan syncline (B). Diagram showsthe decrease in Romaxfrom the upright limbs ofboth structures to the vertical or overturned limbs. Dips only approximate. there is substantial change (Fig. 16). This suggests that a substantial component of the coalification is postfolding.
Rank distribution in subsurface sections Figure 17 shows reflectance values determined Dn samples from oil wells positioned on a northwest-trending section line roughly parallel to the Rocky Mountains. In all of these wells, a variable number of thrust slices were penetrated which resulted in multiple intersections of the Kootenay. The data presented in this figure allow some evaluation of rank change in the Kootenay when the dimension of variable depths of present-day burial is added to results from surface sections. A comparison with surface data shows some general similarities. The occurrence of lower reflectances toward the southeast and higher reflectances toward the northwest again appears, b u t this pattern is distorted by values at relatively shallow depths in some wells that are higher than values measured
235 BLEASDELL CREEK
WEARY
500
0.7 ,
,
400
300
1.00
1.0
,
•
,
L
500
0.5
2.00 ' ........
800
J
'
1.00
1,0
'
'
' ~
900
700
"
•
800
"
300
"
600
"
ee
7O0
'
600
500
•
•
3.00 I
•
400
-
"
500
•
~p
s.
g
I
O-
2.00 i
I
-
100'
•
0.7 '
400
e 100
ALLAN
(upright)
%
200-
200
MT.
ALLAN
(overturned)
Rolnnx
Romax 0.5
MT.
RIDGE
o
;
300
-
200
-
100
•
0
400
•
•
•
•
e~
300
"
200
•
100
-
0
ee~
•
Fig. 16. Reflectance(Ro.~,)-depth profiles for 4 sections plotted on Figure 15, e.g., Elk Valley upright (Fig. 13, section N, Weary Ridge) and vertical (Fig. 13, section O, Bleasdell Creek); Mount Allan upright (Fig. 13, section U) and vertical (not shown on Fig. 13).
at greater depths in wells to the north, e.g., comparison of well 48 with wells 50 and 51. The distribution of reflectances shown in Figure 17 is distorted by the fact that different thrust slices are involved in different wells. It is quite conceivable that within a given thrust slice a consistent pattern of reflectance is present, but it is very difficult to correlate with certainty individual thrusts from well to well. The distribution of reflectance values on Figure 17 does suggest something about the influence on rank of deeper burial by multiple thrusts. In nearly all the wells where measurements were made on Kootenay "repeats", the deeper intersections show higher reflectances, e.g., wells 23, 37, 40 and 52. Similar variation also appears in some of the wells projected on the cross section of Figure 11. Although the progressive increase in rank of deeper Kootenay sections in most wells is probably a function of coalification after thrusting, there is a possibility that the deeper slices, which during thrusting were moved to the northeast a shorter distance than the higher slices, were coalified to a higher degree before movement. Thus, there would exist in the Kootenay a situation
236 NW
SE 57
58
37 56. 55
52 51 54 53
50
49 "T" 48
.
1.81
,.8~
.Oil .25
,~
1.( 1.(
•
~:I
.1.73
" =.oo
1.84" " 1.8g~ ~
1,26. 1.37
"2.0IB %61 •
, :1.16
1,3
~:~
1.70 -1.74
, 1.71 ~1.62 ,1.67
1
43
1.2'7 .
~.3.188
' "0.90
;;
l:~°
23
1.251"23:
f
1.27
1.03 -1.01
~
1 39 ~1.44 ~1.46
•
1,24" ~ 1.28
.1.81 1.72 1,90 2.27 2.32" "
:1.7! 1.71 .69
~
50 A
e
km
m
0,84
"1.12
.29 1.50
S ea Level
/o.8,
13,
1,61
2 1
r-
2.03
0
18
23
~" 34 1.48/ "F1.9~
"1.78
45
)9
48 1.8
1 . 8 5 :~ $
40 47
0.9] 0.94
1.52 "1.58
084
0.87" : 0,83 0.84'
0.78
0.79 ~ 0.76'
1,84 '1.06
8OO
f°
IOOO
Fig. 17. Reflectance (Romax)data measured on subsurface samples of Kootenaycoals intersected in oil wells on section line 1-58 (Fig. 10B). Kootenayintersectionsindicated by heavyhorizontal bars; thrust faultsby diagonallines. Welltops at groundlevel.ThicknessofKootenayintersections not drawn to scale; most are less than 100 m and most were selected for study because of an apparently normal contact with underlyingFernie Formation. comparable to t h a t described by Kalkreuth and McMechan (1984) for northeast British Columbia and adjacent Alberta where the higher ranks are not found near the western limit of those coal-bearing rocks, but farther east (Fig. 6). However, the previously discussed data on the K o o t e n a y surface sections suggest t h a t this is not the case. An exception to this trend is the pattern of reflectances for Kootenay repeats in wells 1, 2 and 18 at the southeastern end of the section line (Fig. 17). These wells show the lowest reflectances measured in the oil-well samples and also show little or no variation with depth. Some quite low reflectances were encountered at great depth, e.g., a value of 0.76 at a depth of about 3600 m in well 2. Clearly, in this area of southwestern Alberta the paleogeothermal gradient, at least since the inception of Laramide deformation, has been quite low. Here, extra burial by thrusting seems to have had little or no effect on coalification. Of possible relevance to rank in this southwestern corner of Alberta are the results of Majorowicz et al. (1985). T h e y found the lowest ( < 20 ° C / k m ) geothermal gradient in the province in this area and their belief is t h a t these gradients extend well back into the Tertiary. Variation in levels of coalification for Kootenay coals are not related to a single cause. Predeformational depth of burial undoubtedly contributed an imp o r t a n t component. Deep-seated intrusions may have influenced rank in some
237 areas (Hacquebard and Donaldson, 1974). Extra burial by thrust faulting should also be taken into account and is a complex factor involving rate of movement and thickness of the plates, rate of erosion and the disruption and re-establishment of thermal equilibrium. Yet another factor is the influence of ground-water movement on geothermal gradients. Studies by Hitchon (1984) and Majorowicz et al., (1985) have shown that geothermal gradients in the mountains and foothills are influenced by the recharge of cold meteoric water into the sedimentary column in topographically higher areas. They suggest this process has been operative since the early Tertiary with the effect of reducing geothermal gradients along the Mountain Front compared to farther out on the Plains. To further complicate the picture, there are variations in geothermal gradients parallel to the Mountain Front because lithological and structural variations inevitably result in variation in ground-water movement. ATLANTICPROVINCES
Geology o[ coal measures The coal measures of the Atlantic Provinces are Pennsylvanian (Late Carboniferous) in age. These strata were laid down in subbasins of the larger Maritimes Basin (Bradley, 1982) which, in turn, contain a number of coal fields as shown in Figure 18. Of these fields the most important in terms of resources and production is the Sydney coalfield. Other fields with past or present production are the three smaller fields 8, 9 and 10 on western Cape Breton Island, fields 5, 6 and 7 on the mainland of Nova Scotia and 1, 2 and 3 in New Brunswick. The coals in the different fields occur in different stratigraphic units which, in ascending order, are: Riversdale, Cumberland and Pictou/Stellarton Groups (Bell, 1944; Hacquebard, 1972). The Morien sequence in the Sydney field is equivalent to the Pictou/Stellarton Group. Deformation within these fields ranges from gentle to moderately severe. The most disturbed field structurally is probably Springhill (Fig. 18, Field 5 ). In the Sydney field, structure is characterized by broad, open folds superimposed on a gentle eastward dip toward the offshore. The deformation observed in the Atlantic Provinces coal basins resulted from the Appalachian orogeny at the close of Pennsylvanian (Carboniferous) time, which corresponds to the Caledonian phase of the Hercynian orogeny in Europe. Coal ranks in the Atlantic fields are virtually all bituminous, most of them high-volatile A bituminous coal. Some anthracite has been reported from the Debert-Kemptown field (Fig. 18, Field 6). As mentioned above, most of the coalification is believed to be postdeformational. The rationale for this conclusion will be discussed in detail.
238 COALFIELDS 1
~":i~
~9 Vhite
Bay
NEW- ~
GULF OF ST LAWRENCE
1. 2. 3. 4. 5. 6. 7. 8, 9.
10. 11, 12. 13,
MINTO LAKESTREAM BEERSVILLE JOGGINS-CHIGNECTO SPRINGHILL DFBERT-KEMPTOWN PICTOU PORT HOOD MABOU-INVERNESS ST. ROSE-CHIMNEY CORNE~[ SYDNEY ST GEORGES HOWLEYCOAL AREA
St. 6~orges~c~p12
B=y/
~
/~
Magdalen ~ : ~ Islands
~C
,S/'°-
11
1 ~:" ta:;
ATLANTIC ocEAN
Kilometers
ROCK GROUP
STAGE
<=
RIVERSDALE -
PERIOD
PICTOU/ STELLARTON
CUMBERLAND 1
MORIEN
PERMIAN
MINTOI
BEERSVILLE : OEBERTKEMPTOWN ~
D ~ ~
c B
PORTHOOD ST GEORGES ST ROSE/ CHIMNEY
NAMUREAN
JOGGINS- i i 1 ~ I CHIGNECTO SPRINGHILL
PICTOU MABOUINVERNESS
VISEAN TOURNAISIAN
j3~
SYDNEY [J B
PENNEYLVANIAN
MISSISSIPPIAN
~ Period o/ coat deposition
DEVONIAN
Fig. 18. Map showing distribution of coalfields in Atlantic Provinces of Canada. Diagram in lower part of figure shows coal-bearing stratigraphic units in each coal field (from Smith, 1989).
Fundamental aspects of coalification in Atlantic Canada Evidence for postdeformational coalification
In postdeformational coalification, the rank increases with the present depth
239 NAME OF SEAM 0-m
PT. ACONI BONAR STUBBART
200-
MEAN MAXIMUM REFLECTANCE, R o - % 0i70 0i7S 0.801 0i85 0ig0 •
I. "I
HARBOUR
9 uJ
400-- _ ~ B L A C K R O C K m COLLINS
0 0
m SPENCER
GREAT BRAS D'OR CLIFF SECTION
.'1" I.
Iw
6O0-
Z )-
g
I i I
800.
w ffJ 1000. m
"1a.
COALBROOK
•
_ TRACY
I
"I
MIRA BAY CLIFF SECTION
1200- w I-n,I,-
I I
1400_ SHOEMAKER 160n METRES
McAULAY
•
I I
Fig. 19. R variations of surface coals and stratigraphicposition,Sydney coal field (afterHacquebard and Donaldson, 1970). ....
below the surface, and does not follow stratigraphy in surface exposures (Hacquebard and Donaldson, 1970). Figure 19 illustrates that in a series of surface coals exposed in cliff sections of the Sydney coal field the rank (as measured by Rom~) does not increase with stratigraphic depth. The explanation for this is offered in Figure 20, which shows four inclined seams (A to D ) with a total stratigraphic separation of 300 m. At the surface (wavy line) these coals all have a rank of V7, i.e., they all have reflectances between 0.70% and 0.79%. However, in boreholes (at vertical right hand side of the diagram) the rank increases with depth from 0.75 to 0.80, 0.85 and 0.90% Ro max,respectively (or from V-7 to V-9 reflectance (rank) levels). The isograds (dashed lines) run horizontally and are not parallel to the seams as is the case in predeformational coalification. This means that the coal obtained its present rank from the maximum overburden that existed after deformation. In the example shown the eroded overburden was calculated at 3700 m, using the method employed by Suggate (1959).
Effect of stratigraphic separation In predeformational coalification, the stratigraphic separation between the coals and attendant higher temperatures and duration of heating were the con-
240
tlmmltl
tm l L lillTIILtli
,E,,~o?F?,' pVE,,R~U,R~N,
(3700 m. ACC. TO SUGGATE INDEX @31
%Ro
° o
'"P]UIIIIJJJII'"'IUIIIIU]II' " IIUI II"" 2001
0.80
0.85
kO0
(Sydney-N.S.)
~
,
0.90
m. Fig. 20. Diagnostic features of postdeformational coalification (after Hacquebard,1975). 0.8 I
0
0.9 I
I.o f
1.1 I
1.2 I
1.3 I
1.h I
1.5 l
(~)DOM. NO. 14
1.6 J
"]
X McBEAN
[ ) • SPRINGHILL NO. 2 |
\ ~ " Oi;:~-//O~'~,O~ ~
400
Ak DRUMMONDNO. l
!X
,2o0
~ ~"~..
]
~FO\ "~
;
ua
~.
- '~'~" ]
~ ~kPRE-FOLDING ~(Strat.
I
Separation)
"-..
COLLI ERY
J
~(Vertieal Sequences)
POST-FOLDING ~"..~{IndividualSeams)
I
"
I
1600
% R0
""-
I
"~'
~-
I
\ HV i
36
I
34
"'
%VM
I
~
I
I
MV
I
I
I#
32
30
28
I
26
I
LV
22
20
,
l
I
24
18
Fig. 21. Determination of predeformational coalification in Carboniferous of Maritime region {after Hacquebard, 1975).
trolling rank factors. In this case, maximum overburden was reached before folding. Although essentially postdeformational in origin, the coals of eastern Canada were affected to a minor degree by predeformational coalification also, as shown in Figure 21. In this figure, the middle curve (postfolding) shows the change in rank of individual seams with the present depth of mining. It is a
241 composite curve, put together from the rank changes observed in four slope mines, namely: Dominion No. 14 of Sydney field; McBean and Drummond No. 1 of Pictou field; and No. 2 Mine of Springhill field (see Fig. 18). As can be seen, the changes in rank are considerable. Over a depth of 500 m, for instance, the rank increases in Dominion No. 14 from a high-volatile bituminous (HV) coal with 36% volatile matter to a medium-volatile bituminous (MV) coal with 30% volatile matter. The coaliflcation gradient of this curve amounts to 0.044% R . . . . per 100 m of depth. As individual seams are involved, the 0.044 rate of increase is caused by post-deformational coalification only, because there is no stratigraphic separation. The upper curve of Figure 21 (resultant rank) shows the change in reflectance of successive seams cut in boreholes. It also is a composite curve that was derived from several wells that have been examined previously by Hacquebard and Donaldson (1970). Its coaliflcation gradient is 0.061/100 m. This is 0.017 higher than the gradient obtained on the middle curve, and this value represents the increase caused by the stratigraphic depth, or by predeformational coalification. It is shown separately in the lower curve. In the Maritime region, the postdeformational coalification greatly exceeds the predeformational coalification. A coal at position A in Figure 21 on the lower curve, with a rank of about 34% volatile matter before deformation, obtained the rank of B on the upper curve (equal to about 25% volatile matter), because of overburden that accumulated after deformation.
Effect of overburden and geothermal variations Regional changes in coalification are due mainly to differences in the original depth of overburden, but superimposed on these are changes in the paleogeothermal gradients. The effect of this is revealed by coal rank studies in the Sydney coalfield and in the Carboniferous basin of New Brunswick.
Rank changes in Sydney coalfield Rank~overburden relationship. The lateral changes in rank in the Sydney coalfield are shown on the isoreflectance map of Figure 22, which pertains to the Harbour seam (Hacquebard, 1983 ). Within this seam the rank increases from V-7 in the west to V-9 in the east of the field. This change occurs in coal that lies at about the same depth below the surface. It is also apparent by comparing readings obtained in the offshore area at greater depth. The Harbour seam intersected at - 9 1 4 m in borehole H-1A at Lingan has a rank of 1.11% R . . . . . whereas at - 707 m in borehole H-8 at Donkin it reached a reflectance of 1.13% Ro max. This means that it requires 207 m less depth of mining at Donkin than at Lingan to encounter coal of the same MV rank. Apart from the regional increase in rank from west to east, the map of Figure
242
ATLANTIC OCEAN ..........
.°
i,.....
" ............ 4000
~Sydney V-TYPE
% V.M'~
V7
38-41
eH'2 BOREHOLE
V8
36-38
...... CONTOURS
V9
33-36
- - ' - - OUTCROP
vlo VII
31-33 29-31
-__
EXTENT OF WORKINGS
0 ()
Km Mi,
5
i " ~
......
4 GSC
Fig. 22. Regional rank variations in the Harbour seam of the Sydney coalfield, plotted in increments of equal vitrinite reflectance (Ro max) (after Hacquebard, 1983). V.M.-- volatele-matter content.
22 also shows a distinct increase in the degree of coalification, as measured by Ro max,from southwest to northeast. This direction closely follows the downdip structure of the seam, and results in higher-rank coals being present at a greater depth of mining (and greater distance from shore). Noteworthy is the observation that lines of equal rank cross the structure contours, thus showing that the coal had obtained its present rank position after folding took place. In other words, postdeformational coalification is clearly indicated. As was mentioned previously, such coalification reflects the maximum amount of overburden that existed after the deformation. The observed regional increase in rank indicates that there existed less burial in the northwestern than in the southeastern parts of the coalfield. Calculations according to the method of Suggate (1959) gave 3700 m of eroded overburden in the western part of the field as compared to 4200 m at Donkin. This result is in agreement with the transgressive nature of the upper coal-bearing zone, which shows a thickening from west to east.
Rank/paleogeothermal relationship. The effect of variations in paleogeothermal conditions on the rank of coal can be deduced from changes in the coalification gradient of vertical seam successions. For the Sydney field, as shown
243
in Figure 23, rank-depth relationships of sixty-three coals intersected in ten boreholes are illustrated in four diagrams (Hacquebard, 1984a). Each diagram relates to an area in which the slope of the coalification curves in each of the four subfigures is subparallel, signifying almost identical coalification gradients, which are expressed in %R . . . . change per 100 m increase in depth. Different gradients were obtained in the four diagrams, from a low of 0.052% to a high of 0.088% Ro ~ J 1 0 0 m (underlined numbers). These considerable variations (the latter is 1.7 times the former) are likely the result of marked changes in the paleotemperatures at the different sites. These temperatures can be calculated from coal-rank data according to the method outlined by Bostick et al. (1979), and then can be used to determined the paleogeothermal gradient of each well. A variation of 2.5-6.7°C/100 m was obtained; with the majority of the wells in the central part of the field showing a gradient of 4.3 ° C/ 100 m, a value which compares with 4.0 and 4.3°C/100 m obtained in the Carboniferous coalfields of the Ruhr and Dutch Limburg (Hacquebard, 1984a). The detailed correlation between the two gradients in the Sydney coalfield is shown in Figure 24. It amounts to a change in paleogeothermal gradient of 1 °C per 0.01% change in the coalification gradient. This value is not constant, but varies between different coal areas because different rank relationships and different coalification times are represented. LEGEND
0.7 oo .
, .>.
,e~?, ,-,%
,
...... ~~ : < ~ ~
i
%Ro max '.,
'
'
'
1.2 '
1
Structure and well location map wilh contours on Harbour seam 0.8 1.3 500
IIOC
X
O.088=Coaliflcatlon Gradient in %Ro/lOOm de~rh • • :Samples of individual coal seams WELL AND SAMPLE IDENTIFICATION I: Murphy el al North Sydney P-05, " 2 : Shell el al North Sydney F 24; • 3: DEVCO C IlL • 4:NSDM GIace Buy H IA(1977), 5: H 2 (~978), 6= H-8A(1978), 7: H 8(1977); 8: H-SB(1977), 9: H 6 H977), I0: Birchgrove No I well, •
0.7 O 0.8 I O O i ~ '
1.2 '
,
,
0.072 "% ' ~ ' X 4 5 0.052 800
6
80C
Fig. 23. Coalification curves of ten wells in the Sydney Basin (after Hacquebard, 1984a).
244 0.100
/
CORR.COEE:0.9753 /
I
-
0.080
6 .5"4~ 0.060
.10
2 0.0401
2:0
" 3:0
4'o
5:o
6:o
7'o
°C/100rn
Fig. 24. Correlation of coalification gradients and paleogeothermal gradients in the Sydney coalfield (after Hacquebard, 1984a).
Rank changes in Carboniferous basin of New Brunswick Relationship with underlying igneous basement. The total Carboniferous cover in the central basin of New Brunswick is less than 2 km thick and rests with marked angular unconformity on a basement of earlier Paleozoic and Precambrian rocks. These earlier sediments were considerably metamorphosed by tectonism and intrusions of granite during the Acadian orogeny in Devonian time (Gussow, 1953 ). All igneous activity had ceased when the coal measures were laid down during Westphalian C and D and Stephanian times. The coals present in the central Carboniferous basin show a progressive increase in rank from HV-C bituminous coal to anthracite via HV-B, HV-A, MV, LV, and semianthracite, when proceeding from northeast to southwest (Fig. 25), (Hacquebard and Avery, 1984). As the coal-bearing sediments also become progressively older in the same direction, the rank changes can, in part, be related to an increase in the thickness of the original overburden, but only to the rank of HV-A bituminous coal. Beyond this rank, the amount of original overburden required to reach the anthracite stage probably never existed in the area (an additional 2200 m would be required, whereas the stratigraphy only provides 200 m). Therefore, as deduced from wells in eastern Prince Edward Island, a heat source other than that provided by greater depth of burial is required. This heat source may have originated from the igneous rocks that surround the southwest corner area and most likely underlie it. This is deduced from the
245 64 o
66° CHALEUR BAY
LEGEND %Ho MAX
L
Icl c
0.6 ~
OB ~
"4 fill Sil
I+8~;:: t 2.6~r~,~
HIGH VOLATILE
GULF OF G[ LAWRENCE
I~I
. . . . OL. . . . . SEMIAHTHRACITE
ANTHRACITE
i:"~
!~i.'~' ..... ii!ii~ i::i:i:i::.::i: i!
46°
fS
0
KILBMETRES,
50
64°
Fig. 25. Generalized coal rank map of the Carboniferous Basin of New Brunswick (after Hacquebard and Avery, 1984).
Bouguer gravity map (Fig. 26, Chandra et al., 1980) and shows the gravity variations in 20 milligal increments. Negative gravity values of - 20 milligals and more are interpreted as expressions of igneous rocks, whereas those less than - 20 milligals denote metamorphic and sedimentary sequences. The map indicates that the pre-Carboniferous igneous rocks that border the basin in the southwest corner of the area may continue past Fredericton in a northeast direction. Other igneous rocks of the pre-Carboniferous basement complex may occur near Bathurst in the north and in the extreme southeast at the border between New Brunswick and Nova Scotia. The possible effect of the igneous rocks on the variations in coal rank is indicated by the isoreflectance contours that have been superimposed on the gravity map (Fig. 26). Areas of higher rank appear to be underlain by igneous rocks or lie in close proximity to them. Because the latter predate the coal
246 64 °
66 °
GRAVITY IN MILLIGALS -60
~I~
-40
-20
0
+20
ISOPLETH Of VITRINITEREFLECTANCE (%Ro)
GULFOFETLAWRENCE Jpl
~-2o?" I
/
s
fl t,~
~'\\ !
",
] J
/
11
~
~l \\
/I
::
~ : .:::::;
~\
I
i
L--.+ ,o',
/
4!iii: : ?
/ /
..:::::::::::. *.: : : : -
i_
:::
/:
iI
J"
/---40~ /
E
/
i/I I//
/
-/
•
.,:.:.:. ~: : : : : :
E'---
;
)~
d6°
64 •
Fig. 26. Relationship between gravity variations and coal rank (after Hacquebard and Avery, 1984).
measures by a considerable amount of time [they are Devonian and Late Carboniferous (Mississippian) in age ], direct heating from intrusion or volcanism did not occur, but additional heat flow due to the high conductivity of igneous rocks likely did take place. This view is supported by present-day heat flow measurements in the area (Hyndman et al., 1979), which show the highest value (72 m Wm -2) at Mount Pleasant (in extreme southwest corner). This compares with values of 57 and 64 south of Bathurst, 45 in central Prince Edward Island, and 49 at Wallace, Nova Scotia. The progressive increase in heat flow towards the igneous masses appears to offer a better explanation for the occurrence of high-rank coals in the southwest corner of the central basin than the 2200 m of additional overburden from younger formations that was mentioned previously.
247
Some geological applications of coalification studies in A tlantic Canada Depth of burial determinations Subbituminous coals and lignites. The coalification process is caused by the actions of pressure, temperature, and duration of heat. As mentioned earlier, the process is irreversible; once a particular coalifica'tion level has been reached it cannot revert back to a lower level; therefore, rank data can provide information on the paleoburial conditions under which coal was formed. This includes the depth of the original overburden required to reach the rank position that has been attained, under existing paleogeothermal conditions. During the early stages of diagenesis it is mainly pressure that advances the degree of coalification. The pressure caused by the weight (or thickness) of the original overburden causes a loss of moisture content, until the rank of high-volatile C bituminous coal is reached. On the basis of a series of German data, Hacquebard (1977) found that an asymptotic relationship exists between "bed" (or equilibrium) moisture content and depth of burial. The German data were later augmented by moisture determinations on subbituminous coals of Alberta by Nurkowski ( 1985 ), as shown in Figure 27. The relationship found in Alberta coals can be expressed in the following formula: DOB = (1.865 - log. MEQ)/0.00046
DEPTHOF BURIALIN FEET 5000
0 i
i
L
i
J
i
L
10000 i
i
J
5O 70 3Ot 3
i
Ro
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-0.4
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/4
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o
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1000 2000 DEPTHOF BURIALIN METRES
I
3000
Fig. 27. Modified moisture-depth of burial diagram (Hacquebard, 1977 ), including the coal ranks
as found in the plains of Alberta (after Nurkowski, 1985). Brown coal as used in this diagram corresponds roughly to the German soft brown coal (Weichbraunkohle) whereas lignite refers to part of the Mattbraunkohle of the German classification (Teichmtiller and Teichmtiller, 1982). Lignite as used here also roughly corresponds to the ASTM lignite A. Ro = mean maximum vitrinite reflectance.
248
in which D O B = m a x i m u m depth of coal burial and M E Q = equilibrium moisture content. W i t h the aid of this formula, the depths of burial of two Nova Scotia lignite deposits, with 30 and 35% equilibrium or "bed" moisture contents have been calculated at 760 and 780 m (Hacquebard, 1984b). As these deposits, which are of Early Cretaceous age, occur in close proximity to the surface it can be concluded that at least some 750 m of sediments have been removed by erosion. The lignite deposits form part of very limited and isolated Cretaceous deposits that occur on the mainland of Nova Scotia and Cape Breton Island. At one time they may have been much more extensive, as is still the case in the present offshore Cretaceous sediments on the Nova Scotia Shelf.
Bituminous coals. Once the coalification level of bituminous coal is reached, the equilibrium moisture content remains fairly constant and is generally below 5%. In bituminous coals, the volatile-matter content and vitrinite reflectance are the most sensitive rank parameters. Following Hilt's Law (1873), which states that in vertical sequences coalification increases regularly with depth, the amount of original overburden can be deduced from coal-rank determinations. In Atlantic Canada, the composite coalification curve of (Hacquebard (1974) can be used for rank determination. It is based on the changes in coal rank with depth of a series of Mesozoic and Carboniferous coals. The rank data were obtained from vitrinite reflectance (R . . . . ) measurements, which are indicated on the abscissa at the top of Figure 28; the corresponding volatile-matter contents (VM) and the A S T M (1979) rank classes are shown at the bottom. The composite curve (Fig. 28) was derived from Ro max determination of 29 Mesozoic coals (upper curve) intersected in boreholes of the Scotian Shelf, and 39 Carboniferous coals (lower curve) from onshore boreholes in Atlantic Canada. The two curves overlap in the rank range from 0.63 to 0.95% Ro max, where they have almost identical coalification gradients, namely 0.033/100 m and 0.036/100 m. Because of the identical gradients it is acceptable to consider the two curves as one general coalification curve for the Maritime region. The asymptotic relationship between rank and depth is clearly indicated and when plotted on semi-log grid a linear curve will result (Hacquebard and Avery, 1984 ). The Maritime coalification curve permits direct conversion of coal rank to original depth of overburden. The depth shown on the ordinate is thought to relate to the maximum sediment thickness that ever existed on the Scotia Shelf (McIver, 1972). Therefore, from the curve it is deduced that on Brion Island 2240 m of strata have been eroded (Fig. 28). The general coalification curve can be used to convert the rank of individual surface or near-surface coals to overburden thickness, when borehole sequences are not available, but it will give an average value only. However, when a vertical succession of coals is present, the coalification curve of that succes-
249 .2
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Fig. 28. Composite coalification curve of Mesozoic and Carboniferous coal sequences in the Maritime region (after Hacquebard, 1975 ). Ro = mean maximum vitrinite reflectance; V M = volatilematter content (daf).
sion should be used. Its gradient may differ from the general curve and a more precise overburden determination will result. The maximum depth of burial is obtained by projecting the curve to the 0.2% Ro maxlevel, which is the reflectance of newly formed vitrinite (huminite) (Dow, 1977; Fig. 29). This level, therefore, may be regarded as the zero position of coalification, a conclusion supported by numerous east coast offshore wells that are believed to be at maximum burial depth at present (Vonk, 1986).
250 Ro/PERCENT LOG SCALE 0.4 0.6
0.2
0.8
1
1.4
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PROJECTED: 0.2% R o = -1530m 0.44% Ro= 0m
.__1 I I.n
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Fig. 29. Coalification curve of the Bradelle L-49 well with projected original depth of overburden (after Vonk, 1986).
Rank as aid to structural interpretations
The Upper Carboniferous coals of Atlantic Canada have been only mildly affected by the Hercynian orogeny. Folding of the coal measures has been largely the result of initial dip, of differential compaction, and of variable uplift due to diapiric movements. Most of this deformation took place during the early stages of coalification, but this was followed later by the development of major faulting, particularly along the west coast of Cape Breton Island and in western
251 Newfoundland. A large fracture zone can be traced in this region and even may represent the pre-continental drift extension of the Great Glen Fault of Scotland (Hacquebard, 1972). Therefore, the faulting represent the major tectonic event that affected the coal measures in Atlantic Canada, but the age of this faulting and its relationship to the Hercynian orogeny has not been resolved. As will be shown here, the interpretation of coal-rank variations in the Mabou coalfield of western Cape Breton Island (Fig. 18) has thrown light on this problem. The rank:depth relationship of four coals intersected in four offshore wells drilled in the Gulf of St. Lawrence Basin is illustrated in Figure 30A (Hacquebard, 1986). In the diagram, the lines of equal rank, or isograds, run horizontally and correspond with specific depth positions, because postdeformational coalification is represented. These positions correspond with maximum depth of burial values shown in the ordinate on the right, which were obtained from the Maritime coalification curve previously discussed. The Maritime curve relates a rank of 0.5% Romax to an overburden of 2658 m (8720 ft), which is indicated at the upper end of the ordinate. The scale below this value corresponds to the present depth scale and therefore takes into account the gradient of the curve, which differs somewhat from the general Maritime curve. The curve shows a near-perfect linear correlation between depth and rank (plotted on logarithmic scale) when the Ro m a x data on the two Mabou coals of Borehole M-2A and the six surface coals are not included. The latter all have nearly the same rank of about 0.64% Ro maxand, therefore, should have plotted at a depth of 762 m (2500 ft), and the coals in Borehole M-2A at a depth of 1158 m (3800 ft). The present position of these coals is related to the faulting shown in Figure 30B. These faults are part of the major fracture zone that occurs along the west coast of Cape Breton Island, as previously described. Figure 30C shows that at Mabou Mines some 2286 m (7500 ft) of additional sediments must have been present to meet the rank-overburden requirements of the coals involved. These additional strata most likely accumulated during Permian time, as can be deduced from the fact that a few thousands of meters of red beds of Permian age are still present today in most wells drilled in the Gulf of St. Lawrence (Hacquebard, 1986). The rank of the surface coals also required additional overburden, and, therefore, the coals cannot have been placed in their present position until after the Permian red beds had been deposited. It is concluded from this analysis that the faulting took place in postPermian time, probably Early Triassic time. This event probably constituted the final phase of deformation of the Fundy epieugeosyncline. It led to the formation of a complex rift valley, which is bounded by high-angle faults (Hacquebard, 1972 ). Apart from determining the age of faulting, rank studies also can provide information on the displacement along various faults. At Mabou Mines the total displacement was of the order of 762 m (2500 ft), as this is the difference
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A. GULF OF ST. LAWRENCE C O A L I F I C A T I O N CURVE FROM B O R E H O L E Ro.-DATA, AND RANK POSITION OF SURFACE C O A L S IN UPTHROWN FAULT B L O C K S
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253 in depth between the Ro m,x of 0.6% of the surface coals and the R . . . . of 0.6% in Borehole M-2A (Fig. 30B). A displacement of this magnitude indicates a major tectonic event was involved. The M a b o u data also gave information on the duration of the coalification process. Because it was postfolding, but prefaulting, only the time span of the Permian, or about 40 million years, may have been involved (van Eysinga, 1975).
Rank as aid to provenance determinations of sedimentary rocks from contained detrital particles of coal Under certain conditions the rank of detrital particles of coal can be used to determine their source area. These conditions are as follows. The particles should be predominantly of one rank and derived from in situ coal seams (not from bark vitrain), because true coal seams might possess certain petrographic compositional features and a palynological assemblage that would help in identification and age dating. The coals of the possible source area should have limited rank variations, restricted geographic distribution of the rank level represented, and erosional possibilities of exposed coal seams. This set of conditions was encountered in a study of coal detritus present in samples of sand collected from below the ocean floor, in the Sohm Abyssal Plain, some 760 km east of Bermuda (Fig. 31; Hacquebard et al., 1981). The samples were from a piston core that intersected 13 m of unconsolidated Late Pleistocene to Holocene sediments at the ocean floor. Below 8 m they consisted of graded turbidite clays with basal laminae of silt and sand, which contained IO0o
o
Fig. 31. Physiographic regions of the northwest Atlantic Ocean with coal sample location and onshore areas with high-volatile bituminous coal (hatched areas) (after Hacquebard et al., 1981).
254 minute grains of coal. The latter were I mm or less in size, and the total amount of coal available for study was about 50 mg. Microscopic examinations of polished surfaces under reflected light revealed that a normal banded coal is represented. All coal maceral groups occur, i.e., the vitrinite, liptinite and inertinite maceral groups, as well as finely divided pyrite. This indicates origin from ancient peat accumulations that led to the formation of normal banded coal. Therefore, the detrital coal particles must have been derived from in-situ coal seams. The rank of the coaly fragments is HV-A bituminous, which was determined from vitrinite reflectance. An average Ro maxof 0.80% was obtained which correlates with 36% volatile matter (KStter, 1960). Because the reflectogram has a unimodal distribution, it can be assumed that coal from only one provenance is present. In eastern North America, surface or near-surface coals with a rank of HVA bituminous occur in the Appalachian and Interior coal provinces of the United States and in the Maritime Provinces of Canada (Fig. 31) (Moore, 1947). These coals are all of Carboniferous age and only those regions bordering the coast of the Atlantic Ocean, or possessing main drainage systems into this ocean (e.g., the Hudson and St. Lawrence rivers), need be considered as possible source areas for the Sohm Abyssal Plain coal occurrence. The main drainage system for the Interior and Appalachian coal provinces is into the Gulf of Mexico. Such source regions are present only in Nova Scotia, namely in the coalfields of Joggins on the Bay of Fundy and Sydney on the Laurentian Channel (Fig. 31). The petrographic composition of the detrital coal particles closely resembles that of the Sydney coals. Identical microlithotypes and similar forms of pyrite are present. Most interesting is the observation that the maceral sporinite is derived from plant spores and probably not from pollen. This indicates that the coal most likely is of Carboniferous age, because pollen-bearing plants did not exist until the late Mesozoic, when the flowering plants first appeared in geologic time. A study of isolated spores carried out by M.S. Barss of the Atlantic Geoscience Centre confirmed the above view: a Carboniferous coal is represented and it can be dated as Westphalian D, because the Thymospora zone is clearly indicated (M.S. Barss, pers. commun., 1988; also Barss and Hacquebard, 1967). This age strongly suggests a Sydney source for the detitral coal because only in this field do coals of Westphalian D age occur and are exposed at the surface, both onshore and in the nearshore submarine area (see fig. 4, Hacquebard et al., 1981). The spore dating rules out derivation from the Joggins coal field, because there the coals are Westphalian B in age. With the Sydney coalfield as provenance area the question may be asked: what was the mode of transport to move the detrital coal particles a distance of some 1800 km, from Sydney to the Sohm Abyssal Plain? Turbidity flow is
255 believed to be the answer. This view is supported by evidence obtained from the 1929 Grand Banks earthquake. This quake jarred the continental slope and shelf, setting submarine slumps in motion, which triggered a large turbidity current. This current moved from the Laurentian Cone southeast towards the west flank of the Mid-Atlantic Ridge and then south along the east side of the Sohm Abyssal Plain. How far the Grand Banks turbidite reached is not known, but the observation that at 740 km from its source the velocity was still 20 km per hour suggests that the area affected extended hundreds of kilometers farther south (Heezen and Ewing, 1952). It should be noted that the direction of flow of the Grand Banks turbidite of 1929 pointed directly at the coal location in the Sohm Abyssal Plain. The coal attests to the fact that a previous turbidity flow, which took place some 35,000 years ago, apparently followed nearly the same path, and reached a point that is some 1,500 km south of the continental rise. This result supports the view expressed by Heezen and Ewing (1952) that sediment can be transported far out into the oceanic basins through the medium of turbidity flow. The value of detrital coal in sediment transport analysis was shown also by Burgess (1987), who traced his "coffee grounds" particles of the Mississippi Delta to the Interior Coal Province, some 1600 km upstream from the site. Here too, coal-rank determinations and spore identifications provided the dual approach in reconstructing provenance, transport history, and origin of the detrital coal particles. ACKNOWLEDGEMENTS The authors deeply appreciate assistance in a variety of forms from a number of colleagues at The Atlantic Geoscience Centre (AGC) and the Institute of Sedimentary and Petroleum Geology (ISPG). Special thanks are due to Donna Smith at ISPG who typed the final draft of the manuscript, to Carol Boonstra at ISPG who assisted with typing and also drafted a number of the figures, Nelly Koziel (AGC) who typed the initial draft of the Maritimes portion of the manuscript and to Ken Pratt (ISPG) and Mike Avery (AGC) who carried out many of the reflectance determinations upon which the paper is based. The paper was reviewed by R.M. Bustin and N.H. Bostick.
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