Recent depositional conditions in the St. Lawrence River and Gulf — A reconnaissance survey

RECENT DEPOSITIONAL CONDITIONS IN THE ST. LAWRENCE RIVEI~ AND G U L F - A RECONNAISSANCE SURVEY D. J. G. N O T A 1 A N D D. H. L O R I N G

Geology and Mineralogy Department, Agricultural State University, Wageningen (The Netherlands) Fisheries Research Board of Canada, Atlantic OceanographicGrotto,Bedfordlnstitute of Oceanography Dartmouth, N.S. (Canada) (Received April 29, 1964)

SUMMARY

The results of a sedimentological reconnaissance in the area of the River and Gulf o St. Lawrence are discussed. The study is mainly concerned with the relationshi t between submarine topography, surface sediments, sediment sources and presen processes of deposition. The bathymetry of the basin revealed that Pleistocene glaciation largely deter. mined the present shape of the St. Lawrence submarine trough. The distributior pattern of the sediments is fairly regular and characterized by poorly sorted coarse grained nearshore deposits and an extensive area of soft pelite bottom in the deepeJ parts of the trough. Inspection of the P D R sections shows that the thickness of the soft sedimentary top layer, which forms the postglacial sediment addition, varie~ strongly regionaUy and the maximum thickness is 72 ft. In the area between Quebec city and the mouth of the Saguenay River stiff heavy pelites were found to be th~ characteristic deposits; they are not recent but residual from former conditions. The importance of ice-rafting as a dispersing agent is demonstrated and the cause of th~ almost constant granulometrical composition of the material ~ 16 ~ for the postglacial pelites discussed. The mineralogy of the sands has shown the presence of unstable heavy and lighl mineral assemblages throughout the basin. The mineralogical composition indicate, that the crystallines of the Canadian Shield are the principal sources for the sands The chemistry of the sediments has emphasized the lack of intensive chemical decom. position of the source material. The physical conditions in the area set it apart as particular environmental type.

1 Visiting Associate Professor in Marine Geology in 1961-1962 at the Institute of Oceanography, Dalhousie University, Halifax, N.S. (Canada). Marine GeoL, 2 (1964) 198-23.'

DEPOSITIONAL CONDITIONS IN THE ST. LAWRENCE REGION

199

INTRODUCTION (N.)

The last decade has seen a great increase in the study of modern marine sediments and many reports of recent data concern the study of nearshore and shelf sediments. The wide variation in conditions which have been found to prevail on different continental shelves, and in inland seas, however, makes it desirable to collect data from more and more regions. The present report deals with the preliminary results of a survey in the Gulf and River of St. Lawrence. The results reported are of a reconnaissance nature since the program was planned to determine only the major sedimentological features of this large area. This study is mainly concerned with the study of the submarine topography, its relationship to the distribution of surface sediments, and the present processes of deposition. Pleistocene glaciation and present climatic conditions set the Gulf and River of St. Lawrence apart from most of the other sedimentary environments where detailed studies have been carried out. The Gulf of Mexico, the Orinoco delta and vicinity, the shelf area off southern California, the R_h6ne delta, the Niger delta and the Persian Gulf belong to the areas which have been intensively studied in recent years. Most of these areas are environments under influence of large amounts of supplied terrigenous materials (delta areas), lying in tropical or subtropical climates and have not been glaciated during the Pleistocene era. Previous work which has contributed to the knowledge of the regional sedimentary conditions in the area of the Gulf and River of St. Lawrence is scarce. Up to 1961 only scattered observations have been made; the first systematic bottom sampling campaign in the Gulf and River of St. Lawrence was carried out by the authors on board of the C.N.A.V. "Sackville" in the summer of 1961. The origin and physiography of the St. Lawrence Trough was treated by JOHNSON (1925), SrIEPARO (1931, 1963) and by McNEIL (1956). The structure of the Cabot Strait Trough, leading outward from the Gulf and River of St. Lawrence to the open ocean, has been reported by PRESSand BECKMANN(1954). The conclusions of these reports will be a subject of discussion later on in this paper. This report is based mainly on the results of two short cruises in July 1961 ($56) and May 1962 ($62) into the Gulf and River of St. Lawrence (Fig.l). The locations of the sample stations are indicated by a letter and number combination: S stands for the research vessel "Sackville", and the number directly following the letter S is the number of the cruise; the number following the hyphen is the number of the particular station. The somewhat circular shaped shallow water area around Prince Edward Island, the Magdalen Islands and off Chaleur Bay has not been included in this study.

Marine Geol., 2 (1964) 198-235

SUBMARINE TOPOGRAPHY (N.)

The Gulf of St. Lawrence is an epicontinental marginal sea of a somewhat triangula shape comprising an area of approximately 57,000 sq. miles. There are two mai~ openings to the ocean, the straits of Cabot and Belle Isle (Fig.2). From the St. Lawrenc River system, which extends inland approximately 2,000 miles, the Gulf of St. Law rence receives the drainage of approximately 500,000 sq. miles (LAUZIERet al., 19571 The adjacent hills and mountains on the south side of the St. Lawrence Rive belong to the Appalachian system; the rocks are mainly Palaeozoic limestones, shale., sandstones and extend through the district of Quebec eastward to the Gasp6 peninsul and then to the shore areas of New Brunswick, Nova Scotia, Prince Edward Islan, and Newfoundland. The north side of the St. Lawrence River from Quebec eastwar, and north to the Labrador coast is composed of the highlands and mountains of th Canadian Shield, and is characterised by metamorphic and igneous rocks of pro Palaeozoic age. As sedimentary conditions can be influenced to a great extend by the shape c the valley, by relief and absolute depth, a discussion of the submarine topograph is essential to this study. The sources of information available for this report on the bathymetry of th Gulf and River of St. Lawrence, were the various Canadian hydrographic charts and Mark V Precision Depth Recorder (PDR) which was continuously operating on boar the research vessel "Sackville". There were several limitations in the interpretation of these charts and the PD] recordings. East of Anticosti Island the number of soundings available is insufficier to allow accurate construction of countours; consequently the detailed map of Fig. does not cover any of this area. Due to lack of time both the P D R recordings an sediment samples were taken during the same traverse; the possible error introduce by the variation in speed was minimized as far as possible by keeping constant recorc o f ship speed. DECCA and L O R A N were the main aids to navigation; in areas witI out this coverage, celestial navigation and dead reckoning were used. In construction of the bottom profiles the position of the ship was establishe as accurately as possible. Where the soft sedimentary top layer is very thin, carefi attention was required to distinguish between real (sub) bottom reflections and gho: echoes. The St. Lawrence submarine valley extends inland to the vicinity of the city Quebec, while its seaward continuation extends right across the shelf. The mo: striking feature of the morphology of the valley is the presence of a deep submarir trough (usually referred to as the Laurentian Channel, or Cabot Strait Trough) wit depths over 200 fathoms and which extends from the edge o f the continental shelf t a point near the mouth of the Saguenay River, a distance of about 750 miles (Fig.2 Most of the area of the St. Lawrence River valley between the mouth of the Saguen~ River and Quebec city is fairly shallow, and does not exceed depths of 20 fathom The transition from the deep trough to the shallow area farther upstream is fair'~ Marine Geol., 2 (1964) 198-2!

O0

STATIONS:

NAUTICAL

5o

MILES

1oo

,o,;~<,

2e S - 6 2

70 s-s6

OF

LEGEND

..,,'

- "]/,.9/,I/i, 'A

o ~ s P

65 °

_

~-;-o;:

--,so..'.

600

/ ,/

60 °

(

,.~ 46 °

48 °

r.

t,J

© Z

rn Z d3 rn

r~

rr~

=

.]

o 2~

Z N

r~ ©

50 °

Fig.l. Sampling stations in the area of the Gulf and River of St, Lawrence (S 56 and S 62). M. Is = Magdalen Islands; P.E.I. = Prince Edward Island;

o

OIS6 F-L

70 ° W

~o N,F. = Newfoundland.

t~

QUEBEC

..

..¢

T~ O0

5'

I

I

0

,3

70 ° W

NAU3"tCAL

50

MILES

POll'#

MAP

100

BATHYMETRIC

CONTOURS IN FATHONS

SIMPLIFIED

~j~

rl---L~

65 °

65 °

~,.bo"'"

P. F.I.

~.15.

OF ST LAWRENCE

-- ~so.,',

Fig.2. Simplified bathymetric map of the entire region of the Gulf and River of St. Lawrence; contour interval 50 fathoms.

QUEBEC

48 c

I

70 ° W

GULF and RIVER ST. LAWRENCE

!

"'~

60 °

6001

46 °

48 °

N

-50 °

STRAIT OFI BELLE I S L ~

DEPOSITIONALCONDITIONSIN THE ST. LAWRENCEREGION

203

abrupt. The deep trough has a branch towards the Strait of Belle Isle and another on the north side of Anticosti Island. The origin of the St. Lawrence valley has been discussed by various authors (JOHNSON, 1925; SI-mPARD, 1931; PRESS and BECKr~AN, 1954; MCNEIL, 1956). There can be little doubt that the geologic framework of the area, as characterised by the St. Lawrence Arc (Logan fault), the Belle Isle Strait Arc and the fault patterns of Nova Scotia and Newfoundland, favors a structural origin for the valley. Its location along the boundaries of different kinds of rock is significant; the valley parts the Archaen crystalline rocks of the Canadian Shield from the younger sedimentaries of the northern Appalachians (Fig.3). The seismic results (PRESS and BECI~r~AN, 1954) seem 70 ° W

65 °

60 °

50 ° N

N

4a °

QUEBEC

46 °

ARCHAEAN CRYSTALLINES OFCANADIAN SHIELD ~ / ~

PALAEOZOIC SEDIMENTARY ROCKS

Fig.3. Generalized geologicmap of the St. Lawrence and Gulf area. Arrows indicate glacial movement into and through the valley. Prepared mainly from Geological map of Canada (1955) and Glacial map of Quebec (1957). P.E.I. = Prince Edward Island; M. Is. = Magdalen Islands; N.F. = Newfoundland. to confirm that the Cabot Strait Trough leading outward from the Gulf of St. Lawrence is structural in origin, and earthquake activity in June 1951, pointed to a location o f the epicenter in the eastern continuation of the trough. There is quite a diversity of opinions as to the origin of the present shape of the valley. JoI-I~SON (1925) believed that the Gulf of St. Lawrence was essentially a submerged lowland cut by stream erosion and modified only slightly by glaciation. SHEPARD (1931) concluded that there is a trough in the Gulf of St. Lawrence, which is the result primilary of glacial erosion. MCNEIL (1956) suggested that when sea-level reached its present elevation, turbidity currents would have followed the drowned St. Lawrence valley and would have been sufficiently powerful to deepen it. Mud Marine GeoL, 2 (1964) 198-235

slides and creeps would have operated to widen the trough and incidentally to cor tribute additional sediments to the eroding current. These processes would hay given rise to the Cabot Strait Trough that exists to day. HEEZEN and EWING (1952) first called attention to the possible significance c the activity of turbidity currents and submarine slumps in causing the cable break at the time of the 1929 Grand Banks earthquake. The location of the earthquak epicenter was in the seaward continuation of the Cabot Strait Trough near the edg of the continental shelf. The fact that the cables broke in an orderly sequence dow~ the slope away from the earthquake epicenter and the location of this happening i~ the area of the edge of the continental shelf and down the continental slope present strong case in support of the turbidity current hypothesis (KUENEN, 1950). HeezeJ and Ewing's remarks, however, only refer to the area of the shelf edge and McNeil' assumption that the activity of turbidity currents would have given rise to the mor phology of the Cabot Strait Trough that exists to day is certainly not warranted The morphological features generally considered to be characteristic of submarin, valleys shaped by the activity of turbidity currents (a roughly V-shaped winding gorgq sloping almost continuously outward, generally cutting across the continental shel for just a few dozen kilometers, and running straight down the continental slope t~ great depth) are not those of the St. Lawrence submarine valley. It has a broad trougl shape extending from the shelf edge to a distance of about 750 miles inland, ar undulating floor and basin depressions along its course; these features indicate tha it must have been shaped by agencies other than turbidity currents. The difference in submarine topography between the shelves or inland sea~ which are adjacent and not adjacent to glaciated landmasses leaves little doubt tha glaciation has played an important role in shaping the characteristics of the former SHEPARD (1931) pointed out that off coasts that were glaciated during the Pleistocem era, a particular type of submarine valley is met with. He postulates that feature~ of that sort have been shaped principally by glacial excavation. The broad base the relatively steep and straight walls and undulating profile are among the mair characteristics of such valleys. According to KUENEN (1950) one can hardly doubl that Shepard's interpretation is correct. A glance at the glacial map of Quebec (1957) showes overwhelming evidenc~ that great ice sheets from the surrounding landmasses have moved into the valley ol the St. Lawrence (Fig.3). The submarine traces of ice movements down the St. Lawrence valley can be inferred from the bottom topography as well as from the PDR records and sedimentary data. The bathymetric map shows the presence of large, irregularly shaped, deep, rimmed depressions, elevations of oval-shaped form and an undulating longitudinal profile of the St. Lawrence valley (Fig.4). A comparable basin topography can be found in the Great Lakes of North America (HouGH, 1958), the Skagerak and the Baltic Sea in northern Europe (GRIPENBERG, 1939). All these areas were intensively glaciated during the Pleistocene period and it is known that movements of ice bodies cause the development of a complex hummocky surface of the underlying rock Marine Geol., 2 (1964) 198-235

DEPOSITIONAL CONDITIONS IN THE ST. LAWRENCE REGION

66 °

W

65 °

6~ °

~o.J 62 °

63 °

-50 °

./.9 °

Fig.4. Detailed bathymetry of part of the St. Lawrencetrough system. mass. From the P D R sections it appears that postglacial deposition has partly modified the original Pleistocene bottom topography. The accumulation of the soft sedimentary toplayer has been confined to the deeper parts of the trough, leveling off the irregular topography down below. It is significant that a core sample from the topographic high breaking through the soft sedimentary toplayer near station $6256 showed a rather stiff, light gray pelitic sediment full of angular sand and pebbles, resembling typical till, and completely different from the soft toplayer (cf. Fig.5). Evidence of the occurrence of glacial till (under the postglacial deposits) was also found from other localities, such as east of Anticosti. A thin section of the part of a core between 450-460 cm below the surfacO, showed a reddish brown clay-rich matrix (26.7 ~/o of the material is smaller than 2 ~t) with angular particles of sand and pebble size distinctly resembling the red-drumlin tills from Nova Scotia. 1 This sample was kindly placed at the author's disposal by Dr. Maurice Ewing (Lamont Geological Observatory, Palisades, N.Y., U.S.A.). Marine Geol., 2 (1964) 198-235

In addition, the study of the regional sediment distribution (see under sectio "Lithology") has revealed, that most of the surface sediments collected in the Gu are similar in having a dark greenish gray colour (5 GY 4/1). However, at sore stations in the deeper parts of the Cabot Strait Trough (e.g., stations $56-6, 7, l 1 brownish-gray (5 YR 4/1) coloured surface sediments were obtained. HEEZZN an DRAKE (1964) speak of a red sediment in and south of Cabot Strait, which is expose or buried under a gray coloured layer. It is most probably that here the same types c deposits are being discussed. Heezen and Drake suppose that the red sediment i glacial in origin and also our data seem indicative of exposed glacial till. Howeve~ our available information does not permit any definite conclusion. More coring il this area will be necessary to find out the stratigraphic relations between the greenish gray and the brownish-gray coloured layers, and in how far the latter layer is expose~ as a glacial deposit or originated from reworking of submarine glacial drift or fron eroded coastal deposits of that type. Since only few longer cores were obtained during the reconnaissance surve2 of the area under discussion, sedimentary data as yet are too scarce to assume definitel2 the regional presence of glacial till under the postglacial deposits. Yet the availabl~ data seem to support the conclusion that the present bottom configuration of the St Lawrence valley can be largely explained along the following lines: (a) Glacial erosion during the Pleistocene, making it a submarine glacia trough; glacial erosion most probably took place along a pre-existing valley system started by river erosion, along fault lines between Archaen and Palaeozoic strata. As the density of glacier ice is about 0.9, even a valley glacier of some 600 m thickness would have been thick enough to scoop the valley bottom without floating. But the pressure on the substratum would be so small that a much thicker ice tongue was probably responsible. (b) Uneven deposition from Pleistocene ice unevenly charged with debris and from streams that flowed on, in or under the ice; fluvioglacial activity locally will have been levelling off the glacial topography when at the end of the Pleistocene period the glacial ice in the valley started to melt and flotation occurred again. (c) Reworking (-- erosion and redeposition) of glacial deposits and deposition of recently supplied material since the rise of sea level after the melting of the Pleistocene ice masses. The explanation of the submarine topography of the area of Gulf and River of St. Lawrence along the lines set forth above would mean that three major ice masses have moved down the valley. One major lobe must have originated from the valley of the Saguenay River, a beautiful example of an U-shaped valley with oversteepened walls and hanging valleys, which has long been recognized as a typical fjord. It is significant that near the mouth of the Saguenay River the St. Lawrence valley first shows its trough characteristics. A second major lobe of ice must have moved eastward through the tributary directly north of Anticosti. The island, lying at right angles to the direction of flow of Marine Geol., 2 (1964) 198-235

31

30

29

28

27

26

25 2 4

23

I.° -200

VERTICAL. EXAGGERATION 50 TIMES 21

j

22

l

I

23

SEA LEVEL

34

C

E

I~ 0

--

35

13

o

24

I

s 56

36

£

10 NAUTICAL MILES I I

2

'mS

~

100

33

32

77 76

75

74 73

~ @

~

~

100

•...

_

.~.

37 38 _ I _ s E LAEVEL I

39 '

40 '

_

.

41 '

.00

111 110

42 '1 ~m$

109

~_~

108 107

j.o

fins 100

2O0 .....~.

52 |~

53 ~

54 I

55 I

SEA LEVEL

•

56

.~"

...

57

I

~

58 59 6 0 I

.~

66 I

--=

67 I

--u

68 |

---=

69 I

SEA LEVEL

-:~d

",

70 I

71

of

I*,lg

I

I

I| 0

/ t ,r.,

72 I| ~m$

lib

~J

~k

Fig.5. Bottom profiles across the St. Lawrence submarine trough; vertical exaggeration 50~times. a = pelite ( > 30%); h = pelitic (5-30%); c = silty pelite ( > 30%); d = sand ( > 30%); e = sandy ( 5 - 3 0 % ) ; f = gravelly ( 5 - 3 0 % ) ; g = ca]carenite ( > 30%); h = calcarenitic ( 5 - 3 0 % ) ; j = calcipelitic (5-30%); k = calciruditic (5-30%); M. Is. = Magdalen Islands. The thinner line underneath the bottom line presents the base of the soft sedimentary top layer.

the ice coming from the north, must have formed a barrier for the basal ice. The thus became deflected in an eastward direction, vigorously scouring the trough no~ of Anticosti Island. The third major valley extends up towards the Strait of Belie Isle. The ice flowi southward from the highlands of Labrador and western Newfoundland would ha widened and deepened this northern branch of the St. Lawrence submarine trou~ The explanation of the submarine topography o f the St. Lawrence trou system on the basis of glacial excavation is necessarily a glacial erosion strongly ce trolled by the preglacial topography. The ice masses would naturally have be thicker over the existing valleys than over the adjacent uplands, thus making for i creased excavation of the valley floor. The result was a widening, deepening aJ straightening of the valleys by subglacial erosion, when they were repeatedly filled i Pleistocene ice masses. It is thought that the same argument holds true for t seaward continuation of the St. Lawrence trough, which completely extends acre the continental shelf; that is to say, it is the natural continuation of the preglacial Lawrence valley, modified by glacial erosion during the Pleistocene. The deep, rimmed depressions in the Cabot Strait as well as between Antico~ and Gasp6 must be attributed to increased erosion by the basal ice; this increas~ erosion being caused by the more rapid flow required for the ice to pass through the narrows. Finally, it would be possible through a petrological analysis of the till, using tl pebble and sand fraction, to find out definitely and in detail the movements of tl ice masses through the St. Lawrence trough system; it would also make it possib to trace the source regions of the sands and pebbles of the ground moraine.

LITHOLOGY (N.)

General Since the present study has been planned as a reconnaissance survey and the samplin was designed for regional coverage, preference was given to obtaining a large numb~ of samples spread over the entire region. Grab samples and short cores have bee recovered, and only few longer cores were taken. The composition of the surface sediments (top few cm) and their region.' distribution, reflect the present-day depositional conditions and also to a certai degree the depositional conditions that have been effective earlier. This section wi be devoted to a description of the sediments on the surface; it will include a discussio on the outcome of the mechanical analyses. The sediment descriptions are largel based on a binocular microscope study and to provide standards, a fair number c the samples have been analysed to ascertain the particle size distribution and th carbonate content. The limits and names of the size grades in this report are: gravel, for particle Marine Geol., 2 (1964) 198-23

0 1

'

I

I SEA LEVEL I

100 _L;,;,,,,,,,,,,,,I,;,:,,,,,,,~,.~.,. %

I p CARSONATE ~

S 0 ~

~

:~:~'k~'

~

~

'~'~'~

t;.'. ......

l

: .'.-!-.L~ '" ~ , ' . ~ - ~ : G R A V E L

PEUTE

- -

0~

52

0 -L |

53 I

5/,

55

t

56

I

I

57

SEA LEVEL

58 59 60

I

t

t

S 6" 2 0 0 -~

~

"~ " "

%~:i:i:i:!:i:i:i:i:~i:i:!:!~XN~:i:i:i:i:y"

100.

% . . . . . . . . . .L ...

• :.~.i.~.~.~.:.i.

. . .,. . . .,I

.....

~ , ,

J . . ., . l

~ . .CARBONATE .

.i.;.~.i.;.i.i.~:.~

......

I.

• i i , ,

, i i

,

, ,

/ ,

, .i i

,t,

i

\~l

.....-....!..I.--.

Fig.6. Variations in carbonate-gravel-sand-pelite ratios along two profiles across the St. Lawrence trough. Numbers indicate sampling stations. coarser than 2 mm; sand, for particle diameters between 2 and 0.05 mm; for material smaller than 0.05 mm, the term pelite is used instead o f the non-sharply defined name " m u d " ; silt for the material between 0.05 and 0.002 mm, and clay for material finer than 0.002 mm. The term catcirudite has been applied to calcareous material over 2 mm in size; calcarenite is calcareous material of sand-grain size; calcareous material smaller than 50 ~ is called calcipelite. In his study of the sediments of the western Guiana Shelf, Nota used a system of classification based on the main components of the sediments. The same system of nomenclature has been applied in this study (NOTA, 1958, pp.21-22). The critical limits are 5 ~ and 30~o. Components representing less than 5 ~ of the total sediment are not considered. One of the advantages of this system is that the 30 ~o limit can be more easily estimated in thin sections or by means of a binocular microscope than the 50~o limit, which is so often used. The colours of the sediments are recorded according to the Rock-Color-Chart o f the Geological Society of America, based on the Munsell System. The colours were estimated from samples which were still wet. The regional variations in composition o f the surface sediments in the area of the St. Lawrence submarine trough system are represented and characterized in Marine Geol., 2 (1964) 198-235

Fig.5, 6 en 7. Though in fact, the sediment composition can be given only for t sample locations, in Fig.6 preference was given to an overall picture of the sedime distribution along the bottom profiles, the pictures being based on an interpretati, of the sediments found at the sampling stations. The sedimentary and acoustic da obtained from bottom profiles other than those represented in the accompanyiJ figures also constituted important sources of information for the interpretation of t regional sediment distribution. The sediments from the St. Lawrence submariJ trough and those areas adjacent to it will be discussed first, and they will be describ~ from the central deep towards the nearshore shallow areas. Sediments from the ar~ between Quebec city and the mouth of the Saguenay River will be a subject of discu sion later on. An extensive area of petite bottom is found in the deeper central parts of tt submarine trough throughout the whole area studied. These deposits will be calle deep water petites, throughout this report; they constitute the soft sedimentary tc layer, mentioned earlier. In the main trough of the St. Lawrence valley system the~ petite deposits generally occur in water depths greater than about 150 fathom whereas in the branches towards Belle Isle and on the northern side of Anticosti the were found in depths from 100 fathoms. The deep water petites are very soft (wat~ content about 6 0 ~ bij weight), dark greenish-grey in colour (5 GY 5/1) and have clay content of some 60~o on the average. The top few millimeters of the sample are dark yellowish brown (10 YR 4/2). Inspection of the PDR sections (Fig.5 and shows that there is a definite relation between submarine topography and the thick ness of the soft deep water petites. The greatest thickness of the soft sedimentary top layer, which forms the last sediment addition was found where the river enters int, the gulf and in the area between the West Point of Anticosti and Gasp& The maximur thickness measured for the soft sedimentary top layer is 72 ft. Most of the deep wate petites are characterized by an admixture of some coarser material, of the size o both sand and gravel. The percentage of the material coarser than 50 ~ generall I amounts to only a few per cent, though in some places it may comprise even more tha~ 10 ~ of the total non-calcareous part of the sediment. The coarser particles are mor, or less homogeneously mixed with the petite, although in some cores (e.g., S 62-27 63) there was an indication of a concentration of the coarser particles at certai~ levels. The study of the size frequency distributions of the deep water petites (se~ below) strongly points to the influence of ice-rafting; this agency is considered to b~ responsible for the presence of the coarser components as an admixture in these pelit~ deposits. Finally, the abundance of faecal pellets in many of the pelite deposits (e.g. $62-26, 57, 68, 70, 75; $56-23) points to the activity of mud-eating animals, mixin~ together the various sediment components. The sediments from the shallower parts of the trough lying closer inshore generally show shoreward a decrease in the pelite content while the percentage ol material coarser than 50 ~t increases (Fig.7). The sediments are very loose and usually dark-greenish-grey in colour (5 GY 5/1). Some distinctive differences have been found for sections lying in the vicinity Marine Geol.,

2 (1964) 198-235

DEPOSITIONALCONDITIONSIN THE ST. LAWRENCER.~L/ION

~.~

of Anticosti Island (e.g., section $62-37-42) and for those lying at greater distances from Anticosti (e.g., $62-52-60). A glance at the bottom profiles of sections $62-37-42 and $62-52-60 shows that the carbonate content for each of the samples from section $62-37-42 is distinctly higher (cf. Fig.6). A map showing the regional distribution of carbonate content of the bottom sediments (Fig.7) shows that generally the carbonate content is low in the area from Quebec city to the mouth of the St. Lawrence River, somewhat higher as the River enters the Gulf, up to about 7 ~ in the center of the basin, and distinctly higher in the vicinity of Anticoste Island. The chart indicates that the river does not supply into the Gulf any substantial quantity of carbonate detritus from any sources, either above Quebec city, from the adjacent river banks or from tributaries such as the Saguenay River, with the exception of isolated anomalies near Quebec city (Orleans Island) and near the Saguenay River. Fig.7 indicates that the highest carbonate contents occur in the nearshore samples around Anticosti, while carbonate contents decrease away from the island. Anticosti Island is a cuesta with a gentle southward dip composed mainly of limestones and other calcareous sedimentary rocks. The eastern end of the island juts outward under the sea and forms a submerged reef swinging northeast and can be easily traced out to the 100 fathomline. Samples from this area ($56-14, $62-31) contain hard calcareous rock, mainly composed of the remains of colonial type organisms, such as lime-secreting worms, corals and algae. Hence, it is not surprising that substantial carbonate contents have been found in the sediments surrounding the island. A visit in May 1962 to Ellis Bay and vicinity showed that the beaches are dominantly composed of limestone particles, derived from the adjacent coastal cliffs. TWENrIOFEL(1927), who made a survey of Anticosti, found similar beaches all around the island. Accordingly, erosion of the shoreline of the island and dispersing of the calcareous detritus into the waters around it, is considered to be the cause for the relatively high carbonate content of the bottom sediments in the vicinity of Anticosti. Limestone particles of gravel and sand-size can clearly be recognized in core and grab samples from the area around the island. The general picture that carbonate contents decrease away from the island is somewhat confused by the influence of the Devonian limestones of the Gasp6 Peninsula. The distribution pattern of the carbonates clearly demonstrates the prominent influence of ice-rafting as a dispersing agent. The predominance of the northerly winds, which largely control the ice-movements seems clearly reflected. Further comment on this matter will be given under "Size frequency distributions". The nearshore sediments bordering the submarine trough are characterized by the abundance of material from the coarser size grades, while the clay content is low (cf. Fig.7). The bottom profile given in Fig.7 clearly reveals the relationship between submarine topography and sediment composition: the topographic highs showing concentration of coarser fractions, while the depressions in between are relatively rich in pelite material. Hence, there is no absolute relationship between depth and sediment composition, but there is a distinct one between protected-basinal deposits (fine grained sediments) and those occurring on topographic highs (coarser grained sediments). The topographic highs will cause turbulant conditions of the water, thus Marine Geol., 2 (1964) 198-235

65 ° W

60 °

.

v

•

50

©

':-" ..... 0"--/Oo

...;9_

%

D ,--.-. :.

:.. -..:,-_,~-~ ....... o oAsP~

---._ ,,,., ,,

,~

- .........

_

pENINSULA

C

% < 0 . 0 0 2 mm

<11

o

•

o

11-20 21-30

•

31-40 • 41-50 O 51-60 • >60

¢'~/~

so I

I

I

'

I

o .... "'-

d,'t'~ o C

loo4/'2/¢'/ . . . .

NAUTICAL

A

L'i.

-~o

~6~&

o I

~.,s.

I

MILES

60 °

65 v W

65 ° W

I

t

r9'

60 °

u~ ~/_E

jO.-~,'.-~,.,.'./;"-~:7.....l~:

50 q

!.B

.........

J E

c 2 ~ : ~ .,~

'

+.~ 'i- ...............~:: .......... .; :

,-"-

-

N

r . - - ; ~ .....

.,--:o-

,

[;'~t~.~'~l~

"

48'

.

~:~1 ~

% > 0.05 mm ~ ~ %

• 11-20

? .... B

I

~

~

d,:i:.- "

~.., ~ M.is.

~ ~-'~Zs2

s--

'%.,.

,;q k,, u-,_

,?o

c e P ~0~t~s

MILES

1

-~

I

~

"........::~w~.~.` i

/~/

/~ -~

~o . . . .

NAUTICAL

.

" "'

":UU;'^L-O'~' ..

G A ~

o 21-30 • 31-50 051-70

46 ~

:~ " ' . ' - - < b ' Z r ~ ............. Q" '~'! ........... "" "'''~'Z7--7::~='-* "i¢~.~..:~ - ' - ' - , . " , "''--~'--"

C p E

I

I--

I

0

0

65 ° VERTICAL

o

-

"I:QII',~'_J r

.'-'~.~o ,0 ;, " - ~ -"--~J .: . ' ~ Y : "/ ". . . . . "'"

~ I

,' ' ," " / " ' /'

../ "-'~

.......

~

•

. _

••C

EXAGGERATION

50 TIMES

Fig.7. Regional variations of surface sediments in clay content ( < 0.002 mm), material coarser than 0.05 m m (insoluble residues); carbonate content.

Marine Geol., 2 (1964) 198-235

L~

v

la

< 2 o/o

(3

O I

,

50 , , , l NAUTICAL

7 j° W

~3

I

I

t

~ : = MILES

G

"L.

CONTENT

I I

w

o,o-2o O/ol I I e > 2o o/o II111

.5,o0/.

o 2-5%

*

Fig.7C Legend see p212

C

N

7o ° ;

CARBONATE

I

:

I

1OO l

:::

I.

65 °

%

? E N ~N S U LA

a~sP~

0

I Q

?

i":J"

......,:..........

".... -.. ~,.~.~.~

, .. ,., .., . ~'.'" r', r.., / "~L r -~__.,._,"~o..1 >,.- :::. I'.~::,~---.L_L / "1 | "i" I

~....--.

60 °

60 °

50

'""

"":

t ~ ::

I

I'

,

.....

.f~3

.2:.

l

A"

:""

50

46 t

48 ~

N

preventing the accumulation of fine grained materials in substantial quantities. Th rough bottom topography of the nearshore topographic highs is certainly indicativ of erosional conditions; the coarse grained deposits covering these areas are considere mainly as local Pleistocene glacial drift, being reworked since the Pleistocene glacie~ wasted away and sea-level gradually reached its present height. Evidence of th occurrence of reworked glacial drift material as a thin top layer was very probabl met at station $62-55, where underneath a sandy, loose, indistinctly layered depos: (thickness approximately 10 cm) a rather stiff light gray pelite with till characteristic was found. Supply of recent ice-rafted coarse detritus will result in an admixture c "foreign components", in these presently being reworked glacial deposits (see unde "Size frequency distributions"). The occurrence of glacial till material in the deepe parts of the trough has been mentioned earlier in this report (cf. p.205). At stations $62-50, 54, 72 and 73 silty pelites have been sampled. The last tw, stations are both located on steep open slopes and their location makes it very likel that the winnowing effect of turbulence caused by wave action prevents a substantia accumulation of particles of fine silt and clay size. On the other hand, the sample from $62-50 and 54 were recovered from small protected basins where unhindereq accumulation of the supplied suspended matter could be expected. The silty characte of these sediments is more likely explained by the assumption that accumulatioJ has taken place under the influence of continuous or nearly continuous sluggisl currents able to prevent accumulation of fine silt and clay size material in substantia quantities. Such an assumption is more plausible than the supposition that it wa caused by a winnowing effect of wave action. So far, the sediment descriptions have been concerned only with the deposit from the submarine trough and the adjacent area. Most of the core and grab samples from the area between Quebec city, and thq mouth of the Saguenay River have been obtained using a small motorboat. Thq sediments from this area contrast markedly with those found farther downstream, i~ or near the submarine trough. The most striking differences concern compaction, sizq frequency distribution, and colour. Throughout the whole area a homogeneous stir light olive gray (5 Y 6/1) heavy pelite was found to be the characteristic deposit. Thq stiffness (water content about 4 0 ~ by weight) and the very high clay content (usuall, 80-90~ of the material is smaUer than 2 ~t) are very conspicuous. The differences iF compaction and also in size frequency distribution (see under "Size frequency distri butions") indicate that these pelites are not recent deposits but residual from forme~ conditions. At some places the stiff light olive gray pelites were covered by a layer o sand or gravel, at a few other places only sand or gravel material was obtained b~ the Van Veen grab. The contact between top and bottom layer was always found tc be very sharp. Secchi disc measurements, which are plotted in Fig.8, show that th~ maximum turbidity occurs in the river upstream from the mouth of the Saguenay. A the same time this is also the area where fresh and saline waters are mixing (Dr R. W. Trites, personal communication, 1963) and where floccules of rather exceptiona sizes were observed. Marine Geol., 2 (1964) 198-23'

70 ° W

)

l

85 °

1

I

I

I

60 °

I

l

C

l

.; .50 =

'

N

P'////M 5-10 m"x ~ III]111110-15 m_ \~ V//]>

15rn~, 48 °

04~

PEI 46 °

70 ° W

65 °

6TO°

Fig.8. Transparency of the water (m), according to Secchi disc readings. P.E.I. = Prince Edward Island; M. Is. = Magdalen Islands; N. F. = Newfoundland. The sediment characteristics together with the very low transparency of the water (Secchi disc measurements gave transparencies as small as 50 cm) and the topographical features as revealed by a portable echosounder, distinctly point to erosional conditions for the larger part of the area under consideration. For further comment on processes of erosion and sedimentation the reader may refer to the next paragraph. Size frequency distributions The analyses for the particle size distribution were carried out by the normal combined pipette-sieve method, developed and standarized for sedimentological and pedological investigations in The Netherlands. The samples were treated with 10~o H20~ on a steambath and with 0.2 N HC1 at room temperature in order to remove organic matter and carbonates. A solution of sodium oxalate and sodium carbonate was used as a dispersing agent. The results of the analyses have been illustrated as cumulative curves on arithmetric probability paper as used by DOEGLAS(1946) for his extensive studies on the relationship between size frequency distribution and environment of deposition. The same system for representation was used in the studies of the sediments of the Rh6ne delta (KRuIT, 1955) and of the Orinoco shelf area (VAN ANDEL and POSTMA, 1954; KOLDEWUN, 1958; NOTA, 1958). Comparison of the cumulative curves of the sediments from the St. Lawrence valley showed that three main groups of size frequency distributions can be distinguished; their classification is based on the shapes o f the curves. One type of sand distributions (type I) and two types of (sandy) pelite distributions (type II and type Marine Geol., 2 (1964) 198-235

0.3

0.4 r n m

99.6

I

1 2 3 95 - - ~

O/o

S-62-66 S-56~28 S-62-42 S-56-96

0.2

0

0,1

Oj

TYPE I

95

5 S- 62-25 6 7

75-

S- 6 2 - 3 6 S- 6 2 - 5 2

~7,5 • ,5(

50 [ - - -

i2.,

25~

==•............ 0,3

0,4 m m

0.4 m m

9

7

0,3

S- 62-25 2 S-62-69

oh

-

0.2

i .

.

i

_t~ 0.2

-

-

0.1

5-62-70

[

0.3

.

~5

.

. . 0,1

.

.

i ]

.

~o, 0

0.1 m m

S-62-1F S-62-1C S-56-56E S-62-3E S-62-2A S-62-2 Y

TYPE m

L

0.4 m m

.

I 2 2 4 5 6

TYPE,]]

S-56-30 S=56-15 S-62-28 S-56-7 S-62-57

.

.

!

3 4 5 6 7 8

.

0.2

0.1

0.1 mrn

5

Fig.9. Size frequency distribution types of surface sediments of the Gulf and River of St. Lawrence.

111) were established. Representative examples of each group are given in Fig.~ The study of size frequency distributions of numerous samples from variot environments indicates that usually a simple sediment has been formed by a sing] process under uniform conditions. Thin section studies of sandy pelites show th~ they are laminated and consist of laminae of sand an pelite (DOEGLAS, 1960). Sinc the sampling technique does not permit the collection of the simple units, mechanic~ analysis are carried out mostly on mixtures. The curves which have been classified as type [ represent samples from tt Marine Geol., 2 (1964) 198-2.:

DEPOSITIONAL CONDITIONS IN THE ST. LAWRENCE REGION

217

nearshore areas in relatively shallow water depths. Most of the curves from type I cover a rather wide range of size grades and therefore stand for deposits not very well sorted. However, at closer examination at least some of the curves show a tendency to a better sorting: a curvature to the right at the coarse end can be discerned in the size range somewhere between about 60 and 300 ~z in samples 28, 36, 42, 66 and 96. This means that the coarse tail above approximately 300 ~z does not belong to the same size distribution. The curves which have been classified as type II represent samples from the deep water pelites. These pelites contain up to 6 0 ~ of clay and usually some 3 5 ~ of silt. The sand part of these mixtures forms an almost horizontal straight line and thus represents a poorly sorted distribution. The sandy petites from type II are composite sediments and mixtures of two simple sedimentary components viz. a petite supplied in suspension and a poorly sorted sand transported independently from the pelite. The curves from type III are petite distributions. They represent samples from the stiff light gray (5 Y 6/1) petite, found in the generally shallow water area between Quebec city and the mouth of the Saguenay. The size frequency distributions of type III are mainly characterized by the very high clay content, with precentages between 75 and over 90. As was mentioned earlier, these petites are considered as not recent but deposited during an older cycle of sedimentation. Water movements in the area of investigation are governed by the outflow of river water and by the tidal currents. Currents caused by winds or waves and combined wave and current action can also have considerable influence on the depositional conditions in the basin. The influence of the above mentioned agents of transport will be at its maximum along the coastline in the shallow nearshore waters and in areas where a sudden change in water depth occurs (e.g., around topographic highs; near the mouth of the Saguenay River, where the St. Lawrence Trough ends abruptly). The maximum distance of transportation for particles of sand-size in bathyal dephts, however, is quite small for any of the mentioned agents. This means that sand transport by the above agents will be confined to the nearshore shallow waters and will not reach to the central deeper parts of the trough (NOTA, 1958, fig.27). The particles of fine silt and clay size are transported in suspension and carried over great distances before deposition, independently of the sands. There is no size limit to rafting by ice or organisms. Ice-rafting is considered to be a prominent factor in the area of investigation, because of the climatic conditions of the area. This mode of transportation can carry detrital material over considerable distances, although it will always result in haphazard distribution of unsorted material, mostly causing a minor coarse addition to fine sediments. On the basis of both the foregoing considerations and the distribution of surface sediments throughout the area of investigation it is assumed that (1) particles of sandsize are being transported to the central deep areas of the trough almost exclusively by ice-rafting, (2) the pelite component of the (composite) deep-water petites is being supplied in suspension and admixed with ice-rafted unsorted material, (3) the sandy sediments in the shallower coastal waters adjacent to the deep trough are mainly Marine GeoL, 2 (1964) 198-235

derived from more or less intensively reworked Pleistocene deposits, and (4) the pelit~ component of the shallow-water sandy deposits has been supplied recently. Hence the composite character of the curves of type I is caused by the mixing of three simpk sedimentary components• They are: (1) a pelite component: it represents the recen' supplied suspended matter; (2) a sand component in the size range between about 6( and 300 ~: its sorted character to the coarse end of the curve points to local reworkin~ under marine conditions of an originally unsorted material, most probably of glacia origin; (3) a minor coarse addition forming the tail of the size frequency distributior curves: it covers the material supplied by ice-rafting. The pelite components of the distribution types [[ and [I[ differ rather widely In Fig.10 the ratios between the percentages < 2 !z and 2-16 ~ are given, not onl 3

%2-16/z 59-

40

-

30

• . ...'~: •

°

.

2 ~ lllltlll

•

20 ¸ • ,.

..-

Zk

• .].

10

A

ZX Lx

/x

LX

~Xa~ x

o • ~"

,5, dx

0

I 10

30

I

I

50

I

I

70

l

I

I

90 %~2t~

Fig. 10. Showing the relation between percentages < 2 ~z and 2-16 ~z in samples from the Gulf and River of St. Lawrence• Group 1 refers to recent supplied pelites, group 2 refers to late-glacial pelite., (see text). The mechanical analysis excluded carbonates and organic matter.

for the distribution types I1 and III, but also for those samples of type I, which contai~ more than 10~ of particles < 2 ~t. The various pelites (or pelite components) fall into two groups. The majority of the samples (indicated by dots) show approximately constant ratios for widely diverging percentages < 2 ~t. The dots represent the results of analyses from samples throughout the area between the mouth of the Saguena~ River and the Cabot Strait, from the central-deep as well as from the nearshoreshallow areas• The second group (indicated by small triangles) refers to samples from the stiff light gray pelite, recovered in the area between Quebec city and the mouth of the Saguenay. The almost constant granulometrical composition of the material < 16 ~t for the majority of the pelite deposits (group 1) can only be explained by assuming that Marine Geol., 2 (1964) 198-235

DEPOSITIONAL CONDITIONS IN THE ST. LAWRENCE REGION

219

the suspended matter has a homogeneous composition before it is deposited. Several authors (DOEGLAS, 1946; FAVEJEE, 1951; ZUUR, 1951; WIGGERS, 1955; ZONNEVELD, 1960; VAN STRAATEN, 1963) have discussed the constant ratios between the subfractions of the suspended material for Dutch marine deposits (mostly formed in tidal fiat environments). Doeglas suggests that in the sea the suspended material of various sources remains for a long time in suspension and is thouroughly mixed, thus obtaining a great homogenity. Favejee ascertained that for the Dutch tidal fiat deposits the constant granulometrical composition goes together with a constant mineralogical position. Such a homogenity can only be expected when (1) the suspended material is thouroughly mixed and (2) no sorting takes place during transportation. The second condition will be more easily fulfilled when the particles have formed small aggregates (floccules), since sorting will not affect the particles which have coagulated in the aggregates (the formation of floccules can be safely assumed since salinities as high as 29 ~o have been measured far upstream at station $56-64). This does not necessarily mean that all floccules have the same constant granulometrical composition as is postulated by some of the above authors. Here it is suggested that (a) due to intense water movements the suspended fine material remains for a long time in suspension, (b) that in this manner all floccules get thouroughly mixed and (c) thus an average (at random) composition of the fine suspended material will have been obtained when it is finally deposited. The strong tidal currents in the Gulf and River in combination with the great depth of the St. Lawrence Trough create favourable conditions to mix thouroughly all suspended material that gets into it. Along these lines it can probably be explained that a fixed granulometrical composition of the material < 16 bt has been found in sediments with widely diverging percentages <2~. It is worthwhile to mention that in such open sea deposits as off the Orinoco River (NoTA, 1958, fig.27) and offthe Rh6ne delta (VAN STRAATEN,1959) the material 16 ~t has not a fixed granulometrical composition at all. In those sediments a distinct relation was found between the granulometrical composition of the material 16 bt and the distance to the coast, i.e., the further away from the coast, the finer the material which was found. VAN STRAATEN(1963) paid attention to these different environmental conditions and supposed that the concentration of suspended material and the mineralogical composition of the clay may play an important part. To the present authors it seems probably that in such cases, due to less intense water movements, smaller depth of the water column and higher rate of deposition the suspended material has no opportunity to get thouroughly mixed. The pelites from the second group (Fig. 10) have no constant ratios and moreover show rather exceptionally high contents of the grade < 2 u. Such distributions can be found in cases as off the Orinoco delta (see above) but can also be expected when the water is practically free of electrolytes and hence the suspended material is very well peptized. Sorting can then affect the finest size grades. The finest fractions can thus long remain in suspension and finally settle in stagnant bodies of water, viz. in lakes and flood plain basins of rivers.

Marine Geol., 2 (1964) 198-235

The postglacial history of glaciated lands has been found very complex becau of the interference of sea-level changes, retreat of the ice-sheet and uplift of t] whole area. In Baltoscandia an alternation of several lake stages and marine stag was discerned. A similar complexity of the postglacial history seems highly probab for the entire region of the Gulf and River of St. Lawrence. The study of the PD records (Fig.5) has shown that the soft sedimentary top layer, which forms the la sediment addition, generaUy is well defined by a strong subbottom reflection. Earti considerations have made it clear that the subsurface discontinuity most probab marks the boundary between the Pleistocene subbottom and the sediments whfi have accumulated since the last transgression. Generally the sounding records shc acoustically homogeneous sections of the soft sedimentary top layer, while only tl water-sediment interface and the above mentioned discontinuity are recorded. some cases (for example section $56 112-116), however, two additional reflectio which parallel the sea floor are recorded from layers within the overburden. Suq acoustic profiles mark an alternation of different stages of deposition and usually environmental conditions. Hence, it might well be possible that they are related different stages of postglacial deposition. The available information does not pern any more definite conclusion. Additional use of bottom penetrating acoustic reflecti, equipment and coring together with a regional study of raised beaches will help reveal the postglacial history. As has been mentioned earlier, the stiff light olive gray (5 Y 6/I) heavy petit are considered as being not recently deposited but residual from former conditior The light gray colour of the pelites makes it highly improbable that they have be, accumulated during a marine stage; non-organic marine pelites are usually dark gray in colour, because of their sulfide content. Firm light gray pelites, extreme fine-grained and hence comparable with the 5 Y 6/1 coloured pelites under disoussio have been reported to occur over wide areas in the Baltic Sea. GRIPENBERG(193 concluded that those pelites have accumulated in an ice-lake (the Baltic iee-lak during retreat of the ice-sheet in late-glacial time. This conclusion is strengtitened 1 the fact that the low amount of electrolytes in the melt water of ice will have favour aoeumulation of very well sorted pelites. Accordingly, it is tentatively assumed th the light olive gray pelites of the area between Quebec city and the Saguenay ha accumulated in late-glacial or Early Recent time during a lake stage, possibly in ice-dammed lake, rather than under marine conditions.

MINERALOGY (N.)

Sediments are not only the product of transport and environment of deposition, b also of provenance. Consequently, a short survey of the mineralogical compositfi of the sediments was carried out. The mineralogical composition of the sediments a depositional basin will be largely determined by the nature of the rocks in t source areas. However, the composition is also a function of weathering of unstat Marine Geol., 2 (1964) 198-~

tJi

~

2

2

2

2

1

1 1 1

1

17 16 25 10 6 17 10 17 6 16 11 20

3 3 2 3 3 3 3 1 1 1 1 4

7 2 3 3

2 2 2 1 3 5

44 46 35 48 56 49 58 53 52 48 50 48

1 Not including hypersthene. 2 The percentage ofalbite usually is less than 6%.

$56-7 $56-23 $62-25 $62-37 $62-52 $62-63 $56-35 $62-66 ~ 62-72 $56-108 ~" $56-93 ~ $56-56E

Heavy minerals

11 12 11 16 7 6 9 8 11 15 12 8

12 16 13 16 17 10 8 13 12 13 15 10 1 2

4 2 3

2

4 1

1

2

1 2

1

2 1

1

1 1 2 3

1 3 9 3 2 2 3 3 7 2 3 1 2

1 1 2

4 1

HEAVY AND LIGHT MINERAL ASSEMBLAGES OF GULF AND RIVER OF ST. LAWRENCE, SIZE GRADE 50--500

TABLE I

0.08-0.22 0.09-0.25 0.12-0.32 0.09-0.32 0.0~0.20 0.08-0.30 0.08-0.35 0.15-0.35 0.08-0.20 0.09-0.24 0.08-0.32 0.08-0.32

2.6 9.1 2.5 10.5 10.1 11.9 14.7 11.5 5.7 11.1 7.8 12.8

48 31 70 30 32 27 28 30 28 28 24 38

18 17 7 11 16 15 13 21 17 18 22 16

Light minerals

23 43 12 44 51 52 53 47 41 47 49 35

11 6 11 14 3 6 5 2 14 6 3 7

1 2 4

1

1

3

t,d bd

o z

e

r~ ¢3

.q

minerals (in the source areas, during transport, or after deposition) and of selectiv sorting during transport (according to size or density), both factors which ca modify the composition between source rocks and depositional site. In this report the mineralogy of the sediments has been based mainly on min~ ralogical analysis of the sands. As usual in sedimentary petrological research th mineralogical analysis has been carried out after separation into a light and a heav fraction. Heavy mineral analysis was used as the main tool to characterize the miner~ associations. Light fraction analysis was carried out only on a few selected sample., The light minerals were identified by a combined method of staining (modified b Favejee) and the use of immersion liquids (NoTA and BAKKER, 1960). The method c heavy mineral analysis applied has been described in detail in various publication (DOEGLAS, 1950; VAN ANDEL, 1950; NOTA, 1958). However, to prevent destructio of minerals like apatite, biotite, and olivine, the samples were not boiled in concer trated HC1 and HNOz, but only treated with Na2S204. Of each slide about 15 transparent grains were indentified and their frequencies were given as a percenta~ of the whole. The analyses exclude the opaque minerals. The fraction used for th heavy and light mineral analysis ranges from 0.5-0.05 ram. Since gravels, sands an pelites generally will be transported quite independently, the conclusions on th sources of the sand fraction will not necessarily apply to those of the gravels an pelites. Most of the samples contain heavy minerals in sufficient quantities to carry ot a normal counting. There is no seaward limit of heavy mineral occurrence and eve the deep-water pelites yield sufficient heavy minerals for analysis. This is in contra~ to the seaward boundary for the occurrence of heavy minerals which Van And~ (VAN ANDEL and POSTMA, 1954) found in the area of fine grained pelites in the cent~ of the Gulf of Paria. One reason for the lack of such a boundary in the St. Lawren¢ region is the prominent factor of ice-rafting. The other reason is that in the majorit of the samples the quantity of heavy minerals is high; in many cases it amounts t 105o of the insoluble residue (of the material coarser than 50 ~). This high ratio c heavy to light minerals has to be considered as a source characteristic. Inspection of Table I and Fig. 11 shows that the heavy mineral suite of the Gu and River sediments is characterized by the abundance of hornblendes, pyroxen~ and garnets. Hornblendes and pyroxenes usually make up at least 60)~ of the tran~ parent heavy minerals. Epidote and titanite are currently present, though in mine quantities only, while apatite, biotite and olivine form minor constituents in a numbt of the samples. Such minerals as tourmaline, zircon and the members of the met~ morphic group (staurolite, kyanite, andalusite, sillimanite and chloritoid) are preset only in very subordinate quantities or are completely lacking. The predominan¢ of minerals like hornblende and pyroxene, which are generally considered as minera of low stability, indicates that the heavy mineral suite of the Gulf and River sedimen~ reflects a first-cycle deposit. Consequently it is highly improbable that selecti~ weathering of unstable minerals has modified the mineral composition between sour~ rocks and depositional site to any appreciable extent. The markedly fresh appearan~ Marine GeoL, 2 (1964) 198 25

La

f

~D

I-.)

-

F

,

J

(

i

i

I

5o

I

l

I

I

I 70 ° W

,

I I

o }

NAUTICAL MILES

~

I

! I

~

/

j

L

.-'.-"

_/.'

I

I

I ~

I Q

I

85 °

U

I

E

I

B

1

E

I

C

.

~

I

4 v

•~

~

--

/ . ~• ,...~-' '

6,.

I

-'')

-

/

4 --1[:

~

/2

A

~

'-.

I "~""~

.~

I,

,

""

~"

"

~

,' .......

" ~ ' ~

", "<

r

/-~

' --

I~l

--#

I ,//'"

,

~I BO °

_ /

Ijl

,

I

'1

",, "'-, ", ', "~._ ",

,

"--.'-,,,o ;

-I-48

I °

,,_'_SOo ..

f-z_

/

..

'-'4N.y..I

f

z 4 a /

',, I /"

;

,

,:

,' "

. : - " " "' " . ~ / J" , I' " •

'-,,',%

If

BO°

, " P "~-" ' ., ' .~

",

/ .~ I / _(o" .~,o~ /~g~" ~

#* M. Is

"'M~3

-'--" ~ ' - . "'-:::::---, .

_~/

"----

~°o

-,oo.._. ",, ,~-,'-, _

&"."h~'k.~

I~

%

n

.]x

~q

I ~I ~i 65 °

'C/.(

14//..

~

"~"

~

"~%mm~4~;l~,l]-'--'-" ..........

.~2oo'-."2 ~ ' ~"" . .

Z" ~'~__

"v~'l., ,

/

v"

V

__,,,_

.

.

_ ,. ,, , .

c./k S P E

im..--.~ii

-. .

~ " -.... -~. ~'~-.~4,: Z : . . . B ~ Z ~. .C. . .I. - , ••. ~ " , ~", ml]~]~[3 ~ , - " C ~._ ,~, ,,L,, ,,. . . . . . . . . f ~ ] . ~ "--"~ [ ~ ~ ' ~ ' ~ . Z "~ loo... "~%". (, ~ .I~M,. . ~" " - \ ,-, . . . ., ,. l.i.l ~", ,.' . ~. ] . . ."-.

"-';>'~

-

lOO

,.//

"." ...

J

t" ~

I

ST. L A W R E N C E

MINERALS

//

m - ~ / . "' ~~ ~

"

~

[[~][]O T H E R

HYPERSTHENE

I

Fig.ll. Variations in heavy mineral composition of surface samples. Hatched strip diagrams give mutual percentages of components concerned. Components which make up less than 4% of the heavy fraction are included in the group "other minerals". P.E.I. = Prince Edward Island; M. Is. = Magdalen Islands; N.F. = Newfoundland.

"

GARNET

EPIDOTE ~ AMPHIBOLE mm p YR o XENE

~

hUEBEC J _

48 °

N

_ ==,,~ v

I

70 ° W

G U L F and RIVER

I

of the mineral grains, the nearly total absence of altered material and the extremel low percentage of stable minerals like tourmaline, zircon and rutile support thJ assumption. Hence it can be expected that the heavy mineral composition will closel reflect the provenance of the material. The source of the heavy mineral assemblag established must be sought in a terrain with acid and basic rocks. It thus is apparer that the heavy mineral assemblage has been derived essentially from the Canadia Shield and hardly bears on the northern Appalachians which border the valley on th south side. The almost uniform character of the heavy mineral composition throughou the entire region of the Gulf and River of St. Lawrence (Fig.11) is most striking, l emphasizes that the sediments are a product of a vast source area delivering a mor or less homogeneous heavy mineral suite which has hardly been effeeted by seleetiv sorting during transport. Previous discussions have shown that the samples analyse, represent material either of more or less reworked glacial drift (viz. the nearshor shallow water deposits) or of the unsorted coarse addition (introduced by iee-raftin8 of the pelite deposits. This means that glacial activity under Pleistocene as well a under present conditions must be considered as one major cause of the uniformit of the heavy mineral assemblage throughout the area: viz. (1) extensive Pleistocen glaciation by which glacial drift of a homogeneous distributive province was widel distributed and (2) recent ice-rafting by which material along the coastlines is pickeq up, and spread over the entire region. A glance at Table I shows that differences exist in the ratios of light to hear minerals. In most samples the amount of the heavy fraction is high, and this is consi dered to be a source characteristic. The associated suite of light minerals is preponde rantly plagioelase--an average of 41 ~ compared to 3 4 ~ quartz and 16~ potasl feldspar. The lack of lithic fragments and the abundant feldspar would suggest tha this is an arkose, but the potash feldspar is too low. Rather it has the high plagioclas content one would expect to be derived from the predominant granodiorite of th Canadian Shield. It definitely is a first-cycle product, resulted from the non-chemica erosion of a complex crystalline igneous terrain and it thus forms a unity with th heavy mineral suite. The percentage of heavy fraction for samples $56-7 and $62-25 is well belo~ the average for the sediments of the St. Lawrence region. The associated light fractioJ differs clearly in that it has much higher quartz/feldspar ratios. Several possibilitie have to be considered to explain these anomalies in the mineral composition. On, possibility is that the mineral assemblage has been derived from a source in the imme diate vicinity. Nolan's study of the heavy minerals of the beach sands of Now Scotia (NOLAN,1963) established the presence of an assemblage with mainly garnet epidote, hornblende and saussurite for the northeastern shore of Cape Breton Augite was reported in two samples only (11%), while hypersthene appeared to b, lacking. The analyses of two samples along the northwestern shore of Cape BretoJ showed the predominance of altered grains and 4-8 o / o f augite. Thus the availabl, data seem to indicate that the heavy mineral suites of Cape Breton have no direc Marine Geol., 2 (1964) 198-23

DEPOSITIONAL CONDITIONS IN THE ST. LAWRENCE REGION

225

bearing upon those of the Cabot Strait Trough. The Magdalen Islands, which lie to the northwest of Cape Breton are known to contain volcanic rocks. The assumption that these present islands were not glaciated during Pleistocene time, at least not during the Wisconsin (PREST, 1957), reduces the possibility that they have been a potential source of the pyroxenes. Another possibility to explain the anomalous mineral compositions of $56-7 and $62-25 is to assume a complex origin for these sediments. Since different sources may possess great differences in the ratios of light to heavy minerals, it can occur that the heavy mineral composition of the compound sediment is almost completely defined by the assemblage of the one with the high percentage of heavy minerals. In such cases the compound character may appear only from differences in the light mineral suite. The notable change in the light fraction suite could be explained by assuming a contribution of multi-cycle material from the extensive sedimentary rocks in the vicinity, to the first-cycle products, derived mainly from the Canadian Shield complex. It should ne noted that the light fraction of $59-9 is quite similar to the assemblage of $56-7. The anomalous high epidote percentage of the heavy fraction might be explained by a contribution of local material, but no data from the adjoining coastel area are available. In shorL the mineralogical reconnaissance has revealed (1) that the crystallines of the Canadian Shield are the principal sediment sources; (2) that the fresh appearance of the mineral grains, the high percentage of heavy fraction and the abundance of minerals of low stability throughout the area indicate that modification of the composition of the sands through transport or chemical weathering seems to be of little significance. In addition it should be noted that X-ray analysis of the clay fraction has revealed the presence of minerals such as plagioclase feldspar (mainly oligoclase), amphibole and chlorite next to kaolinite, illite, montmorillonite and quartz (Dr. J. Ch. L. Favejee, personal communication, 1964). Pleistocene glaciation and present climatic conditions have a direct bearing upon these depositional characteristics.

GEOCHEMISTRY (L.)

This section will consider the main implications of the chemical characteristics of the sediments occurring between the lower part of the river (section $56-111-107) and eastwards towards Anticosti Island (section $62-51-43; cf. Fig. 1). The purpose of this particular study is to relate major element distribution to the component minerals or mineral with which they are associated. Inferences drawn from the major element distribution can also be related to the physical conditions of sedimentation and the extent of the chemical modification of the sediments (NIcHOLLSand LORING, 1962). The discussions are based on the quantitative chemical (rapid silicate analysis, RILEY, 1958) analysis of some 50 samples for the major element oxides of Si, A1, Na, K and Ca. Samples used for chemical analysis were washed with distilled water Marine Geol., 2 (1964) 198-235

to remove soluble sea salt following the method used by EL WAKEEL and Rn.E (1961). The distribution of many of the major elements (A1, Fe, Na, K, Mg and Ti in sediments, developped by normal sedimentary processes, is usually determined b their varying clay mineral content (HmsT, 1962) and to a lesser extent by the mor important aluminium bearing minerals such as the feldspars and micas. Such is th case where the primary aluminosilicates of the source material have been weathere, to form clay minerals richer in Al and other elements than the original silicates Material however, derived under arctic and sub-arctic climatic conditions, unde which mechanical action attains its maximum and chemical decomposition is at minimum, hinders the development of secondary aluminosilicates and allows primar I silicates to escape chemical modification and be deposited in even the finest siz, fractions (see p.225). As a result secondary chemical enrichment of the detrita material is at a minimum and the chemical composition is controlled by its mineralog: to a greater extent than by the physical conditions of sedimentation. Silicon

The silicon contents of the river and gulf sediments vary between 23.13 and 34.03 (average value 27.81). The regional distribution pattern of this element (Fig.12 shows: (1) SiO~ contents decreasing in value away from the shorelines of the rive~ and estuary towards the central submarine trough; (2) a slight but distinct decreas~ 68 ° W

67 °

I

J

J

~

_ ~

~'-

~

66 °

65 °

I

r,

-

•2 9 . 3 2

"2"~57~-;

~•2Z79

.25.1o

i

~-~

3o.5s

~

6~

1

50 ° N

~/~55c_~

~

P~t

" ~ ' ,s

.30.30 ~2~ 79

~

~ ,23, 2

•

" Oo

,5

z.S °

P ,

•

6~5o

6'8°W

Fig. 12. Regional distribution of silicon contents. A. Is. -- Anticosti Island.

Marine Geol., 2 (1964) 198-235

DEPOSITIONALCONDITIONSIN THE ST. LAWRENCEREGION

22 /

in the SiOz contents of the deep water pelites from the river into the gulf which continues in the sediments along the center of the submarine trough at least as far as the pelites occupying the trough between Anticosti Island and the Gasp6 Peninsula; (3) SiO~ values are high in the sediments occupying the banks or topographic highs west of Anticosti Island. Much, it not all, of the Si found in these sediments has been brought to the present site o f sedimentation either as detrital quartz or that structurally combined in the aluminosilicates. Silicon thus occurs in the following compounds in the river and gulf sediments: free quartz, feldspars, micas, chlorite, kaolinite and the minor amounts of other aluminosilicates. The distinct relationship between higher Si contents and the higher concentration of the sand size material (Fig.7) in the nearshore sediments, indicates the higher concentrations o f free quartz and undecomposed aluminosilicates in these sediments. The lower values of Si in the deep water pelites, especially those found in the central part of the submarine trough (stations $62-63, 64, 56 and 57) are due to the lower quartz contents and lower Si contents of the finer grained aluminosilicates. TABLE II COMPARISON OF THE ALUMIN1UM CONTENTS OF THE ST. LAWRENCE SEDIMENTS WITH OTHER ROCKS

Igneous rocks (CLARKEand WASmNGTON,1924) Grartodiorite (BARTH,1962) Average 52 terrigenous clays (CLARKE,1924) Average 6 greenish muds from the Gulf of Paria (HmsT, 1962) Average of 8 light fractions (size grade 50-500 Ft),St. Lawrence River Average of 3 up-river pelites, St. Lawrence River, stations: $56, 56B, 56E, 56I Average 9 deep-water pelites, St. Lawrence River, stations: $56-112-115, $56-110-108, $62-74-75 Average 14 deep-water pelites, St. Lawrence Gulf, stations: $62-67-71,62-64, 56-58, 44-46 Average 7 shallow water sediments (< 200 m), stations: $62-61,59, 72, 73, 43, $56-107, 116 Average 2 bank sediments (north shore), stations: $62-53,54 Average 2 bank sediments (Bane Parent), stations: $62-49,47

.4t %

si/m

8.13 8.29 9.10 8.79 7.68 8.92

3.4 3.8 3.1 4.3 2.7

7.72

3.6

7.75

3.5

7.52 7.63 6.97

3.9 3.7 4.3

Aluminium

On a regional basis, AI contents vary between 6.49 and 8.13 ~o (average value 7.63 ~). The distribution of aluminium is almost uniform throughout the river and gulf sediments and shows little differentiation in respect to sediment types or geographical locations although there is a slight tendency for the values to be higher in the deep water pelites o f the river, and somewhat lower on the bank (Bane Parent) west of Anticosti Island (Fig. 13). Table II compares the average A1 contents of the different sediments found in the St. Lawrence river and gulf with the average A1 figures of other rocks. The AI Marine GeoL, 2 (1964) 198-235

68° W

67 °

I

66 °

I

:

55°

r

fi4e

[/

/

i

\\

%.

50 N

~b •"Z51

~

P~rent

t,7,Gt

%

"'~.~

N.~ \_~. •

.8.07 .ZSf ~771

G

A

l'9c

50 */o < 0 . 0 0 2 rnm --Al--

f ~ y

?

io

~o

30

•oo%[ 'J:

Fig.l 3. Regional disttibution of alumirdumcontents. A. Is. = Anticosti Island. contents generally are lower than those normally recorded for argillaceous rocks, although the contents of the up-river pelites are comparable with the data quoted by CLARKE (1924). In view of the fresh state of most of the aluminosilicates in these sediments (see under "Mineralogy") it follows that the lower aluminium contents of these sediments when compared to other argillaceous sediments (Table II) reflect the lack of intensive chemical weathering of the source material. The almost uniform distribution of this element irrespective of the grain size of the material indicates the consistency of the aluminosilicates in the sediments. Thus, the distribution of A1 in these sediments is not directly controlled by size fractions, as in the normal case, but rather by the mineralogical nature of the bulk sample. This view is supported by two chemical analyses of the coarse fractions of two of the samples from different geographical positions in the area (stations $62-52 and 76; Fig. 1) which indicates that A1 is equally divided between the coarse ( > 0.125 mm) and the pelite fraction. In the former, feldspars account for the main source of A1 whilst in the latter phyllosilicates are in greater quantities than the feldspars. The variation of the Si/A1 ratios over the region reflect the relationship between quartz and the aluminosilicates. The inshore sediments are characterized by higher Si/A1 ratios (Table II) than those of the pelites. These differences reflect, no doubt, the enrichment of the coarse grained inshore sediment in detrital quartz whilst the finer material of the river and gulf contain less quartz, and aluminosilicates of lower Si/A1 ratios. Marine Geol., 2 (1964) 198-235

ZZ~

DEPOSITIONAL CONDITIONSIN THE ST. LAWRENCEREGION TABLE IlI

COMPARISON OF NA, K~ NA/K~ NA/AL AND K/AL IN THE ST. LAWRENCE SEDIMENTS WITH VALUES DERIVED BY VARIOUS WORKERS FOR OTHER ROCKS

Igneous rocks (RANKAMA and SAHAMA,

1950)

Granodiorite (BARTH,1962) Average 8 light fractions (size grade 50-500 tz), St. Lawrence River Argillaceous sediments (RANKAMAand SAHAMA,1950) Average 52 terrigenous muds (GOLDSCHMIDT,1954) Average 7 bay sediments (MooRE, 1963) Average 9 deep-water pelites, St. Lawrence River Average 10 deep-water pelites, St. Lawrence (upper part) Average 3 deep-water pelites, St. Lawrence (lower part); stations: $62, 56, 57 and 58 Average 7 shallow water sediments ( < 200 m) Average 2 bank sediments (north shore) Average 48 sediments of the River and Gulf

Na%

K%

Na/AI K]AI Na/K

2.38 2.85

2.59 2.55

0.34

0.31

1.09 1.12

2.89 0.97 0.97 1.96 2.08 2.16

2.24 2.70 1.87 2.41 2.53 2.29

0.38 -

0.29 -

-

-

0.30 0.27 0.28

0.35 0.33 0.30

1.29 0.36 0.42 0.88 0.82 0.94

1.70 2.19 2.11 2.12

2.24 2.61 1.94 2.38

0.22 0.29 0.28 0.28

0.29 0.35 0.25 0.31

0.76 0.85 1.08 0.89

Sodium and potassium The s o d i u m contents o f the sediments vary between 1.12 ~o a n d 2.89 ~ (average value 2.11 ~ ) whilst the p o t a s s i u m c o n t e n t s vary between 1.84 ~ a n d 3.15 ~o (average value 2.37 ~ ; Table III). The N a contents (Fig.14) o f the sediments tend to diminish with 68 ° W

67 °

I

1

t

66 °

65 °

I

r/

6Z,°

/

I

"2.~I

c, _50 ° N

.ZM

,5

-49°

/ ~

--Na-'

nat~tical

tiles

'

Fig. 14. Regional distribution of sodium contents. A. Is. = Anticosti Island.

Marine Geol., 2 (1964) 198-235

decreasing grain size, whilst K (Fig.15) exhibits no systematic distribution patten The Na/A1 ratios tend to remain relatively constant with change in the texture of tt sediments (Table [II). The sediments are also characterized by higher Na/K ratio (average value 0.89; Fig. 16) than is normally found in argillaceous sediments (ca. 0.4( RANKAMA and SAHAMA, 1950), but are comparable to the ratios found by Moor (1963) for feldspathic marine sediments in Buzzard's Bay. The average of 8 lig[ fractions (size grade 50-500 ~; cf. Table I) compares very well with the values fc granodiorite. The distribution of Na in sediments is usually controlled by ionic exchan~ reactions at the sediment-water interface, sodic feldspars, and in some cases sod micas (brammallite), whilst the geochemistry of K is controlled by ionic exchang reactions at the sediment-water interface, potash bearing micaceous minerals (mu~, covite, biotite, illite) and potash feldspars. From the mineralogical evidence (section "Mineralogy") it follows that Na i mainly located in the plagioclase feldspars of these sediments, although mino amounts are probably contributed by the ino- and phyllosilicates and perhaps b ionic exchange reactions at the sediment-water interface. Although the latter can b an important factor in the geochemistry of Na and K (NICHOLLSand LORING, 19601 the extent to which these reactions affect the behaviour of Na and K in these sediment cannot be evaluated because of the presence of detrital sodic and potash feldspar in the finest sediments. The decrease in soda content with decreasing grain size a well as a decrease in the Na/AI ratios indicates that plagioclase feldspar is concen trated in the coarser grained inshore and bank sediments, to a greater extent than il the finer grained sediments. Potassium in these sediments, however, is mainly locater in the potash feldspars and the mieaceous minerals. Its distribution and the constanc, of the K/AI ratios indioates that these mineral components are more or less evenl, distributed in the sediments. A similar relationship between K contents and the feld spar and clay content has been established by MOORE(1963). The variation of the Na/K ratios brings out the relationship between the plagio clase feldspars and the potash feldspars along with the micaceous minerals (Fig. 16) The decrease of Na/K ratios with decreasing grain size reflects the decrease in sodi~ feldspars away from the shore lines of the river and gulf as the K contents remair relatively constant throughout the gulf. Thus the presence of undecomposed aluminosilicates, especially the feldspars accounts for the high Na/K ratios and underlines the general immaturity of thes, sediments. Calcium In the river and gulf sediments the calcium contents vary between 1.55~ and 5.39~,, (average value 2.95%). Calcium probably can occur in four main positions in the river and gulf sediments: (1) as CaCO3 of limestone and shell detritus; (2) as calciurr phosphate; (3) in plagioclase feldspars; (4) in the phyllosilicates. Marine Geol., 2 (1964) 198-235

231

DEPOSITIONAL CONDITIONS IN THE ST. LAWRENCE REGION 68° W

I

67°

I

66°

I

~

I/

[~

l

50

4¢,

6~

65 °

I

•

19.5

°2.31

-z0~

- Z 1~

•

.50 °

,2.17

N

2,46

o2.26~......~2.32

s'k,.

6A cc :c::

;.:;:,:::~;~.~ so ~ < o o o 2 , . , . --K--

p / f

o,

10

20

neutral n~iles

,;ow

,:

Fig.15. Regional distribution of potassium contents. A. Is. = Anticosti Island.

68°

W

66°

67 °

I

t

J

~ £,.,1 . 2 9 ~

.

Ii

• 1.23 ,US

4<1

6~

65°

1

~

"t.04

, O.e9 .

.

.

.

.

.

.

.

.

.

50 ° N

.

0.70

U4.

~..-.~0.92--~._ G

50 *~

< o.oo2 ,~,,,

A

\.

0.73

s\

h9 °

-- Na/K-,~"

0

10

210

nadtica miles B~.o

Fig.16. Regional variations in Na/K ratios. A. Is. --- Anticosti Island. M a r i n e Geol., 2 0964) 198-235

(1) The significance of Ca as CaCO~ of limestone and shell detritus in th sediments has been discussed on p.211. (2) Calcium phosphate is considered to occur as organic compound or detrital apatite. The lithological data (section "Lithology") indicate that faec~ pellets are present and thus could account for the bulk of the phosphate in the sampJ although some apatite is present in small quantities. The amount of faeceal materi~ and apatite required to utilize the P (not reported in this paper), which varies frm 0.063%-0.308% (average value 0.11%) would not be large. In most sediments onl small proportions of Ca can be located in calcium phosphate. (3, 4) Calcium probably enters the river and gulf structurally combined in th plagioclase feldspars and phyllosilicates. Fig.17 shows the distribution pattern of C

68 ° W

67 °

66 °

65 c

6.

I • 2.98

"3.24

G 26

/

"

,

.2.5

)7.88

•

I

.1.89

G ,t,4

~> O

,:

,/¢,~:

/ I •

49

) _J

.

"

/

,~/ ~.~" .7.s

"'.~

7~ 7.96.1 ~ 5

30

~0.4 "

" 7.41 •

•

.09~.J y:/ --Ca--

618° W

~7 °

6'6 °

65 °

6L °

Fig. 17. Regional distribution of calcium contents (see tex0. A. Is. -- Anticosti Island.

after substraction of the amount required to fullfil the requirements of the CaC(3 in the sediments. It is clear that the higher detrital Ca contents are found in the in shore sediments and the values decrease with decreasing grain size of the material. As this pattern is similar to that of Na for which plagioclase feldspars are con sidered to be responsible for its distribution, non-carbonate Ca is most likely control led by the plagioclase feldspars found in these sediments (section "Mineralogy"; The lesser amounts found in the pelites reflect not only the decrease in the feldspar contents of the sediments but also Ca in the phyllosilicates. Marine Geol., 2 (1964) 198-23

D E P O S I T I O N A L C O N D I T I O N S IN T H E ST. L A W R E N C E R E G I O N

~a~

CONCLUSIONS (N.) The general conclusions of the sedimentological reconnaissance in the St. Lawrence River and Gulf may be summarized here. (1) Extensive Pleistocene glaciation largely determined the present shape of the St. Lawrence submarine trough; the location of the valley is tectonically controlled. (2) The sedimentology of the basin is closely related to Pleistocene glaciation and present sub-arctic climatic conditions. (3) The sediment distribution in the submarine trough was found to be fairly regular and characterized by poorly sorted coarse grained deposits nearshore and an extensive area of pelite bottom in the deeper parts. However, there is a distinction between protected basinal deposits (fine grained sediments) and those occurring on topographic highs (coarser grained sediments). (4) Erosional conditions predominate in the area between Quebec city and the mouth of the Saguenay. It is suggested that erosion of the stiff light olive gray (5 Y 6/1) pelites forms a substantial source for the pelites which presently are being deposited farther downstream. X-ray analysis of the clay fractions have shown a close resemblance in their mineral associations. However, a comparison of the ratios between the fractions < 2 ~z and < 16 ~ (Fig.10) shows a shortage of particles between 2--16 microns for the stiff 5 Y 6/1 coloured pelites. Extensive Pleistocene glaciation and present climatic conditions under which mechanical action still attains its maximum and chemical decomposition is at a minimum make it likely that sufficient quantities of that fraction will be supplied by the numerous smaller streams that empty into the basin. (5) Ice should be considered as a prominent factor of erosion, transportation and deposition of unsorted material. Its importance ts clearly demonstrated by the distribution pattern of carbonates around Anticosti and the unsorted coarse addition (up to over 25 ~ of the total sediment) to the deep water pelites. (6) The nearshore areas bordering the submarine trough are mainly characterized by reworking and redistribution of glacial drift while fresh coarse detritus is added by ice-rafting. Maximum deposition occurs in the central deeper parts of the trough. The maximum thickness measured for the soft sedimentary top layer, which forms the postglacial sediment addition, is 72 ft. When it is supposed that postglacial deposition began about 10,000 years ago, the maximum rate of accumulation is approximately 22 cm in 1,000 years. Since it is probable that the glaciers retreated later from the area, a higher postglacial rate of deposition can be expected. There is no evidence that in the central parts of the trough the slow particle by particle accumulation has been interrupted by catastrophic deposition of turbidity currents. (7) The mineralogy and the chemistry of the sediments have shown that they are mineralogically immature. The composition of the heavy fraction and the associated light fraction revealed that the crystallines of the Canadian Shield are the principal sources for the sands. Marine GeoL, 2 (1964) 198-235

ACKNOWLEDGEMENTS

The senior author is greatly indebted to Professor Dr. F. R. Hayes, Director Institut of Oceanography and Professor Dr. C. G. I. Friedlaender, Head of the Departmer of Geology, Dalhousie University, Halifax, N.S., Canada, for providing the facilitie of the Institute and for helpful advice. The authors express their sincere appreciation to Professor Dr. D. J. Doegla~ Professor Dr. Ph. H. Kuenen, Dr. J. Ch. L. Favejee, It. K. J. Hoeksema, Dr. H. B. Cooke and Dr. G. C. Milligan for stimulating interest and constructive comment on the manuscript. We are grateful to miss A. M. G. Bakker, Mr. A. T. J. Jonker and Mr. R. J Lahey who ably assisted in the laboratory investigations. We also are grateful to Mr. G. Buurman, Mr. Z. van Druuten and Mr. W. F Andriessen for their painstaking attention in the preparation of the illustrations. It is a pleasant duty to express our thanks to the officers and men of the researcl vessel C.N.A.V. "Sackville", who contributed so much to the results of the cruises.

REFERENCES

BARTH, T. F. W., 1962. Theoretical Petrology. Wiley, New York, N.Y., 415 pp. BOUMA, A. H. and NOTA, D. J. G., 1961. Detailed graphic logs of sedimentary formations. Intern Geol. Con,gr., 21st, Copenhagen, 1960, Rept. Session, Norden, pp. 52-74. CLARKE, F. W., 1924. The data of geochemistry. U.S., Geol. Surv., Bull., 770 : 841 pp. CLAkKE, F. W. and WASHINGTON, H. S., 1924. The composition of the earth's crust. U.S., Geol. Surv. Profess. Papers, 127 : I17 pp. DOEGLAS, D. J., 1940. The Importance of Heavy Mineral Analysis for Regional Sedimentary Petrology U.S. Natl. Res. Council, Washington, D.C., 22 pp. DOEGLAS, D, J., 1946. Interpretation of the results of mechanical analysis. J. Sediment. Petrol. 16 : 19-40. DOEGLAS, D. J., 1960, Sedimentological data for soil mineralogy. Trans. Intern. Congr. Soil Sci.. 7th, Madison, 1960, 4 : 534-547. EL WAKEEL, S. K. and RILEY, J. P., 1961. Chemical and mineralogical studies of deep sea sediments. Geochim. Cosmochim. Acta, 25 : 110-146. FAVEJEE, J. CH. L., 1951.The origin of the "Wadden" mud. Mededel. Landbouwhq?eschool Wageningen, 51 : 113-141. GOLDSCHMIDT, V. M., 1954. Geochemistry. Clarendon Press, Oxford, 730 pp. GRn'ENBERG, S., 1939. Sediments of the Baltic Sea. In: P. D. TRASK (Editor), Recent Marine Sediments. Am. Assoc. Petrol. Geologists, Tulsa, Okla., pp.298-321. HEEZEN, H. C. and DRAKE, C. L., 1964. Grand Banks slump. Bull. Am. Assoc. Petrol. Geologists, 48 (2) : 221-225. HEEZEN, H. C. and EWING, M., 1952. Turbidity currents and submaline slumps, and the 1929 Grand Banks earthquake. Am. J. Sci., 250 : 849-873. HIRST, D. M., 1962. The geochemistry of modern sediments from the Gulf of Paria. 1. The relationship between the mineralogy and distribution of major elements. Geochim. Cosmochim. Acta, 26 : 309-333. HOUGH, J. L., 1958. Geology of the Great Lakes. Univ. Illinois Press, Urbana, I11., 313 pp. JOHNSON, D. W., 1925. The New England-Acadian Shoreline. Wiley, New York, N.Y., 708 pp. KeLDEWlJN, B. W., 1958. Sediments of the Paria-Trinidad Shelf. Reports of the Orinoco Shelf Expedition. Mouton, the Hague, 3 : 109 pp.

Marine Geol., 2 (1964) 198-235

DEPOSITIONAL CONDITIONS IN THE ST. LAWERNCE REI_IION

,~.9.)

KRUIT, C., 1955. Sediments of the Rhfne delta. 1. Grain size and microfauna. Verhandel. Koninkl. Ned. Geol. Mijnbouwk. Genoot., Geol. Ser., 15 : 357-513. KtJEr~EN, PH. H., 1950. Marine Geology. Wiley, New York, N.Y., 551 pp. LAUZIER, L., TrIXES, R. W. and HACnEY, H. B., 1957. Some features of the surface layer of the Gulf of St. Lawrence. Report of the Atlantic Herring Investigation Committee. Bull., Fisheries Res. Board Can., 111 : 195-212. MCNEIL, D. J., 1956. The transverse trough of Cabot Strait. Trans. Roy. Soc. Can., Sect. Ill, 50 : 39-46. MOORE, J. R., 1963. Bottom sediment studies, Buzzarda Bay, Mass. J. Sediment. Petrol., 33 : 611-558. NICHOLLS, G. D. and LORIN6, D. H., 1960. Some chemical data on British Carboniferous sediments and their relationship to the clay mineralogy of these rocks. Clay Minerals Bull., 4 : 196-207. NICHOLLS, G. D. and LOmNC, D. H., 1962. The geochemistry of some British Carboniferous sediments. Geochim. Cosmochim. Acta, 26 : 181-223. NOLAN, F. J., 1963. Heavy Mineral Analysis of the Beach Sands of Nova Scotia, Canada. Thesis, Geology Department, Dalhousie University, Halifax, N.S., Canada, 126 pp, unpublished. NorA, D. J. G., 1958. Sediments of the Western Guiana shelf. Reports of the Orinoco shelf expedition, 2. Mededel. Landbouwhogeschool Wageningen, 58 : 98 pp. NOXA, D. J. G. and BAKKER, A. M. G., 1960. Identification of soil minerals using optical characteristics and specific gravity separation. MededeL Landbouwhogeschool Wageningen, 60 : 1-11. PETXIJOHN,F..I., 1957. Sedimentary Rocks. Harper, New York, N.Y., 718 pp. PRESS, F. and BECKMANN, W., 1954. Geophysical investigations in the emerged and submerged Atlantic Coastal Plain. Part VIII. Grand Banks and adjacent shelves. Bull. Geol. Soc. Am., 65 : 299-314. PRESX, V. K., 1957. Pleistocene geology and surficial deposits. Geology and Economic minerals of Canada. Economic geology, Ser. 1, 4 ed. Geol. Surv. Can., Ottawa, pp.462-468. RANKAMA,K. and SAHAMA,TH. G., 1950. Geochemistry. Univ. of Chicago Press, Chicago IlL, 912 pp. RILEY, J. P., 1958. The rapid analysis of silicate rocks'and minerals. Anal. Chim. Acta., 19 : 413-428. SHEPARD, F. P., 1931. St. Lawrence (Cabot Strait) submarine trough. Bull. Geol. Soc. Am., 42: 853-864. SHEPARD,F. P., 1931. Glacial troughs of the continental shelves. J. Geol., 39 : 345-360. SHEPARD,F. P., 1963. Submarine Geology. Harper and Row, New York, N.Y., 557 pp. TWENHOEEL,W. H., 1927. The geology of Anticosti Island. Geol. Surv. Can., Mere., 154. VAN ANDEL, TJ., 1950. Provenance, Transport and Deposition of Rhine Sediments. Thesis, State Agricultural University, Wageningen, 129 pp. VAN ANDEL, TJ. and POSTMA,H., 1954. Recent Sediments of the Gulf of Paria. Reports of the Orinoco Shelf Expedition. North-Holland, Amsterdam, 1 : 245 pp. VAN STRAATEN,L. M. J. U., 1959. Littoral and submarine morphology of the Rhone delta. Proc. Coastal Geograph. Conf., Louisiana State Univ., 2nd, pp. 233-264. VAN STRAATEN,L. M. J. U., 1963. Aspects of Holocene sedimentation in The Netherlands. Verhandek KoninkL Ned. Geol. Mi]nbouwk. Genoot., Geol. Ser., 21-1 : 149-172. WIGGERS,A. J., 1955. De Wording van het Noordoostpoldergebied. Thesis, University of Amsterdam, Amsterdam, 214 pp. ZONNEVELD, I. S., 1960. De Brabantse Biesbosch. Een studie van bodem en vegetatie van een zeewatergetijdendelta. MededeL Sticht. Bodemkartering, Bodemk. Studies, 4. A. Summary with text figures and tables, 220 pp. B. Nederlandse tekst, 396 pp. ZtJOR, A. J., 1936. Over de Bodemkundige Gesteldheid van de Wieringermeer. Landsdrukkerij, Den Haag, 113 pp. ZtJUR, A. J., 1951. Ontstaan en Aard van de Bodem van de Noordoostpolder. Van Zee tot Land, I. Tjeenk Willink, Zwolle, 19 pp.

Marine GeoL, 2 (1964) 198-235