Sedimentological and palynological evidence of regional climatic changes in the Campanian to Paleocene sediments of the Rocky Mountain Foothills, Canada

Sedimentary Geology, 59 (1988) 29-76 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

Sedimentological and palynological evidence of regional climatic changes in the Campanian to Paleocene sediments of the Rocky Mountain Foothills, Canada T. JERZYKIEWICZ and A.R. SWEET Geological Survey of Canada, 3303 - 33rd St. N. W., Calgary, Alta. T2L 2,47 (Canada) Received October 6, 1987; revised version accepted April 4, 1988

Abstract Jerzykiewicz, T. and Sweet, A.R., 1988. Sedimentological and palynological evidence of regional climatic changes in the Campanian to Paleocene sediments of the Rocky Mountain Foothills, Canada. Sediment. Geol., 59: 29-76. Evidence of paleoclimatic variations in the upper Campanian to lower Paleocene post-Wapiabi sequence of strata is visible both laterally between the central and southern Foothills, and vertically in the stratigraphic record. These differences are expressed by the distribution of climatically sensitive sediments, i.e. coal and caliche, and associated palynological assemblages within floodplain facies, as well as by changes in the style of fluvial channels. The interpretation of a semi-arid environment for mature caliche paleosols is supported by the impoverished character of the associated palynological assemblages, both in terms of diversity and the number of specimens recovered, and by the conspicuous presence of Classopollis. The lateral extent of the semiarid floodplain facies and associated broad and mobile channel deposits is limited to the southern part of the basin. No signs of a caliche facies have been found in the post-Wapiabi strata of the central Foothills. Instead, some of the floodplain deposits associated with meandering streams in this part of the basin contain numerous, thick, coal-bearing intervals. The relative climatic differences between the more humid central part and the drier southern part of the basin prevailed throughout the entire post-Wapiabi interval. As this cannot be satisfactorily explained by the position of the sea shore or by orographic influences alone, there was probably another external factor. This could have been the pattern of atmospheric circulation, such as that responsible for the present-day climatic differences existing between the southern and central Foothills. Semiarid floodplain facies occur at two levels in the stratigraphic column of the southern Foothills (in the late Campanian, Belly River Formation and in the upper Maastrichtian to lower Paleocene, Willow Creek Formation). They correspond to regressive episodes of the epicontinental seaway. Intervening between these semiarid floodplain facies are the marine shales of the Bearpaw Formation and, both overlying and underlying them, thin coal beds. These represent recurrent periods of swamp growth and peat accumulation in back-barrier environments (lagoon-fill and supratidal marsh respectively). Because of the proximity of these swamps to the sea shore it is difficult to assess the influence of climate on the relative humidity of these settings on strictly sedimentological grounds. However, the terrestrial components of the palynologicai assemblages recovered from these marginal-marine settings and correlative lacustrine sediments (containing fresh-water stromatolites but no coal) in the central Foothills are in sharp contrast with the impoverished assemblages known from the caliche facies. The former are prolific, diverse, and contain a number of triprojectate pollen species, which indicate a relatively humid climate during the latest Campanian time.

G.S.C. Contribution No. 28687. 0037-0738/88/$03.50

© 1988 Elsevier Science Publishers B.V.

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Introduction Investigation of the post-Wapiabi, continental strata in the southern and central Foothills of Alberta revealed very distinct facies differences. A major economic coal zone associated with floodplain facies in the central Foothills (Jerzykiewicz and McLean, 1980) is not present in the southern sections. Floodplain deposits in the southern Foothills are characterized by red beds and caliche facies (Jerzykiewicz and Sweet, 1986b). The scope of this paper is to demonstrate and explain these facies changes in terms of differences in climate that existed between central and southern Alberta in the Late Cretaceous and early Paleocene. It was also the intention of this study to provide the sedimentological and palynological evidence of climatic control upon sedimentation. It became apparent that the complex mosaic of facies in the post-Wapiabi sections of the Foothills (Lerand and Oliver, 1975; Rahmani and Schmidt, 1975; Jerzykiewicz and McLean, 1980; Lerand, 1982; Rosenthal and Walker, 1987) is not only the result of interplay between tectonism and sea-level changes (McLean and Jerzykiewicz, 1978) but is also due to changes in climate. Although caliche deposits may occur in the soil profiles of various climates, the development of mature and thick pedogenic limestone horizons, analogous to those described in this paper, requires semiarid conditions for at least hundreds of thousands of years (Gile et al., 1981). On the other hand, extensive seams of autochthonous coal, up to several metres thick, which occur within the floodplain deposits in the central part of the basin, indicate long lasting, fairly humid conditions for peat formation. The palynological studies enabled a stratigraphic correlation to be made of the almost entirely non-marine post-Wapiabi strata between the central and southern Foothills. In addition, information was obtained about the influence of the climate on the floral assemblages, namely, that the assemblages from the caliche facies are impoverished both in terms of diversity and the actual number of specimens recovered. Conversely, the coal-beating facies yielded prolific and diverse assemblages, including triprojectate and

allied pollen. Care was taken to distinguish more detailed differences imposed on the assemblages by different lithofacies. Although an extensive discussion of the Cretaceous/Tertiary boundary is beyond the scope of this paper, it should be mentioned that it occurs within the Foothills in two paleoclimatically different alluvial plain settings, i.e. humid and semiarid. These different settings affect both the lithofacies and the flora that are present within the Cretaceous/Tertiary boundary interval. Relative abundances of palynomorphs were based on counts of at least 200 specimens from unsieved residues. Only previously unfigured or infrequently figured specimens from the older parts of the section are shown. Figures of species associated with the late Maastrichtian and Paleocene are given in Jerzykiewicz and Sweet (1986a, b). In the explanation of the figured specimens the species name is followed by a Geological Survey of Canada (GSC) type number. This number can be used to access permanent records, which give the slide number and microscope coordinates for each specimen.

Stratigraphy Standard sections of the post-Wapiabi sequence of strata have been measured and studied in the southern and central Foothills (Fig. 1). The southern composite section is based on outcrops located along Crowsnest, Oldman and Castle Rivers, and the central composite section from outcrops along Blackstone River and in the Coalspur-Robb area (Fig. 2; Jerzykiewicz, 1985; Jerzykiewicz and Sweet, 1986b). The post-Wapiabi sequence of strata in the southern Foothills has been subdivided into five formations: Belly River, Bearpaw, St. Mary River, Willow Creek and Porcupine Hills (Hage, 1943; Wall and Rosene, 1977). Their stratigraphic correlatives in the central Foothills include three formations: Brazeau, Coalspur and Paskapoo (Jerzykiewicz, 1985; Fig. 2). This difference in stratigraphic nomenclature is due to important facies changes between the southern and central Foothills. For example, the marine Bearpaw shale, which facilitates the litho-

31 [ Grande i Prairie

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Fig. 1. Location of the study sections in the southern and central Foothills of Alberta.

stratigraphic subdivision of the southern section, is absent in the central Foothills. The coal beds in the southern Foothills are associated with these Campanian marine shales. Correlative coals are absent in the central Foothills. Conversely, in the central Foothills, numerous coal seams occur in the Maastrichtian and Paleocene. Correlative horizons in the southern Foothills are barren of coal (Fig. 2). Another essential difference in facies is the occurrence of caliche in the southern Foothills. It appears twice in the post-Wapiabi sequence; in the upper portion of the Belly River Formation and in the Willow Creek-Porcupine Hills interval

(Jerzykiewicz and Sweet, 1986b). In the central Foothills the caliche facies is absent (Fig. 2). Critical to this study was the establishment of five fines of correlation between the post-Wapiabi sequences in the southern and central Foothills (Fig. 2). These are based in part on palynological studies and in part on correlative horizons recognized through other lines of evidence as summarized below. The upper limit of the last regional marine transgression within the Foothills is taken as approximately the time line that provides the basis for correlating the lower part of the Belly River Formation of southern Alberta with the base of

32

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Fig. 2. Stratigraphic correlation of the post-Wapiabi strata in the southern and central Foothills of Alberta. Formation names and members (indicated by numbers) in the southern section adapted from Hage (1943), Douglas (1950) and Wall and Rosene (1977) with some modifications pertaining to the boundaries and age. Formation names and cyclothems in the central section adopted from Jerzykiewicz (1985). The bases for the lines of correlations shown in the figure are discussed in the text. Circled numbers indicate sections discussed in the text.

the Brazeau Formation in the central Foothills. The Campanian/Maastrichtian boundary is the second line of correlation shown in Fig. 2. The position of this time line is based on the presence of similar uppermost Campanian assemblages (for

selected species see Plate I, 11-19) in both the southern and central areas, linked to the first occurrences of Wodehouseia and associated lower Maastrichtian species (Plate II, 6, 7), The third line is based in part on lithostrati-

33 graphic correlations and in part on biostratigraphy. A laterally persistent tuff horizon, termed the Kneehills Tuff, occurs throughout the Plains of central Alberta (Irish and Havard, 1968) and at the top of the St. Mary River Formation in a section east of the Foothills (Tozer, 1953, 1956), overlying beds containing the Scollardia trapaformis Zone VI assemblage of Srivastava (1970). Index species (Plate II, 10-12) of this zonal assemblage are present in the coal-bearing interval directly underlying the Entrance conglomerate in the Blackstone River section (Figs. 2 and 19, section 12). Although the Kneehills Tuff has not been identified in the central Foothills, the presence of the Scollardia trapaformis Zone assemblage implies a correlation between the upper parts of the Brazeau and St. Mary River Formations as shown in Fig. 2. The fourth and most precise time line is the Cretaceous/Tertiary boundary. It is determined palynologically to be at a horizon that represents the uppermost limit of several morphologically exotic angiosperm pollen species typified by those of the triprojectate complex (Aquilapollenites and related genera). A geochemical anomaly, usually characterized by the abundance of iridium, coincides with or immediately overlies this horizon (Jerzykiewicz and Sweet, 1986a, b; Lerbekmo et al., 1987). In the southern Foothills the Cretaceous/Tertiary boundary occurs within alluvial plain deposits (Figs. 2 and 7, section 6) as determined palynologically, although from a much reduced assemblage (Jerzykiewicz and Sweet, 1986b) and by the coincident occurrence of an iridium anomaly (J.F. Lerbekmo, personal communication, 1986). In the central Foothills this boundary lies at the base of the Mynheer coal (Jerzykiewicz and Sweet, 1986a). The basal few centimetres of coal contain abundant angiosperm pollen but the assemblage is not very diverse. Although most morphologically exotic species characteristic of the Maastrichtian have the uppermost limit of their range preceding the base of the coal, many other morphologically simple species and a few of the more exotic species (VVodehouseia spinata Stanley 1961, Aquilapollenites immiser Sweet 1986, and A. reticulatus (Mchedlishvili) Tschudy & Leopold 1971) do persist above the

Cretaceous/Tertiary boundary. A few different species enter the record near the base of the Paleocene, including a new species of triprojectate pollen. The first appearance of the classic lower Paleocene species, Wodehouseia fimbriata Stanley 1961, is in a 20 cm rider seam the base of which is 1.15 m above the top of the main Mynheer coal zone or about 11.3 m above the Cretaceous/ Tertiary boundary (Jerzykiewicz and Sweet, 1986a; Lerbekmo et al., 1987). The fifth, and stratigraphically highest, time line is provided by a shift in the type of palynomorph assemblage from the very low diversity that typifies the early Paleocene, to the somewhat increased diversity of the middle Paleocene, or from the P1-P2 style assemblages to the P3-P4 style assemblages of Nichols and Ott (1978). The exact position of this shift to a more diverse middle Paleocene flora is not well established in either the central or southern Foothills sections.

Lithofacies The various lithofacies that were recognized in measured sections of the post-Wapiabi sequence along the Foothills are presented in Fig. 3. Each facies is characterized by its lithotype and sedimentary structure. Inorganic sedimentary structures as well as biogenic features and fossils were taken into account for descriptive and interpretative purposes. The following features were particularly useful for the interpretations of depositionai environmeats: - - i n situ caliche (glaebules, rhizocretions and hardpan), --redeposited caliche fragments (lag deposit composed of rip-up clasts derived from caliche paleosol), --upright plant rootlets and stems, --oyster beds, --fresh-water pelecypod and gastropod layers, --fresh-water stromatolites and oncolites, --rhythmically laminated siltstones and claystones (rhythmites), --wavy, lenticular to flaser laminae, muddrapes and mud-couplets.

34

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B

/

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Fig. 3. Lithofacies symbols and codes in the sections studied. 1 = Conglomerate composed mainly of extraformational clasts, stratified (Gs). 2 = Conglomerate composed mainly of extraformational clasts with an erosional base (Ge). 3 = Conglomerate composed mainly of intraformational clasts (Gi); mud-chips and plant remains common, coaly fragments and large tree trunks (t) occasionally present, erosional base. 4 = Conglomerate composed mainly of caliche clasts with an erosional base (Gc). 5 = Conglomerate composed mainly of Ostrea shells with an erosional base (Go). 6 = Sandstone fine- to coarse-grained (most commonly medium-grained), horizontal to low-angle inclined bedding a n d / o r massive, parting lineation ( p l ) occasionally present (Sh). 7 = Sandstone fine- to coarse-grained (most commonly medium-grained), planar crossbeds (Sp). 8 = Sandstone fine- to coarse-grained (most commonly medium-grained), trough crossbeds (St). 9 = Sandstone fine- to medium-grained, ripple drift crossbeds, ripple marks (rm) present in places (Sr). 10 = Sandstone very fine- to medium-grained (most commonly fine-grained), low-angle inclined lamination a n d / o r massive appearance ($1). 11 = Sandstone fine- to medium-grained, low-angle inclined lamination with mud drapes solitary (lenticular) or grouped (flaser) (Smd). 12 = Sandstone fine- to very fine-grained and siltstone, horizontal to low-angle inclined lamination with mud couplets (Smc). 13 = Mud-shale to silt-shale interbedded with fine-grained sandstone showing parallel to wavy lamination. Marine fossils common (Sv + Fb). 14 = Oyster bank (Ob). 15 ~ Coal (C). 16 = Mud-shale, carbonaceous, rich in plant remains and rootlets (r) (Fmc). 17 = Mudstone to silty mudstone, dark-grey, organic-rich (Fm) a n d / o r greenish grey (Fg), ironstone concretions sporadic (i) (Fm + Fg). I8 = Siltstone to very fine-grained sandstone, fine parallel a n d / o r ripple lamination, plant fossils ( p ) in places (Fs). 19 = Mud-shale a n d / o r mudstone rich in fresh-water pelecypods and gastropods (Fmf). 20 = Siltstone and claystone, fine rhythmic lamination (rhythmites), very fine- to fine-grained sandstone interbeds. Fresh-water stromatolitic and oncolitic structures (st) present (F1). 21 = Silt-shale to mud-shale a n d / o r mudstone, dark-grey, organic-rich, ironstone concretions large and numerous (Fsm). 22 = Silt-shale with rhythmically alternating thin beds of fine-grained sandstone and sideritic siltstone (s) (Frh). 23 = Mudstone to silty mudstone, grey to dark-grey, caliche glaebules scarce to common (Fcm). 24 = Mudstone to silty mudstone, olive-green, caliche glaebules scarce to common (Fco). 25 = Mudstone to silty mudstone, pink to red, caliche glaebules scarce to common (Fcr). 26 = Caliche features (Cap); glaebules (g) and hardpan (K). 27 = Bentonitic claystone (B). 28 = Tuff (T).

35 The occurrence of one or more of the above features in a given sequence of lithofacies often provided a clue for an environmental interpretation, which otherwise would have been impossible or at the best equivocal. Many of the lithofacies that are characterized only by inorganic structures that reflect physical processes of sedimentation can represent more than one depositional environment. None of the cross-bedding types are diagnostic for a particular depositional environment. Ripple drift cross-bedded sandstone (lithofacies Sr) can occur in both channel and overbank settings of the fluvial environment, as well as in marginal-marine and lacustrine settings. Equally, the channel sandstone facies is not diagnostic of any one fluvial channel type. Additional information about the facies assemblages and the geometry of the sand body is needed to recognize the channel type and the depositional environment of a fluvial sandstone sequence (Galloway, 1981; Miall, 1984, 1985). Although the external geometry of a lithosome was observed in some postWapiabi sections along the Foothills, in many instances the size of the outcrop was insufficient to apply the architectural-clement analysis of Miall (1985). In these relatively small outcrops the sedimentary facies analysis method was still useful for interpreting the depositional environment using the features listed above. For example: the occurrence of the large oncolitic and stromatolitic structures in association with lithofacies F1 and Sr enables the interpretation of the entire sequence in terms of lucastrine facies association (LAC), representing a large and perennial lake environment. Marginal-marine interpretation (MS facies association) of the coal-bearing sections, below and above the open-marine Bearpaw shale, is based on the presence of the wavy, lenticular and flaser laminae and mud-drapes as well as on the occurrence of oyster beds and other evidence of biotic activity. Mature caliche paleosol and the autochthonous coal are considered climatically diagnostic facies (Habicht, 1979; Hallam, 1984) and are used for paleoclimatic interpretations (FCA-semiarid, and FCO--humid fluvial facies associations in Figs. 22 and 23).

Caliche facies "Caliche" and "calcrete" are broad and informal terms for terrestrial calcium carbonate, which occurs in soil, rock or sediment as a result of displacive a n d / o r replacive introduction into a weathering profile. Of the two terms caliche is the one traditionally used in North American geological literature (Blake, 1902; Price, 1925; Sidwell, 1943; Bretz and Horberg, 1949; Brown, 1956; Blank and Tynes, 1965; Reeves, 1970; Esteban and Klappa, 1983). Caliche may occur in a variety of forms. The most common are: caliche glaebules (Brewer and Sleeman, 1964), rhizocretions (Kindle, 1923), and hardpan. They are characteristic of the caliche facies (Esteban and Klappa, 1983). The glaebules are discrete bodies usually subspherical or cylindrical to conical in shape (rhizocretions) and are easy to identify in the host mudstone due to their greater resistance. They may coalesce in larger irregular masses or layers of hardpan.

Occurrence and facies context The caliche facies occurs in the southern Foothills in the uppermost part of the Belly River Formation and in the Willow Creek-Porcupine Hills interval (Fig. 2). It appears to be the main lithofacies within the "concretionary member" of the Belly River Formation of Wall and Rosene (1977). Hage (1943) considered this member as "a useful horizon marker" in the Cowley map-area. Douglas (1951) has also mapped this member further southeast in the Pincher Creek map-area as "green, grey and rare red shales, with interbedded thin sandstone and brown, nodular to concretionary limestones". This caliche-bearing member, herein called the caliche member, is best exposed in the Crowsnest River valley west of Lundbreck (Fig. 4, sections 1 and 2; Fig. 5A). The lower part of the caliche member is composed of multistoried, fining-upward layers of sandstone interbedded with thick intervals of mudstone containing caliche glaebules and hardpan (Fig. 4, section 1). The sandstone

36

® \

F

100 m - - I

ap +Cap

ap ~r ~h |r 3t 3i+Gc

+Cap

~r

Sh Gi+Gc 71Mi=TRES ABOVE THE TOP OF THE WAPIABI FM

ap

Fig. 4. Caliche member of the Belly River Formation exposed along Crowsnest River west of Lundbreck. Stratigraphic settings of the sections are given in Fig. 2. Lithofacies symbols and codes are explained in Fig. 3. The inset sketch shows the major channel layers and the hardpan layers K-l, K-2 and K-3 (compare with Fig+ 5A).

layers have sharp, erosional bases and show the fining-upward trend in grain size and the arrangement of sedimentary structures characteristic of a point bar. Multistoried layers composed of amalgamated units of flat to low-angle, inclined bedded, medium-grained sandstone in the lower part, and tipple bedded, fine-grained sandstone in the upper part are most common. Layers of medium-grained sandstone with intraformational

lag deposits composed of tip-up clasts of mudstone and subangular limestone fragments derived from caliche occur in the lower part of the caliche member (Fig. 4, section 1). The fine-grained recessive intervals consist of greyish green to pale yellowish green (10 GY 5/2 to 10 GY 7/2) mudstone, silty mudstone and very fine-grained sandstone containing caliche glaebules and hardpan. The fine-grained sediment shows rubbly weather-

37

Fig. 5. Caliche member of the Belly River Formation exposed in section 2, along Crowsnest River. A. General view of section 2. Note the hardpan layers (K-l, K-2 and K-3) on both limbs of the anticline. B. Channel lag deposit composed of redeposited caliche cobbles. Location of the caliche cobbles is marked by the arrow in Fig. 5A. C. Hardpan layer K-2. Note the glaebular character of the hardpan. The hammer is on top of the layer. D. Close-up view of the hardpan. ing a n d reveals n o stratification except for thin interbeds of very fine-grained s a n d s t o n e which is occasionally laminated. The c o n t a c t b e t w e e n the fine-grained sediments a n d the u n d e r l y i n g c h a n n e l

s a n d s t o n e is g r a d a t i o n a l b u t rather rapid, the s a n d s t o n e a n d m u d s t o n e with the caliche glaebules f o r m i n g a n overall f i n i n g - u p w a r d cycle. The best-developed caliche features in the form of

38

Fig. 6. Caliche features of the Belly River Formation. A. Large irregular masses of the caliche glaebules coalescing along bedding planes in section 2. B. Close-up view showing details of the irregular masses of the caliche glaebules. C, D. Cylindrical- and conical-shaped caliche glaebules (rhizocretions) in section 1. glaebules, rhizocretions and h a r d p a n (Fig. 6) usually occur in the middle part of the recessive intervals, but occasionally they are found in the gradational contact between the channel sandstones and overbank mudstones.

The upper part of the caliche m e m b e r (Figs. 4 and 5, section 2) contains similar lithofacies forming fining-upward cycles: G i + G c - S h and/or S t - S r - F c o + C a p - K . The channel layers contain coarser debris that includes cobble-sized intra-

39 formational lag deposits composed of caliche fragments, as well as almost intact redeposited glaebules (Fig. 5B). The hardpan occurs as laterally persistent layers up to 0.5 m thick, which can be recognized on both limbs of an anticline exposed along the Crowsnest River and traced laterally over a distance of about 200 m (inset in Fig. 4 and Figs. 5A, C-D). The caliche facies appears for the second time in the post-Wapiabi sequence at the base of the Willow Creek Formation (Fig. 2). Although the caliche features occur throughout the entire Wil-

low Creek-Porcupine Hills interval in the southern Foothills, the full development of the caliche facies characterized by red beds with caliche glaebules (the glaebular paleosol) and hardpan is characteristic for the lower member of the Willow Creek Formation. This member, herein called the caliche member of the Willow Creek Formation, extends from the base of the formation up to the Cretaceous/Tertiary boundary (Fig. 2). The caliche member of the Willow Creek Formation is laterally persistent throughout the southern Foothills and adjacent Plains. It coin-

1870

1865

St Cap 2 Cap

1860 Cap

Sh

Gi

2

1855

;-T ~ound

1850 St Gi+G 2

r

1845 ~ap

i

2

Cap 1840 3ap

r

St Sh METRES ABOVE THE TOP OF THE WAPIABI FM

Fig. 7. Caliche member of the Willow Creek Formation exposed along Crowsnest River, northwest of Cowley(section 5) and along Castle River, southeast of Cowley(section 6). Stratigraphic settings of the sections are given in Fig. 2. Lithofaciessymbolsand codes are explained in Fig. 3.

40

Fig. 8. Caliche member of the' Willow Creek Formation. Section 5 near Cowley. A. General view of section 5. Note the hardpan layer (K-2) indicated by arrow. Compare with section 5 in Fig. 7. B. Close-up view showing the hardpan (indicated by arrow). C. Coalesced cafiche glaebules revealed on the lower, bulbous surface of the hardpan. The sample was taken from layer K-2. D. Internal structure of the same sample sectioned parallel to the sole of the hardpan. Note the coalesced glaebules built up with microcrystalline calcite (M), and the cracks (C) infilled with sparry calcite cement. The frame indicates the outline of the next figure. D'. Close-up view showing details of caliche glaebules affected by circumgranular (CC) and intergranular (IC) cracks.

cides with the outline of the formation on the existing geological maps so that its northern termination is due to the erosional unconformity

mapped by Douglas (1950) in the Stimson Creek map-area some 75 km north of the Crowsnest River valley. All the characteristic features of the

41 caliche member can be seen in the fiver b a n k northwest of Cowley (Fig. 7, section 5; Fig. 8). Section 5 shows two major channel sandstone layers and several thin beds of tipple-drift stratified sandstone alternating with mudstone containing caliche glaebules and hardpan. The lower major sandstone layer is composed of two vertically stacked channel units interbedded with thin over-

bank mudstone. The lower of them is in turn two-storied (Fig. 7, section 5 at 1850 m). Both the lower and the upper major sandstone layers reveal well developed medium- to large-scale trough crossbedding. The lower contacts of the layers are erosional. The channel lag contains mud-chips and redeposited caliche debris. Both major sandstone layers are well exposed in the outcrop so

t |i + G c

;t S~

ap

"-11M~'TRES ABOVE THE TOP OF THE WAPIABI FM Fig. 9. The upper member of the Willow Creek Formation and multistoried channel sequence at base of the Porcupine Hills Formation exposed along Crowsnest River northeast of Cowley. Stratigraphic settings of the sections are given in Fig. 2. Lithofacies symbols and codes are explained in Fig. 3.

42

that the internal geometry and the relationships between individual second-order channels can be seen. They seem to represent the mobile channel type of Friend (1983) or broad channel-fill type of Miall (1985). The recessive intervals consist of varicoloured mudstone to silty a n d / o r sandy mudstone containing caliche glaebules and hardpan. Although the pink to red coloured (5 R 7 / 4 to 5 R 6/6) mudstone seems to be the most characteristic for the caliche member of the Willow Creek Formation, the greyish olive-green and brown varieties (5 GY 3/2 to 5 Y 4/1) are at least equally common. The caliche features occur in both red and grey mudstones although they are better developed in the red beds. The upper member of the Willow Creek Formation, which is about 600 m thick in the valleys of the Crowsnest, Oldman and Castle rivers (Figs. 2, 7 and 9, sections 6-8), still contains the caliche facies but the frequency of caliche gradually decreases upwards, the caliche facies giving way to lithofacies Fmf (mud-shale a n d / o r mudstone rich in fresh-water pelecypods and gastropods). The caliche glaebules are still occasionally present in some beds of grey to dark grey mudstone which occur in association with the Fmf lithofacies. In some beds the caliche glaebules are very common but small. They occasionally form the glaebular paleosol (Blokhuis et al., 1969) composed of rubbly weathering mudstone with numerous, scattered, small glaebules. Such a layer occurs at the top of the Willow Creek Formation immediately below the multistoried channel sequence, which is herein considered as the base of the Porcupine Hills Formation (Fig. 9, section 8 at 3223 m; Fig. 10A and B). The Porcupine Hills sandstone layers very often contain redeposited caliche debris as a constituent of the channel lag deposit. The recessive mudstone intervals between the sandstone layers also reveal the caliche features in the form of small glaebules, pellets and pisolites (Fig. 10C, C', D), but this uppermost portion of the postWapiabi sequence is poorly exposed and information is limited to the subsurface data (Jerzykiewicz and Sweet, 1986b).

Caliche features. The glaebules (Brewer and Sleeman, 1964) are the most common caliche features in the Belly River and Willow Creek sections. They are easy to identify in outcrop because of their characteristic shape, difference in colour from surrounding mudstone, greater resistance and sharp boundaries that make them readily separable from the host rock (Figs. 10B and l l A , B). Pebble-sized, subspherical glaebules seem to be the most common, but the size of discrete glaebales ranges from sand sized up to several centimetres in diameter. They are often vertically elongate, cylindrical or conical in shape (Figs. 6C, D; 12A, B). Some of them resemble taproots (Figs. 6D and 12A). The glaebules tend to coalesce, forming the compound types of Brewer and Sleeman (1964), or large irregular masses (Fig. 6A, B), and when they coalesce along horizontal surfaces, laterally continuous, indurated layers of hardpan are produced (Figs. 5A, C, D; 8B). Internally, the glaebules contain patches of irregularly shaped cryptocrystalline micrite and cracks infilled with sparry cement. The cryptocrystalline groundmass of the glaebules from the Willow Creek Formation is red to yellow in colour (most commonly dusky red, 5 R 3/4), while that of the Belly River Formation glaebules tends to be light grey to pinkish grey (N 7 to 5 YR 8/1). The main mineral constituent of the glaebules and hardpan from both formations is low-magnesium calcite. Cryptocrystalline silica-rich lenses in the upper portion of the hardpan layer occur in the lowermost hardpan within the Willow Creek Formation (Fig. 7, section 5 at 1840 m). The internal fabric of the glaebules is shown in Fig. 11. A polygonal pattern composed of a series of radiating cracks resembling septarian structure (Pettijohn, 1949, fig. 47) seems to be the most common. Some glaebules that have a system of concentric cracks (Fig. 11F) or just a single concentric crack ring (Fig. 11B) may be compared to the contraction spheroid of Pettijohn (1949). The root-shaped glaebules also reveal an internal fabric composed of polygonally arranged infilled cracks (Fig. 12C, D). They represent fossilized roots and have been named "rhizocretions" (Kindle, 1923),

43

Fig. 10. Caliche features in the upper member of the Willow Creek Formation and in the lowermost Porcupine Hills Formation. A. Glaebular paleosol (Gp) at the top of the Willow Creek Formation in section 8. B. Close up view of the glaebular paleosol. Note small caliche glaebules (g) scattered in rubbly weathering mudstone. C. Pelletoid conglomerate. All pellets resulted from inplace growth within a sandstone framework. Note the pattern of recemented cracks and rims around and within some pellets. PL = limestone pellet, BL = black limestone pellet, PS = pisolite. C'. Close-up view showing details of the pisolite and adjacent pellets within the sandstone framework. D. Limestone pellets scattered in silty mudstone.

44

Fig. 11. Caliche glaebules from the Willow Creek Formation. A. External surface of a discrete glaebule. B. Internal structure of the same glaebule. Note the concentric crack ring ( C R ) . C-F. Internal structure of the compound glaebules. Note the polygonally and concentrically arranged cracks forming separate systems within the cryptocrystalline groundmass. S S = septarian structure, C S = concentric structure. " p e d o t u b u l e s " (Brewer a n d Sleeman, 1963) or " r o o t petrifications" (Klappa, 1980). The i n t e r n a l fabric of the larger caliche masses a n d h a r d p a n also has a glaebular character. The

c o m p o u n d structure of the larger caliche masses m a y be i n t e r n a l l y m a r k e d by cracks f o r m i n g separate systems within the cryptocrystalline g r o u n d mass (Fig. l l C , E). T h e glaebular n a t u r e of the

45

hardpan is usually clearly visible on the surface of the layers (Figs. 5C, D; 8C) as well as in any section through it (Fig. 8D, D'). The upper parts of some hardpan layers are structureless or crudely bedded and probably correspond to the "laminar horizon" of Gile et al. (1966). The glaebules are clearly of accretionary origin ("accretionary structure" of Pettijohn, 1949) and resulted from a process of calcium carbonate accumulation in a subaerially exposed diagenetic environment (Esteban and Klappa, 1983). Calcium carbonate accumulation may have begun at plant roots. The glaebules grew by precipitation from downward-percolating soil water enriched in calcium carbonate. The septarian crack pattern developed by case-hardening of the glaebule exterior and shrinkage by dehydration of the interior ("irreversible chemical desiccation" of Pettijohn, 1949). The process of glaebule formation requires several alternations of calcium carbonate dissolution and reprecipitation. Authigenic calcium carbonate in the form of pellets, ooids and pisolites * occurs occasionally in the sandstone and siltstone beds of the Porcupine Hills Formation (Fig. 10C, C', D). Most commonly they are scattered in a sandy or silty matrix but occasionally they form "conglomerates" similar to the "calcrete conglomerate" of Tandon and Narayan (1981). All constituents of the conglomerate that are larger than the sand fraction are authigenic and consist principally of micritic calcite with some iron oxide pigment, which produces the yellow to brown hues of most of the pellets. Some, however, are dark grey to black and may be compared with the "black pebbles" that are a noticeable component in some caliche hardpans (Esteban and Klappa, 1983). Debris consisting of subangular limestone fragments derived from caliche, as well as almost intact redeposited glaebules, is common in some

* The terminology used by H a y and Wiggins (1980) has been adopted here: pellet refers to a spherical or oval particle of authigenic origin lacking a nucleus; ooid refers to a spherical or oval particle less than 2 m m in diameter comprising a nucleus enclosed by one or more laminae. The majority of ooid coatings are concentrically banded; pisolites are structurally similar to ooids, but greater than 2 m m in diameter.

channel lag deposits of the Belly River, Willow Creek and Porcupine Hills formations. Debris is usually of pebble size but in some instances the maximum clast size is 20 cm (Fig. 5B). The large size and discoidal shape of the clasts suggest fragmentation and redeposition of a caliche hardpan. The caliche clasts are easily distinguished from the extraformational pebbles, which are quartz, quartzite and chert.

Associated palynological assemblages The recovery of pollen and miospores from samples of the Willow Creek Formation is typically poor. Out of the 63 samples (19 from the caliche member and 44 from the upper part) processed for pollen and miospores, these being mostly from grey mudstone or other apparently favorable lithologies, 11 samples (26% from the caliche member and 14% from the upper member) were effectively barren of palynomorphs. Only 14 samples yielded assemblages sufficiently rich to be counted; a more or less equal number of productive samples were obtained from each member. The recovery of indigenous palynomorphs was sparse in 33 samples, although nine of these, all from the upper part of the formation, yielded abundant reworked Early Cretaceous and Jurassic palynomorphs. The remaining five samples, also from the upper member of the formation, were found to contain only reworked palynomorphs. In addition to the erratic recovery of palynomorphs from the Willow Creek Formation, the diversity of the assemblages from the lower, caliche member of the formation is usually low compared to typical late Maastrichtian assemblages (Snead, 1969; Srivastava, 1970; Sweet, 1978; Jerzykiewicz and Sweet, 1986b). Indeed, other than the single specimens of Cranwellia rumseyensis Srivastava 1966 and questionable Aquilapollenites conatus Norton 1965 immediately below the Cretaceous/Tertiary boundary, no angiosperm species used in central Alberta to characterize the Maastrichtian (Sweet and Hills, 1984; Jerzykiewicz and Sweet, 1986a) were encountered. Of the four residues from lower Willow Creek samples that could be counted, angiosperm pollen is conspicuous in three, the fourth being dominated by Concentricystes. Those in which angiosperm pollen

46

is prominent contain few species, the assemblage being dominated either by Ulmoideipites tricostatus Anderson 1960 a n d / o r U. hebridicus (Simpson) Sweet 1986 and simple tricolpate pollen. This dominance of the angiosperm portion of the assemblage by only a few, probably wind distributed, pollen species contrasts sharply with the numerous, relatively large, exotic angiosperm pollen species which are conspicuous in late Maastrichtian assemblages from the central Foothills (Jerzykiewicz and Sweet, 1986a). In contrast, in the upper, early Paleocene portion of the Willow Creek Formation, several samples yielded assemblages equally diverse as those usually recovered from the early Paleocene in central Alberta (Snead, 1969; Jerzykiewicz and Sweet, 1986a). A last observation on the general character of the assemblage recovered from the caliche member relates to the excellent state of preservation of the palynomorphs in some of the samples with a low diversity and recovery, or in which Concentriqvstes is at least present, if not dominant. This characteristic is typified by samples in which either Cyathidites minor Couper 1953, Laevigatosporites sp., or Concentricystes is dominant. This excellent preservation of individual palynomorphs contrasts with that of the more organic rich and higher yielding samples. Many of the latter spores and pollen grains appear degraded in that the outlines of individual palynomorphs lack sharp definition. In addition to these more general aspects of the Willow Creek flora, the frequent occurrence of

Classopollis sp. and Concentricystes is unique to this caliche-bearing facies. Classopollis sp. occurs as an accessory species (from a few specimens to up to 6% of the total assemblage) in several samples in which there is no evidence of reworking. Concentricystes sp., usually represented by excellently preserved specimens, is often the dominant, if not the only, species in samples that otherwise contain too few specimens to enable a quantitative relative abundance to be established. Associated with Concentricystes in some samples are relatively common fungal spores and hyphae. Like those from the caliche member of the Willow Creek Formation, samples from the caliche member of the Belly River Formation (Fig. 4, sections 1 and 2) yielded assemblages that had a low number of specimens and a low diversity. Ten samples were processed from this facies; six were essentially barren of palynomorphs, from two the recovery was very sparse and from two the yield was good. These latter two samples are used to characterize the flora of the caliche member in the upper Campanian, Belly River Formation. The palynoflora is dominated by angiosperm pollen (54%) with gymnosperm pollen being subdominant (Taxodiaceae-Cupressaceae pollen, 34%; bisaccate pollen, 7%). The angiosperm pollen assemblage (Plate I, 2-10) is dominated by Subtriporopollenites alpinus (Wolf) Tschudy 1973 (30%) with the remainder of the assemblage being composed mostly of Tricolpopollenites sp. and Tricolporites spp. accompanied by scarce Liliacidites dovlei Ward 1986 and Striatopollis sp., and rare

Plate I. Figures 1 to 10: Representative palynomorphs from the caliche member of the late Campanian Belly River Formation (section 2, located on the Crowsnest River, 49 o 35' N, 114 o I 1' W). 1. Equisetosporites amabilis Srivastava 1968; GSC 89697.2, 3. Cf. Cranwellia sp.: (2) GSC 89698; (3) GSC 89699. 4. Siberiapollis sp.; GSC 89700. 5. Subtriporopollenites alpinus (Wolf) Tschudy 1973; GSC 89701. 6, 7. Tricolporites spp.: (6) GSC 89702; (7) GSC 89703.8. Striatopollis sp.; GSC 89704. 9. Tricolpopollenites sp.; GSC 89705. 10. Liliacidites doylei Ward 1986; GSC 89706. Figures 11 to 19: Representative latest Campanian palynomorphs in both the basal marginal-marine, coal-bearing facies of the St. Mary River Formation (section 4, located on the Crowsnest River, 49 ° 30' N, 114 ° 03' W) and the lacustrine facies within cyclothem lb of the Brazeau Formation (section 10, located on the Blackstone River, 5 2 ° 4 3 ' 2 0 " N , 116°16'30"W). 11. Aquilapollenites augustus Srivastava 1969; GSC 89707. 12. A. clairireticulatus Samoilovitch 1965; GSC 89708.13. A. drumhellerensis Srivastava 1969; GSC 89709. 14. A. funkhouseri Srivastava 1968; GSC 89710. 15. Tricolporopollenites sp. 2 in Norris et al. (1975); GSC 89711. 16. Aquilapollenites trialatus Rouse 1957; GSC 89712. 17. A. senonicus Mchedlishvili in Samoilovich & Mchedlishvili 1961; GSC 89713. 18. A. quadrilobus Rouse 1957; GSC 89714. 19. A. rectus Tschudy 1969; GSC 89715. All figures ×750.

Jl

ii

nm

r

i

48 specimens of Erdtmanipollis, Siberiapollis, cf. Cranwellia and Tricolporopollenites sp. 2 in Norris et al. (1975). Miospores constitute only 3.5% of the assemblage (Laevigatosporites sp., 2%; and equal numbers of Cyathidites sp. and Heliosporites altmarkensis Schulz 1962). Equisetosporites amabilis Srivastava 1968 (Plate I, 1), with ephedralean affinities, makes up about 1% of the assemblage. Only one specimen of Concentricystes was seen. and Classopollis was not observed.

Paleoclimate and depositional environment Although calcium carbonate is known to accumulate in the soil in various climatic zones, including polar regions, significant caliche accumulations are characteristic of warm, semi-arid regions (Gile, 1961; Gile et al., 1966, 1981; Reeves, 1976; Esteban and Klappa, 1983; Goudie, 1983). The amount and frequency of precipitation seem to be the most important controlling factors. If precipitation is excessive, leaching of the soil is complete and no calcium carbonate will accumulate. If rainfall is not sufficient, the degree of leaching is inadequate to mobilize calcium carbonate, and only minor accumulations of calcite occur in the soil. The most favorable conditions for caliche formation exist in the regions where annual rainfall is between 400 and 600 mm (Goudie, 1983). Essential for caliche formation also appears to be the sporadic distribution of rainfall, i.e. alternation of periods of rainfall and long-lasting droughts (Woolnough, 1930). It also has been shown that the depth of the caliche zone in the soil profile depends on the amount of annual rainfall (Jenny and Leonard, 1939). With increased annual rainfall, the zone of caliche formation moves to a greater depth and finally disappears when the annual precipitation (in temperate regions) exceeds 1000 mm (Blatt et al., 1980). It is therefore likely that the caliche glaebules and hardpan of the Belly River and Willow Creek Formations were formed in a soil profile that developed in semiarid conditions where rainy seasons succeeded long-lasting periods of drought. The overbank mudstone with scattered glaebules and rhizocretions should be interpreted in terms of a glaebular paleosol (Bernard and Le Blanc, 1965; Blokhuis et al., 1969; Singh and Singh,

1972), which represent stages I and II of caliche development (Gile et al., 1966, 1981). The hardpan can be described in terms of the pedogenic limestone (Gile, 1961; Gile and Hawley, 1966; Reeves, 1970) or petrocalcic horizon often referred to as a K horizon. Such advanced forms of calcium carbonate accumulations forming indurated horizons (stages III and IV of Gile et al., 1966) require in excess of 10 4 years and perhaps as much as 105 or 106 years to form (Gile et al., 1981). In the last part of stage III the plugged horizon develops: "most or all pores and other openings in the soil become filled by carbonate; primary grains have been forced apart; bulk density has increased; and infiltration rate has markedly decreased." Stage IV is characterized by the "laminar horizon", formed on top of the former one, composed almost entirely of carbonate with no allogenic skeletal grains (Gile et al., 1981, p. 67). Hardpan layers in the Belly River Formation correspond to the upper part of stage III, whereas the Willow Creek layers are close to stage IV. The mature caliche paleosol indicates that the overbank deposits were subaerially exposed for extended periods of time, during which they underwent in situ modification by pedogenic processes. During these periods very little or no sedimentation took place and the groundwater table was low. The position of the water table caused oxidizing conditions and the evaporation of vadose water. This led to the capillary movement of soil water and the precipitation of calcium carbonate within the soil profile. Even during rainy seasons, the groundwater table was low enough to prevent formation of extensive ponds or swamps during sedimentation of the caliche members. The floodplain was drained by broad, mobile channels of low sinuosity. Periodic heavy rainfall modified the floodplain into a braidplain with numerous ephemeral streams eroding the caliche soil. Large amounts of caliche debris in the channel lag deposit (including cobble-sized conglomerate in the Belly River caliche member) indicate erosion of a significant volume of already indurated caliche soil. Incomplete caliche paleosol profiles (lacking the hardpan on top), which are common in both the caliche members, may sug-

49

Fig. 12. Rhizocretions (fossilized roots) ~from the Willow Creek Formation, section 5 near Cowley. A, B. Root-shaped glaebules (rhizocretions) in mudstone. C, D. Internal structure of the rhizocretions. Note the polygonally arranged cracks in the cryptocrystalline groundmass infilled with sparry calcite.

50 gest erosion of their upper portions. Although erosion of some soil profiles might have happened prior to lithification of the pedogenic calcium carbonate, it is clear that many mature and indurated caliche soil profiles were subjected to erosion at the surface. The erosion took place sporadically after long periods of relative stability in the floodplain area. Some of these erosional episodes, caused by particularly vigorous flood events, took place during the sedimentation of the Belly River caliche member, as indicated by the cobble-sized channel lag composed of reworked hardpan overlain by subhorizontal to low-angle inclined sandstone (lithofacies Sh). This lithofacies, commonly interpreted in terms of being a product of flash floods depositing sand under upper flow regime plane bed conditions (Miall, 1977, 1984; Rust, 1978; Tunbridge, 1981, 1984), occurs at the base of the channel layers in the caliche member of the Belly River Formation. The channel sandstone units in the caliche member of the Willow Creek Formation usually represent a lower-energy environment of deposition. Although the redeposited caliche debris is also common in the channel lag, it is of granule or pebble size. The overlying sandstone is usually trough crossbedded (lithofacies St) and may be compared with similar channel fills described by Williams (1971) in flood deposits of the sand-bed ephemeral streams of central Australia. Caliche paleosols analogous to those from the Belly River and Willow Creek Formations have been recorded from other Late Cretaceous deposits. They are known to occur in the Two Medicine Formation of northwestern Montana (Lorenz, 1981) which is stratigraphically correlative with the Belly River Formation. Mature caliche profiles capped by up to 0.5 m thick and laterally persistent layers of pedogenic limestone have been studied by the first author in Bayn Dzak, a locality in southern Mongolia. Although the caliche soil profile from the Djadokhta Formation (Lefeld, 1971, figs. 2, 3 and Plate XX, 1) has been erroneously interpreted as " . . . c a l c i u m carbonate precipitation within the arenaceous sediments which took place under the lacustrine conditions..." (Lefeld, 1971, p. 118), the author has correctly interpreted the paleoclimate stating:

"The climate of the Djadokhta times may be tentatively considered as a warm one, with possible intermittent semi-arid periods represented by the arenaceous beds. The warmth of the climate is demonstrated by the presence of crocodiles which, at present cannot survive in moderate climatic conditions with colder seasons." (Lefeld, 1971, pp. 125-126). The pedogenic origin of the limestone concretions and extensive hardpan in Bayn Dzak is unquestionable. The section presented by Lefeld (1971) in his fig. 3 should be interpreted as stage IV in the morphogenic scheme of caliche development (Gile et al., 1966). Furthermore, there are other indications of semiarid climate during deposition of Upper Cretaceous dinosaur-bearing formations in southern Mongolia, including welldeveloped eolian dunes, and ephemeral lakes and streams (Gradzinski and Jerzykiewicz, 1974). The comprehensive discussion about the semiarid floodplain as a possible environmental setting for the Upper Cretaceous dinosaur fauna is beyond the scope of this paper and is presented elsewhere (Jerzykiewicz and Sweet, 1987). It is noteworthy, however, that a layer with numerous tyrannosaurid and some hadrosaurid bones as well as a complete skull of Tyrannosaurus rex was recently found in the caliche member of the Willow Creek Formation near Cowley (D. Fisk, personal communication, 1987; Abler, 1984). The late Maastrichtian assemblage from southwestern Alberta contains, with rare exceptions, only a few, probably wind distributed, angiosperm pollen. This contrasts sharply with the assemblages from the central Foothills in which relatively large, morphologically exotic species of angiosperm pollen are common (Jerzykiewicz and Sweet, 1986a). In central Alberta, the early Paleocene is the time of lowest diversity (Jerzykiewicz and Sweet, 1986a) but samples from southwestern Alberta containing the greatest diversity of angiosperm pollen are from the upper (lower Paleocene) part of the Willow Creek Formation. This is a reversal of the usual trend towards decreased diversity from the late Maastrichtian to early Paleocene and can be explained by the local environmental conditions overriding the regional trends. In the upper part of the Willow Creek Formation, red and green beds occur infrequently

51 and, although there are zones bearing calcrete glaebules, these are less frequent and the glaebules are generally smaller and less common than in the lower, Maastrichtian part of the formation. Presumably this represents a progressive amelioration of the climate, allowing for the coexistence of a greater diversity of plants. Hence, corresponding with the observed changes in lithology, the change in diversity within the angiosperms is the second line of evidence of a biologically-stressed, semiarid environment during the late Maastrichtian in southwestern Alberta. Semiaridity during the deposition of the Willow Creek Formation is also suggested by the impoverished nature of the palynoflora, especially in the lower Willow Creek. This is to be expected in a biologically-stressed environment. It might seem possible to interpret the low numbers of palynomorphs recovered, from the caliche member of the Willow Creek Formation in particular, as reflecting an environment unsuitable for preservation. However, the excellent condition of Concentricystes and other miospores in samples nearly barren of angiosperm pollen would appear to negate this argument. Havinga (1971) thought that the decay of pollen and spores depended in part on soil type, soil pH and climate. In addition, biological degradation appeared to increase the vulnerability of sporopollenin to oxidation. All of Havinga's test sites were water saturated or periodically wet. In this study, those samples containing a high amount of organic matter and yielding large numbers of pollen and spores were presumably deposited in ephemeral, marsh-like settings. As these are habitats with intrinsically.high levels of biological activity, it is not surprising, by inference from Havinga's results, that the preservation of individual specimens was relatively poor. In contrast, one might speculate that in samples presumed to be of fossil soil horizons from a semiarid, organic-poor environment, the excellent preservation would be due to very low levels of biological activity. This would indicate that selective preservation is not a factor in low floral diversity when the overall level of preservation is excellent. A comparable argument can be developed using samples from the caliche facies of the Belly River Formation.

Although a relatively wide range of habitats has been ascribed to Classopollis-bearing plants (Srivastava, 1978; Vakhrameev, 1981; Alvin, 1982), it seems fairly certain that towards the end of the Late Cretaceous their ecological niche was mainly xerophytic (Pons et al., 1980). This is shown partly by the fact that "The frenelopsids (to which Classopollis belongs) of the Cretaceous all share to a lesser or greater extent the same syndrome of xeromorphic characters: reduced leaves, photosynthetic stems, usually very thick cuticles and sunken stomata, generally with the pit protected by at least one ring of papillae, if not two" (Alvin, 1982, p. 90). In addition, Sladen and Batten (1984) and Vakhrameev (1981, 1987) made a direct correlation between the high relative abundances of Classopollis and warm, arid and semiarid climates during the Jurassic. They maintained that the decrease in abundance during the Early Cretaceous was related to the onset of more humid conditions. With the advent of the angiosperms as a dominant group in the Late Cretaceous, warm, arid or semiarid habitats may have provided the final refugiums for this group. Hence, the probable presence of the xerophytic Classopollisbearing plants in the early Paleocene and late Maastrichtian of southwestern Alberta is predictive of a semiarid climate. Within this semiarid climatic setting the presence of water fern megaspores of the genus Azolla (Snead, 1969) provides palynological evidence for the existence of lakes in which muds were presumably deposited. These lakes could have provided an ecological niche for plants producing Concentricystes, which have been associated with relatively wet habitats in many parts of the world (Rossignol, 1962; Thiergart and Frantz, 1962; Norris, 1965; Shugayevskaya, 1969; Wang and Han, 1983). In this study, the presence of abundant Concentricystes is associated with fossil soil horizons, many of which contain caliche glaebules that have developed within a relatively dry climatic setting (see above). Hence, the occurrence of Concentricystes would be compatible with its having been derived from a soil fungus inhabiting welldrained soils within a semi-arid setting. However, as suggested previously, it is equally possible that the fungus(?)-producing Concentricystes lived in or

52

near ephemeral lakes, the muds of which eventually formed the soil horizons where caliche glaebules developed. Such a setting would explain its sometimes being associated with abundant fern miospores.

Coal-bearing facies Coals in the post-Wapiabi sequence occur both in the southern and central Foothills (Fig. 2).

They differ in stratigraphic setting, depositional environment and thickness. Thin coal beds separated by the Bearpaw marine shale and associated marginal-marine facies occur in the uppermost Belly River and in the lowermost St. Mary River Formations of the southern Foothills (Fig. 2). Uppermost Belly River strata with thin beds of coal are exposed at a Crowsnest River cutbank about 1 km northeast of Lundbreck (Fig. 13, section 3). The lower member of the St.

mc

tiC

1125

1120

~d

1115

~md

Smc

GO IC

;md

Ob 1110

1105 C

METRES ABOVE THE TOP OF THE WAPIABI FM Fig. 13. Coal-bearing marginal-marine sequences in the uppermost Belly River Formation exposed along Crowsnest River near Lundbreck (section 3), and in the lower member of the St. Mary River Formation exposed along Castle River south of Cowley (section 4), Stratigraphic settings of the sections are given in Fig. 2. Lithofacies symbols and codes are explained in Fig. 6.

53

Fig. 14. Coal-beating tidal flat sequence in the lower member of St. Mary River Formation at the Castle River cutbank (section 4). A. The middle part of the sequence: C = coal, Ob = oyster layer, Stud = low-angle bedded sandstone (compare with section 4 in Fig. 13). B. Close-up view of the oyster layer (Ob) underlain by coal (C). C. Closely packed shells of Ostrea glabra Meek and Hayden. D. Tiny sponge (?) borings visible on oyster shell.

M a r y R i v e r F o r m a t i o n w i t h t h i n c o a l b e d s at t h e t o p is e x p o s e d in t h e s t u d y a r e a in t h e C r o w s n e s t

k m s o u t h o f C o w l e y at t h e C a s t l e R i v e r c u t b a n k .

R i v e r v a l l e y n o r t h o f C o w l e y , as w e l l as s o m e 7

l i t h o l o g i c a l l y v e r y s i m i l a r ) a n d m a y s e r v e as a n

T h e l a t t e r e x p o s u r e is m o r e c o m p l e t e ( b o t h are

54

example of a marginal-marine, coal-bearing sequence (Fig. 13, section 4; Fig. 14). In the central Foothills, the stratigraphic equivalent of the marginal-marine, coal-beating facies of the southern Foothills is the " b " part of the first cyclothem within the Brazeau Formation. This part of the Brazeau Formation contains alluvial plain facies and lacustrine facies, sometimes with fresh-water stromatolites. Thin coal beds appear in the Brazeau Formation above the lacustrine facies in the " b " part of the second cyclothem. They become thicker upward in the " b " parts of the two subsequent cyclothems and finally form several thick and economically important coal seams in the "b" part of the fifth cyclothem (the Coalspur coal zone). These coals were formed in extensive swamps in an alluvial environment (Jerzykiewicz and McLean, 1980). Thin coal beds associated with fluvial facies have also been found in the southern Foothills within the second member of the Belly River Formation (the lower sandstone-shale member of Wall and Rosene, 1977). In the Crowsnest River valley area this coal forms thin lenses within carbonaceous shales but farther northward its thickness may reach 1.8 m locally (MacKay, 1934).

Marginal-marine facies Coals associated with marginal-marine deposits occur both below and above an open-marine Bearpaw shale (Fig. 13, sections 3 and 4). A marginal-marine environment of deposition for both sections may be inferred from the inorganic sedimentological features of the deposits as well as from the fossils. The coal beds in both sections form end members of fining-upward cycles composed of fine- to very fine-grained sandstone (lith-

ofacies Smc), organic-rich mud-shale and siltstone with minor intrabeds of rooted mudstone and ironstone concretions (lithofacies Fsm), and densely rooted carbonaceous mudstone (lithofacies Fmc), which grades into coal. The coal bed in section 4 is overlain by an oyster layer of up to 2.0 m in thickness (Figs. 13 and 14). The lower portion of this layer (lithofacies Ob) is built up with randomly scattered and closely packed shells of Ostrea glabra Meek and Hayden (Fig. 14C), and varieties and/or subspecies of Ostrea glabra (for synonyms see Warren, 1931; Allan and Sanderson, 1945). Small crevices between the shells are filled with mud and rare debris derived from shells. Some of the shells seem to be attached to each other, but the characteristic internal structure resulting from the upward growth of undisturbed colonies (Galtsoff, 1964; Frey and Howard, 1969) was not observed. The shells are generally well preserved, with some signs of erosion and leaching. The upper portion of the oyster layer (hthofacies Go) contains a sandy matrix and occasionally reveals crude, subhorizontal bedding as well as concave-up secondary erosional surfaces. The shells are more loosely packed and eroded than those in the lower portion of the layer. The contact of the oyster layer with the underlying coal is gradational over a thin interval (Fig. 14A, B); the lowermost portion of the layer immediately overlying the coal contains carbonaceous mud infilling crevices between the shells. Communities of oysters, thick-shelled epifaunal bivalves capable of producing bioherms, are highly tolerant of salinity fluctuations. They may occur in marginal-marine hypersaline environments as well as in brackish waters (Sellwood, 1978). Pres-

Plate II. Representative latest Campanian palynomorphs occurring in both the basal marginal-marine, coal-bearing facies of the St. Mary River Formation (section 4) and the lacustrine facies within cyclothem Ib of the Brazeau Formation (section 10). 1. Inaperturotetradites scabratus Tschudy 1973; GSC 89716. 2. Erdtmanipollis procumbentiformis (Samoilovitch) Krutzsch 1966; GSC 89717.3. Cranwellia rumseyensis Srivastava 1966; GSC 89718. 4. Mancicorpus albertensis Srivastava 1968; GSC 89719. 5. Liliacidites mints Srivastava 1969; GSC 89720. 6. Mancicorpus glaber (Chlonova) Krutzsch 1969; GSC 89721. 7. Aquilapollenites sentus Srivastava 1969; GSC 89722. 8. Expressipollis sp. cf. E. barbatus Chlonova 1961; GSC 89723.9. Pulcheripollenites krempii Srivastava 1969; GSC 89724. 10. Mancicorpus tripodiformis (Tschudy & Leopold) Tschudy 1973; GSC 89725. 11. Siberiapollis montanensis Tschudy 1971; GSC 89726. 12. Montanapollis endannulatus Tschudy 1971; GSC 89727. All figures × 750.

.A

Ib

~iii~!ii!iiiil i

.....

i i i ~ ¸¸

~

i ~

mm

56

ent-day oyster deposits of the salt-marsh estuarine environment in Georgia (Hoyt et al., 1963; Redfield, 1967) described by Wiedemann (1972) occur in the intertidal and shallow subtidal zones as well as in supratidal marsh settings. The oyster layer in section 4 may be interpreted as a shell chenier associated with washover fan sandstone (lithofacies Smd, represented by layers of medium-grained sandstone with low-angle bedding, separated by thin intrabeds composed of fine-grained sandstone to sandy mudstone with wavy to flaser carbonaceous lamination and muddrapes). This would have been deposited in a supratidal marsh environment similar to that described by Wiedemann (1972, fig. 4). Such cheniers and washover fans may form at the margins of major sounds near the inlets where storm surges have their greatest effect (Chapman and Ronaldson, 1958; Greensmith and Tucker, 1969; Wiedemann, 1972). The oyster shells may be redeposited from the intertidal biocoenosis or subtidal accumulations. The latter possibility seems to be indicated by tiny borings on some oyster shells (Fig. 14D). Similar structures produced by the boring sponge Cliona are characteristic of shells from the subtidal zone of a Georgia salt-marsh estuary (Wiedemann, 1972, plate I, fig. 5). Oyster shells from the intertidal zone do not have these borings. The association of coal with lagoonal facies (lithofacies Fsm) and tidally influenced clastic sediments strongly suggests a supratidal marsh environment for the coal beds that occur above the Bearpaw shale in the southern Foothills. The coal-bearing sequence that occurs below the open-marine Bearpaw shale (Fig. 13, section 3) was probably also deposited in a tidally influenced marginal-marine depositional setting. The se-

quence comprises several fining-upward cycles. The lowest (section 3, between 702 and 708 m) consists of medium- to fine-grained sandstone with wavy mud-drapes (lithofacies Smd, probably of barrier bar origin) in the lower part, passing upward into dark, organic-rich mud-shale with numerous, large ironstone concretions (lithofacies Fsm of lagoonal origin). Several overlying cycles (section 3, between 708 and 722.5 m) are composed of fine-grained sandstone and siltstone (lithofacies Smc) in their lower parts, and beds of the Fsm lithofacies in the upper parts. Lithofacies Smc, consisting of alternating thin beds of fine- to very fine-grained sandstone and siltstone showing horizontal to low-angle inclined laminations marked by mud couplets may represent infilling of the lagoon by distal washover material. Coal beds underlain by rooted, carbonaceous mud-shale (lithofacies C and Fmc) are interpreted as deposits of back-barrier marsh environments. The classic "back-barrier" model of peat deposition (Hobday, 1974; Home et al., 1978), which depicts a coal-forming environment directly behind an active coastal barrier, can probably be applied only to thin and laterally discontinuous coals. A limitation of this model has been discussed by Cohen (1984), who postulated that: "all ancient "back-barrier" coals may not have formed near to an active shoreline" (Cohen, 1984, p. 233). A similar opinion recently was expressed by Breyer and McCabe (1986). They interpreted coals associated with tidal sediments as having been formed in swamps of a tidal channel complex extending 10-30 km inland from the main coastline. Although some sedimentological features of the coal-bearing sequences associated with the Bearpaw shale in the southern Foothills seem to

Plate III. Figures 1 to 5: Representative latest Campanian palynomorphs from the basal marginal marine, coal-bearing facies of the St. Mary River Formation (section 4). 1. Alterbidinium sp.; GSC 89728. 2. Pediastrium sp.; GSC 89729. 3. Aquilapollenites leucocephalus Srivastava 1968; GSC 89730. 4. Cicatricosisporites ornatus Srivastava 1972; GSC 89731. 5. Foveosporites pantostikos Phillips & Felix 1971; GSC 89732. Figures 6 to 9: Index species for the early Maastrichtian from the Brazeau Formation, top cyclothem Ib and cyclothem IIa (section 10). 6, 7. Wodehouseia edmontonicola Wiggins 1976: (6) GSC 89733; (7) GSC 89734. 8. Kurtzipites andersonii Srivastava 1981; GSC 89735. 9. Orbiculapollis globosus Chlonova 1961; GSC 89736, Figures 10 to 12: Index species for the mid-Maastrichtian Scollardia trapaformis Zone VI assemblage, Brazeau Formation, cyclothem IVb (section 11, located on the Blackstone river, 52042'55" N, 116°18'30 '' W). 10. Mancicorpus gibbus Srivastava 1968; GSC 89737.11, 12. Scollardia trapaformis Srivastava 1966: (11) GSC 89738; (12) GSC 89739. All figures x750.

V

ii ¸

V

58 indicate proximity to the shoreline (e.g. lithofacies Ob), much more information would be needed to determine the type of shoreline and the nature of the swamps that developed prior to the main transgression and during the regression of the Bearpaw sea. Any attempt at a broader paleogeographic interpretation should include the fact that these recurrent periods of swamp development and peat accumulation in the southern Foothills coincide with lacustrine sedimentation without peat accumulation in the central Foothills.

Palynology. Samples from the coal and associated mudrocks from the basal beds of the St. Mary River Formation (Fig. 13, section 4) provide examples of the character of the palynoflora within a coal-beating, marginal-marine setting. The assemblages described below are characterized by the frequent presence of morphologically exotic angiosperm pollen species (Plate I, 11-19; Plate II, 1-12, Plate III, 3) including triprojectate pollen (Aquilapollenites, and Mancicorpus). A very similar assemblage of angiosperm pollen is present in the latest Campanian lacustrine facies of the Blackstone River section, cyclothem lb. As these assemblages of angiosperm pollen are associated with both high water table marginal-marine and lacustrine facies, they can be taken as being representative of a humid, latest Campanian palynoflora assemblage. The overall diversity of this assemblage associated with wetness contrasts sharply with that illustrated for the slightly older, calichebearing facies of the Belly River Formation (Plate I, 1-10); this difference is unrelated to their relative ages. Superimposed upon the climate related characteristics of the assemblage are the effects of the local environment of deposition. An analysis of the succession of assemblages recovered from section 4 is given below to illustrate differences imposed by depositional facies, as factors separate from climate. Samples from the two Fsm lithofacies in the lower part of the section all contain abundant cuticle and fusinitic debris. Three of the samples also contain numerous specimens of gymnosperm pollen, angiosperm pollen and miospores, together with rare dinoflagellates. A1-

though Taxodiaceous-Cupressaceous pollen dominates, considerable diversity exists in the more morphologically exotic angiosperm pollen and miospores present, albeit at abundances of less than 1%. Angiosperm pollen present include: Aquilapollenites borealis Srivastava 1968, A. clarireticulatus Samoilovitch 1965, A. funkhouseri Srivastava 1968, A. leucocephalus Srivastava 1968, A. quadrilobus Rouse 1957, A. rectus Tschudy 1969, A. sentus Srivastava 1969, and A. trialatus Rouse 1957, Cranwellia rumseyensis Srivastava 1966, Expressipollis sp. cf. E. barbatus Chlonova 1961, Mancieorpus glaber (Chlonova) Krutzsch 1969, M. tripodiformis (Tschudy & Leopold) Tschudy 1973, Montanapollis endannulatus Tschudy 1971, Pulcheripollenites krempii Srivastava 1969, Siberiapollis sp. and Tricolporopollenites sp. 2 in Norris et at. (1975). Spores present include massulae of the freshwater fern Azolla, several species of Ghoshispora, Liburnisporis adnacus Srivastava 1972, Triletes bettianus Srivastava 1972 and Triporoletes sp. One specimen of the freshwater algae, Pediastrium (Plate III, 2) was seen. A sample of dark-grey to black mudstone overlying the grey to olive-grey mudstone more typical of the Fsm lithofacies and underlying the coaly shale of the Fmc lithofacies contains numerous specimens falling within the combined morphological variation of Cicatricosisporites ornatus Srivastava 1972 and Foveosporites pantostiktos Phillips & Felix 1971 (Plate III, 4 and 5), a pair of species not found in association with the lacustrine facies of the Blackstone River Section. The assemblage of the Fmc coaly shale lithofacies differs from that of the underlying Fsm lithofacies by the presence of Aquilapollenites augustus Srivastava 1969 and Inaperturotetradites scabratus Tschudy 1973; common Aquilapollenites funkhouseri, A. leucocephalus and the dinoflagellate Alterbidinium (Plate lII, 1); and, like the underlying dark mudstone, contains abundant miospores of the Cicatricosisporites ornatus-Foveosporites pantostiktos complex. The overlying coal (Fig. 13, section 4, lithofacies C) is like the underlying coaly shale in containing Aquilapollenites augustus and common A. leucocephalus but differs in the infrequent occurrence of Aquilapollenites trialatus, the common

59 presence of A. senonicus Mchedlishvili in Samoilovitch & Mchedlishvili 1961 and Liliacidites mirus Srivastava 1969, and the absence of the other species of Aquilapollenites listed above. Rare specimens of Erdtmanipollis were also observed. Up to 9% of the total pollen assemblage of the coal is formed by monolete spores (Laevigatosporites and Hazaria) in an assemblage otherwise dominated (80%) by Taxodiaceae-Cupressaceae pollen. The remainder of the assemblage is composed of angiosperm pollen (9%; of which 3% are Cranwellia ) and Cyathidites (1%). Like the coaly shale underlying the coal, the oyster coquina above the coal also contains a number of dinoflagellates (about 1% of the total assemblage), most also being Alterbidinium. In addition, unique to this facies is the abundant presence of the miospore Gleichenidites, which constitutes 11% of the assemblage. Modern representatives of the family Gleicheniaceae are generally subtropical to tropical in distribution and weedy in habit, growing on well drained or marshy, sterile soils often marginal to forests (Tryon and Tryon, 1982). Such a setting fits with that of the Ob lithofacies. The following paleoenvironmentally significant inferences may be drawn from the sequence of palynological assemblages in section 4. It would appear that the main source of organic material during deposition of the Fsm lithofacies was continental, as indicated by the type of organic debris, the presence of a diverse suite of pollen and miospores and the only rare and sporadic occurrence of dinoflagellates. In addition, the apparent responsiveness of species to changing microenvironments (for example the conspicuous presence of the Cicatricosisporites ornatus-Foveosporites pantostiktos complex in the dark-grey to black mudstone at the top of the Fsm lithofacies) suggests that a continental flora existed at the site of deposition; at least by the time of deposition of the top of the Fsm lithofacies. As Alterbidinium is commonly found in both the Ob lithofacies and the Fmc coaly shale lithofacies, the latter was presumably deposited under at least brackish conditions. The coal is therefore bounded by sediments deposited under a direct marine influence, although no evidence of a marine

incursion during its deposition exists. It is therefore likely that the precursor swamp was raised and supratidal, as concluded from analysis of sedimentological data. It is also likely that the swamp was treed by gymnosperms, as pollen of the Taxodiaceae-Cupressaceae complex totally dominate the palynological assemblage of the coal. The percentage of herbaceous vegetation present is difficult to determine reliably from the pollen and spore profile, although its presence is indicated by the accessory occurrence of fern miospores. The variations in the plant assemblages detailed above are directly related to the immediate environment of deposition. However, in general the assemblages from this interval are diverse and many of the angiosperm pollen species present are morphologically complex. These assemblages are like those found in association with correlative lacustrine deposits along the Blackstone River and in the stratigraphically higher coal at the top of the Brazeau Formation (see following discussion). By inference, it is therefore concluded that the palynological assemblages indicate the existence of humid conditions during the deposition of the marginal-marine sequence at the base of the St. Mary River Formation. This climatic factor would have contributed to the formation of peat when superimposed upon the depositional environment associated with the proximity of the Bearpaw seaway.

Lacustrine facies Although the thickest interval of lacustrine rhythmites (lithofacies F1) containing freshwater stromatolites occurs in the central Foothills within the barren portions of the Brazeau Formation (correlative to the coal-bearing deposits associated with the Bearpaw shale of the southern Foothills discussed previously), they have also been encountered in association with coal-bearing facies in the upper part of the Brazeau Formation and in the uppermost part of the Coalspur Formation (Fig. 20, section 15). The lacustrine facies within the barren '° b" part of the first cyclothem of the Brazeau Formation (Fig. 15, section 10; Fig. 16A, B) is represented by rhythmically laminated siltstone and claystone (F1

60

3h le

~r

~i~

METRES ABOVE THE TOP OF THE WAPIABI FM

Fig. 15. Fluvial and lacustrine facies of the lower part of the Brazeau Formation in the standard section along Blackstone River. Stratigraphic settings of the sections are given in Fig. 2. Lithofacies symbols and codes are explained in Fig. 6. Section 9 shows a fragment of "a" part of the first cyclothem. Section 10 shows the lacustrine facies within the "b" part of the first cyclothem.

lithofacies) associated with fine-grained microc r o s s - b e d d e d sandstone, d a r k - g r e y structureless m u d s t o n e , thin c a r b o n a c e o u s shale a n d bentonite. H e r e a n d there are layers or lenses of limestone revealing s t r o m a t o l i t i c structures. The most characteristic features of this F1 lithofacies are the distinct l a m i n a t i o n s c o m p o s e d of a l t e r n a t i n g d a r k - a n d light-coloured l a m i n a e (Fig. 16B) ranging from less than 1 m m to several centimetres in thickness. L a m i n a couplets a b o u t 1 - 3 m m in thickness are the m o s t c o m m o n . The couplets are usually c o n t i n u o u s over several metres of exposure. Some of t h e m are slightly inclined to

the c o u p l e t b o u n d a r y . Small scours in some l a m i n a couplets, i n d i c a t i n g w e a k wave or current activity, are o c c a s i o n a l l y present. P e n e c o n t e m p o r a n e o u s d e f o r m a t i o n a l structures are c o m m o n a n d consist of: (1) c o n v o l u t e l a m i n a t i o n s , (2) small d o m e structures, which d i s r u p t the l a m i n a t i o n s a n d are believed to be w a t e r escape structures (Lowe, 1975), a n d (3) small vertical tubes, which are most likely to be relicts of rootlets or p l a n t stems (Fig. 16B). O t h e r evidence of biotic activity is not apparent. T h e darker, clayey m u d s t o n e l a m i n a e contain organic matter, thus differ f r o m the lighter ones. T h e p a r t i c l e size difference in the l a m i n a e is

61

Fig. 16. Fluvial and lacustrine facies of the lower part of the Brazeau Formation exposed along Blackstone River. A. Transition between mainly fluvial ("a ") and mainly lacustrine ("b") portions of the section. B. Rhythmically laminated siltstones and claystones of lacustrine origin. Note the water escape structure (E), and the burrows (B). C. Fining-upward cycles of the "a" portion of section 9. n o t always visible, although some of the light l a m i n a e are coarser a n d consist of silt a n d very fine sand. The rhythmically l a m i n a t e d siltstone a n d clay-

stone facies is occasionally very intensively silicified. The process of silicification has been attrib u t e d to s y n d e p o s i t i o n a l volcanic activity (Jerzykiewicz a n d McLean, 1977). As a result of silicifi-

62 cation, the laminated siltstones and claystones are altered into very dense chert-like rock. Microscopically, the rock is predominantly cryptocrystalline with a small percentage of microcrystals. Much of the cryptocrystalline groundmass and most of the crystals show a preferred extinction position parallel to the lamination. The lamination is very well preserved. Semi-quantitative X-ray diffractography indicated that the dark laminae are composed of 86% quartz, 10% feldspar, and 4% illite. The light laminae are composed of 91% quartz and 9% feldspar. Rhythmically laminated sediments (rhythmites) are common in ancient lacustrine deposits (van Houten, 1964; McLeroy and Anderson, 1966; Link and Osborne, 1978; Tucker, 1978; Schafer and Sneh, 1983). Conditions favorable for deposition of such continuous, even and parallel laminae of fine-grained clastic or carbonaceous sediments may exist in various low-energy, quiet-water settings. Seasonal changes in water viscosity, chemical composition, and number of clastic particles may lead to a marked separation of the different grain sizes a n d / o r an alteration in sediment com-

p o s i t i o n ( S c h w a r z b a c h , 1963; S t u r m and Matter, 1978). Particularly well known rhythmites are the Pleistocene varved clays, but similar deposits, not necessarily of glaciolacustrine origin, are found throughout the stratigraphic record from the Precambrian, as well as from recent lake environments (Johnston, 1922; Kindle, 1930; Clemmey, 1978). The open-lacustrine rhythmites may grade laterally into marginal lake a n d / o r fluvial facies (Fannin, 1969; Tucker, 1978; Schafer and Sneh, 1983). An association of the rhythmically laminated siltstone and claystone lithofacies with the finegrained, micro-cross-bedded sandstone and the dark-grey, organic-rich mudstone containing the stromatolitic forms (Fig. 15, section 10) indicates a transition from an open- to marginal-lacustrine environment of deposition. The stromatolitic structures are visible in limestone, forming either layers up to 0.2 m in thickness or lenticular bodies enveloped in dark-grey, structureless mudstone. Internally, the limestone layers and lenses consist of alternating pale laminae of pure calcite and dark-grey laminae of

Fig. 17. Stromatolitic structure in a tabular layer of limestone. Note the convex upward laminae of calcareous mudstone (S) partly disrupted and deformed by the laminae built up with calcite crystals (C); lower part of the Brazeau Formation (for location see Fig. 15, section 10).

63

Fig. 18. Largeoncoliticstructure. Note the concentricorganizationof laminae.The dark, calcareousmudstonelaminae are deformed by calcite crystals due to the diagenetic neomorphism; lower part of the Brazeau Formation (for location see Fig. 15, section 10).

calcareous mudstone. The internal fabric of the rock resembles a stromatolitic (Fig. 17) or oncolitic structure (Fig. 18). Under the microscope, the alternating laminae that form stromatolitic patterns appear mineralogically different, but algal filaments are not preserved. The dark-grey, calcareous mudstone laminae are composed of yellow-brownish micrite with some clay minerals, the light ones consisting of well-developed calcite crystals. These overgrow and deform the micrite laminae indicating that the diagenetic neomorphism was very intensive. The algal filaments must have been destroyed by oxidation and then obliterated by diagenetic recrystallization. The tabular layers are composed of convex-upward laminae and may be compared with the laterally linked algal structure (Logan et al., 1964). They are similar to the stromatolite sheets and stromatolite fragments described by Fannin (1969, fig. 2a) and to the tabular stromatolites of Schafer and Stapf (1978, fig. 5). The lenticular forms, showing a concentric organization of laminae (Fig. 18), are similar to the encapsulating stromatolites or oncolites described by Schafer and Stapf (1978, fig. 6) and to

"Algen-Stromatolithen" of Wagner and Lamprecht (1974, Abb. 2). They resemble the ridged oncolites of Dixit (1984) both in terms of internal structure and ridged ornamentation on their surfaces. The oncolitic structures that occur in the Brazeau Formation indicate long-lasting high-energy conditions in the marginal zone of a lake. The waves and currents in this perennial lake must have been occasionally strong enough to roll the large oncolites around as they formed (Dixit, 1984). Although most algal limestones with stromatolitic fabric have been recorded and classified from marine environments (Mawson, 1929; Rezak, 1957; Ginsburg, 1960; Logan et al., 1964), they are also known in geological records from lacustrine facies (Bradley, 1929; Fannin, 1969; Stapf, 1973; Wagner and Lamprecht, 1974; Surdam and Wray, 1976; Schafer and Stapf, 1978; Dixit, 1984). Recent lacustrine algal limestones and stromatolites have been described from the shore zones of various lakes in North America (Dean and Eggleston, 1975; Eggleston and Dean, 1976; Osborne et al., 1982), Africa (Abell et al., 1982) and Europe (Schottle, 1969; Schneider, 1977; Schafer and Stapf, 1978).

64

AIluvial facies The major post-Wapiabi coal deposits in the central Foothills are associated with units of floodplain and channel lithofacies. The coalbearing intervals in the upper parts of the Brazeau and Coalspur Formations are correlative with the upper parts of the St. Mary River and Willow Creek Formations respectively (Fig. 2). The coals occur within two types of lithofacies sequences. The first is composed mainly of fine-grained litho-

types represented by organic-rich mudstone, mud-shale, silty mudstone and siltstone. These usually form sequences several metres thick and devoid of rapid lithological changes (Fig. 19, sections 11 and 12). Interbedded sandstones are fine-grained and limited to thin beds. The major channel layers are very rare. Coal beds are usually less than 1 m thick. The second type of coal-bearing sequence is characterized by rapid lithological changes. It con-

St ,Ge+Gi :g ;h ii

3p

St 921

Gi

) Sh Gi / /

METRES ABOVE THE TOP OF THE WAPIABI FM

Fig. 19. Coal-bearing upper part of the Brazeau Formation in the standard section along Blackstone River. Stratigraphic settings of the sections are given in Fig. 2. Lithofacies symbols and codes are explained in Fig. 3.

65

1370~

Sh

1366~

1362~ Sr

Sr

Sh Sr

Sh

St Sh Sh r

~h ~r

METRES ABOVE THE TOP OF THE WAPIABI FM Fig. 20. Coal-bearing upper part of the Coalspur Formation in Coalspur-Robb area. Stratigraphic settings of the sections are given in Fig. 2. Lithofacies symbols and codes are explained in Fig. 3.

tains thick coal beds as well as layers several metres thick of medium-grained sandstone (Fig. 20, sections 13 and 14). These two types of lithofacies sequences represent different settings within the meandering stream environment. The first was a floodplain, isolated from the active channel, while the second was probably a backswamp area, behind levees of active channels (Jerzykiewicz and McLean, 1980).

The main floodplain lithotype is dark-grey, organic-rich mudstone. The organic material is either of submicroscopic size, dispersed throughout a non-laminated rock mass (mudstone lithofacies Fm), or forms concentrations of larger plant fragments, mainly leaves and twigs, resulting in distinct laminations (mud-shale lithofacies Fmc). Thin beds of the mud-shale usually underlie coal beds. Upright rootlets, root casts and root bur-

66 rows are common in the mudstone but have also been encountered in sandstone layers interbedded with coal (Fig. 21C). Characteristic features of the organic-rich mudstone are the common occurrences of sideritic nodules. Pebble-sized nodules are the most common, but some reach 0.5 m in diameter. In some sections there are sideritic beds up to 0.2 m in thickness. Today, organic-rich mud and peat accumulate in poorly-drained swamps. Such swamps form in floodplain areas where the groundwater table is normally at, or slightly above, the depositional interface (Weimer, 1973). Extensive and long-lasting swamps may develop in the delta plain environment (Coleman and Gagliano, 1965; Horne et al., 1978) as well as in non-deltaic alluvial settings (Coleman, 1966; Gradzinski and Doktor, 1985). Stagnant water conditions are the major factor affecting sediments deposited in poorlydrained swamps. Reducing conditions are caused by high accumulations of organic matter under continuous water cover. Under such conditions the sediment is rich in well preserved, indigenous plant fragments, including spores and pollen, as well as in syngenetic mineral inclusions. Syngenetic calcium and iron carbonate concentrations often occur in the form of nodules and rims surrounding rootlets. Iron carbonate concentrations (siderite nodules) are much more abundant, especially in deeper and older layers. They are probably the result of diagenetic processes changing the original CaCO 3 nodules to siderite (Coleman, 1966). The accumulation of organic-rich sediment in the poorly-drained swampy floodplain can be periodically interrupted either by flood events or by a lowering of the groundwater table. Examples of the latter are recorded in the occurrence of light-greenish grey and light-brown mudstones (lithofacies Fg) containing much less, or virtually no, carbonaceous material. These mudstones represent periods (seasons ?) of better drainage in the swamp environment resulting in oxidizing conditions. Flood events are marked by thin layers of siltstone and fine-grained sandstone (lithofacies Fs, Sh and Sr) of splay origin. Lacustrine sedi-

ments represented by rhythmites and fossiliferous mudstones (lithofacies FI and Fmf) were laid down in ephemeral floodplain ponds. The flood events are particularly well pronounced in the second type of coal-bearing sequence. Here the proximity of active channels results in alternation of coal with numerous thin mudstone and siltstone interbeds as well as with thick layers of fine- to medium-grained sandstone (Fig. 20, sections 13 and 14; Fig. 21A, B). Sandstones form compound layers up to 4 m thick. Their internal structure is considerably different from that of major channel layers. Neither the channel lag deposits nor the concave-up erosional bases are present. Unlike the major channel layers, they have at their base a fine-grained sediment forming a thin bed of rippled or structureless fine-grained sand, siltstone or silty mudstone. This basal portion of the compound sandstone layer contains abundant carbonaceous debris including leaves and twigs. Overlying fine- to mediumgrained sandstone reveals horizontal or slightly inclined bedding. The lower contact of this unit is usually erosional, although a gradation between the incipient fine-grained deposits and the overlying medium-grained sandstone has also been seen. The fine- to medium-grained sandstone in the thicker compound layers (Fig. 20, section 14 at 1360 m; Fig. 21A) is interbedded with thin beds of mudstone. These subdivide the compound layer into individual sandstone beds that show an obscure fining-upward trend. The compound sandstone layers enclosed in coal can be interpreted in terms of crevasse splay deposits prograding into a backswamp environment. Crevasse splay deposits of considerable thickness are known from recent and ancient fluvial systems (Coleman, 1969; Gersib and McCabe, 1981; Smith, 1983; Gradzinski and Doktor, 1985). The geometry and lithofacies distribution within the crevasse splay deposits are probably the most variable of all fluvial deposits. Crevasse splay deposits similar to those described above have been recorded in modern anastomosing fluvial systems by Smith (1983). They also show a consistent pattern of coarsening-upward then fining-

67 u p w a r d : prior to deposition of the m a i n splay

Discussion and conclusions

s a n d sheet, a thin basal u n i t of silt a n d fine sand, followed b y a n organic waterlogged litter, is laid d o w n o n m a r s h or peat deposits.

Three

external controls u p o n

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m

Fig. 21. Coal-bearing sections in Coalspur. A. Section 14 in road cut along Highway #47. For designation of units compare with columnar section 14 in Fig. 20. B. Section 13 in abandoned open pit on a hill east of Coalspur. Compare with columnar section 13 in Fig. 20. C. Upright root casts in sandstone interbedded with coal.

68

corded in the post-Wapiabi sequence of the Rocky Mountain Foothills. Although the tectonic factor seems to be the major one (McLean and Jerzykiewicz, 1978), the other controls are also lithologically expressed in the stratigraphic record. An attempt to assess the interrelationships among these three controls is now becoming possible with the development of lines of correlation between post-Wapiabi deposits in the southern and central Foothills (Fig. 2). The stratigraphic subdivision of the entirely

non-marine, mainly fluvial, post-Wapiabi sequence in the central Foothills is based on cyclicity interpreted as developing in response to source area tectonism (McLean and Jerzykiewicz, 1978). Five mappable cyclothems related to major orogenic pulses in the Cordillera have been distinguished in the Brazeau-Coalspur sequence (Jerzykiewicz, 1985; Fig. 2 and Fig. 22). Although some of the cyclothems (II, III and IV) are laterally confined to the central Foothills area, the overall cyclic lithostratigraphic framework in the

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69 central Foothills can be correlated with the lithostratigraphic subdivisions of the southern Foothills. Cyclothem I (or lower part of the Brazeau Formation) corresponds with the Belly River and Bearpaw Formations of the southern Foothills; cyclothems II, III and IV (or upper part of the Brazeau Formation) correspond with the St. Mary River Formation; and cyclothem V (or Coalspur Formation) corresponds with the Willow Creek Formation. The overlying Paskapoo Formation is correlative with the Porcupine Hills Formation (Fig. 22). The penesynchroneity of the major lithostratigraphic changes in the central and southern Foothills, as indicated above, strongly suggests a regional control. If this control was tectonism, then the major pulses of orogenic activity must have occurred almost synchronously along much of the Rocky Mountains. However, for the Cretaceous portion of the post-Wapiabi sequence deposition, approximately 15 Ma, three eustatically controlled regressive events are recognized (Kauffman, 1977, regressive cycles 8-10; Haq et al., 1987, third-order cycles within upper part of supercycle UZA-4). The lowest one of these three regressive cycles is probably represented by the Belly River Formation. The transgressive cycle separating the lower and middle regressive cycles of Kauffman is probably represented by the Bearpaw Formation in southern Alberta with the correlative interval in the central Foothills being represented by lacustrine and alluvial deposits. The transgressive cycle separating the middle time of regression from the highest regression (Kauffman, 1977; regressive cycles 9 and 10, respectively) is not recorded by a marine transgression in the Foothills. The highest of the three regressive cycles probably corresponds to the long recognized late Maastrichtian regression. It is therefore possible that some of the major lithological cycles in the Foothills reflect eustatic changes in sea level but that the effects of this control are superimposed upon the effects of tectonism. These two external controls are interdependent, as discussed by Kauffman (1977). Paleoclimatic variations expressed by the distribution of climatically sensitive facies are visible both laterally between the central and southern

Foothills and vertically in the post-Wapiabi sequence of strata. The lateral differences between the central and southern parts of the basin are expressed not only by the distribution of coal- and caliche-bearing facies and their associated palynological assemblages within floodplain deposits, but also by changes in the style of fluvial channels. Post-Wapiabi sedimentary facies in the Alberta Foothills may be grouped into six facies associations (Fig. 22). Three distinguishable fluvial facies associations (FCO, FCA and FIT) represent climatically different environments. The humid fluvial facies association (FCO) contains organicrich to coal-bearing floodplain deposits associated with meandering channels of high sinuosity. The semiarid fluvial facies association (FCA) is composed of varicoloured floodplain mudstones containing mature caliche paleosol horizons. During deposition of the FCA facies association a vast semiarid alluvial plain drained by broad and mobile channels extended eastward from the flanks of the rising Rocky Mountains. Periodic heavy rainfall modified the floodplain into a braidplain with numerous ephemeral streams eroding the caliche soil. The semiarid fluvial facies is limited to the southern part of the basin. No signs of a caliche facies have been found in the post-Wapiabi strata of the central Foothills. Instead, floodplain deposits in this part of the basin contain numerous coal-bearing intervals. Spatial distribution of the semiarid and humid fluvial facies associations in the central and southern Foothills and central Plains in the late Maastrichtian and early Paleocene (Fig. 23) may serve as an example of climatic diversity across the basin. The upper Maastrichdan semiarid fluvial facies assemblage of the Willow Creek caliche member is correlative with the lower parts of the Coalspur and Scollard Formations that contain grey or greenish grey mudstone, and are barren of coal and devoid of caliche facies. This type of floodplain deposit, usually associated with low sinuosity meanderbelt facies, commonly occurs throughout the post-Wapiabi sequence both in the central and southern Foothills (Fig. 22). It is referred to as the intermediate fluvial facies association (FIT in Figs. 22 and 23). The facies differences between the lowermost

70

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Paleocene strata i n the southern a n d central parts of the b a s i n indicate that the relative climatic differences had b e e n m a i n t a i n e d ; the u p p e r part of the Willow Creek F o r m a t i o n is represented by two facies associations, semiarid ( F C A ) a n d intermediate (FIT), which are correlative with the

Coalspur coal zone of the central Foothills, conraining n u m e r o u s thick coal seams a n d n o signs of aridity (Fig. 23). A h u m i d alluvial p l a i n with well developed, poorly d r a i n e d swamps, which were the sites of peat a c c u m u l a t i o n in the central part of the basin, was n o t developed in the southern

71 part of the basin, with one minor short-term exception. The 2 cm coaly shale associated with the Cretaceous/Tertiary boundary in southern Alberta is unique within this predominantly calichebearing facies. It is likely that this thin layer is indeed a record of a short term increase in wetness in the environmental conditions prevailing immediately subsequent to the Cretaceous/Tertiary boundary event. The semiarid fluvial facies association occurs twice in the stratigraphic column of the southern Foothills: in the upper part of the Belly River Formation and in the lower part of the Willow Creek Formation (Fig. 22). These semiarid fluvial facies may be considered as end members of successions consisting of the following facies associations: marine (MR), nearshore marine (MS) and intermediate fluvial (FIT). Such positions of the semiarid facies in the stratigraphic record strongly suggest an interrelationship between the semiarid facies and the location of the seashore. The Belly River semiarid facies coincides with the peak of the regression in mid-Campanian time and the one in the Willow Creek Formation coincides with the major late Maastrichtian regression (Obradovitch and Cobban, 1975; Williams and Stelck, 1975; Kauffman, 1977; Haq et al., 1987). The conclusion that the regressions of the sea resulted in a trend of increasing aridity, as recorded in the stratigraphic column of the postWapiabi succession, is therefore justified. These trends are marked in the central Foothills by changes from the humid fluvial facies associations (coal-bearing intervals) to the intermediate fluvial facies associations (barren intervals) which stratigraphically coincide with the intermediate and semiarid facies associations of the southern Foothills (Fig. 22). This coincidence of the changes in the paleoclimatic conditions across the basin supports the idea of a broad control on the climate. The changing distance from the seashore might be expected to have an influence on the energy regime of the distributary systems and on the position of the groundwater table in the floodplain environment, and therefore indirectly upon the facies present. However, the coincidence of the facies changes between the central and southern parts of the basin together with the overall tend-

ency for the southern part of the basin to be drier during times of greater continentality requires additional explanation. Although tectonically generated physiographic changes in the source area may produce local climatic differences reflected in facies variations (Miall, 1984), in the case discussed here, the orographic influence on the climate was probably combined with another external control. The mode m climatic regime in Alberta can be taken to represent times of regression of the mid-continental seaway. At present, significant climatic differences exist between southern and central Alberta. The map of soil moisture regimes (Fremlin, 1974, p. 43) shows semiarid to subarid regimes in the south and southeastern part of the province, whereas the soil in central and northern Alberta remains subhumid to humid. Indeed, the difference in the soil profiles between southern and central Alberta is quite distinct and is expressed by the common occurrence of calcium carbonate concentrations (incipient caliche) in the southern part of the province. The aridity of this area, and the prairies of the northwestern interior of the United States, is caused largely by the rainshadow effect of the northwest-southeast-trending Rocky Mountains (Birdsall and Florin, 1978) in combination with the upper altitude jet stream patterns. However, this effect is modified to the north to produce more subhumid conditions in the central and northern parts of the Foothills and adjacent plains. This modification is the result of polar air masses which are directed parallel to the mountain front, and westerlies interacting to produce more precipitation over the northern and central areas than further south. It might be assumed that during times of maximum transgression, the epicontinental seaway would provide an additional eastern and southeastern source of moisture-laden air which would reach the southwestern Foothills area unimpeded, thereby counteracting the effect of the rain shadow to some extent. From the palynological perspective, it is apparent that sample yield and the diversity and species composition of assemblages can provide climatically sensitive information. It is apparent from studying the sedimentological and palynological data how great an effect both large-scale

72

changes in facies associations and small-scale changes in lithofacies have on the composition of the palynological assemblages. The most unique compositional characteristics of the palynoflora from Campanian and Maastrichtian semiarid facies are the abundance of morphologically simple types of pollen and the near absence of Aquilapollenites and allied triprojectate pollen. This provides a basic tool for distinguishing semiarid from more humid facies in which triprojectate pollen, considered ubiquitous and biostratigraphically important throughout the Western Interior Basin of North America, are common. The above observations raise the question of how meaningful it is to connect the magnitude of Cretaceous/Tertiary boundary floral changes to apparent latitudinal shifts in the regional extent of floras using as a data set plant localities that are broadly based, with respect to age and geographic locality. For example, the purported upper Maastrichtian "Kneehill macrofloral locality" of Wolfe and Upchurch (1986) is in reality from the uppermost Campanian or lower Maastrichtian, silicified and laminated lacustrine sediments that are described in this paper. In addition to the implied age being incorrect in Wolfe and Upchurch, the locality is in a different facies association from those present in the late Maastrichtian of central Alberta. It is this "Kneehill locality" which presumably was the reason for extending a late Maastrichtian, subhumid, notophyllous, broad-leafed evergreen forest as far north as the latitude of the Edmonton basin. When a comparison was made with post-boundary floras it appeared as though a major shift southward in the deciduous forest regime had occurred at the beginning of the Paleocene. Without additional documentation, however, this can not be proven. It is realized that the subdivision of the postWapiabi stratigraphic record into facies associations is an attempt to simplify a very complex mosaic of facies resulting from the interplay between tectonics, sea level changes and climate. In some instances the impact of changing climate is well recorded, but some facies associations (such as the FIT) lack definitive climate sensitive deposits. In addition, the contribution of climate to the development of climate sensitive deposits in

settings obviously under the influence of other changing factors, such as sea level, is more difficult to interpret paleoclimatically. In these instances a second set of data can be obtained from palynology and climatic inferences can then be made. The foregoing type of study provides a logical basis for expressing the coal-bearing potential of specific, regionally restricted, stratigraphic units.

Acknowledgements J.H. Wall, Grant Smith and J.E. Brindle provided useful reviews. Their detailed written and verbal comments resulted in many improvements in the text. The technical competence of R.M. Kalgutkar and Brenda Davies was exemplified by the excellent quality of the palynological preparation available for this study. Curtis Evans contributed extensively to the field work during the summers of 1985 and 1986. Greg Nadon is acknowledged for providing palynological samples from the upper St. Mary River Formation.

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