Preliminary Observations on the Acid-resistant Microfossils from the Lower Paleozoic of Southern Saskatchewan

P.L. Binda 1, D.E. Sparks 1, N.C. Beaudoin 1, LO. Stasiuk 2, S.L. Bend 1, and A.A. Buchanan 1

Binda, P.L., Sparks, D.E., Beaudoin, N.C., Stasiuk, L.D., Bend, S.L., and Buchanan, A.A. {1996): Preliminary observations on the acid-resistant microfossils from the Lower Paleozoic of southern Saskatchewan; in Summary of Investigations 1996, Saskatche­wan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4.

The Lower Paleozoic siliciclastic rocks of the subsur­face of southern Saskatchewan reach a maximum thick­ness slightly in excess of 500 m and belong to the upper part of the Sauk and to the lower part of the Tippecanoe sequences of Sloss (1963). The lower part of the succession constitutes the easterly thinning of the Cambrian-Lower Ordovician sedimentary wedge deposited on the western passive margin of the North American continent (Figure 1 ). The upper part was deposited in a proto-Williston Basin that became separated from the western continental margin by the emergence of positive areas in Alberta (Mossop and Shetsen, 1994).

The Lower Paleozoic siliciclastic succession has been variously subdivided by different authors, but always on physical characteristics, viz. geophysical logs, lithology of drilling chips and of scant core material. Neither bios­tratigraphic nor isotopic analyses have been made to at­tempt a chronostratigraphic subdivision and correlation.

In this paper, we report a first attempt at obtaining acid­resistant microfossils and identifying some microfossil assemblages in the lowermost Paleozoic rocks of Saskatchewan. The data presented here were obtained from laboratory exercises carried out by two students (D.E.S. and N.C.B.) in a class taught by the senior author and by some follow-up with the other authors. At this stage, it is not yet possible to give a firm biostrati­graphic zonation of the succession because of the small number of samples analyzed and the ''tentative" taxonomic level of identification of the fossils. However, it is proposed to show that:

1) rocks suitable for palynological analysis occur in the succession, and

2) a variety of planktonic microfossils occur in these rocks, and

3) a biostratigraphic zonation may be possible.

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(1) Geology Department. Universily of Regina, Regina, SK S4S OA2. (2) Geological Survey of Canada, 3303 - 33rd Street, Calgary, AB T2L 2A7.

Saskatchewan Geological Survey

References to early stratigraphic work on the Lower Paleozoic silici­clastic rocks of Saskatchewan can be found in Fyson ( 1961 ) and Paterson (1971). Fyson, from a study of 72 oil exploration wells from the southwest comer of Saskatchewan, subdivided the siliciclastic succession into lower and middle Deadwood units, and an upper unit comprising both the top of the Deadwood Formation and all of the Winnipeg Formation. All three units, which were identi­fied mainly on the basis of geo­physical logs, tend to become finer grained to the west; however, the lower unit contains a larger amount of medium and coarse sand. Fyson (1961, p12-13) consid­ered the sandstones of the Winnipeg to be laterally equivalent

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to the shales of the upper Deadwood. He interpreted the pu~lish siltstones of the Deadwood as having formed 1n shallow water with periodical desiccation whereas greener glauconitic sediments would have been deposited in quieter water, in broad swales.

Paterson (1971 ), using criteria established by Kupsch (1952) and by others, discriminated the basal sand­stone of the Winnipeg Formation (Black Island Member) from the underlying glauconitic sandstone of the D~ad_wood Formation. The shaley upper part of the Winrnpeg was assigned to the Icebox Member. It should be noted that, in the Dakotas, Lefever et al. (1987) treated the two sub-units as formations, thus ele­vating the ~innipeg !O the rank of Group. Stratigraphy ~nd depositional environment of the Winnipeg Forma­t1~n are also treated by Vigrass (1971 ), and aspects of d1agenesis are discussed by Binda and Simpson (1989) and by Frizzo and Binda (1989).

~n. the basis of geophysical logs, Paterson (1989) sub­d1v1ded the Sauk Sequence of Saskatchewan into a lower unit correlative to the Earlie Formation of Alberta and an upper unit, which retained the name Deadwood Formation. In an unpublished honours thesis, Labelle (1994) subdivided the Sauk Sequence of Saskatchewan into four allomembers, the lower of which corresponds to Paterson's Earlie Formation.

Lefever et al. (1987) divided the Deadwood Formation of North Dakota into six correlatable informal lithostrati­graphic units. The basal A unit is a quartz arenite to gla~conitic quartz arenite with minor conglomerate, resting unconformably on the Precambrian basement. The th~ee uppermost units (D, E, and F) do not appear to continue into Saskatchewan on the isopach maps of Lefever et al. Members Band C, predominantly fine- to medium-grained sandstone with minor mudstone and carbonate, are shown to continue north of the interna­tional border and are probably equivalent to the Deadwood Formation of Paterson (1971, 1989).

Lefever et al. (1987) extrapolated the age of the Deadwood Formation from paleontological work done in Montana. Units A to Care interpreted to span the time between Dresbachian and middle Tremadocian. Member Fis shown to reach the middle Arenigian. The Cambrian-Ordovician boundary is inferred to occur near the top of the B member, thus within the Deadwood of Saskatchewan. An erosional unconformity representing some 30 million years of missing section separates the top of the Deadwood Formation from the overlying Caradocian Black Island Formation of North Dakota.

Reports of fossils in the Lower Paleozoic rocks of Saskatchewan are indeed scant. Jodry and Campau (1960) reported the occurrence of palynomorphs and ch_itinozoans in Ordovician carbonates overlying the Winnipeg Formation. Stasiuk (1994) reported the occur­rence of the coccoidal cyanophyte, Gloeocapsomorpha, in the Cambrian and Ordovician of Saskatchewan. Binda (1991) illustrated pyrite-infilled chitinzoans, scole­codonts, and filamental algae from the Icebox Member of the Winnipeg Formation. Recently, Nowlan et al. (1995) reported the occurrence of poorly preserved

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palynomorphs (acritarchs) in Cambrian strata from the subsurface of Alberta.

2. Sampled Lithologies

A detailed treatment of the lithostratigraphy and sedi­mentolog~ of the units is beyond the scope of this pa­per. The lithology of some fossiliferous cored inter­sections from two of the drill holes shown in Figure 2 are given in Figure 3.

In general, black, grey, and green shale and clayey silt­stone are the lithologies most favourable for preserva­tion of organic matter, whereas reddish and purplish shale, and well-sorted sandstone are conducive to its oxidation and destruction. As shown in Figure 3, both Earlie and Deadwood formations contain grey shales, both as relatively thick packages and as thin layers within sandstone. Most grey shale from the sampled intervals contain acid-resistant microfossils. Some fine­gr~ined g~aucon itic sandstone samples also yielded m1crofoss1ls. It should be emphasized again that our sampling of the Sauk Sequence was:

1) limited to a few drill holes (Figure 2), and

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Summary of Investigations 1996

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2) merely targeted at establishing the existence of favourable lithologies and not at a detailed zonation.

Acritarchs and other acid-resistant microfossils were found in the Icebox Member of the Winnipeg Formation in many drill holes sampled not only for this study but also in connection with investigations by Binda and Simpson (1989) and Binda (1991).

3. Methods

Grey and green shale, siltstone, and a few samples of glauconitic fine-grained sandstone were selected from cores drilled by various oil companies and stored at Saskatchewan Energy and Mines Subsurface Laboratory in Regina. Samples of 10 to 50 g each were thoroughly dusted and cleaned to avoid recent contami­nation.Twenty-six samples from the Earlie and Deadwood formations (Sauk Sequence) and approxi­mately an equal number of samples from the Icebox Member of the Winnipeg Formation were analyzed.

Most samples were treated according to standard palynological techniques (Traverse, 1988), avoiding, however, the use of HN03 in order not to destroy thin­walled acritarchs. Some samples were also macerated in HF, decanted, wet-sieved through a 100 mesh (149 µm) screen, and the residues picked with a fine brush under a stereoscopic microscope, using a slight modification of the technique illustrated by Butterfield (1990).

In addition, some Earlie and Deadwood samples were processed by one of us (L.D.S.) using epoxy­impregnated, whole rock samples, cut in sections parallel and perpendicular to bedding, ground and pol­ished with isopropyl alcohol-alumina slurry and exam­ined using reflected light microscopy (total magnification x190 to x640). Fluorescence spectral analyses were conducted using a Zeiss MPM 11 Universal incident light microscope and an Epiplan-neofluar oil immersion objective (Stasiuk et al., 1991 ). The thermal maturity of each sample was evaluated using the following fluores­cence parameters for the alginites and acritarchs: (i) Lmax which is the wavelength (in nm) representing the mean maximum fluorescence intensity, and (ii) the Red/Green quotient = lssonm/lsoonm-

4. Microfossil Assemblages

a) The Classification of Alginite and Acritarch Macerals

Alginite macerals are defined as being wholly organic, microscopic entities (<15 µm, >100's µm). that occur in fine-grained sedimentary rocks. The morphology of each alginite maceral represents the intact remnants of organic-walled phytoplanktonic and benthonic blue­green and green algae, and alginite macerals are often subdivided into 'unicellular' (e.g. Tasmanities, Leiosphaeridia), 'coccoidal' (e.g. Gloeocapsomorpha). or 'filamentous' (e.g. Nostocaceae) based upon their respective morphologies, and organizational habit (Stasiuk, 1994). Organic-walled macerals with spines,

160

cystal segmentation and other adorning features are un­officially classified as acritarch macerals within the liptinite maceral group. All sphaeromorphs from the Earlie and Deadwood formations in Saskatchewan have been classified as alginite sub-macerals Leiosphaeridia, with a further subdivision into Protoleiosphaeridia and Synsphaeridium categories.

b) Gloeocapsomorpha (Plate I: 1 and 2)

Microfossils belonging to the cyanophyte genus Gloeocapsomorpha, and probably of the two species G. prisca and G. hebeica, have been found in several samples of the Earlie, Deadwood, and Winnipeg forma­tions. In some samples they occur in great abundance. G/oeocapsomorpha has been reported from rocks as old as Proterozoic, thus it is of little biostratigraphic significance; however, in the Western Canadian Basin, the earliest recorded occurrence was from the Winnipeg Formation (Osadetz et al., 1989). The importance of Gloeocapsomorpha resides in the fact that it is the main organic component of Ordovician hydrocarbon source rocks (Stasiuk and Osadetz, 1990; Stasiuk et al .. 1991 ). Our finding of abundant remains of this cyanophyte in the oldest Paleozoic rocks in Saskatchewan may expand the scope for the search of hydrocarbon source rocks to lower parts of the stratigraphic section in the region.

c) The Earlie Formation Assemblage (Plate I: 3, 4, 5, 15, 17, and 18; Plate II: 1 to 4)

Characteristic acritarchs of the Earlie Formation are smooth to slightly ornamented sphaeromorphs that can be assigned to the form-genera Leiosphaeridium, Protoleiosphaeridium, Synsphaeridium, Timofeevia, and Michrystridium(?). It must be noted that Timofeevia is a common microfossil of the European Middle Cambrian (Vanguestaine, 1978); however, more work on these fossils is needed before the Earlie Formation can be assigned a Middle Cambrian age.

In addition to acritarchs, a number of organic fragments have been recovered. Some appear to be spines or elongated conical appendages (Plate I: 15; Plate II: 1 ), others (Plate I: 14 and 18; Plate II: 2 to 4) consist of arrays of up to 20 conical or cylindrical bodies, 10 to 30 µm long and 5 to 8 µm in diameter, attached to a tube a few µm in diameter. For now, these microfossils must be considered as incertae sedis. Photographs of the objects were sent to a few specialists on Lower Paleozoic palynology, but no identification was possible. One expert noted the morphological similarity to grap­tolites; however, the much smaller size of these forms makes an attribution to the class Graptolithina dubious at best.

d) The Deadwood Formation Assemblage (Plate I: 6, 7, 8, 14, and 16)

Samples of the Deadwood Formation contain acritarchs which occur also in the Earlie Formation, and forms which do not. Common to the two units are Gloeocapso­morpha, Leiosphaeridium, and Synsphaeridium. Among

Summary of Investigations 1996

• . I ... .

Plate I - 1 and 2: Gloeocapsomorpha sp.; 3: Leiosphaeridium sp., Earlie Fonnation; 4: Synsphaen"dium sp., Earlie Fonnation; 5: Timofeevia sp., Earlie Fonnation; 6: Eliasum sp., Deadwood Fonnation; 7 and 8: Acanthomorphitae, Deadwood Formation; 9 to 12: Acanthomorphitae, Icebox Member; 13: Dicommopalla maccadamii, Icebox Member; 14, 16, and 19: lncertae sedis frag­ments, Deadwood Formation; 15, 17, and 18: lncertae sedis fragments. Earlie Formation. Scale bar= 0.05 mm.

Saskatchewan Geological Survey 161

Plate II- 1 to 4: lncertae sedis, Earlie Formation.

the forms that were not recovered from the Earlie, are the elongated form of Plate I: 6, which is here tenta­tively attributed to the Cambrian genus Eliasum, and spiny acritarchs (Acanthomorphitae). Among the latter are forms that, on the basis of their different types of spiny processes (Plate I: 7 and 8) are probably different species of the genus Balthisphaeridium.

e) The Winnipeg Formation Assemblage (Plate I: 9 to 14; Plate Ill: 1 to 18)

Shales of the Icebox Member have yielded abundant acid-resistant microfossils, whereas sandstones of the Black Island Member tend to be barren. The Icebox as­semblage consists of the following three microfossil groups: Acritarchs, Chitinozoans, and Scolecodonts.

Acritarchs

Abundant Acanthomorphitae, probably belonging to the genera Balthisphaeridium, Multiplicitosphaeridium, and Ve,yachium are present (Plate I: 9 to 12). Also of note are a few well-preserved microfossils of the type shown in Plate I: 13. General morphology, surface texture, and

162

smooth raised aperture identify the specimens as Dicommopal/a maccadamii (Loeblich, 1970), an Ordovician index fossil with range from early Caradocian to Ashgillian.

Chitinozoans

The chitinozoan assemblage of the Icebox Member is diverse and rich in number of individuals. Classifications of these small extinct animals are several, each empha­sizing different features of the fossils; however, in general they are based on the silhouette of the flask­like exoskeleton, on the type of aperture, and on the ornamentation. The biological systematic position of chitinozoans is unknown. In Plate Ill: 1 to 15 are illus­trated some typical forms found in the Icebox Member. They can be assigned to genera Rhabdochitina, Conochitina, Kalochitina(?), and Hercochitina(?). The doubt expressed by the question mark is due to the fact that Jenkins (1968) demonstrated a continuous transi­tion between some spiny forms of Conochitina and Hercochitina. The forms illustrated in Plate Ill: 12 to 14 have the complex spines that start appearing in the Caradocian (Jenkins, 1968). The rnicrofossil of Plate Ill:

Summary of Investigations 1996

Plate Ill • 1 to 9: Transmitted light photomicrographs of typical chitinozoans from the Icebox Member showing different silhouettes; 10 to 15: S.E. M. images of chitinozoans from the Icebox Member showing different surface textures (note the lambda-shaped spines in 13 and magnification 14 · to note in 15, the "bumpy" texture given by pyrite crystals which formed diagenetica/ly within the test): 16 to 18: Scolecodonts from the Icebox Member (transmitted light photomicroscopy). Scale bar= 0.1 mm except 14.

Saskatchewan Geological Swvey 163

13 and 14 conforms to the diagnosis of the genus Hercochitina whose known range is Llandoverian to lower Ashgillian (Traverse, 1988). As pointed out by Binda (1991 ), chitinozoans of the Winnipeg Formation are commonly infilled by diagenetic pyrite which confers a "bumpy" texture to the surface of the exoskeleton.

Scolecodonts

Scolecodonts, the fossil jaws of marine polychaetous annelid worms, are common in the acid-resistant resi­dues of the Icebox Member. The forms illustrated in Plate 111 can probably be attributed to genera Elleriprion {16), Arabellites (17), and Albertaprion (18) by compari­son with forms illustrated by Jansonius and Craig (1971) and Jansonius (1974). Their stratigraphic range is not precisely known.

f) Maceral Fluorescence, Thermal Maturity, and Source Rock Potential

The thermal maturity of the Cambrian samples was evaluated by observing and measuring the fluorescence characteristics of the coccoidal and unicellular alginites Gloecapsomo,pha and Protoleiosphaeridia, and acanthomorphic acritarchs. For any given sample, unaltered (i.e. pristine) macerals of Gloecapsomo,pha and acanthomorphic acritarchs generally exhibit the bluest fluorescence, with average fluorescence spectra maxima (lambda max) of 450 nm for samples at the shallowest depth of burial (<1850 m), which shift to a higher wavelength (520 nm) at approximately 2000 m. In contrast, the acanthomorphic acritarchs and Protoleiosphaeridia alginite do not exhibit the same 'red­shift' in their respective fluorescence spectra over the same depth interval. The fluorescence characteristics of all Cambrian samples examined (and their associated strata) are probably thermally immature with respect to the generation of oil (i.e. 0.45 to <0.60 %R0).

Gloecapsomo,pha is a common alginite maceral in sedi­mentary rocks ranging in age from Precambrian to Upper Ordovician, and probably in strata as young as Silurian. When thermally mature and preserved in signifi­cant quantity, G/oecapsomorpha is associated with an excellent oil generative potential. However, to date, all of the Cambrian samples studied from Saskatchewan are associated with a relatively low total organic carbon content (TOC), with a maximum of 1.28 wt% TOG for a sample from the Deadwood Formation. This relatively low TOG content, coupled with low levels of thermal maturity, render these sedimentary rocks as an unlikely source of liquid hydrocarbons.

5. Concluding Remarks

The most important conclusions that can be drawn from this preliminary study are:

1 . Shales and siltstones amenable to yielding micro­fossils upon maceration in HF occur in Cambrian and Ordovician rocks of the subsurface of southern Saskatchewan.

164

2. A diverse assemblage of acritarchs occurs in rocks of the Sauk Sequence. Although it is premature at this stage to propose a biostratigraphic zonation based on the microfossils reported here, indications are that this may be possible with more detailed sampling and taxonomic work.

3. The incertae sedis fragments recovered from the Earlie Formation, and previously not reported, have a structural complexity that warrants more investiga­tion. The possibility that they may be fragments of Burgess Shale-type organisms, or precursors of graptolites, must be kept in mind.

4. The occurrence of abundant remains of the cyano­phyte Gloeocapsomorpha suggests that hydrocar­bon source rocks may exist in the lowermost strata of the Sauk Sequence of the Western Canadian Basin.

5. An assessment of thermal maturity, using fluores­cence colour and spectral characteristics, suggests that all Cambrian samples examined are probably immature with respect to the onset of oil generation.

6. Acritarchs and chitinozoans of the Icebox Member of the Winnipeg Formation are consistent with a Caradocian age of the unit.

6. References Binda, P.L. (1991): Anoxic sulphidic diagenesis in the

Ordovician Winnipeg Formation of Saskatchewan; in Christopher, J.E. and Haidl, F.M. (eds.), Sixth International Williston Basin Symposium, Sask. Geol. Soc., Spec. Publ. 11, p257-264.

Binda, P.L. and Simpson, E.L. (1989): Petrography of sulphide­coated grains from the Ordovician Winnipeg Formation of Saskatchewan; European J. Mineral., v1, p439-453.

Butterfield, N.J. (1990}: A reassessment of the enigmatic Burgess Shale fossil Wiwaxia corrugata (Matthew) and its relationship to the polychaete Canadia spinosa Walcott; Paleo biol., v16, p287-303.

Frizzo, P. and Binda, P.L. {1989): Diagenetic pyrite in recent sediments of the Venice Lagoon and in an Ordovician sandstone from western Canada; in Sviluppi teorici e sperimentali della mineralogia, Soc. Ital. Mineral. Petrol., p88-89 (abstract).

Fyson, K.F. (1961 ): Deadwood and Winnipeg stratigraphy in southwestern Saskatchewan; Sask. Dep. Miner. Resour., Rep. 64, 37p.

Jansonius, J. (1974): Some scolecondonts in organic associa­tion from Devonian strata of western Canada; Geosci. and Man, v9, p15-26.

Jansonius, J. and Craig, J.H. (1971): Scolecodonts: I. Descrip­tive terminology and revision of systematic nomenclature; II. Lectotypes, new names for homonyms, index of species: Can. Assoc. Petrol. Geol. Bull., v19, p251-302.

Jenkins, W.A.M. (1968): Chitinozoa; Geosci. and Man. v1, pt-21.

Summary of Investigations 1996

Jodry, R.L. and Campau, D.E. (1960): Small pseudochitinous and resinous microfossils: New tools for the subsurface geologist; AAPG Bull., v44. p1378·1391.

Kupsch, W.O. (1952): Ordovician and Silurian straligraphy of east-central Saskatchewan; Sask. Dep. Miner. Resour., Rep. 10, 62p.

Labelle, D.G.P. (1994): Allostratigraphic analysis of the Middle Cambrian Deadwood Formation in southern Saskatche­wan; unpubl. B.Sc. thesis, Univ. Regina, 44p.

Lefever, R.D., Thompson, S.C., and Anderson, D.B. (1987): Earliest Paleozoic history of the Williston Basin in North Dakota; in Carlson, C.G. and Christopher, J.E. (eds.), Fifth International Williston Basin Symposium. Sask. Geol. Soc., Spec. Publ. 9, p22·36.

Loeblich, A.R., Jr. (1970): Dicommopalla. a new acritarch genus from the Dillsboro Formation (Upper Ordovician) of Indiana, U.S.A.; Phycologia, v9, p39-43.

Mossop, G.E. and Shetsen, I. (compilers) (1994): Geological Atlas of the Western Canada Sedimentary Basin; Can. Soc. Petrol. Geol. and Alta. Res. Counc., 51 Op.

Nowlan, G.S., Hein, F.J., Coskun, S.B., Stasiuk. L.D .. Fowler, M.G., Norford, B.S .. Palmer, B.R., and Addison, G.D. (1995): Characterization of Cambrian and Ordovician strata in the subsurface of Alberta using lithostratigraphy, biostratigraphy, organic petrology, and image analysis; in Ross, G.M. (ed.), Alberta Basement Transect Workshop, LITHOPROBE Rep. 47, p97-112.

Osadetz, K.G., Snowdon, L.R., and Stasiuk, l.D. (1989): Association of enhanced hydrocarbon generation and crustal structure in the Canadian Williston Basin; in Current Research, Geo1. Surv. Can., Paper 89-lD, p35-47.

Paterson, D.F. (1971): The stratigraphy of the Winnipeg Formation (Ordovician) of Saskatchewan; Sask. Dep. Miner. Resour., Rep. 140, 57p.

Saskatchewan Geological Su,vey

_____ (1989): The Earlie Formalion (Cambrian) in Saskatchewan; in Summary of Investigations 1989, Saskatchewan Geological Survey, Sask. Energy Mines. Misc. Rep. 89-4, p117-119.

Slind, O.L., Andrews, G.D., Murray, D.L .. Norford, B.S., Paterson, D.F., Salas, C.J., and Tawadros. E.E. (1994): Middle Cambrian to Lower Ordovician Strata of the Western Canada Sedimentary Basin; in Mossop, G.E. and Shetsen, I. (comps.). Geological Atlas of the Western Canada Sedimentary Basin; Can. Soc. Petrol. Geol. and Alta. Res. Counc., pB?-108.

Sloss. L.l. (1963): Sequences in the cratonic interior of North America; Geol. Soc. Amer. Bull, v74, p93-114.

Stasiuk. L.D. (1994): Oil-prone macerals from organic-rich Mesozoic and Paleozoic strata, Saskatchewan, Canada; Marine and Petrol. Geol., vl 1, p20B·218.

Stasiuk, L.D .. Goodarzi, F., and Gentzis, T. {1991): Organic microfacies and basinal tectonic control on source rock accumulation; A microscopic approach with examples from an intracratonic and extensional basin; in Proceedings of the Peter Hacquebord Symposium, Calgary 1990, Soc. Org. Petrol. Chem., v19, p457-481.

Stasiuk, L.D. and Osadetz, K.G. (1990): The life cycle and phyletic affinity of Gloeocapsomorpha prisca Zalesski 1917 from Ordovician rocks in the Canadian Williston Basin; in Current Research, Geol. Surv. Can., Paper 90-lD, p127-137.

Traverse, A. (1988): Paleopalynology; Unwin Hyman, Boston, 600p.

Vanguestaine, M. (1978): Criteres palynostraligraphiques conduisant a la reconnaissance d'un pli couche Revinien dan le sondage de Grand-Halleux; Ann. Soc. Geol. Belgique, vlOO, p249-276.

Vigrass. L.W. (1971): Depositional framework of the Winnipeg Formation in Manitoba and eastern Saskatchewan; Geol. Assoc. Can., Spec. Pap. 9, p225-234.

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