Preliminary Palynological Investigations of Upper ...

Preliminary Palynological Investigations of Upper Cretaceous Strata, Southwestern Saskatchewan

C.F. Gilboy and E.M.V. Nambudiri1

Gilboy, C.F. and Nambudiri, E.M.V. (1991): Preliminary palynological investigations of Upper Cretaceous strata, southwestern Saskatchewan; in Summary of Investigations 1991, Saskalchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 91·4.

Twelve core samples from four wells penetrating Upper Cretaceous strata in southwestern Saskatchewan were analyzed for their palynomorph contents. The main aim of the investigation is to learn whether palynological as­semblages obtained from core are helpful in estab­lishing detailed age relationships of source rocks which generally lack identifiable megafossils. In addition, the use of palynomorphs in supplementing sedimentologi­cal information about depositional environments is as­sessed.

1. Results

Cored intersections from two of the wells are of Second White Speckled Shale, one (06-25T-14-30W3} in the basal sand unit and an associated bentonite (B ben­tonite, Gilboy, 1988a, b}, the other (11-28-02-28W3) in the uppermost sandy unit and a distinctive regional!y recognized bentonite (C bentonite, Gilboy, 1988a,b}.

a) NCO Hatton 06-25T-14-30W3, Four Samples

Sample 1, at 667.18 m (sample 1 of Nambudiri, 1991 ): dark grey to black, finely laminated shales with rare, siltstone laminae (less than 1 mm thick); very little biotur­bation; sporadic fish-scales and spines, and 1 to 2 cm long casts of unbroken pelecypod valves. The palynomorph assemblage comprises: Cicatricosisporites sp., Cicatricosisporites augustus Singh, Cyathidites minor Couper, Cyathidites australis Couper, Gleicheniidites senonicus Ross, Lycopodiumsporites marginatus Singh, Appen­dicisporites bilateralis Singh, Trilobosporites apiver­rucatus Couper, Biretisporites potoniaei Delcourt and Sprumont, Cycadopites sp., Podocarpidites granulatus Singh, Alisporites bilateralis Rouse, Laricoidites mag­nus (Potonie) Potonie, Thomson and Thiegart, Cerebropo/Jenites mesozoicus (Couper} Nilsson, Abiespo/Jenites sp., Taxodiaceaepo/Jenites hiatus (Potonie) Kremp, Clavatipo/Jenites hughesii Couper, Liliacidites inequalis Singh, Tricolporate pollen, Tricol­pites sagax Norris, and abundant dinoflagellates and acritarchs. The presence of Taxodiaceaepo/Jenites hiatus, Cicatricosisporites sp., Gleicheniidites senonicus, Alisporites bilatera/is and angiosperm pollen such as Tricolpites sagax suggests possible attinities of this assemblage with the early Tricolpate suite of Norris et al. (1975), the upper part of which has been assigned

(1) Department of Geology. University of Regina, Regina. Saskatchewan

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a Cenomanian age. The abundance of black wood indi­cates offshore deposition or oxidizing environments.

Sample 2, at 665.07 m (sample 3 of Nambudiri, 1991): parallel laminated fine sandstones and shales, common­ly graded in 1 to 3 cm thick units some of which are moderately bioturbated, others are non-bioturbated; im­mediately overlying these is a 15 cm thick unit of black shale, possibly representing a flooding surface. The palynomorph assemblage is: Cyathidites minor Couper, Trilobosporites tribotrys Dettmann, Gleicheniidites senonicus Ross, Deltoidospora ha/Iii Miner, Taxodiaceaepof/enites hiatus (Potonie) Kremp, Laricoidites magnus (Potonie) Potonie Thomson and Thiegart, Vitreisporites pallidus (Reissinger} Nilsson, Podocarpidites granulatus Singh, Cedripites canaden­sis Pocock, Tricolpites sp., Tricolpites parvus Stanley, Liliacidites magnus Singh, Betulaceoipollenites sp., Cupuliferoidaepo/lenites minutus (Brenner) Singh, Clavatipo/Jenites minutus Brenner, Veryachium sp., and abundant dinoflagellates and hystrichosphaerids. The continued appearance of Taxodiaceaepollenites hiatus and G/eicheniidites senonicus along with the an­giosperm pollen Cupuliferoidaepollenites minutus, Liliacidites sp. and Tricolpites sp. again suggests af­finities of this assemblage with the early Tricolpate suite of Norris et al. (1975). However, major differences exist, and the lack of diagnostic palynomorphs make age determination for this sample imprecise. Continentally derived bisaccate conifer pollen is abundant, and may have been transported a long distance. Both black and brown woods are present.

Sample 3, at 662.62 m (sample 5 of Nambudiri, 1991): finely laminated black shale with rare siltstone laminae and lenses, very weakly bioturbated (several subhorizon­tal, sand-filled tubes are present). This unit separates in­tensely Terebellina-bioturbated, medium grey sandstone below from overlying, weakly bioturbated, greenish, lo­cally ripple cross-bedded fine sandstones and inter­bedded shales. No palynomorphs were recovered.

Sample 4, at 660.92 m (sample 4 of Nambudiri, 1991): very weakly bioturbated to non-bioturbated, greenish, fine, thinly laminated (laminae up to about 1 mm thick), ripple cross-bedded sandstones with thin shale partings; beds are mostly 1 to 2 cm thick, and many are normally graded with coarser-grained basal parts cemented by carbonate. No palynomorphs were recovered.

Summary of Investigations 1991

Sample 5, at 659.18 m (sample 2 of Nambudiri, 1991 ): dark grey to black, finely laminated shales with rare, siltstone laminae less than 0.5 mm; small flakes of mica (including biotite) are present, as are sporadic fish remains. No patynomorphs were recovered.

b) United Bata Resources Noel Senate 11-28-02-28W3, Three Samples

Sample 6, at 819.06 m (sample 8 of Nambudiri, 1991): interlayered spotted and non-spotted, dark grey shales with rare lenticles of fine sandstone up to 3 mm thick; weakly bioturbated (subhorizontal, sand-filled burrows); contains biotite flakes, abundant plant remains, and fish­scales. The palynomorph assemblage inc!udes Appen­dicisporites sp., Deltoidospora ha/Iii Miner, Concavis­simisporites punctatus (Delcourt and Sprumont) Singh, Taxodiaceaepollenites hiatus (Potonie) Kremp, Podocar­pidites sp., Abiespollenites sp., and numerous dinof!agellates and organic-walled microforaminifera. The lack of age-diagnostic palynomorphs and the limited variety of species preclude correlation with other assemblages. The presence of microforaminifera and dinoflagellates suggests marine depositional environ­ments.

Sample 7, at 804.73 m (sample 6 of Nambudiri, 1991 ): moderately speckled, dark grey shales containing fish­scales and -spines as well as a layer of parallel Baculites shells (mostly at least 9 cm in length) and sporadic unbroken pelecypod valves up to 2 cm across. The base of the 64 cm thick C bentonite (Gilboy, 1988a,b) is present 82 cm above the sample location, which is situated 5 cm below a scour surface where low­angle cross-bedded sand laminae less than 1 mm thick are eroded and overlain by shale. No palynomorphs were recovered.

Sample 8, at 800.77 m (sample 10 of Nambudiri, 1991 ): richly speckled medium to dark grey shales with fish debris, including vertebrae; contain interlaminated car­bonate-rich siltstone layers, generally less than 1 mm thick; the sample location is 2.4 m above the top of the 64 cm thick C bentonite. The palynomorph assemblage is made up of Deltoidospora ha/Iii Miner, Cyathidites minor Couper, Concavissimisporites sp., Concavis­simisporites variverrucatus. (Couper) Brenner, Trilobosporites apiverrucatus Couper, Cycadopites sp., Podocarpidites radiatus Brenner, Podocarpidites granulatus Singh, Taxodiaceaepol/enites hiatus (Potonie) Kremp, Laricoidites sp., Abiespol/enites sp., Classopol/es c/assoides Pflug emend. Pocock and Jan­sonius, Alisporites sp., Tricolpites sagax Norris, Tricol­pites reticulatus Cookson ex Couper emend. Potonie, Retitricolpites vulgaris Pierce, Clavatipollenites sp., Liliacidites sp. (abundant), Odontochitina sp., numerous dinoflagellates and very abundant hystrichosphaerids. Al­though no precise age can be assigned to this as­semblage, it can be compared with the early Tricolpate suite of Norris et al. (1975). Species of Odontochitina are commonly Albian in age, but Norris et al. have found specimens in an assemblage of probable Cenomanian age. Black woods are abundant in this sample, brown woods rare. Bisaccate grains indicate long distance transport.

Saskatchewan Geological Survey

c) CON Roxy AEC Cypress 07-22-09-28W3, Two Samples

This well was cored in the Medicine Hat Sandstone.

Sample 9, at 639.03 m (sample 12 of Nambudiri, 1991): highly speckled, medium grey, laminated fine sandstone and shale, sand laminae up to 2 mm thick. The palynomorph assemblage is: Gleicheniidites senonicus Ross, Alisporites sp., Cycadopites sp., Liliacidites mag­nus Singh, and Tricolpites microreticu/atus Belsky, Bol­tenhagen and Potonie. The lack of index palynomorph species preclude age assignments and comparison with other assemblages.

Sample 10, at 634. 73 m (sample 11 of Nambudiri, 1991): highly speckled, medium grey shale with fish­scales up to about 3 mm across along with other fish debris including bones (vertebrae) and spines up to 5 mm long. The palynomorph assemblage includes Gleicheniidites senonicus Ross, Appendicisporites sp., Cyathidites minor Couper, Taxodiaceaepollenites hiatus (Potonie) Kremp, Trudopo/lis sp., Retitricolpites vulgaris Pierce, Proteacidites retusus Andersen, Tubuliferoidites sp., Cfavatipollenites hughesii Couper, Tricolpites reticulatus Cookson ex Couper emend. Potonie, Cer­cidiphyllites brevicolpites Mtchedlishvili, Betulaceaoipol­lenites sp., Dinogymnyum acuminatum Evitt et al., Varyachium sp., and an abundance of hystrichos­phaeridia and other dinoflagellates.

This palnomorph assemblage is typical of the early Triporate suite of Norris et al. (1975), to which the basal part of the Lea Park Formation in Alberta belongs. Several redeposited spores were identified.

d) City of Medicine Hat Hatton OB-15-16-28W3, Two Samples

This well was cored in the Milk River Formation.

Sample 11, at 500.3 m (sample 7 of Nambudiri, 1991): medium grey, poorly sorted, generally fine-grained, im­pure sandstone containing about 50 percent clay minerals as well as flakes of biotite and white mica; abundant small fragments of carbonized wood impart a salt-and-pepper appearance to the rock, which has a generally massive texture suggestive of intense bioturba­tion; isolated shale lenses are present. The palynomorph assemblage is made up of Trilobosporites trioreticu/osus Cookson and Dettmann, Gleicheniidites senonicus Ross, Deltoidospora halfii Miner, Cyathidites minor Couper, Lycopodiumsporites marginatus Singh, Laevigatosporites ovatus Wilson and Webster, Concavis­simisporites sp., Taxodiceaepolfenites hiatus Brenner, Laricoidites sp., Podocarpidites radiatus Brenner, Tricol­pites microreticulatus Belsky, Boltenhagen and Potonie and Cfavatipollenites hughesii Couper. It is poorly preserved, and the lack of characteristic index species prevents age and environmental interpretations.

Sample 12, at 436.61 m (sample 9 of Nambudiri, 1991): Medium grey, fine, impure sandstone (up to 70 percent clay content) with numerous shell fragments showing an iridescent sheen. The palynomorph assemblage com-

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prises Lycopodiumsporites sp., Deltoidospora ha/Iii Miner, Gleicheniidites senonicus Ross, Gleicheniidites bo/chovitinae Doring, Lophotriletes babase (Brenner) Singh, Dictyophyllidites sp., Ciratriradites teter Norris, Cicatricosisporites ha/Iii Delcourt and Sprumont, Acan­thotriletes sp., Cyathidites minor Couper, Biretisporites potoniaei Delcourt and Sprumont, Trilobosporites sp., Osmundacidites sp., Taxodiaceaepo/lenites hiatus (Potonie) Kremp, Podocarpidites granulatus Singh, Alisporites bilateralis Rouse, Abiespollenites sp., Cibotiidites arlii Srivastava, Triatriopollenites costatus Norton, Aquilapollenites calvus Tschudy and Leo!pold, Aquilapollenites quadri/obus Rouse, and abundant dinoflagellates and hystrichosphaerids. It is comparable with the early loranthaceous suite of Norris et al. (1975) in Alberta, which contains pteridophyte spores such as Cicatricosisporites hallii, Cyathidites minor, Del­toidospora hallii and Gleicheniidites senonicus, and conifer pollen (Abiespo/Jenites sp. and Taxodiaceaepol­lenites hiatus). The occurrence of species of Aquilapol­/enites, especially A.ca/vus and A. quadri/obus, is par­ticularly significant in correlating this sample with the early loranthaceous suite. Norris et al. (1975) proposed this suite to be characteristic of the middle part of the Lea Park Formation. They suggested a Santonian to Campanian age for this formation, but recent dinoflagel­late studies by Harker et al. (1990) indicate a Cam­panian age. This sample contains much opaque to dark brown and brown wood, as well as an abundance of spores and pollen (including bisaccate conifer pollen), dinoflagellates and acritarchs. The black wood indicates offshore environments (Cross et al., 1966; Muller, 1959) or oxidizing conditions (Pocock et al., 1987-1988). Melia (1982) suggested that terrestrial palynomorphs (pol!en and spores) decrease in abundance away from continen­tal margins towards shelf and slope, where sediments contain an admixture of pollen, spores, dinoflagellates and acritarchs.

2. Conclusions

Of the samples used in this study, palynomorphs were not recovered from four, three yielded palynomorph as­semblages too mediocre to a!low for age or environmen­tal interpretations, and five provided data of some use in defining the age and/or the depositional environment of the host rocks. Cenomanian ages indicated for Second White Speckled Shale samples (1, 2 and 8) are in agree­ment with expected results (Gilboy, 1987), as is a Cam­panian age for the uppermost Milk River Formation (12). Both the basal Lea Park Formation and the uppermost Medicine Hat Sandstone (10) are generally considered to be of Santonian age. Palynomorph assemblages and preserved wood remains indicated that the host rocks were originally deposited in outer shelf environments. As­semblages in southwestern Saskatchewan are closely

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comparable with those at similar stratigraphic levels in Al­berta.

Reconnaissance-level palynomorph studies of Upper Cretaceous elastic sedimentary rocks from southwestern Saskatchewan are of broad use in defining age relation­ships and depositional environments.

3. References Cross, A.T., Thompson, G.G. and Zaitzeff, J.B. (1966): Source

and distribution of palynomorphs in bottom sediments, southern part of the Gulf of California; Marine Geol., v4, p467-524.

Gilboy, C.F. (1987): Aspects of the regional geological framework of low-permeability shallow gas reservoirs in Upper Cretaceous strata (Colorado and Montana Groups), southwestern Saskatchewan; in Summary of Investiga­tions 1987, Saskatchewan Geological Survey, Sask. Ener­gy Mines, Misc. Rep. 87-4, p199-213.

-~~-~ (1988a): Geology and natural gas production of the Upper Cretaceous Second White-speckled Shale, southwestern Saskatchewan; in Summary of Investiga­tions 1988, Saskatchewan Geological Survey, Sask. Ener­gy Mines, Misc. Rep. 88-4, p183-195.

_____ (1988b): South-north stratigraphic cross-sec­tion through Upper Cretaceous Second White-speckled Shale in southwes', Saskatchewan; with Summary of Inves­tigations 1988, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 88-4.

Harker, S.D., Sargeant, WAS. and Caldwell, W.E.G. (1990): Late Cretaceous (Carnpanian) organic-walled microplankton from the Interior Plains of Canada, Wyom· ing and Texas: Biostratigraphy, palaeontology and palaeoenvironmental interpretation; Palaeontographica B, v219, pl-243.

Melia, M.B. (1982): The distribution and relationship between palynomorphs in aerosols and deep-sea sediments off the coast of northwest Africa; Palynol., v6, abstr., p285.

Muller, J. (1959): Palynology of Recent Orinoco delta and shelf sediments; Micropaleont., v5, p1-32.

Narnbudiri, E.M.V. (1991 ): Preliminary investigation of the palynology of the Cretaceous strata of southwestern Sas­katchewan; U. Regina, Energy Resear. Unit Contrib. No. 248, 11p.

Norris G., Jarzen, D.M. and Awai-Thorne, B.V. (1975): Evolu­tion of the Cretaceous terrestrial palynoflora in western Canada; in Caldwell, W.G.E. (ed.), The Cretaceous Sys­tem in the Western Interior of North America; Geel. Assoc. Can., Spec. Pap. 13, p333-364.

Pocock, S.A.J., Vasanthy, G. and Venkatacha-la, B.S. (1987-1988): Introduction to the study of particulate organic materials and ecological perspectives; J. Palynol., v23-24, p167-188.

Summary of Investigations 1991