Palynology of the Shaunavon and Gravelbourg Formations of Southern Saskatchewan
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Palynology of the Shaunavon and Gravelbourg Formations of Southern Saskatchewan L.K. Kreis Kreis, L.K. (1989): Palynology of the Shaunavon and Gravelbourg Formations of southern Saskatchewan, in Summary of Inves tigations 1989, Saskatchewan Geological Survey; Saskatchewan Energy and Mines, Miscellaneous Report 89-4. This paper reports preliminary examinations made in 2. Palynological Results 1989 of palynological data from Jurassic strata in southern Saskatchewan. Sample preparation and iden The focus of this investigation is on the palynology of tification were conducted by Dr. E.M.V. Nambudiri, with the Shaunavon and Gravelbourg Formations of south the Energy Research Unit, University of Regina. The western Saskatchewan, and the Red Jacket Formation author acknowledges Dr. Nambudiri's invaluable con of the southeast. Although most samples are from the tribution towards an interpretation of the palynomorphs Wapella- Moosomin area, the results have aided present. stratigraphic correlations in both areas. To supplement Pocock's (1970, 1972) work, 52 samples from the The investigation is part of an ongoing study by the Shaunavon and Gravelbourg Formations were taken author entitled, 'Stratigraphy of the Jurassic System in from 20 wells across southern Saskatchewan (Figures the Wapella - Moosomin area, southeastern Sas 1a and 1b , in pocket). Only 38 samples from 18 wells katchewan' ('Study Area' in Figure 1a, in pocket). The proved to have sufficiently preserved, identifiable major goals of the study are 1) to establish the palynomorph specimens. A summary of typical stratigraphic relationships between the Jurassic section palynomorph assemblages for the upper and lower in the Wapella-Moosomin area of southeastern Sas members of the Gravelbourg Formation, upper and katchewan and the type area for the Jurassic in south lower members of the Shaunavon Formation, Rocanville western Saskatchewan (Figures 1a and 1b, in pocket), Member, Moosomin Member (units A and B) and Bur and 2) to provide an interpretation of the depositional rows Member (units A and 8) is given in Table 1. history for the Jurassic System in the Wapella Moosomin area. A more detailed discussion of the a) Lower Gravelbourg Member stratigraphic and ecological implications of the palynological results will be published later. Only three of seven samples taken from the lower Gravelbourg member yielded specimens of sufficient preservation to warrant examination, two from unit A 1. Previous Work and one from the overlying unit B. Poor preservation of Previous palynological investigations of the Jurassic palynomorphs in the latter sample likely resulted from strata in Saskatchewan are limited to reports by Pocock slow deposition in a high pH environment; conditions (1970 and 1972). Pocock (1972) established a considered by Traverse (1988) to be corrosive to framework of palynomorph assemblages for the major palynomorphs. The presence of abundant organic stratigraphic units defined by Milner and Thomas (1954) walled microforaminifera in unit B supports Pocock's for the Jurassic section in southwestern Saskatchewan, (1972) interpretation of a marine depositional environ namely (oldest to youngest) the Watrous, Gravelbourg ment. Microforaminifera were not found in Unit A, but and Shaunavon Formations and the Vanguard Group. the presence of acritarchs like Leiosphaeridia staplinii and Leiosphaeridia tangentensis suggest a marine in Numerous depositional breaks and lithofacies changes fluence for this unit as well. This compliments the inter within the Shaunavon Formation and upper member of pretation that the dolomitic and locally algally-laminated the Gravelbourg Formation in southeastern Sas limestones of unit A were deposited in a restricted shal katchewan make correlation with strata in the type area low marine environment; whereas the calcareous of southwestern Saskatchewan very difficult when at mudstones and bioclastic limestones of unit Bare inter tempted on the basis of lithological and geophysical log preted to have been deposited in a more open marine characteristics (Kreis, 1988). Kreis invoked an arbitrary environment. lithofacies boundary to separate the Shaunavon Forma tion and upper member of the Gravelbourg Formation The palynomorph assemblage in the lower member of of southwestern Saskatchewan from the equivalent the Gravelbourg Formation in the present study is strata in southeastern Saskatchewan, which he named, similar to that found in the same member by Pocock the Red Jacket Formation (Figures 1a and 1b). He sub (1972). Leiosphaeridia staplinii, Leiosphaeridia tangen divided the Red Jacket Formation into three members tensis, Murospora minor, and species of Concavis (0-Y): Rocanville Member, Moosomin Member and Bur simisporites are index species from unit A in this study, rows Member. For a more detailed discussion of and Lycopodiumsporites pseudoannotinus and species nomenclature see Kreis (1988). of Leiosphaeridia are the index species from unit B. All of these palynomorphs are also index species for the Saskatchewan Geological Survey 133 Table 1 - Typical Palynomorph Assemblages lower member of the Gravel- bourg Formation described by STR1''l'IGRAPlllC UNITS Pocock (1972). LGA LGB UG LSl us RM MMll MMD BMA BMB -------·-·--------- Classopollis spores, reported PALYNOMORPHS "in abundance" by Pocock Terrestr ial spec ies (1972) in the lower member of the Gravelbourg Formation Bacula t i sporites truncatus x Bennet t i teaepollenites canadens is x x are rarer in unit A, and absent sennet tite aepolleni tes l ucif er x x in unit B of this report. How- Bennetti teaepollenites shaunavonansis x x Calamospor a mesoz oic a x x x x ever, in only one well did unit Calli alasp0rites triloba tus x x Ceratosporit eP spinosus x B yield identifiable Cerebropolle nites macrovorrucocus x x palynomorphs, and these Cerebr opolleni tes mesozoicus x Cerebr opol lenites s p . x were poorly preserved. Classopollis clas s oides x x Classo pollis i tunensi s x x x Concavissimisporit es ~elcourtii x Since Pocock (1972) does not Concavissimispor i tes southeyensis x x x Concavis simisporites subgranulatus x indicate the well location or Concav i ssimi s porites sp . x depths of recovery for most of Corrugatis porites ampl ectlformis x Corrugatis porit e s wallii x x his samples, it is difficult to Cyathidite s mi nor x Cycadopi t es jansonii x determine the southwestern cycadopite s minimus x x stratigraphic equivalents of Deltoidosp0ra harr1sii x x x Deltoi dospora minor x x x units A and B. Unit A appears Dictyophyl lidites s p. x Dictyotrilete s c r aterin x to be more similar than unit B Dis tanulis porites verrucosus x to the lower member of the Eucommildite s troedsonii x exesipollenites s cabratus x Gravelbourg described by Exesipolleni t es t umulus x Cleicheniidltes del i c atus x Pocock, having a greater num- Gloichcniidites granu lat us x ber of the palynomorph index Gl eicheniidites minor x Gleicheniidltes nil s s onii x species. On the other hand, Gl aich eniidi t es r ouse ii Har ri sis pora cqui eKi nus x unit B was found to be In aperturopol l 6ni tes tur batus x x x marine, and Pocock ( 1972) Lycopodiumsporites ba cculatus x Ly copodiumspori tes dejer s eyi x does not recognize a marine Lycopodi.uJDSporite s pseudoannotinus x sequence in the upper Gravel- Manumia verrucata x Murospora bicolla tera lis x x bourg. Unit 8, therefore, is Murosp0ra minor x Muro spora sp. x taken to be the uppermost Ovalipolli s canadensi s x unit of the lower member of Pityos porite s div ulg~tus x x Pl acysac cus lopsi nens i s x the Gravelbourg. Podocarpidites l angii Podocarpi dites waptllaensis x x Protoc oni rerus micros accus x Unit B is not present in the Protopicea e xilioidcs x x x Re ticulatisporite s juras s i cus x type section of the Gravel- Reticul a tispor jtes sp. x Triangulopsi s discoidal i s x x bourg Formation (well number 1 in Figure 1b ), instead, the Marine Species upper Gravelbourg rests un- organ i c - wa lled for a•inifera x x conformably on what appears d i noflagellat es (indetermi nate) x Chyt roeisphaerjdia variabilis to be unit A of the lower Comasphaeridium s p. A x Cymatiosphttens sp. x Gravelbourg. East of this well, Gonyaulacysta j uras sica x unit B overlies unit A all the Conyaulacysta ornata x Gonyaulax canad~nsis x way to the Wapella-Moosomin Leiot usa deunrfii x Le.i osphacridia hyallna x area (Figure 1b). A well- Leiosphaer idia s t aplinii x x x defined unconformity which Le iosphaer idi a tangentansis x x x x Leiosphaeridia s p . x separates these units in both Rugidinium orna tum x the southeast and southwest, Rugi d i nium undula turn x Rugi d i nium sp. x exhibits weathered dolomite, Sol i sphaeridium deflandrei x Tasmani t es cla icmontensis )( with vugs filled by secondary Tasmanites s uevi cus x x quartz and bluish grey chal- Ta smanj t es y arboensis x cedonic chert (Kreis, 1988). Ahbrev lat1ons: LGA - Lowe r Gra velbour g, Unit ,. The contact between the LGB - Lower Gravel bourg, Uni t B UG - Upper Gravelbourg upper and lower member of LSl - LO.-er Shaunavon, Unit 1 US - Upper Shauna von the Gravelbourg Formation is RM - Rocanv i l le Me na.her sharp, but evidence of erosion MMA - MoosoJ1.i n Member, Uni t A MMB - Moosomin "efflber, Unit B and weathering is lacking, ar- Biii\ - BU ~ro~s Member, Un it A BMB - Burro ws Member, Un it B guing against a clear unconfor- mity. This contact more probably represents a paraconformity. 134 Summary of Investigations 1989 b) Upper Gravelbourg Member d) Upper Shaunavon Member Seven samples taken from the upper member of the The palynomorph assemblage found in four samples of Gravelbourg have a combined palynomorph as the upper member of the Shaunavon Formation differs semblage including: Bennettiteaepollenites canadensis, significantly from Pocock (1972); the only common Calamospora mesozoica, Cerebropollenites macrover palynomorph is Chytroeisphaeridia variabilis.