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 Inves­tigations 1989, Saskatchewan Geological Survey; Saskatchewan Energy and Mines, Miscellaneous Report 89-4.

This paper reports preliminary examinations made in 1989 of palynological data from Jurassic strata in southern Saskatchewan. Sample preparation and iden­tification were conducted by Dr. E.M.V. Nambudiri, with the Energy Research Unit, University of Regina. The author acknowledges Dr. Nambudiri's invaluable con­tribution towards an interpretation of the palynomorphs present.

The investigation is part of an ongoing study by the author entitled, 'Stratigraphy of the Jurassic System in the Wapella - Moosomin area, southeastern Sas­katchewan' ('Study Area' in Figure 1 a, in pocket). The major goals of the study are 1) to establish the stratigraphic relationships between the Jurassic section in the Wapella-Moosomin area of southeastern Sas­katchewan and the type area for the Jurassic in south­western Saskatchewan (Figures 1a and 1 b, in pocket), and 2) to provide an interpretation of the depositional history for the Jurassic System in the Wapella­Moosomin area. A more detailed discussion of the stratigraphic and ecological implications of the palynological results will be published later.

1. Previous Work Previous palynological investigations of the Jurassic strata in Saskatchewan are limited to reports by Pocock (1970 and 1972). Pocock (1972) established a framework of palynomorph assemblages for the major stratigraphic units defined by Milner and Thomas (1954) for the Jurassic section in southwestern Saskatchewan, namely (oldest to youngest) the Watrous, Gravelbourg and Shaunavon Formations and the Vanguard Group.

Numerous depositional breaks and lithofacies changes within the Shaunavon Formation and upper member of the Gravelbourg Formation in southeastern Sas­katchewan make correlation with strata in the type area of southwestern Saskatchewan very difficult when at­tempted on the basis of lithological and geophysical log characteristics (Kreis, 1988). Kreis invoked an arbitrary lithofacies boundary to separate the Shaunavon Forma­tion and upper member of the Gravelbourg Formation of southwestern Saskatchewan from the equivalent strata in southeastern Saskatchewan, which he named, the Red Jacket Formation (Figures 1a and 1b). He sub­divided the Red Jacket Formation into three members (0-Y): Rocanville Member, Moosomin Member and Bur­rows Member. For a more detailed discussion of nomenclature see Kreis (1988).

Saskatchewan Geological Survey

2. Palynological Results The focus of this investigation is on the palynology of the Shaunavon and Gravelbourg Formations of south­western Saskatchewan, and the Red Jacket Formation of the southeast. Although most samples are from the Wapella- Moosomin area, the results have aided stratigraphic correlations in both areas. To supplement Pocock's (1970, 1972) work, 52 samples from the Shaunavon and Gravelbourg Formations were taken from 20 wells across southern Saskatchewan (Figures 1 a and 1 b, in pocket). Only 38 samples from 18 wells proved to have sufficiently preserved, identifiable palynomorph specimens. A summary of typical palynomorph assemblages for the upper and lower members of the Gravelbourg Formation, upper and lower members of the Shaunavon Formation, Rocanville Member, Moosomin Member (units A and B) and Bur­rows Member (units A and 8) is given in Table 1.

a) Lower Gravelbourg Member

Only three of seven samples taken from the lower Gravelbourg member yielded specimens of sufficient preservation to warrant examination, two from unit A and one from the overlying unit B. Poor preservation of palynomorphs in the latter sample likely resulted from slow deposition in a high pH environment; conditions considered by Traverse (1988) to be corrosive to palynomorphs. The presence of abundant organic­walled microforaminifera in unit B supports Pocock's (1972) interpretation of a marine depositional environ­ment. Microforaminifera were not found in Unit A, but the presence of acritarchs like Leiosphaeridia staplinii and Leiosphaeridia tangentensis suggest a marine in­fluence for this unit as well. This compliments the inter­pretation that the dolomitic and locally algally-laminated limestones of unit A were deposited in a restricted shal­low marine environment; whereas the calcareous mudstones and bioclastic limestones of unit Bare inter­preted to have been deposited in a more open marine environment.

The palynomorph assemblage in the lower member of the Gravelbourg Formation in the present study is similar to that found in the same member by Pocock (1972). Leiosphaeridia staplinii, Leiosphaeridia tangen­tensis, Murospora minor, and species of Concavis­simisporites are index species from unit A in this study, and Lycopodiumsporites pseudoannotinus and species of Leiosphaeridia are the index species from unit B. All of these palynomorphs are also index species for the

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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 ia l spec ies (1972) in the lower member of

the Gravelbourg Formation Bacula t i sporites truncatus x are rarer in unit A, and absent Bennet t i teaepollenites canadens is x x sennet tite aepolleni tes l uci f er x x in unit B of this report. How-Bennetti teaepollenites shaunavonansi s x x ever, in only one well did unit Calamospor a mesoz oic a x x x x Calli alasp0rites triloba tus x x B yield identifiable Ceratospori t eP spinosus x Cerebropollenites macrovorrucocus x x palynomorphs, and these Cerebr opolleni tes mesozoicus x were poorly preserved. Cerebr opol leni tes s p . x Classopollis clas s oides x x Classo pollis i tunensi s x x x

Since Pocock (1972) does not Concavissimispori t es ~elcourtii x Concavissimispor i tes southe yensi s x x x indicate the well location or Concavis simisporites subgranulatus x Concav i ssimi s pori tes sp . x depths of recovery for most of Corrugati s pori tes ampl ectlformis x

his samples, it is difficult to Corrugatis pori t e s wallii x x Cyathidite s mi nor x determine the southwestern Cycadopi t es jansonii x cycadopite s minimus x x stratigraphic equivalents of Deltoidosp0ra harr1sii x x x

units A and B. Unit A appears Deltoi dospora minor x x x Dictyophyl lidites s p. x to be more similar than unit B Dictyotrilete s c r aterin x Di s tanuli s porites verrucosus x to the lower member of the Eucommildite s troedsonii x

Gravelbourg described by exesipollenites s cabratus x Exesipolleni t es t umulus x Pocock, having a greater num-Cleicheniidltes del i catus x Gloichcniidites granu lat us x ber of the palynomorph index Gl eicheniidites minor x species. On the other hand, Gleicheniidltes nil s s onii x Gl aich en iidi t es r ouse ii unit B was found to be Har r i sis pora cqui eKi nus x

marine, and Pocock ( 1972) In aperturopol l 6ni tes tur batus x x x Lycopodiumsporites ba cculatus x does not recognize a marine Ly copodiumspori tes de jer s eyi x 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 taken to be the uppermost Murospora sp . x Oval ipolli s canadensi s x unit of the lower member of Pityos porite s di vulg~tus x x the Gravelbourg. Pl acysac cus lopsi nens i s x Podocarpidites l angii Podocarpi dites waptllaensis x x Protoc on i rerus micros accus x Unit B is not present in the Protopicea e xi lioidcs x x x type section of the Gravel-Re ticula tisporite s juras s i cus x Reticul a ti spor jtes sp. x bourg Formation (well number Triangulops i s discoidal i s x x

Marine Species 1 in Figure 1 b), instead, the upper Gravelbourg rests un-

organ i c - wa lled for a•inifera x x conformably on what appears d i noflagel lat es (indetermi nate) x Chyt roeisphaerjdia variabilis to be unit A of the lower Comasphaeridium s p. A x Gravelbourg. East of this well, Cymatiosphttens sp. x Gonyaul acysta j uras si ca x unit B overlies unit A all the Conyaulacysta ornata x

way to the Wapella-Moosomin Gonyaulax canad~nsis x Leiot usa deunrfii x area (Figure 1 b). A well-Le.i osphacridi a hyallna x Leiosphaer idia s t aplinii x x x defined unconformity which Le iosphaer idi a tangentansis x x x x

separates these units in both Leiosphaeridia s p . x 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 with vugs filled by secondary Tasmani t es cla icmon tensis )(

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 - Lower Gra velbour g, Unit ,. The contact between the LGB - Lower Gravel bourg, Uni t B

upper and lower member of UG - Upper Gravelbourg LSl - LO.-er Shaunavon, Unit 1 the Gravelbourg Formation is US - Upper Shauna von RM - Rocanv i l le Me na.her sharp, but evidence of erosion MMA - MoosoJ1.in Member, Uni t A MMB - Moosomin "efflber, Unit B and weathering is lacking, ar-Biii\ - BU~ro~s Member, Un it A guing against a clear unconfor-BMB - Burro ws Member, Un it B

mity. This contact more probably represents a paraconformity.

134 Summary of Investigations 1989

b) Upper Gravelbourg Member

Seven samples taken from the upper member of the Gravelbourg have a combined palynomorph as­semblage including: Bennettiteaepollenites canadensis, Calamospora mesozoica, Cerebropollenites macrover­rucosus, Concavissimisporites southeyensis , Gleicheniidites nilssonii, lnaperturopollenites turbatus, Lycopodiumsporites pseudoannotinus, Pityosporites divulgatus and Protopicea exilioides, that is quite similar to Pocock's (1972). Pocock noted an abrupt change in character of the palynology of the assemblages at the boundary between the upper and lower members of the Gravelbourg Formation, indicating an abrupt change in the depositional environment. He also felt that this change was indicative of an unconformity at this con­tact. Pocock suggested that the lack of marine palynomorphs in the upper member indicated a lacustrine depositional environment.

While major components of the terrestrial palynological assemblage in both studies are similar, the occurrence of species of Leiosphaeridia, Rugidinium undulatum and of Tasmanites in the upper Gravelbourg in the present study suggests some marine influence. Taylor (1981 ) suggests a marine origin for the genera Tas­manites. Thus a coastal marine environment is en­visaged for the upper member of the Gravelbourg For­mation.

c) Lower Shaunavon Member

Palynomorph recovery from four samples from the lower member of the Shaunavon Formation, was rather poor. A particularily poor sample (1-17-20-23W2, 2465-2466 ft) was mounted as a epoxy pellet, examined under ultraviolet light, and found to contain abundant zoned dolomite rhomboids. Also present were pyritized microforams, scattered inertinite and several acritarchs of the Veryhachium type.

The lower Shaunavon samples come from what ap­pears to be a transitional unit between the upper mem­ber of the Gravelbourg Formation and the lower mem­ber of the Shaunavon Formation. This lithostratigraphic zone has also been recognized by Christopher (1989, pers. comm.) and is designated as unit 1 of the lower Shaunavon on the cross section in Figure 1 b. It occurs in well number 6 (i.e. 14-29-7-29W2) of the cross sec­tion, but is difficult to recognize east of the arbitrary lithofacies boundary (Figures 1 a and 1 b, in pocket).

Several palynomorph species found in both this study and Pocock's (1972) are Baculatisporites truncatus, Classopollis c/assoides, Tasmanites suevicus and Protoconiferus microsaccus, but the abundant dinoftagellates reported by Pocock (1972) are not ap­parent in the present samples. Only scarce specimens of the genera Tasmanites and Leiosphaeridia and a few unidentified dinoflagellates are found. The relative scar­city of dinoflagellates in unit 1 of the lower member of the Shaunavon suggests that the lower Shaunavon coastline was nearby (probably to the northeast), and may also be attributed to slow deposition in a high pH environment.

Saskatchewan Geological Survey

d) Upper Shaunavon Member

The palynomorph assemblage found in four samples of the upper member of the Shaunavon Formation differs significantly from Pocock (1972); the only common palynomorph is Chytroeisphaeridia variabilis . Sedimen­tological evidence suggests that shallow near-shore sedimentation prevailed during most of upper Shaunavon time, and that broad shifts in the strand-line was common (Christopher, 1964). This shifting of en­vironments may have caused the differences in the palynological assemblages, observed between Pocock's (1972) and the present study.

The palynological assemblage for the upper member of the Shaunavon is only similar to Pocock's with respect to the relative abundance of terrestrial species, but several marine species were identified that support a near-shore depositional environment (Table 1).

e) Rocanville Member

Most of the eight samples taken from the upper half of the Rocanville Member yielded poorly preserved and commonly unidentifiable specimens. Poor preservation of palynomorphs in the oxidized dolomitic and cal­careous mudstones of this unit is attributed to slow deposition in a high pH environment (Traverse, 1988). Evidence for subaerial exposure is seen in the oxidized and variegated nature of the mudstones. Subaerial ex­posure may have led to further corrosion of palynomorphs by bacterial action (ibid). Additional lithological and stratigraphic evidence of exposure is cited by Kreis (1988).

One sample taken from a one-metre thick car­bonaceous sandy siltstone unit at the base of the Rocan­ville Member (6-33-14-1 W2, 2492 feet) in the Wapella­Moosomin area yielded the palynomorphs Calamospora mesozoica and Protopicea exilioides which are index species for the upper Gravelbourg described by Pocock (1972). Other palynomorphs found which are index species for both the Rocanvifle Member and the typical assemblage for the upper member of the Gravelbourg in this study are: Classopollis itunensis, Concavis­simispori tes southeyensis, Cyathidites minor, and Podocarpidites wapellaensis. The presence of these index species supports the idea that some of the lower­most section of the Rocanville Member in the Wapella­Moosomin area may be correlated on lithological and palynological grounds with the upper member of the Gravelbourg Formation, west of the arbitrary lithofacies boundary (Figures 1a and 1b).

The presence of Calamospora mesozoica, Concavis­simisporites southeyensis , Tasmanites suevicus and some dinoffagellates (indeterminate) in both the Rocan­ville Member and the lower member of the Shaunavon supports the argument that these units are stratigraphic equivalents. Thus the Rocanville Member appears to be stratigraphically equivalent to both the lower member of the Shaunavon Formation and the upper member of the Gravelbourg Formation of southwestern Saskatchewan.

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f) Moosomin Member

A total of 10 samples, 3 from Unit A and 7 from Unit B, were taken from the Moosomin Member of the Red Jacket Formation in the Wapella-Moosomin area, yield­ing an abundant and diverse terrestrial palynological as­semblage. This suggests that the Moosomin is equivalent to at least part of the upper member of the Shaunavon Formation of southwestern and south­central Saskatchewan which also has an abundant and diverse palynological assemblage.

Although both units A and 8 contain a diverse and abun­dant terrestrial assemblage, unit B shows more marine forms than unit A of the Moosomin Member (Table 1 ). This supports the author's opinion that unit A represents a sequence of estuarine valley-fill sediments and the overlying unit B was deposited in a near-shore deposi­tional setting.

On the basis of geophysical log correlations, the Moosomin Member is most likely equivalent to the upper member of the Shaunavon Formation. A number of the palynomorphs listed as typical for units A and B of the Moosomin Member are found in the upper mem­ber of the Shaunavon in this investigation implying that they are stratigraphically equivalent {Table 1). In addi­tion, units A and B have produced a number of palynomorphs which are index species for Pocock's upper member of the Shaunavon, including: Podocar­pidites langii, Rugidinium ornatum and Solisphaeridium deflandrei.

Sedimentological evidence for a disconformity between the Rocanville and Moosomin Members is noted by Kreis (1988), possibly suggesting that some of the palynomorphs found in the Moosomin Member may have been derived from the underlying Rocanville. Evidence of extensive reworking, however, was not ap­parent in samples from this study.

g) Burrows Member

Three samples were taken from the Burrows Member, two from unit A and one from the overlying unit B. The mudstone which comprises unit A is marine and con­tains over 45 percent dinoflagellates. The presence of abundant Gonyaulacacean dinoflagellates suggests

136

these sediments were deposited in open marine condi­tions (Williams, 1978). The low frequency of terrestrial palynomorphs also supports an open marine interpreta­tion following Traverse (1988) who suggests that spores and pollens are present in virtually all environments but their abundance decreases towards open ocean.

Gonyaulacysta ornata is the only index species of Pocock's (1972) assemblage for the upper member of the Shaunavon Formation found in Unit A of the Bur­rows. In the present study, Cycadopites minmus, Del­toidospora minor and Leiofusa deunffii all belong to the typical palynomorph assemblages for the upper mem­ber of the Shaunavon Formation and unit A of the Bur­rows Member, suggesting that they are stratigraphic equivalents.

Unhappily, the single sample taken from unit B of the Burrows Member did not yield any palynomorphs.

3. References Christopher, J .E. (1964): The Middle Jurassic Shaunavon For­

mation of southwestern Saskatchewan; Sask. Dep. Miner. Resour., Rep. 95, 95p.

Kreis, L.K. (1988): The Red Jacket Formation of southeastern Saskatchewan; in Summary of Investigations 1988, Sask. Geol. Surv., Misc. Rep. 88·4, p211-223.

Milner, R.L. and Thomas, G.E. (1954): Jurassic System in Sas­katchewan; in Western Canada Sedimentary Basin; Am. Assoc. Pet. Geo!., Rutherford Mem. Vol., p250-267.

Pocock, S.A.J. (1970): Palynology of the Jurassic sediments of western Canada; Part 1, Terrestrial Species. Palaeon­tographica, Abt.8., v130, p12-72.

(1972): Palynology of the Jurassic sediments of - -w-e-s"'"te-rn Canada; Part 2, Marine Species. Paleon­

tographica, Abt.B., v137: p85-153.

Taylor, T.N. (1981): Paleobotany; McGraw-Hill Book Com­pany, NY, 583p.

Traverse, A. (1988): Paleopalynology; Allen and Unwin, Inc., Mass., 600p.

Williams, G.L. (1978): Dinoflagellates, Acritarchs and Tas­manitids; in Haq, B.U. and A. Boersma, (eds.), Introduc­tion to Marine Micropaleontology, Elsevier, NY, p293-326.

Summary of lnwstigations 1989