Review of Regional Stratigraphic Relationships of the Winnipeg Group (), the Deadwood Formation (Cambro-Ordovician) and Underlying Strata in

D.F. Paterson

Paterson, D.F. (1988): Review of regional stratigraphic relationships of the Winnipeg Group (Ordovician), the Deadwood Forma­ tion (Cambro-Ordovician) and underlying strata in Saskatchewan; in Summary of Investigations 1988, Saskatchewan Geological Survey; Saskatchewan Energy and Mines, Miscellaneous Report 88-4.

The lowermost Phanerozoic rocks in southern Sas­ are Late (Dresbachian through T rempeal­ katchewan and adjoining areas to the east, west and eauan) and Units C through F are Early Ordovician south comprise a sequence of interbedded , (Tremadocian through Arenigian). Their isopach maps siltstones and underlying carbonates of the Or­ show that it is mostly Units A and B, 100 m at their thick­ dovician . Dowling (1900) and Dar­ est development, which extend into Saskatchewan, with ton (1901) reported on outcrops of the sequence from perhaps 50 m of Unit C present in the extreme Lake Winnipeg and respectively, and southeast. Units D through F are restricted to the central numerous later studies included much subsurface data part of the and are therefore entirely ab­ from areas where deep wells had been drilled (see, sent in Saskatchewan. most recently, Anderson (1988) for and, for a comprehensive list of references, Lefever et al. The above implies that the Deadwood Formation in east­ (1987)). ern Saskatchewan is essentially Late Cambrian, with pos­ sibly a small area of Early Ordovician (T remadocian) in The uppermost strata of the sequence in Saskatchewan the southeast. Units C through E extend westward into form the Winnipeg Formation, which has a maximum , consistent with finds there of Lower Or­ thickness of 67 m. Paterson ( 1971) subdivided it into a dovician by Ross (1957). lower Black Island Member and an upper Icebox Mem­ ber, and documented their stratigraphic and areal ex­ In the western part of southern Saskatchewan, Fyson tents. His subdivisions agreed essentially with those of (1961) called the entire sequence Deadwood Formation. Carlson (1960) who recognized a third uppermost mem­ He proposed three subdivisions: 1) Lower Deadwood ber called the Roughlock. Carlson's proposal that a thin Unit, 2) Middle Deadwood Unit, and 3) Upper Dead­ band of the Roughlock extends into extreme southeast wood and Winnipeg Unit. He claimed the Winnipeg, Saskatchewan has not so far been confirmed. Carlson which was poorly developed in the eastern part of his and Anderson (1965) raised the Winnipeg to group area, as a facies of the Deadwood and postulated the status and the members to formations. Cambro-Ordovician boundary to lie near the top of his Middle Deadwood Unit. In , Vigrass (1971) and McCabe (1978) similar­ ly defined the Winnipeg Formation but subdivided it into Van Hees (1964) went much further. He correlated the Upper and Lower Units. lower part of the sequence in western Saskatchewan with formations of Middle Cambrian age lying below the There is general agreement that the Winnipeg Forma­ Deadwood Formation in . These are, in ascend­ tion is Middle Ordovician in age (Lefever et al. (1987) ing stratigraphic order, the Cathedral, Stephen and specify Caradocian) and rests uncomformably upon the Eldon Formations. He recognized also the Pika Mem­ underlying strata. In the eastern part of southern Sask­ ber, a carbonate development at the top of the Eldon. atchewan, it directly overlies metamorphic Preliminary work being done by the author for the new rocks. In the west, towards the Alberta border, it overlies Geological Atlas of the Western Sedimentary a wedge of sedimentary strata which increases gradually Basin seems to substantiate some of these correlations. to a maximum recorded thickness of 514 m. Geologists Van Hees's maps show these strata to extend east­ in Saskatchewan have generally recognized this se­ wards from the Alberta border for some 275 km at the quence as the Deadwood Formation and considered it latitude of Uoydminster and for some 150 km into the to be Cambrian in age, although van Hees (1964) sug­ southwestern corner of Saskatchewan where they attain gested the presence of several formations below the a thickness of approximately 170 m. The rocks reach a Deadwood, and Ross (1957) recovered Lower Or­ thickness of nearly 250 m 100 km south of Lloydminster. dovician fossils from the Deadwood in northeastern Montana. Van Hees recognized the upper part of the sequence as Deadwood Formation, assigning it a Late Cambrian - Lefever et al. (1987) showed that the Deadwood Forma­ Early Ordovician age (Dresbachian through Tremad­ tion is over 250 m thick where it is most fully preserved ocian), and the uppermost strata to the east as Win­ in the central part of the Williston Basin in North Dakota. nipeg Formation. His maps show the Deadwood extend­ They subdivided it into six units, A through F in ascend­ ing almost to the Manitoba border, thickening in the ing stratigraphic order, and reported that Units A and B west to some 300 m in the south-central part of the

224 Summary of Investigations 1987 province and to approximately 340 m in an area 50 km Carlson , C.G. (1960): Stratigraphy of the Winnipeg and Dead­ north of Lloydminster. He has attempted to separate the wood Formations in North Dakota; N. Oak. Geo!. Surv., Cambrian and Ordovician portions of the formation Bull. 35, 149p. using the ·m· marker of Fuller and Porter (1962). This Carlson, C.G. and Anderson, S.S. (1965): Sedimentary and separation implies the presence of some 200 m of tectonic history of North Dakota part of the Williston Cambrian Deadwood and about 100 m of Ordovician Basin; Am. Assoc. Petrol. Geo!. Bull., v49, p1833-1846. Deadwood. In comparison, Lefever's figures are 100 m of Cambrian and 150 m of Ordovician in the Deadwood Darton, N.H. (1901): Preliminary description of the geology of North Dakota. It is instructive to compare the 300 m and water resources of the southern half of the Black Hills of Van Hees's Deadwood and the 250 m of Lefever's and adjoining regions In and Wyoming; Deadwood with the much thicker 514 m of "Deadwood" U.S. Geo!. Surv., 21st Annu. Rep., Pt.4, p502·508. presently ascribed to western Saskatchewan. Dowling, D.S. (1900): Report on the geology of the west shore and islands of Lake Winnipeg; Geol. Surv. Can., Annu. Conclusions Rep. F, 100p. Fuller, J.G. and Porter, J .W. (1962): Cambrian, Ordovician and 1) The lowermost Phanerozoic strata in western Sask­ formations of the northern Great Plains, and their atchewan are probably Middle Cambrian and corre­ regional connections; Alberta Soc. Petrol. Geol. J., v10, late with the Cathedral, Stephen and Eldon Forma­ no8, p455-485. tions of southern Alberta. 2) The overlying strata in western Saskatchewan Fyson, W.K. (1961): Deadwood and Winnipeg stratigraphy in belong to the Deadwood Formation and are Late southwestern Saskatchewan; Sask. Miner. Resour., Cambrian to Early Ordovician (Dresbachian­ Rep. 64, 37p. Tremadocian). Lefever, A.O., Thompson, S.C. and Anderson, D.S. (1987): Ear­ 3) In southeastern Saskatchewan, the Deadwood For­ liest Paleozoic history of the Williston Basin in North mation rests directly on Precambrian basement and Dakota; in Fifth International Williston Basin Symposium; comprises strata of Dresbachian through Tremadoc­ Sask. Geol. Soc./ N. Oak. Geol. Soc., Spec. Pub!. 9, p22· ian age. It is not known if the Tremadocian strata are 36. laterally continuous with their western counterparts across southern Saskatchewan. McCabe, H.R. (1978): Reservoir potential of the Deadwood and Winnipeg Formations in southwest Manitoba; Manit. 4) In eastern Saskatchewan, only the Cambrian portion Dep. Mines, Geol. Pap. 78-3, 54p. of the Deadwood is preserved, resting directly on Precambrian. Paterson, D.F. (1971): The stratigraphy of the Winnipeg Forma­ 5) The Winnipeg Formation is present from the tion (Ordovician) of Saskatchewan; Sask. Miner. Resour., Manitoba border to within 100 km of the Alberta bor­ Rep. 140, 57p. der. It overlies the Deadwood Formation in central southern Saskatchewan and rests directly on Ross, R.J. (1957): Ordovician fossils from wells in the Williston Precambrian in the extreme east. It is believed to be Basin, eastern Montana; U.S. Geo!. Surv., Bull. 1021, Pt.M, p439·510. Middle Ordovician in age, possibly Caradocian. Van Hees, M. (1964): Cambrian ; in McCrossan, A.G. and Glaister, A.P.(eds.), Geological History of Western References Canada; Alberta Soc. Petrol. Geol., Calgary. Chap. 3, Pt.1, p20-28. Anderson, 0. (1988): Progradational sequences in Lower Or­ dovician portion of Deadwood Formation. Williston Basin Vigrass, L.W. (1971): Depositional framework of the Winnipeg (abstract); Am. Assoc. Petrol. Geol., Rocky Mtn. Sect. Formation in Manitoba and eastern Saskatchewan; Geol. Meet., Bismarck, N.D. Assoc. Can., Spec. Pap. 9, p225-234.

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