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Geology

Geological Setting

The Manitoba Escarpment, a physiographic feature that rises above the Red River Valley, extends north-westerly across the southern of Manitoba. Cenozoic glacial activity is responsible for the current topography of Manitoba, especially the escarpment. This escarpment represents the easternmost edge of Cretaceous rocks within Manitoba.

All of the excavation sites during the 2011 field season were located in or directly adjacent to previously mined bentonite quarries where layers of shale are exposed. Collection and excavation were specific to the Boyne Member of the Carlile Formation, and the Gammon Ferruginous, Pembina, Millwood, and Odanah Members of the Pierre Shale.

FIGURE 1: Composite stratigraphic column of the Cretaceous rock sequence along the Manitoba Escarpment highlighting the geological formations and members covered in this report (Bamburak and Nicolas, 2010)

Carlile Formation

The Carlile Formation is composed of non-calcareous, carbonaceous shale of the 55 m thick Morden Member, overlain by the 75 m thick calcareous, speckled, chalky shale of the Boyne Member (Bamburak and Nicolas, 2009).

 

Boyne Member

The buff, grey, calcareous shale of the Boyne Member is composed of two units: the lower Calcareous Unit, and the upper Chalky Unit, separated by a resistant siltstone and sandstone sequence informally designated as the “Babcock Beds” at the top of the calcareous unit (Nicolas and Bamburak, 2009). Outcrop exposures documented by the CFDC Field Team throughout the Pembina Mountain area typically only expose various sections of the upper chalky unit. The lower calcareous unit was only observed in the Snow Valley area, along road cut exposures west of the town of Roseisle, MB where it is capped by the Babcock Beds.

Multiple outcrops of the seemingly monotonous Boyne Member exhibit varied stratigraphic portions of the Member, with little change in the deposition and/or the lithofacies representing this time of the Cretaceous. However, the CFDC Field Team was able to piece together a rough stratigraphic picture of what a nearly complete Boyne Member (Chalky Unit) section would roughly look like, with the most complete exposure outcropped along a road cut in Snow Valley.

Outcrops were observed across a range of 53 kilometres (28.5 nautical miles) from as far south as the Pembina Gorge west of Walhalla, North Dakota, along compass heading 165.26 degrees across the Canada/US international border, into the upland region of Pembina Mountain, and as far north as Snow Valley. The Chalky Unit of the Boyne Member is only subtlety diverse and requires intensive field investigation before various sections of the member become discernible from one another. Based on observations and documentation with Snow Valley and again at Pembina Valley Provincial Park, two stratigraphic layers of “coquina shells” occur in-situ near the base of the Boyne’s upper Chalky Unit. These units could prove to be useful biostratigraphic datum markers for the Boyne Member of the Carlile Formation, and could possibly correlate with similar oyster-shell beds from the Smoky Hill Chalk of the Niobrara Formation of Western Kansas (Everhart and Everhart, 1992). One such correlation has recently been made by measuring bentonite beds within the Boyne Member, and we can now correlate one outcrop of the Boyne Member from the Pembina Gorge in North Dakota, to another outcrop 38 kilometres to the northwest of the same Boyne Member in Manitoba, at CFDC Site 13.

 

Pierre Shale

Gammon Ferruginous Member

The Gammon Ferruginous Member of the Pierre Shale is composed of non-calcareous, carbonaceous, hard, and grey to black shale containing many red-weathering siderite concretions (McNeil and Caldwell, 1981). Typically, the Gammon Ferruginous is absent within outcrop exposures in the Pembina Mountain region, producing a geological unconformity between the Boyne Member of the Carlile Formation and the Pembina Member of the Pierre Shale. However, the Gammon Ferruginous Member is known in Manitoba’s subsurface where the Member has recently been measured at a maximum thickness of over 56 m in south-western Manitoba, with a strong thinning of the deposits to the east (Bamburak and Nicolas, 2010). It was postulated in 1981 by McNeil and Caldwell that subsidence of post-Boyne deposition uplift allowed for the Gammon sediments of the earliest Pierre Sea to make inroads into the bevelled Boyne surfaces, and then subsequently, the Pierre Sea would spread out further across Manitoba and lead to the deposition of the Pembina sediments (McNeil and Caldwell, 1981).

Although rarely exposed in outcrop throughout the Manitoba Escarpment, the CFDC Field Crew has spent the past two full field seasons (2010 and 2011, respectively) excavating extensively in this unique lithology. The Gammon Ferruginous Member was reported by McNeil and Caldwell to consist of three units as identified in electric logs (McNeil and Caldwell, 1981), but lithologic descriptors were not provided. Excavation by the CFDC over two summers in this Member confirms the presence of three distinctive units which our Field Team have dubbed as the “Lower Gammon, Middle Gammon, Upper Gammon,” respectively. Vertebrate skeletons have been recovered by the CFDC from all three units: The Lower Gammon Ferruginous is a grey carbonaceous, non-calcareous shale with at least four bentonite layers, sometimes turbulently mixed into one thinker band, and has produced CFDC specimens M.09.01.13 (Clidastes) and F.09.03.13 (Xiphactinus) which were discussed in the 2012 field report. The Middle Gammon Ferruginous is composed of black, waxy, non-calcareous, carbonaceous shale with abundant red-weathering siderite concretions and has produced CFDC specimen M.2011.01.13 (this report). The Upper Gammon Ferruginous is comprised of fissile, grey, clay-rich swelling non-calcareous to calcareous shale and has produced one fossil avian, CFDC specimen B.2010.02.13 (Hesperornis) which was discussed in the 2010 field report.

This one particular outcrop of the Gammon Ferruginous Member of the Pierre Shale in Manitoba is the second thickest outcrop of this lithology in the Manitoba Escarpment (Bamburak and Nicolas, 2010) and continues to produce vertebrate fossils of tremendous paleontological significance. The Manitoba Geological Survey has found anomalous occurrences of Rare Earth Elements (REEs) within the Gammon Ferruginous Member, particularly Platinum and Palladium values, which has led to a hypothesis that shallow pools where Gammon deposition occurred, trapped these Cretaceous animals, and the mineral richness of the depositional environment carried a high degree of toxicity, which could partially explain why the CFDC is finding so many taxa within a very localized outcrop (J. Bamburak, pers. comm.).

 

Pembina Member

The basic lithology of the Pembina Member consists of non-calcareous, carbonaceous, black shale with numerous bentonite horizons located in the lower portion of the Member (Bamburak and Janzic, 2007). The sequence of alternating bentonite and carbonaceous shale layers is commonly known as the “Ardmore Bentonite Succession” in equivalent beds on the United States (Bertog et al. 2007). The Pembina Member has an average thickness of 7 metres with a trend to thin out towards the north (Bamburak and Janzic, 2007). The Pembina Member has produced the majority of the fossil collection at the CFDC to date, however it has not been determined if this represents a particularly high fossiliferous zone or if the high yield of fossil vertebrates is due to a collecting bias from previous bentonite mining activities within the Pembina Member (Nicholls, 1988).

 

Millwood Member

The Millwood Member conformably overlies the Pembina Member of the Pierre Shale and is exposed in many outcrops and former bentonite mines. Within the upland region of Pembina Mountain, the Millwood Member is an average 18 m thick and consists of grey, non-calcareous shale interbedded with light grey calcareous shale, both of which having a high content of montmorillonite (McNeil and Caldwell, 1981; Bannatyne, 1970).

Banded concretionary layers have been observed near the top of the Millwood section at sites 4, 16, and 26. These concretionary layers provide for the only physical stratigraphic datum point in the Pembina Mountain area outcrops of the otherwise monotonous-looking shale of the Millwood Member. Research published in 2007 announced the first occurrence of a single fossil decapod specimen from a concretion in the Millwood Member of Manitoba (Feldmann et al, 2007). A future study which looks closer into any possible decapod assemblages in the Millwood concretionary layers could prove very useful for establishing a stratigraphic datum within the Millwood Member.

 

Odanah Member

The Odanah Member of the Pierre Shale is the thickest member of this Cretaceous formation, outcropping through the transition of the Second and Third Prairie Levels of the Manitoba Escarpment. Vertebrate fossils are rare in the Odanah Member, though invertebrate trace fossils are typically more common. The Odanah Member is composed of manganese and iron rich, highly siliceous shale rendering it more resistive to weathering at the surface and as such, municipal aggregate shale quarries abound in areas where the Odanah Member is near the surface. The Rural Municipality of Thompson operates mines in the Odanah Member for use on the country roads, due to its siliceous content and resistance to rapid weathering. The CFDC has recently provided research assistance for a non-related project by the Rensselaer Polytechnic Institute’s Department of Astrobiology in New York which has demonstrated that a sodium bentonite has been identified which differs from all other known bentonites in Manitoba and thus forms a new bentonite class and proves to have originated from a very different magmatic source (Aldersley et al, 2011).

Bar graph showing the stratigraphic occurrence of the fossils collected by the CFDC during the 2011 Field Season.

FIGURE 4: Bar graph showing the stratigraphic occurrence of the fossils collected by the CFDC during the 2011 Field Season.

References

Aldersley, M.F., J.D. Bamburak, P.C. Joshi, J. Thompson, J.W. Delano, and J.P. Ferris. 2001. Evaluation of Manitoba bentonites in the catalysis of RNA synthesis by montmorillonite (parts of NTS 62G1, 8, 10, K3, N1); in Report of Activities 2011, Manitoba Innovation, Energy and Mines, Manitoba Geological Survey, p. 150-157.

Bamburak, J.D. and M.P.B. Nicolas. 2010. Gammon Ferruginous Member of the Cretaceous Pierre Shale in southwestern Manitoba: distribution and mineral potential (parts of NTS 62F, G, J, K, N, O, 63C); in Report of Activities 2010, Manitoba Innovation, Energy and Mines, Manitoba Geological Survey, p. 170 – 177.

Bamburak, J.D. and M.P.B. Nicolas. 2009. Current Status of the Cretaceous Stratigraphic Nomenclature of Southwestern Manitoba. Proceedings Volume and Field Trip Manual, 2nd Manitoba Paleontology Symposium. Canadian Fossil Discovery Centre, pp. 10-11.

Bamburak, J.D. and A. Janzic. 2007. Mesozoic Stratigraphy of the Manitoba Escarpment (Pembina Mountain). Manitoba Paleontology Seminar, Abstracts and Field Manual. Canadian Fossil Discovery Centre, 34 p.

Bannatyne, B.B. 1970. The clays and shales of Manitoba; Manitoba Department of Mines and Natural Resources, Mines Branch, Publication 67-1, 107p.

Bertog, J., W. Huff, and J.E. Martin. 2007. Geochemical and mineralogical recognition of the bentonites in the lower Pierre Shale Group and their use in regional stratigraphic correlation; in Martin, J.E. and Parris, D.C., eds., The Geology and Paleontology of the Late Cretaceous Marine Deposits of the Dakotas. Geological Society of America Special Paper 427, p. 23-50.

Everhart, M. J. and P. Everhart. 1992. Oyster-shell concentrations; a stratigraphic marker in the Smoky Hill Chalk (upper Cretaceous) of western Kansas. Kansas Academy of Science, Transactions, 11(Abstracts):12.

Feldmann, R.M., R. Li, and C.E. Schweitzer. 2007. A new family, genus, and species of crab (Crustacea, Decapoda, Brachyura) from the Upper Cretaceous (Campanian) of Manitoba, Canada. Canadian Journal of Earth Sciences, 44: 1741–1752.

McNeil, D.H. and W.G.E. Caldwell. 1981. Cretaceous rocks and their Foraminifera in the Manitoba Escarpment. Geological Association of Canada Special Paper, 21: 1-439.

Nicholls, E.L. 1988. Marine Vertebrates of the Pembina Member of the Pierre Shale (Campanian, Upper Cretaceous) of Manitoba and their Significance to the Biogeography of the Western Interior Seaway. Ph.D. Thesis, University of Calgary, 317 p.