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The buff, grey, calcareous shale of the Boyne Member of the Carlile Formation are 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 Canadian Fossil Discovery Centre throughout the Pembina Mountain area typically only expose various sections of the upper chalky unit. The lower calcareous unit has only been observed in the Snow Valley area of, along road cut exposures west of the town of Roseisle, Manitoba 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 Canadian Fossil Discovery Centre 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 one 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 Canadian Fossil Discovery Centre Dig Site #13.


REFERENCES

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.

Nicolas, M.P.B. and J.D. Bamburak. 2009. Geochemistry and mineralogy of Cretaceous shale, Manitoba (parts of NTS 62C, F, G, H, J, K, N): preliminary results; in Report of activities 2009, Manitoba Innovation, Energy and Mines, Manitoba Geological Survey, p. 165-174.