Ichnofabrics and Palynology from the Cretaceous Mannville Group, McMurray Formation and Wabiskaw Member: From Example from the Athabasca Region, Northeast Alberta, Canada

Geoffrey Musial and Daniel Michoux
Exploration-Production, Total, Pau, France

The Cretaceous Mannville Group contains the main reservoir units (McMurray Formation) of the Athabasca oil sands province. The McMurray Formation was deposited within fluvio-lacustrine, estuarine and transitional depositional paleoenvironments and is capped by nearshore strata of the Wabiskaw Member of the Clearwater Formation. The nature of the sedimentation, with a complex interplay of erosion and deposition makes placing these strata within a sequence stratigraphic context an extremely difficult task. Sequence analysis relies on seismic facies analyses, regional seismic investigations, petrophysical interpretations and, when available, direct observation of sedimentary features in cored sections.

Ichnofossils, which are common in the McMurray Formation and overlying Wabiskaw Member, have been studied extensively in this context. Palynology has so far been used for chronostratigraphic purposes as well as helping discern the depositional paleoenvironments. Microplankton of continental, brackish and marine origin are present in the palynofloral assemblages, sporadically but invariably present in the lower McMurray Formation, and more consistently in the upper McMurray and overlying Wabiskaw. The overall composition of the palynofloral assemblages, the ratio of marine versus continental palynomorphs, and microplankton diversity are here used in conjunction with ichnofossils in assessing the depositional paleoenvironments in the Manville Group and provide support to the sequence stratigraphic interpretations.

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