The Athabasca Oil Sands — A Regional Geological Perspective, Fort McMurray Area, Alberta, Canada

Most of the bitumen in the Athabasca deposit is hosted within fluvial, estuarine, and marginal marine deposits of the Lower Cretaceous Wabiskaw-McMurray succession. The present study is an integration of recent outcrop and subsurface studies, mainly focused in the Fort McMurray area of northeastern Alberta. The basis of the regional geologic framework includes outcrop sections (78), detailed core descriptions (165), and a net of subsurface wire-line log sections (14), all framed within modern concepts of regional correlation and sequence-stratigraphy.The paleogeographic evolution of the Athabasca Wabiskaw-McMurray succession includes five main phases: (1) Lower McMurray fluvial as lowstand deposits; (2) the lower part of the Upper McMurray fluvio-estuarine channel complexes which formed during early transgressive conditions; (3) the upper part of the Upper McMurray A sequences as relict bay-fill and marginal marine deposits formed during early and middle transgressive phases; (4) Wabiskaw D valley-fill developed during a relative sea-level drop at the end of McMurray time (valley-incision phase), which was backfilled during the ensuing transgression; (5) Wabiskaw D regional marine shale, deposited during widespread flooding of the main McMurray-Wabiskaw transgression; and (6) Wabiskaw C deposits formed during continued transgression or early regressive pulses.The regional geological framework has both economic and academic significance, providing better documentation and understanding of the compartmentalization of the oil sands mainly the result of the inherent geological heterogeneity of the Wabiskaw-McMurray succession. Such regional correlation and framework will aid in predicting subsurface and surface reservoir quality and in increased understanding of marginal marine and non-marine sequence stratigraphy.

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