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Tidal-Dominated Estuarine Sequence in Lower Cretaceous Athabasca Basin, Northeast Alberta

Grant D. Wach, Miles O. Hayes, Adel O. Tammam, Gordon A. Stewart

In northeastern Alberta, the Athabasca oil sands of the Lower Cretaceous McMurray Formation were deposited unconformably in a broad drainage basin developed on an eroded Devonian surface of argillaceous limestone. The Lower Cretaceous Clearwater sea, of the Western Interior seaway, progressively flooded the region from the northwest, and the basin was filled with sediment during an overall transgressive sequence.

To reconstruct an interpretation of the paleogeography, a suite of 74 maps was produced at 1-m intervals or "slices" above and below the contact of the upper and middle McMurray units. The depositional framework was examined in the context of a high mesotidal to macrotidal estuarine model developed by M. O. Hayes. Ord River of northern Australia and Bristol Bay, north of the Alaskan Peninsula, were used for comparison as modern analogs.

The depositional environments passed through several stages: from a fluvial channel and flood-plain environment in the lower McMurray unit; a tidal-dominated estuarine sequence in the middle unit; and a nearshore and open-marine system in the upper unit. The McMurray Formation in Secs. 3, 4, 9, and 10, T93N, R11W on the Syncrude Canada Ltd. oil-sand leases was examined to discern the history and patterns of sedimentation.

An enhanced model of the depositional sequence can be used to develop more efficient use of the oil sands during drilling and planning for in-situ or open-pit development schemes.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.