Ichnological Assemblages as Depositional Environmental Indicators in McMurray Formation: Athabasca Oil Sands of Northeastern Alberta

Blair W. Mattison, S. George Pemberton

Detailed study of over 100 drill core from an area of extreme core control within the surface mining area of the McMurray Formation of the Athabasca oil sands reveals that trace fossil assemblages may be extremely useful both in interpreting the depositional history of the deposits and ultimately in developing an effective mining strategy based on the prediction of high-grade reservoir trends.

Distinct trace fossil suites characterize distinct environmental facies within all but the lowermost sections of the McMurray Formation and indicate deposition within a marginal marine setting. The formation itself may be divided into three members, reflecting a depositional evolution from primarily paludal and fluviatile into estuarine (containing intimately associated estuarine channel, channel margin, and tidal flat sediments) and finally into highly bioturbated shoreface sediments. Environmental microfacies breakdown of this broad three-fold division is based primarily on an understanding of trace fossil dynamics in tidally influenced marginal marine depositional systems.

Highest-grade reservoirs are restricted to the middle unit of the McMurray within estuarine channels. Prediction of the trends of these channels is accomplished through highly detailed mapping made possible by close core control. In this way, the channelized reservoirs may be exploited with the mining of as little waste rock (typically channel margin and tidal flat silts and muds) as possible.

An understanding of trace fossils (which may at first glance seem to be rather innocuous structures) may thus prove to be an extremely powerful aid in the delineation and profitable development of this immensely important resource.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.