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The AAPG/Datapages Combined Publications Database

CSPG Bulletin

Abstract


Bulletin of Canadian Petroleum Geology
Vol. 39 (1991), No. 2. (June), Pages 228-228

"Origin and Facies Variability of Overthickened Sandstones in the Doig Formation, West-Central Alberta [Abstract]"

Wittenberg, J.1, Moslow, T.F.1

ABSTRACT

Within the Middle Triassic Doig Formation of west-central Alberta, a number of anomalous sandstones occur that attain thicknesses of up to 60 m. These sandstone bodies have been previously interpreted as channel or valley-fill deposits. Evidence from core, dipmetre logs and regional cross-sections suggests that these sand bodies are deposited penecontemporaneously with the laterally adjacent sedimentary facies.

The fine grain size, oversteepened bedding - extensive elongation of sand body geometry along depositional strike, the confinement of the sand bodies to narrow trends generally less than 2 km wide, and the lack of bifurcating trends, suggest that these bodies are not related to channels. In core, the abundance of soft sediment deformation features, and presence of synsedimentary fault zones and lack of exposure surfaces also preclude the interpretation of these features as channels. Instead, it is proposed that the overthickening and linear geometry of the Doig sandstone is a product of eastward-verging, synsedimentary, listric normal faults at or near the shelf margin. Continued rotation and subsidence of slump blocks provide more room for the accommodation of sediment. Rotation of these blocks also accounts for the oversteepening and divergence of the dips of the strata in overthickened sandstones, as observed in core and dipmetre logs.

The overthickened sandstones are deposited as a series of normally graded beds or bedsets 0.5 to 5 m thick, are generally sharp based, and are interpreted as amalgamated sediment gravity flow deposits. These deposits have been reworked at their tops as a result of subsequent transgression preceding the initiation of the next progradational parasequence.

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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES

1 University of Alberta, Edmonton, Alberta T2G 2E3

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