--> Abstract: Long Linear Sand Bodies in the Viking Formation (Upper Albian): Evidence for Lowstand Incised Shorefaces, by T. R. Wiseman and R. G. Walker; #90987 (1993).

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WISEMAN, TERRENCE R., and R. G. WALKER, McMaster University, Hamilton, Ontario, Canada

ABSTRACT: Long Linear Sand Bodies in the Viking Formation (Upper Albian): Evidence for Lowstand Incised Shorefaces

Highstand, lowstand, and transgressive systems tracts and their depositional systems are identified within the Viking Formation of the Western Interior Seaway, Alberta. New data, particularly from Joarcam field, show depositional systems separated by regionally mappable unconformities that establish the relative stratigraphic positions of oil and gas fields within the lowstand systems tract.

The first and oldest depositional system encompasses a series of eastward-offlapping, stacked, coasening-upward shelf-to-shoreface successions forming the progradational highstand systems tract. These successions downlap onto a depositional discontinuity separating the Viking Formation from the underlying Joli Fou shale.

The second depositional system is characterised by long, narrow, en echelon sand bodies encased in marine shale. Previous work describes these sandstones as gradationally rooted in offshore mudstones, suggesting highstand offshore "bar" or "ridge" interpretations. However, these descriptions have failed to recognise erosional surfaces underlying the sandstones. These surfaces form elongate, northwest-southeast trending asymmetric scours that we interpret as shoreface incisions eroded into beds of the underlying highstand depositional system. Thus, the sandstones at Joarcam, Chigwell, and Sunnybrook `A' and `B' are here re-interpreted in terms of shoreface (rather than "offshore bar") deposition controlled by fluctuations of relative sea-level. The deposits therefore belong in the lows and rather than highstand systems tract.

The third and oldest depositional system consists of thin conglomeratic lag overlain by offshore mudstones forming the transgressive systems tract. The conglomerates were deposited during transgression, mantle ravinement surfaces, and terminate that phase of Viking deposition.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.