Sequence stratigraphic analysis of individual depositional successions: Effects of marine/nonmarine sediment partitioning and longitudinal sediment transport, Mannville Group, Alberta Foreland Basin, Canada
- Institute of Sedimentary and Petroleum Geology, Alberta (Canada)
In the Falher Member of the Mannville Group (Aptian-Albian) of western Canada, two shoreline successions contain the reservoir conglomerates for the giant Elmworth gas field. The Falher B succession has basal sheetlike shoreface unit of hummocky cross-stratified sandstone that thins seaward and terminates about 30km north (seaward) of the landward limit of the transgression. Another 25 km farther basinward, the succession shows a 20-30-m-thick sandstone, unattached to the prograding shoreface, and an overlying coarsening-upward shoreface succession with thin muds and coals, interpreted as back-barrier deposits. In the upper (Falher A) succession, immediately landward (south) of the barriers, fluvial valleys were incised into nonmarine mudstones and coals during the base-level fall. As relative sea level subsequently rose, in nonmarine areas the valleys were filled by estuarine and fluvial sands, then a widespread sheet of fine-grained nonmarine sediment was deposited. At the same time, the shoreline migrated back across the shelf. As it reached the original shorezone (structurally controlled), reworking of underlying deposits successively generated three gravelly barrier islands superimposed on the sandy shoreface succession. The conglomeratic reservoirs all rest above the unconformities, in the transgressive depositional system. Westward (alongshore) toward the thrust belt, no falling or lowstand sea level succession developed. Instead, a wide regressive shoreface sandstone with a transgressive cap occurs. Subsidence rates were higher in this area, and relative sea level appears always to have risen, but at varying rates. Any two-dimensional sequence stratigraphic model, therefore, is inadequate to describe the lateral variation of the sequence and distribution of shoreface sandstones, because the subsidence gradient was not parallel to the direction of shoreface progradation.
- OSTI ID:
- 68381
- Journal Information:
- AAPG Bulletin, Vol. 79, Issue 5; Other Information: PBD: May 1995
- Country of Publication:
- United States
- Language:
- English
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