--> Abstract: Controls on the Evolution and Distribution of Fluvial Deposits in a Foreland Basin: Late Jurassic to Tertiary of the Western Canadian Foreland Basin, by D. A. Leckie and G. C. Nadon; #90937 (1998).

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Abstract: Controls on the Evolution and Distribution of Fluvial Deposits in a Foreland Basin: Late Jurassic to Tertiary of the Western Canadian Foreland Basin

LECKIE, DALE A., Geological Survey of Canada, 3303-33rd St. NW Calgary, Alberta, Canada, T2L 2A7; GREGORY C. NADON , Dept. of Geological Sciences, Ohio University, Athens, OH, USA

Abstract

Fluvial deposits of the Alberta foreland basin span the Late Jurassic to Oligocene. The lateral and vertical variation in fluvial styles - braided sheet, braided valley fill, meandering, and anastomosed are a response to major variations in tectonic, climatic, eustatic, and source rock factors in basin evolution. Petrographic variations show laterally-shifting drainage divides throughout the evolution of the foreland basin. Braided sheets, characterized by basin-axial flow and overlying a profound unconformity, occur twice in the lowermost Cretaceous and Tertiary. The braided sheets are associated with lulls in tectonic activity. Multiple deeply incised, braided valley fills of Albian age have east-directed paleocurrent vectors, perpendicular to the cordillera. The provenance of the braided valley fill resulted from the drainage divides shifting to the west for a brief period of time, originating from the west of the plutonic belt. The coarse, braided deposits formed in response to low rates of formation of accommodation space in SW Alberta combined with high rates of denudation. The braided conglomerates and sandstones throughout the section are intercalated with meandering fluvial deposits that reflect slightly higher rates of formation of accommodation space. Anastomosed fluvial deposits are abundant in Upper Cretaceous to Lower Tertiary strata being the result of a combination of high rates of subsidence, a mud-rich source rock, and seasonal precipitation which provided the low slopes mud-dominated fluvial systems required to form the deposits.

High frequency eustatic control is only a factor in lower reaches, within 100-200 km of the sea. While longer term fluctuations can potentially affect proximal basin settings, they can only affect fluvial styles when the combination of tectonic and climatic factors keep the sediment flux at a minimum.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah