--> Abstract: Thrust Controlled Foreland Basin Fluvial Architecture, St. Mary River Formation, Southwestern Alberta, Canada, by G. C. Nadon; #91004 (1991)

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Thrust Controlled Foreland Basin Fluvial Architecture, St. Mary River Formation, Southwestern Alberta, Canada

NADON, GREGORY C., University of Wisconsin, Madison, WI

The style of fluvial system in foreland basins varies depending on the distance from the fold-and-thrust belt, and is especially influenced by the location and timing of blind thrusts within the basin. The St. Mary River Formation (Campanian to Maestrichtian) in southwestern Alberta contains lenticular, medium- to fine-grained, single- to two-story, ribbon sandstones deposited in fluvial channels of an anastomosing river system that flowed to the north and northeast from northwestern Montana. Separating the sandstones is a complex assemblage of sandstone/siltstone crevasse splay sheets interbedded with lacustrine and marsh siltstones and shales. The anastomosed fluvial system developed between (1) the region of maximum subsidence adjacent to the thrust front in northwestern Montana an (2) the region of uplift associated with contemporaneous blind thrusting in southwestern Alberta. The sandstone lenses are stacked vertically in two patterns: (1) lenses separated laterally by distances of up to 1 km, and (2) numerous lenses present in close lateral proximity to one another. The first stacking pattern represents normal sedimentation on a broad, low-gradient floodplain. The second pattern arises from the local confinement of channels because of topography produced by the growth of blind thrusts. The presence of lenticular or ribbon sandstone bodies in the stratigraphic record of foreland basins elsewhere may be a good indication of syndepositional compartmentation of a basin.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)