ABSTRACT: Intra- and Extrabasinal Tectonism, Climate, and Intrinsic Factors-Controls on Early Cretaceous Fluvial Architecture, Western Wind River Basin, Wyoming

MAY, MICHAEL T., Indiana University, Bloomington, IN

Chert-bearing conglomerates in the Cloverly Formation (Aptian) of the western Wind River basin can be used to evaluate the relative importance of intra- and extrabasinal tectonism, climate, and intrinsic geomorphic factors as controls on fluvial deposition in an incipient foreland basin. Although Cloverly detritus was derived from basin-margin sources, intraforeland tectonism controlled the geometry and geographic distribution of coarse bodies, as is suggested by isopach mapping. Furthermore, the relative influence of basin-margin tectonism on the thickness and nature of nonmarine foreland fill diminishes toward the medial-to-distal parts of the basin where intrinsic, climatic, and local tectonic factors dominate.

In the western Wind River basin, flashy discharge events associated with an inferred semi-arid climate were important processes active in the transportation and deposition of Cloverly sediments. Local downcutting of upper, meandering Cloverly channels into basal, braided Cloverly channels may be explained by localized uplifts or by avulsion, as opposed to renewal of extrabasinal tectonism.

An overall upward decrease in grain size through the Cloverly section reflects a decreasing extrabasinal influence though time, which, presumably, forced the fluvial systems to evolve from braided to meandering. Multiple coarse-clastic intervals in the Cloverly also could be related to episodic, isostatic readjustment of the basin-margin source area, reflecting drainage-basin evolution rather than multiple extrabasinal tectonic pulses.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)