Ancient fluvial response to uplift and aggradation
The Cloverly Formation of the western Powder River Basin represents nonmarine sedimentation during eastward migration of the Western Interior foreland basin coeval with orogenic activity in the Cordilleran fold-thrust belt. It provides an opportunity to evaluate aggradational responses to tectonic uplift. The Cloverly Formation overlies the Morrison Formation (Jurassic) with a sharp basal contact marked by a cross-bedded, pebble conglomerate consisting of black chert clasts; conglomerates are overlain by a thick, dominantly trough cross-bedded, medium to fine grained quartzarenite. Fining upward sequences are rare. Sedimentary structures suggest these sandstones to be deposited in fluvial channels with a highly sinuous northerly paleoflow. In outcrop, discontinuous sandstones represent distinct channel systems, with some channel sands being laterally adjacent to levee, overbank, and swamp facies of bioturbated, carbonaceous siltstones, mudstones, and thin coals. In subsurface, the Cloverly Formation thins and thickens over short horizontal distances, suggesting channel erosion into the upper Morrison Formation. Cloverly channel sands show width-depth ratios which are consistent with Holocene meandering systems. The Cloverly Formation was part of a rapidly aggrading alluvial plain with swamps and meandering fluvial systems. This aggradation limited development of fining upward sequences. Rapid aggradation was correlated also to either a large clastic influx from the Sevier orogenic belt, or a rise in sea level causing aggradation within stream valleys, or both.
- Research Organization:
- Univ. of Illinois, Urbana (USA)
- OSTI ID:
- 6457858
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Vol. 17; ISSN GAAPB
- Country of Publication:
- United States
- Language:
- English
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