ABSTRACT: Paleocene Tectono-Facies Relationships Between the Hanna, Carbon, and Cooper Lake Basins, Wyoming

CAVAROC, V. V., North Carolina State University, Raleigh, NC, R. M. FLORES, D. J. NICHOLS, and W. J. PERRY, Jr., U.S. Geological Survey, Denver, CO

The Hanna, Carbon, and Cooper Lake basins occur along a 100-km southeasterly trend in southern Wyoming. The Hanna basin contains at least 3300 m of fluvial dominated, coal-bearing Paleocene Ferris and Hanna formation strata. These formations decrease in thickness southeastward to about 300 m in the Carbon basin before pinching out in the Cooper Lake basin (Rock Creek coal field). Deformed older strata and Precambrian basement rocks of the Seminoe and Shirley Mountains portions of the Granite Mountains-Sweetwater arch (GMSA) parallel the northern margins of the basins. Similar deformed rocks in the Medicine Bow Mountains bound the basins to the south.

Facies studies, combined with palynologic analyses from all three basins, suggest a sequence of Paleocene Laramide tectonic events, part of the complex Paleocene Laramide transpressional tectonic development of south-central Wyoming. The initial phase began with the accumulation of the Ferris coals of the western Hanna basin during the early Paleocene (palynostratigraphic zones P1-P2), whereas erosion of areas to the east and north (GMSA) reflected tectonic growth of a broad Laramide-Front Range arch. Subsequently, the coal-bearing Hanna Formation strata of the eastern Hanna and Carbon basins were deposited above the Ferris Formation in the middle to late Paleocene (zones P3-P6), as the depocenter shifted eastward. Detrital influx was primarily from uplift to the north (GMSA). Facies elations and paleotransport indicators of the Hanna Formation in the Carbon basin suggest that the predominantly southeastward-flowing braided-channel complexes of the Hanna Formation were concentrated initially along the rapidly subsiding northern basin margin and later developed into laterally shifting avulsion belts. Most persistent mire development initially occurred along the more slowly subsiding southern basin margin. However, later coals were less predictably draped between en-echelon stacked sandstone bodies. Northward paleodrainage, beginning in the late Paleocene (zone P5), marked initial growth of the Medicine Bow Mountains, and structural growth of the north-bounding Arlington thrust system.

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