Eocene climates, depositional environments, and geography, greater Green River basin, Wyoming, Utah, and Colorado

Abstract

The climates, depositional environments, and geography of Eocene rocks in the greater Green River basin are investigated to determine the origin, mode of deposition, and areal distribution of the Wasatch, Green River, Bridger, and Washakie Formations. The data indicate that Eocene climates ranged from cool temperature to tropical and were affected by both terrestrial and astronomical factors. The terrestrial factors were mainly latitude, altitude, regional geography, tectonism, and volcanism. The astronomical factors are interpreted from reptitious rock sequences in the Wilkins Peak Member of the Green River Formation that record seasonal changes, 21,000 year precession of the equinox cycles, 100,000 year eccentricity cycles, and an undetermined cycle of 727,000 years. Eight depositional environments are identified, discussed, and illustrated by diagrams, columnar sections, and photographs. They are: (1) fluvial, (2) paludal, (3) freshwater lacustrine, (4) saltwater lacustrine, (5) pond and playa lake, (6) evaporite (salt pan), (7) mudflat, and (8) volcanic and fluviovolcanic. The areal distribution of the eight depositional environments in the Wasatch, Green River, Bridger, and Washakie Formations is illustrated by photographs and 13 paleogeographic maps. 76 refs., 90 figs.