Notes on the Tertiary deposits of the Bighorn Basin. Bulletin of the AMNH ; v. 31, article 5.

Abstract

"1. The Lower Eocene sediments of the Bighorn Basin represent the alluvial filling of an intermontane trough of downwarp. 2. They have been transported from the surrounding mountains as shown by the lithology of the gravels, sands and clays. No volcanic ash occurs. 3. They are stream transported and have been deposited in stream channels or spread over flood plains. No evidence in favor of wind transportation has been observed. 4. The Eocene clays are banded in more or less regular alternation, red and blue. This may be due to climatic causes leading to concentration of iron salts and their oxidation. 5. The beds are divisible into three formations, the Knight, Lysite and Lost Cabin, readily separable by their fossils, but not differing lithologically and conformable throughout. The Wind River (comprising the Lysite and Lost Cabin) is confined to the southwest portion of the basin (McCulloch Peak possibly excepted) and has been removed elsewhere by erosion. 6. The Lower Eocene formations are overlain conformably by another set of beds, containing much lignite, the Tatman Formation, in which determinable vertebrate fossils have not yet been found. Invertebrate fossils suggest that it may be of Eocene age, possibly Bridger. 7. The Tatman Formation is overlain by andesitic gravels of doubtful age, of which but a remnant on the top of Tatman Mountain is preserved in place. 8. Deformative stresses have acted on the basin filling after the deposition of the Tatman formation, flexing it into marginal anticlines and synclines and increasing the centripetal dip of the beds. 9. The major dissection of the basin is, probably, a comparatively late event, geologically speaking, perhaps referable, in part, to the Pleistocene"--P. 66-67.