Thick, steeply dipping, and generally conformable Upper Cretaceous and lower Paleogene strata are well exposed on the western Casper arch, central Wyoming. They record deposition prior to, during initiation of, and following onset of subsidence and basement-involved thrusting of the Laramide orogeny. Confusion has permeated the distributions, thicknesses, and ages of these strata, adjacent to the Wind River Basin's east-central margin. New lithostratigraphic mapping near Hell's Half Acre (HHA) revises identification of nonmarine units overlying the marine Lewis Shale (of Campanian and/or earliest Maastrichtian age). The homogeneous, mostly fine-grained Meeteetse Formation (MF) represents paludal conditions following deposition of the Lewis Shale's “lower tongue.” The local MF exceeds 3,200 feet (nearly 1.1 km) in thickness, almost 7.5 times greater than previously reported. The MF near HHA, although much thicker, exhibits characteristics strikingly similar to the Meeteetse elsewhere in the Wind River and Bighorn Basins. Most strata identified here as MF previously were considered as Lance Formation. The top of the MF near HHA matches the previously recognized contact with the Fort Union Formation (mostly Paleocene). Dominance of sandstone above that contact implies a more energetic fluvial regime that may, in part, represent latest Cretaceous time. Reflecting existing uncertainties, rocks above the MF and below the lacustrine Waltman Shale Member (Fort Union Formation) are designated here as “Fort Union (unnamed lower part) and Lance Formations, undifferentiated.” Upper surfaces of the Fort Union Formation were eroded early in Eocene time, and local scouring near HHA cut as deeply as the MF. Thus it is improbable that youngest parts of the Paleocene are recorded paleontologically in strata near HHA. The unexpectedly great thickness of the MF reflects onset of major, differential subsidence and provides evidence that the Laramide structural axis of the Wind River Basin originated several million years earlier than previously considered.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 2004 • No. 36