Depositional environments of Upper Cretaceous Dad Sandstone Member of Lewis Shale, south-central Wyoming
The Lewis Shale of Carbon County, Wyoming, was deposited in marine environments during Maestrichtian time and consists of three members: lower and upper unnamed, predominantly mudstone members; and the intervening Dad Sandstone, characterized by alternating units of sandstone and mudstone. The Dad Sandstone is 139 to 264 m thick and contains three distinctive lithofacies. The first lithofacies coarsens upward and is composed of interstratified units of sandstone and mudstone. Sandstone units are typically less than 1.5 m thick (although amalgamated beds are as much as 20 m thick) and contain hummocky stratification, ripple lamination, and contorted and massive bedding. These rocks were probably deposited on a delta front during storms. The second lithofacies consists of sandstone units that are generally 12 to 43 m thick and contain abundant Ophiomorpha. This sandstone commonly has horizontal to subhorizontal bedding but locally has tabular cross-bedding, and massive and contorted bedding. These rocks are more proximal than the first lithofacies and are interpreted as upper delta-front deposits. The third lithofacies is composed of thick mudstone units that probably accumulated in shallow-water environments. Sediments of the Dad Member in the eastern part of Carbon County apparently had a southeastern source; those in the western part of the county were most likely derived from the Sheridan delta of northwestern Wyoming. West and southwest of the study area in the Great Divide and Washakie basins, laterally equivalent sandstone units were deposited beneath storm base by sediment gravity flows at the toe of the delta.
- Research Organization:
- Univ. of California, Berkeley
- OSTI ID:
- 6962657
- Report Number(s):
- CONF-8609129-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 70:8; Conference: AAPG Rocky Mountain Section meeting, Casper, WY, USA, 7 Sep 1986
- Country of Publication:
- United States
- Language:
- English
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