Stratigraphy and nomenclature of some Upper Cretaceous and lower Tertiary rocks in south-central Wyoming

Abstract

Upper Cretaceous rocks described and correlated in this report are the Steele Shale, Mesa verde Group (consisting of the Rock River l!'ormation (new name), Haystack Mountains)formation (new name), Allen Ridge Formation, Pine Ridge Sandstone, and Almond Formation), Lewis Shale, E'ox Hills Formation, Medieine Bow ll..,ormation, and the lower part of the Ferris Formation. '.rhe lower Tertiary rocks described consist of the upper part of the Ferris ll..,ormation of Paleocene age and the overlying Hanna ll..,ormation of late Paleocene and Eocene age. 'l'he oldest unit Jnvestigated, the Steele Shale, consists of 2,300-8,800 feet of dark-gray marine shale that contains limestone concretions, beds of bentonite as much as '5 feet thick, and• thin layers of siltstone ami very fine grained sandstone. It becomes sandy upward nnd grades into the overlying Mesaverde Group. 'The Mesaverde Group, in the Rawlins-Medicine Bow area, consists of the following formations, from oldest to youngest: Haystack Mountains Formation, Allen Ridge Formation, Pine Ridge Sandstone, and Almond Formation. The Haystack Mountains Formation comprises a sequence of mostly shallow-water marine sandstone and shale that thins southwestwardly across southcentral 'Vyoming from 2,550 to 850 feet. It contains three persistent ridge-forming sandstone members interpreted as beach and barrier-bar deposits. The oldest member, Tapers Ranch Sandstone (new name) , is 270 feet thick •and forms the base of the formation. The second member, O'Brien :Spring Sandstone (new name) is 220 feet thick and lies 1,350 feet below the top of the formation. The Hatfield Sandstone Member, as much as 167 feet thick, lies 450 feet •below the top. Nonmarine sandstone, shale, and carbonaceous beds largely mal{e up the Allen Ridge Formation, but some sandstone and shale of brackish-water and marine origin are included. The Allen Ridge is conformable with the underlying Haystack Mountains Formation. It is as much as 1,500 feet thick. It intertongues with the Rock River Formation, and in the Laramie Basin area, it is replaced by that formation. Dlsconformably overlying the Allen Ridge Formation is the Pine Ridge Sandstone, a white t<l light-gray nonmarine sandstone 60-450 feet thick. The :formation contains carbonaceous shale and impure coal, •and <lrdinarily f<lrms a conspicuous tree-covered ridge. The Almond Formation, 30-575 feet thick, conformably overlies the Pine Ridge Sandstone. It is a sequence of sandstone, shale, and coal, representing fluviatile, brackish-water, and nearshore marine environments of deposition. In the southeastern part of th4~ area (Laramie Basin), the Mesaverde Group consists of the Rock River F<lrmation and Pine Ridge Sandstone. The Rock River is a 1,500-foot-thick sequence of nonresistant sandstone and sandy shale of shallow-water 108' 42'

Scaphites of the “Nodosus Group” from the Upper Cretaceous (Campanian) of the Western Interior of North America

“…They hypothesized that the absence of these ammonite zones may be due to submarine erosion. Gill et al (1970) documented a widespread unconformity farther west in the south-central part of Wyoming at the base of the Teapot Sandstone Member of the Mesaverde Formation, which may correspond to this interval. In contrast, the Baculites compressus-B.…”

Origin and distribution of six heavy-mineral placer deposits in coastal-marine sandstones in the Upper Cretaceous McCourt Sandstone Tongue of the Rock Springs Formation, southwest Wyoming

“…Three of the deposits described by Dow and Batty (1961 ), at Richards Gap, Titsworth Gap, and near Black Butte, were included by Houston and Murphy (1962, 1970, 1977Murphy and Houston, 1955) in investigations into the occurrence and distribution of black sandstones in Cretaceous rocks of the Rocky Mountain states. This report provides important stratigraphic, paleogeographic, and sedimentologic details, not previously published.…”

Coal resource occurrence and coal development potential maps of the Hanna Quadrangle, Carbon County, Wyoming

“…Weitz and Love (1952) compiled a geologic map of Carbon County which incorporates available data, published and unpublished, to that date. Gill, Merewether, and Cobban (1970) The oldest unit exposed in the quadrangle is the Mesaverde Formation of Late Cretaceous age as mapped by Dobbin, Bowen, and Hoots (1929). Later studies by Gill, Merewether, and Cobban (1970) have resulted in elevating the Mesaverde to group status and measuring and defining four separate formations within the group.…”

“…Gill, Merewether, and Cobban (1970) The oldest unit exposed in the quadrangle is the Mesaverde Formation of Late Cretaceous age as mapped by Dobbin, Bowen, and Hoots (1929). Later studies by Gill, Merewether, and Cobban (1970) have resulted in elevating the Mesaverde to group status and measuring and defining four separate formations within the group. Surface mapping delineating the formations of the Mesaverde Group has not been extended into the Hanna quadrangle, however, and the group is considered in this report as a unit.…”