Contributions to Geology 9.2

Precambrian gneiss at Sheephead Mountain, Carbon County, Wyoming, and its relationship to Laramide structure

CARLIE E. BANKS Department of Geology, University of Wyoming, Laramie, Wyoming 82071

Pages
54-65

Keywords
basement, Laramide, Wyoming, Precambrian, gneiss, Sheephead Mountain, subfabrics, deformation

Abstract
Although the Precambrian gneiss at Sheephead Mountain anticline apparently assumes the form of the Laramide fold, the gneiss does not reflect the fold in its fabric on either a mesoscopic or microscopic scale. A predominantly northwest-trending foliation and two possible regional fold axes in the gneiss, one plunging northwest and the other southeast, show no meaningful relationship to the north-plunging Laramide anticline. Four of the ten quartz subfabrics analyzed display weak monoclinic symmetry related to the regional fold axes of the gneiss but unrelated to the Laramide structure. The remaining six quartz subfabrics are random in orientation and could possibly reflect Laramide disruption of pre-existing fabrics.

The basement is envisioned as having behaved as a more or less rigid block during Laramide deformation, except in the southeastern portion of the fold where the basement may have adjusted to Laramide stresses by movement along fractures. These fracture surfaces parallel the Laramide thrust fault that bounds the mountain on the east, and if they existed prior to Laramide deformation, they may have influenced the orientation of the thrust fault.

The stratigraphy and paleontology of Bridger A

PAUL O. McGREW Department of Geology, University of Wyoming, Laramie
RAYMOND SULLIVAN Department of Geology, San Francisco State College, San Francisco, California

Pages
66-85

Keywords
Bridger, Opal, Laney, mammal, fauna, Wyoming

Abstract
A series of lithologic sections establishes the stratigraphic position of fluvial, mammal-bearing strata in the vicinity of Opal, Wyoming as Bridger A as defined by Matthew (1909). Near Opal Bridger A is divided into upper and lower parts by a 50-foot lacustrine unit. To the south the lower Bridger A becomes lacustrine and interfingers with the main body of the Laney Shale.

The mammal fauna is from the lower Bridger A and for the most part is identical to the fauna of Bridger B. It differs, however, in the presence of Paleosyops fontinalis, Bathyopsis middleswarti and a distinct size group of Notharctus.

The Tertiary deposits of the Rocky Mountains -- a summary and discussion of unsolved problems

PETER ROBINSON Curator of Geology, University of Colorado Museum, Boulder, Colorado

Pages
86-97

Keywords
Tertiary, Rocky Mountains, deposits

Abstract
This article is an outgrowth of another which I recently submitted to the Rocky Mountain Association of Geologists, as a chapter entitled "Tertiary History of the Rocky Mountains" for their Atlas, The Geology of the Rocky Mountains. During the extensive research of the literature, my own studies, and discussions with many other paleontologists and field geologists, a concept of the multiplicity of unsolved problems has gradually emerged. A few of the major ones are discussed briefly here in the hope that by calling attention to them, curious and ambitious students of all ages will be encouraged to provide answers.

Foraminifera in the Medicine Bow Formation, south-central Wyoming

JAMES E. FOX Department of Geology, University of Wyoming, Laramie, Wyoming 82071

Pages
98-101

Keywords
foraminifera, Medicine Bow, Wyoming, Maestrichtian

Abstract
Maestrichtian planktonic and benthonic Foraminifera have been discovered in southcentral Wyoming in a coal-bearing sequence formerly thought to be entirely nonmarine. The Foraminifera-bearing dark shales are interbedded with coal beds and siltstone beds containing fresh-water bivalves such as unionids.

Conodonts from the lower Goose Egg Formation (Permian) of southeastern Wyoming

EUGENE F. PEARSON Department of Geology, University of Wyoming, Laramie, Wyoming 82070

Pages
102-104

Keywords
conodonts, Permian, Goose Egg, Wyoming

Abstract
The lower Goose Egg Formation (Burk and Thomas, 1956) of southeastern Wyoming consists of interbedded carbonates, red-brown mudstones, and gypsum. The Minnekahta and Forelle carbonate members are tongues of the Park City ("Phosphoria") Formation of western Wyoming and Idaho (Thomas, 1934). Each consists of fifteen to twenty-five feet of sparsely fossiliferous bedded limestone, dolomite, and gray shale