Contributions to Geology 14.2

Seismicity and the possibility of earthquake related landslides in the Teton-Gros Ventre-Jackson Hole area, Wyoming

R. B. SMITH and J. R. PELTON Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112
J. D. LOVE U. S. Geological Survey, Laramie, Wyoming 82071

Pages
57-64

Keywords
Gros Ventre, Wyoming, slide, earthquake, Jackson Hole

Abstract
Jackson Hole, Wyoming, is a high intermountain valley bounded on the west by the impressive Teton fault, along which the famed Teton Range was uplifted. About 9 km of vertical displacement has occurred along this fault during late Cenozoic time, and some Quaternary alluvial fans are displaced as much as 50 m. Historic accounts indicate sporadic earthquake activity from the time of early settlement, around 1870, to about 1933, and lesser activity continuing to the present. Regional seismicity from about 1950 to 1973 indicates moderate earthquake activity in the Gros Ventre Range as well as scattered events throughout the southern Teton area, but there has been little historic activity along the Teton fault. Several widespread zones of earthquakes were located by detailed earthquake surveys in 1974 and 1975 in the Gros Ventre Range and in the Mt. Leidy Highlands east of Jackson Hole. These active seismic zones coincide with areas of highly unstable slopes and numerous prehistoric landslides. Residents indicate that the Jackson Hole area was seismically active several years before the 1925 Lower Gros Ventre slide and that numerous small earthquakes occurred in the Gros Ventre Canyon in the spring of 1925. An earthquake, estimated to be of magnitude 3 to 4, occurred 20 hours before the slide. Although evidence is not conclusive, this earthquake may have triggered parts of the slide into creep by induced liquefaction followed by the massive slide failure.

Diagenetic image reversal in a Triassic pelecypod

DONALD W. BOYD Department of Geology, The University of Wyoming, Laramie, Wyoming 82071
NORMAN D. NEWELL Department of Fossil and Living Invertebrates,
The American Museum of Natural History and Columbia University
Central Park West at 79th Street (AMN

Pages
65-68

Keywords
pectinacean, Dinwoody, Nevada, Triassic, pelecypod, calcite

Abstract
A collection of the pectinacean Claraia cf. stachei from the lower Dinwoody Formation in northeastern Nevada demonstrates that the outer layer in both left and right valves is prismatic calcite. This layer, the only remaining part of the original valve, was thickened diagenetically by uniform addition of calcite over its exterior. Selective dissolution of the inner shell layers, presumably aragonite, exposed the inner surface of the outer layer. This surface is deceptive in that it is a mirror image of the external form and may easily be mistaken for the outer surface.

Small mammals from the Miocene Batesland Formation of South Dakota

JAMES E. MARTIN Thomas Burke Memorial Washington State Museum, University of Washington, Seattle, Washington 98195

Pages
69-98

Keywords
Dakota, Miocene, Batesland, mammals, fauna, Hemingfordian

Abstract
The Batesland faunas collected from three localities in Bennett County, South Dakota indicate a middle Hemingfordian age. The faunas are similar, but younger than faunas from Quarry A of Martin Canyon in northeastern Colorado and from a local fauna in the Rosebud Formation. There are also similarities with the fauna of the Monroe Creek Formation of middle Arikareean age. The two faunas from the Batesland which seem closest to that of Quarry A indicate a stream border environment. The third locality seems to have been farther removed from the stream border or was deposited in quieter water. Elements of the fauna in common with European fomms suggest that the Burdigalian age faunal interchange had already begun.

The subfamily Leptochoerinae (Artiodactyla, Dichobunidae) of North America (Oligocene)

PAUL EDWARDS University of Nebraska State Museum, Division of Vertebrate Paleontology, Lincoln, Nebraska 68588

Pages
99-114

Keywords
Leptochoerinae, Stibarus, Leptochoerus, Oligocene

Abstract
The taxonomy of the Leptochoerinae (Mammalia, Artiodactyla, Dichobunidae) is revised, recognizing Stibarus and Leptochoerus as valid genera. Four species of the genus Leptochoerus are recognized as valid: L. supremus, L. elegans, L. spectabilis, and L. emilyue, new species. The validity of three species of the genus Stibarus is confirmed: S. obtusilobus, S. quadricuspis, and S. montanus. The stratigraphic range of each species has been reevaluated up on additional material. A phylogeny of the subfamily is proposed. The bunodont teeth are assumed to indicate that the leptochoerines were basically browsers, but modifications in molar morphology suggest that the feeding habits of Stibarus and Leptochoerus may have been somewhat different.

Fish coprolites from Fossil Butte, Wyoming

PAUL EDWARDS University of Nebraska State Museum, Division of Vertebrate Paleontology, Lincoln, Nebraska 68588

Pages
115-117

Keywords
coprolites, fish, Green River, Fossil Butte, Wyoming, apatite

Abstract
Fish coprolites with a rope-like shape are abundantly preserved in the Green River Formation of Wyoming at Fossil Butte. Composed primarily of apatite, their occurrence and preservation are unique in the fossil record.