Contributions to Geology 20.1

Petrography of Upper Cambrian Lodore Formation, Northeast Utah and Northwest Colorado

RANDY G. HERR Union Oil Company of California, Midland, Texas 79701
M. DANE PICARD Department of Ceology and Ceophysics, The University of Utah, Salt Lake City, Utah 84112

Pages
1-22

Keywords
Lodore, Cambrian, Uinta, Utah, Colorado, diagenesis, source rock

Abstract
The Lodore Formation, an Upper Cambrian transgressive sandstone, crops out along the Uinta Mountain uplift in northeast Utah and northwest Colorado. The formation is dominated by sandstone, but siltstone, claystone and, rarely, sandy glauconitic dolomite are present in its upper part.

Sandstone in the Lodore Formation is multicyclic, moderately to well sorted, subrounded quartzarenite, subarkose, and arkose. Orthoclase is the most abundant feldspar; sedimentary rock fragments the most common rock fragments. Matrix material constitutes less than 12 percent of the sandstone, and rock fragments constitute less than 1 percent. Rounded zircon, tourmaline, and rutile are the principal heavy minerals.

Diagenesis of sandstone in the Lodore Formation is marked by an early stage cementation by silica and a late stage introduction of calcite cement. Other minerals introduced during diagenesis include hematite, apatite, dolomite and gypsum.

Study of rock fragments and heavy minerals in the formation indicates that the underlying Precambrian Uinta Mountain Group was the primary source rock.

The Draney Limestone: Early Cretaceous lacustrine carbonate deposition in western Wyoming and southeastern Idaho

ROGER E. BROWN and BRUCE H. WILKINSON Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan 48109

Pages
23-32

Keywords
Lake Draney, Cretaceous, Wyoming, Idaho, Gannett, limestone, Sevier

Abstract
Late Jurassic and Early Cretaceous continental deposition occurred over much of the central western United States, with the most rapid deposition occurring in linear foredeep basins developed east of the Sevier overthrust belt. Representative of this type of synorogenic sedimentation is the Gannett Group, now well exposed throughout the Overthrust Belt of western Wyoming and southeastern Idaho. The Draney Limestone, a lacustrine carbonate composed of alternating calcareous mudstone and lithographic limestone within the predominantly clastic Gannett Group, presently covers over 1S,000 km2. Six lithofacies which make up the Draney Limestone are: molluscan wackestone, ostracodal wackestone, pelletal micrite, molluscan packstone, nodular micrite, and limonitic mudstone. The vertical and lateral distribution of these lithofacies suggests that Lake Draney was a shallow, low-salinity, perennial lake. Infrequent fluctuations in lake level occasionally exposed bathymetric highs, which resulted in the subaerial alteration of lacustrine carbonate muds. Production of carbonate within Lake Draney can be compared with modern temperate-region hard-water marl lakes, as carbonate was produced by biochemical precipitation around charophytes, and possibly by physiochemical precipitation induced by the photosynthetic activity of planktonic algae. Analogy with modern temperate-region marl lakes is imperfect, however, because Early Cretaceous climates were more equitable, and Lake Draney was a considerably larger system.

Preliminary report on late Pleistocene vertebrates from the Selby and Dutton archeological/paleontological sites, Yuma County, Colorado

RUSSELL W. GRAHAM Quaternary Studies Center, Illinois State Museum, Springfield, Illinois 62706

Pages
33-56

Keywords
Selby-Dutton, Pleistocene, Colorado, mammal, vertebrates

Abstract
The Selby-Dutton fauna is composed of a diverse late Pleistocene mammal collection from three major stratigraphic units (Peorian Loess, lacustrine, and gleysol) below a Clovis cultural horizon. There are at least twenty-two mammalian species of which seven are extinct and two are extirpated. The accumulation of these remains may be attributed to natural processes as well as human agents that predate a Clovis occupation of North America. The fauna is indicative of a well developed grassland in eastern Colorado during the latest Pleistocene but stratigraphic changes in fauna and sediments suggest an increase in effective moisture during this time.

Paleosols in the Oligocene of northwest Nebraska

CHARLES R. SINGLER Department of Geology, Youngstown State University, Youngstown, Ohio 44555
M. DANE PICARD Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112

Pages
57-68

Keywords
Oligocene, Nebraska, paleosols, Brule, Whitney, eolian, fluvial

Abstract
The Oligocene Brule Formation of Northwest Nebraska consists largely of fluvial and eolian deposits. The Lower Ash Bed and the White Bed of the Whitney Member are considered (Schultz and others, 1955) to be paleosol complexes. These soil units were studied to determine their soil properties. The Lower Ash Bed shows distributions of organic matter, clay, and calcium carbonate which suggest the formation and preservation of a soil similar to an Aridisol or a Mollisol. Comparison of its characteristics with a modern soil, including the depth and thickness of the zones of accumulation, indicate that the soil originated in a semi-arid climate with an average annual precipitation of about 30 to 45 cm.

In contrast, the White Bed of the Whitney Member does not display distinct trends in the distribution of organic matter, clay, and calcium carbonate. A simple paleosol therefore is not indicated. Although some workers (Schultz and others, 1955) suggest that the White Bed may be part of a more complicated paleosol complex, there is no evidence of it.