Contributions to Geology 12.1

Early Miocene mammals from northeast Nebraska

M. R. VOORHIES Department of Geology, University of Georgia, Athens, Georgia 30601

Pages
1-10

Keywords
Miocene, mammals, Nebraska, fauna, jaws

Abstract
A newly discovered micromammal locality in Knox County, Nebraska has produced a small but important collection of jaws. The joint occurrence of Paleolagus hypsodus, Protosciurus sp., Paleocastor cf. nebrascensis, and Nanotragulus cf. intermedius strongly suggests an early Arikareean (earliest Miocene) age for the fauna. An erinaceid closely allied to Geolabis is also present, representing the latest record of the Geolabidinae. The fossils occur in pink silts immediately above the Pierre Shale-Tertiary contact and well below the base of the Valentine Formation which was formerly thought to be the oldest Tertiary rock unit in northeastern Nebraska. The pink silts appear to represent an eastern equivalent (in age if not in lithology) of the Gering, Sharps, and type Rosebud formations which fortuitously escaped destruction during the pre-Valentine erosion cycle. The known eastward extent of lower Miocene rocks and fossils on the Great Plains is considerably increased by this discovery.

Inversion of aragonite to calcite in Corbicula (Leptesthes) fracta from Upper Cretaceous strata of Wyoming

HEINRICH TOOTS Department of Geology and Geography, C. W. Post College, Greenvale, New York 11548
J. E. FOX: Littleton, Colorado

Pages
11-14

Keywords
Corbicula fracta, inversion, Cretaceous, Wyoming, weathering

Abstract
Shells of Corbicula (Leptesthes) fracta undergo inversion from aragonite to calcite during weathering processes at the present land surface. The strontium percentage is reduced during this inversion. Entombment in an impermeable sediment has been the traditional explanation for the preservation of pre-Quaternary aragonite. Such an explanation is not applicable in this instance where the sediment surrounding the aragonitic shells is porous and permeable. Results of this study are consistent with findings of Kennedy and Hall (1967) that amino acid envelopes protect the crystallites of aragonite from inversion as long as the envelopes persist in a reducing environment.

The significance of small bones in paleoecological interpretation

PETER DODSON Department of Geology, Yale University, New Haven, Connecticut 06520

Pages
15-20

Keywords
paleoecological, bones, experiment, small animals, fossil record

Abstract
In order to assess the potential of small animals for preservation in the fossil record, a mouse, a frog and a toad were decomposed in an aquarium for up to 77 days to observe rates and modes of disarticulation, and their bones were tested in a flume to determine relative susceptibilities to movement and competent velocities. On the basis of these experiments it is concluded that the bones of small animals have great susceptibility to dispersal by flowing water, and their uncritical use in paleoecological studies is questioned.

Geothermal measurments by the University of Wyoming

EDWARD R. DECKER Department of Geology, University of Wyoming, Laramie, Wyoming 82071

Pages
21-24

Keywords
geothermal, drill holes, conductivities, depth

Abstract
Geothermal studies by the University of Wyoming include measurements of temperature in underground openings, and laboratory determinations of thermal conductivity, uranium (U), thorium (Th), and potassium (K). Temperatures are measured to depths of 1.83 km using thermistor probes in combination with three-lead compensated Wheatstone-type bridges and null detectors. In remeasured drill holes, absolute temperatures have always been reproducible to within + 0.06 C, and differences of temperature over 5-, 10- and 20-meter intervals have been reproducible to within + 0.02 C. Thermal conductivities are measured using divided-bar methods. Thermal conductivities of individual samples are reproducible to within + 2%. U, Th and K are determined in 600 gram samples using g-ray spectrometry. For most rock samples, determinations of U, Th and K are considered accurate to within ranges of + 15%, + 10% and + 2%, respectively, of the actual amounts present.

Qualitative X-ray diffraction and X-ray fluorescence analyses of some Oligocene coprolites

PAUL D. EDWARDS University of Nebraska State Museum and Department of Geology, Lincoln, Nebraska

Pages
25-26

Keywords
coprolites, Oligocene, Nebraska, Wyoming, x-ray, apatite

Abstract
Carnivore coprolites from the Oligocene of western Nebraska and eastern Wyoming have the crystal structure of apatite. Sr, Y, Fe, As, and Ba are present as minor elements in these coprolites. Original organic material is preserved in these fossilized specimens.

Age and stratigraphic relations of the Fowkes Formation, Eocene, of southwestern Wyoming and northeastern Utah

MICHAEL E. NELSON Department of Geology, Fort Hays Kansas State College, Hays, Kansas

Pages
27-32

Keywords
volcanic, Eocene, Wyoming, Utah, Fowkes, Norwood, tuff

Abstract
Lithologic, structural, radiometric, and paleontological evidence indicates that widespread, continental, largely volcanic sediments of northeastern Utah and southwestern Wyoming, formerly thought to constitute a single late Eocene formation (Fowkes Formation) are better regarded as two distinct formations, the Fowkes Formation and the Norwood Tuff. Each is characterized by a distinct fauna: the Fowkes being late middle Eocene in age, the Norwood late Eocene-early Oligocene?.

Fossil mammals from the upper part of the Cathedral Bluffs Tongue of the Wasatch Formation (Early Bridgerian), northern Green River Basin, Wyoming

ROBERT M. WEST Department of Biology, Adelphi University, Garden City, New York 11530
MARY R. DAWSON Section of Vertebrate Fossils, Carnegie Museum, Pittsburgh, Pennsylvania 15213

Pages
33-41

Keywords
fauna, Green River, Cathedral Bluffs, Wasatch, Bridgerian, mammals

Abstract
The mammalian fauna from a locality in the Cathedral Bluffs Tongue of the Wasatch Formation in the northern Green River Basin now totals 40 species, some of which are probably new. This locality is early Bridgerian in age, and appears to represent a different facies from that which produces the classic Bridgerian faunas in the southern part of the Green River Basin.