Contributions to Geology 4.1

Lithogenesis of a distinctive carbonate rock fabric

GORDON E. TEBBUTT Department of Geology, Rice University, Houston, Texas
CURTIS D. CONLEY Oasis Oil Co., Tripoli, Libya
DONALD W. BOYD Department of Geology, University of Wyoming, Laramie

Pages
1-14

Keywords
fenestrae, carbonate, lithogenesis, laminae, Wyoming, New Mexico, Colorado

Abstract
Carbonate rock in which crust-like laminae of detrital particles are separated by irregular, discontinuous partings of sparry calcite is found in Permian back-reef strata in New Mexico, Permian shelf deposits in Wyoming, and Mississippian shelf deposits of Colorado. The sparry calcite bodies appear in most cases to fill unsupported former voids. Such primary or penecontemporaneous gaps in rock framework, larger than grain-supported interstices, are termed fenestrae regardless of the degree or character of subsequent filling.

The fabric described in detail is characterized by laterally elongate fenestrae, and is termed laminoid-fenestral fabric. Variable aspects of specimens studied include size and shape of fenestrae, size and origin of carbonate particles, and amount of dolomite. In the most distinctive specimens, very elongate spar-filled fenestrae outline crust-like laminae of carbonate sand and silt consisting of aggregate particles, irregular ooliths, structureless grains, and some skeletal grains.

Fenestrae in laminoid-fenestral fabric commonly have scalloped roofs above relatively smooth floors. Laminae with reverse grading of particles (larger above) are common in some samples. Laminoid fenestrae can probably be caused by decay of sediment-covered algal mats, shrinkage during drying, and accumulation of pockets of fluid. Desiccation structures similar to those described in modern algal-bound sediments are associated with laminoid-fenestral fabric in Wyoming and New Mexico.

An example of the quantitative study of echinoid morphology

JAMES C. KELLEY Department of Geology, University of Wyoming, Laramie

Pages
15-20

Keywords
morphology, echinoid, dendraster, sand dollar

Abstract
In the study of many groups of animals, morphological analysis can be facilitated by the application of established statistical methods and criteria. In the case of Dendraster excentricus a Pacific Coast sand dollar, quantitative analysis served to clarify the differences between two forms from dissimilar environments, and to provide a criterion by which a taxonomic decision may be reached. The use of similar techniques in paleontology can also lead to clarification of taxonomic difficulties.

The carnivora of the Trail Creek fauna

M. R. VOORHIES Geology Department, University of Wyoming, Laramie

Pages
21-26

Keywords
Miocene, Trail Creek, Wyoming, carnivore

Abstract
The occurrence of late Miocene rocks immediately east of the Laramie Range in southeastern Wyoming is indicated by the presence of a Barstovian mammal fauna at the Trail Creek fossil locality north of Cheyenne. The very advanced aspect of the Merychippus in the Trail Creek fauna is the principal criterion for dating the deposit as Barstovian but this assignment is supported by the presence of merycodont horncores of the Meryceros type. The carnivores, herein referred to Tomarctus rurestris and Pseudaelurus intrepidus, also suggest (but do not prove) late Miocene age in that the holotypes of both species are Barstovian. The value of species within these genera of carnivores for distinguishing Barstovian from Clarendonian rocks is not known because most are represented by inadequate series of specimens.

Applied geology in the Shirley Basin uranium district, Wyoming

ROBERT V. BAILEY Mineral Development and Geology Department, Utah Construction & Mining Co., 142 East 3rd South, Salt Lake City, Utah

Pages
27-36

Keywords
ore, Shirley Basin, uranium, Wyoming, alteration

Abstract
At Utah Construction & Mining Co's. Shirley Basin underground mine in the central part of southeast Wyoming, uranium ore has been mined from poorly consolidated sandstone units in the Eocene Wind River Formation. Loose ground and abundant water created difficult mining conditions. A geologic mapping program of the mine, accompanied by detailed drill hole logging and geologic cross section construction, has revealed habits and relationships of the mineralization and associated alteration. Mineralization and ore for the most part lie along the periphery of tongues of altered sand. The greenish to rusty altered sand is usually recognizable in hand specimen and is considered to represent the ground through which the mineralizing solutions passed. The major tongue of alteration is as much as 70 feet thick, hundreds of feet across, and several miles long. The best ore occurs on geochemical fronts, or rolls, at the terminal edges of the altered zones, and additional ore is found in subsidiary rolls on the upper and lower surfaces of the altered zones. This concept of ore occurrence has been successfully applied to exploration and development drilling, to ore projections ahead of mine workings, and to reserve estimates.

Sequence of disarticulation in mammalian skeletons

HEINRICH TOOTS Department of Geology, University of Wyoming, Laramie

Pages
37-40

Keywords
mammal, disarticulation

Abstract
The sequence in which the skeleton of a dead mammal becomes disarticulated is determined by the character of the joints and the tissues surrounding the joints. It begins with the skull and limbs becoming disconnected and proceeds through disarticulation of ribs, individual limb bones and finally disarticulation of the vertebral column. The activity of carnivores and carrion feeders as well as partial burial may modify the sequence of disarticulation.