Contributions to Geology 10.2

Earliest Eocene mammalian fossils from the Laramie Basin of southeast Wyoming

KATHRYN A. PRICHINELLO Department of Geology, University of Wyoming, Laramie, Wyoming 82070

Pages
73-88

Keywords
Eocene, mammal, Wyoming, Laramie, vertebrate, Wind River

Abstract
A small vertebrate fauna recovered from sediments of the Wind River Formation in the Laramie Basin is considered to be of earliest Eocene age. At least fifteen vertebrate species have been recovered to date, nine of which are mammals.

The lithology and paleontology of the deposits support a fluviatile origin for the sediments; depositional environments include stream channels, floodplains, and possibly forest swamps.

Data reduction in experimental rock deformation

FRED A. DONATH and NECIP GUVEN University of Illinois, Urbana, Ill. 61801

Pages
89-116

Keywords
program, rock deformation, experimental, stress, strain, conversion

Abstract
Procedures in experimental rock deformation require continuous or repeated measurement during a test of applied load, piston displacement, elapsed time, and other variables required by specific experiments. Important deformation characteristics, such as sustained differential stress and longitudinal strain, are subsequently calculated from these laboratory measurements. Although the equations involved in these conversions are relatively simple, they involve corrections for changes in specimen dimensions and for elastic distortion of apparatus with continued loading, and therefore must be executed many times for each test. To do this by hand or even with a desk calculator is tedious and time-consuming, and the possibility of operator error is always present.

In this paper the authors describe the data obtained from four basic types of triaxial test (standard compression, standard extension, constant load compression, and constant load extension) which might be utilized in experimental rock deformation, present equations for the reduction of raw data from these test types, and provide a program written in FORTRAN language for the IBM 360 which executes the necessary calculations for each test type. The output of the DATA REDUCTION STRESS/STRAIN program (hereafter referred to as the DARESS program) includes a listing of the input and reduced data, a linear interpolation of values between observed data points, a curve of differential stress versus percent longitudinal strain obtained from the CALCOMP plotter, a summary sheet consisting of important data for each of the tests processed at any given time, and a card output containing test parameters and reduced data.

A controlled rate automatic scanning data collection program in PAL III assembler language for use with PDP/8-type computers

NECIP GUVEN and FRED A. DONATH Department of Geology, University of Illinois, Urbana, Ill. 61801

Pages
117-130

Keywords
program, data collection, reduction, digital

Abstract
In experimental geology, PDP-8 type small-scale computers are very useful for controlling the collection of analog and/or digital data from several experiments continuously or at desired intervals. They provide means for collection and reduction of large amounts of experimental data accurately, automatically, and at high speed. For this purpose a VIDAR 5200 Series Digital Data Acquistion System (VIDAR 5206 D-DAS) under the control of a PDP-8/S computer has been installed in the Department of Geology, University of Illinois, Urbana. The VIDA 5206 D-DAS collects analog signals generated by such devices as thermocouples, spectrometers, strain gages, pressure and load cells, displacement transducers, and similar devices, and converts them into digital values.

A Controlled Rate Automatic Scanning program (CRAS), written in PAL III Assembler Language especially for the VIDAR 5206 system, controls the collection of signals from the available channels in the D-DAS at rates (timing intervals) from 0.12 up to 100,000 seconds between readings on any given channel. The program gives printed and punched tape output, and is perfectly general for use in any kind of data collection.

Chemical data for major Precambrian rock types, Bighorn Mountains, Wyoming

R. A. HEIMLICH Department of Geology, Kent State University, Kent, Ohio 44242

Pages
131-140

Keywords
Bighorn Mountains, Wyoming, Precambrian, chemical, granitic, gneiss

Abstract
Chemical analyses of quartz monzonite and quartz diorite, from the northern part of the Bighorn Mountains, and gneiss, from the southern part, support the concept of formation of the granitic rocks, particularly the quartz monzonite, by regional metasomatism of the gneiss. The data suggest also that likely parent rocks for the gneiss are limited to graywacke or several varieties of felsic plutonic or volcanic igneous rocks.

Authigenesis of the Wagon Bed Formation, central Wyoming

JAMES R. BOLES Department of Geology, University of Otago, Dunedin, New Zealand
RONALD C. SURDAM Department of Geology, University of Wyoming, Laramie, Wyoming

Pages
141-144

Keywords
mineralogy, Wagon Bed, Wyoming, Eocene, Beaver Rim, Conant Creek

Abstract
The authigenic mineralogy of the predominantly lacustrine middle and upper Eocene Wagon Bed Formation was studied along the Beaver Rim escarpment between U.S. Highway 287 and the Conant Creek anticline in central Wyoming. The authigenic minerals can be divided into three vertical zones based on characteristic mineral suites. Montmorillonite characterizes the Lower Zone, clinoptilolite and chabazite characterize the Middle Zone, whereas K-feldspar and analcime characterize the Upper Zone.

The authigenic minerals probably formed through a series of reactions between volcanic glass or alkali-rich zeolite precursors, and saline alkaline lake water. The differing authigenic mineral zones formed as a result of changing lake water chemistry. During authigenesis the lake water became progressively more saline because of an increase in erosion of Paleozoic
limestone exposed on the flank of the Conant Creek anticline. Moreover, floral assemblages
indicate an increase in aridity from the middle to upper Eocene in the Rocky Mountain region. Thus, tectonic and climatic factors were responsible for the increase in salinity and alkalinity of the lake water, which resulted in the formation of a sequence of progressively less hydrated authigenic minerals.