Contributions to Geology 26.1

A proposal for graphic presentation of orientation data from fossils

ANTHONY R. FIORILLO Department of Geology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, and Department of Vertebrate Biology, Academy of Natural Sciences of Philadelphia, 19th and the Parkway, Philadelphia, Pennsylvania 19103

Pages
1-4

Keywords
fossils, rose diagrams, stereographic, orientation

Abstract
Rose diagrams and stereographic projections are the two most popular methods of graphically presenting orientation data of fossils. Of these two methods, stereographic projections present much more objective information to the viewer without any of the subtle subjectivity inherent to rose diagrams. Further, contouring of data point density on stereographic projections, a relatively quick and simple method, serves to highlight any pattern which may be present on the projection.

Planktic foraminifera and age of the Niobrara Formation in its type area

WILLIAM E. FRERICHS and CHARLES GASKILL Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071-3006

Pages
5-14

Keywords
foraminifera, Niobrara, Austin Chalk, Taylor, planktonic

Abstract
Forty-four species of planktic foraminifera were identified from a nearly complete section of the Niobrara Formation in its type area. The base of the section is dated as Coniacian and the top of the section is determined to be late Campanian or early Maastrichtian in age. Therefore, the type Niobrara is correlative to the Austin Chalk through the Upper Taylor of the northern Gulf Coast Cretaceous. Benthic foraminifera are absent throughout much of the section and the bottom of the seaway is characterized by anoxic conditions during deposition of the type Niobrara Formation.

Magnetic survey of the Circus Flats Dome and western flank of Bear Butte, northern Black Hills, South Dakota

JOHN B. JOHNSTON and DONALD F. PALMER Department of Geology, Kent State University, Kent, Ohio 44242

Pages
15-20

Keywords
Bear Butte, Black Hills, Circus Flats, magnetic, rhyolite, South Dakota

Abstract
A magnetic survey consisting of 1015 stations and covering 10.5 km2 west of the Bear Butte rhyolite intrusion was conducted to evaluate the character of the intrusive mass responsible for the structural dome of Circus Flats and to test interpretations based on field mapping and gravity surveying. Magnetic susceptibility measurements show a strong contrast between the magnetization of the intrusive rocks and the surrounding sedimentary rocks in the area. The Bear Butte rhyolite has reversed remanent magnetization. The survey data show a large-amplitude magnetic low over Circus Flats which is consistent with the reversely magnetized intrusive rocks. Three-dimensional magnetic models show the intrusive body to be a laccolith centered under the Circus Flats dome with a tenuous connection to the Bear Butte rhyolite.

Geologic history and palynologic dating of Paleocene deposits, western Rock Springs uplift, Sweetwater County, Wyoming

MARK A. KIRSCHBAUM U. S. Geological Survey, Denver, CO, 80225
SHELDON N. NELSON Chevron USA Inc., Denver CO, 80222

Pages
21-28

Keywords
Paleocene, Wyoming, Rock Springs, anticline, paleosol, Almond Formation, Wasatch Formation

Abstract
During the latest Cretaceous or earliest Paleocene, a northwest-southeast trending anticline developed in the area of the present Rock Springs uplift in southwestern Wyoming. This ancestral structure was eroded to a surface of fairly low relief on which a paleosol developed. The surface was formed on the Upper Cretaceous Almond Formation throughout the study area. In the early middle Paleocene (P3 palynomorph zone), topographic lows on the erosion surface were infilled by alluvial deposits that accumulated in channel, floodplain, and backswamp environments. The core of the uplift was not a major topographic feature at any time during deposition of the Paleocene section, but controlled the geometries of paleochannels which paralleled the axial trend of the uplift. Drainages maintained a predominantly north-south orientation during the early middle Paleocene (P3 zone).

The Paleocene deposits include a lower organic-rich facies and an upper organic-poor facies. A previously recognized red-bed facies is here considered to be the result of secondary diagenetic alteration that probably occurred during the Oligocene. The organic-rich facies contains numerous coal beds and is middle to late Paleocene in age (P3 to P5 zones). The assemblage of pollen that defines the late middle Paleocene (P4 zone) is absent from the area suggesting a hiatus, although no lithologic break was observed at this boundary. The younger organic-poor facies begins in the late Paleocene (P5 zone) and continues to the top of the studied sequence. This change in facies has been used to map the contact between the Fort Union Formation of Paleocene age in this area, and the Wasatch Formation which was thought to be of Eocene age. This study demonstrates that, as currently mapped, the lower part of the Wasatch Formation is Paleocene in age. Stratigraphically higher parts of the Wasatch, which presumably contain rocks of latest Paleocene (P6 zone) and earliest Eocene age, were not studied.

Chemical weathering in the West Glacier Lake drainage basin, Snowy Range, Wyoming: implications for future acid deposition

ELIZABETH A ROCHETTE and JAMES I. DREVER Department of Geology and Geophysics, The University of Wyoming, Laramie, WY 82071
FRANK S. SANDERS                Wyoming Water Research Center, The University of Wyoming, Laramie, WY 82071

Pages
29-44

Keywords
West Glacier Basin, dikes, Wyoming, acid deposition, solutes, chemistry

Abstract
West Glacier Basin is underlain by quartzite intruded by mafic dikes, which make up to 20 to 25 percent of the bedrock in the watershed. The dikes consist mainly of actinolite, epidote, and albite, and, because they weather selectively, they are generally obscured by quartzite talus at the ground surface. Soils in the basin contain a significant aeolian input. The major sources of solutes in the surface waters are atmospheric deposition and weathering of the mafic dikes. The chemistry of waters which have come in contact with mafic rocks reflect weathering of actinolite, epidote, and albite to a smectite-rich phase and an amorphous aluminum hydroxide or kaolinite. The cationic denudation rate of the drainage basin is approximately 7.9 kg/ha/yr (444 eq/ha/yr). This low value suggests that waters in the drainage basin would be sensitive to an increase in acid deposition. Even a small additional input of acidity from the atmosphere could cause temporary acidification during snowmelt. If buffering by soil processes were negligible, West Glacier Lake would become permanently acidified within a year if the average precipitation pH was 4.3 or lower. Reactions within the soil might provide buffering against acidification for about 11 years under such conditions.