Contributions to Geology 25.1

Northern Medicine Bow Mountains, Wyoming: revision of structural geology, northeast flank

D. L. BLACKSTONE, JR. Department of Geology and Geophysics, The University of Wyoming, Laramie, Wyoming 82071-3006

Pages
1-10

Keywords
Medicine Bow, Wyoming, faults, Arlington, Corner Mountain

Abstract
The northeast flank of the northern Medicine Bow Mountains is bounded by two west dipping thrust faults. The Arlington fault redefined is the most easterly and lies at a lower elevation structurally. The thrust fault at Corner Mountain northeast of Centennial, Wyoming previously considered to be part of the Arlington thrust is a separate fault herein named the Corner Mountain thrust, terminating in the Precambrian core of the range. The fault lies at a higher elevation topographically, and to the west of the Arlington fault. The problems of the structural relationships at Cooper Hill are not resolved.

Planktic foraminifera from the type area of the Fort Hays Limestone

WILLIAM E. FRERICHS Department of Geology and Geophysics, The University of Wyoming, Laramie, Wyoming 82071-3006
ALLORY P. DEISS Graphics Arts Services, The University of Wyoming, Laramie, Wyoming 82071-3006

Pages
11-22

Keywords
planktic, foraminifera, Fort Hays, Cretaceous, Kansas

Abstract
Twenty-six samples were examined for planktic foraminifera from the type area of the Fort Hays Limestone (Upper Cretaceous) in Trego County, Kansas. Thirty species, indicating a middle Coniacian to early Santonian age, were identified from the section. The Coniacian Santonian boundary is located three feet below the top of the studied section at Hackberry Creek and this section is equivalent to the Atco Member of the Austin Chalk as developed near Austin, Texas.

A new Clarendonian (late Miocene) fauna from eastern Nevada

MICHAEL E. NELSON                Department of Earth Sciences and Sternberg Memorial Museum,
Fort Hays State University, Hays, Kansas 67601-4099
JAMES H. MADSEN, JR. Antiquities Section, Division of State History, Salt Lake City, Utah 84101-1182

Pages
23-28

Keywords
Roglove, Miocene, fauna, Nevada

Abstract
The Roglove local fauna of late Miocene age (Clarendonian NALMA) occurs in an unnamed tuffaceous siltstone and sandstone in southeastern Elko County, Nevada. The l.f. includes a lagomorph (Hypolagus vetus), canids (Leptocyon vafer, Epicyon suevus), camels (Aepycamelus sp., Procamelus cf. P. grandis, and a protolabine), an antilocaprid (Merycodus furcatus), a horse (hipparionine or merychippine), a rhinoceros (Teleoceras fossiger), a gomphothere (Gomphotherium productum) and a rodent. These taxa are similar to those described from the "Upper Ricardo" faunas of California, the Ash Hollow faunas of Nebraska, and the Truckee faunas of Western Nevada.

The bivalve, Musculiopsis MacNeil, in Lower Cretaceous non-marine strata, Rocky Mountains

R. W. SCOTT Amoco Production Company, P. O. Box 3385, Tulsa, Oklahoma, 74102

Pages
29-34

Keywords
bivalve, Cretaceous, Musculiopsis MacNeil, Neomiodontidae

Abstract
Two species of the small bivalve, Musculiopsis MacNeil range through Barremian?, Aptian-Lower Albian lacustrine strata in western North America. The southern species, M. russelli MacNeil ranges from Nevada and Arizona to southwestern Alberta. The northern species, M. onestoe (McLearn) extends from Alberta to Utah. A silicified valve of M. russelli exhibits dentition characteristic of the Jurassic-Cretaceous family, Neomiodontidae.

Storm-influenced shelf deposition of the lower sandstone member, Lower Cretaceous Thermopolis Shale, southwestern Montana

ALAN D. STINE and JAMES G. SCHMITT Department of Earth Sciences, Montana State University, Bozeman, Montana 59717

Pages
35-54

Keywords
Thermopolis, Montana, Cretaceous, shoreface, shelf

Abstract
The lower sandstone member of the Cretaceous (Albian) Thermopolis Shale in the Bozeman, Montana area has previously been interpreted as a transgressive marine shoreface sequence. Detailed observation and interpretation of lithologies and sedimentary structures in the lower sandstone member document deposition in a setting that closely resembles modern shallow marine shelves. The proposed shelf environment is characterized by simultaneous deposition of sand and mud, with their distribution controlled by sediment availability, bathymetry, and distribution of marine currents and storm paths. First order geomorphic features on this shelf consist of sand ridges which exhibit a hierarchy of bedforms. Megaripples and ripples are the second and third order bedforms, respectively. Sand ridges, as well as isolated sand bedforms, migrated upon a substrate comprised of mud and complexly interbedded sand and mud (heterolithic deposits). Heterolithic intervals are interpreted as storm deposits while the mud is thought to be deposited in low energy environments where storm influence is minimal. The hydraulic regime controlling deposition on the shelf was characterized by genetically related unidirectional and oscillatory currents, that share an origin in storm events. Documented transgressive processes recorded in the strata include shoreface erosion of marginal marine deposits between the lower sandstone member and underlying non-marine Kootenai Formation. Additionally, rapid transgression subsequent to lower sandstone member deposition resulted in the sharp contact separating the lower sandstone member from the overlying offshore marine, middle shale member of the Thermopolis Shale.

The Hottell Ranch rhino quarries (basal Ogallala: medial Barstovian), Banner County, Nebraska. Part I: Geologic setting, faunal lists, lower vertebrates

M. R. VOORHIES Division of Vertebrate Paleontology, University of Nebraska State Museum, Lincoln, Nebraska 68588
J. ALAN HOLMAN The Museum, Michigan State University, East Lansing, Michigan 48824
XUE XIANG-XU Department of Geology, Northwestern Universi

Pages
55-70

Keywords
fossil, Hottell Ranch, rhinoceros, Nebraska, Ogallala, vertebrates, snake boid

Abstract
Numerous fossil rhinoceros remains were quarried from the Hottell Ranch sites in the southwestern Nebraska Panhandle during the 1940's but no paleontological study of the locality has been published. Renewed collecting at the quarries, including screenwashing, has resulted in recovery of a diverse and abundant sample of vertebrates comprising fishes (3 species), amphibians (9 species), reptiles (14 species), birds (unstudied), and mammals (50+ species) from basal Ogallala sediments at the main sites. An age of medial Barstovian (approximately 14 million years) is indicated by a mammalian fauna judged to post-date the Lower Snake Creek Fauna (early Barstovian) and to pre-date most of the later Barstovian faunas from the Valentine Formation in north-central Nebraska. A less diverse late Barstovian fauna was collected from strata directly superposed on the principal fossiliferous unit. The herpetofauna from the sites is taxonomically close to other Barstovian assemblages from the Great Plains (especially the quarry samples from Norden Bridge, Egelhoff, Myers Farm, Kleinfelder Farm and Bijou Hills) but differs in 1) lacking boid snakes and 2) having comparatively few remains of fishes or other aquatic vertebrates. Many of the fossils are water-rolled suggesting considerable transportation; however, the lack of associated igneous and metamorphic pebbles indicates that the paleo-stream that deposited the fossiliferous sediment did not have its headwaters in the nearby Laramie Range, but was a local, perhaps ephemeral, drainage. A mild paleoclimate, with frost-free winters, is suggested by the presence of large tortoises (Geochelone) and the curl-tail lizard (Lelocephalus). Both forested areas and open grasslands are inferred to have been present near the site of deposition.