Natural Resources, School of

 

Date of this Version

1984

Document Type

Article

Citation

Swinehart, James B., Robert F. Diffendal, Jr., Mary Rebone, and Robert Hunt. 1984. Cenozoic Geology of the Southern Nebraska Panhandle: Old Valleys, Volcaniclastics, and Vertebrates: 1984 Fall Field Trip, Nebraska Geological Society. Lincoln: Nebraska Geological Society.

Comments

Published 1984 by the Nebraska Geological Society.

Abstract

Two-day field trip:

Duer Ranch Locality, Morrill County, Nebraska

The Duer Ranch locality contains some of the finest and most easily accessible examples of different styles of alluvial cuts and fills in the Cenozoic of Nebraska. It offers a unique area in which to examine the geometries and alluvial fills of several Miocene and Pliocene age paleovalleys and paleogullies. Good exposures of eolian volcaniclastic siltstones and a regionally important volcanic ash of the Oligocene age Brule Formation are also present at the Duer Ranch locality.

Early Miocene Mammals and Lithostratigraphy of the Indian Creek Drainage, Near Bridgeport, Morrill County, Western Nebraska

The Bridgeport Quarries produced great quantities of fossil mammal remains in the 1930s, when field parties from the University of Nebraska worked several sites in sections 9, 10, and 16, T. 21N, R. 50W, Angora SE 7.5′ topographic quadrangle (1965 edition) (fig. B-1). Most abundant are bones of Early Miocene rhinoceros, accompanied by horses, camel, dromomerycid deer, rodents, four species of carnivores (including the largest North American sample of the rare primitive ursid Cephalogale). A fluvial origin for the principal bone deposits in section 10 is indicated by the abraded condition of many bones from the quarries; these fossils also show evidence of scavenging by carnivores, indicating a history of environmental processing before sediment burial. The mammals from the Bridgeport Quarries comprise the largest geographically localized fauna of Miocene age from the north rim of the North Platte valley in Nebraska, yet the lithostratigraphy of the area has not been carefully worked out.

Ancient Alluvial Deposits in Pumpkin Creek Valley and Beneath the Cheyenne Tablelands, Nebraska

The youngest pre-Quaternary deposits beneath the Cheyenne Tablelands to the south of Pumpkin Creek Valley are conglomerates, sandstones, siltstones, caliches, diatomites, volcanic ash, and their uncemented equivalents belonging collectively to the Ogallala Group. A major paleovalley filled with Ogallala sand and gravel and/or conglomerate, characterized by rhyolite and metamorphic clasts, has a slightly sinuous course along or just south of the tablelands escarpment (fig. P-l). The principal source of this deposit was in the vicinity of North Park in Colorado.

Late Cenozoic Geology, Scotts Bluff National Monument, Nebraska

Significance of Locality: The exposures of the Arikaree and White River group along the summit to Museum Trail (fig. S-1) are certainly the most accessible of any in western Nebraska. A wide variety of sedimentary structures, diagenetic features, trace fossils, and volcaniclastic sediments are well displayed along the trail. An excellent panoramic view of the North Platte River Valley is provided from the north overlook (fig. S-2) and one can see why the bluff—an erosional outlier of Wildcat Ridge to the south like nearby Chimney Rock—was an important landmark along the Oregon Trail.

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