Contributions to Geology 28.1

Stratigraphy and mammalian paleontology of the Ash Hollow Formation (Upper Miocene) on the north shore of Lake McConaughy, Keith County, Nebraska

MICHAEL B. LEITE Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071

Pages
1-30

Keywords
Ash Hollow, paleontology, Nebraska, fossils, mammalian, Miocene, Shoreline, Lemoyne

Abstract
Collecting localities in the Ash Hollow Formation along the north shore of Lake McConaughy in Keith County, Nebraska, yield late Miocene age vertebrate remains. Four stratigraphically lower localities, grouped as the "Shoreline localities," are fluviatile sand and conglomeratic sandstone. A fifth locality, Lemoyne Quarry, is located higher in the section and contains fossils preserved in a lacustrine claystone. Diagnostic mammalian fossils from the shoreline localities indicate a late, but not latest, Clarendonian age for that fauna. Mammalian fossils from Lemoyne Quarry indicate an age in the late part of the early Hemphillian. The Lemoyne local fauna contains a species of Megalonyx which is an early North American occurrence. Selective extinction of browsing taxa between times of the two faunas is interpreted to be a result of environmental stress due to climatic cooling and drying.

A Pliocene record of the giant marmot, Paenemarmota sawrockensis, in northern Utah

MICHAEL E. NELSON Department of Earth Sciences and Sternberg Memorial Museum, Fort Hays State University, Hays, KS 67601
DAVID M. MILLER U.S. Geological Survey, 345 Middlefield Road, MS-975, Menlo Park, CA 94025

Pages
31-37

Keywords
marmot, Pliocene, Utah, Paenemarmota sawrockensis, Mimomys

Abstract
A right dentary of the giant marmot, Paenemarmota sawrockensis, was collected from an unnamed loess unit in Box Elder County, Utah. The loess underlies an ash bed tentatively correlated with an ash bed exposed near Alturas, California, and an ash bed found in deep-sea cores off northern California. The age of the California ash is estimated as 4.8 Ma. Paenemarmota sawrockensis is now known from northeastern Nebraska, (Santee l.f. and Devils Nest Airstrip l.f.), southwestern Kansas (Sawrock Canyon l.f) and north-central Utah. The Sawrock Canyon l.f. is early Pliocene (early Blancan) as it contains two species of the definitive microtine immigrant, Mimomys. The Santee and Devils Nest Airstrip l.fs. contain native microtines and are late Miocene (late Hemphillian). Because of its association with the ash exposed near Alturas, California, and the record of Paenemarmota from the Sawrock Canyon 1. f., the Utah locality is considered to be earliest Pliocene (earliest Blancan).