HOLOCENE EPISODIC LANDSCAPE CHANGE AND THE HUDSON-MENG BISON KILL SITE, NORTHWESTERN NEBRASKA, U.S.A

The Hudson-Meng bison kill site, located on a north-facing upland slope of the Pine Ridge escarpment in northwestern Nebraska, is an early Holocene mass death assemblage of Bison antiquus. Radiocarbon dates of the bone bed date it at 9,820 years b.p. +/- 160 years. The goal of this study is to identify and define sedimentary units preserved at the site to better understand the depositional environment and landscape changes before, during, and after deposition of the bison assemblage. The oldest unit, a clayey silt with mottled Munsell colors 10YR 4/2 and 10YR 5/3 containing fresh water snails and hackberry seeds represents a paludal environment. A fine sandy silt, color 2.5Y 4/2, indicates a change to an eolian depositional environment. This unit contains multiple thinly-developed paleosols; the bone bed rests upon the youngest. A massive, carbonate-rich silty fine sand, color 10YR 4/3, is eolian and preserves the bone bed. The fine to coarse poorly sorted sand, color range of 5Y 3/2 - 5Y 6/3 and 10 YR 3/2 - 5/3, represents eolian deposition with frequent colluvial additions. A very fine sandy silt deposit, colors 10YR 2/1 - 4/3, is eolian. A fine sand, color 10YR 3/1, contains the modern soil and is eolian. Colluvial cobble lenses found throughout the site can not be correlated. Except for the modern soil, the eolian units contain multiple paleosols, likely entisols, indicating intermittent periods of landscape stability during rapid landscape evolution throughout the Holocene. The change in depositional environments observed at the site coincides with climate change, episodic erosion and filling of small valleys with eolian sediments, and reactivation of sand dunes throughout the Great Plains region.