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Application of end-member mixing analysis (EMMA) of grain-size distributions to characterize site formation processes of Rimrock Draw Rockshelter (35HA3855), Harney Basin, Eastern Oregon

Author(s): Richard Langford ; Joe Collins ; Thomas Gill

Year: 2015

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Summary

Sedimentological investigations were conducted on Unit 2 of Rimrock Draw Rockshelter (35HA3855), a deeply stratified, multi-component Paleoindian site located in the Harney Basin, eastern Oregon. Field descriptions and end-member mixing analysis (EMMA) of grain-size distributions of 13 sediment samples identified six stages of site formation: three stratigraphic units (SU), two unconformities, and a Bt soil horizon. EMMA resulted in the characterization of three end-members (EM) that correlate with field descriptions. EM's 1 and 2 represent 88.4% of the total variance among samples and are present within SU1 and SU3. EM 1 correlates well with the bottom stratigraphic unit, SU1, a well-sorted fluvial deposit. EM 2 correlates well with the upper stratigraphic unit, SU3, a poorly sorted aeolian deposit punctuated by colluvium derived from a nearby colluvial wedge and the brow of the rockshelter. EM 3 correlates well with the poorly developed Bt horizon that overprints an eolian deposit within the middle stratigraphic unit, SU2. These results demonstrate the applicability of EMMA to distinguish between depositional units within an archaeological context and provide geologically meaningful interpretations of paleoenvironments for the development of hypotheses related to human-environment interactions.

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Application of end-member mixing analysis (EMMA) of grain-size distributions to characterize site formation processes of Rimrock Draw Rockshelter (35HA3855), Harney Basin, Eastern Oregon. Joe Collins, Richard Langford, Thomas Gill. Presented at The 80th Annual Meeting of the Society for American Archaeology, San Francisco, California. 2015 ( tDAR id: 397334)


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min long: -122.761; min lat: 29.917 ; max long: -109.27; max lat: 42.553 ;

Arizona State University The Andrew W. Mellon Foundation National Science Foundation National Endowment for the Humanities Society for American Archaeology Archaeological Institute of America