Geoarchaeology and Chronostratigraphy of the Sheep Rock Spring Site, Late Pleistocene to Holocene, Missouri River Headwaters Region, Southwest Montana

Summary

The Sheep Rock Spring site (24JF292) lies in a small SW Montana valley between Sheep Rock and a residual tor. A late Quaternary sequence (>5 m) supports a chronostratigraphic model from dates on charred material in the upper two units: (1) basal rock landslide diamicton; (2) down-valley debris flows; (3) final Pleistocene-early Holocene (FP-EH, >10,200-8700 RCYBP) channel/floodplain alluvium and paleosols; and (4) mid-Holocene (MH, ca. 6000-5430 RCYBP) alluvial/colluvial fan with paleosols. Radiocarbon (N=26) and stable isotope measurements underpin the age-model, with local events superimposed on regional early Holocene warming and drying. Samples include charred material (n=11), organic sediments (n=5), bone "collagen" (n=7) and wood (n=3). Residual bone organics from extinct megafauna among the landslide boulders gave a pre-Last Glacial date of ~20,700 RCYBP, doubtful given a 13C/12C ratio of -33.1 o/oo. Dated contexts provide evidence for introduction of relatively small corner and/or side-notched projectile point types from terminal Paleoindian times onward. Artifacts suggest intermittent, short-term camping and tool production. Artifact redeposition also raises concern for some dating samples. Organic sediment dates agree with the age-model (9060-8200 RCYBP for FP-EH, 5510-4720 RCYBP for MH), while wood and some measurements on acid-insoluble bone fractions do not; water-table fluctuations may be responsible.

This Resource is Part of the Following Collections

• Society for American Archaeology 82nd Annual Meeting, Vancouver, BC (2017)

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Record Identifiers

Abstract Id(s): 16661