Geoarchaeology and Chronostratigraphy of the Sheep Rock Spring Site, Late Pleistocene to Holocene, Missouri River Headwaters Region, Southwest Montana
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.
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Geoarchaeology and Chronostratigraphy of the Sheep Rock Spring Site, Late Pleistocene to Holocene, Missouri River Headwaters Region, Southwest Montana. Michael Wilson, Christopher L. Hill, Patrick J. Rennie, David C. Batten, Linda Scott Cummings. Presented at The 81st Annual Meeting of the Society for American Archaeology, Vancouver, British Columbia. 2017 ( tDAR id: 428963)
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min long: -113.95; min lat: 30.751 ; max long: -97.163; max lat: 48.865 ;
Abstract Id(s): 16661