2 Quaternary Geoarchaeology: Honoring the Work of John Albanese

Thursday, 21 May 2015
1:00 PM - 4:35 PM
South Ballroom

ARCHAEOLOGICAL GEOLOGY OF THE SHEEP ROCK SPRING SITE, LATE PLEISTOCENE TO HOLOCENE, MISSOURI RIVER HEADWATERS REGION, SOUTHWEST MONTANA

Paper number: 2-10
Program: Symposia Sessions
Time: 3:55 PM – 4:15 PM

Authors

Abstract

The Sheep Rock Spring site (24JF292) is located on the south flank of Bull Mountain NE of Whitehall, MT, in the Missouri River Headwaters region, in a small valley between the resistant mass of Sheep Rock and a smaller bedrock tor (“Camel’s Hump”) to the west. Excavations revealed a four-fold sequence of late Quaternary deposits: (1) a basal boulder diamict marking a rock avalanche of angular clasts from the tor; (2) diamicts and stratified sediments from down-valley debris flows; (3) late Pleistocene to early Holocene channel and overbank alluvium with a paleosol ~10.0 14C ka; and (4) a Holocene cross-valley alluvial/colluvial fan, reflecting intermittent deposition and lowered effective vegetative cover. The sequence reflects local events superimposed upon a regional signal of early Holocene warming and drying, a time-transgressive trend as demonstrated by Albanese and Frison in 1995 for Wyoming and Montana, and by Wilson in 1983 for the Canadian plains and foothills. Twenty-seven radiocarbon measurements on bone collagen, charcoal, wood, and organic sediment from alluvium and colluvium range back to >10.2 14C ka and cultural associations reach in excess of 9.0 14C ka. Bones of extinct megafauna are in interstitial sediments among the landslide boulders but a date of ~20.7 14C ka on residual bone organics is problematic because of an unusual 13C/12C ratio. This Late Pleistocene fauna includes large mountain sheep, camel, horse, and cheetah. Regional evidence suggests ice-free conditions after ~14.5 14C ka. Archaeological evidence suggests intermittent, very short-term camping by humans, with associated tool-production activities. Given the depositional setting, some artifacts probably have been fluvially or colluvially redeposited, a concern also for some of the radiocarbon samples. Projectile points in dated contexts add to growing evidence for introduction and use of relatively small corner, side, and corner/side-notched types from terminal Paleoindian times forward to the late Holocene.