ABSTRACT Developing accurate chronologies is important for understanding the formation and evolution of glacial environments in the Quaternary. Radiocarbon dating is a prominent technique for creating chronologies for glacial events during the late Pleistocene, and although radiocarbon dates from vertebrate fossils are relatively abundant, these dates have been underutilized for timing glacial events. Here, the utility of using radiocarbon dates from large mammal fossils for dating glacial events is explored further. Specifically, this study examines the potential of exclusive use of dated mammal remains to establish a chronology of deglaciation in New York State after the Last Glacial Maximum. We predict the earliest occurrence dates of megafauna to represent a minimum age for the initiation of deglaciation because glacial ice would have needed to have melted for plants and animals to begin to inhabit the state. We also predict dates to progress to more recent ages from south to north following recession of the Laurentide ice sheet. The data support these predictions. The earliest occurrence dates for mammoth and caribou, the suspected first large mammal species to occur within the state, are between 17,470 and 16,430 calibrated yr B.P. These dates imply first occurrence of large mammals in New York State and thus a minimum age of deglaciation beginning ca. 17,000 calibrated yr B.P. Because of the likely delay between the timing of deglaciation and the first mammal inhabitants of the state, this date must be viewed as a minimum age, with deglaciation having occurred sometime prior to this age. Comparing south to north, as an indicator of glacial regression, dates from New York State south of 42°N latitude are earlier compared to dates collected north of this latitude. This progression of dates from south to north supports the prediction that megafauna expanded northward following recession of the Laurentide ice sheet, and it implies that radiocarbon-dated mammalian megafauna data are useful, even exclusively, in identifying the timing of certain glacial events.

ABSTRACT The Marias River canyon in north-central Montana, incised into Upper Cretaceous strata of the Great Plains during latest Pleistocene to Holocene time, served as a locus of human activity tied to the unique floral and faunal resources it provided ancient peoples. Erosion of the main canyon walls resulted in deposition of tributary junction alluvial fans characterized by debris-flow and hyperconcentrated flow sediment transport processes where side canyons emerged onto the alluvial valley floor. These alluvial-fan deposits preserve Late Precontact archaeological remains accessible due to their postburial exposure where partially eroded by the meandering channel of the Marias River (Goose Bill site complex). Archaeological materials are also preserved high on the dissected canyon walls where movement of hillslope sediment and colluvium by sheetwash led to their burial (Sparrowhawk site). Deposition of sediment of contrasting physical attributes (grain size, sorting, clay mineral content) within the canyon influences soil substrate properties, favoring growth of specialized plant communities in both alluvial-fan and fluvial environments. These relations exemplify the strong geoecological connections among depositional environment and sediment characteristics, substrate properties, and vegetation community development. The plant communities, interacting in conjunction with the physical landscape, provided a range of habitats utilized by such large mammals as plains bison, Rocky Mountain elk, Audubon sheep, pronghorn, Rocky Mountain mule deer, and white-tailed deer. Four major bison bone layers, some including bison hair and other soft tissues, with associated stone arrow points and stone flakes (artifacts) and evidence of bone processing are preserved in alluvial-fan deposits exposed along the bank of the Marias River at the Goose Bill site complex. These relations illustrate: (1) human activities dating to ~100-595 yr B.P. (falling within the Late Precontact Period of regional archaeological prehistory) that reflect subsistence reliance on bison as a food source, (2) the importance of tributary alluvial fans proximal to canyon walls in preserving archaeological remains, and (3) the role of the meandering Marias River channel in destroying these deposits over a time period of <100 yr. Sediment deposition by overland flow higher up the canyon walls at the Sparrowhawk site preserves a somewhat older (710-830 yr B.P.) archaeological record suggestive of a broader spectrum of resource (food) processing spatially decoupled from an area of bison kill/death.