Paleoindian environmental change and landscape response in Barger Gulch, Middle Park, Colorado

摘要

Middle Park, a high-altitude basin in the Southern Rocky Mountains of north-central Colorado, contains at least 59 known Paleoindian localities. At Barger Gulch Locality B, an extensive Folsom assemblage (similar to 10,500 C-14 yr B.P.) occurs within a buried soil. Radiocarbon ages of charcoal and soil organic matter, as well as stratigraphic positions of artifacts, indicate the soil is a composite of a truncated, latest-Pleistocene soil and a younger mollic epipedon formed between similar to 6000 and 5200 C-14 yr B.P and partially welded onto the older soil following erosion and truncation. Radiocarbon ages from an alluvial terrace adjacent to the excavation area indicate that erosion followed by aggradation occurred between similar to 10,200 and 9700 C-14 yr B.P, and that the erosion is likely related to truncation of the latest-Pleistocene soil. Erosion along the main axis of Barger Gulch occurring between similar to 10,000 and 9700 C-14 yr B.P was followed by rapid aggradation between similar to 9700 and 9550 C-14 yr B.P., which, along with the erosion at Locality B, coincides with the abrupt onset of monsoonal precipitation following cooling in the region similar to 11,000-10,000 C-14 yr B.P. during the Younger Dryas oscillation. Buried soils dated between similar to 9500 and 8000 C-14 yr B.P. indicate relative landscape stability and soil formation throughout Middle Park. Morphological characteristics displayed by early Holocene soils suggest pedogenesis under parkland vegetation in areas currently characterized by sagebrush steppe. The expansion of forest cover into lower elevations during the early Holocene may have resulted in lower productivity in regards to mammalian fauna, and may partly explain the abundance of early Paleoindian sites (similar to 11,000-10,000 C-14 yr B.P., 76%) relative to late Paleoindian sites (similar to 10,000-8000 C-14 yr B.P., 24%) documented in Middle Park. (c) 2005 Wiley Periodicals, Inc.