Superposed neoglacial and late Pinedale (Wisconsinan) tills, Titcomb Basin, Wind River Mountians, western Wyoming

Abstract

Late Pinedale (Wisconsinan) and Neoglacial deposits mantle most valley floors above the timberlane in the Wind River Mountains. Although these tills are generally assigned ages by radiocarbon, relative topographic position, weathering characteristics, and soil morphology, they are rarely superposed. This paper describes a sequence of moraines in Titcomb Basin where early Neoglacial till (now called Indian Basin Till) is superposed on a moraine of late Pinedale age, providing important information on relative ages for the two tills. Late Pinedale deposits radiocarbon date at ca. 8000 yr. B.P., from bog bottom organic materials. Time of onset of Neoglaciation is unknown, while the termination of the Indian Basin advance is placed at ca. 3000 yr. B.P. Differences in soil profile morphology, particle size, mineralogy and chemistry are described and discussed with respect to relative age assignment. While profile morphology and particle size differences appear important in differentiating the two soils, differences in clay mineral composition appear to have greater utility in discriminating post-Indian Basin soils from post-late Pinedale soils.