Late pleistocene and holocene soils of the Carter/Kerr-McGee archeological site, powder river basin, Wyoming

Abstract

Soil character and stratigraphy at the Carter/Kerr-McGee site indicate poorly drained conditions along the bottom of the paleo-arroyo in late Pleistocene time. This occurred under a relatively cool and humid climate during Clovis (ca. 11,400 B.P.) and Folsom (ca. 10,700 B.P.) occupation and subsequently during occupation by Agate Basin (ca. 10,400 B.P.), Hell Gap (ca. 10,000 B.P.), and Cody (ca. 8700 B.P.) cultural groups. Under these conditions, Wiesenboden or Low Humic Gley or Humic Gley soils (BALDWIN et al. 1938, THORP & SMITH 1949), i.e., probably Typic Argiaquolls and Haplaquolls (SOIL SURVEY STAFF 1975, 276, 279–280), formed near the arroyo bottom under grasses and sedges in association with azonal (BALDWIN et al. 1938; THORP & SMITH 1949) and composite soils along its flanks. Wiesenboden or Low Humic Gley or Humic Gley soils do not now form in the area. Climatic change at the Pleistocene-Holocene boundary is marked by superposition of a calcareous soil, i.e., probably a Brown soil (BALDWIN et al. 1938; THORP & SMITH 1949) or Calciustoll or Haplustoll (SOIL SURVEY STAFF 1975, 301–302), into the late Pleistocene paleosols—a process indicative of ensuing dry and warmer climatic conditions and improved soil drainage thought to have occurred during Altithermal time. Following this, probably toward the end of the Altithermal, renewed arroyo cutting and slope instability partially or totally truncated this soil sequence. In turn, post-Altithermal events were marked by weak azonal soil formation (Ustifluvents and Ustipsamments; SOIL SURVEY STAFF 1975, 191, 207) in alluvium and colluvium along the paleo-channel as well as renewed arroyo incision and filling. The arroyo is presently incising itself and is cutting mainly along the alluvium-bedrock contact.