Abstract

Five paleosols in five superposed diamicts (probably tills) on Mokowan Butte permit subdivision of pre-Wisconsinan drift and a description of Quaternary and probably late Tertiary soil-forming environments. The surface soil and upper two buried paleosols (soils 5, 4, and 3, respectively) have strongly developed, 1–5 m thick, leached, reddish, clay-rich (20–48% clay), argillic horizons overlying indurated petrocalcic, calcic, or leached B horizons. The lower two buried paleosols (soils 2 and 1) are strongly developed and have 40–150 cm thick, clay-rich (18–49% clay) argillic horizons over calcic, petrocalcic, or leached B horizons. Based on their resemblance to Paleudalfs, Paleustalfs, or Palexerults, soils 5, 4, and 3 probably formed under interglacial climates that were moister and at least 6 °C warmer than the present. Properties of soil 2 (Petrocalcic Paleustalf) and soil 1 (Typic Croboralf) imply soil formation under warm, semi-arid climates and a modern type of climate, respectively. Estimates of soil age based on degree of soil formation, paleomagnetic data, and regional correlation with dated glacial chronologies suggest soils 5 and 4 are in middle and early Pleistocene tills (= early Illinoian or Kansan and Nebraskan?), respectively, and soils 3, 2, and 1 are in late Pliocene till or diamict.

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