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Lateral Variability of Hydromorphic Paleosols Spanning the Paleocene/Eocene Boundary in the Denver Basin, Colorado
FARNHAM, Timothy M., Denver Museum of Nature and Science, 2001 Colorado Boulevard, Denver, CO 80205-5798|

A widespread terrestrial condensed section separates two sequences of synorogenic strata in the Denver Basin, Colorado. Six types of paleosols distinguished by hydromorphic and pedogenic features have been identified in the condensed interval which developed from early Paleocene to early Eocene time. Paleosols in the study interval formed on granite-rich floodplain and fluvial strata deposited by uplift of the Front Range, and have been studied in two cores and one outcrop in the Denver Basin. Hydromorphic and pedogenic features vary across the basin and highlight controls on paleosol development. Type A and B paleosols occur at Castle Pines, Colorado, on the western edge of the basin and contain features of poorly drained, immature soils. Type C paleosols are found at Castle Pines and along the Comanche Creek escarpment in the eastern Denver Basin and are characterized by features common to well drained, immature soils. Types A-C paleosols formed in a depositional setting where sedimentation rate periodically exceeded pedogenesis burying paleosols before they could become mature. Type D and E paleosols developed along the Comanche Creek escarpment and have characteristics of well drained and relatively poorly drained paleosols respectively. Sedimentation rate only occasionally exceeded pedogenesis for Type D and E paleosols, allowing a vertical succession of mature soils to develop. A Type F paleosol developed at Kiowa, Colorado, where pedogenesis kept pace with sedimentation allowing a cumulative paleosol to develop. The paleosol at Kiowa contains features common to both poorly drained and well drained soils. Variations in paleosol maturity across the Denver Basin are controlled by depositional processes. Sedimentation rates episodically exceeded pedogenesis in study areas where immature paleosols are preserved; mature and cumulative paleosol profiles indicate areas where sedimentation rate only rarely exceeded pedogenesis or matched it for long periods of time.