ABSTRACT

A Late Mississippian paleosol satisfying all of the morphological criteria required for classification of Holocene Vertisols provides quantitative paleoclimate information, in addition to the now commonplace interpretation of precipitation seasonality based on the presence of vertic features. Paleoprecipitation was estimated using the empirical relationship between depth to pedogenic carbonate horizon in Quaternary soils. Burial compaction, erosional truncation, and high paleoatmospheric CO₂ concentration, all factors that complicate paleoprecipitation estimates, are unusually well constrained for this paleosol. Allowing for 10% compaction, the paleosol had a pre-burial depth of 100 cm for the pedogenic carbonate horizon, yielding a mean annual paleo-precipitation estimate f 648 ± 141 mm. This is comparable to the mean annual precipitation for Brownsville, Texas, where similar soils are found today. A dolomicrite crust, developed in gilgai microlows, is well preserved in the paleo-Vertisol. Higher Late Mississippian paleotemperatures and rates of evapotranspiration associated with a lower-latitude paleogeography for central Tennessee during the Late Mississippian may explain in part why Holocene coastal Vertisols in the Brownsville region lack surficial crusts similar to that of the paleo-Vertisol. We qualitatively define the Late Mississippian climate of central Tennessee as semiarid.