Paleopedology and geochemistry of Late Mississippian (Chesterian) Pennington Formation paleosols at Pound Gap, Kentucky, USA: Implications for high-frequency climate variations

Abstract

Climate during the Late Mississippian (late Chesterian) in the southern Appalachian Basin was characterized by alternating periods of aridity and humidity. Pennington Formation paleosols at Pound Gap record climate and ecological changes for latest Chesterian time, ending at the Mississippian–Pennsylvanian systemic boundary. Forty paleosols were identified, described, and assigned to seven pedotypes. Inferred soil orders considered as analogs include Histosols, Entisols, Inceptisols, Alfisols and Oxisols, but are dominated by Vertisols. Classification of an Oxisol was determined by field and geochemical evidence of intense leaching and kaolinite-dominated clay mineralogy. Field and micromorphologicial evidence suggests a polygenetic character of the Vertisols, resulting from changing soil drainage through time. Variations in soil drainage are quantified using proxy estimates of inferred soil processes such as base loss, leaching, lessivage, and oxidation. Using the CIA-K proxy, mean annual precipitation (MAP) estimates range from 519 to 1361 mm/yr. Changes in MAP correspond with variation in inferred soil processes. The flora of this time period, in response to variations in precipitation and soil drainage, also changes through time as evidenced by changes in abundance and depth of root traces. Reconstructed ecosystems range from sparse vegetative cover with shallow, tabular root systems in early Pennington soil development, to dense, deeply penetrating root systems suggestive of arborescent floral associations at the top of the succession approaching the Mississippian–Pennsylvanian boundary. This study provides greater resolution of changing climate and pedogenic processes than what is provided in previous studies of Late Mississippian climate, and suggests that the documented variability in paleosol types and soil drainage might represent the record of high-frequency climate changes likely associated with expansion and contraction of the paleo-Intertropical Convergence Zone (ITCZ).