2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 1
Presentation Time: 8:00 AM-12:00 PM


KAHMANN, Julia A., Geology, Baylor University, One Bear Place #97354, Waco, TX 76798-7354 and DRIESE, Steven G., Department of Geology, Baylor University, One Bear Place #97354, Waco, TX 76798-7354, Julia_Kahmann@baylor.edu

The extraordinarily complete, 280 m thick outcrop section of the Pennington Formation (Upper Mississippian) at Pound Gap, KY provides a record of climate changes at different spatial and temporal scales. Early Pennington paleosols suggest local climate and soil drainage variations during high-frequency cycles of deposition. Thin, gleyed, and poorly drained paleo-Vertisols and paleo-Alfisols indicate pedogenesis in wetter, more humid climates. Overlying paleosols are thicker, reddened, and have well-developed Bk horizons, which signal the onset of drier, semiarid to subhumid conditions and development of better soil drainage. Local to regional climate variations may have been influenced by the paleo-Intertropical Convergence Zone (ITCZ), whereby paleo-ITCZ-influenced climate conditions were more humid and less seasonal than those in which the paleo-ITCZ was absent. Latest Pennington compound paleosols (paleo-Vertisols and paleo-Alfisols) developed after a 3rd-order sequence boundary, after which transgressive seas deposited the 8 m thick, Little Stone Gap Limestone Mbr. and the 33 m thick, black, organic C-rich (anoxic) Pride Shale Mbr. These compound paleosols began initially well-drained with Bk horizon development, but were overprinted by later redoximorphic features. At the close of the Pennington deposition, poorly developed and poorly drained paleosols (paleo-Entisols and paleo-Inceptisols) are present, followed by deposition of thin paleo-Histosols (coal), thus indicating a regional shift in paleoclimate from the semiarid to subhumid and highly seasonal Late Mississippian to the ever-wet conditions of the Early Pennsylvanian. This interpretation of major climate shift is also supported by preliminary geochemical analyses of paleosols employing the chemical index of alteration minus potassium (CIA-K) as a paleoprecipitation proxy. Paleoprecipitation values range from 884mm to 1293mm per year; the lowest value representing the earliest Pennington paleosol and the highest value a late Pennington paleosol. Clay illuviation and calcium carbonate formation calculations also support similar climate and drainage trends as predicted by field descriptions.