TABOR, NEIL J. and ISABEL P. MONTANEZ
University of California-Davis, Davis, CA

Abstract: Paleosols as indicators of Permo-Pennsylvanian Climatic Change in Equatorial Western Pangea and Development of Megamonsooal Circulation

Late Pennsylvannian and Permian time is a dynamic period in earth history demarcated by the formation of supercontinent Pangea, development of the Pangean Megamonsoon, and the last icehouse-to-green house transition; all of which are hypothesized to have widely affected Earth's climate. Recent paleoclimate models suggest that construction of the supercontinent Pangea restricted circumequatorial circulation effecting a change from Late Pennsylvannian zonal circulation to Early Permian global-scale monsoonal circulation. This shift in atmospheric circulation is hypothesized to have produced widespread aridity in continental interiors and equatorial regions. However, paleoclimatic indicators used to construct climate models are usually end-member indicators, such as evaporites and coal deposits, that provide only crude resolution of climate dynamics between arid and moist conditions. Paleosols can potentially provide a much more sensitive source of paleoclimate data that spans the gap between end-member climatic indicators.

Detailed macromorphological, micromorphological, geochemical and mineralogical analysis of Permo-Pennsylvanian paleosols from north-central Texas (equatorial western Pangea) indicate a gradual climatic change from perenially moist conditions, demarcated by Gleysols and Histosols, to a seasonally moist climate characterized by an extended dry or add season, as suggested by carbonate-bearing Vertisols. Paleosols also suggest that the climate became increasingly more arid through Permian time. These observations are corroborated by paleobotanical and clay mineralogical analyses. We interpret this observed climatic change in Permo-Pennsylvanian paleosols from north-central Texas as a transition from predominantly zonal atmospheric circulation to monsoonal circulation in Early Permian time.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas