THE RESPONSE OF MID-LATITUDE LATE PALEOZOIC TERRESTRIAL SYSTEMS TO DEGLACIATION AND FLORAL REORGANIZATION

Paleosols of the Pennsylvanian Paganzo Group, Paganzo and Río Blanco basins, northwestern Argentina, preserve a climate history that captures a marked shift from the continental ice sheet-climate feedbacks of the mid-Carboniferous glacial event to a climate regime characterized by progressive aridification driven by ecologic and geomorphic change and atmospheric chemistry. Stable carbon isotopes of fossil plant matter indicate cold and dry conditions prior to the youngest glaciation recorded in the Paganzo Group, consistent with paleobotanical interpretations. A subsequent shift to post-glacial high frequency (<100 ky) oscillations in relative humidity and mean annual precipitation is indicated by changes in carbon isotope compositions of fossil organic matter and major element geochemistry of paleosols. This oscillatory trend in relative humidity and floral regime is perturbed by two intervals of more arid conditions, and ultimately this climate trend terminates to an environment characterized by steppe/dry scrub floral provinces of a dry subhumid moisture regime. Quantitative estimates of seasonal soil temperature regime derived from hydrogen and oxygen isotopes of pedogenic goethite indicate a ~3ºC increase in temperature over 100 ky, indicating that eccentricity may have been an important in the regulation of post-glacial climate variability. Together, the qualitative paleopedology and sedimentology and the quantitative geochemistry of late Pennsylvanian paleosols in the Paganzo Basin indicate a substantial departure from climates suitable for the maintenance of tidewater glaciers documented in the mid-Carboniferous and reveal a quasi-stable climate similar to mid-latitude continental regions under interglacial or perhaps greenhouse climate conditions.