MID-LATITUDE AND HIGH-LATITUDE SOIL FORMING PROCESSES DURING THE PERMIAN: PALEOSOL LANDSCAPES FROM ARGENTINA AND ANTARCTICA

Soils and soil-forming processes are described here from paleo mid-latitude region of Gondwana and compared with roughly time equivalent strata at paleo-polar latitudes of Gondwana. Notable contrasts in state-factor soil-forming processes occurred between these latitudinal regions, however, the resulting soil profiles that developed in equilibrium with these state-factors reveal surprising differences. Paleo mid-latitude soils from the Early to Middle Permian of western Argentina developed under an arid to semi-arid climate and developed often thick accumulations of pedogenic carbonate and, rarely petrocalcic horizons. Vegetation that once existed in this landscape is poorly preserved and, thus poorly understood. Eastern Argentina saw the development of soils in a montane or hinterland setting, with clay-rich redoximorphic soils forming directly on crystalline basement rocks of Ordovician-age granite along the flanks of a deeply dissected paleovalley setting. In this higher relief setting, arborescent taxa dominated. These two field areas at nearly the same paleolatitude reflect a micro-climate style contrast that likely influenced vegetation regimes, and in turn influenced soil-forming processes. The paleo-polar latitudes at roughly the same time interval reflect an entirely unique set of soil-forming processes. Unlike the western sector of Gondwana, these latitudes hosted functionally diverse forested ecosystems, which thrived under the polar light, temperature, and precipitations regimes unlike anything equator-ward of the polar circle. Soils that hosted these forest stands, which ranged in tree density from 400 to 0ver 1000 trees per hectare, are almost ubiquitously Protosols and Histosols, varying most notably in the grain size of the sediment that formed the soil substrate. However, unlike the paleo-mid-latitudes, these weakly developed polar soils illustrate nuanced relationships with sedimentation conditions in riparian ecosystems, forming as weakly developed soils on stabilized islands in low-sinuosity streams, or as wetland soils on adjacent poorly-drained floodplain ecosystems. The geometry of the rhizosphere in these weakly developed soils further influenced the sedimentary-pedogenic cycle in these fluvial systems through contribution of large woody debris into fluvial channels during floodplain erosion.