STABLE CARBON ISOTOPE GEOCHEMISTRY OF PALEOSOLS, MEAN ANNUAL RAINFALL ESTIMATES AND ITS CORRELATION WITH TETRAPOD DIVERSITY IN PERMO-TRIASSIC STRATA OF THE AFRICAN CONTINENT (Invited Presentation)

Paleosol morphology and geochemistry in sedimentary strata have accumulated to produce a high resolution record of Permo-Triassic (PT) paleoclimate and paleoenvironments that spans a large swath of the African continent. This geographically-extensive dataset records changes in climate during a major mass extinction event and time of terrestrial environmental reorganization, and provides a basis to assess paleoecological links between climate and vertebrate diversity as well as a framework for understanding impacts of climate-driven mass extinction.

PT paleosols in Niger include no notable stratigraphic trends in morphology and record an arid climate. Middle-Upper Permian strata of Zambia and Tanzania record an important environmental transition from humid lake-plain systems in the lower-Madumabisa and Ruhuhu formations to subhumid to semi-arid fluvial and floodplain systems in the upper-Madumabisa and Usili Formations. Triassic strata in Zambia and Tanzania contain paleosols indicative of seasonal rainfall. Collectively, the paleosol morphological data indicate similar environments and climatic conditions prevailed throughout the PT in Niger, whereas there is evidence for a major transition from humid to arid conditions in Tanzania and Zambia in the middle-late Permian, with a trend toward strong seasonality in the Triassic.

δ¹³C values of pedogenic calcite and occluded organic matter range from -5.6 to 1.0‰ and -29.4 to -22.5‰, respectively, in thePT of Niger. In Tanzania and Zambia, δ¹³C values of pedogenic calcite from -15.9 to -7.6‰, and the δ¹³C values of the associated, occluded organic matter ranges from -26.7 to -23.4‰. δ¹³C values of pedogenic calcite and associated organic matter (δ¹³C_cc-om) in modern soils correlates strongly with mean annual precipitation (MAP), such that MAP(cm) = (δ¹³C_cc-om – 25.4)/-0.31. Based on this, PT δ¹³C_cc-om values yield average MAP estimates of approximately 12cm for Niger (n=23) and 37cm for Tanzania and Zambia (n=17). Both morphological and geochemical data indicate that paleoclimate during the PT was consistently more arid in Niger than Tanzania and Zambia. This climate zonation may explain the greater levels of endemicity in the terrestrial vertebrate fauna of Niger and the more cosmopolitan nature of Tanzanian and Zambian faunas at this time.