The Impact of Late Eocene/ Early Oligocene Climate Change on the Continental Biota of Patagonia

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AbstractThe end of the Eocene and the beginning of the Oligocene mark an important change in world climate, when it transitioned from 'greenhouse' to 'icehouse'. The timing and biotic impact of the change has been studied in the continental records of North America, Europe and Asia and they show a response to both local and global influences. As yet, however, no continental mammal and plant sequence has been studied in the Southern Hemisphere. Recent revision of the ages of rock units and biotas in Patagonia has demonstrated that the Sarmiento Fm at Gran Barranca in Patagonian Argentina spans the late Eocene through early Oligocene interval; this is the only known continental vertebrate and plant sequence so far identified from the Southern Hemisphere that spans this interval. Preliminary analysis of the mammalian herbivores suggests that dramatic changes occurred over a comparatively short interval of geologic time. The same sedimentary interval contains plant microfossils that document important change in the plant communities. This proposal requests funding for further study of this terrestrial biotic change. The geochronology of the Sarmiento Fm at Gran Barranca will be refined using radiometric dating, chemical identification of tephra, and paleomagnetism. Stratigraphically-controlled collections will be made of vertebrates and plant microfossils. Climate change and its impact on the biota will be assessed 1) by documenting changes in mammalian community structure (richness, origination and extinction rates and ecological morphology); and 2) by documenting changes in vegetation and floral composition from the study of phytoliths.