Geochemistry, Geophysics, Geosystems

Early Eocene to middle Miocene cooling and aridification of East Antarctica

Authors


Abstract

[1] Few high-latitude terrestrial records document the timing and nature of the Cenozoic “Greenhouse” to “Icehouse” transition. Here we exploit the bulk geochemistry of marine siliciclastic sediments from drill cores on Antarctica's continental margin to extract a unique semiquantitative temperature and precipitation record for Eocene to mid-Miocene (~54–13 Ma). Alkaline elements are strongly enriched in the detrital mineral fraction in fine-grained siliciclastic marine sediments and only occur as trace metals in the biogenic fraction. Hence, terrestrial climofunctions similar to the chemical index of alteration (CIA) can be applied to the alkaline major element geochemistry of marine sediments on continental margins in order to reconstruct changes in precipitation and temperature. We validate this approach by comparison with published paleotemperature and precipitation records derived from fossil wood, leaves, and pollen and find remarkable agreement, despite uncertainties in the calibrations of the different proxies. A long-term cooling on the order of ≥8°C is observed between the Early Eocene Climatic Optimum (~54–52 Ma) and the middle Miocene (~15–13 Ma) with the onset of transient cooling episodes in the middle Eocene at ~46–45 Ma. High-latitude stratigraphic records currently exhibit insufficient temporal resolution to reconstruct continental aridity and inferred ice-sheet development during the middle to late Eocene (~45–37 Ma). However, we find an abrupt aridification of East Antarctica near the Eocene-Oligocene transition (~34 Ma), which suggests that ice coverage influenced high-latitude atmospheric circulation patterns through albedo effects from the earliest Oligocene onward.

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