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Article Dans Une Revue Palaeogeography, Palaeoclimatology, Palaeoecology Année : 2022

Insights on the Cenozoic climatic history of Southeast Australia from kaolinite dating

Résumé

Australia hosts some of Earth’s oldest regolith. They were preserved through geological time thanks to exceptionally low erosion rates affecting large parts of this continent. Accurate chronological constraints about their formation and evolution are abundant in its northern and western regions, but they remain underexplored in its southern and eastern parts, limiting the determination of the extent and impact of Cenozoic paleoclimatic events over this continent. To address this question, we provide a new set of chronological data obtained from a tropical regolith from southeastern Australia close to the western side of the Australian Great Escarpment (Syerston–Flemington, New South Wales). The Syerston regolith, known for its anomalous Sc content, exhibits a thick duricrust (18 m deep) comprising both an in situ and a detrital component. The thickness of these indurated horizons, and particularly the presence of the detrital duricrust protecting the profile from secondary vertical weathering of low intensity and erosion, were favourable conditions for the conservation of a long-term record of local paleoweathering history. Electron Paramagnetic Resonance (EPR) dating of phyllosilicates allows the discrimination of two generations of kaolinite formed at 10.1 ±2.3 Ma and 3.8 ± 0.9 Ma, trapped within the in situ duricrust. In parallel, the detrital horizon hosts phyllosilicates with an age of 8.2 ± 2.8 Ma and 1 ± 0.3 Ma close to its top. Such ages confirm the hypothesis that, following the end of tropical Middle Miocene period, the Late Miocene climate in southeast Australia was still favorable to the development of tropical weathering covers. These results, combined with other dating studies from the literature, suggest that a large part of the extended coastal regions of Australia suffered a warm and wet climate from the Mid-Miocene to the beginning of Late Miocene. However, this hypothesis, as well as the extent of hot and wet climate over Central Australia during the Late-Miocene, period of the onset of the Australian aridity, still need to be constrained by complementary paleoregolith dating studies.
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hal-03845324 , version 1 (09-11-2022)

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Maximilien Mathian, Mathieu Chassé, Georges Calas, William L Griffin, Suzanne Y O'Reilly, et al.. Insights on the Cenozoic climatic history of Southeast Australia from kaolinite dating. Palaeogeography, Palaeoclimatology, Palaeoecology, 2022, 604, pp.111212. ⟨10.1016/j.palaeo.2022.111212⟩. ⟨hal-03845324⟩
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