Variations in aridity across the Asia–Australia region during the Neogene and their impact on vegetation

Abstract

Scientific drilling provides extended records of continental environmental conditions during the Neogene in Asia and northern Australia. Spectral data allow reconstruction of the environment using abundances of hematite and goethite. Hematite formation is favoured by dry or seasonal conditions. Hemipelagic sites show the most regular records. Monsoon strengthening started in the Early Miocene and peaked at 17–20 Ma in the Bay of Bengal and at 10–15 Ma in southern China before weakening after c. 12 Ma and c. 10 Ma, respectively. The Indus Basin dried after c. 8 Ma and again after 3 Ma, while aeolian sediment sources to the Sea of Japan show increased aridity after 5 and 3 Ma. The Mekong Fan indicates increasing aridity after 6 Ma, similar to Eastern Australia. In contrast, NW Australia shows a trend towards wetter conditions after 8 Ma, with a humid period at 4–6 Ma followed by drying. There is a link between drying and vegetation in the Mekong and Pearl River basins, as well as Eastern Australia. Monsoon strengthening is linked to topographic uplift in the Himalaya, together with Tethyan gateway closure. Long-term drying is likely driven by global cooling since the Middle Miocene.