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Clay mineral records of East Asian monsoon evolution during late Quaternary in the southern South China Sea |
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| Authors: | |
| Institution: | 1. Laboratory of Marine Geology, Tongji University, Shanghai 200092, China 2. FRE 2566 Orsayterre, Universite de Paris Xl, 91405 Orsay, France 3. UMR PBDS du CNRS, Universite de Lille I, 59655 Villeneuve d'Ascq, France 4. Laboratoire des Sciences du Climat et de I'Environnement, Laboratoire mixte CNRS-CEA, 91198 Gif-sur-Yvette, France |
| Abstract: | High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 190 ka during late Quaternary from core MD01-2393 off the Mekong River in the southern South China Sea are reported to reconstruct a history of East Asian monsoon evolution. The dominating clay mineral components indicate a strong glacial-interglacial cyclicity, with high glacial illite, chlorite, and kaolinite contents and high interglacial smectites content. The provenance analysis indicates the direct input of clay minerals via the Mekong River drainage basin. Illite and chlorite derived mainly from the upper reach of the Mekong River, where physical erosion of meta-sedimentary rocks is dominant. Kaolinite derived mainly from active erosion of inhered clays from reworked sediments in the middle reaches. Smectites originated mainly through bisiallitic soils in the middle to lower reaches of the Mekong River. The smectites/(illite+chlorite) and smectites/kaolinite ratios are determined as mineralogical indicators of East Asian monsoon variations. Relatively high ratios occur during interglacials and indicate strengthened summer-monsoon rainfall and weakened winter-monsoon winds; relatively lower ratios happened in glacials, indicating intensified winter monsoon and weakened summer monsoon. The evolution of the summer and winter monsoons provides an almost linear response to the summer insolation of the Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution. |
| Keywords: | clay minerals East Asian monsoon late Quaternary Mekong River South China Sea |
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