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Sediment Dynamics and Morphodynamics of River-Sea Sediment Dispersal Systems through Space and Time: A Source-to-Sink Perspective
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Marine Records of Himalayan Erosion and Monsoon Climate Change in Southwest Asia
Tuesday 8th @ 1430-1450, Conference Room 1
Peter Clift* , Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana, USA
Peng Zhou, Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana, USA
Denise Kulhanek, nternational Ocean Discovery Program, Texas A&M University, 1000 Discovery Drive, College Station, TX 77845-9547, USA
Daniel Stockli, Jackson School of Geosciences, The University of Texas as Austin, Texas 78712-0254, USA
Jurek Blusztajn, Department of Geology and Geophysics, Woods Hole Oceanographic institution, Woods Hole, Massachusetts, USA
Presenter Email: pclift@lsu.edu |
| International Ocean Discovery Program (IODP) drilling in the Arabian Sea has recovered a relatively continuous sequence of sediments dating back to 11 Ma that when combined with industrial drilling close to the Indus River mouth provides a record of erosion, chemical weathering and environment stretching back into the middle Miocene. Nd isotope data show a progressive modest increase in flux from the Karakoram until around 10 Ma followed by a reverse towards Himalayan sources until the present day. Zircon U-Pb detrital ages confirm that the dominant source is from the Indus River with relatively little material from peninsular India. Erosion of the Lesser Himalayas increased sharply after 5.7 Ma but especially since 1.9 Ma as the crystalline inner Lesser Himalaya were exposed across the basin. The shift to more Himalayan compositions occurs at a time of weakening monsoon. Reduced chemical weathering accompanies the change in vegetation in Southwest Asia from C3 to C4 dominated, indicating drier conditions starting after 8 Ma. Since 1.9 Ma the composition of the deep-water sands has been similar to the modern river but not that seen at the Last Glacial Maximum, suggesting that most of the erosion in the basin occurs when the monsoon is strong during interglacial times. Sediment is however stored in the delta and on the continental shelf during sea level highstands and is reworked into the deep basin as sea level falls resulting in a lag time of around 100 k.y. in the recent geologic past. Monsoon intensity appears to be the primary control over the rate of erosion on such timescales, yet faster erosion in the Lesser Himalayas occurred when the monsoon weakened, which we attribute to a southward shift in the maximum rainfall band of the summer monsoon, as well as the building of an imbricate thrust stack over a basement ramp within the basal Himalayan thrust during the Miocene and Pliocene. |
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