HR: 15:25h
AN: H53E-08    [Abstracts]
TI: Marine Sedimentary Record of Cenozoic Monsoon Intensity Preserved in the Asian Marginal Seas
AU: * Clift, P D
EM: p.clift@abdn.ac.uk
AF: University of Aberdeen, Department of Geology and Petroleum Geology, Kings College, Aberdeen, AB24 3UE United Kingdom
AB: Climate models predict that the intensity of the Asian monsoon is largely controlled by the elevation of the Tibetan Plateau. However, the elevation of Tibet and the erosional response to monsoon intensification is contentious. Compilation of seismic data from the marginal seas of East Asia now shows that sedimentation rates sharply increased across the region, and especially in the Red River catchment after around 33 Ma and continued to increase until around 11 Ma. The dating of potassic magmatism and strike-slip faulting on the eastern flanks of the Tibetan Plateau starting at 35-30 Ma suggests that this tectonism may accompany a period of accelerating surface uplift in Tibet. At present few climate records exist for this time period, though the monsoon might be expected to have strengthened in stages since that time. Most notably new data from ODP Site 1148 in the northern South China Sea show a sharp increase in clastic and carbonate mass accumulation rates associated with a change in clay mineralogy to greater illite dominance (physical weathering) starting around 17.2 Ma. I interpret this to reflect a change to a more erosive, more monsoonal climate starting at that time in southern China. Falling sedimentation rates at 11-8 Ma and lasting until 4 Ma indicate drier conditions across Asia at that time, also recorded by strong eolian sedimentation in the North Pacific, slower sedimentation on the Indus and Bengal Fans, and change to a more smectite dominated mineralogy on both these fans, indicating a less erosive environment. Only in the Mekong does erosion increase after 8 Ma, driven by local tectonic uplift in the Vietnamese Highlands. Faster sedimentation and a return to an illite dominated mineralogy after 4 Ma accompanies a series of proxies that indicate a stronger summer monsoon at that time, and a return to faster erosion driven by rains in East and South Asia. The evidence shows a broad positive correlation between monsoon strength and erosion over long periods of geological time. Pulses of sediment caused by faster erosion do not appear to be strongly dampened over time scales >100 kyr by sequestering in continental sedimentary basins, but mostly reach the continental margins of the South China Sea.
UR: http://www.whoi.edu/pclift/asia\_erosion.html
DE: 8110 Continental tectonics--general (0905)
DE: 4267 Paleoceanography
DE: 3022 Marine sediments--processes and transport
DE: 1815 Erosion and sedimentation
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting