Summary of Abstract Submission

Abstract Submission No. IO50-06-0021PresentationOral

INDIAN MONSOON EVOLUTION ASSOCIATED WITH HIMALAYAN UPLIFT AND CLIMATE CHANGE OVER THE PAST 30 MYR: RECORDS FROM ODP SITE 758 IN THE BAY OF BENGAL, INDIAN OCEAN

Sajid Ali*1, Ed C. Hathorne2, Martin Frank2

1 PRL, Ahmedabad, India
2 1GEOMAR Helmholtz Centre for Ocean Research Kiel, D-24148 Kiel, Germany

ABSTRACT :

Indian monsoon variability, on long time scales, has been linked with tectonic uplift and global climate changes but monsoon records prior to 17 Myr ago remain poorly constrained. Here we present results of clay-size fraction radiogenic Sr, Nd, and Pb isotope compositions and clay mineral assemblages obtained from sediment core ODP Site 758 in the Bay of Bengal to understand the tectono-climatic impact on weathering and erosion of the Himalaya and Indian monsoon evolution over the past 30 million years. Over this time interval εNd values range from -10.7 to -8.3 (average -9.4) and 87Sr/86Sr ratio range from 0.709 to 716 (average 0.712). This indicates a relatively constant source of the clays from the Himalaya and further supported by Pb isotope records. However, in greater detail the results show a systematic change in the isotope compositions of the detrital clays deposited in the Bay of Bengal. Significant increases in εNd and 207Pb/206Pb, as well as a decrease in 87Sr/86Sr occurred between 25 and 20 Ma, 14 and 8 Ma and 4 Ma to present. These time periods most likely reflect increased sediment supply from the Tethyan Sedimentary Series (TSS) over the High Himalayan Crystalline (HHC) as a result of Himalayan uplift during late Oligocene/early Miocene, middle-Late Miocene and late Pliocene-Pleistocene. These events coincided with low smectite/(illite+chlorite) ratios suggesting increases in physical erosion and decreases in chemical weathering and hence a stronger Indian monsoon. These data clearly document a relationship between Himalayan uplift, climate change and the India monsoon.