Evidence of Himalayan erosional event at 0.5Ma from a sediment core from the equatorial Indian Ocean in the vicinityof ODP Leg 116 sites

Abstract

Asediment core collected from an area 100 miles south of the ODP Leg 116 (distal Bengal Fan) in the equatorial Indian Ocean was investigated for microfossils, mineralogy, mineral chemistry, magnetic susceptibility, grain size, major, minor and rare-earth element geochemistry, organic carbon and total nitrogen contents in the bulk sediments. Distinct changes in depositional characteristics (including presence of abundant sand-sized micas and other detrital minerals) occur at two sub-surface depths corresponding to 0.5 and probably0.8Ma time periods. The detrital mineral suite of this core resembles that of turbidite unit I sediments of ODP cores in the distal Bengal Fan. The core site has received an increased supplyof terrigenous sediments at these two time periods, the older pulse (0.8Ma) stronger than the younger pulse. Several lines of evidence such as the nature of the mineral suite, lower magnetic susceptibilityvalues, Si/Al in mica mineral separates; major element composition; discrimination plots of Ca/Ti versus K/Ti and K2O/Al2O3 and La/Yb ratios suggest a highly metamorphosed source such as higher Himalayan crystalline (HHC) series indicating two events of increased physical weathering and erosion in the Himalayan region. While the erosional event of 0.8Ma is well known, the episode of 0.5Ma was not reported earlier.