DOWN AND OUT IN ZANSKAR: CONTROLS ON SEDIMENT BUFFERING AND PROVENANCE IN THE HIMALAYAN RAIN SHADOW, NORTHWEST INDIA

Marine sediment records in deltas and fans are often used to reconstruct continental paleoenvironmental records yet the extent to which buffering and recycling of sediment occur during source-to-sink routing is controversial. Shredding of sediment signals suggests that marine records may not necessarily record climatic conditions of the mountain sources at the time of sedimentation, and instead preserve smeared accounts of continental erosion. If robust records are to be made, resolving influences on sediment pathways during transport is vital.

The Zanskar River is part of the final unstudied segment in a concentrated effort to characterize the Indus River from source to sink. Here we use complementary mineral provenance techniques in this basin to quantify sediment buffering and identify the dominant control(s) on Quaternary erosion in the northwest Himalayan rain shadow.

Detrital U-Pb zircon ages and bulk petrography indicate modern sands are dominated by 600–850 Ma zircon grains likely sourced from Greater Himalayan lithologies located adjacent to the modern rainfall maximum. River terrace sands suggest no significant shift in regional erosion and provenance has occurred since ~11.5 ka regardless of changes in Asian Summer Monsoon strength. Detrital apatite fission track ages argue that erosion rates have been stable for at least the last 6.4 Myr in Zanskar, in spite of the changing monsoonal climate. Together these data indicate most sediment in the Zanskar River is freshly-eroded and transmitted immediately downstream into the Indus River with only modest buffering in terraces.