『Abstract
The Himalayas represent the archetype of mountain building due
to active continental collision and are considered in many studies
as the locus of intense interactions between climate, denudation
and tectonics. Estimates of modern denudation rates across the
entire range remain, however, relatively sparse.In this study,
in situ-produced cosmogenic 10Be concentrations were
measured in detritic quartz in order to determine basin-scale
denudation rates for the central part of the Himalayan range.
River sand was sampled over several yeas in the main trans-Himalayan
rivers, from the Himalayan front to the Ganga outlet in Bangladesh.
The calculated 10Be denudation rates of the trans-Himalayan
river basins range from 0.5 to 2.4 mm yr-1 (average
1.3 mm yr-1) and vary by up to a factor of 3 between
sampling years. These denudation rates strongly contrast with
the 0.007 mm yr-1 denudation rate of southern tributary
basins draining the Indian craton. This work also shows that in
the Ganga basin, no systematic evolution of average 10Be
concentrations is observed during floodplain transfer, implying
that distal samples can be used to estimate the integrated denudation
rate of the whole central Himalayan range. Samples from the Ganga
in Bangladesh display remarkably low variability in 10Be
concentration, implying an average suggest a recent perturbation
of sediment transport dynamics with a recent increase in the relative
sediment contribution from southern tributaries. The Himalayan
sediment flux, deduced from the 10Be denudation rate
of the range, is 610±230 Mt yr-1. This flux is consistent,
within uncertainty, with sediment fluxes derived from sediment
gauging. The similarity of the two flux estimates suggests that
Himalayan erosion fluxes have remained stable over the last centuries,
even if the large uncertainties associated with each method hamper
more precise assessments.
Keywords: Ganga basin; Himalaya; 10Be; cosmogenic;
denudation rates; sediment flux』
1. Introduction
2. Setting
3. Methods
3.1. Sampling
3.2. AMS measurement
3.3. Denudation rate and sediment flux calculations
4. Results
5. Discussion
5.1. Variability of denudation rates
5.2. Floodplain signal transfer
5.3. Comparison with gauged sediment fluxes
6. Conclusion
Acknowledgments
Appendix A. Supporting information
References