Abstract. Accurately quantifying sediment fluxes in large rivers draining tectonically
active landscapes is complicated by the stochastic nature of sediment inputs.
Cosmogenic 10Be concentrations measured in modern river sands have
been used to estimate 102- to 104-year sediment fluxes in these
types of catchments, where upstream drainage areas are often in excess of
10 000 km2. It is commonly assumed that within large catchments, the
effects of stochastic sediment inputs are buffered such that 10Be
concentrations at the catchment outlet are relatively stable in time. We
present 18 new 10Be concentrations of modern river and dated
Holocene terrace and floodplain deposits from the Ganga River near to the
Himalayan mountain front (or outlet). We demonstrate that 10Be
concentrations measured in modern Ganga River sediments display a notable
degree of variability, with concentrations ranging between ∼9000 and
19 000 atoms g−1. We propose that this observed variability is driven
by two factors. Firstly, by the nature of stochastic inputs of sediment (e.g.
the dominant erosional process, surface production rates, depth of
landsliding, degree of mixing) and, secondly, by the evacuation timescale of
individual sediment deposits which buffer their impact on catchment-averaged
concentrations. Despite intensification of the Indian Summer Monsoon and
subsequent doubling of sediment delivery to the Bay of Bengal between ∼11 and 7 ka, we also find that Holocene sediment 10Be
concentrations documented at the Ganga outlet have remained within the
variability of modern river concentrations. We demonstrate that, in certain
systems, sediment flux cannot be simply approximated by converting detrital
concentration into mean erosion rates and multiplying by catchment area as it
is possible to generate larger volumetric sediment fluxes whilst maintaining
comparable average 10Be concentrations.
INFLUENCE OF LARAMIDE DEFORMATION ON THE PROTEROZOIC BASEMENT IN THE SOUTHERN SANGRE DE CRISTO MOUNTAINS, NEW MEXICO