Goodbred, Steven L.1
(1) Stony Brook University, Stony Brook, NY
ABSTRACT: A Source-to-Sink View of the Ganges Dispersal System Since the Last Interstade
This paper presents a comprehensive overview of Ganges dispersal-system behavior since the last interstade, which, in addition to expected responses to sea level, reveals major, coeval responses to changes in the South Asian monsoon climate. At > 3000 km from its Himalayan source to Bengal fan sink, the Ganges dispersal system is immense and yet shows tight coupling of sedimentary responses among source area, catchment basin, and coastal and marine depocenters. Furthermore, the downstream transfer of sedimentary signals appears to occur at least as fast as our current temporal resolution of 1-2 kyr. This tight linkage of source-to-sink components is considered a function of the southwest (summer) monsoon's overwhelming control on regional hydrology. About 80% of the Ganges discharge and 95% of its sediment load are delivered to the margin during only four months, making the system extremely sensitive to this seasonal forcing. Also, the regional scale and distribution of the monsoon weather system means that changes in atmospheric circulation affect the entire drainage basin rather than local subcomponents. Finally, despite its present intensity, strength of the summer monsoon has varied significantly over the past 150 kyr under orbitally driven changes in insolation and global (glacial) boundary conditions. The resulting changes in precipitation, both well above and below modern values, have forced system-wide responses ranging from glacier advance/retreat to sediment fluxes to the margin and deep-sea fan. The overall conclusions are (1) that this immense dispersal system responds to multimillennial-scale (<104 yr) climate change in a system-wide and largely contemporaneous manner and (2) that major sedimentary signals can be transferred rapidly from source to sink with little apparent attenuation. Furthermore, these acute responses to climate change have produced sedimentary/stratigraphic features that diverge from traditional sequence models in their nature and timing.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.