Weathering in the Himalayan Foreland

Large volumes of sediment have been shed from the Himalaya over the last 50-60 Myr. Weathering of the silicate mineral fraction of these sediments consumes atmospheric CO2, whereas weathering of the carbonate mineral fraction does not. Quantifying alkalinity fluxes from silicate versus carbonate weathering is therefore essential for evaluating the role of Himalayan weathering in cooling Neogene climate. Many studies have linked the uplift and subsequent weathering of the Himalaya to changes in the chemical budget of the oceans and in the global CO2 cycle. Weathering in the Himalayan uplands has been thoroughly studied, whereas the potentially large weathering contribution of weathering on the Indo-Gangetic Plain—past and present—remains virtually unstudied.

Our purpose is to examine weathering processes and alkalinity losses from Indo-Gangetic soil/paleosol profiles on the floodplain over the Neogene. The Himalayan foreland is the wettest and warmest part of the Himalayan system, and as such probably contributes significantly (or, perhaps, dominates) alkalinity of the Ganges and Brahmaputra Rivers. Using quantitative mass balance, this study quantifies present-day losses from both carbonate and silicate weathering along a transverse extending from western (dry) to eastern (wet) India and compares present-day weathering fluxes in the Gangetic lowlands to the mass losses over time using buried paleosols in the Siwalik sequence. We also examine weathering losses of Sr in floodplain soils and the implications for the impact of Himalayan weathering on marine 87Sr/86Sr ratios.