Woods Hole Oceanographic Institution

Valier Galy

»Complete publication list
»C residence time in the Ganges-Brahmaputra system - Nature Geoscience 2011
»Chemical composition of Ganges-Brahmaputra River sediments - JGR 2011
»Plant biomarkers in Ganges-Brahmaputra sediments - EPSL 2011
»Petrogenic carbon in the Amazon basin - Geology 2010
»Stable erosion regime in Himalaya - EPSL 2010
»Geological stabilization of C in the crust - Science 2008
»Paleovegetation LGM to present - QSR 2008
»Loading and fate of particulate organic carbon - GCA 2008
»Efficient organic carbon burial in the Bengal fan - Nature 2007
»Determination of TOC and 13C/12C - GGR 2007
»PhD Thesis

Valier Galy, Christian France-Lanord, Bernhard Peucker-Ehrenbrink & Pascale Huyghe, Sr–Nd–Os evidence for a stable erosion regime in the Himalaya during the past 12 Myr, Earth and Planetary Science Letters, 2010

Modern erosion of the Himalaya, the world's largest mountain range, transfers huge dissolved and particulate loads to the ocean. It plays an important role in the long-term global carbon cycle, mostly through enhanced organic carbon burial in the Bengal Fan. To understand the role of past Himalayan erosion, the influence of changing climate and tectonic on erosion must be determined. Here we use a 12 Myr sedimentary record from the distal Bengal Fan (Deep Sea Drilling Project Site 218) to reconstruct the Mio-Pliocene history of Himalayan erosion. We use carbon stable isotopes (δ13C) of bulk organic matter as paleoenvironmental proxy and stratigraphic tool. Multi-isotopic — Sr, Nd and Os — data are used as proxies for the source of the sediments deposited in the Bengal Fan over time. δ13C values of bulk organic matter shift dramatically towards less depleted values, revealing the widespread Late Miocene (ca. 7.4 Ma) expansion of C4 plants in the basin. Sr, Nd and Os isotopic compositions indicate a rather stable erosion pattern in the Himalaya range during the past 12 Myr. This supports the existence of a strong connection between the southern Tibetan plateau and the Bengal Fan. The tectonic evolution of the Himalaya range and Southern Tibet seems to have been unable to produce large re-organisation of the drainage system. Moreover, our data do not suggest a rapid change of the altitude of the southern Tibetan plateau during the past 12 Myr. Variations in Sr and Nd isotopic compositions around the late Miocene expansion of C4 plants are suggestive of a relative increase in the erosion of High Himalaya Crystalline rock (i.e. a simultaneous reduction of both Transhimalayan batholiths and Lesser Himalaya relative contributions). This could be related to an increase in aridity as suggested by the ecological and sedimentological changes at that time. A reversed trend in Sr and Nd isotopic compositions is observed at the Plio-Pleistocene transition that is likely related to higher precipitation and the development of glaciers in the Himalaya. These almost synchronous moderate changes in erosion pattern and climate changes during the late Miocene and at the Plio-Pleistocene transition support the notion of a dominant control of climate on Himalayan erosion during this time period. However, stable erosion regime during the Pleistocene is suggestive of a limited influence of the glacier development on Himalayan erosion.

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