『Abstract
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 paleo-environmental 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.
Keywords: Himalaya; erosion; Miocene; climate; radiogenic isotopes;
Bengal Fan』
1. Introduction
2. Material and methods
2.1. Sampling
2.2. Organic carbon analysis
2.3. Analyses of Sr and Nd isotopic composition
2.4. Analysis of Os concentration and isotopic composition
3. Results
3.1. Organic carbon
3.2. Radiogenic isotopes
4. Discussion
4.1. Age model
4.2. Sediment provenance
4.3. Implications for the history of the Himalaya links between
erosion, tectonics and climate
5. Conclusion
Acknowledgments
References