Climate change and erosion: view from the Himalaya - Archive ouverte HAL Accéder directement au contenu
Communication Dans Un Congrès Année : 2018

Climate change and erosion: view from the Himalaya

Résumé

Late Cenozoic climate cooling and glaciations left evidence worldwide in mountains and may have inducedan increase of erosion rates (accelerated erosion). While this postulate may be supported for the high andmid-latitude regions by low-temperature thermochronometry, the links between climate and erosion remainhighly controversial for the sub-tropical regions, particularly for the Himalaya. On the one hand, bedrock low-temperature thermochronometry was interpreted as pointing to accelerated erosion in some parts of theHimalaya. On the other hand, detrital thermochronometry may point to relatively stable erosion rates sincethe middle Miocene, suggesting that climate change played a minor role in the control of erosion. Thesedifferences may originate from inherent methodological biases, but also from the lack of data in someregions. Therefore, it appears difficult to resolve the links between climate change and erosion in theHimalaya without a complementary approach.Here we discuss about new terrestrial 10Be paleo-concentrations obtained from the quartz fractions of bothsediments cored within the Bengal fan, and sediments sampled along a new Siwalik (frontal Himalaya)section. 10Be is produced within rocks at the earth's surface by exposure to cosmic rays. 10Be extracted fromsediments integrates erosion from the contributing watershed over millennial timescales (for the Himalaya).Commonly applied to modern sediments, 10Be also allows to measure past erosion when applied to detritalseries and complements detrital thermochronometry, which integrates erosion over longer timescales.The Bengal fan consists of sandy-rich turbidites integrating sediments from the Brahmaputra and Gangawatersheds, i.e. a region covering ~2/3 of the Himalaya. IODP Expeditions 353 and 354 recently drilled onesite at 14°N and a transect of sites at 8°N in the fan. The cores were dated by magnetostratigraphy andbiostratigraphy. Additionally, a new continental section was investigated in the central Himalaya. The Siwalikmolasses consist of erosion products accumulated in the Ganga plain during the late Cenozoic, and presentlyexposed at the front of the range by thin skin tectonics. Located in front of the Narayani-Gandak fan apex,South of the Chiwan Dun (Bihar, northern India), the new section presents almost continuous sandy to finefractions of sedimentary rocks. This section was chosen since the Narayani watershed is one of the majorwatersheds in Central Himalaya, and is extensively documented in terms of structural geology,geomorphology, geochemistry or erosion rates. The new section was dated by magnetostratigraphy.Viewed from the Bengal fan, the 10Be-derived erosion rates, inversely correlated to 10Be concentrations, showa relatively constant average value since 6 Ma onwards, and roughly similar to modern erosion rates. Inparticular, there is no dramatic increase of erosion rates at the Quaternary transition. The 10Be concentrationsfrom the new Siwalik section similarly show a relatively stable average since 5 Ma onwards. However, bothdatasets present short-term variations of high amplitude since the late Miocene. The interpretation of thesevariations can be discussed in view of independent data on tectonic or climatic changes in the Himalaya.
Fichier non déposé

Dates et versions

hal-02930758 , version 1 (04-09-2020)

Identifiants

  • HAL Id : hal-02930758 , version 1

Citer

Sébastien Lenard, Jerome Lave, Christian France-Lanord, Julien Charreau, Raphaël Pik. Climate change and erosion: view from the Himalaya. Thermo, International Conference on Thermochronology, Sep 2018, Quedlinburg, Germany. ⟨hal-02930758⟩
36 Consultations
2 Téléchargements

Partager

Gmail Facebook X LinkedIn More