Paleo-denudation rates at the Plio-pleistocene transition from in situ produced cosmogenic isotopes (10Be): method and new results from the Tianshan and the Himalayas
Abstract
At the geological and orbital time scales, long term evolutions of denudation rates remain poorly constrained, which inhibits a good understanding of the complex forcing and feedback between climate and tectonics For the past 20 years, the analyses of in situ cosmogenic isotopes have been widely developed and applied in various geological settings. This method is particularly powerful in present river sand because it enables reliable estimations of recent (100-100 000 yr) denudation rates from whole drainage basins (several m2 up to more than 200 000 km2). So far, however, very few studies have extended this approach to ancient sediments. Although technical limitations and geological uncertainties have yet to be overcome, this method enables the quantification of denudation rate from 0 up to ~10 Ma with a high temporal resolution. Importantly, the variation of world-wide denudation rates during this period is a matter of intense debate. Indeed, an apparent dramatic increase in sediment accumulation rates have been reported at the onset of Quaternary glaciations (~3.5 to 1 Ma), in numerous areas of the world with different tectonic settings. It had thus been proposed that this Plio-Pleistocene climatic transition was responsible for enhanced denudation rates and hence sediment fluxes. However, this increase is established from sediment budgeting from various basins, a method which can suffer from severe drawback and flaws. To better address this issue, a pioneer study was carried out on a continuous and independently dated continental sequence located along the Kuitun River in the Northern Tian Shan piedmont (Central Asia). Because of its intracontinental endorheic setting, the denudation in this region is insensitive to global sea-level variations and is a key area regarding the ongoing debate. The record displayed an apparent ~5 fold increase in denudation at ~2.5 Ma but then a decrease at ~1.6 Ma. Given the large uncertainties, this transient increase remained questionable and could be due to local tectonics. Therefore, to better constrain these preliminary results we present here new and complementary cosmogenic based paleo-denudation studies from different locations. In the Tian Shan range, we have enhanced the Kuitun River sampling, and completed three new paleo-denudation records located in both sides of the range. We also sampled a well documented and dated section of the Siwaliks Mounts (southern piedmont of the Himalayas) along the Surai Khola river. While all these records have displayed local and sometimes significant variations of denudation rates since ~10Ma, they do not show any synchronous increase in denudation at the Plio-Pleistocene transition. Our results thus question the paradigm of a worldwide increase in denudation rates linked to Quaternary glaciations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMEP53E1076P
- Keywords:
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- 1150 GEOCHRONOLOGY / Cosmogenic-nuclide exposure dating;
- 1815 HYDROLOGY / Erosion;
- 8177 TECTONOPHYSICS / Tectonics and climatic interactions;
- 9605 INFORMATION RELATED TO GEOLOGIC TIME / Neogene