Plio-Pleistocene cosmogenic erosion rates of the Northwestern Argentine Andes
Abstract
The relationship between climate, tectonics, and erosion rates in mountainous terrain remains poorly understood over long timescales. Whereas studies of modern systems allow spatial erosion rate comparison across modern climatic and tectonic gradients, long-term records are required to test erosion rate response to global climate cycles and long-term climatic and tectonic trends. The Central Andean foreland basin deposits exposed in the Río Iruya canyon present an exceptional opportunity to develop such a long-term record of erosion rates using cosmogenic 10Be. The 100-m deep canyon in northwestern Argentina exposes an extraordinary section of ~7500 m of sedimentary rock deposited in the Andean foreland basin during growth of the sub-Andean fold and thrust belt. The nearly 10-Myr-old section was only recently re-exposed when the Río Iruya river overwhelmed a flood control canal in 1898. Minimal post-burial cosmogenic production, along with reliable age control through paleomagnetic stratigraphy and dates on volcanic ashes, makes the canyon an unusually favorable location to study erosion rate responses to changes in tectonic activity and climate cycling. Thus far, 16 (out of 50) samples have been analyzed for cosmogenic 10Be erosion rate estimations. These samples span 1-3.5 Ma and bracket the Plio-Pleistocene climate transition at ~100,000 year resolution. Detailed detrital zircon signatures from the section constrain sedimentary provenance over this same time period, allowing comparison of paleo-erosion rates with climate proxies and models of Andean and sub-Andean tectonic growth. Preliminary rates between 3.5 and 1 Ma show 400,000 year cyclicity before 2.5 Ma, followed by a tripling in erosion rates since then. The 400,000 year cyclicity suggests an orbitally controlled forcing mechanism, whereas the subsequent erosion rate increase was likely the result of tectonically forced watershed reorganization in the Eastern Cordillera. Although results are still preliminary, the observed cyclicity and variability in erosion rates is striking and should improve current understandings of erosion rate responses to long-term climatic and tectonic trends in the Central Andes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMEP23B..06L
- Keywords:
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- 1625 GLOBAL CHANGE Geomorphology and weathering;
- 1150 GEOCHRONOLOGY Cosmogenic-nuclide exposure dating;
- 1520 GEOMAGNETISM AND PALEOMAGNETISM Magnetostratigraphy;
- 1115 GEOCHRONOLOGY Radioisotope geochronology