COSMOGENIC 10BE EROSION RATE ESTIMATES BETWEEN 3.2 AND 1 MA IN THE RIO IRUYA WATERSHED, NORTHWESTERN ARGENTINA

The relationship between climate, tectonics, and erosion rates in mountainous terrain remains poorly understood over long timescales. Although studies of modern systems allow comparison across modern climatic and tectonic gradients, long-term records are required to test the importance of disequilibrium landscape conditions created by global climate cycles and long-term climate trends. Erosion rates across the onset of Northern Hemisphere glaciation are of particular interest in light of an observed increase in global sedimentation rates over the last 5 Myr (Zhang et al., 2001). To address the question of erosion rate response to changes in tectonic setting and climate cycling, we present a record of temporal variations in paleo-erosion rates as determined from cosmogenic ¹⁰Be from the Río Iruya watershed in the northwestern Argentine Andes. The 100 m deep Río Iruya canyon is an extraordinary section of ~7500 m of sedimentary rock deposited in alluvial and fluvial environments during growth of the sub-Andean fold and thrust belt and only recently re-exposed when the river overwhelmed a flood control canal in 1898. Minimal post-burial cosmogenic production, along with published paleomagnetic stratigraphy data, makes the Río Iruya canyon an exceptional location to develop a long-term record of erosion rates. This study presents U-Pb zircon dates from 5 new interbedded ashes and higher resolution paleomagnetic measurements to further refine the stratigraphic framework, as well as 16 new basin-scale erosion rates estimated from 10Be in quartz separated from foreland basin sandstone strata deposited between 3.2 and 1 Ma. Thrust related uplift in the Subandean belt has contributed to increased sedimentation rates and changes in provenance in the Río Iruya section, which we plan to track using detrital zircons. We will also test for possible sediment recycling by comparing ¹⁰Be, ²⁶Al, and ²¹Ne ratios in each of the samples. Comparisons of erosion rate data with climate proxies (amplitude and frequency of δ¹⁸O from marine records) and tectonic models of sub-Andean and Andean growth over the same time period should newly inform our understanding of the relative contribution of each forcing in the erosional history of the northwest Argentine Andes and provide key methodological insights for future studies.