HR: 17:45h
AN: H52E-08    [PDF]
TI: Quantifying Sediment Storage Rates and History in the NW Argentinian Cordillera Using Luminescence Dating Techniques
AU: * Spencer, J Q
EM: jqgs@st-andrews.ac.uk
AF: School of Geography and Geosciences, University of St Andrews, St Andrews, Fife, KY16 9AL United Kingdom
AU: Robinson, R A
AF: School of Geography and Geosciences, University of St Andrews, St Andrews, Fife, KY16 9AL United Kingdom
AU: Strecker, M R
AF: Institut f\"{u}r Geowissenschaften, Universit\"{a}t Potsdam, Postfach 60 15 53, 14415, Potsdam Germany
AU: Richter, A
AF: Institut f\"{u}r Geowissenschaften, Universit\"{a}t Potsdam, Postfach 60 15 53, 14415, Potsdam Germany
AB: The quebradas of the Eastern Cordillera of NW Argentina contain Late Quaternary sedimentary sequences that reflect repeated alluvial fill and incision events that have created a series of inset terrace surfaces. Variation in climate is considered to be the principle trigger driving episodes of erosion and sediment deposition, even though ongoing tectonic uplift and deformation provides oversteepened slopes and can interrupt drainage patterns. The current chronological framework is based on tephrochronology and $^{14}$C, but there are insufficient ash beds or organic remnants to produce a high resolution chronology of erosion and sediment storage. We are therefore producing a detailed chronological record of alluviation using optically stimulated luminescence (OSL) dating, combined with cosmogenic radionuclide dating to quantify erosion rates. Recent advances in single aliquot measurements of quartz have improved both precision and accuracy of the OSL dating method for sediments, where an age assessment is possible for each aliquot measured. Although initial OSL results are consistent with $^{14}$C of shells and wood samples, the majority of alluvial samples studied have wide, multimodal age distributions. There are various possible explanations for these distributions, including inadequate bleaching of some quartz grains. However, we believe the age distributions are a result of variations in the interplay of sediment source and transport mechanisms, in concert with variability in grain-to-grain bleaching, and therefore contain an archive of the inherited grains from past sedimentation events. To improve our understanding of the age distributions we are investigating small aliquot (about 50-100 quartz grains) approaches in combination with a variety of distribution analysis techniques that identify not only the age since the last solar exposure, but also the age of inherited grains. In addition to providing rates of sediment accumulation and storage, such archives of basin sedimentation (and erosion) improve our understanding of the cycling of sediments within a basin through time and identify periods of alluvial storage and erosion.
DE: 1035 Geochronology
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 9360 South America
SC: Hydrology [H]
MN: 2003 Fall Meeting