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Can We Use Cosmogenic Isotopes to Date Stone Artifacts?Ivy-Ochs, Susan; Wüst, Raphael; Kubik, Peter W.; Müller-Beck, Hansjürgen; Schlüchter, Christian (Department of Geosciences, The University of Arizona, 2001-01-01)Two chert artifacts from the region near Luxor, Egypt have yielded concentrations of cosmogenic 10Be that allow calculation of nominal exposure ages of 326,000 and 304,000 years. Both artifacts are flakes that were collected atop limestone benches of the Eocene Thebes Formation which form cliffs along the west side of the Nile. The site is at elevation 240 m and is about 15 km from the Nile. Tools associated with these artifacts can be attributed to the Late Acheulean or early Middle Paleolithic (the transition has been suggested to have been on the order of 250,000-300,000 years ago). This area, where abundant chert nodules have weathered out, has been a collection, extraction, and fabrication site since the Early Paleolithic (since at least 400,000 years ago). Surface exposure dating records all periods of exposure. That means these ages represent composite ages, comprised of exposures both before and after working. But what fraction of the 10Be concentration we have measured was acquired before the flakes were produced? Here we propose several approaches to deconvolute the different exposure periods and better approximate the real age of the artifacts. As there is no a priori reason that the two ages should agree with the typological ages of the artifacts, nor for the two independent ages to agree, these first results are especially exciting and intriguing.
Combination of Numerical Dating Techniques Using 10Be in Rock Boulders and 14C of Resilient Soil Organic Matter for Reconstructing the Chronology of Glacial and Periglacial Processes in a High Alpine Catchment during the Late Pleistocene and Early HoloceneFavilli, Filippo; Egli, Markus; Brandova, Dagmar; Ivy-Ochs, Susan; Kubik, Peter W.; Maisch, Max; Cherubini, Paolo; Haeberli, Wilfried (Department of Geosciences, The University of Arizona, 2009-01-01)Glacier fluctuations and paleoclimatic oscillations during the Late Quaternary in Val di Rabbi (Trentino, northern Italy) were reconstructed using a combination of absolute dating techniques (14C and 10Be) and soil chemical characterization. Extraction and dating of the stable fraction of soil organic matter (SOM) gave valuable information about the minimum age of soil formation and contributed to the deciphering of geomorphic surface dynamics. The comparison of 10Be surface exposure dating (SED) of rock surfaces with the 14C ages of resilient (resistant to H2O2 oxidation) soil organic matter gave a fairly good agreement, but with some questionable aspects. It is concluded that, applied with adequate carefulness, dating of SOM with 14C might be a useful tool in reconstructing landscape history in high Alpine areas with siliceous parent material. The combination of 14C dating of SOM with SED with cosmogenic 10Be (on moraines and erratic boulders) indicated that deglaciation processes in Val di Rabbi were already ongoing by around 14,000 cal BP at an altitude of 2300 m asl and that glacier oscillations might have affected the higher part of the region until about 9000 cal BP. 10Be and 14C ages correlate well with the altitude of the sampling sites and with the established Lateglacial chronology.