BE-10 AND AL-26 PRODUCTION-RATES DEDUCED FROM AN INSTANTANEOUS EVENT WITHIN THE DENDRO-CALIBRATION CURVE, THE LANDSLIDE OF KOFELS, OTZ VALLEY, AUSTRIA

Surface exposure dating requires the knowledge of cosmogenic nuclide p roduction rates. When determining time-integrated production rates the exposure ages of the calibration samples need to be accurately known. The landslide of Kofels (Austria) is very well suited for this purpos e. It is the largest landslide in the crystalline Alps of Austria dati ng back to 7800 +/- 100 years BC (AMS C-14 dating of buried wood), whi ch is well within the C-14 dendro calibration curve. Exposed quartz ve ins were sampled from the tops of large boulders from the toe of the l andslide for analysis of Be-10 and Al-26. TO calculate sea level, high geomagnetic latitude (greater than or equal to 60 degrees), open sky radionuclide production rates, corrections were applied for altitude a nd latitude, for shielding by surrounding mountains, for sample geomet ry, vegetation and snow cover, and for sample thickness. The productio n rates for an exposure age of 10,000 years are 5.75 +/- 0.24 Be-10 at oms/yr g SiO2 and 37.4 +/- 1.9 Al-26 atoms/yr g SiO2. A Al-26/Be-10 ra tio of 6.52 +/- 0.43 can be calculated. The influence of the geomagnet ic held on these production rates has been estimated using two differe nt geomagnetic field records. Our production rates should be a good ap proximation for the use of surface exposure dating between about 5000 and 13,000 years BP. (C) 1998 Elsevier Science B.V. All rights reserve d.