Earth Surface Processes and Landforms Earth Surf. Process. Landforms 28, 493–506 (2003) Published online 24 April 2003 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/esp.454 COMPLEX EXPOSURE HISTORIES OF CHERT CLASTS IN THE LATE PLEISTOCENE SHORELINES OF LAKE LISAN, SOUTHERN ISRAEL ARI MATMON, 1 * ONN CROUVI, 2 YEHOUDA ENZEL, 2 PAUL BIERMAN, 3 JENNIFER LARSEN, 3 NAOMI PORAT, 4 RIVKA AMIT 4 AND MARC CAFFEE 5 † 1 Geology Department, University of Vermont, Burlington, VT 05405, USA 2 Institute of Earth Sciences, Hebrew University, Jerusalem 91904, Israel 3 Geology Department and School of Natural Resources, University of Vermont, Burlington, VT 05405, USA 4 Geological Survey of Israel, 30 Malkhe Yisrael St., Jerusalem 95501, Israel 5 Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA Received 24 August 2001; Revised 30 May 2002; Accepted 28 July 2002 ABSTRACT Activities of 26 Al and 10 Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert-bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio 26 Al/ 10 Be, total clast histories range from 0Ð46 to 4Ð3 My, unrelated to the clasts’ current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20Ð0 š 1Ð4 ka and 36Ð1 š 3Ð3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP. If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0Ð4 and 12 m My 1 . The relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright  2003 John Wiley & Sons, Ltd. KEY WORDS: cosmogenic nuclides; shorelines; Lake Lisan; alluvial storage INTRODUCTION Estimating rates of sediment production, transportation, and deposition is important for understanding the interplay between climate, tectonics, and lithology over a variety of temporal scales. Basin-scale studies reveal the variation in sediment production and transportation rates along different parts of fluvial systems and suggest the importance of sediment storage (e.g. Trimble, 1977, 1999; Meade, 1982; Stallard, 1987; Granger et al., 1997; Clapp et al., 2000). Rivers carry debris fed into them by tributaries, mass wasting, and overland flow. They respond to changes in base level, climate, and tectonic activity by aggrading and degrading their channel, forming alluvial terraces (Summerfield, 1991). Therefore, alluvium in transit may be stored for varying lengths of time before reentering the active channel. Low rates of rock weathering, especially in arid climates, enable significant periods of * Correspondence to: A. Matmon, U.S. Geological Survey, 345 Middlefield Road, MS 977 Menlo Park, CA 94025, USA. E-mail: amatmon@usgs.gov † Current address: Prime Laboratory, Physics Department, Purdue University, West Lafeyette, IN 47907, USA. Copyright  2003 John Wiley & Sons, Ltd.