Complex exposure histories of chert clasts in the late Pleistocene shorelines of Lake Lisan, southern Israel

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.

Geomorphology of Lake Lisan terraces along the eastern coast of the Dead Sea, Jordan

“…Our dates correlate with the relative age of the terraces. Moreover, they correlate well with ages of the highest beach ridges (up to −150 m) found by Bowman and Gross (1992) in the south-west of the Dead Sea and dated by Matmon et al (2003) to 20-36 ka BP. Also our dates are consistent with the age estimates of the Lake Lisan high stand derived from dating of the Lisan Formation to 27-23 cal.…”

The geological significance of cosmogenic nuclides in large lowland river basins

“…Pairing cosmogenic 10 Be 181 with stable noble gases such as 21 Ne measured in quartz (Niedermann, 2000;182 Niedermann, 2002), or the longer-lived 26 Al (half-life of 0.72 Myr; Samworth et al 183 (1972) Be ratios (Granger and Muzikar, 2001; 184 Granger, 2006;Balco and Shuster, 2009), is common to e.g. extend the time frame of 185 investigation required for these applications (Granger and Muzikar, 2001;Schaller et 186 al., 2002;Matmon et al, 2003;Partridge et al, 2003;Schaller et al, 2004;Balco and 187 Stone, 2005;Stock et al, 2005;Haeuselmann et al, 2007;Kong et al, 2009;Hu et al, 188 2011;Matmon et al, 2011;Wittmann et al, 2011b;Charreau et al, 2012;Bekaddour 189 et al, 2014;McPhillips et al, 2016). Recently, the in situ-cosmogenic nuclide 14 C 190 which has a much shorter half-life of 5730 yrs (Libby, 1955) was added to the family 191 of cosmogenic isotopes measured in quartz (Lifton et al, 2001).…”

Diffusion of helium in carbonates: Effects of mineral structure and composition

“…Typical radiocarbon dating of shell material can suffer from potentially large reservoir corrections in alkaline lakes (Broecker and Kaufman, 1965). Conventional cosmogenic dating of shoreline berms has also proven difficult because clastic material tends to be reworked from longer-lived alluvial features, and thus suffers from inheritance of cosmogenic isotopes produced during earlier periods of exposure (Matmon et al, 2003). In contrast, shell material Wolf et al, 1998, assuming isotropic diffusion in a spherical domain driven by diffusion kinetics reported for the c-parallel direction in this paper.…”