Denudation of the Golan Heights basaltic terrain using in-situ 36Cl and OSL dating

Abstract

While erosion rates of carbonates along the Dead Sea fault (DSF) and its margins have been determined in several studies, information about denudation of basalts along the DSF are absent. Here we report concentrations of in situ cosmogenic 36Cl in bedrock and sediment samples combined with OSL ages of terraces from the Meshushim basin, a typical basaltic basin in the Golan Heights, northern Dead Sea Rift (DSR).Denudation rates of exposed and soil-covered bedrock basalts, range from 12.3 ± 1.4 mm/ka to 176.1 ± 47.4 mm/ka, well within the range of DSR values, regardless of lithology and climate. In all locations where exposed and soil-covered bedrock were samples next to each other, the soil-covered basalt erodes faster. This is regardless of notable variations in average annual temperature and precipitation. This means that bedrock outcrops were not covered and exposed very frequently, and that chemical weathering at the bedrock-soil interface is a significant erosional factor.Sediments in the Meshushim basin are stored in soil pockets and blankets on the upper plateau, colluvial material on slopes, and alluvial terraces. The difference in 36Cl concentrations between soil-covered and exposed bedrock indicates coverage duration of ca. 3–6 ka. The residence time estimate of only several thousands of years for sediments stored in alluvial terraces is 170 ± 20 y to 4000 ± 290 y. Nowhere in the Meshushim drainage system did we find evidence for storage of sediment longer than a few thousands of years.36Cl concentrations in colluvial and alluvial sediments are similar to those measured in soil-covered basalts. This similarity suggests that sub-surface weathering of basalts is the major source for sediments in upper and central segments of the basin, concurrent with the higher denudation rates of buried bedrock. However, very low 36Cl concentrations measured in samples collected in the lower parts of the basin indicate involvement of landslides which instantaneously expose previously shielded sediments that were incorporated into the drainage system. The effect of landslides is also manifested by the high basin scale denudation rates calculated from alluvial samples in various locations, as well as the geomorphological profile of the Meshushim basin. Sediment yield calculated from 36Cl concentrations measured in this study suggest temporal changes in denudation rates over the Holocene and up to the last ∼60 ka, with higher past denudation rates and sediment yield even in most of the Holocene related to present rates and yields.Overall, the results of this study show that the fact that the Golan lithology is basaltic does not result in different denudation process and rate from other locations investigated along the Dead Sea Rift, which are mostly of carbonate lithology and that relief and climate are stronger parameters than lithology in controlling denudation.