Quaternary morphotectonic mapping of the Wadi Araba and implications for the tectonic activity of the southern Dead Sea fault

摘要

The Dead Sea strike-slip fault accommodates the northward motion of Arabia relative to Sinai at a rate of ～5 mm/yr. The southern segment of the fault, the Wadi Araba fault, runs along a valley blanketed in Quaternary sediments. We first focused on understanding the relative and absolute timing of emplacement of the alluvial surfaces. We then determined the probable source of the sediments before assessing their lateral offset to constrain the late Pleistocene fault slip rate. Seven successive morphostratigraphic levels were identified. At two sites, we recognized an alluvial sequence of five to seven successive levels with ages getting younger northward, a pattern consistent with the western block moving southward relative to two fixed feeding channels located to the east. Surface samples were collected for ~(10)Be cosmogenic radionuclide dating. Fans F3 and F5 were found to be synchronous from site to site, at 102 ± 26 ka and 324 ± 22 ka, respectively, while F4 could be dated at 163 ± 19 ka at one site only. These are minimum ages, assuming no erosion of the alluvial surfaces. At least two of these periods are correlated with wet periods that are regionally well documented. Further analyses of tectonic offsets are affected in most cases by large uncertainties due to the configuration of the sites. They indicate maximum offsets of ～5.5 km for the oldest, possibly ～1 Ma old, surfaces. They lead to bracketing of the fault slip rate between 5 and 12 mm/yr, with preferred values of 5-7 mm/yr, for the last 300 ka.