T307 Quantifying Mountain Evolution from the Lithosphere to the Landscape I

Wednesday, 30 October 2013
8:00 AM - 12:00 PM
Mile High Ballroom 3C

DATING MIOCENE-PLIOCENE DEAD SEA RIFT SEDIMENTS - AT THE LIMIT OF COSMOGENIC TWO ISOTOPE BURIAL DATING

Paper number: T307-7
Program: Technical Sessions
Time: 9:30 AM – 9:45 AM

Authors

Abstract

The Dead Sea rift (DSR) is a young and active continental rift. It provides an unparalleled opportunity to investigate the relation between the tectonic evolution of a rift and its morphological development. Ages of Neogene sediments (Sedom and Amora Formations) of the Dead Sea basin are determined using in-situ cosmogenic nuclide burial dating. Sediments of the Sedom Fm. were deposited during the final stages of the Sedom Lagoon, which was connected to the Mediterranean Sea. Sediments of the overlying Amora Fm. were deposited during the establishment of terminal lakes which have occupied the Dead Sea basin since the Pliocene. The sediments of the Sedom Fm. yielded very low 10Be concentrations and 26Al is absent. These low concentrations reflect the antiquity of the sediments and their recent exhumation following their extremely rapid rise to the surface. Using different assumptions to constrain age limits, we suggest that the top of the Sedom Fm. dates between 5.0±0.5 Ma and 6.2+inf/-2.1 Ma. These ages are at the very limit of the cosmogenic isotope burial dating range. Considering the extremely rapid exhumation rate of these sediments, post burial production of cosmogenic isotopes may cause the TCN ages presented above to be underestimated by 0.5-1 Myr. The base of the overlying Amora Fm., 3.3+0.9/-0.8 Ma, indicates the minimum age for initial deposition in a terminal lake disconnected from the Mediterranean Sea.

The transition from a marine lagoon to a terminal lake resulted from major subsidence of the Dead Sea basin, and subsequent uplift of its margins that also initiated the escarpments of the Dead Sea. These processes may express a significant change in the behavior of the Arabia-African plate boundary along the DSR, a change that enabled a complete reorganization of relief in the region. The earlier water bodies such as the Sedom Lagoon evolved in a subdued landscape without pronounced topographic relief. The younger terminal lakes evolved under increasingly larger relief that promoted major escarpment incision and formation of deep canyons. Burial ages of sediments within caves close to the top of the Dead Sea escarpment, 3.4±0.2 Ma and 3.6±0.4 Ma, are consistent with the above description and indicate the timing of initial bedrock canyon incision that directed waters toward the newly established SDR.