Abstract Details

ID: 360
Title: Dating lacustrine sediments in the central Jordan Valley, Israel: Implications for cosmogenic burial dating

We apply the cosmogenic two isotope burial method to Pliocene to Pleistocene lacustrine sediments (Erk-El-Ahmar (EEA) formation) in the central Jordan Valley, Israel, in the attempt to extend the applicability of the method to common geological settings in which exposure-burial histories are not well constrained. Previous estimates attributed an age of ~1.8 Ma to the bottom of the EEA formation. 26Al and 10Be concentrations were measured in 11 samples collected from the 170 m tectonically-tilted section. 21Ne concentrations were measured in two of these samples. All samples yielded burial ages that range between 3.5 and 5.3 Ma, much older than the previously estimated age of the EEA formation. All three isotopic pairs (26Al/10Be, 26Al/21Ne, and 10Be/21Ne) yielded similar burial ages within 1?. Samples of identical age that were collected from a specific horizon are presently located at decreasing depths below the surface due to the tectonic tilting. Nevertheless, they yielded identical burial ages suggesting rapid recent erosion in this tectonically active region and insignificant production of cosmogenic isotopes at depth by muons.
All samples were found to contain two distinct populations of grains (chert and quartz) mixed at various ratios. These two grain-types were eroded from different sources with significantly different pre-burial exposure histories. The cosmogenic nuclide concentrations in the samples are in accordance with those expected for the mixing of two such sources. Calculations of two-source mixing show that initial 26Al/10Be ratios may be lower relative to the expected surface ratios and result in burial ages overestimated by as much as 500 ka.
Our burial ages suggest that the water body that deposited the EEA sediments was contained within the initial topographic depression that formed along the central Jordan Valley segment of the Dead Sea rift.

Session: 84 Cosmogenic nuclides and the dating of Quaternary landforms
Authors: Michael Davis
Ari Matmon
Hagai Ron
David Fink
Samuel Niedermann
Dylan Rood
Presenter:Ari Matmon
Type: oral