Browsing by Author "Ron, H"

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    Dating lacustrine sediments in the central Jordan Valley, Israel: Implications for cosmogenic burial dating
    (18th INQUA Congress, 2011-07-21) Davis, M; Matmon, A; Ron, H; Fink, D; Niedermann, S; Rood, DH
    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. Copyright (c) 2011 INQUA 18
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    Dating Pliocene lacustrine sediments in the central Jordan Valley, Israel - Implications for cosmogenic burial dating
    (Elsevier, 2011-05-15) Davis, M; Matmon, A; Fink, D; Ron, H; Niedermann, S
    Cosmogenic burial dating of sediments is usually used at sites with relatively simple or known exposure-burial histories, such as in caves. In an attempt to extend the applicability of the method to other common geological settings (i.e. the dating of late Neogene sedimentary formations), where much less is known about the exposure-burial history, we apply the cosmogenic burial method on Pliocene-early Pleistocene (1.5-4.5 Ma) lacustrine sediments in the central Jordan Valley, Israel. (26)Al, (10)Be, and (21)Ne concentrations in quartz were obtained from a 170 m tectonically-tilted section. Assuming fast burial and no post-burial production we obtained burial ages which range between 3.5 and 5.3 Ma. Integrating simple geological reasoning and the cosmogenic nuclide data, post burial production is found to be insignificant. We also found that the samples contain two distinct populations of grains (chert and quartz) from two different sources which experienced different pre-burial exposure histories. The cosmogenic nuclide concentrations in the samples are in accordance with those expected for the mixing of two sources, and the burial ages computed for both end members agree. Theoretical calculations of two-source mixing show that initial (26)Al/(10)Be ratios are depressed relative to the expected surface ratios and may result in burial ages overestimated by as much as 500 ka. Using ages derived from cosmogenic nuclides, independent age constraints, and magnetostratigraphy we correlate the bottom of the section to the Cochiti Normal magnetic subchron (4.19-4.30 Ma) within the Reverse Gilbert chron, and the top of the section to the Reverse subchron at the top of the Gilbert chron (3.60-4.19 Ma). (C) 2011 Elsevier B.V.