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A Quaternary fluvial sequence tells the story of a drainage reorganization

Field observations across the globe show that drainage reversal toward a cliff is a common type of drainage reorganization. Drainage reversal occurs when a channel reverses its flow direction by 180 degrees while exploiting its antecedent valley. In these settings, fluvial deposits of the antecedent, pre-reversal drainage potentially record valuable information about the process of drainage reorganization. However, such fluvial deposits are rare because they are typically eroded by the reversed channels.

We present a spectacular case of a reversed channel in the Negev desert, Israel, that forms a narrow canyon with several-meters high vertical walls exposing a sequence of fluvial deposits that reflect the reversal process. At the base of the sequence, a <1 m thick conglomerate layer is characterized by clast imbrication consistent with the westward flow direction of the antecedent drainage. Overlying the conglomerate, reddish fine-grained sediments (~1-2 m thick) indicate a decrease in flow energy, reflecting the reversal of the flow toward the current eastward flow direction. Paleosols and scattered calcite nodules within the sediment imply phases of soil development, most likely during a more humid climate than today. The uppermost layer (<1 m thick) consists of sediments of alluvial fans fed from the neighboring hillslopes, that play a key role in the development of the reversed channel through their avulsion cycling. Using geomorphic mapping based on high-resolution DEMs and preliminary dating results, we propose a holistic approach for better understanding the relationships between sedimentary systems, climate changes, and erosional processes in landscapes experiencing drainage reorganization.


Elhanan Harel1, Liran Goren1, Eitan Shelef2, Onn Crouvi3, Naomi Porat3, Hanan Ginat4
1Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.; 2Geology and Environmental Science, University of Pittsburgh, 4107 O'Hara Street, Pittsburgh, Pennsylvania 15260- 3332, United States; 3Geological Survey of Israel, Yesha'yahu Leibowitz 32, Jerusalem 9692100, Israel.; 4The Dead-Sea and Arava Science Center, Tamar Regional council Dead-Sea mobile post 86910, Tamar Regional council, Israel.
GeoBerlin 2023