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A regional truncation surface developed during the Oligocene in the northern Red Sea and southern Levant as a result of the combined effects: (1) the formation of an ~3000 km × 1500 km crustal dome affecting the northeastern sector of the Afro-Arabian continent above the Afar plume, and (2) widespread fl uvial erosion that truncated the northern edge of this dome. The regional truncation surface separates two main stratigraphic divisions: (1) middle Eocene-early Oligocene prerift clastics preserved below the regional truncation surface and (2) late Oligo cene-Holocene Red Sea Supergroup deposited after the regional truncation surface developed. The prerifting sequence is composed of two major units: (1) Eocene marine intraformational debris fl ows (Themed clastics), and (2) fl uviolacustrine continental conglomerates, most of them monomictic (Mahatardi Conglomerate). The Red Sea Supergroup is composed of polymictic conglomerates, which include fragments of older rock units, down to the Precambrian. The reconstructed regional truncation surface and its subcrop map shed new light on the initial stages of the Afro-Arabian breakup, indicating two principal phases: (1) an Oligocene slow crustal doming, with reactivation of preexisting faults and the development of the regional truncation surface, all triggered by the upwelling of the Afar plume; and (2) late Oligo cene-early Miocene rifting of the Red Sea and Suez rift, which refaulted the region, including the initiation of the Dead Sea Transform along a preexisting suture line. This two-stage model indicates the mutual genetic relationship between the early Oligocene phase of tectonic development following the penetration of the Afar plume and the post-Oligocene rifting and continental breakup of the Afro-Arabian continent.

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Drainage reversals, an end-member case of drainage reorganization, often occur toward cliffs. Reversals are commonly identified by the presence of barbed tributaries, with a junction angle >90°, that preserve the antecedent drainage geometry. The processes that form reversed drainages are largely unknown. Particularly, barbed tributaries cannot form through a spatially uniform migration of the cliff and drainage divide, which would be expected to erase the antecedent drainage pattern, and tectonic tilting toward the cliff that could reverse the flow direction is inconsistent with geodynamic models of large-scale escarpment, where many reversals are documented. Here, we propose a new mechanism for drainage reversal, where the slope imbalance across a cliff, together with the high erodibility of sediments that fill cliff-truncated valleys, result in faster divide migration along valleys compared to interfluves. We demonstrate this mechanism along channels that drain toward the escarpment of the Arava Valley in Israel. Reversal is established by observations of barbed tributaries and opposite-grading terraces. We show that drainage reversal occurs when erodible valley fill exists, and that the reversal extent correlates with the thickness of this fill, in agreement with the predictions of the proposed mechanism. This new reversal mechanism demonstrates that valley fill could play an acute role in fluvial reorganization processes, and that reversals could occur independently of tectonic tilting.