Quaternary evolution of a hyperarid drainage under climatic fluctuations and rift-margin base-level fall, NE Negev, Israel

Abstract

The long-term bedrock incision of streams in the northeastern Negev has been dictated, since the Early Pliocene, by the subsidence of the Dead Sea basin. However, this incision is accompanied by very long intervals of sediment aggradation. Here, we document the Quaternary-scale fluvial response to changing base-level, lithology, structure, and climate along the hyperarid Nahal Zafit, NE Negev. The oldest (~1–2 Ma) alluvial remnants point to a widespread beveled bedrock pediment at the base of the Hazera anticline. This pediment, like other stream-pediment-anticline relationships in the region, provides the baseline framework into which Nahal Zafit incises. During the Early to Middle Pleistocene, this pediment was the base-level for all streams emerging out of the anticlines. The tectonic subsidence of the regional base-level at the rift margin farther downstream, has caused incision and upstream migration of bedrock knickpoints, triggering the development of a wide incised valley in the Mazar syncline, adjacent to the Hazera anticline. Since ~330 ka, fluvial terraces, landslides and taluses record intervals of basin-wide fluvial deposition under prevailing hyperarid to arid climate. Despite the general arid climate, prolonged fluvial deposition intervals occurred at ca. 330–265, 230–125, and 110–20 ka. Rapid and quite short-duration bedrock incision occurred in-between these, much longer, intervals of aggradation. In addition to the proposed climatic imprint on fluvial aggradation-incision cycles and the first-order base-level control of the rift margin fault, the formation of strath terraces and distribution of stored sediments within the drainage basin point to the fundamental role that lithology and structure play in the Quaternary evolution of the NE Negev watersheds.