Late Miocene evolution of Jordan Rift Valley recorded on its eastern flank

The Jordan Rift Valley (JRV) is a depression produced by the active Dead Sea Transform (DST), separating the Sinai subplate and the Arabian Plate. Its beginning is related to the late Miocene (~6 Ma), when sinistral displacement of the DST gained an extensional component, thus accentuating the subsidence of the JRV. This shift is recorded by Messinian basalt flows that cover JRV eastern slopes (Zerqa Ma, Mujib, and Tafila basalts; 6–3.4 Ma) and the Cover basalt (5.8–3.6 Ma) in the Galilee region. Sediments from the Sedom Lagoon since ~12 Ma suggests that the JRV was already a shallow depression connected with the Mediterranean Sea, which at the early Pliocene (5–4 Ma) lost permanently this connection due to the uplift of the JRV flanks. More information about geomorphology and drainage pattern of the region during the Late Miocene is limited to information available along the western side of the JRV, including the fluvial/lacustrine Hazeva Fm (~20–6.4 Ma) in the Arava region and lacustrine/marine formations in the lower Galilee (~17–5 Ma). Here we discuss the implications of Zarqa Valley geomorphological features and its volcano-sedimentary infill to the Miocene evolution of the JRV. The Zarqa Valley is carved into Cretaceous/Paleogene bedrocks at the Eastern Flank of the JRV, and it hosts a perennial water drainage system flowing westward to the Jordan River. The oldest dated filling of the Zarqa Valley is represented by a series of late Miocene lava flows, named collectively as “Lower Basalt” (LB), spanning 5.82 to 5.51 Ma. It records the existence of a pre-existing valley in the late Miocene, with already at least 300 m of incision, observed by the difference of the base of the LB and the bedrock summits surrounding the valley. The LB outcrops ca. 40 km east of JRV axis and its thickness increases eastward to more than 100 m. W-NW paleocurrent data in conglomerates underlying the LB indicate that the Zarqa River maintained the same flow towards the JRV since the Late Miocene. The occurrence of the LB in the Zarqa Valley is synchronous with the dramatic sea level fall of Messinian Salinity Crisis (MSC, 5.97–5.33 Ma), when the Sedom Lagoon lost temporarily the connection to the Mediterranean Sea. Opposite to what is observed throughout the Mediterranean Sea, where rivers underwent a profound incision phase, the Zarqa Valley experienced aggradation of conglomerates and thick basalt flows. We propose that this is an indication that Sedom Lagoon acted as local base level of an endorheic drainage by the time when the MSC started, possibly with an increasing water table, necessary to produce the accumulation space to account for the Zarqa Valley deposition. We hypothesize that a highstand of the base level in the JRV during the MSC can be explained by a favorable climate and several stream capture in the Levant that caused rivers to migrate to the endorheic drainage of the Sedom Lagoon.