Morphometric and geomorphic approaches for assessment of tectonic activity, Dead Sea Rift (Israel)

Abstract

A series of 31 short, parallel, steep channels, mostly of first or second order, occur at intervals of 300–500 m along 16 km of the western margin of the northern Dead Sea Rift (Israel). The analysis of tectonic and geometric activity along the marginal faults between the various segments is based on morphometric parameters, such as sinuosity of the mountain front, channel gradients, drainage basin elongation ratio, planimetric ratio, facet areas, hypsometric curves, and integrals. Longitudinal profiles of the channels were studied in relation to the underlying lithology and the presence of marginal faults. Despite the great differences in climatic and geomorphologic settings, comparison with other studies worldwide showed morphometric values similar to other tectonically active regions. The southern segments of the study area, which face the Hula deep depression, indicate enhanced geomorphic and tectonic activity. The northern segment proved dissimilar to the others, and is explained by its different tectonic setting. Six sedimentary, fan-like units composed of polymictic conglomerates were deposited along the mountain piedmont at the channel mouths. The units were dated by OSL, K–Ar, and archaeology to < 1.1 Ma (Q 1 and Q 1–1), < 0.56 Ma (Unit Q 2), ~ 120 ka (Unit Q 3), and < 10 ka (Units Q 4 and Q 5). The morphology and structure of the sedimentary units indicate pulses of depositional activity, followed by periods of quiescence and calcic-soil development. No major faulting occurred along the Naftali escarpment during the Upper Pleistocene, despite the high tectonic morphometric values obtained for the study area. The marginal faults displaced Unit Q 2 during the Mid-Pleistocene, and since then tectonic activity has shifted from the western marginal faults eastward to younger faults deeply buried in the center of the graben. The field data calibrate the morphometric analysis: carbonate (limestone and dolomite) hillslopes developed in the Mediterranean climate have maintained ‘active tectonic class’ morphology since the last major faulting events during the Mid-Pleistocene.