The Dead Sea Rift

Abstract The Dead Sea Rift, a classic strike-slip lineament, occurs along a transform plate boundary that connects the Red Sea, where sea-floor spreading is occurring, with the Taurus Mountains, where there is plate convergence. The total strike slip along the transform since the Miocene is 105 km with the last 40 km having occurred in Plio-Pleistocene time, that is when the present Dead Sea Basin began to subside. The Dead Sea Basin, an active rhomb-shaped graben, is located within the Dead Sea transform. It is bounded on the east and west by two nearly vertical, north-striking normal faults, on the south by listric(?) normal faults, that dip steeply to the north and on the north by a gently sloping, south-facing flexure in the basement. Displacement along a zone of en echelon strike-slip faults formed 3 sedimentary basins whose depocenters migrated northward with time. Deposition began in the early Miocene, when a thick succession of continental red beds (the Hazeva Formation) were deposited in a basin south of the modern Dead Sea. Deposition migrated northward in the Pliocene, as an arm of the Mediterranean flowed south through the transform into the newly evolving Dead Sea Basin; there, marine clastic sediment and evaporites, including the Sedom Salt, were laid down. The youngest rift sequence, of Plio-Pleistocene to Holocene age, fills the northern basin of the Dead Sea with over 3,500 m of lacustrine evaporites and fluvial-deltaic clastic sediments. Only the youngest syn-rift sequence crops out along the west bank of the northern basin, where it was mapped at a scale of 1:50,000 for a distance of 50 km, and is divisible into three stratigraphic units. From oldest to youngest these are the Samra Formation (debris-fan gravel); the Lisan Formation (fan-delta gravel, and lacustrine limestone and marl); and a unit of deltaic sands and beach gravels. Sedimentation along the rift is controlled by the interaction of rift tectonics and climate. Whereas tectonic activity creates the rift, the resulting rift morphology significantly modifies the climate. Thus it may be observed that as moist air from the Mediterrean Sea rises over the shoulders of the rift, it cools adiabatically yielding as much as 800-1,000 mm of rain per year. This rainfall contributes to high-discharge ephemeral streams that transport huge quantities of coarse clastic sediment eastward onto the narrow shelf of the Dead Sea; and to the drainage basin of the Jordan River, a perennial stream, that carries mud and fine-grained clastic sediment along the axis of the rift, where it constructs a large delta at the head of the Dead Sea. On the other hand, as the air descends into the basin, it warms adiabatically, evaporating more than 2,000 mm of water per year, thereby causing a concomitant drop in the Dead Sea level, precipitation of evaporites, and the reworking of shelf sediment into deeper water. In the absence of recurrent syn-depositonal faulting in the stratigraphic record, such actualistic models convincingly explain Pleistocene-Holocene sedimentary patterns along the Dead Sea.