Cross-Shelf Redistribution of Coarse Gravel and Fluvial Incision Following Shelf Exposure: Observations from the Dead Sea

Global eustatic lowstands can expose vast areas of the continental shelf and occasionally also the shelf edge and the continental slope. Although limited connectivity of the fluvial system to the receding shore may influence the evolution of the newly emerged landscape, direct studies of such systems are rare, simply because the continental shelf is currently submerged. The Dead Sea basin offers a rare opportunity to examine a field-scale example of channel response to shelf emergence: a falling lake level with one channel which is flowing across the shelf and an adjacent channel which preserves limited fluvial connectivity to the regressing shoreline. We use a time-series of high-resolution topography, annually-acquired aerial imagery, field mapping, and grain size analyses to explore the setting of these two channels. The fluvial response includes cross-shelf channel incision, sediment redistribution, and alluvial fan progradation. The timing of coarse gravel traversing the muddy shelf is determined and the initiation and intensification of sediment flux across the shelf is recorded, as channel gradients downstream of a migrating knickpoint progressively increase. We suggest that the lag time of gravel transport from a highstand to a lowstand fan is affected by hydroclimatology, catchment area and continental margin gradients as well as by the virtual velocities of the transported coarse material and the gravel potential interaction with the shelf mud. The recorded setting provides an analogue to fluvial processes operating on continental shelves during glacial maxima sea level lowstands. Our observations suggest that high spatial and temporal variability of sediment routing patterns can exist in adjacent fluvial systems primarily due to continental margin geometry and the local hydrology. They also highlight the possibility that a common response of streams to sea level fall involves disconnectivity with the sea, and that large volumes of coarse sediment may be stored on the continental shelf.