High-resolution geomorphology of active rift margin submarine fans, Gulf of Corinth, Greece

High-resolution seafloor data from the Gulf of Corinth, Greece, collected using an autonomous underwater vehicle, reveal new insights into submarine fans deposited at the base of normal fault scarps. The steep (13°) Sythas canyon cuts into the submarine Lykoporia Fault and is carpeted by low relief, elongate rhomboidal bedforms. Across the fault the canyon passes abruptly into the 6 km radius Sythas submarine fan. The proximal fan (~3° gradient) contains multiple, discontinuous channels, erosional cyclic steps and scour fields. Channels shallow and broaden onto the medial fan (~1° gradient), which is characterized by trains of depositional cyclic steps that pass into subtle, low-relief lobes on the distal fan (~0.18° gradient). Sediment gravity flows were most likely stratified, with a thin, concentrated and supercritical basal layer. Smooth interchannel areas on the proximal fan suggest the basal layer was contained within the erosional relief (<5 m thick). The basal layer dissipated rapidly, within ~3 km of the canyon mouth, and flows transformed into dilute, subcritical turbidity currents on the distal fan and basin floor. Seafloor observations suggest base of fault scarp submarine fans share morphological similarities to the submarine slopes of fjord deltas and submarine cones, but contrast markedly with the widely used distributary models of submarine fans where avulsion of channel-levee systems is seen as the fundamental control on fan stratigraphic evolution. The geomorphology of the Sythas fan suggests rapid downflow changes in stratigraphy and grain size from a proximal coarse-grained succession dominated by amalgamated scours and supercritical bedforms, to distal, laterally extensive fine-grained turbidites. Switching of the locus of activity across the fan surface is likely to be marked by condensed intervals of fine-grained turbidite deposits. Our findings are generally applicable to the interpretation of both marine and lacustrine deep-water depositional systems in rifts and other steep-sided basin margins.