Giant slope scars and mass transport deposits across the Rhodes Basin, eastern Mediterranean: Depositional and tectonic processes

Abstract

High-resolution multichannel seismic reflection profiles and multibeam mosaic maps of the seafloor are used to document the presence of two prominent regions representing major sediment failure(s) and the subsequent gravity-driven mass transport across the southwestern continental margin of Anatolia. These regions are characterized by very sugged morphology (referred to as Scars 1 and 2), where the upper slope regions include several concave, interconnected steep seafloor escarpments marked by semi-circular indentations that link with one another by cusp-like features creating a sharp and very narrow curvilinear zone. The slope face across the rugged region there are numerous sharply irregular pinnacles/protrusions on the seafloor, consisting of exposed older bedrock successions. Scars 1 and 2 occupy seafloor areas of 1947 km2 and 1350 km2, solid volumes of 214–257 km3 and 92–111 km3, and masses of 467–681 Gt and 245–294 Gt, respectively, with a total solid volume of 307–368 km3 and a mass of 812–975 Gt. Mass transport deposits are identified at various stratigraphic levels across the Rhodes Basin characterized by chaotic seismic reflector configurations with zones of contorted and convoluted reflector geometries. The base of this facies is characterized by erosional down-cutting. The thickest and the regionally most extensive such deposits are found at the base of Unit 1, immediately above the upper bounding surface of the Messinian evaporites (the Top Erosional Surface or the former M-reflector). The lower mass transport deposit (L–MTD) is calculated to have a volume 205–171 km3, or a solid mass of 543–452 Gt, assuming that porosities of 40–50% and average grain density of 2.67 t m−3. Comparisons between the total mass of the L–MTD and the estimated masses of sediments mobilized across Scars 1 and 2 (812–975 Gt) indicate that there is ~360–432 Gt deficit in the calculated mass of the L–MTD. The missing sediments represent 17.5–21.0% of the total mass contained within Unit 1 across the present-day Rhodes Basin. This mismatch is remarkably large: it may arise from the uncertainties involved in the estimations of the masses of sediments contained in Scars 1 and 2; however, it is also possible that some of the gravity driven mass transports transitioned into turbidity currents, thus travelled great distances across the Rhodes Basin, and that some of these turbidity currents crossed the basin longitudinally, and exited it at its southwestern deeper regions (i.e., the present-day Strabo Trench). This is particularly plausible because the physiography of the Rhodes Basin was dramatically different during the early Pliocene and the southern and southwestern portions of the basin provided a possible exit route.