Sedimentological processes in the southern margin of the Cretan Sea (NE Mediterranean)

The Cretan Basin can be characterized as a back-are basin of the Hellenic T rench System, that is related to the subduction zone of the African Plate u nder the Eurasia Plate. The study area includes the narrow and relatively s teep (gradient 1.5 degrees) continental shelf of the island of Crete follow ed by the steep slope (2 degrees-4 degrees) and the rather flat deeper part of the Cretan basin (water depths >1700 m). Surficial sediments of the coastal zone are coarser and of terrigenous orig in, while in deeper waters finer sediments, of biogenic origin, are more ab undant. Sand-sized calcareous sediment accumulations, identified in middle- lower slope, may be attributed to the aggregation of seabed biogenic materi al related to the near bed current activity. High resolution profiles (3.5 kHz) taken from the inner shelf shows a typic al sigmoid-oblique progradational configuration, implying prodelta sediment accumulation during the Holocene. In the upper-middle slope, sub-bottom re flectors indicate continuous sedimentation of alternating fine and/or coars e grained material. Small-scale gravity induced synsedimentary faults appea red, locally. In contrast, a series of gravity induced faults, identified i n the lower slope, are associated with sediment instabilities due to seismo tectonic activity. Sediment cores taken from the shelf-break consists of ca lcareous muddy sand with small amounts of terrigenous silt and fine sand, w hile the cores recovered from the middle slope has revealed a more homogene ous fine sediment texture of hemipelagic deposition. The prevailing accumulation processes in the southern margin of the Cretan basin are: (i) prodelta deposition in the inner-middle shelf; (ii) settling from bottom nepheloid layers in the shelf and upper slope; (iii) calcareou s sediment formation due to settling from suspension and post accumulation aggregation (middle-lower slope); (iv) long-term episodic sediment gravity processes in the lower slope; and (v) to a lesser extent, redeposition from resuspension due to gravity processes and bottom currents. (C) 2000 Elsevi er Science Ltd. All rights reserved.