Sedimentation processes in a tectonically active environment: the Kerkyra-Kefalonia submarine valley system (NE Ionian Sea)

The Kerkyra-Kefalonia valley system is the northwestern extension of the He llenic are-trench system, representing the collision zone of the Apulian Pl atform and the Hellenides. The system is distinguished by two different phy siographic regions: the northern part, U-shaped, and oriented NNW-SSE, with relatively gentle slopes and a wide floor; and the southern part, oriented NE-SW, V-shaped, and with much steeper side walls and a narrow floor. Both parts are formed tectonically, with the former coinciding with a collision zone, and the latter being the morphometric expression of the Kefalonia st rike-slip fault. Sediments recovered in the piston cores from the region co nsist of fine-grained material, deposited by a variety of sedimentation pro cesses such as: gravity-driven mass movements, associated with seismic acti vity (i.e., slumping, sliding, debris flows, grain flows, turbidites-seismo turbidites); and, to a lesser extent, by hemipelagic deposition, Measured n ear-bed currents and their associated shear stresses indicate resuspension of the material, mainly within the northern part of the valley. Sub-bottom acoustic (seismic) profiling data reveal various sedimentary provinces, rel ated to different mechanisms of sediment accumulation: (i) the i:astern mar gin of the Apulian Platform with hemipelagic sedimentation, together with p ossible advection of suspensates from; the Adriatic, in response localised to seabed erosion; (ii) the western Hellenic margin, with down-slope episod ic sliding and slumping, induced primarily by earthquake activity, together with an input from hemipelagic settling; (iii) the collision zone, coincid ing with the northern part of the Kerkyra-Kefalonia valley system, with dep osition mostly from resuspension, the occurrence of local mass gravity flow s and the advection of some material from the north; and (iv) the Kefalonia strike-slip fault region, where mass gravity flows are the dominant mechan isms, related to erosion/deposition from resuspension. Overall sedimentatio n within the tectonically-active Kerkyra-Kefalonia valley system is charact erised by the coupling of the mass gravity-driven flows, which are the pred ominant mechanisms, with the near-bed current regime related with resuspens ion phenomena and the advection of suspensates. These latter mechanisms is likely more pronounced during the winter period, when dense water masses fo rmed in the Adriatic inflowing into the Ionian Sea. (C) 1999 Elsevier Scien ce B.V. All rights reserved.