NEAR-BOTTOM SEDIMENTATION PROCESSES REVEALED BY ECHO-CHARACTER MAPPING STUDIES, NORTHWESTERN MEDITERRANEAN BASIN

Subbottom echoes recorded on 5.5 kHz echo sounders in the northwestern Mediterranean Basin from 1978 to 1991 can be classified into five mai n categories of echo character: (1) Continental shelf (CS) echo charac ter characterizes the continental platform and areas of shallow relief and commonly is related to consolidated sediments, (2) Hyperbolic (H) echo character is recorded from areas with rough bottom morphology, E cho type H1 corresponds to steep slopes; echo type H2 reflects very co arse grained sediments deposited by energetic turbidity currents. (3) Bedded (B) echo character is widely observed throughout the study area and corresponds to terrigenous deposits distributed by turbidity curr ents. Echo type B1 is related to thin turbidites deposited on overbank portions of channel levees by lateral overflow of turbiditic currents moving down the channels; echo type B2 corresponds to coarser turbidi tic materials. (4) Rugged (R) echo character is observed in the axes o f submarine canyons and channels and characterizes hard sea floor with coarse heterogeneous turbiditic deposits subjected to energetic gravi ty-flow processes. (5) Transparent (T) echo character is ubiquitous in the study area and is attributed to mass-movement deposits, The wides pread occurrence of those deposits testifies to the general instabilit y of the study area. Types and distribution of echo character througho ut the study area show the importance of gravity-dominated depositiona l processes (turbidity currents and mass wasting) in this region. This remobilization of siliciclastic sediments, induced by high sediment r ates, steep slopes, and halotectonics, theoretically could create pote ntial hydrocarbon reservoirs within the deep-water portions of the con tinental margin.