DISTRIBUTION OF MUD DIAPIRISM AND OTHER GEOLOGICAL STRUCTURES FROM LONG-RANGE SIDESCAN SONAR (GLORIA) DATA, IN THE EASTERN MEDITERRANEAN-SEA

Extensive long range sidescan sonar coverage, obtained with the GLORIA system in the Eastern Mediterranean Sea, has been reinterpreted in th e light of subsequent ''ground truth'' data. Several types of high bac kscattering patches are recognised. About 150 circular to sub-circular patches have been identified on the shallower and inner part of the M editerranean Ridge accretionary complex. Some can occur in groups or i n ridge parallel alignments, associated with deep-seated structures. O n the basis of core stratigraphy they have been interpreted as mud vol canoes and mud ridges, with surface or near surface mud breccia. It se ems that mud volcanoes are not imaged by the 6.5 GLORIA system if ther e is a cover of more than about 2 m of pelagic sediments. Few such pat ches are present in those external parts of the Calabrian and Cyprus a rcs that have been surveyed. It is thus confirmed that mud diapirism i s more common where the covering Messinian salt is thinner, that is on the crest and inner part of the Mediterranean Ridge. Larger, more elo ngated patches, up to 80 km long and usually associated with steep slo pes, are found in the Hellenic Trough System; they are attributed to h ard rock outcrops. Similar shaped patches, associated with lower relie f, found near the eastern and western ends of the Mediterranean Ridge, are attributed to dissolved evaporites at the top of salt diapirs whi ch leave a rough, karst like surface topography. Other elongate patche s of high backscatter at the foot of the Nile Cone may be due to diffe rences in grain size and/or to chemical crusts. They are on diapiric f old crests that are probably due to salt mobilisation. A few small cir cular patches, found at the foot of scarps on the Nile Cone, are attri buted to debris flow deposits.