STRATIGRAPHY AND SEDIMENTATION IN THE MEDITERRANEAN RIDGE DIAPIRIC BELT

Two basic sediment types are recorded in the Mediterranean Ridge diapi ric belt: the host sediment and the mud breccia. The host sediment con sists of hemipelagic marl as dominant lithology, associated with sapro pels and tephras as minor isochronous lithologies. A high resolution s tratigraphy, which allows much more detailed and precise correlations than those based on biostratigraphy (essentially calcareous nannofossi ls) is applicable to the over 20 cores considered in this study, that were obtained during cruise TTR3-Leg 2 in 1993. The mud breccia is mat rix-supported and contains submillimetric to pluricentimetric clasts i n various amounts (Staffini et al., 1993). This lithology is consisten tly related to doming physiographic features of different size and sha pe (Camerlenghi et al., 1992), and to high reflectivity patches record ed on long-range side-scan sonar. The mud breccia can be intruded or e xtruded. The massive, coarse nature of the mud breccia recorded in the large majority of the 16 cores that contain this lithology may sugges t intrusion. Cores from Napoli Dome, which is typically an active mud volcano (Cita et al., 1994), are fine-grained and very gaseous. Contac ts between the mud breccia and the host sediment are mostly distinct, but may be gradational. Two cores document interlayering of the mud br eccia with pelagic sediments, but no turbidites were ever recovered. A mong the main results of the study we mention: the strong slope instab ility documented by the pelagic host sediments from the ridge diapiric belt (hiatuses, microfaults, hardgrounds); the wide distribution of d iapiric features across the ridge axis (from the Inner Deformation Fro nt to the Toronto Dome, some 50 km to the south); the age of the mud b reccia (matrix essentially) which is consistently early-middle Miocene with some older elements, but strictly middle to Late Cretaceous for the southernmost Toronto Dome.