MUD DIAPIRS OF THE MEDITERRANEAN RIDGE: SEDIMENTOLOGICAL AND MICROPALEONTOLOGICAL STUDY OF THE MUD BRECCIA

Abstract

Two recent sea-going expeditions showed that mud diapirism is a common feature in the accretionary wedge of the Mediterranean Ridge, but unlike in other prisms, it is well expressed exclusively in the most elevated areas of the Ridge. Three diapiric fields were discovered on the Mediterranean Ridge and informally called, from west to east, Pan di Zucchero, Prometheus 2 and Olimpi. They are located on the crestal part of the Mediterranean Ridge between Creta and the Cirenaic Promontory. Sedimentological, micropaleontological, and mineralogic investigations were performed on the mud breccia recovered in 15 cores raised during cruises BAN88 and BAN89. The sedimentological analyses allowed to recognize several sedimentary facies which are suggestive of different emplacement processes: 1) three massive facies are indicative of intrusion; 2) three organized facies are indicative of submarine extrusion and probably reworking. The micropaleontological study based on planktonic foraminifera and calcareous nannofossils provided an Oligocene age for the source sediments and/or for the sediments possibly involved in the diapiric processes of the Pan di Zucchero, and an Early Miocene age for the Olimpi and Prometheus 2 fields. No evidence was found of the typical Messinian lithologies, such as dolomite and gypsum, and microfossils (lago-mare biofacies). X-ray diffraction analyses allow to identify the major mineralogic component of the mud breccia and a westward decrease in the smectite content. Our investigations reveal that major differences occur between the Pan di Zuccchero and Olimpi areas, whereas minor differences are recorded between the Olimpi and Prometheus 2. Moreover, the Napoli Dome, located in the Olimpi area, differs from the other diapirs in several sedimentological, micropaleontological and mineralogic characters, and is interpreted as a mud volcano.