ORGANIC-CARBON PROVENANCE AND MATURITY IN THE MUD BRECCIA FROM THE NAPOLI MUD VOLCANO - INDICATORS OF ORIGIN AND BURIAL DEPTH

Mud volcanism on the Mediterranean Ridge is caused by extrusion of ove rpressured sediments, with consequent formation of spectacular dome-sh aped features composed of mud breccias at the seafloor. The organic ma terial in the mud breccia of the Napoli mud volcano is a mixture of di fferent facies, stratigraphic origin and thermal maturities. One porti on is synsedimentary organic material with only minor diagenetic alter ations and represents sedimenting material that was embedded into the mud volcano during its extrusion. The mud breccia also contains therma lly mature organic material of mainly terrestrial provenance with alga e of fresh- and brackish-water origin. Vitrinite reflectance data of t his maturity generation range from 0.65 to 0.90% R(oil) and thus chara cterize thermally mature source rocks, a rank which is corroborated by fluorescence and molecular characteristics. The predominance of vitri nite in the maceral assemblages and the occurrence of biomarkers of te rrigenous origin suggest that the major part of the mud matrix derives from a lacustrine or riverine sedimentary unit in the subsurface, pos sibly from the Messinian stage. A third generation of organic material includes inertinites and vitrinites of high reflectance, which repres ent recycled organic matter present in any marine sediment. By use of the Lopatin method for modelling the thermal maturation of hydrocarbon source rocks from the vitrinite reflectance data, we calculated that the depth of mobilization ranges from 4900 m to 7500 m, depending upon the temperature gradient used.