Some clues about the Napoli and Milano mud volcanoes from an integrated log-core approach

Abstract

A full set of conventional logging data and Formation MicroScanner (FMS) data were acquired on the flanks of the Milano mud volcano and the Napoli mud volcano on the Mediterranean Ridge, and provide a complete and continuous record of the petrophysical and geological features of these structures. On the basis of the logging data, and of mineralogical and geochemical sample analyses, the composition, sedimentation, and internal sedimentary and structural features of the mud volcanoes were studied. Conventional logging data indicate composition and/or texture-related variations and indicate different sedimentation episodes. These changes are also recognizable on FMS images. Layered intervals are identified at different depths within both mud volcanoes. Most features that are recognized, possible bedding surfaces, dip to the west to northwest in the Milano mud volcano and to the north-northwest and north-northeast in the Napoli mud volcano. The dip of the beds is consistent with gravitational deposition and the present-day morphology of the Napoli mud volcano. The dip and strike of inferred bedding features at the Milano mud volcano suggest either the existence of a depositional slope and a source of gravitational flows to the east, or tilting of the bedding surfaces by subsidence after deposition. Steeply dipping planes (>45°) that dip north-northwest at Napoli are likely to represent fractures. These features are recognized as electrically resistive features indicating that they are filled with a nonconductive material, possibly either halite or gas. The results of core sample analysis indicate that diagenetic mineralogical transformations have not affected the mud volcano material, that the clay minerals are of detrital origin, and that Fe-Al-rich smectites are predominant.