Marine geology of the Medriff Corridor, Mediterranean Ridge

Abstract Thirty-one piston and/or gravity cores not exceeding 10 m in length were raised in selected areas of a 300 km-long transect (Medriff Corridor) crossing the Mediterranean Ridge, an accretionary complex subject to continent/continent collision, containing an important evaporitic body (Messinian evaporites), in order to ground-truth the geological make-up. Core location, very accurate with reference to a complex bottom configuration, was preceded by swathe mapping, seismic profiling and side-scan sonar investigations. Most sediment cores have a pelagic facies, with biogenic marls as dominant lithology, and sapropels and tephras as minor, isochronous lithologies. A combination of isochronous lithologies and calcareous plankton biochronology permits high resolution stratigraphic correlations. Pelagic facies sediments are Middle Pleistocene to Holocene in age. Two cores associated with mounds located along thrusts contain a matrix-supported mud breccia of deep provenance, Burdigalian-Langhian in age, similar to that characteristic of the Mediterranean Ridge diapiric belt (Cita et al. 1995 ). Three new brine-filled anoxic basins (Urania, l'Atalante and Discovery) were discovered. The brines originated from submarine dissolution of Messinian evaporites and are different in the various basins. The sedimentary record strongly differs from basin to basin. These brine lakes are very young (35 000 years or less). A drastic change in sedimentation rate recorded in the Discovery Basin suggests that basin collapse was sudden and followed by progressive development of basin anoxia. Some cores were analyzed with a prototype multisensor for P-wave velocity, magnetic susceptibility and density. Sapropels show up as abrupt decreases in P-wave velocity and density, and tephra as sudden increases in magnetic susceptibility. Mud breccia displays P-wave velocities greater than pelagic marls, with peaks related to lithic clasts. Anoxic sediments have high P-wave velocities; peaks are associated with gypsum crystals.     

Quaternary evolution of the southern sector of the Campanian Plain and early Somma-Vesuvius activity: insights from the Trecase 1 well

Summary The present review of data on the Trecase 1 well, including stratigraphy, updated ⁴⁰ Ar/³⁹Ar ages and the results of newly performed calcareous nannofossil studies, serves to resolve the chronological contradictions pointed out by Bernasconi et al. (1981) and Balducci et al. (1983) concerning the onset of volcanic activity in the area now occupied by the Somma-Vesuvius Volcanic Complex. New ⁴⁰ Ar/³⁹Ar data indicate that volcanic activity in this area started about 0.4 myr B.P. After such time, tephritic magmatic activity, distributed in small scattered centers, developed and alternated with periods of volcanic quiescence and marine sedimentation. This first phase of magmatic activity ended in the Vesuvian area about 0.3 myr B.P. and was followed by a period of marine sedimentation in a marginal environment. Complete emergence of the shoreline occurred about 37,000 yr B.P. as a result of sea level changes during the last glacial period and deposition of the 60 m thick Campanian ignimbrite (CI). Volcanic activity reappeared in the Vesuvian area only after the CI eruption. Magma rising along and at the intersection of linear and curved tectonic and volcano-tectonic elements (linked to the pre-existing Pleistocene tectonic trend and formation of the vast Phlegraean Fields caldera) formed a number of small lava and scoria edifices. One of these tephritic centers lies above the CI deposits under the Trecase 1 well area. The CI bottom in the Trecase 1 well is currently at an altitude of − 120 m a.s.l.; this allows estimating the maximum tectonic subsidence over the last 37,000 yr. by the southern sector of the Vesuvian area to be about 30 m. Received April 12, 2000; revised version accepted March 1, 2001