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

The present review of data on the Trecase 1 well, including stratigraphy, u pdated Ar-40/Ar-39 ages and the results of newly performed calcareous nanno fossil studies, serves to resolve the chronological contradictions pointed out by Bernasconi et al. (1981) and Balducci et al. (1983) concerning the o nset of volcanic activity in the area now occupied by the Somma-Vesuvius Vo lcanic Complex. New Ar-40/Ar-39 data indicate that volcanic activity in thi s area started about 0.4 myr B.P. After such time, tephritic magmatic activ ity, distributed in small scattered centers, developed and alternated with periods of volcanic quiescence and marine sedimentation. This first phase o f magmatic activity ended in the Vesuvian area about 0.3 myr B.P. and was f ollowed by a period of marine sedimentation in a marginal environment. Comp lete emergence of the shoreline occurred about 37,000 yr B.P. as a result o f sea level changes during the last glacial period and deposition of the 60 m thick Campanian ignimbrite (CI). Volcanic activity reappeared in the Vesu vian area only after the CI eruption. Magma rising along and at the interse ction of linear and curved tectonic and volcano-tectonic elements (linked t o the pre-existing Pleistocene tectonic trend and formation of the vast Phl egraean 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 altitu de of -120 in a.s.l.; this allows estimating the maximum tectonic subsidenc e over the last 37,000 yr. by the southern sector of the Vesuvian area to b e about 30 in.