Environments and tectonic instability in central Italy (Garigliano Basin) during the late Messinian Lago-Mare episode: new data from the onshore Mondragone 1 well (Garigliano plain, central Italy)

The Mondragone 1 well, drilled in 1968 by Agip, for hydrocarbon exploration, cut across siliciclastic fine-to-coarse-grained upper Miocene–Quaternary deposits, for a total depth of 2002 m. Thirteen cores have been recovered from 495 down to 2002 m. This paper deals with both the results of the biostratigraphical analyses performed on a new sampling of the cores and the significance of the well stratigraphy in the context of the late Messinian Lago–Mare episode in central Mediterranean. The Lago–Mare biofacies has been characterised from 675 down to 2002 m by the ostracod assemblages that are made of species belonging to the Loxocorniculina djafarovi Zone, as defined by Carbonnel [Carbonnel, G., 1978. La zone a Loxoconcha djaffarovi Schneider (Ostracoda,Miocène supérieur) ou leMessinien de laVallée du Rhône. Rev.Micropaleontol. 21, 106–118.] (e.g. L. djafarovi, Loxoconcha eichwaldi, Cyprideis anlavauxensis, Amnicythere palimpsesta, Zalanyiella venusta). Thus, the Lago–Mare deposits have a true thickness of about 938 m since the strata show a mean dip value of 45°. Similar thickness (530 m) has been measured in the pre- Pliocene sediments drilled at ODP Site 652, which can be correlated withMondragone 1 by the occurrence of brackish-water forms. In both these areas syn-rift depositional processes have been suggested to explain the unusual thickness of the late Messinian sediments. Data from seismic lines have been used to reconstruct the geometry and the structural setting of the Garigliano Basin during the latest Messinian. Moreover, the analysis of the SP log integrated with the palaeoecological indications from the ostracod assemblages allows us to suggest a possible sequence stratigraphy evolution of the Garigliano Basin during the late Messinian Lago–Mare episode. Different tectonic behaviour with differences in subsidence rates between the northern and the southern Tyrrhenian Basin have been suggested since the uppermost Messinian syn-rift clastic wedges recognized in the onshore of northern Latium and Tuscany show thickness lower than that drilled at the ODP Site 652 and at the Mondragone 1 well.