The Late Messinian Lago-mare episode in the Central Mediterranean Basin: New data from the onshore Mondragone 1 well (Garigliano Plain, central Italy).

The Mondragone 1 well, drilled in 1968 by Agip, for hydrocarbon exploration, is located in the plain of the Garigliano River, at about 3 km to the east of Cellole village (lat. 41° 12’ 17”, long. 13° 48’ 52”). The Mondragone 1 well cut across siliciclastic fine-to-coarse-grained upper Miocene-Quaternary deposits, for a total depth of 2002 m.Drilling the Mondragone 1 well, fourteen sediments cores have been recovered from 495 m down to 2000 m; SP and resistivity logs have been also recorded. The Mondragone 1 sediment cores have been recently re-sampled and analysed. This paper deals both with the results of the biostratigraphical analyses performed on the Mondragone 1 re-sampled sediment cores and with the significance of the Mondragone 1 well stratigraphy in the central Mediterranean scenario during the late Messinian Lago-Mare episode. 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 allows us to suggest a possible sequence stratigraphy evolution of the Garigliano Basin during the late Messinian Lago-Mare episode.Since the ostracod assemblages in sediment cores 2-14 contain species belonging to the Loxoconcha djafarovi Zone, as was defined by Carbonnel (1978) (e.g. Loxoconcha (Loxocorniculina) djafarovi, Loxoconcha (L.) eichwaldi; Cyprideis anlavauxensis; Amnicythere palimpsesta; Zalanyiella venusta), it is reasonable to refer this portion of the Mondragone 1 drilled sediments (from -675 m down to –2002 m) to the late Messinian Lago-Mare biofacies.The uppermost Messinian Lago-Mare deposits drilled by the Mondragone 1 well provided an apparent thickness of 1327 m and a true thickness of about 938 m considering a mean dip value of 45° in the strata measurements. Similar thickness (530 m) of pre-Pliocene sediments has been drilled at ODP Site 652, in the Tyrrhenian bathyal plain. The occurrence in the Unit 4 of the ODP Site 652 of scarce Ammonia beccarii tepida and Cyprideis sp. (Borsetti et al., 1990; Robertson et al., 1990) together with its magnetostratigraphy (Channell et al., 1990) point to time-correlate the ODP Site 652 pre-Pliocene deposits with those drilled at Mondragone 1.Different behaviour between the northern and the southern Tyrrhenian Basin have been shown by differences in the total subsidence rates computed in the late Messinian Lago-Mare rifting areas of the Tyrrhenian Basin. North of the Tiber delta, the uppermost Messinian syn-rift clastic wedges recognized in the northern Latium and in the Tuscany Tyrrhenian margins show similar thickness (250 m and 230 m respectively), lower than that drilled in the Mondragone 1 well and in the ODP Site 652.Taking into account the duration of the late Messinian Lago-Mare episode (260 ka), a total subsidence rate of about 1 mm/a could be computed for the sedimentary basins north to the Tiber delta, whereas >4 mm/a of subsidence rate affected the sedimentary basins developed SE of the R. Selli lineament. This lithosphere feature distinguishes two sectors with different amounts of horizontal stretching (Finetti and Del Ben, 1986): 1) a northern Tyrrhenian area, characterized by a thinned continental crust and lower values of late Messinian total subsidence rates; 2) a southern Tyrrhenian area, characterized by an ocean-type crust and higher values of late Messinian total subsidence rates.