The Adriatic foreland record of Messinian events (Central Adriatic Sea, Italy)

Commercial wells and seismic data made available by Eni-Agip and their integration with the sedimentary successions cropping out along the steep sea-cliffs of the Gabicce and Conero Riviera allow to extend the geologic-stratigraphic model proposed in the last years for the Messinian inner and central depozones of the Apennine foredeep system to outer foredeep and foreland ramp settings. Primary autochthonous evaporites, consisting of thick-bedded, cyclically stacked selenites have been recognized in the subsurface of the present-day Adriatic offshore in narrow, semi-closed, Late Miocene basins, formed in an extensional regime within the foreland ramp. Evaporites are cut by an erosional surface characterized by a strong seismic reflector, corresponding to the widespread intra-Messinian unconformity (MES) that can be traced basinward into a correlative conformity at the base of a resedimented evaporites complex observed in outcropping successions, where pre-evaporitic deposits have a deep-water character. Similarly to the inner and central foredeep areas, post-evaporitic deposits above the MES can be split in two units separated by a minor unconformity. The Miocene/Pliocene boundary consists of a sharp transition to relatively deep-marine deposits; a notable exception occurs in the Conero Riviera, where this boundary is characterized by a biocalcarenitic lithosome (Trave calcarenites) with a thoroughly bioturbated and reddish horizon at top, here interpreted as a firmground, directly overlain by Lower Pliocene (MPl3 biozone) clays and thin-bedded turbiditic sandstones. This suggests a Late Messinian embryonic growth of the Mt. Conero structure as an intrabasinal high related to the compressional reactivation of former extensional faults. The observed erosional features associated to the MES (canyons, gullies, slump scars) probably formed in sub-aqueous settings over a prolonged time interval encompassing a large part of the Early Pliocene. During this period the almost sediment-starved foreland ramp acted as a transfer zone for small-volume gravity flows feeding the main foredeep from minor lateral sediment sources.

Keywords: Messinian salinity crisis, Northern Apennines, Foreland basins