DEPOSITIONAL AND STRUCTURAL DYNAMICS OF THE PLIOCENE PERI-ADRIATIC FOREDEEP.,NE ITALY

Seismic analyses and detailed wefl-io^ correlations have been used to define the depositional patterns and the relative timing of thrust movements in the highly mobile Peri-Adriatic Foredeep, a gas-bearing basin ofPliocene age in NE Italy. Due lo the high rates ofʹsedimentation and subsidence, up to 8,000m of mostly deep-water elastics were deposited in the foredeep in the Marche-Abruzzo area during the Pliocene-early Pleistocene. Three phases of foredeep evolution can be recognised. In the first phase, during which there was little structural activity, a sandy turhidite system of regional dimensions (the Cellino Turhidite System) developed on aflat, stable substratum. Discrete sand-bodies belonging to this system can he traced over distances of up to 80 km. This turbidile system is a key unit in the analysis ofthe foredeep. The rapid deposition and burial f)f organicrich sediments favoured the generation ofhiogenic gas. The second phase of foredeep evolution coincided with the onset of structural deformation. Sediments are mainly deep-marine shales and minor turhidite sandslones, which were deposited during a period of almost continuous tectonic activity. A major eastward migration of the deep-marine depocentre then occurred, in the study area, this phase is represented by a series of closely-spaced local unconformilies which, can be correlated eastwards with a major late Pliocene turbidile system. The high frequency of the unconformities is a distinctive feature of this interval, The third phase was characterised by thrusting in the eastern part ofthe foredeep and by the development of aʹpiggy-hack basin. During this phase, shallow-water, coarsegrained deltas replaced the deep-water turhidite systems. Accommodation space for the coarse-grained deltas was provided to begin with by rapid, subsidence. The progressive decrease in accommodation resulted in delta progradation eastwards and ultimately in the infilling ofthe foredcep.