Subsurface basin analysis of fault-controlled turbidite system in Bradano Trough, southern Adriatic Foredeep, Italy

Subsurface data (seismic lines, wireline logs, cores, and drill cuttings) from intensive hydrocarbon exploration in the Pliocene-Pleistocene Bradano Trough were used in performing a three-dimensional basin analysis and in reconstructing the time-space evolution of the basin. A middle Pliocene sedimentary system characterizes the hydrocarbon-bearing sands of the major gas field of the Bradano Trough, the Candela field. This system includes two phases of deposition in a migrating basin. The first phase of deposition, caused by strong subsidence due to continental shortening, was accompanied by the influx of large quantities of clastic material. The outer part of the basin was filled with turbidites; the inner part is characterized by olistostromes (formed by gravitational sliding along the slope), which progressively prograded basinward. The fault-controlled bottom physiography acted as a channel for turbidity currents that deposited elongate bodies between the inner slope and the compressional faults growing outward. The coarser grained material, deposited in the trough by currents, onlapped the upthrown flanks of the faults, thus providing potential hydrocarbon traps. Turbidity currents carrying the finer grained material flowed over the fault scarps. In the meantime, other external faults were activated. As the turbidity currents spilled over the former faults, deposition expanded laterally. Continuous basin subsidence kept pace with deposition, and superposed wedges accumulated to a thickness of at least 1,000 m (3,281 ft). The second phase of deposition is characterized by a decreasing rate of subsidence. Currents filled a flat trough with tabular turbidites, which accreted longitudinally. The sand bodies became more muddy-clayey in the distal southern part of the basin. At this point, the system consisted of a major fan-shaped sand body upcurrent; downcurrent, partially overlapping lobate sand bodies with large lobe fringes migrated transversally. The entire fan system was later blanketed with mud and finally with a transient carbonate platform, which preceded a new cycle of subsidence.