ORIGIN AND DEFORMATION OF THE NEOGENE RECENT MAGHREBIAN FOREDEEP AT THE GELA NAPPE, SE SICILY

SE Sicily contains one of the few exposures of orogenic foreland to the Maghrebian-Apennine orogenic system in the central Mediterranean. Here the African foreland is represented by the Hyblean plateau, adjacent to the frontal thrust structures of the Maghrebian chain. These structures include the disrupted foredeeps to earlier parts of the thrust system. One of these, the Gela nappe, is a major structure composed of late Oligocene to early Pliocene sediments emplaced onto Pliocene-Pleistocene rocks of the buried foreland. This paper presents a correlation of late Miocene stratigraphic units between the foreland and the foredeep basin. Abrupt lithological and thickness variations of these units suggest that the foredeep basin was limited towards the foreland by normal faults. In the hinterland these foredeep sediments lap back onto previously emplaced thrust sheets, including the far-travelled units of 'Numidian flysch'. The precursor Oligocene-Serravallian foredeep may also have been controlled by normal faulting. Compressional tectonics are reflected in folding and thrusting which post-dates deposition of lower Pliocene chalks (Trubi Formation), although minor folding and erosion preceded this unit. Larger thrusts repeat the basin stratigraphy and carry it out onto the adjacent foreland. A minimum of 8 km shortening since Messinian times can be demonstrated although a more realistic figure is c. 25 km, at a time-averaged rate of c. 0.5 cm/a-1. The stratigraphic relationships on the foredeep sedimentary sequences may provide analogues for offshore areas of the thrust belt.