Foredeep geometries at the front of the Apennines in the Ionian Sea (central Mediterranean)

Abstract

A new regional seismic section in the Ionian Sea across the Apennines belt and related foreland shows how the present foredeep geometry may be an example for interpreting discontinuous, tilted and deformed earlier basins now incorporated in the internal parts of the accretionary wedge. Onlap stratal terminations of the foredeep sediments on the foreland monocline may simulate downlap geometries once involved and tilted by back-thrusting. The geometry of the Ionian foredeep is controlled by the dip of the regional monocline, and internally by the variable dip and length of the limb of the external fold, which may be either foreland-verging or hinterland-verging. The generation of a new fold within the foredeep splits the basin into a new foredeep toward the foreland and a thrust-top basin toward the hinterland. The thrust-top basin dimension is primarily controlled by the distance between the two folds and related thrusts at its margins. The foredeep, in its overall history, is composed by a series of concave heterogeneous lenses, progressively displaced and piled up toward the foreland to the east. The formation of each sedimentary lens is controlled by the development of a new fold and the contemporaneous retreat of the regional monocline which creates new accommodation space. The complex 3D geometry of the Apennines foredeep mainly results from lateral variations of the latter parameters, as well as variations in sediment supply and eustasy.