Tectono-sedimentary evolution of the Amantea basin, Western Calabria. Evoluzione tettono-sedimentaria del Bacino di Amantea, Calabria occidentale

The Amantea basin (DI NOCERA et alii, 1974; ORTOLANI et alii,1979; COLELLA, 1995) is one of many Neogene basins along the Tyrrhenian margin of Calabria. The onset of the basin occurred inresponse to tectonic subsidence induced by extensional faulting during the early Tortonian. The sedimentary infill has been subdivided into five main depositional units, bounded by stratigraphic discontinuities. The first unit is strongly influenced by a combination of tectonic activity and eustatic rise in sea level; the structural architecture and sedimentary evolution of the basin is time-transgressive from alluvial fan to submarine fan deltas. The second unit overlies the first with an angular unconformity, due to the fall of sea level and synsedimentary activity of normal faults. This unit is constituted by an alluvial fan overlain by a carbonate platform depositional system. During the deposition of upper part of second unit in the late Tortonian, the basin was subjected to contractional deformation with the development of fault related folds. The sedimentation and the architecture of the basin were abruptly influenced by this tectonic change. As a consequence, sedimentary sequences developed numerous unconformities, related with the growth of anticlinal folds. At the same time, a new sea level rise caused the drowning of the basinal area as well as the subsequent transgression over adjacent continental zones. Local emergence of basin-fill, caused by growth of anticlinal structures, produced intrabasinal sediments, and the deposition of a coarse-grained fan at the base of the third depositional unit. The fourth depositional unit is represented by a thin evaporitic succession which lies with an angular unconformity over underlying sediments and bedrock. These facies associations can be explained by the drop in sea level accompanied by structural highs related to growth of the folds (BUTLER & GRASSO, 1993). Thrust activity continued until early-middle Pliocene (PERRI, 1996-1997), probably testifying the last contractional event of Calabrian Arc thrust sheet, when the deformation began to be characterized by the development of NW-SE trending shear zones. The uplift of the basin probably occurred at that time, and continued through the Pleistocene. This event is testified by marine sediments, described as the fifth depositional unit, lying at varied topographic levels (SORRISO VALVO & SYLVESTER, 1993). The last deformation phase, characterized by extensional fault systems (MATTEI et alii, 1999) dipping toward Tyrrhenian Sea, terminated the basin emergence, and represents the propagation of the Tyrrhenian back arc rift system on the western Calabrian margin.