Evidenze di tettonica distensiva Plio-Pleistocenica al margine orientale della Fossa Bradanica: L'horst di Zagarella

Abstract

The Plio-Pleistocene activity of tensional or transtensional faults along the eastern margin of the Bradanic trough (southern part of the Apennines foredeep) is pointed out. A complex (partially buried) NW-SE strike horst-and-graben structure is also recognized. The most important structural element is the "Zagarella Horsf, separated from the "Matera Horst" by the "Garramma Graben". The Zagarella Horst is located along the Bradano river and the Gravina di Picciano stream, both of which cut the Plio-Pleistocene deposits and the Cretaceous substratum of the Bradanic trough. The horst is 12 km long and up to 4 km wide and it is bounded by N40°÷50°W strike faults; its shape is very complicated due to N70°÷h80°W and N30°÷40°E strike faults. The Zagarella Horst partly developed in the Cretaceous substratum ("Calcare di Altamura" Formation) of the foredeep, before the deposition of the lower Bradanic trough units ("Calcarenite di Gravina" and "Argille subappennine" Formations, Plio-Pleistocene in age). Structural, litho-stratigraphic, sedimentologic and geomorphologic features show that tectonic activity developed also during (and probably after) the deposition of the "Calcarenite di Gravina" and "Argille subappennine" Formations. Locally the Upper Pliocene-Lower Pleistocene age of these units is defined on the basis of the Foraminifera and calcareous nannofossil analyses carried out on several samples collected just near the contact between the units; the nannofossil assemblages allow an accurate biozone-determination for this stratigraphic interval: Dictyococcites productus - "large" Gephyrocapsa zones. Finally, the recognized tectonic trend and the dimension of the Zagarella Horst are similar to those of buried structures ("Pomarico High" "Grottole High") occurring in the axial zone of the foredeep (SW of the Zagarella Horst) on the regional monocline ramp, characterized by southwestward dipping steps.