EVIDENZE DI NEOTETTONICA (PLIOCENE MEDIO - PLEISTOCENE SUPERIORE) NEL SETTORE OCCIDENTALE DEL PROMONTORIO DEL GARGANO (ITALIA MERIDIONALE)

Abstract

: L. Spalluto & M. Moretti: Neotectonics of the western sector of the Gargano Promontory (Plio-Pleistocene, southern Italy).
(IT ISSN 0394-3356, 2005).
The analysed area is located in the western part of the Gargano Promontory (northern emerged sector of the Apulian foreland,
southern Italy): this area comprises the Mesozoic and Cenozoic carbonate units of the Apulian foreland and the northern sector of the
Plio-Pleistocene Bradanic Trough.
Many Authors mention the western portion of the Gargano area as an important seismogenic zone, which have suffered some
medium- to high-magnitude historical and instrumentally-recorded earthquakes. In this area, some of the faults with a suggested
recent to present-day activity have probably been active since Mesozoic time and it is often very hard to establish the age of the observed displacements. On the basis of the available stratigraphic and structural data, some Authors have distinguished at least two different tectonic phases in late Cretaceous and Miocene times. Moreover, they mentioned a Plio-Pleistocene tectonic activity as a successive single tectonic phase. According to the regional data, during the Plio-Pleistocene, this area (and the entire Apulian foreland) was subject to two different tectonic phases: the first one (Pliocene to lower Pleistocene in age) was related with the active subduction of the Apulian foreland beneath the southern Apenninic Chain; during this phase, the Apulian foreland recorded an high subsidence rate (about 2 mm/yr); from the Sicilian to present-day, the entire Apulian foreland was subject to a moderate uplift (less than 0,5 mm/yr). It is very important to distinguish the structural elements of the subsidence stage from them associated with the uplift since only the last ones are directly related with the present-day active tectonics.
During the geologic survey for the CARG project (San Severo 1:50.000 sheet) we have found much evidence of Neotectonics in this
area and the aim of this work is to show the stratigraphically–recorded tectonic activity during the Plio-Pleistocene. In the Apricena
area (Masseria Zingari locality), some extensional features have been observed: they are represented by narrow grabens (few tens of
meters in length) which cut Miocene limestones and are transferred to the overlying Calcarenite di Gravina Formation (late Pliocene in
age). The synsedimentary activity of these grabens is documented by the presence of narrow folds and by the variations in thickness of the Calcarenite di Gravina Formation. The maximum displacement is always less than 5 m and it decreases upwards. Along the cuts of the older and inactive railway in the same area, a complex distensive fault occurs in the Calcarenite di Gravina Formation (and in its
Miocene substrate): folds and growth structures involve the overlying calcarenites along the primary and secondary fault planes. The
last evidence of the subsidence phase is given by large-scale neptunian dykes (up to 5 m in height): they are restricted at the contact
between Miocene limestones and the overlying Calcarenite di Gravina Formation and are represented by large conical fractures in the
Miocene substratum which are filled by the overlying Pliocene calcarenites; that is a record of synsedimentary extensional tectonic
activity since the overlying unit suffers soft-sediment deformation and many decimetric beds are downward-projected and/or irregularly folded during the extensional brittle deformation of the substratum.
The middle- to upper-Pleistocene uplift of this area is chiefly documented by the presence of marine and continental terraced deposits that crop out from 140 m a.s.l. to 20 m a. s. l. The documentation of the discrete faults associated with this uplift phase is often very
difficult because there are not extensive and continuous outcrops of the middle-upper Pleistocene units. Nevertheless, in a quarry
located to the NW of Apricena Town we have found an extensional fault that cuts the entire thickness of a marine terraced unit (Colle
degli Ulivi Subsynthem). The fault is subvertical, E-W oriented and the maximum vertical displacement is up to 20 m in height. Similar
tectonic features have been reported in the younger San Severo Subsynthem.