Abstract

The Fortore and Daunia Units represent the more external units of the Apennines thrust belt and therefore their study is a key for interpreting the complex evolution of the outer sectors of this recent chain. New stratigraphic and structural data have been therefore collected from the Fortore Unit in the area between Foiano di Val Fortore and San Bartolomeo in Galdo (Southern Apennines, Italy). According most Authors, the Unit outcrops in the frontal part of the Southern Apennine chain between two major NW-SE regional thrust systems. The first forms the western boundary of the Fortore Unit against the overlying Sannio Unit, while the second forms the outer limits of the Fortore Unit on the Daunia Unit to the east. The aim of this paper is to provide new data on the deformation of the Fortore Unit and on the processes by which it took place, useful to rebuild the tectonic evolution of this important sector of the Southern Apennines. The results obtained show the presence of: (i) a previously unknown turbiditic succession on the top part of the Unit, informally defined in this work "Mt. Barbato Succession"; (ii) a complex deformation pattern characterized by an early deformation phase responsible for the developments of thrust faults and F <sub>1</sub> folds, the latter documented by a E-vergent quasi-recumbent regional fold, and by two late fold systems (F <sub>2a</sub> and F <sub>2b</sub> ) with decimetre to decametre-scale wavelengths and sub-orthogonal axial planes, whose interference give rise to a Type 0 to Type 1 "domes and basins" pattern (Ramsay, 1967) on the limbs of the F <sub>1</sub> folds; (iii) a NE-SW normal fault system accommodating a WNW-ESE stretching direction, displacing the structure previously formed. Moreover, based on detailed field mapping, a SW-NE cross section has been constructed. This has allowed us to outline the main structural features of the Vendemmia, Barbato and Toppo Clemente mountains. It is important to underline that we favor a Serravallian to medium Tortonian age for the Mt. Barbato Succession based on the Langhian age of the Numidian Quartzarenites Fm and the late Tortonian to Messinian age of the S. Bartolomeo Fm as quoted by previous Authors. Moreover we suggest that the deformation described, whose beginning is evidenced by the deposition of the first siliciclastic channelized deposits in the foredeep basin domain of the Fortore Unit, is not older than the middle Tortonian and evolved at least until the Messinian, the age of the top of the S. Bartolomeo Fm.

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