Carta delle principali unità cinematiche dell'Appennino meridionale. Nota illustrativa

Glauco Bonardi(*), Sabatino Ciarcia(*), Silvio Di Nocera(*), Fabio Matano(*), Italo Sgrosso(*) & Mario Torre(*)(**)
(*) Dipartimento di Scienze della Terra, Università degli Studi di Napoli «Federico II», Largo S. Marcellino, 10 - 80138 Napoli. E-mail: bonardi@unina.it; sciarcia@unina.it; sildinoc@unina.it; matano@unina.it; itasgros@unina.it; martorre@unina.it (**) Corresponding author.

The southern Apennine is the segment of the circum-Mediterranean orogenic system between the central Apennine to the North and the Calabria-Peloritani arc to the South, bounded by the Ortona-Roccamonfina and the Sangineto tectonic lines respectively. It consists in a salient north-east verging thrust and fold belt, interposed between the back-arc Tyrrhenian basin to the West and the undeformed Apulian-Adriatic foreland to the East. Its present structural setting is the result both of mainly compressive tectonic events, related to the subduction followed by the roll-back of the Adria plate, and of the extensional tectonics related to the opening, since the late Miocene, of the Tyrrhenian sea (MALINVERNO & RYAN, 1986; PATACCA & SCANDONE, 1989; DOGLIONI, 1991). Aiming to point out the space-time migration of the deformation, a geological map of the area between the Ortona-Roccamonfina tectonic line to the North and the Maratea-Val d'Agri alignment to the South showing the possible kinematic units of the southern Apennine has been elaborated. The above area includes the whole Campania and part, of Lucania, Molise and Puglia regions. A kinematic unit can be defined as a stack of tectonic units (or even only one), eventually covered with thrust top deposits, that piled up during the same tectonic event and afterwards behaved like an unique geological body in respect to more external areas. In the frame of the regional geological setting, some well established sedimentologic and stratigraphic characteristics have been assumed as reference criteria for grouping together some tectonic units in a kinematic unit: (i) the beginning and the gradual increase up to prevail of the immature siliciclastic sedimentation marks the depocentral phase in the evolution of a foredeep basin; (ii) the fore-deep deposits rest conformably on the older successions, as the angular unconformity due to the progressive flexuration of the foreland is not appreciable at a local scale; (iii) the compressive tectonic event, immediately following the foredeep stage, involves a wide portion of the flexured foreland, that is accreted to the nappe stack of the chain. In each tectonic unit this tectonic event is chronologically constrained between the age of its conformable foredeep deposits and by the age of the unconformable thrust-top deposits sealing the contacts among different tectonic units. However this simple relationships may be masked by later compressive and extensional tectonic events, as well as by transcurrent tectonics. The possible presence of younger deposits resting unconformable on the already deformed substratum and related thrust top deposits is a constraint to the age of these later tectonic events. The map has been elaborated tacking into account, besides the numerous and sometimes contrasting data of the literature, even data, often still unpublished, from the surveying of the new geologic map of Italy 1:50.000. The kinematic units, marked with capital letters (A to G from the older to the younger) group together tectonic units, derived from paleogeographic domains that have been affected by the first tectogenetic event in the same chronological interval. In each kinematic unit with lower case have been distinguished: a) the pre-orogenic succession; b) the foredeep stage deposits; c, d) the thrust-top basin deposits. The kinematic unit A includes several tectonic units (Liguride and Sicilide Complexes Auct.), mostly ocean derived, piled up to form accretionary wedge during the Early Miocene, following the closure of an oceanic branch (Lucanian Ocean) of the Neothetys realm. It is subdivided into: a) Jurassic to Aquitanian pre-orogenic successions (the ophiolite basement of some of them crops only SE of the mapped area); b) the Aquitanian-Burdigalian foredeep deposits; c) the upper Burdigalian/Langhian - Serravallian thrust-top deposits (Cilento Group, AMORE et alii, 1988; BONARDI et alii, 1988b; AMORE et alii, 2005); d) the Tortonian further thrust-top deposits. The kinematic unit B groups the units of the chain involved by the orogenic transport during the Serravallian-lower Tortonian. It is formed by: a) the upper Triassic-lower Miocene pre-orogenic successions, of the M. Bulgheria SCANDONE et alii, 1964) and Alburno-Cervati Units (SCANDONE, 1972; BONARDI et alii, 1988a); b) the Langhian foredeep deposits; c) the middle-upper Tortonian thrust-top deposits. The kinematic unit C groups the units of the chain involved by the orogenic transport during the lower-middle Tortonian; in particular they are distinguished in: a) the upper Trias-Langhian pre-orogenic successions, forming the Picentini-Penisola sorrentina, Taburno-M. Marzano-Monti della Maddalena and the Capri-M. Monna-M. Foraporta Units (BONARDI et alii, 1988a; SGROSSO, 1998); b) the Serravallian foredeep deposits; c) the middle-upper (?) Tortonian thrust-top deposits. The kinematic unit D groups the units of the chain involved by the orogenic transport during the middle-upper Tortonian; in particular they are distinguished in: a) the lower Triassic-Langhian pre-orogenic succession belonging to Lagonegro II-Frigento Unit (SCANDONE, 1967, 1972; DI NOCERA et alii, 2002) and to Monte Croce Unit (Scandone & Sgrosso, 1974) and that upper Triassic-Cretaceous of the «Lagonegro I» Unit (Scandone, 1967, 1972); b) the Serravallian-lower Tortonian foredeep deposits; c) the upper Tortonian thrust-top deposits; d) the upper Tortonian-lower Messinian further thrust-top deposits. The kinematic unit E groups the units of the chain involved by the orogenic transport between the upper Tortonian and the lower Messinian; in particular in this unit are distinguished: a) the Trias-middle Tortonian pre-orogenic successions, referred to the Matese-M. Maggiore-M. Camposauro Unit (BONARDI et alii, 1988a; SGROSSO, 1998); b) the middle-upper Tortonian foredeep deposits; c) the lower Messinian thrust-top deposits; d) the upper Messinian further thrust-top deposits. The kinematic unit F groups the units of the chain involved by the orogenic transport during the upper Messinian; in this unit are distinguished: a) the Lias-lower Messinian pre-orogenic successions of the north-western Matese Unit (SGROSSO, 1996, 1998), the Frosolone Unit (SELLI, 1957) and the Daunia Unit (Dazzaro et alii, 1988); b) the Messinian foredeep deposits; c) the upper Messinian -lowermost Pliocene thrust-top deposits. The kinematic unit G groups the units of the chain involved by the orogenic transport during the upper? part of the lower Pliocene; in this unit are distinguished: a) the Tortonian-Messinian pre-orogenic successions of the Vallone del Toro Unit (BASSO et alii, 2002); foredeep deposits are not recognizable; c) thrust-top deposits of the upper part of the lower Pliocene; d) the middle-upper Pliocene further thrust-top deposits. In several tectonic units, elements useful to establish the age of the first deformation, i.e. the foredeep siliciclastic deposits or the immediately following unconformable deposits, are missing, therefore their inclusion in one or another of the kinematic units is matter of debate. Also in this case the geometrical position and the regional framework can be used to formulate reliable hypotheses. The map is aimed to focalize the main open problems and stimulate the discussion about them. The analysis of the areal distribution of the kinematic units leads to some general considerations. On a small scale an irregular spatial distribution of the kinematic units is recognized. In the segment of chain represented by the map, the more internal tectonic units widely outcrop in the south-eastern sector and are missing northward even on the Tyrrhenian side. On the contrary the more external units, crop out only in the north-western sector, whereas in the south-eastern one they have not been recognized even by sub-surface data. This irregularity could be linked to original paleogeographic irregularities or even be the result of Plio-Pleistocene second order archings and of transcurrent faults that cut transversally the chain, but geodynamic causes still not clarified cannot be excluded. The elaboration of a kinematic map is an essential but not sufficient step for the palaeogeographic reconstructions that need further data and informations on the distribution of the units at depth. The difficulty in the palaeogeografic reconstructions is also due to the fact that the chain is at present constituted only by a few and unevenly distributed fragments of the original domains.

Kinematic units, tectono-sedimentary evolution, regional geology, southern Apennines.