Abstract

Completion of the new Geological Map of Italy (CARG 50,000 project of the Italian Geological Survey) has involved a systematic and detailed survey of key sectors of the southern Apennines. The acquisition of new data on the terrigenous units of the Cilento, thanks to a 1:10,000 scale survey, the study of key sections and numerous biostratigraphic analyses, has led to new stratigraphical and structural interpretations. The Mesozoic-Palaeogene carbonate succession and its mostly Miocene terrigenous cover are overthrust by at least three tectonic units comprising terrigenous strata. The uppermost terrigenous unit corresponds to the North-Calabrian Unit of Bonardi et alii (1988b) and consists of pelagic and basinal facies which can be correlated with the upper portion of the Crete Nere Formation, with the Saraceno Formation and with the Cannicchio Sandstones. The age of the stratigraphic succession can be referred to the Bartonian-Burdigalian. This tectonic unit also corresponds to the Cilento Base Unit of Mauro & Schiattarella (1988). The intermediate terrigenous unit corresponds to the Castelnuovo Cilento Unit of Cammarosano et alii (2000) and is characterised by facies very similar to those of North-Calabrian Unit, which, from the bottom to the top, are the Genesio Shales, the T. Trenico Marls and Calcarenites, and the Pianelli Sandstones. The age of this succession is also Bartonian-Burdigalian. The unit corresponds to those described in the literature as "Affinita Sicilide Complex" or "parasicilides" Auctt.. The lower terrigenous unit consists of pelagic and basinal facies correlated with the Tempa Rossa Varicoloured Clays and the Mt. Sant'Arcangelo Formation of the Corleto-Perticara succession. This unit is ascribed to the Sicilide Unit Auctt. and the age of the stratigraphic succession is also Eocene-Early Miocene. The marked similarities in facies and ages suggest that the successions of the North-Calabrian and Castelnuovo Cilento units were deposited in the same basin, and that their present division is essentially due to tectonic processes. These tectonic units probably began to develop in the Late Burdigalian. A succession of piggyback basin deposits of Early Langhian to Early Tortonian age and pertaining to the Cilento Group lies unconformably above the upper terrigenous unit. This succession is in turn unconformably overlain by the Mt. Sacro Conglomerates, which are therefore no older than the Middle Tortonian. The results of field surveys and regional-scale studies highlighted the need for a lithostratigraphic revision of the Cilento Group, here originally consisting of the Pollica and St. Mauro Formations Auctt., each comprising 2 members. The members of the Pollica Formation Auctt. (the Cannicchio and Pollica members) are now considered formations in their own right, and are respectively named "Cannicchio Sandstones" and "Pollica Sandstones". The Cannicchio Sandstones are in continuity with the Saraceno Formation, whereas their upper contact with the Pollica Sandstones is characterised by a marked change in facies and a likely biostratigraphical lacuna. The upper stratigraphic succession of the North-Calabrian unit in the Cilento therefore consists of Cannicchio Sandstones, whereas the Cilento Group consists of the Pollica Sandstones and San Mauro Formation. The San Mauro Formation contains numerous key horizons, some of which are here described for the first time; however, we believe that the rapid variation in facies does not justify, on a regional scale and according to classical lithostratigraphic criteria, its subdivision into two members as proposed by previous studies. Based on the age of the younger terrains at the top of the carbonate unit (the Serravallian-Tortonian Piaggine Sandstones; Castellano et alii, 1997), the emplacement of the terrigenous units above the carbonates occurred no earlier than the Late Tortonian. The main structures which involve the terrigenous flysch and characterise the tectonic edifice are the low-angle thrust surfaces that delimit the tectonic units. These were newly-deformed by transcurrent and extensional faults, with orientation NW-SE to E-W, probably formed in the Pliocene and Pleistocene. The Cilento Group and Cannicchio Sandstones are often detached from the substratum through low-angle extensional faults verging towards the Tyrrhenian Sea. These surfaces also dislocate the thrust planes of the tectonic units, and are compatible with the transtensional faults bordering the southern slopes of the carbonate ranges; this decollement probably also developed during the Plio-Pleistocene extensional phases.

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