Abstract

Geological mapping and detailed biostratigraphic analysis of the shallow-water carbonate successions of the Mt. Fellino Ridge (Campania Appennines), has led to the recognition of a km-scale overturned anticline characterized by tight geometry and associated with a NW-verging thrust which brought Jurassic over Cretaceous successions. The overturned fold is a N50-70 degrees -trending non-cylindrical structure, whereas the thrust is refolded by a N100-120 degrees -trending open anticline. Such a structure is recognizable also toward the south-east not far from the investigated area (i.e. Nola-Lauro Ridge). The angle between the two fold hinges is 40 degrees -60 degrees , as shown by geological mapping. The geometric reconstruction of the geological structures out-cropping in the study area has been realized by means of two viable cross-sections (called AA' and BB' in fig. 6). The construction of the geological sections has been carried out considering the thickness obtained by the stratigraphic analysis of carbonate successions outcropping along the Mt. Fellino Ridge (fig. 2). Further, the stratigraphic analysis of several carbonate successions outcropping both along the Mt. Fellino Ridge and in the wider area of the Avella Mts-Nola-Lauro Ridge allowed five chronostratigraphic units to be characterized, showing different litho-sedimentological features and biostratigraphic content. In particular, the five chronostratigraphic Mesozoic units are, from bottom to top: - Lias: about 700 m of limestones and dolomite containing mainly Palaeodasycladus mediterraneus (Pia), Orbitopsella praecursor (Guembel) and, in the upper part, large spathic shells of bivalves of the "Lithiotis facies" Auct.; - Dogger: about 400 m of oolitic and pseudo-oolitic limestones and subordinate dolomite, containing mainly Valvulina lugeoni Septfontaine, Mesoendothyra croatica Gusic, the dasycladaceans Selliporella donzellii Sartoni & Crescenti, Pfenderina salernitana Sartoni & Crescenti, Pfenderella arabica Redmond, Satorina apuliensis Fourcade & Chorowics; - Malm: about 400-450 of limestones which consist of calcilutites and rarely of calcarenites, sometimes oolitic, containing Cladocoropsis mirabilis Felix, Kurnubia palastiniensis Henson, Valvulina lugeoni Septfontaine, Parurgonina caelinensis Cuvilier, Foury & Pignatti-Morano, Clypeina jurassica Favre, Salpingoporella annulata Carozzi and Campbelliella striata (Carozzi); - Lower Cretaceous (Neocomian-Albian): about 600 m of whitish limestones (from mudstones to grainstones) containing mainly Praechrysalidina infracretacea Luperto Sinni, Orbitolina (Mesorbitolina) texana (Roemer), Orbitolina (Mesorbitolina) parva Douglas, Cuneolina laurentii Sartoni & Crescenti, Cuneolina scarsellai De Castro, Sabaudia minuta (Hofker), Ovalveolina reicheli De Castro, Paracoskinolina tunesiana Peybernes, Neoiraqia insolita (Decrouez & Moullade), dasycladacean algae among which, in the lower part of the succession, Salpingoporella cemi Radoicic, Salpingoporella annulata Carozzi, Praturlonella danilovae (Radoicic), and in the upper part Salpingoporella dinarica Radoicic and Salpingoporella turgida Radoidid. - Upper Cretaceous (Cenomanian-Senonian): about 650 m of limestones (mainly mudstones-wackestones), sometimes loferitic and stromatolitic, with rare intercalations of dolomites in the lower portion, and greenish marls. This interval contains Sellialveolina viallii Colalongo, Pseudorhapydionina dubia (De Castro), Biplanata peneropliformis Hamaoui & Saint-Marc, Nezzazata simplex Omara, Biconcava bentori Hamaoui & Saint-Marc, Cisalve-olina fraasi (Guembel), Pseudolituonella reicheli Marie, Chrysalidina gradata D'Orbigny, Cuneolina pavonia parva Henson, Nezzazatinella cf. aegyptiaca (Said & Kenawy), Dicyclina schlumbergeri Munter-Chalmas, Accordiella conica Farinacci, Moncharmontia apenninica (De Castro), Scandonea samnitica De Castro. Among the macrofossils fragments and shells of Rudists are abundant. The trace of the cross-section AA' is N120 degrees -trending (i.e. sub-orthogonal to the first phase fold axis), whereas the trace of the cross-section BB' is N20 degrees (i.e. perpendicular to the second phase fold axis). In the geological section AA', one can observe the N50-70 degrees -trending overturned fold with a tight geometry (Fleuty, 1964), in the hangingwall of the thrust. Moreover, a splay thrust cuts the Malm deposits, causing the imbrication of two different slices. The tight geometry of the plicative structure could be linked to the evolution of a previous blind-thrust into a breakthrough thrust (Suppe & Medwedeff, 1990). In the geological section BB' is possible to detect the refolding of the first phase fold by a N100-120 degrees -trending open fold.

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