Post-Variscan Verrucano-like deposits in Italy, and the onset of the alpine tectono-sedimentary cycle

摘要: Abstract In the Italian regions stratigraphic successions of Verrucano s.l. consist essentially continental alluvial plain to coastal-neritic siliciclastic redbeds, deposited at different times in Alps (Mid? –Late Permian), Northern Apennines (Mid?–Late Triassic p.p., locally Southern Tuscany also followed by Jurassic Pseudoverrucano Complex) and ‘Calabro-Peloritani Arc’ (Mid?-Late Triassic, exceptionally reaching earliest Jurassic), whereas Sardinia recognition succession is still a topic discussion. The most typical metamorphic lithofacies, Pisan Mts. Tuscany, represented s.s. conglomerates breccias, including quartz clasts minor volcanic lithics, grading laterally vertically quartzitic sandstones pelites. Pisa Symposium term ‘Verrucano’ was suggested only for those detrital deposits laid down, Alpine-Mediterranean areas, after final act Variscan orogeny, use local geographical names. Consequently, terms ‘Verrucano Toscano’, Lombardo’, Brianconnais’ other similar deposits, being linked belt, were generally accepted. ages these ‘Verrucanos’, since they are devoid fossils, can be interpreted indirectly. Lombardo central recently ascribed Mid? Permian interval (Late Guadalupian?–Lopingian p.p.), taking into account that connected Val Gardena Sandstones nearby Venetian region interdigitated with Late Bellerophon Fm. Brianconnais Maritime again mostly related Permian, covered Lower alluvial-deltaic quartzites. easternmost Ligurian Apennines, near La Spezia, Mesozoic section Punta Bianca, which begins fluvial conglomerate, transgressive unconformable on metamorphosed Paleozoic Basement, composed two main cycles, upper one correlates overlying Mt. Serra Quartzites, latter yielding Carnian pelecypods vertebrate footprints. from Mid-Tuscan Ridge Leoni Argentario promontory delimited above Tocchi Formation presumably developed Middle (Late? Ladinian) up (Carnian) times; contrast, Calabria (e.g. Longobucco unit Sila Grande) Sicily Taormina-Longi Unit Peloritani Mts.) so-called (Pseudo-) pertain capped basal succession, determined discovery an Early Hettangian palynoflora. All over their distribution above-mentioned Alpine Verrucanos rest, through unconformity marked gap varying imprecise duration, volcanic/sedimentary or directly underlying basement. Schematically, post-Variscan Italy subdivided three tectono-sedimentary megacycles: first ranges Carboniferous to, slightly second while third cycle Mid?-Late attaining some parts Arc’. After transtensional tectonics many strike-slip basins (cycle I), widespread geodynamic reorganization (‘Mid-Permian Episode’ Auctt.) led development dominant extensional regime, birth tectonic plates oceans (Neotethys, Meliata-Maliak, etc.) between Africa Europe. erosion relief ingression S-E sectors shallow-marine branches Neotethys II). major rifting events Ligurian-Piedmont Ocean started during Middle–Late eastern opening Atlantic Ocean. These gave rise Adria Europe-Corsica-Sardinia conjugate passive margins, characterized asymmetric structural sedimentary evolution. this geological context, Verrucano-like as discontinuous asynchronous ‘tectofacies’ marks dismantling SE border chain.