LATE PALAEOZOIC SEDIMENTARY BASIN FORMATION AND INVERSION IN TUSCANY, ITALY

Relics of late Palaeozoic marine basin fragments form constituents of the Mid Tuscan Ridge, an arcuate belt consisting of discretely uplifted, low to medium grade metamorphic core complexes, present at the external margin of the North Tyrrhenian backarc basin. Details of the complex Alpine deformation history of these Late Palaeozoic basin fragments - starting with Late Triassic to Early Cretaceous passive margin subsidence, Late Cretaceous to Early Tertiary subduction related tectonic burial, east vergent accretion at and obduction as constituents of the Northern Apennines fold-and-thrust belt onto the continental margin of the Adriatic Microplate, Middle to Late Tertiary exhumation from mid-crustal level and finally Late Tertiary to Quarternary segmentation of the belt - are given in Bonciani et al. ( Boll. Soc. Geol. It. 3: 103-118; 2005) and Engelbrecht (Geol. J. 43: 279-305; 2008).

In an early M-Jurassic palaeotectonic reconstruction of the W-Mediterranean area, Roeder & Scandone (In: A continent revealed. Eds.: Blundell et al. 1992: 213-214) point out that Late Hercynian extensional structures influenced style and development of the subsequent Alpine oroclines. According to own studies, it is postulated that second-order sequence stratigraphic cycles of Tuscan late Palaeozoic units deposited in an extensional or transtensional setting (Basin Res. 23/3: 257-290; 2011) - probably in a pre-Ligurian failed rift, situated between the mainlands Corsosardinia (NW) and African Promontory (SE) - , which developed by gravitative collapse of the thickened Palaeoadriatic wedge at the South Hercynian suture.

The Tuscan Late Palaeozoic units start with condensed, dysoxic pelagites of a starved, moderately deep basin of Devonian to early Carboniferous age. Subsequent to partial basin inversion in the Tournaisian, the units above developed as Middle to Late Carboniferous downlapping highstand systems tracts consisting of thick, predominantly siliciclastic shelf, slope and basin margin sediments, which indicate a proximality trend towards NW. During the Permian, the units were overlain by offlapping inner shelf - littoral siliciclastics. Late Permian to Middle Triassic tectonic uplift caused basin inversion, subaerial exposure of upper parts of the basin fill and deposition of the terrestrial Verrucano Group at the base of the Alpine cycle.