Middle-Late Permian sporomorphs from the Farma Formation (Monticiano-Roccastrada Ridge, southern Tuscany); new constraints for the tectono-sedimentary history of the Tuscan domain

This paper is mainly focused on the first evidence of Permian sporomorphs in the metamorphic Farma Fm. exposed in the Monticiano-Roccastrada Ridge (southern Tuscany), and their implications on the tectono-sedimentary history of the Tuscan Domain, to which this unit pertains. Middle-Late Permian microfloristic assemblages were recovered in the Contrada Carpineta area of the Farma Valley, which represents a key-area for studying the stratigraphy and structural evolution of the metamorphic basement of the Northern Apennines. There, in order to better constrain the depositional setting and post-depositional history of the Farma Fm., a 21 m-thick section (Contrada Carpineta section), which typifies the upper part of this unit, has, P been logged, sampled and characterised in terms of sedimentological-structural features and organic matter content. Specifically, the Farma Fm. typified by the Contrada Carpineta section consists of parallel-sided grey sandstones typically grading to dark-grey/black mudstones. Sandstones are sharp-based, locally with small-scale scour-and-fill structures, sole structures such as groove-, flute- and tool-casts and occasional loaded bases. Tb-abe, T-ade and T-abce Bouma-type sequences have been recognised, with the T-a division always well developed and commonly thicker than T-b plus T, divisions. The total organic matter content is high and only of continental origin. These deposits were first affected by syn-sedimentary normal faults and then by dominant contractional deformations during the Tertiary Northern Apennines tectogenesis. To date, the Farma Fm. has been interpreted as a Moscovian flysch emplaced during the final consolidation of the Variscan orogen. The Moscovian age was based on a fusulinids assemblage found in the silty matrix and in the clasts of a debris-flow conglomerate (olistostrome Auct.) exposed in the Contrada Carpineta area, approximately few decametres stratigraphically below the measured section. Nevertheless, the absence in the hemipelagic divisions of the turbidite beds of other microfauna than the Middle-Late Permian microfloristic assemblages, and the presence in the carbonate clasts of the same fusulinids found in the silty matrix, all suggest the latter being reworked and meaningless in determining the Farma Fin. age. Moreover, calcite veins and stylolites affecting the carbonate clasts strongly support this inference. The data presented herein imply a different palaeogeographic scenario for the Farma Fm., suggesting that it emplaced in the Middle-Late Permian mainly by unchannelled, relatively dense turbidity flows within an extensional (transtensional?) basin.