Use of palynology and thermal maturity in deformed geological units: A case study from the Permian succession in the Monte Leoni area (Middle Tuscan Ridge, inner Northern Apennines, Italy)

The reconstruction of the upper Palaeozoic sedimentary evolution of Western Mediterranean area is suffering for scarce age documentation of its stratigraphic units. This is also the consequence of the metamorphism and defor-mation they experienced during the Alpine tectonic events. Based on palynology and thermal maturity assess-ment, we contribute to this issue reporting biostratigraphic and sedimentological results in key-outcrops of the upper Palaeozoic successions of southern Tuscany (Italy), thus offering new data for the Palaeozoic units of the inner Northern Apennines, as well as for their palaeogeographic and palaeotectonic evolution predating the opening of the Alpine Neo-Tethys. This study is focused on the Falsacqua Formation mainly consisting of quartz-itic phyllite, sandstone and carbonate, representing the basal succession of two tectonic units exposed in the Middle Tuscan Ridge, and which age attribution was strongly debated in literature and referred either to late Carboniferous-early Permian or Devonian. Palynological data document the first finding of a microflora of middle-late Permian age adding key chronological constraints. This age assignment permits to correlate the Falsacqua Formation with the coeval deposits of southern Tuscany (i.e., Farma and Poggio al Carpino formations) and Elba Island (Rio Marina Formation) that are all characterized by a similar microfloral content. Optical thermal maturity index as Spore Colour Index is around 9 to 10 and suggests a T peak of about 300-350 degrees C while the Raman spectroscopy on carbonaceous material indicates a T peak around 375 degrees C for both tectonic units. These data provide new constraints for the maximum T values occurred during syn-collisional metamorphism devel-oped in this sector of the Northern Apennines.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study contributes to the reconstruction of the upper Palaeozoic sedimentary evolution of the Western Mediterranean area by providing biostratigraphic and sedimentological results based on palynology and thermal maturity assessment. The study focuses on the Falsacqua Formation in southern Tuscany, Italy, and establishes its age as middle-late Permian based on palynological data. The study also provides constraints on the maximum temperature values during syn-collisional metamorphism in the Northern Apennines.