The Mesozoic continental rifting in the Mediterranean area: insights from the Verrucano tectofacies of southern Tuscany (Northern Apennines, Italy)

Abstract

In the Alpine-Mediterranean region, the continental redbeds and shallow-marine siliciclastics related to the early depositional phases of the Late Permian-Mesozoic continental rifting are referred to as the most common representative of the “Verrucano tectofacies”. The Verrucano-type successions exposed in southern Tuscany are diachronous, spanning from Triassic to earliest Jurassic in age, and accumulated within the Tuscan domain, a paleogeographic region of continental crust that due to the opening of the Piedmont–Ligurian ocean formed part of the Adria passive-margin. They belong to the metamorphic Verrucano Group and the non-metamorphic Pseudoverrucano fm. Viewed overall, these Verrucano-type successions appear to manifest five episodes or pulses of an ongoing continental rifting. With the exception of the first episode that developed entirely within a terrestrial setting, each one is represented by basal Verrucano-type continental siliciclastics overlain by compositionally mixed marine deposits, which resulted from four diachronous, post-Middle Triassic transgressions. This suite of tectonic pulses produced the progressive westward widening (backstepping) of the Tuscan domain in the rifting south-Tuscany area.