The role of Jurassic inherited structures on the post-rift Early Cretaceous extensional faults. Comparison between the “Mt. Cosce Breccia” and the “Ballino Breccia”

The tectono-stratigraphic evolution of Mesozoic sedimentary successions in the Alpine Tethys was influenced by Early Jurassic rift-related extension. Evidence for this normal faulting are in the Alps and in the Apennines, where huge Hettangian carbonate platforms (Calcari Grigi Fm. and Calcare Massiccio Fm., respectively) were dismembered into fault-bounded blocks causing a characteristic horst-and-graben/semigraben setting (e.g. Castellarin 1972; Bertotti et al. 1993; Santantonio 1993, 1994). This is highlighted by facies and thickness variations in the syn- and post-rift Jurassic pelagites. While the occurrence and the effects of the Early Jurassic rifting stage is a well-known theme, evidence for an Early Cretaceous extensional tectonic phase is far more sparse. Direct and indirect evidence for this phase is described for several paleogeographic domains, and includes i) the back-stepping of carbonate platform- and pelagic carbonate platform- (PCP sensu Santantonio 1994) margins, ii) the areal reduction or –locally- drowning of carbonate platforms (e.g. Bièvre & Quesne 2004; Santantonio et al. 2013), iii) the deposition of clastic bodies (e.g. Castellarin 1972; Cipriani 2016; Fabbi et al. 2016), iv) the occurrence of neptunian dykes (e.g. Bertok et al. 2012), v) the development of angular unconformities (e.g. Menichetti 2016). In the Narni-Amelia Ridge (central Apennines), a Cretaceous megaclastic deposit, called the “Mt. Cosce Breccia” (Cipriani, 2016), was recently identified during a geological mapping project. Due to the stratigraphic, sedimentological and paleotectonic similarities with the “Ballino Breccia” outcropping in the Southern Alps (Castellarin 1972), the two sectors were compared. The aim of this work is to understand the influence on inherited Jurassic structures on the development of Early Cretaceous extensional faults in two different paleogeographic domains of Italy, albeit with a comparable tectono-sedimentary evolution.