The tectonic-stratigraphic evolution of Mesozoic sedimentary successions across the Alpine Tethys was influenced by Early Jurassic rift-related extension. Evidence tor this phase of normai faulting are tound in the Alps and the Apennines, where vast Hettangian carbonate plattorms (Calcari Grigi and Calcare Massiccio paleoplatform, respectively) were dismembered into fault-bounded blocks and drowned, giving rise to pelagic carbonate platform (PCP)/basin systems (Santantonio 1994). This is evidenced by facies and thickness variations within the syn- and post-rift Jurassic-Lower Cretaceous pelagites. Direct and indirect evidence tor an Early Cretaceous post-rift extensional tectonic phase has been reported across different paleogeographic domains. Typical stratigraphic and sedimentologica! features include: i) the back-stepping of carbonate platform and PCP margins, ii) the areai reduction or-locally- drowning of carbonate platforms, iii) the deposition of clastic bodies, iv) the occurrence of neptunian dykes and v) the development of angular uncontormities. A field mapping project was performed in the Narni-Amelia and Sabini mountain ranges (Centrai Apennines), where severa! features relateci to Cretaceous normai faulting were identified. In particular, a polygenic breccia made of clasts of lithologies not younger than the Early Cretaceous, dispersed in a matrix of Maiolica-type facies (white Calpionellid-rich mudstone), rests through an erosional surface on a Jurassic horst-block of Calcare Massiccio. ("Mt. Cosce Breccia" - Cipriani 2016). Comparable clastic deposits are embedded in the uppermost part of the Maiolica Fm. in hangingwall-basin successions, associated with soft-sediment detormation. Lower Cretaceous pelagites (Marne a Fucoidi Fm. -Aptian-Cenomanian p.p.) are locally seen onlapping the unroofed Calcare Massiccio Fm. Neptunian dykes made of Maiolica penetrate the PCP-top, condensed Jurassic successions as well as their pre-rift substrate (Calcare Massiccio Fm.). Impressive similarities were recognized along the Jurassic western margin (Ballino escarpment) of the Trento Plateau, albeit at a larger scale. The Trento Plateau is a huge morpho-structural high tormed during the Early Jurassic extensional phase. Polyphasic extension affected the Ballino paleoescarpment during the Mesozoic (mainly Early Jurassic, Early and Late Cretaceous), as testified by conspicuous megaclastic deposits embedded in the basinal succession lying to the west (Lombardy Basin - Castellarin 1972). Our attention was tocussed on the "Ballino Breccia", a Lower Cretaceous polygenic breccia characterized by heterometric (up to >20 m across) blocks made of shallow-water carbonates (Calcari Grigi Group), chert-rich deposits (Lombardy Succession) and horst block-top condensed facies (Venetian Succession). The clasts are associateci with pebbles of Maiolica-type facies (with and without calpionellids), and the matrix of the ruditic deposit is a nannomicritic mudstone (Maiolica Fm.). The breccia rests unconformably on severa I different Jurassic units of the Lombardy basin-margin succession as well as directly on the Calcari Grigi facies, and is sealed by the uppermost part of the Maiolica Fm. Neptunian dykes made of Maiolica facies are also common. Field-evidence therefore suggests that a synchronous phase of reactivation of Early Jurassic rift faults took piace in Centrai Apennines as well as in Southern Alps during the Early Cretaceous, coeval with deposition of the upper part of the Maiolica Fm. Cretaceous faults locally had a higher angle than Jurassic faults, so the latter were displaced. Cretaceous extension could cause the locai exhumation of Jurassic structural highs, which occurred through back-stepping, rejuvenation, or displacement of inherited Early Jurassic margins.
Scheda prodotto non validato
Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo
|Titolo:||Early Cretaceous post-rift extensional faulting and inherited Jurassic structures in Central Apennines and Southern Alps|
CIPRIANI, ANGELO (Corresponding author)
|Data di pubblicazione:||2017|
|Appartiene alla tipologia:||04d Abstract in atti di convegno|