Evidence for Early Cretaceous syn-sedimentary tectonics in the Umbria-Marche Basin (Northern Apennines, Italy)

Under-investigated Barremian-Aptian detrital intercalations embedded in pelagic deposits of the Umbria-Marche- Sabina Domain (Central and Northern Apennines, Italy) are here presented. The study sector corresponds with the Mt. Primo area (Umbria-Marche Ridge, Northern Apennines), where three stratigraphic sections of the Maiolica and Marne a Fucoidi Formations were sampled. Here, gravity-driven breccias and calcarenites (the latter interpreted as debris-flows, or turbidity flows if graded) are embedded in pelagic sediments. The massive lensoid-to-tabular levels are interbedded with the typical tethyan pelagic mudstones of the Maiolica Fm. and with the marly lower portion of the overlying Marne a Fucoidi Fm., forming as a whole a >60 m-thick interval. The microfacies analysis allows to recognize rudstone-tofloatstone and grainstone textures, dominated by mm- to cm-sized lithoclasts and associated with loose grains of benthic foraminifers, dasycladal algae, microbial crusts, microproblematica and bivalves. The latter components indicate productive photozoan-type carbonate platform(s) as source area(s). The lithoclasts are made of: i) Lower Jurassic and Lower Cretaceous shallow-water carbonates; ii) Jurassic mudstones and wackestones referable to the pelagic Umbria- Marche succession; iii) Maiolica-type soft pebbles (with and without calpionellids). The occurrence of primitive hedbergellids in the lowermost sampled pelagic levels, coupled with the occurrence of Montseciella arabica and Suppiluliumaella polyreme in the coeval resedimented material, suggests a Barremian-early Aptian age for the detrital interval. Evidence for abundant resedimented material in pelagic basins are generally related to tectonic perturbations of the depositional setting, to eustatic oscillations, or both. In our opinion the analyzed deposits are related to extensional tectonics for several reasons: i) sudden switch in the succession from pelagic mudstones to a very coarse-grained interval; ii) the abundance of Cretaceous benthic material, sourced from an unknown carbonate platform, coupled with lithoclasts of shallow-water carbonates, which suggest tectonic back-stepping and dismantling of platform margins; iii) the occurrence of Calcare Massiccio lithoclasts along with Jurassic and Lower Cretaceous pelagites; such evidence necessarily implies a tectonic exhumation and erosion of a Jurassic pelagic carbonate platform located nearby the study area, which was buried in the earliest Cretaceous. Direct and indirect evidence for an extensional phase in the late Early Cretaceous are documented in several sedimentary successions of Italy. Our data fit well with this widespread, but poorly studied tectonic phase and, at the same time, provide new implications for the Early Cretaceous paleogeography of the Umbria-Marche Basin.