Detrital events within pelagic deposits of the Umbria-Marche Basin (Northern Apennines, Italy): evidence for Early Cretaceous tectonics?

Resedimented intervals characterize different stratigraphical levels in the pelagic deposits of the Umbria-Marche-Sabina Domain (Central and Northern Apennines, Italy). Gravity deposits related to the Early Jurassic Tethyan rifting are well known in literature; differently, the occurrence of calcirudites and calcarenites interbedded with the Middle-Upper Jurassic and the Lower Cretaceous pelagites is underinvestigated. Barremian-Aptian detrital intercalations, bearing coeval shallow-water material, are known in the pelagic successions of Central and Northern Apennines. That said, while the existence of a wide productive carbonate platform in Central Italy (Latium-Abruzzi Platform) can easily explain the presence of such material in the neighboring basins, the occurrence of detrital bodies in paleogeographic areas far from this platform is less obvious, being those areas separated from the Latium-Abruzzi Platform by belts where the coeval sediments are free of any resedimented shallow-water material. Here we present preliminary results from three stratigraphic sections of the Maiolica and Marne a Fucoidi Formations sampled across the Mt. Primo area (Umbria-Marche Ridge, Northern Apennines), characterized by breccias and calcarenites embedded in pelagic sediments. Facies analysis indicates a gravity-driven origin for the clastic levels, interpreted as debris-flows, or turbidity flows where graded calcarenites are present. The massive lensoid-to-tabular levels are interbedded with the typical pelagic mudstones of the Maiolica Fm. and with the marly lower portion of the Marne a Fucoidi Fm., forming at a whole a >60 m-thick interval. In thin-section, rudstone-to-floatstone microfacies are dominated by bioclasts of benthic foraminifers, dasycladal algae, microbial crusts, microproblematica and bivalves that indicate productive photozoan-type carbonate platform(s) as source area(s). Associated to these loose grains are millimeter-to-centimeter size lithoclasts, made of: i) Lower Jurassic and Lower Cretaceous shallow-water carbonates; ii) Jurassic mudstones and wackestones referable to the pelagic Umbria-Marche succession; iii) calpionellid-rich soft pebbles (lower portion of the Maiolica Fm.). The occurrence of Hedbergella similis in the lowermost sampled pelagic levels, coupled with the occurrence of Montseciella arabica and Suppiluliumaella polyreme in the calcarenites, suggest a Barremian-early Aptian age for the detrital interval. The occurrence of abundant resedimented material in pelagic basins is generally related to tectonic perturbations of the depositional setting or eustatic oscillations, or both. We consider the studied detrital deposits as related to extensional tectonics for several reasons: i) the sudden switch from typical pelagic mudstones to coarse sediments, rich in benthic material sourced from an unknown carbonate platform (most likely located several kms away from the study area), suggests tectonic activity affecting the source area; ii) the occurrence of Cretaceous lithoclasts of shallow-water carbonates, suggests tectonic backstepping and dismantling of the carbonate platform margins; iii) the occurrence of lower Jurassic platform carbonate lithoclasts, as along with calpionellid-rich pebbles and lithoclasts of Jurassic pelagites, is a clue for tectonic exhumation and erosion of the Jurassic pelagic carbonate platforms located nearby the study area, which were buried in the earliest Cretaceous. Our preliminary interpretation well fits with already known and new data coming from others different geological settings of Italy, strongly suggesting the occurrence of a widespread extensional phase in the late Early Cretaceous.