Evidence for the Early Jurassic Western Tethys rifting is in the Alps and the Apennines. This normal faulting phase dismembered a vast carbonate platform (Calcari Grigi and Calcare Massiccio platform) and produced a complex paleogeographic setting made of intrabasinal morphostructural highs and deeper-water basins (i.e. pelagic carbonate platform or PCP/basin system). Basin-fill pelagites and their geometrical and facies variations highlight this complex architecture. There are growing clues for Early Cretaceous, post-rift, synsedimentary normal faults affecting and displacing the margins of PCP, as in the Umbria-Marche-Sabina Domain and the Trento Plateau-Lombardy Basin. Typical stratigraphic and sedimentological features of this syndepositional tectonic phase include: i) the back-stepping of PCP margins, ii) the deposition of calciclastic bodies, iii) the occurrence of neptunian dykes, and iv) the development of angular unconformities. Geological mapping in the Narni-Amelia Ridge allowed to identify field-evidence for this Cretaceous normal faulting. A polygenic breccia (“Mt. Cosce Breccia”) made of clasts of lithologies not younger than the Early Cretaceous, dispersed in a matrix of Maiolica-type facies, rests through an erosional surface on a Jurassic horst-block of Calcare Massiccio. Comparable clastic deposits are embedded in the uppermost part of the Maiolica in hangingwall-basin successions, associated with soft-sediment deformation. Lower Cretaceous pelagites (Maiolica+Marne a Fucoidi) are locally seen onlapping the unroofed Calcare Massiccio, as well as infilling neptunian dykes. Impressive similarities were recognized along the Jurassic western margin (Ballino escarpment) of the Trento Plateau, albeit at a larger scale. Here, a Lower Cretaceous polygenic breccia (Ballino, Pregasio and Prabione breccias) bearing heterometric (up to >20 m across) blocks of Jurassic-Lower Cretaceous deposits referable to the Calcari Grigi Group, the basinal Lombardy Succession and the horst block-top Venetian Succession, occurs. The clasts are dispersed in a Maiolica-type matrix. The breccia rests unconformably on the Calcari Grigi Group and on several Jurassic units of the Lombardy basin-margin succession, and is accompanied by neptunian dykes made of Maiolica facies. Where preserved by Neogene Alpine deformations, Cretaceous normal faults were locally observed, sealed by the calciclastics and the uppermost part of Maiolica. Field-evidence suggests a phase of tectonic instability during the late Early Cretaceous, coeval with the deposition of the uppermost part of Maiolica, affecting PCP-basin systems in both Central Apennines and Southern Alps. Cretaceous faults locally re-activated Jurassic ancestors, locally had a higher angle than Jurassic faults, locally developed as new faults. The result was the displacement and rejuvenation of inherited Early Jurassic escarpments, or the backstepping of PCP-margins producing exhumation of Jurassic structural highs.

Tectono-stratigraphic evolution of Jurassic Tethyan rift basins in the Early Cretaceous: a comparison between the Central Apennines and the Southern Alps

The role of sea-bottom topography in the dispersal of shallow water-derived calciturbidites across a submarine rift, as determined by the local extensional architecture, is under-investigated, namely with pelagic settings along ancient passive continental margins. A comparison with modern carbonate platform/basin analogues, or with siliciclastic systems, is not always feasible, as ancient carbonate systems were commonly home to anachronistic environments (e.g. the Western Tethyan Mesozoic). Geological mapping of the Jurassic rift basin exposed in the Apennines of Central Italy revealed a complex pattern of intrabasinal highs (pelagic carbonate platforms) and intervening basins, controlled by the high density, and oddly variable trends, of faults rooted in a shallow detachment layer corresponding to thick Triassic salt. A map pairing the occurrences of resedimented beds in pelagic successions with an updated palaeogeography becomes therefore the natural descriptor of the itineraries followed by sediment gravity flows. This qualitative method represents a companion, or even alternative, approach to the one strictly based on physical stratigraphy, and it greatly improves our knowledge of regional geology and rift-basin analysis. Our study focuses on: i) a reconstruction of the palaeotectonic architecture of the Umbria-Marche Basin in the Jurassic, and on ii) how this architecture produced a submarine topography which governed the dispersal of sediment, shed by the neighbouring Lazio-Abruzzo Carbonate Platform, for >40 million years. Geological mapping, coupled with the measurement and correlation of stratigraphic sections, shows that the marginal palaeoescarpments of pelagic carbonate platforms formed obstacles to the gravity flows as sediment load was discharged in confined basins at their toes and/or flows were deflected and forced along alternative itineraries. While turbidity currents were locally vigorous enough to climb the escarpments, leaving graded and laminated overbank deposits on the pelagic carbonate platform-tops, a “shelter” effect is evidenced by the resediment-free nature of those basins lying downflow, which were shielded by the highs. Our case study potentially represents the analogue of hydrocarbon fields both inland and in the offshore.

Role of Early Jurassic rift architecture in the dispersal of calciturbidites, as revealed by geological mapping in Central and Northern Apennines

**Session Chairs: **Giovanni Barreca (University of Catania), David Iacopini (University of Naples - Federico II), Stefano Zanchetta (University of Milano - Bicocca), Francesca Cifelli (University of Roma - Roma Tre)

S1. Tectonics and sedimentation I

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Tectono-stratigraphic evolution of Jurassic Tethyan rift basins in the Early Cretaceous: a comparison between the Central Apennines and the Southern Alps

Role of Early Jurassic rift architecture in the dispersal of calciturbidites, as revealed by geological mapping in Central and Northern Apennines

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