Mesozoic Syn- and Postrifting Evolution of the Central Apennines, Italy: The Role of Triassic Evaporites

Jurassic-Cretaceous syn- and postrift successions from the central Apennines were backstripped to gain information on the Mesozoic evolution of the passive margin of the Adriatic Plate. Early Jurassic rifting led to the development of a horst-and-graben paleogeography (the Latium-Abruzzi Carbonate Platform and the Sabina-Umbria-Marche Pelagic Basin). Subsidence curves were built for both carbonate platform and pelagic-basin domains from original and literature stratigraphic data. The paleodepositional depths of the deepwater sediments were reconstructed from field geology data, including new paleontological data. It is proposed that after the deposition of lower Hettangian shallow-water carbonates, an abrupt increase in paleowater depth, to 600-1000 m, occurred during the late Hettangian-Sinemurian synrift stage. The postrift stage was characterized by basin filling, with decreasing paleowater depths during the Jurassic, and by a new deepening during the Cretaceous. Our backstripping curves show, for the Sabina-Umbria-Marche Basin, a short period (<5 m.yr.) of rapid tectonic subsidence at the beginning of the Jurassic, followed by very slow (likely thermally controlled) or absent tectonic subsidence until the Cretaceous. The slight increase in subsidence observed from Cenomanian time is linked to a renewal of extensional tectonics. The Latium-Abruzzi Carbonate Platform shows variable subsidence rates in both place and time. Fast subsidence occurred in the Rhaetian-Hettangian, Toarcian, Berriasian, and Cenomanian and is linked with extensional or transtensional tectonic events. After the Early Jurassic rifting, subsidence rates (on average 30-40 m/m.yr.) affecting the Latium-Abruzzi Carbonate Platform were faster than those recorded by the Sabina-Umbria-Marche Basin. Faster postrift subsidence in carbonate platform areas is a geological paradox that is here explained by the lateral flow of upper Triassic evaporites toward the deepwater domains, as a result of higher sedimentary loading in the carbonate platform areas and the onset of a pressure gradient toward the pelagic basin at the depth of the evaporites.