An exceptionally well-preserved Jurassic plateau-top to marginal escarpment in the Northern Apennines (Central Italy): sedimentological, palaeontological and palaeostructural features

Abstract

Submarine palaeo-escarpment tracts at the basin margins commonly border isolated drowned carbonate platforms in the Jurassic rifted margins of the Western Tethys and bear fundamental structural and palaeogeographic significance. These tectonically generated escarpments, rooted in late Hettangian-early Sinemurian master faults, provide key information on the regional architecture of the rift, and on the nature and timespan of activity of the faults which define them. An isolated drowned carbonate platform (the Sabina Plateau) in the Northern Apennines of Central Italy exhibits a wealth of peculiar details on the Jurassic submarine topography. The deposits covering this escarpment host multiple unconformities related to a margin-failure episode, documented by breccias resting on a submarine-scar surface, perched with respect to the basin bottom and draped discontinuously by condensed ammonite-rich pelagites. Thin lenses of graded and laminated oolitic limestones in the condensed pelagic succession of the Sabina Plateau are interpreted as likely produced by the overbanking of turbidity currents, which were shed into the basin by a neighbouring productive carbonate platform. The final leveling of the submarine rift bathymetry occurred in the earliest Cretaceous, as documented by the onlap of the aggrading basinal succession against the palaeo-escarpment, and the burial of the plateau-top condensed succession. This complex onlap surface exhibits a distinctive overprint, such as diffuse silicification driven by the transit of silica-rich diagenetic fluids sourced by the radiolarian-rich basinal units.