Detrital Modes in a Late Miocene Wedge-Top Basin, Northeastern Calabria, Italy: Compositional Record of Wedge-Top Partitioning

Abstract

Abstract The composition and stratigraphic relations of sandstones and associated conglomerates derived from erosion of the northern Calabrian terranes provide important constraints for paleotectonic and paleogeographic models of the Neogene wedge-top depozone evolution of the southern Italy foreland basin system. After onset of continental collision in the southern Italy orogenic belt during late Oligocene to early Miocene, the Calabrian Arc drifted northeastward, accreting over the Adria lithosphere during mid to late Miocene time. Since the Tortonian, the northern Calabrian terranes represented an uplifted thrust belt in which along its leading edge tectonic subsidence was responsible for accumulation of a thick Tortonian to Quaternary succession, dominantly siliciclastic (up to 3300 meters thick), deposited in the wedge-top depozones (Rossano and Crotone basins). Sandstone assemblages have a homogeneous quartzofeldspathic composition in the Rossano and Crotone basins, characterized by a compositional trend, through time in response to regional tectonics. Evolution of the basins fill occurred during (1) Serravallian?–Tortonian, (2) late Tortonian to early Messinian, and (3) late Messinian. Detritus shed into those basins was derived mainly from terranes within the strongly deformed Sila Mountains allochthon, which was one of the principal structural elements of the nearby northern Calabrian terranes, consisting of Hercynian plutons intruding Paleozoic (Cambrian to Carboniferous) metasedimentary host rocks, and locally having a sedimentary cover of Mesozoic (Longobucco Group) or early Miocene (Paludi unit) clastics. Low- to medium-grade metamorphic and minor plutonic grain types (metamorphiclastic petrofacies) represent the main detritus in the earliest (Serravallian?–Tortonian) sedimentation that accompanied progressive flexural bending of the western margin of the foreland-basin system. Tortonian to early Messinian time was characterized by isolation of the Mediterranean region from the global marine realm, leading to evaporite sedimentation in the foreland in addition to intense regional and local tectonics. Compositional response to those events was a marked increase in sedimentary detritus (sedimenticlastic petrofacies) related to cannibalization of early Messinian evaporite successions; after the evaporitic events within the basins and the gradual re-establishment to the normal marine conditions, sandstone detrital modes are characterized mainly by a return of the Serravallian?–Tortonian compositional modes (i.e., metamorphic–plutoniclastic petrofacies). The post-evaporitic sedimentation corresponds to a major tectonic rearrangement on both Rossano and Crotone basins related to extrusion and inversion of the basal portion of the Serravallian?–Tortonian sequences in the intermediate zone to form an intervening Ciro structural high. In the Crotone Basin during late Messinian, deposition of the Carvane Conglomerate records an abrupt sudden arrival of distinctive sedimentary containing clasts of detritus of reddish limestone, marl, quartz arenite, siltstone and chert derived from Mesozoic to Tertiary basinal sequences of the southern Apennines domains (i.e., Sicilide Complex terranes). Detrital-mode evolution of the inner portions of the late Miocene southern Italy foreland-basin system was in response to abrupt tectonic partitioning due to continuation of accretionary processes, rapid uplift of mid-crustal blocks, and the superposition of wrench tectonics.