The Miocene tectono‐sedimentary evolution of the southern Tyrrhenian Sea: stratigraphy, structural and palaeomagnetic data from the on‐shore Amantea basin (Calabrian Arc, Italy)

Abstract

We report on new stratigraphic, palaeomagnetic and anisotropy of magnetic susceptibility (AMS) results from the Amantea basin, located on‐shore along the Tyrrhenian coast of the Calabrian Arc (Italy). The Miocene Amantea Basin formed on the top of a brittlely extended upper plate, separated from a blueschist lower plate by a low‐angle top‐to‐the‐west extensional detachment fault. The stratigraphic architecture of the basin is mainly controlled by the geometry of the detachment fault and is organized in several depositional sequences, separated by major unconformities. The first sequence (DS1) directly overlaps the basement units, and is constituted by Serravallian coarse‐grained conglomerates and sandstones. The upper boundary of this sequence is a major angular unconformity locally marked by a thick palaeosol (type 1 sequence boundary). The second depositional sequence DS2 (middle Tortonian‐early Messinian) is mainly formed by conglomerates, passing upwards to calcarenites, sandstones, claystones and diatomites. Finally, Messinian limestones and evaporites form the third depositional sequence (DS3). Our new biostratigraphic data on the Neogene deposits of the Amantea basin indicate a hiatus of 3 Ma separating sequences DS1 and DS2. The structural architecture of the basin is characterized by faulted homoclines, generally westward dipping, dissected by eastward dipping normal faults. Strike‐slip faults are also present along the margins of the intrabasinal structural highs. Several episodes of syn‐depositional tectonic activity are marked by well‐exposed progressive unconformities, folds and capped normal faults. Three main stages of extensional tectonics affected the area during Neogene‐Quaternary times: (1) Serravallian low‐angle normal faulting; (2) middle Tortonian high‐angle syn‐sedimentary normal faulting; (3) Messinian‐Quaternary high‐angle normal faulting. Extensional tectonics controlled the exhumation of high‐P/low‐T metamorphic rocks and later the foundering of the Amantea basin, with a constant WNW‐ESE stretching direction (present‐day coordinates), defined by means of structural analyses and by AMS data. Palaeomagnetic analyses performed mainly on the claystone deposits of DS1 show a post‐Serravallian clockwise rotation of the Amantea basin. The data presented in this paper constrain better the overall timing, structure and kinematics of the early stages of extensional tectonics of the southern Tyrrhenian Sea. In particular, extensional basins in the southern Tyrrhenian Sea opened during Serravallian and evolved during late Miocene. These data confirm that, at that time, the Amantea basin represented the conjugate extensional margin of the Sardinian border, and that it later drifted south‐eastward and rotated clockwise as a part of the Calabria‐Peloritani terrane.

Subduction or delamination beneath the Apennines? Evidence from regional tomography

“…Alternatively, Faccenna et al (2004) have proposed that the complex boundary shape in the Apennines region was formed due to the initial evolution of the western Mediterranean subduction zone (WMSZ) followed by trench retreat and back-arc extension. According to their model, the counterclockwise rotation of the Apennines block started at ∼ 35 Ma due to the opening of the Ligurian-Provençal basin, as also proposed by Mattei et al (2002), and then continued due to the spreading of the Tyrrhenian basin. However, the final stage, which resulted in the origin of the narrow subduction zone remains not completely clear.…”

Seismotectonics and landslides of the Crati Graben (Calabrian Arc, Southern Italy)

“…The succession grades upwards into clay with thin laminated gypsum strata, in which are intercalated thick levels of halite. The Messinian succession of the Crati Basin is partially correlated to the evaporite deposits of the Crotone Basin (Zecchin et al, 2013a(Zecchin et al, , 2013b and references therein) and to the Messinian infill of the Amantea Basin (Longhitano & Nemec, 2005;Mattei et al, 2002;. Conglomerate-sand-clay succession, unconformably overlies the above-mentioned Miocene units.…”

“…Neogene transgressive deposits -outcrop along the western and eastern borders of the Coastal Chainmade up of Serravallian conglomerate-arenite, Tortonian mixed arenites (Calcare di Mendicino Formation) passing upwards to clay with shelf turbidites and thin bedded diatomites and marls (Lanzafame & Zuffa, 1976;Mastandrea et al, 2002;Mattei et al, 2002). Messinian deposits consist of evaporite and terrigenous strata and mainly outcrop to the NE margin of the map, in the area comprised between the Rosa River and the Grondo River (Figure 1).…”

Rift and supradetachment basins during extension: insight from the Tyrrhenian rift

“…Recently, the early rifting of the Tyrrhenian region (in late Miocene time) was interpreted as an upper plate extension (back-arc and forearc extension) affecting both margins of Calabria (Milia & Torrente 2014). At that time high-angle normal faults affected the western Tyrrhenian margin bounding synrift basins (Sartori et al 2004), whereas low-angle normal faults were documented on the eastern margin of the Tyrrhenian Sea in Tuscany (Pandeli et al 2010) and Calabria (Mattei et al 2002).…”

“…The detachments of the Stilo and Amantea rifts show a notable similarity because both basins display low-angle normal faults in direct contact with variably tilted rift basin fills. Field stratigraphic data for the Amantea basin (Mattei et al 2002) reveal an older sequence corresponding to the Serravallian sandstone cropping out mainly in the eastern part of the basin. A Tortonian succession rests on the Serravallian deposits and, in the central part of the basin, on the metamorphic substrate.…”