Integrated analysis for intermontane basins studies:tectono-stratigraphic and paleoclimatic evolution of the L'Aquila Basin

Abstract

Although the L’Aquila Basin is one of the central Apennines most seismically active intermontane basins, its long-term geological evolution has long been poorly understood even if, especially after the 6th April 2009 earthquake, several studies were carried out in this area. Particularly problematic in intermontane basins studies are the uncertainties associated with the onset of the extensional tectonic and the age of the older continental deposits, as well as the subsurface bedrock geometries and the stratigraphical relationships of the continental deposits within the basin. A multidisciplinary approach that integrates stratigraphical, geomorphological and structural field surveys with paleontological analyses, geochronological (OSL; 14C) dating, well log analyses and geophysical data interpretation (seismic reflection profile; HVSR), was used in order to reconstruct the L’Aquila Basin tectono-stratigraphic evolution, the regional tectonics and the climate forcing that controlled sedimentation processes within the basin. Our results allowed to review the L’Aquila Basin stratigraphy and to define seven synthems, partly matching stratigraphic units or synthems already described in previous works. In addition the comparison between the tectono-stratigraphic evolution of L’Aquila Basin and other intermontane basins (i.e., Tiberino, Rieti, Leonessa basins), together with the stratigraphy of the Plio-Quaternary succession of the Roman area, allowed to identify some similarities that help to constrain the major regional events that controlled the L’Aquila Basin geological history. The occurrence of a Caspiocypris species flock at the base of the sedimentary fill of the eastern part of L’Aquila Basin (San Demetrio-Colle Cantaro Synthem), which possibly correlate the late Piacenzian-Gelasian ostracod fauna of the Fosso Bianco Formation of the Tiberino Basin, points to a late Piacenzian age for the onset of the extension in the L’Aquila Basin. Interpretation of a seismic reflection profile (Pettino1) shows the occurrence, above the Meso-Cenozoic bedrock, of a wedge shaped seismic unit corresponding to the basal deposits of the western L’Aquila Basin (San Demetrio-Colle Cantaro Synthem), pointing to a late Piacenzian-Gelasian syn-rift stage during the first phase of basin filling. As a result of the correlation among the stratigraphies of L’Aquila Basin and the stratigraphy of Plio-Quaternary successions of the central Italy, the main tectonic phase responsible for the increase of the accommodation space of the L’Aquila Basin ended close to the Gelasian/Calabrian transition with a regional uplift event. Indeed, the second phase of basin fill, which occurred mainly during the Calabrian (Madonna della Strada Synthem), happened in a post-rift stage and was mainly characterized by the development of a fluvial environment, with floodplains and extensive swamp areas close to meandering fluvial channels. After these two major phases of basin filling, the L’Aquila intermontane basin was affected by five shorter tectono-sedimentary events that gave rise to the formation of Middle and Upper Pleistocene unconformity- bounded stratigraphic units, with the younger units carved into the previous ones or even into the pre- or syn-orogenic successions. The Late Pleistocene evolution of the L’Aquila Basin was mainly characterized by the development of three order of fluvial terraces, two of which are strath terraces (T2 and T3). The second order fluvial terrace, belonging to the Campo di Pile Synthem, correlates MIS 3, since it shows a 14C 2σ age of 41,854-40,464 yr cal BP. From this data, a late Quaternary river incision rate between 0.24 to 0.32 mm/yr can be estimated. Our results showing an onset of the L’Aquila Basin that is synchronous with the onset of the Tiberino Basin call into question the notion that these extensional intermontane basins become younger from the Tyrrhenian towards the Adriatic side of the central Apennines.