New multidisciplinary investigations on the tectonic and sedimentary evolution of the southern sector of Sulmona basin (Central Italy)

The Sulmona intermontane plain is a tectonic basin filled by Quaternary fluvio-lacustrine deposits, driven by the recent activity of the Mt. Morrone fault system during the post-orogenic extension of the Central Apennines. Detailed multidisciplinary investigations were carried out in the southern sector of the basin, in the Santa Rufina (SR) borehole. SR was drilled down to a depth of ca. 200 m in the western section of the basin and compared with a ca. 435-m-depth water-well (Medibev Well: MW) in the depocentral portion of the basin, characterized by a lacustrine succession. Although recent studies have explored in detail the stratigraphy of the Sulmona Basin, these are generally limited to the northern sector of the basin, leaving open numerous issues, such as: the overall geometry and stratigraphy of the basin infill, the depth of bedrock/sediment interface, the onset age of the basin formation, and the relations between the basin subsidence rate vs. Mt Morrone fault slip-rate. In both SR and MW sediment cores the lacustrine clayey-silty deposits dominated with respect the coarse grained alluvial-fluvial deposits. The magnetic susceptibility of SR, measured both on the core and on discrete samples, shows higher values corresponding to tephra layers. The paleomagnetic analysis, performed by alternating field demagnetization on 156 samples, identifies the Brunhes/Matuyama boundary (773 ka) at 194 m depth. Tephrochonological analysis in SR core allowed the recognition of several chronologically well-constrained tephra markers, either of regional (e.g., Vico a, ca. 415 ka, White Trachitic Tuff, ca. 320 ka, and Villa Senni, ca. 366 ka) or basinal scale, which constrain the whole succession between ca. 300 and 800 ka. The comparison of the coarse grained alluvial and tephra layers in the two boreholes constrained a geological section crossing the basin, which allowed new insights into its tectonic, sedimentary and paleoenvironmental evolution. Preliminary results from the correlation confirmed an asymmetric half-graben type geometry of the basin, highlighting the Mt. Morrone fault system as a leading factor responsible for the opening of the basin and its Quaternary tectonic-sedimentary evolution.