Late Pleistocene sedimentary, paleoenvironmental and tectonic evolution of the Colfiorito basin (central Italy)

The 60-m deep Plestia1 borehole characterises the most recent fill of the Quaternary Colfiorito basin, an intermontane tectonic depression in the Northern Apennines of Italy. The subsidence rate is controlled by a major SW-dipping, seismogenic normal fault most recently activated (M max = 6) during the 1997-98 seismic sequence. The core has been the subject of lithostratigraphic, paleomagnetic, palynological, tephrostratigraphic and micro-paleontological analyses, which define a sedimentary succession composed predominantly of silts and clays, consistent with deposition in a lacustrine environment. These sediments retain a stable, normal-polarity magnetization. Two tephra layers at 58.67 m and 38.89 m, corresponding to the Maddaloni/X-6 eruption from Campi Flegrei and an undefined eruption sourced at the Latium volcanic complex, have ages of ∼109 ka and ∼86 ka, respectively. A radiocarbon date on ostracod shells extracted from sediments at 8.90 m depth provides an age of ∼26 ka. Pollen analysis shows a succession of vegetational phases consistent with the Late Pleistocene climatic oscillations from MIS 5d to MIS 2, while the ostracod assemblage in the upper part of the succession is consistent with LGM climatic conditions. Overall, the paleomagnetic, radiocarbon, tephra, pollen and ostracod evidence indicates that Plestia1 spans the 110-15 ka interval. A Bayesian age-depth model was developed using these geochronological constraints and biostratigraphic alignments of the Plestia1 pollen profile with well-dated reference records, providing an average sedimentation rate of ∼0.6 mm/yr. Accounting for climatic and sedimentary contributions, this result represents a minimum estimate of the tectonic subsidence rate and implies a similar mid-term fault slip rate.