Late Holocene Abrupt Changes in the Fluvial Dynamics of the Tiber Valley Catchment (Rome, Italy): An Impact of the 4.2 Event?

In the present work, we investigate the post-glacial aggradation of three tributary valleys draining the left hydrographic basin of the Tiber River in central Rome: the Murcia, Caffarella, and Grottaperfetta valleys. We describe the Upper Pleistocene–Holocene stratigraphic record of the alluvial successions occurring in the Caffarella Valley through the core data collected in a dedicatedly performed 35 m deep borehole. We provide seven 14C age constraints to the sediment aggradation which allow us to make a comparison with the Grottaperfetta and Murcia valleys, for which we present previously unpublished borehole data, and with the Tiber River Valley investigated in the previous literature. In particular, we highlight the effects of a mid-Holocene (5200–3800 yr BP) erosional phase, partially overlapping with the global 4.2 ka cooling/drying event, and we discuss the possible occurrence of a sea level fluctuation linked with this paleoclimatic event which has not been detected so far by other sedimentary records. Finally, we provide evidence for the widespread occurrence of a 6th century BCE (2550–2450 yr BP) overflooding phase that was previously observed only in the eastern portion of the Tiber River Valley in central Rome, which we suggest may be originated by concurrent intensive deforestation activity in central Italy.