Environmental analysis of Middle Pleistocene argillified sediments containing Acheulean stone tools filling up a karstic depression at Monte Cònero (Marche region of central Italy)

We report herein the results of sedimentological and palynological analyses of a continuous core drilled through a ~4-m-thick clayey deposit representing a pedogenized loess, which filled up a karstic depression near the top of Monte Cònero, a 576-m-high calcareous promontory protruding on the Adriatic Sea just south of the port city of Ancona (Le Marche region of central Italy). This Middle Pleistocene loess deposit represents a unique occurrence in the Umbria-Marche Apennines, likely because it was preserved in a circumscribed karstic depression near the top of a mountain, which later became a swamp or a pond collecting just meteoric water, and thus it was protected from post depositional fluvial or alluvial washout, or further aeolian deflation. The source of this aeolian sediment was the sand and silt, which was deflated from the dry floor of the Adriatic basin during the glacial maximum when, in fact, the Adriatic Sea level was some 100-120 m lower than Present. Another uniqueness of this deposit in the Palaeolithic context of the Umbria-Marche Apennines is that in the early 1960’s, perfectly preserved bifaces knapped in situ from a distinctive local chert, were found in primary position at about 3-m-depth in this deposit during two well-documented 2 archaeological excavations. These artefacts were attributed to a non-precisely dated Acheulean lithic industry. Unfortunately, our direct geochronological analysis using the optically stimulated luminescence (OSL) method on scanty silt-size quartz separates from 3 samples taken from the bottom, middle, and upper part of this deposit, yielded negative results. Nevertheless, our integrated sedimentological and palyno-stratigraphical analysis of this deposit strongly suggests that this particular area of Monte Cònero was frequented by Acheulean hunters during some stages of the Riss glacial period (i.e., MIS 6) as suggested also by the sedimentological, mineralogical, and palynological analysis of the core drilled near the original pilot excavation of 1963. Subsequently this mountain site was frequented by Acheulean hunters during some stages of the MIS 6 (i.e., Riss glacial, 190-130 kyr BP), and subsequently by Neanderthal hunters starting from MIS 5.