Site formation and post-sedimentary processes affecting Pleistocene archaeological record: depositional environments and sediment deformation at the Middle Palaeolithic site of Peña Cabra rock shelter (central Spain)

Understanding site formation and post-depositional processes is critical for analysing and interpreting the nature, function and environmental setting of human occupations recorded in Pleistocene archaeological deposits. Here we study the sedimentary and post-depositional processes that operated at the Middle Palaeolithic sequence of the Peña Cabra site and its role in the distribution of archaeological remains. This site is located in central Iberia (Guadalajara province, Spain), in a nowadays almost inaccessible spot placed on a vertical rock face, in the slope of the fluvial valley of the Sorbe River (Tagus basin). The geomorphological, sedimentological and micromorphological studies conducted, combined with the intra-site spatial analyses of the archaeological record and the chronometric dating of the sequence, shows that the formation and post-depositional history of the stratigraphic deposit is related to complex geological overlapped processes. These include (1) fluvial dynamics, (2) catastrophic flood events, (3) slope sediment deposition during the human occupation, (4) the freezing and thawing of soil under periglacial climate and (5) the later sudden sedimentary isolation of the cavity from the sediment source due to a rock wall collapse. Some of these events conditioned the periods of occupation of the site by Neanderthals groups during MIS 5, including the accessibility to the rock shelter. Furthermore, they have been a relevant factor affecting the current distribution of the archaeological record due to sediment bed deformation. Our results illustrate the necessity of conducting interdisciplinary geoarchaeological and taphonomic research in Pleistocene sites as a key prerequisite for interpreting the spatial distribution of archaeological assemblages in behavioural terms. Although this is a well-known necessity in current research, issues such as sediment deformation affecting archaeological layers are not yet widely investigated, even though many Pleistocene sites could have been affected by cryoturbation processes during cold periods.