The stepped Quaternary fluvial terrace system of the Somme Valley (northern France) hosts several Middle to Upper Pleistocene sites, thus offering many opportunities to study the potential of archaeological records in alluvial context. This paper will focus on the open-air site of Cagny-l'Épinette in the Middle Somme Valley. Thousands of artifacts and faunal remains have been unearthed from its fine-grained fluvial deposits (MIS 9), at the external part of the terrace near a chalk talus. Despite their apparent freshness, their status has been a continuous debate topic. While some saw pristine Acheulean assemblages, others considered them as mixed reworked remnants of different sites. Through the presentation of the latest analyses conducted at Cagny-l'Épinette, we will discuss the challenging task of deciphering archaeological assemblages embedded in alluvium. As part of a new research project (2016–2021), the first site-wide multi-criteria spatial analysis of Cagny-l'Épinette was performed to provide a new insight into the overall Acheulean assemblages. Several features were then considered for both lithic artifacts and faunal remains, as individuals and as part of refittings: grain-size, orientation patterns, surface alterations, breakage patterns, anthro-pogenic marks and skeletal part representation. Our results suggest one archaeostratigraphic level affected by a post- or sym-burial, vertical size-sorting process. Furthermore, although local disturbances have been identified, the results allow to exclude high energy fluvial or slope processes or intense activity by non-human carnivores before burial. Thus, hominins can be considered as the primary actor in the site formation process. These outcomes help further understanding of the inherent complexity of formation dynamics of sites settled within fluvial terrace systems, and thus, of their archaeological potential.