This paper will present the results of research being conducted in the al-Marj lake basin, a closed and fault-bounded basin located in Cyrenaica, northeastern Libya. This research is being conducted as part of the TRANS-NAP project (“Cultural Transformations and Environmental Transitions in North African Prehistory”). The al-Marj basin was identified using remotely-sensed satellite imagery and digital elevation models. A 30-metre core was drilled in the basin in 2010. Sedimentological analysis of the core reveals a sequence of alluvial fan and ephemeral lacustrine or playa environments, revealing periods of lake expansion and contraction in response to climatic changes. An extensive canal cutting that transects a portion of the basin reveals complex sequences of alluvial and lacustrine sediments. Numerous Palaeolithic artefacts were discovered in situ within the canal’s section exposures. These artefacts include handaxes (possibly late Early Stone Age) and Levallois cores and other types that are typical of the North African Middle Stone Age. Several localities along the canal and sections of the core are being dated by optically stimulated luminescence. This paper will present the project’s findings and interpretations of the geoarchaeological evidence from al-Marj.