Petrographic and Cathodoluminescence Insights into Flint Characterisation Using an Integrated Approach: A Case Study from Fluvial Terrace Deposits in SW Iberia

The accurate characterisation of flint in geologically complex regions remains a major challenge in geoarchaeology, particularly in secondary deposits such as fluvial terraces, where materials derived from multiple geological formations may converge. This study applies combined petrographic and cathodoluminescence (CL) microscopy to flint from the fluvial terraces of the Guadalete River (southwestern Iberian Peninsula). More than 1000 geological samples were examined macroscopically and by stereomicroscopy. A purposive subset of 120 specimens was studied in thin sections, of which 80 were additionally analysed by CL, in order to capture the principal petrographic variability observed in the secondary deposits. Four petrographic groups were identified—oolitic–peloidal flint, bioclastic flint, radiolarian flint with other biogenic components, and pelagic radiolarian flint—together with massive/dolomitised flint, a diagenetically defined type. CL revealed internal structures, carbonate relics, silicification halos and dolomitisation zones that complement transmitted-light observations and support the interpretation of replacement processes and internal variability. Its contribution varies among groups and is limited for pelagic radiolarian flint, whose identification relies primarily on conventional petrography. The integrated observations provide a geological characterisation of the flint varieties represented in the Guadalete terraces and their diagenetic histories. They do not, by themselves, permit attribution of individual specimens to a specific terrace level or demonstrate archaeological provenance. The resulting reference framework provides a basis for future comparisons with archaeological flint assemblages in the Strait of Gibraltar region.