[en] The Upper Frasnian sequence of the Namur–Dinant Basin in southern Belgium consists of mixed siliclastic–carbonate succession of a ramp setting, where the sequence spans the rhenana–linguiformis conodont zones. Earlier studies investigated the chemostratigraphic variations during the Frasnian-Famennian event, but little has been yet known about the nature of the counterpart variations that immediately preceded that time interval. Despite the scarcity of well-preserved brachiopods, sixty–one calcitic shells were collected mainly from beds of the Neuville and Les Valisettes formations (Lower and Upper rhenana zones), to investigate biochemostratigraphic profiles of oxygen-, carbon-isotope and rare earth element (REE) variations of the time interval immediately before the Frasnian-Famennian boundary. The δ18O and δ13 C values of the well-preserved shells range from − 9.5 to − 5.6 ‰ VPDB (− 7.7 ± 1.1, n = 33) and from − 1.8 to 3.8 ‰ VPDB (1.1 ± 1.7, n = 33), respectively, which are within the documented global values. The C- and O-isotope profiles exhibit parallel shifts, particularly at the top of the Neuville Formation (top of the Lower rhenana Zone), which are associated with a sea-level rise and shrinkage in the brachiopod community. Also, the Th/U (0.9 ± 0.6, n = 16) and Ce/Ce* (2.2 ± 0.5, n = 16) ratios suggest deposition under reducing conditions consistent with sea transgression.