The luminescent behaviour and trace element contents (Mg2*, Sr2+, Na+, Ba2+, Fe2+ and Mn2+), for a total of 798 analysed spots distributed in five transects, have been determined in the inoceramid shells (three individuals) from the shallow-marine sediments of the Isla de Castro and Villamartín sections (Santonian of the Basque-Cantabrian Basin). The almost exclusive luminescence of the interprismatic zones and dark-growth lines, related to the decay of their organic-matrix content, indicates their behaviour as the main paths for trace element replacement in the shells. In this context, Mg2*, Sr2+ and Na* profiles tend to decrease clearly at the luminescence zones, whereas Fe2+ and Mn2+ values are considerably increased. By contrast, Ba2+ profiles do not seem to be altered by the luminescent behaviour of the shells, thus they may have preserved patterns close to the originals. Besides, other features such as both the significant absence of luminescence and extremely low contents in Fe2+ and Mn2* at the (intraprismatic) nonluminescent zones suggest the retention of the original patterns in Mg2*, Sr2* and Na+