The realization of geochemical and diagenetical studies on fossil oyster’s shells from the «Calizas Nodulosas
con Ostreidos y Limolitas de Sopuerta unit» has allowed demonstrating the variations in the luminescence of
different microstructures, mainly in the Regular Foliated one (RF), as a result of different burial depths. The
structural properties of the distinguished microstructures made possible, to a greater or lesser extent, the
circulation of diagenetic fluids which provided the shell with diagenetic elements like Fe, Mn or Mg. As a
result of this cationic exchange, the shell enriched the fluids with Na or Sr, considered primitive elements in
oyster’s shells. The importance of the rocky matrix in the geochemical alterations has been demonstrated,
comparing the results of this study with the results obtained by Higuera-Ruiz and Elorza (2006)