The diagenetic history of four vertebrate localities from the western Pyrenees (Laño and Zambrana in the Basque-Cantabrian Region, Ardanatz and Uztarrotz in the Pamplona Basin) is analyzed. The sites range stratigraphically from the Upper Cretaceous (Laño) to the Middle-Upper Eocene (Ardanatz, Uztarrotz, and Zambrana), and correspond to different sedimentary environments. The replacement of biogenic hydroxyapatite by well-crystallized francolite (carbonate fluorapatite) is related to diagenetic changes in all localities.
Geochemical techniques based on variance in trace element composition from different fossil bone assemblages can be used as a test to measure the relative degree of mixing or taphonomic averaging within vertebrate associations. The geochemical composition and trends of the fossil remains suggest that the diagenetic processes were relatively uniform in all the sites, although REE trends in each particular sites are different, which precludes mixing of reworked bone
