Inocerámidos y sedimento carbonatado (Maastrichtiense inferior, Arco Vasco)Comportamiento de la relación 87Sr/86Sr durante la diagénesis (Parte I).

Résumé

Strontium isotopic analysis have been carried out on whole rock and inoceramid shell samples from deep-sea carbonate sediments at Sopelana and Bidart sections (Basque Arc). They were compared with oxygen isotope values provided from the same locations together with published whole rock and inoceramid shell Sr contents. In comparison with Sopelana samples, Bidart ones are characterised by the highest Sr contents and the lowest 87Sr/B6Sr ratios. Furthermore, inoceramid remains usually yield lower isotopic values than whole rock ones. These results suggest that carbonate matrix and inoceramid shells have undergone different behaviour during diagenesis. Most of the strontium isotope ratios measured on inoceramid samples from Bidart fall close to the lower Maastrichtian seawater 87Sr/B6Sr curve and are dominated by a wide, non-luminescent middle shell layer. Nevertheless, Sopelana I inoceramid samples show values which lie far from maastrichtian strontium isotope values, which exhibit a whole luminescent shell. To test these results, the S7Sr/86Sr ratio was also determined on selected luminescent and non-luminescent areas in the same inoceramid shell