Microestructuras, luminiscencia y geoquímica en Crassostrea sp. de la Formación Zufía, Navarra (Albiense superior-Cenomaniense inferior). Parte I

Abstract

Shells of the oyster Crassostrea sp. from the Zufia Formation, deposited in a strongly subsiding basin at the end of the Albian, show the same microstructures than recent and fossil Crassostrea sp., deposited in other less subsiding areas; the best preserved microstructure is the regular foliated (RF), while the most altered one is the complex cross foliated (CCF); the external regular simple prismatic (RSP) microstructure, however, shows different degrees of alteration. Both daily-tidal (La) and seasonal (Lb) growth lines can be seen in the RF microstructure. The CCF and RSP ones show, in the best preserved areas, daily-tidal growth lines. Our trace element analyses, carried out at a fine-scaled resolution along a sclerochronological transect in the condrophore area of the shell, indicate sinusoidal patterns for the Mg/Ca and Sr/Ca ratios. Interestingly, such patterns follow that of the growth lines and, thus, they provide seasonal information. Accordingly, an age of more than 3 years has been assigned to a selected sample. The Na/Ca ratio progressively decreases with the life of the oyster. The Fe/Ca and Mn/Ca ratios are both higher in the luminescent Lb seasonal growth lines