Sedimentary and diagenetic features of the Oolithe Blanche formation (Middle Jurassic): new contribution from Ca, Sr, C, O isotopic compositions
Résumé
The Oolithe Blanche formation is present in the Paris Basin at more than 1500 m depth in the middle of the basin and on outcrops at the basin edges. This Bathonian formation (Middle Jurassic) is composed of very shallow marine oolithic and bioclastic limestones, located within a shoreface depositional environmental (Casteleyn et al., 2010). Calcium, strontium, carbon and oxygen isotopes have been analysed both in ooids and interparticular cement directly extracted from the limestone in order to study sedimentary and diagenetic environment. The 44Ca/40Ca ratios (expressed as 44/40CaSW) were measured by TIMS using a 42Ca-48Ca double-spike. Carbon and oxygen isotopic ratios were measured by IRMS. Preliminary results show a range of 44/40CaSW from -0.74‰ to -1.09‰ in the cement and from -0.85‰ to -1.05‰ in ooids. Carbon isotopic signature show a range of 13Cvs PDB range from 1.5‰ to 2.7‰ in the cement and from 1.5‰ to 2.4‰ in ooids while 18Ovs SMOW vary from 21.5‰ to 23.9‰ in the cement and from 21.2‰ to 24.9‰ in ooids. This first multi-isotopic approach on Oolithe Blanche formation seems to be consistent with the diagenetic evolution of Paris Basin. Effects of diagenesis on the isotopic signatures will be discussed. Reference: Casteleyn, L., Robion, P., Collin, P.Y., Menendez, B., David, C., Desaubliaux, G., Fernandes, N., Dreux, R., Badiner, G., Brosse, E., Rigollet, C., 2010. Sedimentary Geology 230, 123-138.