C- ISOTOPES OF CARBONATE AND CO3 FRANCOLITE MINERAL AS INDICATORS FOR THE CONDITIONS PREVAILED DURING THE EARLY DIAGENESIS OF PHOSPHORITE DEPOSITS IN SOUTHERN TETHYS IN THE LATE CRETACEOUS

The Late Cretaceous succession in Israel is enriched in Si-C-P, and is part of an extensive high productivity upwelling regime that supplied high nutrient levels and deposited successions of phosphates, cherts, porcellanites, and organic-rich carbonates. The Israel phosphorites are part of a large belt deposited during the mid-Cretaceous to Eocene and stretched between Turkey and Morocco. The phosphate records in the synclines show repeated alternation between two main phosphorite facies: pristine and reworked (economic phosphate). These recurrent patterns could result from climatic turnover. The pristine phosphorite deposition occurs under high rates of productivity and sedimentation and a more reduced environment. In contrast, the reworked phosphorite deposits occur under a high-energy environment and relatively more oxidized conditions. We present a high-resolution record of C- isotopes of carbonate and francolite carbonate phase from three massive synclines (Zin, Rotem, and Oron) in southern Israel. The C- isotopes records combined with rare earth elements to study the paleo-environmental and early diagenetic signals. Our results show intriguing differences between the three basins located close to each other (10-40 km) in their stratigraphy and C-isotopes and content. The francolite carbonate phase content (CO₃ wt%) in the pristine layers showed variability between the synclines and had a robust reverse correlation with the Ce anomaly showing that the CO₃ content decreased under reducing conditions. The reverse correlation can be explained by low pH pore water that reduced the precipitation of the CO₃ phase in the francolite and can result from enhanced OM degradation. Hence the CO₃ phase content has the potential to be used as an indicator for the redox state during phosphogenesis. δ¹⁸O values in francolite carbonate phase, vary significantly between the synclines. Eliminating other factors, δ¹⁸O of the pore water seems to be connected with organic matter degradation intensity, where lower values suggest intensive OM mineralization, which can indirectly be affected by the redox state. Rotem syncline, with a reducing condition, also presented the lowest δ¹⁸O and CO₃ values. We suggest that the CO₃ and δ¹⁸O cab be a direct and indirect indicators, respectively, for the redox state during phosphogenesis.