ESTIMATES OF ATMOSPHERIC CO2 LEVELS DURING THE MID-TURONIAN DERIVED FROM STABLE ISOTOPE COMPOSITION OF PALEOSOL CALCITE FROM ISRAEL

Abstract

The carbon and oxygen isotopic composition of pedogenic calcite from mid-Turonian paleosols in Israel was analyzed to evaluate paleoenvironmental conditions and calculate paleoatmospheric pCO2. The central area of Israel was a part of a marine carbonate shelf that emerged during the mid-Turonian stage, as evidenced by karstic phenomena, fluvial sandstone, and soil profiles. The paleosols have the characteristics of equivalent modern calcic Vertisols but are distinguished by the predominance of palygorskite, which formed as an essential part of the soil processes. The pedogenic calcite and the underlying and overlying marine limestone beds have mean δ13C (‰, Vienna Peedee belemnite [VPDB]) values of -6.15 ± 0.93, -2.82 ± 1.87, -1.33 ± 2.17, respectively, and δ18O values of -5.03 ± 1.24, -6.31 ± 0.87, and -5.81 ± 0.97, respectively. In most sections, the δ18O values of pedogenic calcite are much heavier than those of the limestone due to evaporation. Since most of the pedogenic calcite formed at ≥50 cm depth and did not show diagenetic modification, the δ13C values were used to calculate pCO2 according to the Cerling model (as applied by Ekart et al., 1999). This marks the first Turonian pCO2 estimate calculated from pedogenic calcite. The calculated range for the mid-Turonian is 1450-2690 ppmv CO2. This high pCO 2 level is similar to or somewhat higher than other estimates for the Cretaceous and in accord with calculated high Turonian temperatures from many studies. © 2006 Geological Society of America.