Stable isotope record in pedogenic carbonates in northeast Iran: Implications for Early Cretaceous (Berriasian–Barremian) paleovegetation and paleoatmospheric P(CO2) levels

Abstract The Shurijeh Formation (Early Cretaceous) consists of siliciclastic, evaporate, and carbonate facies with associated calcareous paleosols in the Kopet-Dagh basin. These calcareous paleosols (pedogenic carbonate nodules) include specific macromorphological and micromorphological features. Based on macroscopic and microscopic properties, the Shurijeh Calcareous paleosols are divided into pedogenic and non-pedogenic (ground water) types that are each formed under specific conditions. Estimated δ13C values of plant-CO2 for Shurijeh vegetation range from − 20.75‰ to − 22.14‰ (with an average = − 21.31‰). These values are consistent with plant type C3. The contribution of atmospheric CO2 in δ13C values of plant-CO2 of studied calcareous paleosols was 25 to 30%. The Neocomian (Berriasian–Barremian) paleoatmospheric PCO2 gap was reconstructed by interpretation from measured carbon isotopic compositions of the Shurijeh Formation pedogenic carbonates. The paleoatmospheric CO2 levels of the Shurijeh Formation are estimated to be 1226–2196 ppmv. The general trend of Early Cretaceous estimates matches the modeled value trends for these times.