Stable isotopic composition of calcic paleosols of the Early Cretaceous Hasandong Formation, southeastern Korea

Abstract

Abundant pedogenic carbonate nodules are present in the Cretaceous non-marine Hasandong Formation, southeastern Korea. The oxygen isotope compositions of these pedogenic carbonates range from −14.2 to −18.0‰ (PDB). The meteoric water composition estimated from the oxygen isotope composition of the soil-water in equilibrium with the carbonates is much depleted compared with the previous estimate. This suggests that the oxygen isotope compositions of the Hasandong pedogenic carbonates were modified during diagenesis. The carbon isotopic compositions of the Hasandong carbonates range from −2.4 to −9.3‰ (PDB) with an average of −5.6‰ (PDB) suggesting carbonate formation in soils dominated by C 3 type of vegetation. The estimated average composition of the vegetation is about 6‰ (PDB) enriched compared with the present-day C 3 vegetation. This is probably due to atmospheric influence contributing about 35% of the total CO 2 in the soil. An analysis of this contribution using the model of Cerling (1991)indicates that the partial pressure of CO 2 in the Early Cretaceous Hasandong atmosphere was about 2300 ppmV.