Contributions of soot to δ13C of organic matter in Cretaceous lacustrine deposits, Gyeongsang Basin, Korea: Implication for paleoenvironmental reconstructions

This study reports that soot carbon (SC) derived from biomass burning is an important constituent of total organic carbon (TOC) (30–90%) in two Cretaceous lacustrine deposits (Middle Albian Jinju Formation and Early Cenomanian Banyaweol Formation) of the Gyeongsang Basin, Korea and that SC contributed significantly to the carbon isotope composition (δ13C) of the TOC. δ13C of the TOC and δ13C of the SC-corrected (non-SC) organic matter range from − 24.7‰ to − 21.9‰ and − 25.1‰ to − 20.7‰ in the Jinju Formation, and − 24.7‰ to − 23.0‰ and from − 26.4‰ to − 21.7‰ in the Banyaweol Formation, respectively. Based on the δ13C values of coeval charcoal, the calculated δ13C of the original plant material in the surrounding watershed of the paleo-Jinju lake ranged from − 21.8‰ to − 17.8‰ (av. − 19.3‰). These values are considerably different from δ13C of vegetation (av.− 24.3‰) estimated from SC. The estimated δ13C values of non-SC organic carbon are different from those of the TOC, by up to 3.5‰ (either an enrichment or depletion across this value). This discrepancy indicates that the presence of SC in sedimentary organic carbon affected carbon isotope composition of TOC in the studied lacustrine deposits and led to increase uncertainty of interpretation of paleoenvironment of the watershed. For improving the paleoenvironmental reconstructions by utilizing the δ13C values of TOC in ancient lacustrine sediments, a correction for the contribution of SC to TOC needs to be considered.