Relationship between total organic carbon content and sedimentation rate in ancient lacustrine sediments, a case study of Erlian basin, northern China

Abstract

Relationship between total organic carbon content (TOC) and sedimentation rate (SR) had been studied mainly in marine sediments, which is generally thought to be positive or negative correlation. Based on the data sets of sediment intervals from 111 exploration wells of 8 subbasins in Erlian lacustrine basin, northern China, the relationship between TOC and SR in ancient lacustrine sediments has been studied. The result points out that accompanied with increasing SR, TOC tends to increase and then decrease. The turning point of SR in all subbasins approximates 5cm/ka. Based on the research on biomarker and carbon isotope data, it has been found that the relationship between TOC and SR is controlled by the redox conditions when SR is lower than 5cm/ka, while SR is higher than 5cm/ka, the relationship is controlled by the paleoproductivity. When SR is lower than 5cm/ka, TOC tends to increase with increasing SR in all subbasins, indicating that it is the degradation that controls the TOC. Under the oxidation conditions, the degradation is intense, higher SR gets bigger TOC growth, while in reduction conditions, the degradation is weak, higher SR gets smaller TOC growth. When SR is higher than 5cm/ka, TOC tends to decrease with increasing SR in all subbasins, indicating that clastic dilution, instead of degradation, is the key factor controlling the TOC. The dilution effect is more significant in low palaeoproductivity environment than in high palaeoproductivity environment. Higher SR gets bigger reduction in low palaeoproductivity environment while it gets smaller TOC reduction in high palaeoproductivity environment.