Study on Pre-Treatment Methods for the Determination of Organic Carbon Isotope Composition in Sedimentary Rocks

The organic carbon in sedimentary rocks is mainly in the form of kerogen, it is necessary to extract kerogen from samples before obtaining the organic carbon isotope value. The extraction process requires a significant quantity of hazardous chemicals and a long preparation process. Therefore, in daily work, there is an urgent need to develop a more convenient and environmentally friendly pre-treatment method. A simple acid treatment method was established, and 110 sedimentary rock samples with different lithology (limestone, shale, oil shale) and different organic carbon content range (0.83%-35.33%) were selected for comparison experiments of two pretreatment methods. The results show that for 94% of the samples, the difference of carbon isotope values obtained by the acid pretreatment method established in this study and kerogen extraction method was less than 1.0‰, which met the deviation requirements for repeated measurements,. which means that this pretreatment method can accurately obtain the key geological parameter of organic carbon isotope value. Furthermore, the organic carbon content and lithology of the samples did not influence the results, demonstrating the applicability of this method to typical geological samples and fulfilling the requirements of geological exploration and investigation.