Inorganic geochemical characteristics and evaluation of Sinian-Cambrian post-mature source rocks in Sichuan Basin

Abstract

The evaluation of post-mature source rocks gradually invalidates by traditional organic geochemical parameters due to the decreasing of organic matter abundance. However, the inorganic elements in source rocks are not easily affected by thermal evolution. In order to explore the application of inorganic geochemical methods in the evaluation of post-mature source rocks, this paper takes the Sinian-Cambrian source rocks in the Sichuan Basin as an example to conduct an evaluation based on the inorganic (major, trace and rare earth elements) geochemistry method with three controlling factors of source rock development (paleoproductivity, sedimentary environment and sedimentary rate). The concentration of Ba and Ni, MoEF and UEF and Ce anomaly, and TiO2/Al2O3 ratio could be correlated with paleoproducitvity, sedimentary environment and sedimentary rate, respectively. The results showed that the enrichment of organic matter was mainly controlled by sedimentary environment and paleoproductivity, but are barely effected by sedimentary rate. Source rocks in the Lower Cambrian Qiongzhusi Formation in the central Sichuan and Weiyuan-Ziyang areas have high paleoproductivity and the most reduced environment and thus are one of the best quality source rocks. Therefore, inorganic geochemistry method is an effective way to evaluate postmature source rocks.

Keywords

• post-mature source rock
• inorganic geochemistry
• hydrocarbon generation capacity
• source rock evaluation
• sinian
• cambrian
• sichuan basin