Correlation between contents of TOC and strontium distribution within source rocks of Shahejie Formation in Dongying Sag, Eastern China

摘要

The third member of Shahejie Formation of Eogene (Es3) is the primary source rock of the Dongying sag, eastern China. The high-quality source rocks of the lower formation of Es3, usually with laminated structure, are primarily composed of carbonate and clay laminae rich in organic matter. An obvious positive correlation between the content of total organic carbon (TOC) and a microelement, Sr is found in the source rocks. Also, it has been found that Sr is mostly accumulated in the carbonate laminae rather than in the clay laminae. Based on the fact that the carbonate laminae are usually composed of endogenetic thin laminae of carbonates such as calcareous imbricate planks formed by algal blooming, it can be concluded that the source of Sr has a relation with algal blooming. The thin carbonate laminae are resulted from the absorption and assimilation of chemical elements within aquifer by algal blooming. The element of Sr occupies the crystal lattice of Ca, and then accumulates within CaCO3, which results in the synchronous enrichment of TOC and Sr within source rocks.