First lithological and organic geochemical characterization of organic-rich mudstones from Shavar Formation, southeast Bulgaria

The paper reports the first results of the organic geochemical characterization of mudstones from the Shavar Fm (eastern Rhodope Mt., Bulgaria). The rock matrix is unevenly impregnated by amorphous organic matter at the onset of the oil generation (T-max 445oC; PI - 0.1-0.2). High total organic carbon contents (avg. TOC - 5.9 wt. %) and HI (720 mg HC/g TOC) argue for oil-prone source-rocks with very good hydrocarbon potential. The n-alkane distributions with maxima in the range n-C20-25 are consistent with organic matter origin from submerged plants. Additionally, sterane distributions dominated by C28-30 4-methyl steranes, indicate dinoflagellate contribution. High pristane/phytane ratio (Pr/Ph = 2-4) argue for deposition under oxic conditions.

Automated summary

The paper presents the organic geochemical characterization of mudstones from the Shavar Fm in eastern Rhodope Mt., Bulgaria, indicating oil-prone source-rocks with good hydrocarbon potential. The organic matter in these rocks originates from submerged plants and dinoflagellates, and the deposition occurred under oxic conditions.