Fig. S3.

Total ion chromatograms (TIC; from GC-MS) and biomarker distributions in the saturated fractions from selected depths in the Xiamaling Formation: (A) 273.9 m (upper layer of the OMZ), (B) 283.9 m (within the OMZ), and (C) 291.9 m (underlying the OMZ). These chromatograms are compared with overlying coals from the Jurassic Xiahuayuan Formation (D). Steranes and methyl steranes were either not detected or were in very low abundance in the sediments from OMZ, and steranes and methyl steranes were both found in the underlying and upper layers of OMZ. The peaks with question marks are interference peaks.