Figure 1

Stratigraphic column of Upper Cretaceous recovered from the SK1 core in the Songliao Basin, with representative formation, stage, lithology as well as geochronological constraints (Modified after Wang et al., 2013a (Ref. 28)).

(a): Stratigraphic distributions of specific C₃₀ steranes for whole SK1 core; (b): Enlarged view of stratigraphic distributions of specific C₃₀ steranes for the Qingshankou Formation; (c): Enlarged view of stratigraphic distributions of specific C₃₀ steranes for Member 1 and Member 2 of the Nenjiang Formation. Absolute dates in red * are SIMS zircon U-Pb ages and dates in ☆ are paleomagnetic interpolated ages (Ref. 15). mudstone, silty mudstone, muddy siltstone, fine sandstone, sandstone, oil shale.