Formation and evolution of coal– and oil–bearing source rocks in the Lower Cretaceous Shahai Formation in the Fuxin Basin (NE China): Evidence from organic and inorganic geochemical analyses

Two source rocks were deposited in the Lower Cretaceous Shahai Formation (K1sh) in the Fuxin Basin (NE China): the third Member (K1sh3) coal–bearing and the fourth Member (K1sh4) oil–bearing source rock. However, the differences between the two Fuxin Basin source rocks remain poorly constrained. This study systematically reveals the formation and evolution of these source rocks through sedimentological and geochemical analyses. During the K1sh3 deposition, the intermittently warm–humid climate promoted organic matter (OM) input from terrestrial plants. Meanwhile, the restricted swamp with suboxic water conditions enhanced OM preservation and reduced OM dilution. Thus, warm–humid climate, suboxic water conditions of swamp controlled the formation of excellent coal–bearing source rock with highest total organic carbon (TOC) content (avg. 28.68 wt%) and Type III kerogen (perhydrous). The post–mature maturity (avg. 484 °C Tmax) indicates that the K1sh3 coal–bearing source rocks have reached the wet to dry gas generation stage.