Organic geochemical characteristics and sedimentary environment of source rocks in faulted basin: a case study of Zhusan depression

Multiple sets of source rocks have developed in the Zhusan Depression. However, the organic geochemical characteristics and significance of the sedimentary environment haves not been made clear. On this basis, Rock-Eval and gas chromatography-mass spectrometry (GC-MS), Ro, and trace element analyses were carried out. The results demonstrate that: (1) The hydrocarbon generation potential of the Wenchang Formation (WC) in the Wenchang B sag (WCB) is the best, followed by the Enping Formation (EP). The quality of EP in the Wenchang A sag (WCA) varies widely. (2) The parent material of the second member of the Wenchang Formation (WC2) is primarily algae, whereas the first member of the Wenchang Formation (WC1) and EP are mainly resin polymers. (3) The Zhusan Depression is in shallow freshwater and in a transitional-partial oxidation sedimentary environment. The climate of the WCB changed from dry and hot in WC to warm and humid in EP. The bottom of EP in the WCA is dry and hot, and the upper layer is warm and humid. (4) Paleosalinity has a profound influence on EP in the WCA and WC in the WCB, while the EF in the WCB is mainly affected by the paleoclimate.