Geochemical characteristics of the lower cretaceous Xiguayuan Formation mudrocks in the Luanping Basin, northern China: Implications for the hydrocarbon generation potential and sedimentary environments

Thick and organic-rich mudrocks occur in the lower Cretaceous Xiguayuan Formation (K(1)x) of the Luanping Basin, Northern China. Shale oil has been discovered for the first time in Well LT-1, adding to the oil exploration of Mesozoic hydrocarbons in the Yanshan Structural Belt. However, geochemical studies have been very limited. In this study, the core samples in Well LT-1 and several outcrop samples from stratigraphic sections were collected. Organic and inorganic geochemical analyses have been jointly carried out to study geochemical characteristics and paleoenvironments as well as the controlling factors for organic matter accumulation. The studied mudrocks are fair to excellent source rocks (total organic carbon content similar to 3.6 wt%). The main organic sources are aquatic plankton and terrigenous higher plants. The dominant organic matter is of type II and III. The vitrinite reflectance (0.84-1.32 %) and T-max values (440-467 degrees C) indicate mature to highly mature thermal maturity stages. The results indicate that the mudrocks have good hydrocarbon generation potential. Additionally, biomarkers and elemental composition show that they formed under anoxic lacustrine sedimentary environments with a stratified and brackish water column. The paleoclimate was semiarid, the paleoproductivity was moderate and the sedimentary rate was high. Excellent preservation and moderate productivity are the two major controlling factors for organic matter accumulation in the Xiguayuan Formation.

Automated summary

The study found that mudrocks in the Luanping Basin's Xiguayuan Formation have good hydrocarbon generation potential, with the main organic sources being aquatic plankton and higher plants, and the dominant organic matter being type II and III. The mudrocks formed in an anoxic lacustrine sedimentary environment, with a semiarid paleoclimate and key factors for organic matter accumulation being excellent preservation and moderate productivity.