Paleogene sedimentary paleoenvironmental reconstruction and its petroleum geological significance in Western Baiyun Sag, Pearl River Mouth Basin

In recent years, there have been continuous discoveries and exploration in the Western Baiyun Sag, PRMB (The Pearl River Mouth Basin). However, few studies have been conducted on the characteristics of sedimentary paleoenvironment and there is a lack of systematic reconstruction, which could hinder future exploration of the study area. To systematically reconstruct the Paleogene paleoenvironment including paleoclimate, paleowater depth, and ancient landform, quantitative paleoenvironmental recovery methods were developed based on the paleontology, geophysical logging, geochemical and rock physical properties data of the study area. Results show that, from the Wenchang Formation to the Zhuhai Formation, both paleoprecipitation and paleotemperature decreased, ancient landforms continue to flatten and then stabilized due to the weakening detachment fault activity, and the paleowater depth centers were gradually reduced and migrated to the Baiyun Sag, showing an evolution pattern of from narrow deep basin to wide gentle basin and to wide shallow basin. During the period of the Wenchang Formation, the climate of the Western Baiyun Sag was warm and humid, the supply of organic matter was sufficient. Steeper terrain and several deep-water lakes were developed in the early stage. Material supply is from multi-point combined with near-source supply, which resulted in hydrocarbon sources in medium-deep multi-deepwater-centered lake facies, while in the late stage, the deep-water centers merged, and the supply of sources showed a bi-directional source joined with relatively far sources, which resulted in the medium-shallow lake-facies hydrocarbon source rocks with converging deep-water centers. During the period from the Enping Formation to the Zhuhai Formation, the temperature decreased, and a cooler climate occurred in the late stage. The landform underwent flattening, while the water became shallower. The paleowater depth centers further converged. Source supply changes from intra-basin to intra-and-inter-basin distant source, with relatively less organic matter supply. As a result, there were poorly developed, shallow lake-facies hydrocarbon source rocks in paleowater depth centers. The quantitative reconstruction of paleoenvironment have significant implications for studying the evolution of the lake basin, the source-sink system, and predicting high-quality hydrocarbon source rocks in the Western Baiyun Sag, which will serve as a theoretical foundation for the later stages of regional oil and gas exploration.