Search Results (2)

Paleoenvironmental knowledge holds significant scientific value for elucidating the evolutionary history of Earth’s crust and for guiding the exploration of oil and gas resources. This study presents a comprehensive analysis of sporopollen–algae fossils from Well DW-2, located in the Zhu II Depression of the eastern South China Sea. The sampled strata of the well were from 0 to 3230 m in depth, with a substantial number of sporopollen–algae fossils identified within the Enping and Zhuhai Formations spanning from 2501 to 3227 m. Two distinct sporopollen–algae assemblages were delineated from bottom to top. The sporopollen characteristics reveal a transition from tropical and subtropical to subtropical and temperate plant communities, reflecting the warm and humid climate during the formation of the Enping Formation and the relatively cool and dry climate during the formation of the Zhuhai Formation. A significant number of marine dinoflagellate fossils were identified, and the observed changes in algal characteristics suggest that the Enping Formation was accumulated in a shallow marine environment, while the Zhuhai Formation was predominantly formed in a transitional setting between marine and terrestrial conditions at the shelf margin. These findings not only enhance our understanding of the paleoenvironmental conditions in the South China Sea region but also have broader implications for reconstructing global paleoclimates and identifying potential hydrocarbon reservoirs in similar sedimentary basins. Full article

There are two sets of hydrocarbon source rock formations developed in the Paleogene of the Zhu-1 Depression: the Wenchang Formation of semi deep lacustrine facies and the Enping Formation of lacustrine facies. Their basic geochemical characteristics, chemical structures, kerogen components, sedimentary paleoenvironments, etc., are not the same. High quality hydrocarbon source rocks are the basic conditions for oil and gas generation. This article comprehensively evaluates the key depression Paleogene hydrocarbon source rocks in the Zhu-1 Depression, and studies the development mechanism and controlling factors of hydrocarbon source rocks in this area, which is of great significance for understanding the development conditions, quality, and predicting potential high-quality hydrocarbon source rocks. After conducting rock pyrolysis, major and trace element analysis, and infrared spectroscopy experiments on the samples, it was found that the main source rock type of the Wenchang Formation is type II₁, which has a high HI value; the Enping Formation is mainly composed of II₂-III types with low HI values (with a small number of II₁ types), and the source rocks of the Wenchang Formation have a strong hydrocarbon producing aliphatic structure, with the sapropelic and shell formations being larger than the Enping Formation source rocks. By using methods such as CIA values, C values, and Mo-U covariant models, it can be concluded that during the Wenchang to Enping periods, the climate changed from warm and dry to cool and humid, and the overall environment was characterized by freshwater, weak oxidation weak reduction, and gradually decreasing paleo-productivity. At the same time, it was analyzed that the formation of organic rich sediments in the source rocks of the Zhu-1 Depression played an important role in the relative oxygen phase. The ratio of V/(V + Ni) to V/Cr can better indicate the redox environment of the water body and show a good correlation with TOC. Two sets of development models of source rocks controlled by paleooxygen phase were initially established, providing sufficient scientific basis for oil and gas exploration in the area. Full article