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The Dongpu Depression is one of the major petroliferous structures in the Bohai Bay Basin of eastern China. The Shahejie Formation is the key target unit for petroleum exploration in the Dongpu Depression. The current studies on this fossiliferous structure mainly focus on the northern depression, and the detailed study on the southern part of the depression is still scarce. To further study on the southeast subsag located in the southern part of this depression, we examined the geochemical characteristics and origin of petroleum using stable carbon isotopes, components of crude oil and natural gas, micro Fourier transform infrared spectroscopy (FT‐IS), gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). Fluid inclusions and 1D model were employed to reconstruct the burial and thermal history and indicate the timing of hydrocarbon generation. Finally, the petroleum exploration in this region is guided based on the combination of geochemical results and geological setting. The result of geochemical characteristics of crude oils indicates the oil was from the combination of algal and terrestrial plants, deposited in reducing to sub‐oxic and fresh to marginally brackish environment. Furthermore, the oil in the northeastern part could be traced to the Haitongji subsag and has relatively lower thermal maturity than that in the central part. Stable carbon isotope data suggest that natural gas is a mixed oil‐type and coal‐type gas. The equation estimated indicates that natural gas in the northeast is mainly oil‐type gas, with an average ratio of 80.0%, whereas coal‐type gas is dominant in the central part (average percentage: 74.3%). Geochemical characteristics of hydrocarbon indicate that the Changyuan Fault was a migration pathway for the northeastern petroleum, whereas it gradually changed to be sealed towards the central part. [ABSTRACT FROM AUTHOR]

The late Cambrian extinction – Early Ordovician biodiversification represents one of the crucial lower Paleozoic biological changes. However, the mechanisms responsible for this transition remain poorly understood. Here, we reconstructed the paleoenvironmental changes based on a model that integrated the atmospheric-oceanic-biological inputs and provided the first detailed assessment of the Cambro-Ordovician biological turnover. The results show depositional environments evolved into extremely sulfidic conditions with lower nutrient inputs and more restricted water circulation from the Miaolingian to early Furongian, leading to the Steptoean Positive Carbon Isotope Excursion event. The intense volcanic activity in the early Jiangshanian appears to be responsible for the recurrent bio-calamity. Later in the mid-late Furongian (mid-Jiangshanian to Stage 10), enhanced terrestrial weathering contributed to the Earth's cooling and higher inputs of terrestrial nutrients, beneficial to the subsequent biological recovery. In the Early Ordovician and despite reduced terrestrial nutrient input, massive oceanic water upwelling alleviated sulfidic conditions and brought nutrients, laying the foundation for the Great Ordovician Biodiversification Event. • The high-precision Cambro-Ordovician environmental changes were investigated. • Widespread oceanic anoxia and volcanic activity were responsible for the Furongian extinction events. • Early Ordovician massive oceanic water upwelling could have promoted biological recovery. • The co-variation of temperature, nutrient inputs, and redox conditions resulted in the Cambro-Ordovician turnover. [ABSTRACT FROM AUTHOR]

The late Cambrian witnessed significant biological and environmental changes. However, the main triggers responsible for that formidable turnover remain largely unknown. This study investigates mercury (Hg) enrichments from the late Miaolingian to Furongian section in a unique Alum Shale drilled core obtained from southeast Sweden. Our results show that the background level of Hg is relatively high because of the presence of reducing conditions and continuous Hg supply from water mass. However, our most spectacular findings are the presence of four Hg anomalies. The most pronounced Hg anomalies are characterized by the high values in total Hg (~900 ppb) and Hg/TOC ratio (~80), as well as specific signatures of mass independent fractionation of Hg (MIFs; Δ199Hg, Δ201Hg, and Δ200Hg) that we attribute to volcanic-derived Hg. This Hg loading event occurred immediately after the globally recognized Steptoean Positive Carbon Isotope Excursion (SPICE) event and could be attributed to volcanic activities during that period. [ABSTRACT FROM AUTHOR]