Chemical composition of sediments is often used to evaluate paleoclimate condition, provenance, tectonic setting, depositional condition, and paleoproductivity. However, the validity of these proxies has long been questioned. The comprehensive use of organic and inorganic multi-indicators in combination when interpreting issues related to terrestrial shales should be advocated. The paleodepositional environment, origin of organic matter (OM) and factor controlling OM accumulation in the Early Jurassic Badaowan (J₁b) and Sangonghe (J₁s) as well as Middle Jurassic Xishanyao (J₂x) lacustrine shales in the East Fukang Sag are reassessed by using organic geochemical characteristics of the OM. Some previous knowledge is updated, and some knowledge is further supported by more evidence. The typical clay-rich shale developed under a lacustrine sedimental environment, and the thermal maturity of these organic-rich shales has entered the oil window and formed economic hydrocarbon potential for the tight-oil and shale-oil reservoirs. The paleoclimate conditions of the study area were warm and humid from the Early to Middle Jurassic periods but were colder and drier after the Middle Jurassic period. The salinity of the water column ranged from freshwater to brackish conditions. The J₂x Formation was deposited under oxic conditions, while J₁b and J₁s formations developed under suboxic and reducing environmental conditions. The J₂x Formation OM mainly derived from higher plants was deposited in a terrestrial environment,while the OM of J₁b and J₁s formations was a mixed OM derived from higher plants and bacteria with little algae deposited under bay/estuary environments alternated with terrestrial environments. It is effective to reflect the paleoclimate by element index and judge the salinity by the updated element thresholds, but it is not effective to evaluate the paleoredox conditions by common elemental ratios and to evaluate the paleoproductivity by Ba in the study area.

Recently, there has been an increasing focus on deep and ultradeep oil and gas exploration and development. The Upper Jurassic Qigu Formation (Fm.) in the Yongjin region, located in the central area of the petroleum-bearing Junggar Basin, develops typically deep and ultradeep hydrocarbon reservoirs, but there is currently limited knowledge of the geochemical characteristics and origins of the oils in the reservoirs. A comprehensive analysis of the molecular characteristics and carbon isotopes of the oil and extractable organic matter (OM) samples from the Qigu reservoirs, as well as source rocks from the Middle Permian lower Wuerhe and Lower Permian Fengcheng Fm., was carried out to elucidate the thermal maturity, biological sources, and biodegradation scale of the OM, as well as the depositional environment of the related source rocks. The results suggest that the Qigu oils originated primarily from source rocks formed in a hypersaline lacustrine environment with paleoredox conditions of bottom water ranging from reducing to suboxic conditions. Furthermore, the biological sources of oils predominantly originated from bacteria, followed by algae. The degradation scales range between 3 and 4, and the thermal maturity is in the oil window for the samples examined. The OM of the Permian source rocks in the Yongjin region are in the high thermal maturity stage due to their ultradeep burial, thereby providing limited information to oil and source correlation. By combining more than 1000 published data from the entire basin, significant differences between the Jurassic and Permian source rocks, as well as minor differences between the lower Wuerhe (i.e., the ratios of Pr/n-C₁₇ of <0.5, Ph/n-C₁₈ of 1.5, C₂₇/C₂₉ sterane of >0.4, and hopanoids/steranes of >1 as well as the higher C₂₀/C₂₃ Tri ratios) and Fengcheng source rocks (i.e., β-carotane/n-C _max ratios of >0.1 and some samples with C₂₈ steranes concentrations of <10% in the normalized concentrations of C₂₇, C₂₈, and C₂₉ steranes), were observed, and the origins of the oils were determined. The oil-source correlation suggests that the oils most likely originated from the lower Wuerhe Fm. without strictly excluding the possibility of a contribution from the Fengcheng Fm.

The ocean is a significant global reservoir of uranium (U) and thorium (Th). These elements can be incorporated into marine sediments through processes involving organic matter (OM), redox conditions, terrigenous inputs, and mineral interactions. Helium generated through the radioactive decay of U and Th within geological formations represents a critical potential resource. Marine black shales, which are rich in U and Th, are widespread in the Ediacaran Doushantuo Formation of the Upper Yangtze Platform, making them a key target for helium exploration. However, there is limited research on the mechanisms behind U and Th accumulation in these shales. This study focuses on shales from the Doushantuo Formation in Chongqing, China, aiming to explore the mechanisms of U and Th accumulation and assess the potential for helium generation, and argillaceous dolomites are included for comparative analysis. The results show that the average U and Th content in the black shales (17.58 and 9.78 ppm, respectively) is higher than that of argillaceous dolomites (3.52 and 2.75 ppm, respectively). Uranium mainly comes from authigenic precipitation and hydrothermal inputs, while thorium is primarily sourced from terrigenous and hydrothermal inputs. The semi-humid climate in the provenance area facilitated parent rock weathering, with atmospheric precipitation and river systems transporting U and Th to the ocean. However, excessive terrigenous input can dilute the U and Th content in the sediments. In the shales, uranium is primarily adsorbed and/or complexed by organic matter (OM), with the anoxic–euxinic sedimentary environment and high OM content (TOC = 0.06–34.58 wt.%, r = 0.95) promoting U accumulation. Thorium accumulation is largely controlled by adsorption onto clay minerals. The total amount of helium generated from the Doushantuo shales is estimated to be 7.20 × 10¹⁰ m³.