This article presents the results of geological and geochemical studies of the organic matter of source rocks and oil from reservoirs in the Karamay Formation (Anizian–Ladinian stages) in the eastern part of the Fukang Depression in Junggar petroleum basin. The quantity, quality, and degree of maturity of the organic matter in clayey mudstones in upper part of the Karamay Formation (T2k) were considered and the composition of the original organic matter, the conditions of its accumulation and the degree of maturity were reconstructed using pyrolytic parameters and biomarkers. The dark gray and gray mudstone in upper part of the Karamay Formation accumulated in fresh or low salinity lakes with relatively reducing conditions. At present, the organic matter of the Formation within the depression is in the zone of mesocatagenesis MK1–MK3, and therefore has not fully realized its oil-geological potential. It has been previously established that mudstones in upper part of the Karamay Formation provided the hydrocarbon fl uids for the Karamay reservoirs located in the submerged part of the Fukang Depression.

Within the eastern part of the Fukang depression, the main productive series are confined to the Permian and Jurassic oil and gas complexes (OGC), in which the Middle Permian and Lower-Middle Jurassic oil and gas source rocks (OGSRs) are distinguished. The article discusses in detail the oil and gas source characteristics of the Middle Permian and Lower-Middle Jurassic rocks, the molecular composition of oils and bitumoids from the OGSRs, and also interprets the characteristics of the biomarkers in them from the standpoint of the sedimentary-migration theory of oil generation. An attempt is made to explain the reasons for the difference in the properties and composition of oils from different OGCs. It is shown that the composition of hydrocarbon fluids of deposits is determined not only by the geological and geochemical conditions of sedimentation of oil and gas source deposits, but also associated with migration processes and subsequent secondary changes in the accumulation. In terms of composition, three groups of oils were identified: Permian and Jurassic heavy oils with a light carbon isotopic composition and the presence of β-carotene and gammacerane, they underwent different degrees of biodegradation, which depended on the geological conditions of the deposits; Permian medium oils in density (0.84 and 0.87 g/cm3), the composition of biomarkers of which is very close to that of the first group, and Jurassic light oils with a high content of solid paraffins and a heavier carbon isotopic composition, almost do not contain β-carotene and gammacerane concentrations are low.

In recent years, significant success has been achieved in the search for and exploration of oil and gas reservoirs in the Jurassic deposits on the eastern side of the Fukang Depression, which is the least studied part of the Junggar oil and gas basin. In order to determine the hydrocarbon generation source, we have studied source rocks, oil and oil-bearing sandstones (24 samples from 13 wells), from the Badaowan, Sangonghe, Xishanyao, Toutunhe, and Qigu productive reservoirs of the Fukang Depression research area. Based on these studies, the organic matter composition of the Jurassic source rocks, the properties and molecular composition of oils, as well as the composition characteristics of biomarkers in them have been examined in detail. According to the research data and interpretation results, Badaowan mudstones were the source rocks of oil in the Gumudi zone and Fukang Depression, as well as that in the Baijiahai and Shaqi ledges.

Formation of dammed lakes provides exceptionally important information of continental geological processes, responding to tectonic and climatic influences. Establishing accurate geochronological frameworks within lake strata is challenging because the stratigraphy is often bereft of biostratigraphy and directly dateable material. Optically Stimulated Luminescence (OSL) and AMS 14 C dating of pollen concentrates are well-established tools for dating lake sediments. Whether they are suitable for lake sediments in high-alpine settings remains uncertain. In this study, OSL and AMS 14 C dating of pollen concentrate were conducted on the Diaolin section in a high-alpine setting in the eastern Tibetan Plateau. Good match of both dating results suggests that they are fit for dating lake sediments in high-alpine settings. More than 300 g of sediment is required for preparation of pollen concentrates. During the pretreatment, ∼3% NaOH solution should be added to the sample, and then heated until just boiling (≤5 min) because NaOH treatment easily destroys pollen grains. Applying the heavy liquid flotation with specific gravity of 1.74–1.76 is useful to isolate relatively pure pollen grains. Sieving with a 20-μm and 63-μm mesh can concentrate pollen grains substantially. The OSL and AMS 14 C dating yielded the basal age of the Diaolin section (650 AD). This indicates that the dammed-lake formed around 650 AD, probably caused by the earthquake occurring in the study area in 638 AD. The seismites characterized by soft-sediment deformation and phyllite layer happened at 780–980 AD, probably corresponding to the earthquake occurring on November 20, 952 AD in the study area.