| Elemental and comprehensive two-dimensional geochemistry of crude oils is a research highlight in the field of petroleum geochemistry and is challenging. To improve the understanding on this issue, we conduct a case study in the Junggar Basin in this work, which is one of the representative petroliferous superimposed basins in central and western China. Three new lines of evidence were obtained.(1) According to the element geochemical characteristics of crude oils in the Junggar Basin, the oils can be divided into five types. The first type are mainly located in the northwestern basin margin and the Madong area. These oils have high V/Cr ratios as the maximum can reach 3.85. The Sr/Ba and La/Sc ratios are distributed in the range of 0.22-5.65 and 0.16-6.27, respectively. They have positive Ce anomalies and negative Eu anomaly. The second type of crude oils are mainly located in the Shinan and Chepaizi areas. The V/Cr ratios of the oils range in 0.07 to 0.57. The Sr/Ba and La/Sc ratios are high as the highest value can reach 15.62 and 9.18, respectively. They have positive Ce anomalies and negative Eu anomalies. The third type of crude oils are located in the southern and central basin. They have low V/Cr and La/Sc ratios, with the range being 0.05?0.12 and 0.13?0.40, respectively. They have high Sr/Ba ratios, and positive Ce and some Eu anomalies. The fourth type of crude oils are mainly located in the southern basin margin. The V/Cr, Sr/Ba and La/Sc ratios of the oils are lower than those of the oils in other areas. They have positive Ce and negative Eu anomalies. The fifth type of crude oils are mainly located in the eastern basin, with V/Cr ratios ranging in 0.05?0.08. The Sr/Ba and La/Sc ratios of the oils are similar to those in other areas. They have positive Ce and some positive Eu anomalies. These features, combined with conventional organic geochemical characteristics, indicate the oil sources. They are derived mainly from the Permian Fengcheng, Permian lower Wuerhe, Jurassic, Cretaceous and/or Paleogene, Carboniferous source rocks, respectively.(2) The elemental geochemistry of crude oils can be used to discern sedimentary environment, provenance and paleoclimate of the organic matter. The ?REE content can provide clues to identify the degradation of crude oils as a new geochemical indicator. However, the geochemical behavior of trace elements in crude oils is very complex. The indicators suggested for oil-source correlation requires further in-depth research.(3) GCxGC-TOFMS studies of crude oils show that the system can conduct the two-dimensional gas chromatography-mass spectrometry analyse of oils during one-time, whether it is a normal phase column system, or reverse phase column, and achieve a high degree of separation and good recognition. The GC×GC-TOFMS can detect aromatic and some special cycloalkanes effectively, such as adamantane compounds. Thus, this approach has good prospects in the oil and source rock correlation studies.The understandings above not only provide a new basis for the analysis of oil origin in the Junggar Basin, but also investigate the elemental and comprehensive two-dimensional geochemical characteristics and their controls of the oils. Therefore, the research is expected to have general significance on methodology. |
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