关键词: 大煤沟, 有机碳同位素&delta, ¹³Ｃ, C/N, H/C, 古气候

Abstract: The Jurassic strata in the Dameigou area of the North Qaidam Basin recorded the evolution of paleoenvironment in the Northwest. In this paper, the organic geochemical analysis of the Dameigou section is performed to reconstruct the environmental evolution of the Jurassic in the Dameigou area. The analysis reveals that the H/C ratio shows a good negative correlation with the C/N ratio and δ ¹³C. The C/N ratios and δ ¹³C values decrease gradually and the H/C ratio gradually increases during the Early Jurassic. In the Middle Jurassic, the C/N ratio and δ ¹³C remained stable in the early stage and the latter was sharply negative, while the H/C ratio was reversed. During the Late Jurassic, the C/N ratio and δ ¹³C remained largely unchanged and the H/C ratio was stable in the high value range. The C/N ratio of organic elements in the early-middle Jurassic is greater than 15, indicating that organic matter is mainly from terrestrial higher plants. The paleoclimate of the Dameigou section is characterized by two cycles: in the Early Jurassic Xiaomeigou Formation, the paleoclimate was  haracterized by warm-humidity-dry heat and the paleoclimate evolved from warm wet to dry hot in the late Middle Jurassic.

Key words: Dameigou, organic carbon isotope δ¹³Ｃ, C/N, H/C, Paleoclimate