The Jurassic of Caohu depression in the Tarim basin
    developed fully,  with large thickness, but
    the precision of stratigraphic division and correlation is lower, which is one
    of the important reason that restrict the exploration of oil and gas in this
    area. According to the fossil material collected from drilling hole, established
    three palynological assemblages, there are Cyathidites-Osmundacidites-Piceites,
    Cyathidites-Neoraistrickia-Disacciatrileti and Cyathidites- Classopollis- Piceaepollenites, Aneuletes cucuma and A.stellerides-A.lufengensis, A.maxima-Rkucheensis.
    The Jurassic was divided into three series, five formations, From bottom to top
    are Ahe Formation and Yangxia Formation in lower series,  Kizilnur Formation and Qiakmak Formation in
    middle series and Qigu Formation in upper series（Kelazha Formation is lacuna）. Lithological and logging characteristics are obvious in each member,  the “coal stratification” at the lower and
    “black mudstone sagment” at the top of the Yangxia Formation, the “coal
    stratification” in the kizilnur Formation and the “red mudstone sagment” were regarded as the key bed
    in this research area. There is sedimentic absence in the Abe Formation and the
    lower parts in the Yangxia Formation, denuded absence from Qiakmak Formation to
    Kelazha Formation in most area. Jurassic was divided into three second-order
    and five third-order sequences, relied on the seismic sequence stratigraphy and
    borehole sequence stratigraphy,  the detailed
    classification and correlation of Jurassic in the area has been achieved, which
    based on biostratum and combined litology,  sequence and logging strata. Those discoveries
    made it possible to analyze the tectonic evolution, sedimentary facies and
    hydrocarbon accumulation in Caohu sag and neighboring regions.