Sporopollen Assemblage and Geological Significance of 3 538~3 774 m Section in Well Chetan 1, Chepaizi Oilfield, Xinjiang

In Chepaizi oilfield, the stratigraphic age is insufficient, while the views of stratigraphic division and correlation have divergence, for example, the Molaoba formation in well Chetan 1, divided by predecessors, has no Stratigraphic-Time basis. Molaoba formation and Baogutu formation, which belong to different areas, occur simultaneously in well Chetan 1, resulting in the stratigraphic system correlation between the whole oilfield and Baogutu area become very confusion. Sporopollen samples were taken from the cores of the 3 538~3 774 m well section of well Chetan 1 that divided as Molaoba formation for analysis. The results show that content of gymnosperm pollen and fern spore in the samples is 53.50% and 46.50%, respectively The main sporopollen assemblage is Cyathidites minor-Osmundacidites-Deltoidospora-Pinuspollenites-Disacciatrileti-Cycadopites, suggesting that the age of the formation is Middle Jurassic. Combined with rock assemblage, sporopollen age and regional correlation, the original "Molaoba formation of Late Carboniferous" should be redefined as Xishanyao formation of Middle Jurassic. After canceling the name of "Molaoba formation", all stratigraphic sequences of Chepaizi oilfield are similar to Baogutu stratigraphic area.