Mao No. 206 Well is one of the wells of Cretaceous Continental Scientific Drilling Engineering in China; herein 497. 02 m end-to-end core data have obtained in Qingshankou Formation. Through the chronological analysis of the zircon mineral in the bentonite of black interbeded mudstone in the bottom of Qingshankou Formation, three harmonic ages of U-Pb isotope are obtained at three depths: 91. 35 ± 0. 48 Ma at 1 780.1 m depth, 90. 05 ± 0. 56 Ma at 1 705. 8 m depth and 90.4 ± 0.44 Ma at 1 673. 1 m depth. The bottom of Qingshankou Formation is proven to belong to Turanian Stage, not Cenomanian Stage; the obtained age values of 40Ar/39Ar isotope plateau and isochrone in the volcanic rocks of Qingshankou Formation in Jing No. 6 Well are all 88. 0 ±0. 3 Ma, so the top of the formation is made sure to upward extend to Coniacian Stage. At the same time, the discovery of the pollens of Normapolles ignosperm in Qingshankou Formation also proves that the bottom of above formation is extended to Turonian stage.%茂206井是中国白垩纪大陆科学钻探工程井之一,获取了青山口组497.02 m长的连续岩心资料.通过对该井青山口组下部黑色泥岩夹层斑脱岩中锆石矿物的年代学分析,在井深1 780.1 m、1 705.8 m和1673.1 m处得到3个同位素U -Pb谐和年龄,分别为91.35 ±0.48 Ma、90.05±0.56 Ma和90.4±0.44 Ma,证实了青山口组的底界已属Turonian阶,而非Cenomanian阶；金6井青山口组二、三段火山岩所得到的40Ar/39Ar同位素坪年龄和等时线年龄值均为88.0±0.3 Ma,证实青山口组顶界已上延至Coniacian阶.同时,正型粉类被子植物花粉在青山口组的发现,也证明了青山口组底界已经上延至Turonian阶.
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