The Age of the Yixianian Stage and the Boundary of Jurassic-Cretaceous——The Establishment and Study of Stratotypes of the Yixianian Stage
The Age of the Yixianian Stage and the Boundary of Jurassic-Cretaceous——The Establishment and Study of Stratotypes of the Yixianian Stage
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发表时间：
2005
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通讯作者：
Wang Wuli
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作者：
Wang Wuli
易县期孔子鸟、中华龙鸟、翼龙、甲壳纲、昆虫、双壳类和植物（含木化石）属于晚侏罗世晚期或晚铁东世；早白垩世早期或贝里亚期的哺乳动物、鸟臀目和孢子虫类恐龙；介形类和鱼类与晚侏罗世到早白垩世或晚泰托尼—贝里亚期的过渡有关。考虑到宜先期生物群可与德国的Solnhofen生物群、英国的Purbeck生物群、日本的晚侏罗世terori型和ryoseki型植物群进行比较或对比，并与中侏罗世约克郡区系和大河口壳类动物群有关，宜先期的合成时代可确定为晚铁东世至贝里亚世。建山沟层和大康布层的时代分别倾向于晚梯东世和贝里亚世。由于Purbeck群（组或层）的侏罗系-白垩系界线可能与宜仙仙组大致相关，且缺乏实测资料，因此国际地层年表推荐的144 Ma、145 Ma或135 Ma的侏罗系-白垩系界线年龄不能作为可靠的判据。因此，侏罗系-白垩系界线的建立应以义县系层型的合成生物年龄和实测同位素年龄为基础。因此，宜将边界年龄设定在宜仙县下期剑山沟层与宜仙县上期大康布层之间，且目前符合合成生物年龄的同位素年龄宜选择124 Ma。
The Confuciusornis avifauna, Sinosauropteryx fauna, pterosaurs, conchostracans, insects, bivalves and plants (including fossil woods) of the Yixianian Stage are ascribed to the late Late Jurassic or Late Tithonian; the mammalia, dinosaurs of ornithischia and sporopollens to the early Early Cretaceous or the Berriasian Stage; and the ostracods and fishes to the transition from Late Jurassic to Early Cretaceous or the Late Tithonian-Berriasian. Considering that the Yixianian biota may be compared or correlated with the Solnhofen biota of Germany, the Purbeck biota in England, Late Jurassic Terori-type and Ryoseki-type floras in Japan and that they are also related to the Middle Jurassic Yorkshire flora and the Great Estuarine conchostracans fauna, the synthetic age of the Yixianian Stage may be determined as Late Tithonian to Berriasian, and the ages of the Jianshangou Bed and the Dakangbu Bed tend to be the Late Tithonian and the Berriasian, respectively. Because the Jurassic-Cretaceous boundary of the Purbeck Group (Formation or Bed) that may be roughly correlated with the Yixianian Formation is not yet affirmed, and as there lack measured data, the 144 Ma, 145 Ma or 135 Ma data for the Jurassic-Cretaceous boundary ages recommended by the International Stratigraphical time table cannot be used as a reliable criterion. Therefore, the establishment of the Jurassic-Cretaceous boundary should be based on the synthetic biological age and measured isotope age of the Yixianian stratotypes in China. Accordingly, the boundary age is preferred to set between the Jianshangou Bed of the lower Yixianian Stage and the Dakangbu Bed of the upper Yixianian Stage, and the isotope age of 124 Ma is preferably chosen because it conforms the synthetic biological age at present.