新疆西部乌依塔克组的时代

The age the Wuytak Formation in Western Xinjiang

通过对新发现于新疆塔里木盆地西部上白垩统乌依塔克组有孔虫化石的时代分析，认为该组的时限为晚上伦期—赛诺期，综合分析各类化石的时代特征，本区土伦阶和赛诺阶的界线应划在Ｍｉｇｒｏｓ－Ａｍｍｏｂａｃｕｌｉｔｅｓ组合和Ｐａｒａｒｏｔａｌｉａ－Ｎｏｎｉｏｎｅｌｌａ组合之间。

The Upper Cretaceous Yingjisha Group in the western Tarim Basin is represented mainly by sediments of littoral, near-shore neritic dacies and subdivided ascendingly into the Kukebai Formation, Wuytak Formation and Ygezya Formations. Previously, foraminiferal fossils of Upper Cretaceous age were found from the Kukebai Formation. Recently, many well-preserved new forms were found in the Wuytak Formation overlying the Kukebai Formation. Four foraminiferal assemblages in the Wuytak Formation have been recognized in ascending order: the Migros-Ammobaculites Assemblage, the Pararotalia-Nonionella Assemblage, the Cibicidina-Quinqueloculina Assemblage, the Quinqueloculina-Massilina Assemblage. As a result, the age of the Wuytak Formations is assigned from Late Turonian to Senonian according to charateristics of foraminiferal assemblages. Therefrom, the Turonian-Senonian boundary would be placed between the Migros-Ammobaculites Assemblage and the Pararotailia-Nonionella Assemblage.