塔里木盆地西北缘乌什地区奥陶纪牙形类生物地层

ORDOVICIAN CONODONT BIOSTRATIGRAPHY OF THE WUSHI AREA IN THE NORTHWESTERN MARGIN OF THE TARIM BASIN

本文对新疆乌什地区亚巴格剖面“丘里塔格群”至亚巴格组,以及亚科瑞克剖面“丘里塔格群”顶部、亚科瑞克组顶部地层,进行了牙形类生物地层研究。亚巴格剖面“丘里塔格群”自下而上可划分识别Oepikodus evae带和Paroistodus originalis带,亚科瑞克组识别Belodina confluens带下部;亚巴格组识别Belodina confluens带上部及Aphelognathus pyramidalis带。亚科瑞克剖面“丘里塔格群”顶部识别Protopanderodus calceatus-Periodon flabellum带,亚科瑞克组顶部识别Belodina confluens带。上述研究剖面识别的牙形类生物带与塔里木盆地其他相区的奥陶纪牙形类生物带可进行良好对比,与华南、华北板块也具有一定的可对比性。本文中乌什地区“丘里塔格群”出露地层的时代为弗洛期至大坪最早期;亚科瑞克组的时代为桑比期至凯迪早中期,与吐木休克组上部及良里塔格组层位相当;亚巴格组主体时代为凯迪中晚期,但顶界时代未定。本文识别出乌什地区“丘里塔格群”与亚科瑞克组间的不整合接触关系,与塔里木盆地广泛存在的奥陶系内部鹰山组上部与上覆地层间的不整合面可以对比。

The Ordovician strata in the Yabage and Yakrik sections are systematically studied for conodont biostratigraphy.In the Yabage Section,four conodont biozones are identified,in ascending order,including the Oepikodus evae and Paroistodus originalis biozones in the“Qiulitag Group”,the Belodina confluens Biozone in the Yakrik Formation and the lower part of the Yabage Formation and the Aphelognathus pyramidalis Biozone in the Yabage Formation.In the Yakrik Section,Protopanderodus calceatus-Periodon flabellum Biozone is identified on the top of the“Qiulitag Group”,and the Yaoxianognathus neimengguensis Biozone is recognized in the topmost Yakrik Formation.The conodont sequences recognized in the studied sections can be correlated with other areas in the Tarim Basin and other paleoplates as well.The established conodont sequence in the studied sections provides a more precise chronal constraint for the Ordovician strata in the Wushi area.The results suggest a Floian to earliest Dapingian age for the“Qiulitag Group”,an early Katian age for the Yakrik Formation and a middle to late Katian for the Yabage Formation.A prominent sedimentary hiatus is identified between the“Qiulitag Group”and the overlying Yakrick Formationin the Wushi area,spanning the interval from the Dapingian to the Darriwilian.This hiatus can be traced broadly in the Tarim Basin,and is correlative to the unconformity between the Yingshan Formation and its overlying strata in the Bachu area.