塔里木盆地亚科瑞克剖面奥陶系牙形石生物地层初步研究

A Preliminary Study on the Ordovician Conodont Biostratigraphy at the Yakrik Section,Northwestern Margin of the Tarim Basin,Xinjiang

塔里木盆地西北缘乌什县东南亚科瑞克剖面奥陶系发育,并且该剖面也是塔里木盆地上奥陶统沉积最为齐全的露头剖面之一,尤其是上奥陶统的中—上部发育了许多重要的牙形石属种。本文通过对剖面上灰岩层样品的系统采集和牙形石分析鉴定,将该剖面的奥陶系分为4个牙形石组合和2个牙形石带。自下而上依次为: Serratognathus diversus—Bergstroemognathus extensus组合,Protopanderodus calceatus—Periodon aculeatus组合,Aphelognathus sp．—Tasmanognathus sp．组合,Belodina confluens—Phragmodus undatus组合,Yaoxianog- nathus neimengguensis带和Aphelognathus pyramidalis带。其中,上奥陶统上部牙形石的重要属种A．pyramida- lis、A．politus、Y．yaoxianensis和A．neimengguensis以及上奥陶统上部的A．pyramidalis带与Y．neimengguensis带是首次在柯坪地层分区发现。这些发现初步解决了塔里木盆地覆盖区与露头区上奥陶统不能进行精细生物地层对比的问题。

The Yakrik section is located in Wushi County, northwestern margin of the Tarim Basin, Xinjiang, China. The Ordovician System is well exposed at the Yakrik section. And the section contains a lot of important Upper Ordovician conodont species, at the same time, it is one of the sections which involve complete Upper Ordovician in the Tarim Basin. Four conodont assemblages and two conodont zones of the Middle-Upper Ordovician have been established. In ascending order, they are： Serratognathus diversus - Bergstroemognathus extensus assemblage, Protopanderodus calceatus - Periodon aculeatus assemblage, Tasmanognathus sp. - Aphelognathus sp. assemblage, Belodina confluens - Phragmodus undatus assemblage, Yaoxianognathus neimengguensis zone and Aphelognathus pyramidalis zone. Thereinto, S. diversus-B, extensus assemblage is assigned to the Upper Daobaowanian Stage of the Lower Ordoviclan. P. calceatus-P, aculeatus assemblage is refered to the Dawangian Stage of the Middle Ordovician. Other assemblages and the zones are assigned to the Upper Ordovician. T. sp. -A. sp. assemblage can be attributed to the base of the Aijiashanian Stage, B. confluens-P, undatus assemblage is referred to the upper part of the Middle Aijiashanian Stage and Y. neimengguensis zone is identified as the middle part of the Upper Aijiashanian Stage, A. pyramidalis zone is considered as from the Top Aijiashanian Stage to the topmost part of Qiantangjiangian Stage. In addition, The important conodont species of upper Upper Ordovician A. pyramidalis, A. politus, Y. yaoxianensis and Y. neimengguensis are found on outcrop in Kalpin area for the first time, as well as, the topmost conodont zone of the Upper Ordovician A. pyramidalis zone and a upper one of the Upper Ordovician Y. neimengguensis zone are built there firstly. These discoveries at the Yakrik section are significant to the division and correlation of the Upper Ordovician between covered areas and exposed areas of the Tarim Basin.