塔里木西北缘奥陶系-志留系界线地层西克尔层的建立及其意义  

THE ORDOVICIAN-SILURIAN BOUNDARY DEPOSITS IN NORTHWESTERN TARIM,XINJIANG:THE XIKEER BED(NEW UNIT)AND ITS IMPLICATIONS

作　　者：张雨晨 唐鹏[1] 陈清[1] 魏鑫 张园园[1] 王怿[1] 詹仁斌[1] 戎嘉余[1] ZHANG Yu Chen;TANG Peng;CHEN Qing;WEI Xin;ZHANG Yuan Yuan;WANG Yi;ZHAN Ren Bin;RONG Jia Yu(State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences,Nanjing 210008)

机构地区：[1]中国科学院南京地质古生物研究所,现代古生物学和地层学国家重点实验室,江苏南京210008

出　　处：《地层学杂志》2023年第4期396-415,共20页Journal of Stratigraphy

基　　金：中国科学院战略性先导科技专项B类(XDB26000000);国家自然科学基金(42202021、41972011)共同资助。

摘　　要：本研究在塔里木盆地西北缘新发现奥陶系-志留系界线地层,并将该段地层命名为西克尔层,时代为晚奥陶世赫南特晚期至志留纪兰多维列世鲁丹早期,并指定伽师县西克尔镇西克尔服务区北剖面为其正层型,柯坪县印干村西北的大湾沟剖面为其副层型。在正层型上,西克尔层厚1.5 m,下部为灰绿色泥质粉砂岩,上部为灰色砂屑灰岩,产腕足类、珊瑚、苔藓虫、层孔虫等多门类化石。在副层型上,西克尔层厚2.5 m,为灰绿色泥质粉砂岩、粉砂质泥岩,产隐孢子、腹足类、植物、藻类碎片等化石。西克尔层盛产以华夏正形贝(Cathaysiorthis)为代表的腕足类动物群,属于埃吉伍德-华夏动物群(Edgewood-Cathay Fauna)。在时代上,西克尔层与华南板块的五里坡层、石阡层、尾坝层一致或相近,均属于赫南特冰期结束后全球大海侵的产物,都保存晚奥陶世生物大灭绝后的第一个以腕足类占优势的海洋底栖动物群。本区不发育赫南特贝动物群(Hirnantia Fauna),从而确认缺失赫南特早—中期地层。西克尔层在柯坪—伽师地区广泛分布,出露稳定,易于识别,与下伏地层铁热克阿瓦提组(凯迪阶上部)呈平行不整合接触,与上覆地层柯坪塔格组(志留系鲁丹阶)整合接触,是今后开展相关地层划分与对比的重要标志层。受全球奥陶纪末冰川气候事件的影响,柯坪—伽师地区在全球海平面骤降之时遭受剥蚀,直至赫南特晚期冰川气候结束、海平面迅速上升才开始再次接受沉积。对比研究发现,该区域赫南特期的沉积过程、所缺失的地层、冰期之后第一个壳相生物群组合,均与扬子区黔北、滇东北、浙赣边区等地相似,这为研究塔里木盆地的沉积演化和生物古地理背景提供了新的依据。A stratigraphic succession across the Ordovician-Silurian boundary is discovered in the northwestern margin of the Tarim Basin,Xinjiang,NW China,and is named Xikeer Bed,which ranges from uppermost Hirnantian(Upper Ordovician)to lowermost Rhuddanian(Llandovery,Silurian).The holostratotype of the Xikeer Bed is located at the Xikeer Service-area North Section,Xikeer Town,Jiashi County,while the parastratotype is located at the Dawangou Section,northwest of the Yingan village,Kalpin County.In the holostratotype,the lower part of the Xikeer Bed is composed of gray-green argillaceous siltstone,and the upper part consists of gray calcarenite,which produces brachiopods,corals(tabulate and rugose),bryozoans,stromatoporoids,and some other fossils,with a total thickness of 1.5 m.In the parastratotype,the Xikeer Bed has a sequence of gray-green muddy siltstone and silty mudstone with bryozoans,gastropods,cryptospores,algae and land plant fragments,with a total thickness of 2.5 m.In the Kalpin–Jiashi area,the Xikeer Bed is underlain unconformably by the Terekawat Formation(upper Katian Stage,Upper Ordovician),suggesting the absence of the lower–middle Hirnantian rocks in the study area,and is overlain conformably by the Kalpintag Formation(Rhuddanian,Llandovery).The Xikeer Bed is widely and stably distributed in the Kalpintag Mountains and some other places in the Kalpin area,and will serve as an important lithostratigraphic marker for the division and correlation of the equivalent strata.A brachiopod assemblage collected from the bed is typically represented by Cathaysiorthis yushanensis and Leptaena rugosa,which belong to the Edgewood-Cathay(EC)Fauna,the first brachiopod assemblage inhabited shallow marine after the Late Ordovician Mass Extinction(LOME).Based chiefly on the yielded brachiopods,the Xikeer Bed is well correlated with the Wulipo Bed in Meitan County and the Shiqian Bed in Shiqian County,northern Guizhou Province,along with the Weiba Bed in Zhenxiong,northeastern Yunnan Province,South China.These equivalent

关 键 词：奥陶系-志留系界线 塔里木盆地 柯坪塔格山 西克尔层 埃吉伍德-华夏动物群 

分 类 号：P534.42[天文地球—古生物学与地层学] P534.43[天文地球—地质学]