滇东北镇雄北部奥陶系-志留系界线地层的新观察  

NEW INSIGHTS INTO THE STRATA STRADDLING THE ORDOVICIAN-SILURIAN BOUNDARY IN NORTHERN ZHENXIONG,NORTHEAST YUNNAN

作　　者：张小乐 黄冰[1] 王光旭[1] 王怿[1] 吴荣昌 李丽霞 戎嘉余[1] ZHANG Xiao Le;HUANG Bing;WANG Guang Xu;WANG Yi;WU Rong Chang;LI Li Xia;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》2022年第1期40-49,共10页Journal of Stratigraphy

基　　金：中国科学院战略性先导科技专项(B类)(XDB26000000);现代古生物学和地层学国家重点实验室(20192112)共同资助。

摘　　要：针对滇东北镇雄下蒿枝湾剖面晚奥陶世至志留纪兰多维列世过渡时期的沉积地层,本文进行了系统测制和地层古生物学研究,对其地层发育和对比进行了梳理与限定,首次发现该地晚奥陶世至志留纪早期地层自下而上可依次划分为大渡河组、“五里坡层”、龙马溪组底部和“龙马溪组中部”。其中,大渡河组为一套沉积于内陆棚的泥质泥晶灰岩与钙质泥页岩,时代可与五峰组对比。“五里坡层”是一套沉积于内陆棚的钙质粉砂岩地层,向上逐渐过渡为外陆棚相的龙马溪组底部黑色笔石页岩,两者构成了Metabolograptus persculptus带中上部沉积。大渡河组与“五里坡层”呈平行不整合接触,之间缺失观音桥层及Hirnantia-Mucronaspis动物群,指示赫南特期全球性海平面下降。“龙马溪组中部”以内陆棚的砂岩为起始,其中所产腕足动物化石指示其时代为志留纪鲁丹晚期。Edgewood-Cathay动物群缺失表明龙马溪组底部与“龙马溪组中部”之间存在不整合界面,体现了黔中古陆北缘的隆升。下蒿枝湾剖面奥陶纪—志留纪过渡时期的地层发育情况完整记录了在全球和区域事件的影响下滇东北沉积相和生物群的时空分布与发育的响应过程。Systematic measurements and biostratigraphic study were conducted at the Xiahaozhiwan section of Zhenxiong,northeast Yunnan to build a stratigraphic framework,which reveals for the first time that the strata near the O-S boundary could be subdivided into the Daduhe Formation,the “Wulipo Bed”,the lowermost Lungmachi Formation and the “middle Lungmachi Formation” in ascending order.The Daduhe Formation,deposited in the inner shelf setting,is characterized by medium-to thin-bedded argillaceous limestone intercalated with thin-bedded calcareous mudstone/shales.It is stratigraphically correlated with the Wufeng Formation;however,the lithological characteristics suggest discrimination with the latter.The “Wulipo Bed” is a succession of calcareous siltstone,mudstone and shales.Together with the overlying carbonaceous graptolitic shale of the lowermost Lungmachi Formation,they comprise deposition of mid-upper Metabolograptus persculptus biozone.As a result of eustatic dropping during the Hirnantian glaciation,a sedimentary hiatus exits between the Daduhe Formation and “Wulipo Bed”,where the Kuanyinchiao Bed is missing.The “middle Lungmachi Formation” initializes with inner-shelf sandstone,with a geological age of late Rhuddannian,as suggested by brachiopod fossils.The missing of Edgewood-Cathay Fauna suggests a sedimentary gap between the “middle” and lowermost Lungmachi Formation,most likely resulted from the uplift and expansion of the north border of the Qianzhong Oldland.The strata near the Ordovician-Silurian boundary at the Xiahaozhiwan section have recorded the impacts of both global and regional events on spatial-temporal distribution and development of sedimentary facies and biota at northeast Yunnan.

关 键 词：笔石 腕足动物 大渡河组 五里坡层 龙马溪组 生物地层 沉积相分析 

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]