三峡东部地区成冰纪岩石地层格架的再认识  

Recognition of the Cryogenian lithostratigraphic framework in the East Yangtze Gorges

作　　者：张德军 刘鹏举[1] 尚晓冬[1] 杨犇[1] ZHANG Dejun;LIU Pengju;SHANG Xiaodong;YANG Ben(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Shenyang Center of Geological Survey,CGS.Shenyang,Liaoning 110034,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质调查局沈阳地质调查中心,辽宁沈阳110034

出　　处：《地质学报》2024年第11期3332-3340,共9页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号U2244202);中国地质调查局项目(编号DD20230220)联合资助的成果。

摘　　要：以往研究认为,三峡东部地区仅发育可与Marinoan冰期相对应的南沱组冰碛岩,南沱组直接不整合覆于拉伸系莲沱组或黄陵花岗岩之上。然而,近年有学者通过对峡东黄陵背斜西南翼青林口南沱组剖面开展研究提出新认识,认为青林口剖面南沱组包含了上、下两套冰碛岩与二者之间的页岩夹纹层状含锰灰岩。该剖面的地层结构、含锰灰岩的岩石学及地球化学特征、化学蚀变指数(CIA)等与鄂西长阳古城成冰系剖面相似,二者之间可进行横向对比,并据此将峡东青林口剖面南沱组自下而上解体为古城组、大塘坡组和南沱组,分别对应Sturtian冰期、间冰期和Marinoan冰期沉积。针对这一新认识,笔者对青林口南沱组剖面开展详细的野外地质调查工作,在被认为可与间冰期沉积大塘坡组相对比的灰绿色页岩中发现了许多砾度不等的冰坠砾石,指示这套灰绿色页岩实为含冰坠石的冰碛页岩,而非间冰期沉积。此外,这套灰绿色冰碛页岩无论是岩石学特征,还是CIA值或Mn O值,均与鄂西长阳古城、贵州松桃大塘坡等剖面的大塘坡组差异显著,将二者作为同一时期地层进行横向对比的证据不可信。因此,本文认为不宜将三峡东部南沱组解体为古城组、大塘坡组和南沱组。Previous studies suggested that glacial deposits of the Nantuo Formation,correlated with the Marinoan glaciation,directly unconformably overlie the Tonian Liantuo Formation or Huangling Granite in the East Yangtze Gorges.However,in recent years,some scholars have raised doubts about the exclusive presence of the Nantuo Formation in the Qinglinkou section of the southwestern limb of the Huangling Anticline in the East Yangtze Gorges.They argue that the Qinglinkou section of the Nantuo Formation comprises both upper and lower sets of glacial diamictites,as well as interbedded shale and laminated manganese-bearing limestones.They point out that the stratigraphic architecture,lithological signatures,geochemical characteristics,and Chemical Index of Alteration(CIA)values of this section resemble those of the Cryogenian succession in Gucheng,Changyang,western Hubei Province.In their opinion,a lateral correlation can be made between the two sections,suggesting a disintegration of the Nantuo Formation in the Qinglinkou section from bottom to top into the Gucheng,Datangpo,and Nantuo formations.These formations would correspond to the Sturtian glaciation,interglacial period,and Marinoan glaciation deposits,respectively.Based on the aforementioned observations,the authors recently conducted a detailed field geological survey of the Nantuo Formation in the Qinglinkou section.During this survey,many ice-rafted dropstones of varying sizes were found within the gray-green shale beds.These beds were previously considered comparable to the Datangpo Formation,which is interpreted as interglacial deposits.The presence of dropstones indicates that these gray-green shale beds containing glacial dropstones are actually glacial diamictites(moraine-bearing shale)rather than interglacial deposits.Additionally,the gray-green moraine-bearing shale exhibits significant differences in lithological characteristics,CIA values,and MnO content compared to the Datangpo Formation observed in sections such as Gucheng in western Hubei Province and D

关 键 词：扬子克拉通 新元古代 成冰纪 南沱组 冰碛岩 

分 类 号：P534.3[天文地球—古生物学与地层学] P535[天文地球—地质学]