藏北日土县拉竹龙地区志留系  

SILURIAN OF THE LAZHUGLUNG AREA,RUTOG COUNTY,NORTHERN TIBET

作　　者：陈挺恩[1] 张允白[1] 

机构地区：[1]中国科学院南京地质古生物研究所,江苏南京210008

出　　处：《地层学杂志》2010年第4期397-409,共13页Journal of Stratigraphy

基　　金：中国科学院知识创新工程方向性项目(KZCX2-YW-122);国家自然科学基金(No.40532009)资助

摘　　要：根据在西藏西北部日土县拉竹龙地区重新测量了西藏区调大队1984年所测的两个地层剖面——饮水河北岸剖面和兽形湖北岸剖面,在原来定为上奥陶统兽形湖组的底部发现了一套含笔石和几丁石化石的黑色页岩和炭质板岩,其中笔石Pristiograptus和几丁石Ancyrochitina brevicollis、Conochitina sp.为志留系兰多维列统Tely-chian阶的标准分子。同时在兽形湖组中也发现了大量兰多维列世的腕足类化石Hindella xizangensis和竹节石Gotlandellites sp.。证明了拉竹龙地区饮水河北岸和兽形湖北岸两个剖面均未出现真正的奥陶纪地层。通过所采集到的笔石、几丁石、腕足类、三叶虫、头足类、牙形刺、竹节石、珊瑚、遗迹化石的准确鉴定,重新修订了本地区志留系的划分和地层序列:自下而上依次为以笔石相为代表的兰多维列统饮水河组,以碎屑岩相为代表的兰多维列统兽形湖组,以碳酸盐沉积为主的文洛克统普尔错组和以碳酸盐岩相为主的罗德洛统至普里道利统野牛坡组。本区志留系目前发现的最低层位相当于兰多维列统Telychian阶的笔石带Spirograptusturriculatus带和Streptograptus crispus带,最高层位相当于欧洲和藏南壳相志留系的最高一个头足类化石带Kopaninoceras juncudum带或牙形刺组合Neoprioniodus latidentatus-Ligonodina siluria组合。Two Silurian sections were re-measured, one being situated on the northern bank of the Yinshuihe River and the other on the northern bank of the Shouxinghu Lake of the Lazhuglung area of Doima, Rutog, NW Tibet. The lower part of the Shouxinghu Formation is composed of grey-black carbonaceous shales and slates, which contain graptolites Spirograptus sp. and chitinozoans Ancyrochitina brevicollis and Conochitina sp., indicating a Llandovery age, rather than the Upper Ordovician mentioned previously. Real Ordovician rocks have not been found until now there. The Silurian rocks in that area were divided in ascending order into the Llandovery Yinshuihe and Shouxinghu Formations, the Wenlock Pur Co Formation and the Ludlow-Pridoli Yeniupo Formation, a new lithostratigraphic unit here established, on the basis of diversified faunas. The lowermost beds correspond to the Llandovery Spirograptus turriculatus and Streptograptus crispus graptolite zones, and the uppermost beds to the Kopaninoceras juncudum cephalopod zone and its coeval Neoprioniodus latidentatus-Ligonodina siluria conodont assemblage. So far the Lazhuglung sections have been known to be the best sections in North Tibet in both outcrop-completeness and fossil abundance. The erectness of the Silurian sequence there provides important data for the reconstruction of Tibetan Early Plaeozoic history and the Silurian correlation of Qinghai-Xizang Plateau.

关 键 词：岩石地层 生物地层 笔石 几丁石 饮水河组 兽形湖组 普尔错组 野牛坡组 志留系 日土县 藏北 

分 类 号：P534.43[天文地球—古生物学与地层学]