西藏西南部三叠系穷果群的地层学与岩相

发布时间：2018-02-27 06:02

本文关键词： 岩石地层岩相尼多曲组屯具日组屯具场组穷果群修康岩群三叠系仲巴微地体西藏　出处：《地层学杂志》2017年01期 　论文类型：期刊论文

【摘要】：在区域地质调查、实测地层剖面和区域对比基础上,对西藏西南部雅鲁藏布江缝合带西段的穷果群进行了研究,认为穷果群仅分布于萨嘎以西的仲巴微地体,萨嘎以东雅鲁藏布江缝合带中过去识别的穷果群实为构造混杂岩(三叠系—古近系)修康岩群的大型外来岩块;与下伏二叠系曲嘎群呈(侵蚀)假整合接触,上未见顶,与修康岩群之间可能不存在直接的整合/不整合接触关系;时代为三叠纪Induan期—Carnian期。依据岩相、层位差异,穷果群由下向上可划分为屯具场组、屯具日组和尼多曲组3个地层单元。屯具场组以石英砂岩为特征,向上夹含岩屑砂岩、粉砂岩和板岩或互层,厚30~550m,顶与屯具日组整合接触,时代暂置于早三叠世早期的Induan期,大多分布于霍尔巴—仲巴地区,其下部沉积环境为(可含障壁)滨岸,向上演变为为浅表海;屯具日组以晶粒灰岩为特征夹板岩/页岩、粉砂岩,或与之互层,产较为丰富的菊石、双壳类、牙形石等化石,厚200~800m,上未见顶或与尼多曲组整合接触,广泛分布于仲巴微地体,依据Claraia和Eumorphotis双壳动物群、Flemingites和Meekoceras菊石动物群、Neospathodus牙形石动物群,其时代可归属于早三叠世晚期的Olenekian期—中三叠世,沉积于较深陆表海环境;尼多曲组以黑色、深灰色碳质板岩为特征,厚300~500m,与下伏地层整合或假整合或断层接触,上未见顶,分布于仲巴地区,牙形石Metapolygnathus cf.polygnathiformis指示其时代为晚三叠世早期的Carnian期,沉积于深表海。
[Abstract]:On the basis of regional geological survey, measured stratigraphic profile and regional correlation, this paper studies the Chaoguo Group in the western section of the Yalu Zangbo River suture belt in southwestern Tibet. It is considered that the Pengguo Group is only distributed in the Zhongba microbody west of Saga. In the Yarlung Zangbujiang suture zone east of Saga, the Tuangguo Group, which was identified in the past, is a large exotic rock block of the Xiukangyan Group of structural melange (Triassic-Paleogene), and is in contact with the Lower Permian Quga Group in a pseudo-integrated (erosive) way. There may be no direct integration / unconformity contact relationship with the Xiukangyan group, and the age is the Triassic Induan period -Carnian period. According to the lithofacies and horizon difference, the Chaoguo group can be divided into Tughaochang formation from the bottom up. The Tuzhiri formation and the Nidoqu formation are characterized by quartz sandstone, with lithic sandstone, siltstone and slate or interbed, with a thickness of 30 ~ 550m, the top of which is in contact with the Tun Ji-ri formation, and the epoch is temporarily placed in the early Induan stage of the early Triassic. Most of them are distributed in Halba-Zhongba area, their lower sedimentary environment is shoreline (which can contain barrier), and it evolves into shallow sea upward, and Tuzhiri formation is characterized by grain limestone, plystones / shales, siltstones, or interbedded with them, The abundant fossils, such as permethrin, bivalve, conodont and so on, were not found on the top or integrated with the Nidoqu formation, and were widely distributed in the Zhongba micro-terrane. According to the Claraia and Eumorphotis bivalves and the Neospathodus conodont fauna of the Claraia and Eumorphotis bivalves, the Neospathodus conodont fauna, The epoch can be attributed to the late early Triassic Olenekian epoch-Middle Triassic and deposited in the deep epicontinental sea environment, the Nidoqu formation is characterized by black and dark gray carbonaceous slate with a thickness of 300 ~ 500m, and is in contact with the underlying strata or pseudointegration or fault. Distributed in Zhongba area, the conodont Metapolygnathus cf.polygnathiformis indicates that its age is the early Carnian period of late Triassic and deposited in Dehai.
【作者单位】：南京大学地球科学与工程学院;中国地质大学(北京)地球科学与资源学院青藏高原研究中心;
【基金】：中国地质调查局项目“西藏1/5万仲巴县城西地区6幅区调”(编号:1212011121229);“西藏1/5万仲巴县城北地区4幅区调”项目(编号:12112011086037) 国家自然科学基金项目“西藏山南地区上三叠统复理石物源区分析”(No:41072075)联合资助
【分类号】：P534.51

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