CAJ | 학술논문

扬子地块北缘与秦岭接壤，早古生代经历了上扬子克拉通盆地(∈-O2)和隆后盆地( O3-S)两个阶段。区内发育上奥陶统观音桥组或南郑组地层，为研究赫南特期的岩相古地理，探讨赫南特期冰川事件的沉积响应奠定了坚实的基础。根据沉积特征，结合古生物组合，扬子地块北缘观音桥组可划分为滨岸相和陆棚相。按照岩性等，陆棚相可进一步划分为陆缘碎屑陆棚相、混积陆棚相。滨岸相主要由石英砂岩、钙质砂岩和含砾砂岩组成，发育少量生物，以腕足为主；而在陆棚相中，则是以含粉砂泥岩、生屑灰岩、泥灰岩夹钙质泥岩和含钙泥岩为主，富含生物，以三叶虫( Dalmanitina)、腕足以及标志性冷水、浅水Hirnantia动物群为主。在沉积相详细研究的基础上，分析了该时期的岩相古地理面貌及其空间分布。在北部和西部，继续早期的格局，持续存在汉南隆起，围绕隆起分布的是滨岸相；往南至大两会-桥亭一线，为陆缘碎屑浅海陆棚，大两会-桥亭一线往南区域分布为混积陆棚。由于在研究区，无论在滨岸地带还是浅海地区，均发育赫南特贝化石，说明在赫南特期，由于受南冈瓦纳冰川事件的影响，冰水侵进扬子北缘全区。这次冰川事件导致海平面下降，致使扬子北缘水体变浅，早期的深水陆棚变为浅水陆棚，生物也由浮游相笔石迅速变为壳相赫南特贝，早期隆起范围进一步扩大，并出现地层的缺失。
양자지괴북연여진령접양，조고생대경력료상양자극랍통분지(∈-O2)화륭후분지( O3-S)량개계단。구내발육상오도통관음교조혹남정조지층，위연구혁남특기적암상고지리，탐토혁남특기빙천사건적침적향응전정료견실적기출。근거침적특정，결합고생물조합，양자지괴북연관음교조가화분위빈안상화륙붕상。안조암성등，륙붕상가진일보화분위륙연쇄설륙붕상、혼적륙붕상。빈안상주요유석영사암、개질사암화함력사암조성，발육소량생물，이완족위주；이재륙붕상중，칙시이함분사니암、생설회암、니회암협개질니암화함개니암위주，부함생물，이삼협충( Dalmanitina)、완족이급표지성랭수、천수Hirnantia동물군위주。재침적상상세연구적기출상，분석료해시기적암상고지리면모급기공간분포。재북부화서부，계속조기적격국，지속존재한남륭기，위요륭기분포적시빈안상；왕남지대량회-교정일선，위륙연쇄설천해륙붕，대량회-교정일선왕남구역분포위혼적륙붕。유우재연구구，무론재빈안지대환시천해지구，균발육혁남특패화석，설명재혁남특기，유우수남강와납빙천사건적영향，빙수침진양자북연전구。저차빙천사건도치해평면하강，치사양자북연수체변천，조기적심수륙붕변위천수륙붕，생물야유부유상필석신속변위각상혁남특패，조기륭기범위진일보확대，병출현지층적결실。
The northern margin of the Yangzi block has witnessed two stages of evolution including the Upper Yangtze craton basin(∈-O2)and post-uplift basin(O3 -S)during the Early Palaeozoic, and stratigraphically, consist of the Upper Ordovician Guanyinqiao Formation and/or Nanzheng Formation strata. The sedimentary facies in the Guanyinqiao Formation may be classified into the littoral facies and shelf facies. Lithologically, the shelf facies may be subdivided into the epicontinental clastic shelf and mixed shelf. The littoral facies aligned along the Hannan uplift is dominantly made up of quartz sandstones, calcareous sandstones, and gravel-bearing sandstones in which brachiopods occur. The shelf facies in the Dalianghui-Qiaoting zone is significantly built up of silty mudstones, bioclastic limestones and marls intercalated with calcareous mudstones and Ca-bearing mudstones in which trilobites( Dalmanitina) , brachiopods, and cold-water and shallow-water Hirnantia faunas are observed. The occurrence of the Hirnantian fossils recognized both in the littoral zones and shallow-sea zones has mirrored that due to the effects of the southern Gondwana glacial event, the ice water once invaded into the northern margin of the Yangtze Block. The sea-level falling caused by this glacial event led to the shallowing of the sea water, the transition of the deep-water shelf to the shallow-water shelf and planktonic graptolite to the shelly Hirnantia, and steady uplifting and stratigraphic hiatus in the study area.