摘要
观音桥层是晚奥陶世赫南特期在华南上扬子区广泛发育的一套介壳相泥质灰岩地层,位于五峰组和龙马溪组两套页岩气产出层位之间.恢复观音桥层的地理分布,分析其空间分布型式和规律,将有利于重建华南奥陶纪末期的古地理,更好地理解华南奥陶纪末生物大灭绝的环境背景,以及五峰组和龙马溪组黑色页岩形成的古地理背景.本研究基于GBDB数据库收集、整理和厘定了342条剖面的综合数据,利用地理信息系统的Arc GIS软件进行空间模拟,重建了华南上扬子区观音桥层的空间展布.重建结果显示,观音桥层广泛分布于上扬子台地的大部分地区,集中出露于滇东北、黔北、川东南、重庆、鄂西等地,其中厚度最大的区域呈东西向分布于滇黔桂古陆的北缘,形成了一个完整的沉积中心区;而同期的其他岩石地层单元则主要分布于上扬子台地的边缘地区.同时,利用各剖面的沉积学与古生物学、古生态学特征推测该时期各地点具体的古水深值,从而恢复了上扬子区观音桥层沉积期的古地形.结果表明,上扬子区在赫南特中期呈现出"一隆三坳"的古地理格局,"一隆"为湘鄂西水下高地,"三坳"为川东南坳陷、湘中坳陷和鄂北坳陷.这一三面为古陆环绕、局限滞留的古地理环境,是五峰组和龙马溪组富有机质页岩富集的控制因素之一.
The Kuanyinchiao Bed（Hirnantian, Upper Ordovician） is mostly composed of argillaceous limestone and yields the world-famous, cold-water shelly fauna—‘Hirnantia fauna’. It occurs between two black shale units—the Wufeng and Lungmachi formations, and is widely distributed in the Upper Yangtze region of South China. Its consistent lithology, unique fauna, and wide distribution, make it an important maker bed for the stratigraphic subdivision and correlation of regional Ordovician-Silurian boundary rocks, both in outcrop and in drill core. Identification of the Kuanyinchiao Bed is especially important in the recognition of the Wufeng and Lungmachi black shales in the shale gas investigation in South China. Palaeogeographic reconstructions of the occurrence of the Kuanyinchiao Bed can enhance our understanding of the palaeogeographic background of the Late Ordovician mass extinction and the formation of the Wufeng and Lungmachi black shales. In the present study, data from 342 Hirnantian sections（outcrops and drill cores） were collected and standardized through the online Geobiodiversity Database. Geographic Information System（GIS） software was used for the reconstruction of the geographic distribution of the Kuanyinchiao Bed in the Upper Yangtze region. First, a paleogeographic lithofacies map of the study interval and an isopach map of the Kuanyinchiao Bed were constructed based on lithological data and the thickness of the Kuanyinchiao Bed, respectively. The results show that the Upper Yangtze region in the mid-Hirnantian was surrounded by four major oldlands： Central Sichuan Oldland in the west, Yunnan-Guizhou-Guangxi Oldland in the southwest, Cathaysian and Jiangnan oldlands in the east. The Kuanyinchiao Bed is widely distributed in most area of the Upper Yangtze region, intensively in northeastern Yunnan, northern Guizhou, southeastern Sichuan, Chongqing and western Hubei. Coeval strata with different lithologies only occur at the border area of the Upper Yangtze region. The Kuanyinchiao Be
出处
《科学通报》
EI
CAS
CSCD
北大核心
2016年第18期2053-2063,共11页
Chinese Science Bulletin
基金
中国科学院战略性先导科技专项(XDB10010100)
国家自然科学基金(41221001
41290260
U1562213和41272042)资助
