皖中地区茅口晚期地层的划分对比——银屏组的建立及其意义

    THE DIVISION AND CORRELATION OF THE LATE MAOKOU-AGED STRATA IN CENTRAL ANHUI—THE ESTABLISHMENT OF THE YINPING FORMATION AND ITS SIGNIFICANCE

    • 摘要: 安徽长江流域二叠系分布广泛,发育完整,地表出露良好,含有多门类古生物化石,历来是研究我国华南二叠系的重要地区之一。前人曾对其做过大量的工作,取得了不少地质成果。但是,对于早二叠世孤峰组硅质岩之上、晚二叠世龙潭组下部长石石英砂岩段之下,一套以页岩为主的地层——即所谓“不含煤段”或“A煤组”(以下简称砂页岩段),由于缺少生物地层资料,造成划分上的不统一、时代归属问题上的意见分岐。另外,在与繁昌、宿松等地孤峰组之上所谓“茅口灰岩”(胡海涛1951)或“新林段”(何炎等1964)

       

      Abstract: For a long time there exists a diversity of opinions with regard to the division and correlation of the upper part of the lower Permian in central Anhui. The age determination and correlation of the strata yielding no coal, i. e., the lower part of the original Longtan Formation or the so-called Mao- kou Limestone, are not yet resolved because there is no paleontologic evidence. Since 1974, the authors have discovered-two sets of deposits through detailed geologic mapping and fossil collection. The Chaoxian subtype is represented by clastic, siliceous deposits of neritic,littoral and lagoonal facies. The subtype, 4.55-183.50m thick, is composed mainly of shale, carbonaceous shale and silty shale intercalated with siltstone and siliceous rocks with the Shouchangoceras-Gigantopteris-Myalina biota. This subtype is distributed in ateas along the Changjiang (Yangtze)River including Hexian, Hanshan, Chaoxian, Wuwei, Anqing, Huaining, Tongling, Guichi, Xuancheng, Jingxian and Ningguo. The Chaoxian subtype is called the Yinping Formation (new formation name), whose type section is located at Houdong Village in Yinping, Chaoxian. The Susong subtype consists of neritic platform deposits of carbonate facies and is called the Wuxue Formation which was established by Prof. Chen Xu in 1935. The type locality for the formation is situated in the Dalao Mountains in Guangji, Hubei. The authors propose to use the Zuoshan section, usong, as the type section for this formation. The Wuxue Formation, 38.8-213.4m thick and exposed in Susong, Dongzi, Fanchang and Nanling,is chatacterized by limestone and chert nodular and chert banded limestone, containing the Yabeina-Neomisellina fauna. The Yinping and Wuxue formations rest conformably on the Gufeng tormation, which is composed of siliceous rocks with the Altudoceras-Neopliatifera huangi fauna, and are overlain disconformably by the Longtan Formation (or the Wujiaping Formation), which is composed of feldspar silicaenite with the Gigantopteris-Lobatannularia flora. The establishment of the Yinping and Wuxue formations is of major significance for the division and correlation of the late Maokou-aged strata in central Anhui, the determination of the means and dividing standard of the Gufeng and Longtan formations, the establishment of the sequence of the Permian in Anhui and the provision of lithofacies and paleogeographic evidence for the Early Permian.

       

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