摘要
中国西北地区是指贺兰山及六盘山以西和昆仑山以北的我国西北部的广大地区。在各露头及钻井剖面的地层学和岩石学研究的基础上 ,采用单因素分析综合作图法 ,编制出了中国西北地区奥陶系各统的各种单因素图和奥陶纪各世的岩相古地理图。这些岩相古地理图具有定量、多级别和多类型的特点。定量 ,即每个古地理单元的划分和确定都有确切的定量的单因素数据和图件为依据。多级别 ,即已划分出三级古地理单元 ,如陆和海为一级 ;在海中又划分出台地、盆地和斜坡 ,为二级 ;在台地中 ,又划分出滩、坪等 ,为三级。多类型 ,即每个古地理单元 ,主要是二级和三级古地理单元 ,还可根据其岩石特征区分出不同的类型 ,如台地可区分出碳酸盐岩台地、碎屑岩台地、火山岩台地等 ,盆地可区分出泥岩盆地、硅岩盆地、碎屑岩盆地、复理石盆地、火山岩盆地等 ,滩可区分出亮晶颗粒滩 (准滩、雏滩 )、灰泥颗粒滩 (准滩、雏滩 )等。这种古地理图在西北地区还是首次出现。西北地区奥陶纪岩相古地理格局可概括为“海陆并存 ,海中台盆相间分布 ,台中有滩和坪 ,台盆间有斜坡”。早奥陶世继承了寒武纪的海进并进一步扩大 ,至中奥陶世海进达盛期 ,到晚奥陶世开始海退 ,从而完成了西北地区寒武纪和奥陶纪海进海退旋回。
Northwest China in this paper refers to the broad region bounded by the Helan Mountains and Liupan Mountains to the east, and by the Kunlun Mountains to the south. Based on the study of stratigraphy and petrology of outcrop and well sections, according to single factor analysis and comprehensive mapping method, various single factor maps of the Lower, Middle and Upper Ordovician and lithofacies palaeogeography maps of the Early, Middle and Late Ordovician in Northwest China were compiled. These lithofacies palaeogeography maps possess three characteristics, i.e. quantification, multirank and multitype. Quantification means that the determination of each palaeogeographic unit is based on quantitative single factor data and maps. This makes palaeogeography develop to the quantitative stage. Multirank means that palaeogeographic units are classified into three ranks or more than three ranks. For instance, lands and seas are the first rank. In the seas, the platforms, basins and slopes are defined and belong to the second rank. In platforms, the banks and tidal flats are further drawn out and belong to the third rank. Multitype means that the palaeogeographic units, especially the 2nd and 3rd rank units, can be further divided into different types on the basis of their rock types. For instance, platforms can be divided into carbonate rock platforms, clastic rock platforms, volcanic rock platforms ,etc.;basins can be divided into mudstone basins, siliceous rock basins, clastic rock basins, volcanic rock basins, flysch basins, etc.;and banks can be divided into sparry grain banks (penebanks, embryonic banks), and limemud grain banks (penebanks, embryonic banks). The framework of lithofacies paleogeography of the Ordovician in Northwest China can be summerized as following: There were both lands and seas. In seas there were platforms and basins distributed alternately. In platforms there were banks and flats. Between platforms and basins there were slopes. In the Early Ordovician, the Cambrian transgression continued and became larger. In the Middle Ordovician, the transgression reached to its climax. In the Late Ordovician, the regression appeared, and the refore the transgression and regression cycle of the Cambrian and Ordovician in Northwest China was completed.
出处
《古地理学报》
CAS
CSCD
2000年第3期1-14,共14页
Journal of Palaeogeography：Chinese Edition
基金
中国石油天然气总公司科研计划正式项目"中国寒武纪及奥陶纪岩相古地理研究及编图"的阶段性研究成果
关键词
中国西北地区
奥陶纪
岩相古地理
单因素
定量
多级别
多类型
Northwest China, Ordovician, single factor, lithofacies palaeogeography, quantification, multirank, multitype
