滇黔桂盆地及其邻区石炭纪至二叠纪层序地层格架及三级海平面变化的全球对比
Carboniferous to Permian sequence stratigraphic framework of the Yunnan-Guizhou-Guangxi basin and its adjacent areas and global correlation of third-order sea-level change
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摘要: 提要:属于被动大陆边缘裂谷盆地的滇黔桂盆地,自加里东运动之后,泥盆纪开始拉开,整个晚古生代延续发展。受同生断裂的控制,在深水盆地中发育大小不等的孤立碳酸盐台地,因而在滇黔桂盆地及其邻区形成特殊的“台—盆—丘—槽”的古地理格局。对不同古地理背景下的典型剖面进行三级层序划分并对其进行空间追索和对比,在滇黔桂盆地及其邻区的石炭纪和二叠纪地层中可以识别出12个三级层序,相当于晚古生代25个三级沉积层序(2~5 Ma;SQ1至SQ25)中的SQ14至SQ25;以地层记录中的的两种相变面和两种穿时性为基本要素,可以建立研究区石炭系和二叠系的层序地层格架;层序地层格架反映了三级层序的基本特征:空间上相序的有序性和时间上环境变化的同步性。研究区的石炭系和二叠系,主要为一套碳酸盐岩地层,其中在连陆台地上发育3套煤系地层,它们分别组成石炭纪三级层序SQ15、跨系的三级层序SQ19的HST以及二叠纪吴家坪期的三级层序SQ24;而且在连陆台地边缘和孤立台地上,于阳新世的茅口亚世以及乐平世的长兴期发育海绵生物礁,海绵生物礁分别构成了以下二叠系三级层序即阳新世的SQ22和SQ23以及长兴期的SQ25。3套煤系地层和两套海绵生物礁的发育,使研究区的石炭系和二叠系形成了一个与欧美地区完全不同的层序地层序列。在研究区石炭系和二叠系所识别出的12个三级层序中,石炭纪—二叠纪船山世地层可以划分出6个三级层序。这种划分与Busch等对北美相同层位的划分相似,也就是说该6个三级层序的形成时限大于10 Ma;较长的形成时限可能反映了形成在联合古陆汇聚时期即全球构造相对稳定时期三级海平面变化的一个特性。因此,研究区的石炭系和二叠系所识别和划分出的12个三级层序,其数量比Ross和Ross(1985)对欧美地区石炭系和二叠系所划分出的50多个三级层序要少得多。Abstract: Abstract:The Yunnan-Guizhou-Guangxi basin is a passive continental-margin rift basin. After the Caledonian movement,it began to be pulled apart in the Devonian and continued to develop in the whole of the Late Paleozoic. Controlled by the contemporaneous faults,isolated carbonate platforms of varying size developed in the deep-water basin. Thus a special paleogeographic framework of "platform-basin-hill-trough" formed in the Yunnan-Guizhou-Guangxi basin and its adjacent areas. On the basis of the division into third-order sequences in different paleogeographic settings and their tracing and correlation in space,12 third-order sequences may be distinguished in the Carboniferous and Permian strata in the basin and its adjacent areas. They are equivalent to SQ14 to SQ25 of 25 Late Paleozoic third-order depositional sequences (SQ1 to SQ25,2~5 Ma). On the basis of two kinds of facies-change surface and two kinds of diachronism in stratigraphic records,a Carboniferous to Permian sequence stratigraphic framework may be established in the study region,which reflects the basic features of third-order sequences:ordering of facies sequences in space and synchroneity of environmental changes in time. The Carboniferous and Permian in the study region consist predominantly of a suite of carbonate rocks. In this suite of strata,three coal measures are developed in the land-connected platforms,and two suites of sponge reefs are developed on the margins of the land-connected platforms and in the isolated platforms,which make up sequence stratigraphy in Carboniferous and Permian successions that is greatly different from that in Europe and America.