黔桂地区石炭纪层序地层格架及古地理演化

黔桂地区的石炭系可划分为下统和上统,其中下统又划分为岩关阶、大塘阶和德坞阶,上统划分为罗苏阶、滑石板阶、达拉阶和逍遥阶。多年来一直作为石炭系的马平组则成为一个跨系的岩石地层单位,因此石炭系最顶部的地层与下二叠统一起构成1个三级层序。从石炭系到下二叠统构成1个二级层序,其底面为紫云运动主幕产生的不整合面,顶界面为黔桂运动产生的不整合面,包含6个三级沉积层序,分别简称为SQ14,SQ15,SQ16,SQ17,SQ18,SQ19。研究区范围内从连陆台地到孤立台地乃至台沟背景,沉积特征明显不同,连陆台地上发育煤系地层并且发育较多的白云岩地层,孤立台地上则以大套碳酸盐岩地层为特征,台沟背景中以暗色细粒沉积为主。所以,尽管三级层序的相序特征在空间上变化较大,但它们所代表的相对海平面变化过程基本上是同步的。在前人大量的古生物学研究成果的基础上,系列层序地层格架栅状图以及相应的古地理图较为清楚地反映了研究区石炭纪至二叠纪船山世复杂而有序的时间相变与空间相变。

THE SEQUENCE-STRATIGRAPHIC FRAMEWORK AND THE EVOLUTION OF PALEOGEOGRAPHY FOR CARBONIFEROUS OF THE GUIZHOU AND GUANGXI AREAS

Carboniferous system in the Guizhou and Guangxi areas can be divided into two series (the lower series and the upper series): the lower series includes the Yanguanian, the Datangian and the Dewuan stages; and the upper series includes the Luosuan, the Huashibanian, the Dalan and the Xiaoyaoan stages. Therefore, the Maping Formation that has been used as the top strata of Carboniferous system for many years becomes an inter system lithostratigraphic unit. The strata from Carboniferous to the Lower Permian epoch form a second order sequences, the top and the bottom boundaries of which are long term punctuated surfaces genetically related to the unconformities of tectonic movement, the bottom one is the unconformity of the second episode of the Ziyun Movement, and the top one is that of the second episode of the Qiangui Epeirogeny. Six third order sequences that are briefly named as SQ14 to SQ19 can be discerned in the strata from Carboniferous to the Early Permian epoch. In the research areas, there are three different paleogeographic settings such as the attached platform, the isolated platform and the inter platform ditch. Coal measures strata and relative more dolomitic strata make up the strata of the atta ched platform, carbonates constitute the strata of the isolated platform, and in inter platform ditch more dark and fine sediments mainly form the strata from Carboniferous to the Early Permian epoch. The lithofacies succession fabric of third order sequences is changed with the changes of the paleogeographic settings, but there is a synchronism for the process of sea level changes indicated by the lithofacies sucession of the third order sequences. On the basis of the research on paleobiology, a series of the penal diagrams of sequence stratigraphic framework and the corresponding maps of sedimentary facies and paleogeography, can be used to reflect the complex and the regular facies changes in time and in space from Carboniferous to Early Permian in the Guizhou and Guangxi areas.