黔桂地区二叠纪层序地层格架及古地理演化

二叠系包括3个统即船山统、阳新统和乐平统,船山统与阳新统之间的黔桂运动主幕不整合面以及阳新统和乐平统之间的东吴运动主幕不整合面,代表了沉积盆地性质发生较大变化的界面和最为明显的层序界面.黔桂地区的二叠系以其明显的相分异而引人注目,在连陆台地上发育煤系地层,而在连陆台地边缘及孤立台地上发育海绵生物礁,形成一个典型的"台—盆—丘—槽"的古地理格局,并且相分异最明显的时期正好与生物礁发育的时期相对应;由于东吴运动第一幕使钦防残留海槽关闭,古地理格局发生了较大变化.在二叠系中,船山统与下伏石炭系顶部的地层构成一个三级沉积层序(SQ19),阳新统包含4个三级层序(SQ20—SQ23),乐平统包括2个三级层序(SQ24—SQ25).该地区的另一个特点是在二叠系与三叠系之交发生了较为典型的台地淹没事件,形成一个较为典型的淹没不整合面.因此,复杂而有序的时间相变与空间相变,在系列岩相古地理和系列层序地层格架中得到较为系统地反映.

THE PERMIAN SEQUENCE STRATIGRAPHIC FRAMEWORK AND EVOLUTION OF SEDIMENTARY FACIES AND PALEOGEOGRAPHY IN GUIZHOU AND GUANGXI AREAS

The Permian system which includes the Chuanshanian,the Yangsingian and the Lopingian series can be divided into three series in Guizhou and Guangxi areas of South China.There are two obvious unconformities in the sequence,the one refers to the main episode of the Qiangui epeirogeny in the transitio nal period at the turn between Chuanshanian epoch and Yangsingian epoch,and another refers to the main episode of Dongwu movement in the transitional period at the turn between Yangsingian epoch and Lopin gian epoch,both of which not only forms the evident sequence boundaries of type I but also represents the important changing surfaces of sedimentary facies and paleogeography.Obvious differentiation of depositional facies leads to the formation of a special pattern of paleogeography marked by "platform basin hill trough",especially for Lopingian epoch,which is reflected by lots of sedimentary features.For examples,coal measures are developed on the widespread platform,and sponge reefs are developed on the margin of the widespread platform as well as the isolated carbonate platform,furthermore,the period of the evident facies differentiation is corresponding to the development period of reefs,etc.The first episode of Dongwu movement in the transitional period at the turn between Yangsingian epoch and Lopingian epoch results in the great change of the paleogeographic pattern.Seven third order sequences can be discerned in the Per mian of the study areas,i.e.,the top part of Carboniferous and the Chuanshanian series form one sequence (SQ₁₉),four sequences which are from SQ₂₀ to SQ₂₃ are discerned in the Yangsingian series,and two sequences which are SQ₂₄ and SQ₂₅ are divided in Lopingian series.The typical drowned event of the carbonate platforms in the transitional period at the turn between Permian and Triassic shows that the top boundary of SQ₂₅ is a obvious drowned unconformity.Therefore,the complex but regular facies changes in time and in space can clearly be illustrated in the series of the maps of sedimentary facies and paleogeography as well as the panel diagrams of sequence stratigraphic framework.