琼东南盆地崖城组高分辨率层序地层格架与煤层形成特征

在系统分析琼东南盆地钻井、岩心、测井、地震、古生物等资料的基础上,识别了崖城组含煤地层层序界面,并进行了崖城组高分辨率层序地层划分。崖城组含煤地层层序边界主要为不整合面、假整合面和下切谷面,界面上、下地层的岩性、岩相、测井特征、地震反射响应都有明显的差异。崖城组含煤地层可以划分为1个超长周期基准面旋回、3个长周期基准面旋回(LSC1、LSC2、LSC3)和至少12个中周期基准面旋回,短周期基准面旋回类型发育较全(A型、B型、C型),但个数变化较大。长、中周期基准面旋回分别可以在全盆地、次级凹陷内部对比,短周期基准面旋回可以在洼陷内对比。在LSC1中,煤层主要发育在海侵期和高水位期的辫状河三角洲平原泥炭沼泽中,具有层数多、单层厚度小及分布稳定性差的特征;在LSC2、LSC3中,煤层主要发育在海侵期潮坪的潮上带和潮间带上部泥炭沼泽中,其中LSC2煤层层数少、厚度相对较大、稳定性相对较好,而LSC3煤层特征与LSC1的相似。长周期基准面旋回中,海侵期发育的煤层多位于短周期上升半旋回或下降半旋回的底部,高水位期发育的煤层多位于短周期下降半旋回的顶部。

High-resolution sequence stratigraphic framework and coal-forming features in Yacheng Formation of Qiongdongnan Basin

The data of well bores, cores, well logging, seismic and paleontology in Qiongdongnan Basin were systematically analyzed. The sequence boundaries of the coal-bearing strata in Yacheng Formation were distinguished, and the high-resolution strata sequence of Yacheng Formation were divided. The main sequence boundaries of the coal-bearing strata include the unconformable surface, disconformable surface or vertical erosion surface. The characteristics of lithology, lithofacies, logging and seismic reflection are very different in the upper and below the sequence boundaries. The coal-bearing strata of Yacheng Formation can be divided into one super-long-period cycle, three long-period cycles（LSC1，LSC2，LSC3）and at least twelve mid-period cycles. Three kinds of short-period cycles can be distinguished（Type A, Type B, Type C）, but the numbers of them change quickly. The long-period cycles can be collated in the whole basin, the mid-period cycles can be collated in the secondary sag, and the short-period cycles would be collated in the low-lying areas. In the TST and HST periods of the LSC1, coal beds deposited in the peat swamp of braided channel delta plain are characterized by great number of coal bed, thin thickness of single coal bed and unstable distribution. The coal beds in the LSC2 and LSC3 are mainly deposited in the peat swamp of epilittoral zone and the upper eulittoral zone. The LSC2 has less number of coal beds and thicker single coal bed than the LSC1. The LSC3 has the similar characteristics of coal beds to the LSC1.In the long-period cycle, the coal beds developed in the TST period are mostly located at the top of rising hemicycle or descending hemicycle in the short-period cycle. The coal beds developed in the HST period are located at the top of descending hemicycle in the short-period cycle.