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S40界面是琼东南盆地新近系裂后期的重要地质界面,发育时代为晚中新世末期(约11.6Ma),是裂后期充填序列中梅山组和黄流组的分界面.通过对琼东南盆地大量二维测线的精细解释,结合钻井、生物等资料,从海平面变化、地震-沉积相跃迁、沉降速率等方面总结了该界面的特征,指出S40界面在盆地东西部特征差异明显:在盆地西北部浅水区,该界面具有明显的角度不整合特征,“下削上超”特征明显,在局部地区梅山组一段整套地层都被削蚀;在盆地东南部半深水-深水区域,S40界面上下反射具明显差异,界面之上为一组中等连续性、中-强振幅的地震反射同相轴,界面之下地震反射多呈强振幅、中等连续-丘状反射,甚至局部出现前积反射.研究认为,S40界面的东西差异性可能与该界面在盆地东西部受到的控制因素差异相关:盆地西部主要受区域性海平面大规模下降的影响,S40界面表现出对下伏地层的强烈削蚀;盆地东部则可能是西沙海槽在晚中新世以来的加速沉降在琼东南盆地的具体表征.受这次区域性构造活动的影响,盆地东部水体突然加深,接受大规模的沉降,界面上下表现为相的突变和跃迁,此时盆地已经具有“东深西浅”的地貌特征,这种结构一直延续至今.S40界面的性质厘定及其地质意义的重新认识有可能为中国南海新生代盆地形成演化及其动力学背景研究提供新的信息.
The S40 interface is an important geological interface of the late Paleozoic in the Qiongdongnan Basin, and developed in the late Late Miocene (about 11.6Ma), which is the interface between the Meishan Formation and the Huangliu Formation in the post-cracking filling sequence. A large number of two-dimensional line fine interpretation, combined with drilling, biology and other data, from the sea level changes, seismic-sedimentary facies transition, sedimentation rate and other aspects of the characteristics of the interface summarized S40 interface in the eastern and western characteristics of the basin significantly different: In the shallow northwestern part of the basin, the interface has obvious features of angular unconformity. The characteristics of “undercut and over-ultra” are obvious, and a whole set of formations in the Meishan Formation in some areas have been eroded. In the semi-deepwater and deepwater southeast of the basin, There is a significant difference between the up and down reflections of the S40 interface. Above the interface is a set of moderately continuous, moderate-strong amplitude seismic reflection events, with strong amplitude, moderate continuous-dome reflection, and even local pre-seismic Reflection.The study suggests that the difference between the east and west of the S40 interface may be related to the differences in the control factors that the interface receives in the east and west of the basin: the western part of the basin is mainly affected by the large-scale decline of the regional sea level, and S40 Surface shows strong erosion of the underlying strata.The eastern basin may be the specific characterization of Xisha trough accelerated sedimentation in the Qiongdongnan Basin since the Late Miocene.By the regional tectonic activity, Suddenly deepen, accept large-scale subsidence, the interface up and down the phase of the sudden change and transition, at this time the basin already has a “deep east-west” topography, this structure has continued until now.S40 interface properties and its Re-understanding of geological significance may provide new information for the study of the evolution of the South China Sea Cenozoic basin and its dynamic background.