The gravity flow deposit were mainly developed in the lowstand systems tract(LST) of the first member of Upper Miocene Huangliu Formation(Ehl1) in Dongfang area, Yinggehai Basin, has become a valuable target for gas exploration and production. The gravity flow sedimentary characteristics of lithofacies associations, sedimentary texture, seismic facies and logging facies were described in detail on the basis of integrated analysis of cores, logging and seismic data. The sedimentary microfacies types composed of neritic sandbar, continental shelf mud, main channel, bifurcated or cross-cutting distributary channel, overspill, and natural levee are revealed under the constraint of high resolution sequence stratigraphic framework in the Ehl1. The gravity flow deposit system in the LST is divided into three evolution stages corresponding to periods of three parasequence sets. The gravity flow deposit was induced in the early LST, expanded rapidly in the middle LST and decreased slightly in the late LST. But its developing scale decreased sharply in the transgression systems tract(TST) and finally vanished in the highstand systems tract(HST). This spatial evolution rule is constrained by the integrated function of sediments supply of the Vietnam Blue River in the LST, the development of local gradient change in sea floor(micro-topography, i.e., flexure slope break), and the fall in relative sea level. On the basics of the deep study of the coupling relationship among the three main control factors, the sedimentary model is established as an optimal component of "source-channel-sink" for shallow marine turbidite submarine fan.
Ming SunHua WangJihua LiaoHuajun GanJun XiaoJinfeng RenShu'e Zhao
Based on the application of the EBM basin modeling software and 2-D seismic profiles,the Paleogene and Neogene subsidence histories of the Beitang (北塘) sag are simulated with the back-stripping technique,and the relationship between subsidence character and tectonic revolution is dis-cussed. Moreover,the result of the basin modeling reveals that the subsidence history of the Beitang sag has the characteristics of several geological periods,and these succeeding periods have shown certain inheritance and difference characteristics. At the early (Es3) and middle (Es2-Es1) rifting periods,the subsidence reaction of the Beitang sag was mainly in the charge of tectonic activity,while at the late (Ng-Nm+Q) rifting period-post rifting period and post rifting subsidence-acceleration period-the subsidence type is mainly that of thermal subsidence or regional depression effect; from the beginning of the subsidence history to the end,the reason for the basin subsidence has changed from tectonic ac-tivity to non-tectonic activity.
