摘要
轴向沉积体系是陆相断陷盆地油气勘探中的有利相带.为加深对断陷盆地轴向沉积体系发育及其演化的认识,以北部湾盆地涠西南凹陷为例,利用三维地震资料、滨线迁移轨迹特征及钻井信息,揭示涠西南凹陷流一段西部轴向三角洲沉积体系的空间展布及演化特征,认为轴向三角洲沉积通常发育于断陷盆地裂陷晚期,其垂向叠置样式及空间展布受到构造活动、古地貌以及相对湖平面变化的控制.研究结果表明,涠西南凹陷西部轴向三角洲沉积体系由6期加积和进积两种不同类型的准层序组构成.加积型准层序组发育时期,可容空间增长速率较高,顶积层厚度较大,单期厚度约为50~80 m,底积层延伸范围广,以发育S型前积为特征,前积角度相对较低(1.5°~2.0°),滨线迁移轨迹为上升型;进积型准层序组发育时期,可容空间增长速率较低,缺乏顶积层(厚度小于30 m),以发育斜交型前积为特征,前积角度高,平均约为3°,可见顶超现象,滨线迁移轨迹为平缓型.加积与进积两种类型准层序组相互叠置,交替出现,在垂向和横向上对涠西南凹陷进行充填.轴向三角洲沉积发育于涠西南凹陷第2次裂陷晚期,其空间展布及演化受相对湖平面阶段性变化及构造-古地貌格局的控制,相对湖平面经历了多次"上升-稳定"的阶段性变化,沿二号断裂带的差异沉降很可能是导致这种阶段性变化的因素.
Axial sedimentary system developed in continental rift basins is regarded as the favorable facies belt in oil exploration.To deepen the understanding of the development and evolution of axial sedimentary system in rift basins,3 D seismic data,shoreline migration trajectories and borehole data were used to investigate the spatial distribution and evolution of western axial deltaic system within first member of Liushagang formation(L1),Weixinan sag,Beibuwan basin.It is considered that the axial sedimentary system usually developed during late rifting stage in a rift basin and the vertical stacking patterns and spatial distribution were controlled by tectonic activity,geomorphology and relative lake level changes.The results showed that the western axial system in Weixinan sag was composed of 6 parasequence sets which are recognized as aggradational(type A)or progradational(type P)clinothems.During the development of type A parasequence sets,expansion rate of accommodation is high and the topsets are relatively thicker with the thickness of 50-80 m.The type A parasequence sets is characterized by its S foresets,and more elongated bottomsets,with a relatively lower angle(1.5°-2.0°).Furthermore,it has ascending shoreline trajectories.In contrast,clinoforms of type P parasequence sets are characterized by oblique foresets with an average angle of 3°;the expansion rate of accommodation is low and the topsets are absent(with the thickness lower than 30 m).Furthermore,it has flat shoreline trajectories.These two types of parasequence sets occur alternately and overlay by each other,filling the sag vertically and laterally.The axial deltaic system is developed during the late stage of the second rifting phase of Weixinan sag;its spatial distribution is mainly controlled by the cyclical relative lake level changes and tectonic-induced palaeogeomorphology.The relative lake level experienced multi-phase changes of"rising-stabilization",which may be mainly caused by differential subsidence along the No.2 fault system.
作者
秦春雨
王华
姜平
杨希冰
邹康
QIN Chunyu;WANG Hua;JIANG Ping;YANG Xibing;ZOU Kang(Faculty of Earth Resources,China University of Geosciences,Wuhan,Hubei 430074,China;Zhanjiang Branch of CN0OC Co.Ltd.,Zhanjiang,Guangdong 524057,China)
出处
《中国矿业大学学报》
EI
CAS
CSCD
北大核心
2020年第3期542-551,共10页
Journal of China University of Mining & Technology
基金
国家“十三五”油气重大专项(2016ZX05024-006-002)。
关键词
轴向三角洲体系
涠西南凹陷
滨线迁移轨迹
相对湖平面变化
差异沉降
二号断裂带
axial deltaic system
Weixinan sag
Shoreline migration trajectories
relative lake level change
differential subsidence
No.2 fault system
