摘要： 低可容空间陆相湖盆富砂浅水三角洲不仅是沉积学研究热点,也是油气勘探的重点对象。通过追踪国内外学者对低可容空间盆地中浅水三角洲的研究,结合霸县凹陷文安斜坡古近系浅水三角洲的实例,总结了低可容空间富砂浅水三角洲的发育条件、沉积特征、沉积机制及沉积模式。已有研究表明:大型低可容空间浅水三角洲沉积体系的发育受控于相对稳定的构造活动、平缓的地形坡度(常小于1°)、周期性变化的气候、排水通畅的敞流湖盆、频繁波动的浅水环境及高速和高流量的充沛物源; 在低可容空间下,浅水三角洲发育氧化色与还原色泥岩间互沉积,生物扰动强烈,强水动力牵引流沉积构造发育,较强的冲刷作用形成了“有泥”和“无泥”2种间断正韵律,河道不断向盆地中心延伸,形成树枝状、带状和鸟足状三角洲。实例研究表明,霸县凹陷文安斜坡沙一段为低可容空间盆地,在供源充足的背景下发育大面积的浅水三角洲,其中三角洲平原中可容空间和沉积物供给的比值(A/S)最小,河道以垂向加积为主,河道稳定、分叉少,垂向上以“砂冲砂”韵律为主,平面上呈“枝状”; 内前缘A/S值相对增大,河道侧向迁移作用增强,河道分叉多,垂向上“砂冲砂”与“砂冲泥”韵律并存,平面上呈“网状”; 外前缘A/S值达到最大,由于湖浪的改造作用,水下分流河道明显席状化,垂向上表现为孤立砂体,平面上呈孤立河道或大面积席状砂。

关键词: 低可容空间, 陆相浅水三角洲, 沉积特征, 沉积模式, 霸县凹陷

Abstract: The sand-rich shallow delta in continental lacustrine basins with low accommodation is not only the research hotpoint in sedimentology,but also the attractive object in petroleum exploration. By tracking the research of shallow-water delta in low accommodation basins by domestic and foreign scholars,combined with the example of the Paleogene shallow-water delta in Wen'an slope of Baxian sag,the development conditions,sedimentary characteristics,sedimentary mechanism, and sedimentary models of shallow water delta in low accommodation basins are summarized. The development of a large shallow-water delta sedimentary system in low accommodation is controlled by relatively stable tectonic activities,gentle slopes(often less than 1°),periodic climates,open-flow lake basins,frequent fluctuations of the shallow-water environment,and high-speed and high-flux abundant sources. In the low accommodation,the shallow-water delta forms the oxidation color and the reduction color mudstones,which have strong biological disturbances,and sedimentary structures of strong hydrodynamic traction. The strong scouring action forms two kinds of intermittent positive rhythms of‘mud’ and‘mudless’. The river channel continues to extend to the center of the basin,forming deltas of dendritic,bandlike, and bird-foot shapes. The case study shows that the first Member of Shahejie Formation in Wen'an slope of Baxian sag is a low accommodation basin,and a large area of shallow-water delta is developed under the background of sufficient sediment supply. When the shallow-water delta is formed,the ratio of accomodation space and sediment supply(A/S) of the delta plain is the smallest, and the channel is mainly vertically-aggradated,so that the channel is stable and the bifurcation is rarely occurred. In the vertical direction,it is characterized by positive rhythms of‘mudless’,which is characterized by‘branch’ in the plane. In the inner front, the A/S is relatively increased, and the lateral migration of the channel is enhanced,causing the channel being bifurcated. In the vertical direction,positive rhythms of‘mud’ and‘mudless’ coexist,which is characterized by‘mesh’ in the plane. In the outer front, the A/S reaches the maximum; due to the dominance of lake waves,the subaqueous distributary channel is obviously sheeted,which is characterized by isolated sand body vertically and isolated channel or large area sheet sand on the plane.

Key words: low accommodation, continental shallow-water delta, sedimentary characteristics, sedimentary model, Baxian sag

中图分类号: 

• P512.31