鄱阳湖浅水三角洲沉积体系三维定量正演模拟

以鄱阳湖现代浅水三角洲沉积体系为例, 应用三维正演地层模拟软件Sedsim, 在参考前人研究的基础上, 首次将湖盆底部地形、湖(海)平面变化、沉积物注入量及注入方式、气候、沉积物供给速率等动力要素结合在一起, 对该浅水三角洲沉积体系的形成过程及1200年以来的演化进行定量正演模拟, 并采用历史和野外数据对鄱阳湖现代浅水三角洲沉积模型进行约束和校正.模拟结果表明, 鄱阳湖浅水三角洲沉积体系的发育是湖盆地形、湖平面变化、物源供给等多因素作用的综合结果.在该三角洲沉积体系中, 由于水体较浅、沉积底形坡度平坦且基准面变化频繁, 三角洲前缘发育的砂体基本上以席状砂为主, 并主要分布于湖区敞流通道附近.湖平面之上的三角洲平原河道发育与改道的现象主要受湖平面变化速率的影响, 即基准面缓慢上升期间和基准面快速下降期间, 河道发育的现象较明显.该模拟结果不仅能够对大型浅水三角洲的内部特征及形成过程有着更直观的认识, 而且也为今后研究不同地区相似的三角洲沉积体系的形成过程提供了可借鉴的分析模型与理论依据. 

Forward Stratigraphic Modelling of the Depositional Process and Evolution of Shallow Water Deltas in the Poyang Lake,Southern China

Large-scale shallow-water deltas in lacustrine basins have recently been identified as important reservoir plains in the world. The Poyang Lake, the largest fresh water lake of China, develops a series of modern shallow-water deltas, hence provides a good modern analogue for understanding various key depositional processes that control deltaic development and evolution. This paper uses Sedsim, a three-dimensional stratigraphic forward modelling program, to simulate the development and evolution of the shallow-water deltas in the Poyang Lake by considering a number of key processes and parameters affecting the deltaic deposition over 1200 years. According to our simulation results, the construction of the shallow-water deltas in the Poyang Lake is primarily controlled by the lake level fluctuations, the discharge rate of sediment, and the pre-existing topography/bathymetry. It shows that the sand bodies in the delta front are basically sand sheets, which are mainly distributed near the lake open circulation area due to the shallow water depth of the lake, the gentle slope of the depositional basement and the high frequency of lake-level fluctuations. In addition, the frequency of relative lake level oscillation appears to be a significant controlling factor on the development and divarication of river channels on the upper delta plain. A lower rate of the lake level rise and a faster rate of the lake level fall would cause enhanced river channel development and divarication. This study not only enables us to quantitatively understand the dynamic processes of shallow-water delta systems and the key factors controlling the deltaic development and evolution but also provides a reference model for similar ancient depositional systems in sedimentary basins, where active hydrocarbon exploration is currently being undertaken.