断陷湖盆浅水三角洲沉积体系

浅水三角洲不仅可发育在陆相坳陷盆地，也可在断陷湖盆初始期、萎缩期和断-坳转化期发育。浅水三角洲的形成受控于古构造、古地形、古水体、古气候及古物源等因素，在岩性、沉积结构、沉积构造、测井曲线、古生物及地球物理响应等6个方面具有与其他三角洲不同的沉积特征。基于物源体系可将浅水三角洲划分为浅水扇三角洲、浅水辫状河三角洲及浅水曲流河三角洲3种类型。断陷湖盆浅水三角洲的发育具有明显的阶段性和多变性，受构造影响较大。断陷湖盆初始期，由近岸向远岸，A/S值逐渐增加，河道砂体规模变小，连通性变差，席状化程度增强，平面砂体形态由毯状、坨状过渡为朵状、带状。断陷湖盆萎缩期，A/S值较小时，发育丝带状或鸟足状三角洲，水下分流河道推进速度快，单期砂体较厚，横向变化快；A/S值较大时，多发育扇形、舌形或伞状三角洲，水下分流河道不发育，河口坝和席状砂成片出现，砂体横向较稳定，单砂体厚度不大。通过上述研究探讨了断陷湖盆浅水三角洲的发育特征和沉积模式，为完善陆相湖盆浅水三角洲理论提供依据。

Depositional System of Shallow Water Delta in Rifted Lacustrine Basin

The shallow water delta not only develops in the continental depression lacustrine basin, but also develops during the initial, atrophy and fault-depression transition periods in rifted lacustrine basin. The formation of shallow water delta is controlled by palaeotectonics, paleotopography, paleo-water, paleoclimate and paleo-source, and the shallow water delta is characterized by lithology, sedimentary texture, sedimentary structure, well logging, paleontology and geophysical responses, which are different from depositional characteristics of other deltas. According to the source system, the shallow water delta can be divided into three types, including shallow fan delta, shallow braided delta and shallow meandering delta. The development of shallow water delta in rifted lacustrine basin has obvious stage and variability, and is more influenced by the tectonics. During the initial period of rifted lacustrine basin, the A/S value increases gradually from the shore to the far shore, the size of channel sand body becomes smaller, the connectivity becomes worse, and the sheet maturity increases, the shape of planar sand body changes from blanket and lump to lobe and ribbon. During the atrophy period of rifted lacustrine basin, when the A/S value is small, the ribbons or bird-footed delta is developed, the underwater distributary channels advance fast, the single sand body becomes thicker, and the lateral changes quickly; while the A/S value is large, the fan-shaped, tongue-shaped or umbrella-shaped delta is developed more frequently, the underwater distributary channels are not developed, the estuarine bar and sheet-like sand appear in patches, the sand body is horizontal and stable, and the thickness of single sand body is not large. The researches above discuss the development characteristics and depositional models of shallow water delta in rifted lacustrine basin, and provide the new basis for perfecting the shallow water delta theory in the continental lacustrine basin.