异重流发育条件、演化过程及沉积特征

异重流是指河流携带沉积物直接潜入蓄水体底部并沿盆地底部继续前进的高密度流体。通过大量文献调研,归纳总结了异重流的发育条件、沉积过程及相应沉积特征。异重流的形成受构造和气候条件控制,与所处的源汇系统密切相关。母岩固结程度低、半干旱气候、地形高差大、河流流域蒸发量低、一定的河口坡降和低密度的蓄水体等条件有利于异重流发生。异重岩沉积序列与异重流能量演化过程密切相关,反序（Ha）和正序（Hb）二元结构、内部突变/侵蚀界面、典型流动沉积构造和富含陆源植物碎屑等是识别异重岩的重要标志。在总结前人研究成果的基础上建立了由沟道充填沉积-沟道侧缘沉积-天然堤-前缘朵叶体4部分组成的异重流沉积模式。

Development conditions,evolution process and depositional features of hyperpycnal flow

Hyperpycnal flows are dense,formed when a sediment-laden fluid plunges into the bottom of a water body and flows basinward.After a large number of literature review,we summarized the development conditions,evolution process and depositional features of hyperpycnal flow.The formation of hyperpycnal flow is controlled by tectonic and climatic conditions,closely related to the location of the source-to-sink system.And the favorable conditions for its development are loose parent rocks,semi-arid climate,high elevation difference,low degree of evaporation of river drainage area,a significant slope at the river mouth and low-density water body.Typically,sedimentary sequence of hyperpycnites can reflect the evolution of hyperpycnal flow energy.To identify hyperpycnites,we should pay attention to important features such as coupling of inverse and normal grading (Ha-Hb),internal mutation/erosion contact,typical flowing depositional structures and concentration of plant debris.Based on previous workers'studies,we established an ideal model of hyperpycnal facies consisting of channel-filling sedimentation,channel margin sedimentation,natural levees and front lobes.