辫曲转换与共存的主要影响因素及对古代河流沉积环境恢复的启示

河流辫曲转换与共存是自然地理学、水力学、河流沉积地质方面的研究热点问题，也对古代河流沉积环境恢复与储层预测有重要借鉴意义.首先对河流辫曲转换与共存特征的主要影响因素进行了探讨，指出构造变动与地貌单元、坡度（坡降）的陡缓差异、物源远近与水动力条件、气候变化与植被发育状况、海/湖平面变化等主要因素控制着辫曲河型转换过程，其中构造变动与地貌单元是最为关键因素；然后总结了辫曲转换与共存这一理念对古代河流沉积恢复研究的4点启示；再以鄂尔多斯盆地大牛地气田中二叠统下部的下石盒子组为例，结合测井曲线特征、地震属性与砂岩厚度分布规律，把辫曲转换与共存的理念应用于古代河流沉积环境恢复之中，最终再现了气田区H21砂层河流沉积分布格局，明确了该区北辫南曲、辫曲转换与共存的规律，指出在辫曲转换地带与相邻的曲流河发育的区域更易于产生废弃河道. 

Main Influencing Factors of Braided-Meander Transition and Coexistence Characteristics and Implications of Ancient Fluvial Sedimentary Environment Reconstruction

The braided-meander transition and coexistence phenomenon is a hot issue in physical geography, hydraulics and fluvial sedimentary geology. It also has important reference significance for ancient fluvial sedimentary environment reconstruction and reservoir prediction. Firstly, it discusses the main influencing factors of the characteristics of fluvial braided-meander transition and coexistence, and points out that the main factors such as structural change and geomorphic unit, the difference of slope gradient, the distance of provenance and hydrodynamic conditions, climate change and vegetation development, sea/lake level change control the process of braid river type transformation. Among them, tectonic change and geomorphic unit are the key factors. Then, four implications of the concept of braided-meander transition on the study of ancient river sedimentary facies reconstruction are summarized. Taking the Lower Shihezi Formation in the lower part of the Middle Permian in Daniudi gas field, Ordos basin, as an example, combined with the characteristics of well-logging curves, seismic attributes and sandstone thickness distribution law, the concept of braided-meander transition and coexistence was applied to the reconstruction of ancient fluvial environment. Finally, fluvial sedimentary distribution pattern of H21 sand bed in the gas field area was reconstructed. It is indicated that braided river prevailed in the northern part and meandering river was mainly developed in the southern part in the gas field area. It is pointed out that it is easier to form abandoned river channels in the braided-meander zone and the adjacent meandering river area.