Meander-braided Transition Features and Abandoned Channel Patterns in Fluvial Environment
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摘要: 通过总结河流变迁规律,明确了辫-曲转换特征,建立了辫-曲过渡型河流的沉积序列;通过分析弯曲度与废弃河道沉积特征的相互关系,提出不同类型河流中存在分叉分流、串沟取直及颈项截直三类废弃河道,并提出三类废弃河道的分类依据,进而建立了相应的沉积模式。通过解剖北京西山军庄二叠系河流相野外露头,分析了辫状河、以曲流河及其过渡型河流的沉积特征与演变特点,识别出该露头中发育的废弃河道,进而明确该露头中产生辫-曲转换的地质因素是不同气候条件下,由于沉积供源的差异导致河道类型的变化。Abstract: Based on summing up the great variability and dynamic behavior of rivers, we analyzed the meander-braided transition characteristics and constructed its sedimentary sequence. According to the relationship between sinuosity and abandoned channels, we divided abandoned channels into three patterns which are avulsion, chute cutoff- and neck cutoff- abandoned channel, respectively, and each pattern has its particular sedimentary sequence model. Furthermore, by analyzing the sedimentary characteristics from a Permian fluvial outcrop located in Beijing western suburbs, we clarified the evolution of braided, meander-braided transition and meandering channels and distinguished three abandoned channels. We reached the conclusion that the main factor leading to meander-braided transition in the study area is the change of sediment supply caused by different climate conditions.
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