The rarely witnessed process of river avulsion repositions channels across floodplains, which influences floodplain geomorphology and stratigraphic architecture. The way avulsions redirect water and sediment is typically generalized into one of two styles. Avulsions proceeding through rapid channel switching and producing little to no floodplain disturbance are annexational, while those that involve sequential phases of crevassing, flooding, and eventual development of a new channel are progradational. We test the validity of these avulsion style categories by mapping and characterizing 14 avulsion events in Andean, Himalayan, and New Guinean foreland basins. We use Landsat data to identify how avulsions proceed and interpret the possible products of these processes in terms of geomorphic features and stratigraphy. We show that during annexation the avulsion channel widens, changes its meander wavelength and amplitude, or increases channel thread count. During progradation, avulsion channels are constructed from evolving distributary networks. Often beginning as crevasse splays, these networks migrate down the floodplain gradient and frequently create and fill ponds during the process. We also see evidence for a recently defined third avulsion style. Retrogradation involves overbank flow, like progradation, but is marked by an upstream-migrating abandonment and infilling of the parent channel. Avulsion belts in this study range from 5 to 60 km in length, and from 1 to 50 km in width. On average, these events demonstrate annexational style over 22.4% of their length. Eleven of 13 events either begin or end with annexation, and seven both begin and end with annexation. Only one event exhibited progradation over the entire avulsion-belt length. While there are many documented examples of purely annexational avulsions, we see little evidence for completely progradational or retrogradational avulsions, and instead suggest that a given avulsion is better envisioned as a series of spatiotemporal phases of annexation, progradation, and retrogradation. Such hybrid avulsions likely produce significantly greater stratigraphic variability than that predicted by the traditional end-member model. We suggest that a time-averaged, formation-scale consideration of avulsion products will yield more accurate characterizations of avulsion dynamics in ancient fluvial systems.

中文翻译：

---

从卫星遥感量化河流撕裂活动：撕裂如何影响前陆盆地洪泛区地层学的意义

罕见的河流撕脱过程重新定位了泛滥平原上的渠道，这影响了泛滥平原的地貌和地层结构。撕裂改变水和沉积物的方式通常被概括为两种风格之一。通过快速通道转换和几乎没有产生洪泛区干扰的撕脱是吞并性的，而那些涉及裂缝、洪水和最终开发新河道的连续阶段的撕脱是渐进性的。我们通过绘制和描述安第斯、喜马拉雅和新几内亚前陆盆地的 14 次撕脱事件来测试这些撕脱类型类别的有效性。我们使用 Landsat 数据来确定撕裂如何进行，并根据地貌特征和地层学解释这些过程的可能产物。我们表明，在吞并期间，撕脱通道变宽，改变其曲折波长和幅度，或增加通道线程数。在升级过程中，撕裂通道是由不断发展的分流网络构建的。这些网络通常从裂缝展开开始，沿着洪泛区梯度向下迁移，并在此过程中经常形成和填充池塘。我们还看到了最近定义的第三种撕脱风格的证据。回生涉及泛滥的流动，就像推进一样，但以上游迁移的放弃和母通道的填充为标志。本研究中的撕裂带长度为 5 至 60 公里，宽度为 1 至 50 公里。平均而言，这些事件在其长度的 22.4% 上表现出兼并风格。13 个事件中有 11 个以吞并开始或结束，七个都以兼并开始和结束。只有一个事件表现出在整个撕裂带长度上的进展。虽然有许多记录在案的纯粹吞并撕脱的例子，但我们几乎看不到完全渐进或逆行撕脱的证据，而是建议将给定的撕脱更好地设想为吞并、前进和倒退的一系列时空阶段。这种混合撕脱可能产生比传统端元模型预测的显着更大的地层变异性。我们建议，对撕脱产物的时间平均、地层尺度考虑将产生更准确的古代河流系统撕脱动力学特征。虽然有许多记录在案的纯粹吞并撕脱的例子，但我们几乎看不到完全渐进或逆行撕脱的证据，而是建议将给定的撕脱更好地设想为吞并、前进和倒退的一系列时空阶段。这种混合撕脱可能产生比传统端元模型预测的显着更大的地层变异性。我们建议，对撕脱产物的时间平均、地层尺度考虑将产生更准确的古代河流系统撕脱动力学特征。虽然有许多记录在案的纯粹兼并性撕脱的例子，但我们几乎没有看到完全渐进性或逆行性撕脱的证据，而是建议将给定的撕脱更好地设想为兼并、渐进和退化的一系列时空阶段。这种混合撕脱可能产生比传统端元模型预测的显着更大的地层变异性。我们建议，对撕脱产物的时间平均、地层尺度考虑将产生更准确的古代河流系统撕脱动力学特征。而是建议将给定的撕脱更好地设想为吞并、升级和倒退的一系列时空阶段。这种混合撕脱可能产生比传统端元模型预测的显着更大的地层变异性。我们建议，对撕脱产物的时间平均、地层尺度考虑将产生更准确的古代河流系统撕脱动力学特征。而是建议将给定的撕脱更好地设想为吞并、升级和倒退的一系列时空阶段。这种混合撕脱可能产生比传统端元模型预测的显着更大的地层变异性。我们建议，对撕脱产物的时间平均、地层尺度考虑将产生更准确的古代河流系统撕脱动力学特征。