Deep-water deposits are important archives of Earth’s history including the occurrence of powerful flow events and the transfer of large volumes of terrestrial detritus into the world’s oceans. However the interpretation of depositional processes and palaeoflow conditions from the deep-water sedimentary record has been limited due to a lack of direct observations from modern depositional systems. Recent seafloor studies have resulted in novel findings, including the presence of upslope-migrating bedforms such as cyclic steps formed by supercritical turbidity currents that produce distinct depositional signatures. This study builds on process to product relationships for cyclic steps using modern and ancient datasets by providing sedimentological and quantitative, three-dimensional architectural analyses of their deposits, which are required for recognition and palaeoflow interpretations of sedimentary structures in the rock record. Repeat-bathymetric surveys from two modern environments (Squamish prodelta, Canada, and Monterey Canyon, USA) were used to examine the stratigraphic evolution connected with relatively small-scale (average 40 to 55 m wavelengths and 1.5 to 3.0 m wave heights) upslope-migrating bedforms interpreted to be cyclic steps within submarine channels and lobes. These results are integrated to interpret a succession of Late Cretaceous Nanaimo Group deep-water slope deposits exposed on Gabriola Island, Canada. Similar deposit dimensions, facies and architecture are observed in all datasets, which span different turbidite-dominated settings (prodelta, upper submarine canyon and deep-water slope) and timescales (days, years or thousands of years). Bedform deposits are typically tens of metres long/wide, <1 m thick and make up successions of low-angle, backstepping trough-shaped lenses composed of massive sands/sandstones. These results support process-based relationships for these deposits, associated with similar cyclic step bedforms formed by turbidity currents with dense basal layers under low-aggradation conditions. Modern to ancient comparisons reveal the stratigraphic expression of globally prevalent, small-scale, sandy upslope-migrating bedforms on the seafloor, which can be applied to enhance palaeoenvironmental interpretations and understand long-term preservation from ancient deep-water deposits.

中文翻译：

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通过整合海底和深水露头观测资料量化循环阶跃的三维地层表达

深水沉积物是地球历史的重要档案，包括发生强大的水流事件以及将大量陆地碎屑转移到世界海洋中。然而，由于缺乏现代沉积系统的直接观测结果，从深水沉积记录中解释沉积过程和古水流条件受到了限制。最近的海底研究产生了新颖的发现，包括存在上坡迁移的床形，例如由超临界浑浊流形成的循环阶梯，这些循环产生独特的沉积特征。这项研究通过使用现代和古代数据集，通过对沉积物的沉积学和定量，三维结构分析，建立了循环步骤的过程与产品关系的基础，岩石记录中的沉积物构造的识别和古流解释所必需的。使用来自两个现代环境（加拿大的Squamish prodelta和美国的蒙特利峡谷）的重复测深法调查来研究与较小规模（平均40至55 m波长和1.5至3.0 m波高）上坡相关的地层演化。迁移的床形被解释为海底通道和波瓣内的循环步骤。综合这些结果可以解释加拿大加布里奥拉岛上暴露的晚白垩世纳奈莫群深水斜坡沉积物。在所有数据集中都观察到了相似的矿床尺寸，相和构造，这些数据跨越了以浊石为主的不同环境（三角洲，海底峡谷和深水坡度）和时标（天，年或数千年）。床状沉积物通常长/宽数十米，<1 m厚，由一系列由大块沙/砂岩组成的低角度，后退槽形透镜构成。这些结果支持了这些沉积物的基于过程的关系，并与低凝结条件下由具有稠密基底层的浊流形成的相似的循环阶跃床形有关。现代与古代的比较揭示了海底全球普遍存在的小规模，沙质向上迁移的地层的地层学表达，可用于增强古环境解释并了解古代深水沉积物的长期保存。这些结果支持了这些沉积物的基于过程的关系，并与低凝结条件下由具有稠密基底层的浊流形成的相似的循环阶跃床形有关。现代与古代的比较揭示了海底全球普遍存在的小规模，沙质向上迁移的地层的地层学表现，可用于增强古环境解释并了解古代深水沉积的长期保存。这些结果支持了这些沉积物的基于过程的关系，并与低凝结条件下由具有稠密基底层的浊流形成的相似的循环阶跃床形有关。现代与古代的比较揭示了海底全球普遍存在的小规模，沙质向上迁移的地层的地层学表现，可用于增强古环境解释并了解古代深水沉积的长期保存。