Quantifying the three-dimensional stratigraphic expression of cyclic steps by integrating seafloor and deep-water outcrop observations
Quantifying the three-dimensional stratigraphic expression of cyclic steps by integrating seafloor and deep-water outcrop observations
复制标题
通过整合海底和深水露头观测来量化循环步骤的三维地层表达
DOI：
10.1111/sed.12772
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发表时间：
2020
期刊：
影响因子：
3.5
通讯作者：
Englert R
中科院分区：
文献类型：
--
作者：
Englert R
深水沉积物是地球历史的重要档案，包括发生强大的流动事件和将大量陆地碎屑转移到世界海洋中。然而，由于缺乏对现代沉积体系的直接观测，从深水沉积记录中对沉积过程和古水流条件的解释受到限制。最近的海底研究产生了新的发现，包括存在向上倾斜迁移的底形，例如由超临界浊流形成的循环台阶，产生独特的沉积特征。这项研究建立在使用现代和古代数据集的循环步骤的过程与产品关系的基础上，通过提供沉积学和定量的三维结构分析，这些分析是识别和古水流解释岩石记录中沉积结构所必需的。两个现代环境（加拿大斯夸米什米什前三角洲和美国蒙特利峡谷）的重复测深测量用于检查与相对小尺度（平均40至55 m波长和1.5至3.0 m波高）向上倾斜迁移的床型相关的地层演化，这些床型被解释为海底通道和瓣内的周期性台阶。综合这些结果，可解释出露于加拿大加布里奥拉岛的一系列晚白垩世纳奈莫组深水斜坡沉积。在所有数据集中观察到相似的存款尺寸、相和结构，这些数据集跨越不同的浊积岩主导的环境（前三角洲、上部海底峡谷和深水斜坡）和时间尺度（天、年或数千年）。底形沉积物通常为数十米长/宽，厚度<1米，由一系列低角度、后退的槽形透镜体组成，这些透镜体由块状砂/砂岩组成。这些结果支持了这些沉积物的过程关系，与低加积条件下由具有致密基底层的浊流形成的类似循环阶状床相相关。现代与古代的比较揭示了全球普遍存在的海底小规模桑迪上坡迁移床型的地层表达，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。
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.