Ephemeral fluvial systems are commonly associated with arid to semi‐arid climates. Although their complex sedimentology and depositional settings have been described in much detail, depositional models depicting detailed lateral and vertical relationships, and interactions with coeval depositional environments, are lacking compared to well‐recognized meandering and braided fluvial systems. This study critically evaluates the applicability of current models for ephemeral fluvial systems to an ancient arid fluvial example of the Lower Jurassic Kayenta Formation of the Colorado Plateau, USA. The study employs detailed sedimentary logging, palaeocurrent analysis and photogrammetric panels across the regional extent of the Kayenta. A generic model that accounts for the detailed sedimentology of a sandy arid ephemeral fluvial system (drawing upon both ancient and geomorphological studies) is developed, along with analysis of the spatial and temporal interactions with the aeolian setting. Results show that the ephemeral system is dominated by laterally and vertically amalgamated, poorly channelized to sheet‐like elements, with abundant upper flow regime flat beds and high sediment load structures formed between periods of lower flow regime conditions. Through interaction with a coeval aeolian system, most of the fluvial deposits are dominated by sand‐grade sediment, unlike many modern ephemeral fluvial systems that contain a high proportion of conglomeratic and/or finer grained mudstone and siltstone deposits. During dominantly fluvial deposition, high width to thickness ratios are observed for channelized and sheet‐like elements. However, with increasing aridity, the aeolian environment becomes dominant and fluvial deposition is restricted to interdune corridors, resulting in lower width to thickness ratio channels dominated by flash‐flood and debris‐flow facies. The data presented here, coupled with modern examples of ephemeral systems and flood regimes, suggest that ephemeral flow produces and preserves distinctive sedimentological traits that can not only be recognized in outcrops, but also within core.

中文翻译：

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短暂河床-风积演替的沉积学

短暂河流系统通常与干旱至半干旱气候有关。尽管已对其复杂的沉积学和沉积环境进行了详细描述，但与公认的曲折和编织河流系统相比，仍缺乏描述详细的横向和垂直关系以及与同时期沉积环境相互作用的沉积模型。这项研究批判性地评估了暂时性河流系统的当前模型对美国科罗拉多高原下侏罗统Kayenta组的一个古老干旱河流实例的适用性。该研究在Kayenta的整个区域范围内采用了详细的沉积测井，古流分析和摄影测量板。建立了一个解释沙质干旱短暂河流系统详细沉积学的通用模型（借鉴了古代和地貌学研究），并分析了与风沙环境的时空相互作用。结果表明，短暂的系统以横向和垂直方向的合并为主，通道化程度差于片状元素，在低流动状态条件期间形成了丰富的上流动状态平床和高沉积物负荷结构。通过与远古风积系统的相互作用，大多数河流相沉积物都由砂级沉积物控制，这与许多现代的短暂河流相系统不同，后者的砾岩和/或细粒泥岩和粉砂岩沉积物比例很高。在主要河床沉积过程中，对于槽形和片状元素，观察到高的宽厚比。但是，随着干旱的增加，风沙环境占主导地位，河流沉积被限制在沙丘间的走廊上，从而导致以潮水和泥石流相为主的较低的宽厚比通道。此处提供的数据，加上短暂的系统和洪水制度的现代实例，表明短暂的水流产生并保留了独特的沉积学特征，不仅可以在露头而且可以在岩心内识别。导致较低的宽厚比通道以溢洪和泥石流相为主。此处提供的数据，加上短暂的系统和洪水制度的现代实例，表明短暂的水流产生并保留了独特的沉积学特征，不仅可以在露头而且可以在岩心内识别。导致较低的宽厚比通道以溢洪和泥石流相为主。此处提供的数据，加上短暂的系统和洪水制度的现代实例，表明短暂的水流产生并保留了独特的沉积学特征，不仅可以在露头而且可以在岩心内识别。