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Anatomy and facies distribution of terminal lobes in ephemeral fluvial successions: Jurassic Tordillo Formation, Neuquén Basin, Argentina
Sedimentology ( IF 3.5 ) Pub Date : 2020-03-28 , DOI: 10.1111/sed.12712
Marina D. Coronel 1 , Manuel F. Isla 1 , Gonzalo D. Veiga 1 , Nigel P. Mountney 2 , Luca Colombera 2
Affiliation  

In terminal fluvial‐fan systems, characteristic proximal to distal variations in sedimentary architectures are recognized to arise from progressive downstream loss of water discharge related to both infiltration and evaporation. This work aims to elucidate downstream trends in facies and architecture across the medial and distal zones of terminal‐fan systems, which record transitions from deposits of channel elements to lobe‐like and sheet‐like elements. This is achieved via a detailed characterization of ancient ephemeral fluvial deposits of the well‐exposed Kimmeridgian Tordillo Formation (Neuquen Basin, Argentina). The fine sand‐prone and silt‐prone succession associated with the medial to distal sectors of the system has been studied to understand relationships between depositional processes and resulting architectures. Facies and architectural‐element analyses, and quantification of resulting sedimentological data at multiple scales, have been undertaken to characterize sedimentary facies, facies transitions, bed types, architectural elements and larger‐scale architectural styles. Eight bed types with distinct internal facies transitions are defined and interpreted in terms of different types of flood events. Channelized and non‐channelized architectural elements are defined based on their constituent bed types and their external geometry. The most common elements are terminal lobes, which are composite bodies within which largely unconfined sandy deposits are stacked in a compensational manner; a hierarchical arrangement of internal components is recognized. Proximal feeder‐channel avulsion events likely controlled the evolution of terminal‐lobe elements and their spatiotemporal shifts. Stratigraphic relations between architectural elements record system‐wide trends, whereby a proximal sector dominated by channel elements passes downstream via a gradational transition to a medial sector dominated by sandy terminal‐lobe elements, which in turn passes further downstream to a distal sector dominated by silty terminal lobe‐margin and fringing deposits. This work enhances current understanding of the stratigraphic record of terminal fluvial systems at multiple scales, and provides insight that can be applied to predict the facies and architectural complexity of terminal fluvial successions.

中文翻译:

短暂河流演替中终叶的解剖和相分布:侏罗纪 Tordillo 组,内乌肯盆地,阿根廷

在末端河流-扇系统中,沉积结构的近端和远端变化的特征被认为是由于与渗透和蒸发相关的下游水排放的逐渐损失引起的。这项工作旨在阐明末端扇系统中部和远端区域的相和结构的下游趋势,这些区域记录了从通道元素沉积物到叶状和片状元素的转变。这是通过对暴露良好的 Kimmeridgian Tordillo 地层(阿根廷内乌肯盆地)的古代短暂河流沉积物的详细表征来实现的。已经研究了与系统的内侧到远端部分相关的细砂和粉砂倾向序列,以了解沉积过程和由此产生的结构之间的关系。已经进行了相和建筑元素分析,以及在多个尺度上对所得沉积学数据进行量化,以表征沉积相、相变迁、床类型、建筑元素和更大规模的建筑风格。根据不同类型的洪水事件定义和解释了八种具有不同内部相变迁的床类型。通道化和非通道化的建筑元素是根据它们的构成床类型和它们的外部几何形状来定义的。最常见的元素是末端叶瓣,它们是复合体,其中大部分未封闭的砂质沉积物以补偿方式堆积;内部组件的分层排列被识别。近端馈线-通道撕脱事件可能控制了终叶元件的演变及其时空变化。建筑元素之间的地层关系记录了整个系统的趋势,其中以河道元素为主的近端部分通过渐变过渡向下游传递到以砂质终叶元素为主的中间部分,后者又进一步向下游传递到以粉质为主的远端部分末端叶缘和边缘沉积物。这项工作增强了当前对多尺度末端河流系统地层记录的理解,并提供了可用于预测末端河流演替的相和构造复杂性的见解。其中,以河道元素为主的近端部分通过渐变过渡向下游传递到以砂质终叶元素为主的中间部分,后者又进一步向下游传递到以粉质末叶边缘和边缘沉积物为主的远端部分。这项工作增强了当前对多尺度末端河流系统地层记录的理解,并提供了可用于预测末端河流演替的相和构造复杂性的见解。其中,以河道元素为主的近端部分通过渐变过渡向下游传递到以砂质终叶元素为主的中间部分,后者又进一步向下游传递到以粉质末叶边缘和边缘沉积物为主的远端部分。这项工作增强了当前对多尺度末端河流系统地层记录的理解,并提供了可用于预测末端河流演替的相和构造复杂性的见解。
更新日期:2020-03-28
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