High-energy flood events recorded in the Mesoproterozoic Meall Dearg Formation, NW Scotland; their recognition and implications for the study of pre-vegetation alluvium
High-energy flood events recorded in the Mesoproterozoic Meall Dearg Formation, NW Scotland; their recognition and implications for the study of pre-vegetation alluvium
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苏格兰西北部中元古代 Meall Dearg 地层记录的高能洪水事件；
DOI：
10.1144/jgs2017-012
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发表时间：
2017
影响因子：
2.7
通讯作者：
N. Davies
中科院分区：
文献类型：
--
作者：
W. McMahon;N. Davies
苏格兰西北部的中元古代-新元古代Torridonian砂岩在了解植被前冲积层方面取得了最新进展，因此具有新的沉积学意义，因为它是全球此类地层中最广泛和最容易获得的继承层之一。本文介绍了第一个现代沉积学分析的单位的组成Meall Dearg组（晚中元古代），认识到一个优势的冲积相，与从属风成相。Meall Dearg组中的冲积层包含了高能洪水事件沉积的直接证据，包括：（1）广泛的上部和过渡的上部流态元素;（2）连续的下部流态元素的频繁叠加;（3）常见的亚临界水下沙丘场，叠加有涟漪;（4）偶尔出现的薄的干燥泥岩;（5）微生物席在沉积停滞期期间定殖于基质的证据。这些主要沉积地质证据表明，Meall Dearg地层的冲积沉积以高能洪水期间的超临界流动为代表，并被长时间的沉积停滞所打断。高度加积的沉积条件提高了所有特征的保存潜力。这些主要的意见有影响的“规范”在前植被冲积层，并确认，尽管越来越多的认识到前寒武纪河流系统的多样性，经典的前植被图案的高能量冲积洪水沉积物保存为“片编织”冲积层仍然是一个原型的沉积签名在某些情况下。利用来自Meall Dearg地层的支持性证据，我们建议在未来的研究中使用“片状编织”一词，这强调了20：1宽度：厚度河流样式的多成因沉积性质，同时保持了该术语在隔离植被前沉积结构的关键特征方面的价值。
The Mesoproterozoic–Neoproterozoic Torridonian Sandstone of NW Scotland has renewed sedimentological significance following recent advances in the understanding of pre-vegetation alluvium, as it is one of the most extensive and easily accessible successions of such strata worldwide. This paper presents the first modern sedimentological analysis of the unit's constituent Meall Dearg Formation (late Mesoproterozoic), recognizing a dominance of alluvial facies, with subordinate aeolian facies. Alluvial strata within the Meall Dearg Formation contain direct evidence for event deposition by high-energy floods, including the following: (1) widespread upper and transitional upper flow regime elements; (2) frequent stacking of successively lower flow regime elements; (3) common subcritical subaqueous dune fields with superimposed ripple marks; (4) occasional thin, desiccated mudstones; (5) evidence that microbial mats colonized substrates during intervals of sedimentary stasis. Together these strands of primary sedimentary geological evidence indicate that the alluvial deposition of the Meall Dearg Formation was typified by supercritical flows during high-energy floods, punctuated by prolonged intervals of sedimentary stasis. The preservation potential of all of the features was boosted by highly aggradational sedimentary conditions. These primary observations have implications for the ‘norm’ in pre-vegetation alluvium and confirm that, despite increasing recognition of diversity within Precambrian fluvial systems, classical pre-vegetation motifs of high-energy alluvial flood deposits preserved as ‘sheet-braided’ alluvium are still an archetypal sedimentary signature in some instances. Using supportive evidence from the Meall Dearg Formation, we recommend that the term ‘sheet-braided’ be used in inverted commas in future studies; this emphasizes the polygenetic depositional nature of the 20:1 width:thickness fluvial style, while maintaining the value of the term in the isolation of a key characteristic of pre-vegetation sedimentary architecture.
沙丘保存的极端情况：对河流沉积物完整性的控制
影响因子：
12.1
作者：
Reesink A
通讯作者：
Reesink A