区分盆地底泥岩和斜坡泥岩的沉积学和地层学标准:泥浆向深水环境输送的意义

IF 1.9 3区 地球科学 Q1 GEOLOGY
Kévin Boulesteix, Miquel Poyatos-Moré, Stephen S. Flint, David M. Hodgson, Kevin T. Taylor, Rufus L. Brunt
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引用次数: 5

摘要

覆盖盆地底部和斜坡砂岩沉积的深水泥岩通常被解释为在缺沙期沉积的半水层垂帘。然而,对深水环境中的泥浆输送和沉积过程,以及由此产生的泥岩相和结构,仍知之甚少。本研究记录了Laingsburg沉积中心(南非卡鲁盆地)的盆地底部和斜坡泥岩的沉积学和地层学,这些泥岩夹有砂岩沉积。这里提出了沉积学和地层标准,以区分斜坡和盆地底部泥岩,这为完善其他深水序列的古地理重建提供了工具。在露头处绘制了2500个泥岩单元的地图 km2,并使用两个研究钻孔的宏观和微观岩心描述进行调查。盆地底部泥岩表现出以低密度浊积岩为主的床层和以碎屑岩为主的块状包裹体的重复和可预测的交替,有证据表明湍流向层流转变。斜坡泥岩表现出相似的相组合,但低密度浊积岩的比例更高,并且没有识别出重复或可预测的相组织。盆地底部泥岩的有序和可预测的相组织表明,局部点源于活动斜坡导管,负责补偿堆叠的泥质凸起的沉积。斜坡泥岩中缺乏可预测的相组织,这表明沉积发生在更为多变的亚环境中(即积水区、小冲沟/河道填充物、堤坝)。然而,三个泥岩单元的区域测绘表明,沉积走向上向盆地逐渐变细,厚度相似。这种几何形状与盆地边缘斜坡的远端部分一致,表明陆架边缘的横向广泛泥浆输送与沿边缘的输送过程相结合。因此,泥岩的沉积学和几何学表明,在上倾储沙期,泥浆主要通过点源沉积物重力流输送到深水中,并呈区域分布。这些发现挑战了深水泥岩与盆地底部沉积物匮乏时期的共同归因。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Sedimentologic and stratigraphic criteria to distinguish between basin-floor and slope mudstones: Implications for the delivery of mud to deep-water environments

Sedimentologic and stratigraphic criteria to distinguish between basin-floor and slope mudstones: Implications for the delivery of mud to deep-water environments

Deep-water mudstones overlying basin-floor and slope sandstone-prone deposits are often interpreted as hemipelagic drapes deposited during sand starvation periods. However, mud transport and depositional processes, and resulting facies and architecture of mudstones in deep-water environments, remain poorly understood. This study documents the sedimentology and stratigraphy of basin-floor and slope mudstones intercalated with sandstone-prone deposits of the Laingsburg depocentre (Karoo Basin, South Africa). Sedimentologic and stratigraphic criteria are presented here to distinguish between slope and basin-floor mudstones, which provide a tool to refine palaeogeographical reconstructions of other deep-water successions. Several mudstone units were mapped at outcrop for 2500 km2 and investigated using macroscopic and microscopic core descriptions from two research boreholes. Basin-floor mudstones exhibit a repeated and predictable alternation of bedsets dominated by low-density turbidites, and massive packages dominated by debrites, with evidence of turbulent-to-laminar flow transformations. Slope mudstones exhibit a similar facies assemblage, but the proportion of low-density turbidites is higher, and no repeated or predictable facies organisation is recognised. The well-ordered and predictable facies organisation of basin-floor mudstones suggest local point sources from active slope conduits, responsible for deposition of compensationally stacked muddy lobes. The lack of predictable facies organisation in slope mudstones suggests deposition took place in a more variable range of sub-environments (i.e. ponded accommodation, minor gully/channel-fills, levees). However, regional mapping of three mudstone units evidence basinward tapering and similar thicknesses across depositional strike. This geometry is consistent with the distal part of basin margin clinothems, and suggests laterally extensive mud delivery across the shelf edge combined with along-margin transport processes. Therefore, the sedimentology and geometry of mudstones suggests that mud can be delivered to deep-water dominantly by sediment gravity flows through point source and distributed regionally, during periods of up-dip sand storage. These findings challenge the common attribution of deep-water mudstones to periods of basin-floor sediment starvation.

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来源期刊
CiteScore
4.10
自引率
16.70%
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42
审稿时长
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