Alluvial and Destructive Beach Facies From the Archaean Moodies Group, Barberton Mountain Land, South Africa and Swaziland
Alluvial and Destructive Beach Facies From the Archaean Moodies Group, Barberton Mountain Land, South Africa and Swaziland
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南非和斯威士兰巴伯顿山区太古代穆迪群的冲积和破坏性海滩相
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发表时间：
1977
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通讯作者：
K. Eriksson
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作者：
K. Eriksson
摘要穆迪集团，约3,300百万年。是目前已知的最古老的相对未变质的石英质沉积物组合。这一系列包括各种各样的沉积相，这些沉积相除其他外，是在不同的冲积和边缘海洋沉积环境中积累的。全新世的物理沉积过程与第四纪的物理沉积过程具有显著的相似性。提出了一种沉积模式，将不同的冲积沉积环境在空间上联系起来。近端冲积平原沉积物由基质和碎屑支持的砾岩沉积，分别通过质量流和牵引过程。中冲积平原砂岩在幕式洪水下降阶段通过垂向加积和中河道砂坝的形成而发育。最远端的冲积平原沉积物包括向上变细的河道充填序列，封闭在可能为漫滩成因的层间粉砂岩和页岩中。冲积相垂向层序由物源区构造决定。在最活跃的冲积作用期间，冲积平原沉积物以扇三角洲的形式直接建造在陆棚堆积物上。在河流入流停止时，在扇三角洲上发育边缘破坏性的冲沙坝。这次调查表明，暴露的花岗岩地形存在超过3,000万年。以前，它的侵蚀导致了广泛的陆上冲积沉积。河流沉积物的矿物学表明，在其沉积时的缺氧气氛。辫状河的过程中占主导地位，在没有堤坝稳定的植物生长，但一个稳定的地壳，沉积物发生长期改造，正石英质斜坝砂岩。
Abstract The Moodies Group, approximately 3,300 m.y. in age, is the oldest relatively unmetamorphosed quartzitic assemblage of sediments presently known. This succession consists of a wide variety of sedimentary facies which accumulated inter alia in diverse alluvial and marginal marine depositional environments. A remarkable similarity is shown to exist between Holocene physical sedimentary processes and those operative during the Archaean. A depositional model is proposed to relate the different alluvial sedimentary environments in space. Proximal alluvial plain deposits consist of matrix- and clast-supported conglomerates which were deposited, respectively, by mass flow and tractional processes. Mid-alluvial plain sandstones developed through vertical aggradation and mid-channel bar formation during falling stages of episodic floods. The most distal alluvial plain sediments comprise upward-fining channel-fill sequences enclosed within interlayered siltstones and shales of probable overbank origin. Vertical sequences of alluvial facies were determined by source area tectonics. During most active progradation alluvial plain sediments built directly onto shelf accumulations in the form of fan deltas. Marginal destructive swash bars developed on the fan deltas at the cessation of fluvial influx. This investigation has shown that exposed granitic terrains existed greater than 3,000 m.y. ago, the erosion of which resulted in extensive subaerial alluvial sedimentation. The mineralogy of the fluvial sediments is indicative of an anoxygenic atmosphere at the time of their deposition. Braided fluvial processes predominated in the absence of levee stabilization by plant growth but a stable crust, on which prolonged reworking of sediments occurred, is indicated by the orthoquartzitic swash bar sandstones.