Hummocky Cross-Stratification: Shelf or Surf?: Abstract
Hummocky Cross-Stratification: Shelf or Surf?: Abstract
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丘陵交叉分层：架子还是冲浪？：摘要
DOI：
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发表时间：
1986
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通讯作者：
B. Greenwood
中科院分区：
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作者：
B. Greenwood
摘要原生沉积结构表现出单组丘状交叉分层的三个诊断标准（Harms等人，1982年）已被发现在碎波区的风暴波为主的海岸线在加拿大五大湖。箱形岩心（0.45 × 0.30 m）的环氧树脂剥离显示，在波浪破碎和强沿岸流条件下，水深小于2 m的分选良好的细砂中存在丘状层积。波长为0.3至0.6米的驼峰规模比经典的古代类似物略小，但长度与高度的比值范围为8至12，并与驼峰交叉分层的范围重叠。深度的活动棒已被用来确定那些在沉积物输送事件时，近床电流直接使用电磁流量计记录形成的丘。这些实验的结果清楚地表明，丘状纹层是由活跃生长的床层形式产生的，几乎没有或没有侧向迁移。在接近于平坦河床的预期条件下，会出现丘状隆起。在一个垂向层序中，丘状交错纹层下面是近水平的平面纹层，上面是波状纹层，波状纹层向上渐变为小规模的槽状交错纹层。这个序列与一个单一的风暴，似乎代表了一个组合流制度序列与丘状分层代表后涡（？）涟漪床形态在形成丘状体时，近床振荡流占主导地位，达到1.4 m/s，叠加沿岸流为0.27 m/s。然而，后者正在迅速减少，很可能是垂直生长的小丘的原因。因此，丘状交叉分层是一种主要的沉积结构，可由非常浅的碎波带中的振荡流和叠加的单向流相结合而形成。
Abstract Primary sedimentary structures exhibiting the three diagnostic criteria for single sets of hummocky cross-stratification (Harms et al., 1982) have been found in the surf zone of a storm-wave dominated coastline in the Canadian Great Lakes. Epoxy peels of box cores (0.45 × 0.30 m) reveal hummocky lamination in well sorted, fine sands in water depths less than 2 m, under conditions of wave breaking and strong longshore currents. The scales of the hummocks with wave lengths of 0.3 to 0.6 m are somewhat smaller than the classic ancient analogues, but the ratio of length to height ranges from 8 to 12 and overlaps the range for hummocky cross-stratification. Depth-of-activity rods have been used to identify those hummocks formed during sediment transport events when the near-bed currents were recorded directly using electromagnetic flowmeters. The results of such experiments clearly show that hummocky lamination was produced by an actively growing bed form with little or no lateral migration. The hummocks occur under conditions close to those expected for a flat bed. In one vertical sequence, the hummocky cross-lamination is underlain by subhorizontal, planar lamination and overlain by undulatory lamination, which grades upwards into small-scale, trough cross-lamination. This sequence was associated with a single storm and appears to represent a combined-flow regime sequence with the hummocky lamination representing a post-vortex (?) ripple bed form. At the time of hummocky formation, near-bed oscillatory flows were dominant and reached 1.4 m/s with a superimposed longshore current of 0.27 m/s. However, the latter was decreasing rapidly and may well have been the cause of vertical growth of the hummock. Hummocky cross-stratification is, therefore, a primary sedimentary structure that can be formed by combined oscillatory and superimposed unidirectional flows, in very shallow surf zones.