Bedforms, primary structures and grain fabric in the presence of suspended sediment rain
Bedforms, primary structures and grain fabric in the presence of suspended sediment rain
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DOI：
10.1306/212f90f2-2b24-11d7-8648000102c1865d
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发表时间：
1989-11
影响因子：
2
通讯作者：
R. Arnott;B. Hand
中科院分区：
文献类型：
--
作者：
R. Arnott;B. Hand
水槽实验是为了确定一场弥漫的沙雨如何影响沉积床的床形、内部结构和颗粒结构的发展。在其他标准水槽运行，沉积物类似于在床上（Mz = 2.13 ; = 0.63）下雨从头顶上的箱子延伸的9米的再循环水槽的长度。河床淤积的凝结率为4.2 cm min-1。这些实验被认为与浊流沉积特别相关。在上平面床条件下，只要沉积物供给率较低，平行分层就会从快速迁移的毫米级推移质层中发展出来。在高速率的饲料，层压被抑制，这表明快速加积可以解释的“大规模”的结构特征的鲍马A师浊积岩。当水流条件保持在沙丘稳定性场内，用于清水运行时，在所有检查的沉积物沉降速率下（河床淤积<= 4.0 cm min-1），已形成的沙丘持续存在，这显然与浊积岩中中等规模交错层理代表性不足可能归因于沉积物雨对沙丘的抑制的怀疑相矛盾。然而，要测试沉积物雨是否会抑制新生沙丘的发展是不可行的。在所检查的沉降率范围内，涟漪被证明是稳定的。沉积组构，推导出磁化率的各向异性，证实了在上层平面床条件下（代表鲍马师A和B）的晶粒取向是电流平行的，同样发达的所有沉积速率。向上流叠瓦，一贯陡峭的比通常发现在上平面床流沉积，增加了在沉积物沉降成正比的陡度，并可能提供一个有用的基础，估计沉积速率在沉积的司A和B的古代浊积岩。
ABSTRACT Flume experiments were conducted to determine how a pervasive rain of sand might affect the development of bedforms, internal structures, and grain fabric in a bed aggrading from this fallout. During otherwise standard flume runs, sediment similar to that in the bed (Mz = 2.13 ; = 0.63 ) rained from overhead bins extending the length of the 9-meter recirculating flume. Consequent rates of bed aggradation ranged to 4.2 cm min-1. The experiments are viewed as having particular relevance to deposition from turbidity currents. Under upper-plane-bed conditions, so long as low rates of sediment feed prevailed, parallel lamination developed from rapidly migrating, millimeter-scale bed-load sheets. At high rates of feed, lamination was suppressed, suggesting that rapid aggradation can account for the "massive" structure characteristic of Bouma A divisions of turbidites. When flow conditions were maintained within the dune stability field for clear-water runs, established dunes persisted at all sediment fallout rates examined (bed aggradation <= 4.0 cm min-1), apparently contradicting a suspicion that the underrepresentation of medium-scale cross-bedding in turbidites might be attributable to suppression of dunes by sediment rain. It was not feasible to test whether sediment rain might inhibit development of nascent dunes, however. Ripples proved stable across the range of fallout rates examined. Depositional fabrics, deduced from anisotropy of magnetic susceptibility, confirmed that under upper-plane-bed conditions (representative of Bouma divisions A and B) grain orientation is current-parallel and equally well developed for all sedimentation rates. Up-current imbrication, consistently steeper than what is typically found in upper-plane-bed stream deposits, increased in steepness in direct proportion to sediment fallout and may provide a useful basis for estimating aggradation rates during deposition of divisions A and B of ancient turbidites.