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Storm sedimentation and its preservation potential in shallow marine sand-bar deposits

浅海沙洲沉积物的风暴沉积及其保存潜力

基本信息

批准号：
11640457
负责人：
MAEJIMA Wataru
金额：
$ 1.47万
依托单位：
Osaka City University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

Storm flow dynamics and the mechanism of storm flow generation were studied in the Miocene Muraoka Formation, To^^^gane Formation and Misaki Group in southwestern Japan, and the preservation potential of storm processes in ancient, shallow marine sand-bar deposits were examined.The storm deposits in the Muraoka Formation reveal clear facies spectrum from hummocky cross-stratified sandstones to base-cut-out turbidites. This facies spectrum reflects the change in storm flow characteristics across the storm-wave base and is suggestive of the generation of turbidity currents as a storm-induced depositional current. A turbidity current interpretation is supported by off-shore directed paleocurrents shown both by sole marks of hummocky cross stratified sandstones and by ripple cross laminations in turbidites. Thick, storm sandstone beds tend to be covered by thick mudstones. Such couplets represent storm sedimentation controlled by sand availability. Powerful currents generated by extraordin … More ary storms carried considerable volumes of sand away from the coast and resulted in sand-starved condition in coastal zone for some long periods. Lack in coastal sand prevented the generation of powerful turbidity currents even in major storm events. Consequently sand availability on the stormy shelf was extremely low, and storm events were seldom recorded in the shelf deposits.The shoreline deposits in the To^^^gane Formation preserve the sedimentation records of a storm-fairweather cycle in an upper shoreface environments. Backwash action of storm waves or storm-enhanced rip currents swept sediments into the shoreface and emplaced coarse materials as a lag on the erosion surface produced in the peak stage of a storm. During the declining and following stage of storms, long-period swells reworked much of the sediment previously transported offshore and returned them onshore in the form of migrating longshore bars, recovering the shore profile. Longshore bars did not weld to the beachface, and barred system produced in the recovery stage was maintained during fairweather periods.The Misaki Group provides a good example of storm-reworked, shallow marine sand-bars.The Misaki sand-bar deposits are dominantly hummocky cross stratified. However, storms were seldom responsible for sand accumulation. Rather, sand transport and deposition were basically controlled by fluvial discharge from the river mouth. Storm waves reworked bar sands almost completely, and fluvial-influenced sedimentation records were mostly unpreserved. Less

研究了日本西南部中新世村冈组、东方组和三崎群的风暴流动力学和风暴流生成机制，考察了古浅海沙坝沉积中风暴过程的保存潜力。这一相谱反映了风暴波底部风暴流特征的变化，并暗示了浑浊流作为风暴诱导的沉积流的产生。浊流解释得到了离岸定向古水流的支持，既有丘陵状交叉层状砂岩的唯一标志，也有浊积岩中的波纹交错纹层。厚厚的风暴砂岩层往往被厚厚的泥岩覆盖。这样的对联代表了受沙子供应控制的风暴沉积。Extrordin…产生的强大电流更多的风暴将大量的沙子从海岸带走，并导致沿海地区长时间的沙荒状况。即使在重大风暴事件中，沿海沙地的缺乏也阻止了强大浑浊洋流的产生。因此，风暴陆架上的砂粒有效性极低，风暴事件很少记录在陆架沉积中。托^干干组的海岸线沉积保存了上岸环境中风暴-晴朗循环的沉积记录。风暴波或风暴增强的激流的反冲作用将沉积物席卷到岸面，并在风暴高峰期产生的侵蚀面上作为滞后堆积粗质物质。在风暴减弱和随后的阶段，长时间的巨浪重新作用了以前运往近海的大部分沉积物，并以迁移的沿岸沙洲的形式将它们带回岸上，恢复了海岸剖面。滨岸沙坝没有焊接到滩面上，恢复阶段产生的沙坝体系在晴天期间保持不变。三崎组是风暴改造的浅海砂坝的一个很好的例子。米萨奇沙坝矿床主要是隆起的交叉层状。然而，风暴很少导致沙粒堆积。相反，泥沙的输送和沉积基本上是由河口的河流排放控制的。风暴波几乎完全重塑了沙洲，受河流影响的沉积记录大多没有保存下来。较少