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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

对日本西南部中新世村冈组、藤冈组和三崎组的风暴流动力学和风暴流生成机制进行了研究，并对古浅海砂坝沉积中风暴过程的保存潜力进行了考察。村冈组的风暴沉积显示出从丘状交错层状砂岩到底部切去的浊积岩的清晰相谱。这种相谱反映了风暴流特征的变化，在整个风暴波基地，并暗示浊流的产生风暴引起的沉积电流。通过丘状交叉分层砂岩的唯一标志和浊积岩中涟漪交叉纹层显示的离岸定向古水流支持浊流解释。厚的风暴砂岩层往往被厚的泥岩覆盖。这种双联体代表了受沙的可用性控制的风暴沉积。由外星生物产生的强大电流 ...更多信息沙尘暴将大量的沙子从海岸带走，导致海岸带在很长一段时间内处于缺沙状态。即使在大风暴事件中，海岸沙子的缺乏也阻止了强大浊流的产生。因此，风暴陆棚上的砂的可利用性极低，风暴事件很少记录在陆棚沉积物中。To^^^gane组的海岸线沉积物保存了上部滨面环境中风暴-晴天循环的沉积记录。风暴波或风暴增强的离岸流的反洗作用将沉积物扫入滨面，并将粗物质作为风暴高峰期产生的侵蚀面上的滞后物就位。在风暴的下降阶段和后续阶段，长期涌浪重新改造了以前被输送到近海的大部分沉积物，并以迁移的长海岸砂坝的形式将其返回陆地，恢复了海岸剖面。沿岸砂坝没有焊接到海滩表面，在恢复阶段产生的拦砂系统在晴天期间得以维持。Misaki组提供了风暴改造的浅海砂坝的一个很好的例子。Misaki砂坝沉积物主要是丘状交叉分层。然而，风暴很少造成沙子堆积。泥沙的输移和沉积基本上受河口径流的控制。风暴波几乎完全改造了沙洲，河流影响的沉积记录大多未被保存下来。少