Facies variebility and depositional processes of storm deposits

在日本西南地区中新世Muraolka组、Togane组和Misaki群中，研究了风暴沉积的相变异性及其对上海岸-陆架环境中风暴过程分异的响应，并评价了浅海环境中风暴和非风暴过程的保存潜力。村冈风暴沉积的相谱表明，风暴床是由风暴波基底上逐渐减弱的联合流形成的。风暴引起的水流在浅层显著的振荡水运动下沉积沙。在近海下坡区，水流的振荡分量随着水深的增加而迅速减弱，而单向分量仍然足够强，足以输沙。沉积流进一步将更细的沉积物运输并沉积到风暴波基底下更深的水中。在村冈陆架沉积的演替中，厚砂岩层往往被更厚的泥岩所覆盖。这样的对联代表了泥沙可用性控制的沉积作用。由异常风暴产生的强大洋流将大量的沙子带离海岸，导致了长时间的缺沙状况。在此期间，风暴陆架上的可利用沙极低，风暴事件很少记录在陆架沉积物中。托甘河组的岸线沉积是上岸面环境中风暴侵蚀和恢复阶段沉积的一个例子。风暴波或风暴增强的离岸流的反冲作用将沉积物冲刷到岸边，并在风暴高峰阶段产生的侵蚀面上放置粗糙的物质作为滞后物。在风暴消退和随后的阶段，长周期的井重新加工了以前运往海上的大部分沉积物，并以迁移沙洲的形式将它们送回岸上。三崎群浅海沙洲沉积主要记录了风暴过程。然而，风暴很少造成沙尘堆积。相反，沙的搬运和沉积基本上是由河口的河流排放控制的。风暴波对沙洲砂的改造基本受河口径流控制，风暴波对沙洲砂的改造几乎完全，河流影响的沉积记录基本未保存。少

Facies variability of storm deposits and its response to differentiation of strorm processes in upper shoreface to shelf environments were studied in the Miocene Muraolka Formation, Togane Formation and Misaki Group in southwestern Japan, and the preservation potential of storm and non-storm processes in a shallow marine environment was evaluated.The facies spectrum in the Muraoka storm deposits reveals that the storm beds were originated by waning combined-flows across the storm-wave base. Storm-induced currents deposited sand under significant oscillatory water-motion in a shallow depth. Offshore down slope, the oscillatory component of a flow rapidly diminished due to increasing water depth, whereas the unidirectional component was still intense enough to transport sand. The depositional current further transported and deposited finer sediments into deeper water below the storm-wave base.Within the succession of the Muraoka shelf deposits, thick sandstone beds tend to be covered by … More thick mudstones. Such couplets represent sedimentation controled by sand availability. Powerful currents generated by extraordinary storms carried considerable volumes of sand away from the coast and resulted in sand-starved condition for some long periods. During these periods, sand availability on the stormy shelf was extremely low, and storm events were seldom recorded in the shelf deposits.The shoreline deposits in hte Togane Formation provides an example of storm erosion and recovery stage deposition in an upper shoreface environment. Backwash action of storm waves or storm-enhanced rip currents awept 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 awells reworked much of the sediment previously transported offshore and returned them onshore in the form of migrating sand bars.Shallow marine bar deposits in the Misaki Group predominantly records storm processes. However, storms were seldom responsible for sand accumulation. Rather, sand transport and deposition were basically controled by fluvial discharge from the river mouth. Storm waves reworked were basically controled by fluvial discharge from the river mouth Storm waves reworked bar sands almost completely, and fluvial-influenced sedimentation records were mostly unpreserved. Less