General Theory of Epeiric Clear Water Sedimentation
General Theory of Epeiric Clear Water Sedimentation
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表层清水沉积一般理论
DOI：
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发表时间：
1965
期刊：
影响因子：
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通讯作者：
M. L. Irwin
中科院分区：
文献类型：
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作者：
M. L. Irwin
浅海沉积与海洋、海岸沉积形成对比。浅海沉积作用发生在非大洋性陆表海中，那里大陆架的宽度很大，坡度很低（每英里不到一英尺），而且其上的沃茨非常浅，这些都足以限制或消除环流。海洋、海岸沉积通常发生在海底坡度陡峭，波浪和潮汐延伸到海岸的地方。在陆表海中存在三个实际上是沉积环境的海洋水力能区：（1）在波浪深度以下的开阔海中，海流是作用于海底的唯一形式的水力能的几百英里宽的低能区（X区）;（2）一个中等高能带，宽数十英里，从波浪第一次撞击海底的地方开始，从而将其动能消耗在海底，向陆地延伸到潮汐作用的极限（Y区）;（3）一个极浅的低能区，宽几十到几百英里，位于Y区向陆地的方向，其中几乎没有水循环，潮汐基本上是缺乏的，唯一的波浪作用是由当地风暴产生的（Z区）。并给出了在没有受到陆源碎屑物侵入的陆表海中（“清水”），在Y区形成的沉积物基本上是生物成因的，是砂大小或较粗的，并且是最有可能成为良好筛选的原生储集层的沉积物;在Z区形成的沉积物主要是细粒和致密的，并且通常是化学成因的; X带的沉积物主要是来自Y带的细粒碎屑。在海侵过程中，当每个沉积带向海岸迁移时，它与较早沉积的较老沉积物重叠，这些沉积物较早沉积在与当时在向陆地的相邻带中占主导地位的环境相似的环境中。这样，就建立了一个上升的沉积序列，它是在循环限制逐渐减少的条件下沉积的，与在单一时间从陆地延伸到海洋的模式相同。在海退过程中，每个沉积带都向海洋迁移，因此沉积物的上升序列是在越来越多的限制条件下沉积的，并且与从海洋到陆地在一个单一时间到达的序列相同。因此，在海退层序中，一种岩石类型位于另一种岩石类型之上，也会从另一种岩石类型向陆地出现;在海侵期间，其位置将向海。随着海洋的进退，这种连续的沉积重叠过程是解释循环沉积的原理。应注意，地质层（岩相）的年龄在迁移方向上逐渐变年轻，强调时间控制的必要性。两个例子一起提出了进一步的讨论，指出如何定期沉积模式可能会改变障碍（如珊瑚礁），气候，和程度的底部坡度;以及如何分析的正常和改变模式可用于勘探和分级的目的。
Shallow marine sedimentation is described in contrast to oceanic, coastal deposition. Shallow marine sedimentation occurs in non-oceanic epeiric seas where great width of shelves, their low order of slopes (less than one foot per mile), and extreme shallowness of the waters on them are sufficient in themselves to restrict or eliminate circulation. Oceanic, coastal deposition occurs where steep bottom slopes are the rule and where waves and tides extend to the shore. Three marine, hydraulic energy zones, which are in effect environments of deposition, are thought to occur in epeiric seas: (1) a hundreds-of-miles wide, low-energy zone prevailing in the open sea beneath wave depth where marine currents are the only form of hydraulic energy acting upon the bottom (Zone X); (2) an intermediate, high-energy belt, tens-of-miles wide, beginning where waves first impinge upon the sea floor and thus expend their kinetic energy upon the bottom, extending landward to the limit of tidal action (Zone Y); (3) an extremely shallow, low-energy zone, tens- to hundreds-of-miles wide, occurring landward of Zone Y in which there is little circulation of water, where tides are essentially wanting, and in which the only wave action is that produced by local storms (Zon Z). Reasons are given to show that in epeiric seas, which have received no invasion of terrigenous clastics ("clear water"), sediments formed in Zone Y are basically of biogenic origin, are sand-size or coarser, and are those most likely to become well-winnowed primary reservoirs; that those sediments formed in Zone Z are primarily fine-grained and tight, and are generally of chemical origin; that Zone X contains sediments which are mainly fine-grained detritus from Zone Y. During a marine transgression, as each sedimentation zone migrates toward shore, it overlaps older sediments which earlier were deposited in an environment similar to the one then prevailing in the zone adjoining landward. In this manner, an ascending sequence of sediments, deposited under conditions of progressively less restricted circulation, the same as the pattern extending at a single time from land to sea, is established. During regression, each sedimentation zone migrates seaward, so that the ascending sequence of sediments is deposited under progressively more restricted conditions, and is the same as the one reaching at a single time from sea to land. Thus, in a regressive sequence, a rock type found on top of another would also occur landward from it; during transgression, ts position would be seaward. This process of continuous sedimentary overlap, as the sea advances and retreats, is the principle which explains cyclic sedimentation. It is noted that the age of geologic formations (lithofacies) becomes progressively younger in the direction of migration, emphasizing the necessity for time control. Two examples are presented together with further discussion which points out how the regular sedimentary patterns may be altered by barriers (such as reefs), by climate, and by degree of bottom slope; and how an analysis of both the normal and altered patterns may be used for exploration and grading purposes.