Alternating layers

A geological stratum in which two or more layers of different rock types are repeatedly stacked on top of each other. Many combinations are known, such as alternating layers of sandstone-mudstone and alternating layers of chert-limestone. When simply referring to alternating layers, it often refers to alternating layers of sandstone-mudstone. Sandstone-mudstone alternating layers are often formed when turbidity flows are deposited. In this case, one pair of sandstone and mudstone layers is deposited in one turbidity flow, and the alternating layers are formed as a result of repeated turbidity flows.

[Akihiro Murata]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

2種類またはそれ以上の岩質の異なる単層が交互に繰り返し重なり合った地層。砂岩泥岩互層、チャート石灰岩互層など多くの組合せが知られている。単に互層というとき、砂岩泥岩互層をさす場合が多い。砂岩泥岩互層は乱泥流が堆積(たいせき)するときにできたものが多い。この場合、1回の乱泥流で1組の砂岩・泥岩層が堆積し、乱泥流が繰り返しておこることにより、互層が形成される。

［村田明広］

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