Marine regression

Japanese: 海退 - かいたい（英語表記）marine regression

The phenomenon in which the ocean that had invaded the interior of a continent retreats due to the gradual uplift of land or a fall in sea level. As opposed to transgression. The former seabed appears on land due to regression, and landforms such as coastal plains, raised wave-cut platforms, raised coral reefs, raised shorelines, and coastal terraces are created. Large-scale regressions occur during glacial low sea levels due to changes in sea level caused by alternations between glacial and interglacial periods. In the Quaternary Period, large-scale regressions occurred when sea levels fell during the Gunz, Mindel, Riss, and Würm glacial periods. When a river transitions from transgression to regression, the lithology of the sediments gradually becomes coarser toward the top, from mudstone to sandstone to conglomerate. Traces of the coastline that existed during the transgression remain as the old shoreline. When a regression occurs, the location of the river mouth moves downstream, and an extended river is formed, and the river often becomes younger due to the fall in sea level and undergoes undercutting. In Japan, it is said that the Tachikawa terrace on the banks of the Tama River was formed in connection with a regression, probably a fall in sea level during the Würm glacial period.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

大陸の内部に侵入していた海が，陸地の緩慢な隆起あるいは海面の下降によって後退する現象。海進に対する。海退によって以前の海底が陸上に現れ，海岸平野，隆起波食台，隆起サンゴ礁，隆起汀線，海岸段丘などの地形ができる。大規模な海退は氷期，間氷期の交代による海面の変化に基づき，氷期の低位海水準の際生じる。第四紀ではギュンツ，ミンデル，リス，ウルムの各氷期に海面が低下して，大規模な海退があった。海進から海退に移る場合，堆積物の岩相は泥岩，砂岩，礫岩と上部ほど次第に粗粒となる。海進時にあった海岸線の跡は旧汀線として残される。海退が起ると河口の位置は下流へ移って延長河川が生じ，海面低下のために川が若返って下刻を行うことが多い。日本では多摩川河岸の立川段丘が海退，おそらくウルム氷期の海面低下に関連して生じたのであろうといわれる。

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