Marine transgression

Japanese: 海進 - かいしん（英語表記）marine transgression

The coastline moves inland as the sea invades land. This occurs due to widespread subsidence of land or rising sea levels. Areas that were previously denuded become depositional areas, and the sea that invades land deposits new sediments on top of the old ones. Marine transgressions recognized worldwide are based on sea level fluctuations caused by alternations between glacial and interglacial periods, and during interglacial periods, sea level rises due to melting glaciers cause widespread transgressions. The Flanders Transgression is a postglacial transgression seen in the North Sea (about 5,000 to 6,000 years ago), and in Japan the Shimosueyoshi Transgression is well known. This is a transgression seen in the Shimosueyoshi Formation (Upper Pleistocene) that develops on the Shimosueyoshi Plateau in Kanagawa Prefecture, and the strata and topographical surfaces that correspond to this are found almost throughout the country. The shoreline elevation is around 50m. The period is thought to be the Riss-Wurm Interglacial Period, but is still unknown. In the postglacial period, the Yurakucho Transgression, which deposited the Yurakucho Formation near Tokyo, is well known. In the Kanto Plain, the Yurakucho Formation transgression, which occurred at the same time as the Flanders transgression, covered almost the entirety of the current alluvial lowlands with the sea, creating a shell mound environment in the Jomon period. From the distribution of shell mounds in the Tone River and Arakawa River basins, it is known that the coastline extended into the innermost areas during the Early Jomon period, and then transitioned to a marine regression.

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

Japanese:

陸地が海の侵入を受け，海岸線が陸側に移動すること。陸地の広範な沈降または海面の上昇によって起る。以前削剥地域であった地域は堆積地域となり，陸地へ侵入した海は新しい堆積物を次々と古い堆積物の上に堆積する。世界的に認められる海進は，氷期と間氷期の交代による海面変動に基づくもので，間氷期に氷河の融解による海面上昇が広範囲の海進を起す。フランドル海進は北海にみられる後氷期の海進 (約 5000～6000年前) で，日本では下末吉海進が有名。これは神奈川県下末吉台地に発達する下末吉層 (上部更新統) にみられる海進で，これに対比される地層や地形面はほぼ全国的に分布する。汀線高度は 50m内外。時代はリス＝ウルム間氷期とされるがなお不明。後氷期では東京付近に有楽町層を堆積した有楽町海進が有名。関東平野ではフランドル海進と同時期の有楽町層時代の海進で，現在の沖積低地のほとんど全域が海におおわれ，縄文式時代の貝塚形式環境をつくり上げた。利根川・荒川流域の貝塚分布から，縄文式時代前期に，最も奥地まで海岸線が侵入し，以後海退へと移ったことが知られている。

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