Land-building movement

It is a general term for crustal movements in which a wide, non-zonal, continental or subcontinental area gradually sinks or rises, or these are repeated, over a long period of time, on the order of 10 million years. The existence of land-building movements is indicated by the fact that past marine deposits are widely distributed on land and are often overlain by terrestrial deposits, i.e., marine transgression and regression have occurred over a wide area. In addition, there are areas where marine deposits and terrestrial deposits that were deposited in lowlands are widely distributed with almost no deformation at heights that would make it impossible for sea levels to have risen, i.e., continental uplift has occurred. However, some marine transgressions and regressions are not caused by crustal movements, such as those caused by the rise and fall of glaciers in the Quaternary Period of the Cenozoic Era. There are also land-building movements that do not have a fundamental cause within the Earth, such as the Scandinavian Peninsula, which had sunk deeply due to the load of thick glaciers during the ice age, rising in the Holocene (present day) when the glaciers melted and the load ceased.

When mountain building was thought to be an extremely short-term crustal movement, it was thought that land building and mountain building could not occur simultaneously in the same region. However, it is known that there was a time in the Japanese Archipelago when marine transgression and regression occurred as land building at the same time as in the eastern Asian region during the mountain building period.

[Toshio Kimura]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

帯状でない、大陸的ないし亜大陸的な広範な地域が、1000万年オーダーの長期間に徐々に沈降または上昇、あるいはそれらを繰り返す地殻変動を総称していう。造陸運動があったことは、過去の海成層が非常に広く陸上に分布すること、またしばしばその上に陸成層が重なること、すなわち広範な地域に海進・海退があったことに示されている。また海成層や低地で堆積(たいせき)した陸成層が、海水面が上昇したことはありえないほどの高さに、ほとんど変形しないままで広く分布する地域があり、すなわち大陸的な隆起があったことに示されている。しかし、海進・海退には新生代第四紀の氷河の消長に伴うもののように地殻変動によらないものがある。また氷期に厚い氷河の荷重のために深く沈下していたスカンジナビア半島が、氷河が融(と)けて荷重がなくなった完新世（現世）に隆起したように、地球内部に根本原因をもたない造陸運動もある。

　造山運動がきわめて短期間の地殻変動であると考えられたころには、造陸、造山運動は同時に同地域におこることはないと考えられた。しかし日本列島では、造山運動期にアジア東部地区と同時に海進・海退が造陸運動としておこった時期があることも知られている。

［木村敏雄］

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