Mississippian Subperiod

Japanese: ミシシッピ紀 - ミシシッピき（英語表記）Mississippian Subperiod

A geological period in the United States, referring to the first half of the Carboniferous Period. It spans the period from about 358.9 million years ago to about 323.2 million years ago. The first half of the Carboniferous Period in North America is generally a period of transgression, and limestone-based strata are widely distributed in the upper Mississippi River region and elsewhere. The second half of the Carboniferous Period is composed of a sedimentary facies (→ facies) in which transgressions and regressions were frequently repeated, and is classified as the Pennsylvanian Period, in which strata of continental strata including coal beds and shallow marine deposits are well developed, including the Appalachian coalfields. Due to the significant differences in sedimentary facies and the large differences in the contents of fossils, it has been proposed in the United States to divide the Carboniferous Period into the Mississippian Period and the Pennsylvanian Period.

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

Japanese:

アメリカ合衆国の地質時代の年代区分の一つで，石炭紀前半をさす。約 3億5890万年前から約 3億2320万年前までの期間にあたる。北アメリカの石炭紀前半は一般に海進の時代で，石灰岩などを主体とする地層がミシシッピ川上流地域などに広く分布する。石炭紀後半は海進と海退が頻繁に繰り返された堆積相（→層相）からなり，アパラチア炭田をはじめ石炭層を含む陸成層と浅海堆積物からなる地層がよく発達し，ペンシルバニア紀と区分される。このように堆積相の顕著な差と，化石群の内容の差が大きいという理由で，アメリカでは石炭紀をミシシッピ紀とペンシルバニア紀に二分することが提唱されている。

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