Varved clay (English spelling: varve)

Japanese: 氷縞粘土 - ひょうこうねんど（英語表記）varved clay; varve

Also called varves. Fine-grained striped sediments washed down from the terminus of a glacier. When the fine clay particles that were taken up by the glacier due to glacial erosion melt at the terminus of the glacier, they are carried by surface water and deposited. When the flow rate is high due to seasonal changes, relatively coarse material is deposited, and in the dry season when the flow rate is low, fine clay is deposited, so a set of stripes that change from coarse to fine over the course of a year is likely to be formed. The thickness of this set of stripes is about a few millimeters to a few centimeters. By counting the number of stripes per set, the number of years of a glacial period can be determined. It is said that the number of years of varved clay in Northern Europe can be determined. Compared to ordinary clay, varved clay is less chemically weathered and tends to have the properties of fine powder of fresh rock.

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

Japanese:

バーブともいう。氷河の末端から流されて堆積した縞状の細粒堆積物。氷河の浸食作用によって氷河に取込まれた粘土質の細粉が氷河の末端で氷が解けると，表流水に運ばれて堆積する。季節の変化で流量の多いときは比較的粗粒物質が，流量の少い乾季には細粒の粘土が堆積するので，1年間に粗粒から細粒へと変る1組の縞ができやすい。この1組の縞の厚さは数 mm～数 cm程度。この1組の縞を1単位として枚数を数えると，氷期の年数がわかる。北ヨーロッパの氷縞粘土では約 9000年の年数がわかるという。氷縞粘土は普通の粘土に比べて化学的風化作用が進まず，新鮮な岩石の細粉の性質をもつ傾向がある。

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