地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
論説
南中国地塊北東部の陸棚浅海におけるキャピタニアン期(ペルム紀中期)パッチ生物礁の終焉
─南部北上帯,岩井崎石灰岩最上部の岩相層序─
飛田 知世磯﨑 行雄林 隆太郎
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ジャーナル フリー

2018 年 127 巻 6 号 p. 775-794

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 To clarify environmental and biological responses to the extinction-related global change that occurred during the Late Guadalupian (Permian), high-resolution lithostratigraphy is analyzed of the uppermost part of the Capitanian (Upper Guadalupian) shallow-marine Iwaizaki Limestone in the South Kitakami Belt, NE Japan, deposited as a patch reef on a continental shelf at the northeastern extension of South China, with various shallow marine fossils, e.g., rugose corals, fusulines, brachiopods, crinoids, and calcareous algae. The topmost ca. 40 m-thick interval of the limestone (Unit 8) is composed of interbedded limestone and mudstone, which are subdivided into the following four distinct subunits: Subunit 8-A of limestone-dominated alternation with nodular limestone, Subunit 8-B of mudstone-dominated alternation of limestone and mudstone, Subunit 8-C of thickly bedded limestone, and Subunit 8-D of calcareous mudstone, in ascending order. Subunit 8-D is covered directly with a thick black mudstone unit mostly of the Lopingian age. A clear pattern of step-wise disappearance of shallow-marine, tropically-adapted fossil biota, e.g., large bivalves (Alatoconchidae), rugose corals (Waagenophyllum), and large-tested fusulines (Lepidolina), is detected in the topmost Unit 7 and Unit 8 (8A to 8B), regardless of significant fluctuations of water-depth within this interval. The overall stratigraphic change in lithofacies within Unit 8 indicates a deepening trend, which was probably controlled by subsidence of the basement. Nonetheless, tectonic-driven subsidence led to the preservation of continuous stratigraphic records of the topmost Iwaizaki Limestone with the collapsing history of a patch reef, despite a global sea-level drop across the G-L boundary. The appearance of global cooling probably led to the extinction of warm water-adapted benthic tropical biota and the collapse of a reef complex during the Capitanian.

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© 2018 公益社団法人 東京地学協会
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