| 长江中游地区晚二叠世生物碳酸盐岩岩隆生成机制 |
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| 关键词:Lale Permian carbonate building-up control conditions. |
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| On Original Conditions of Late Permian Carbonate Building-up in Middle Yangtze River Area |
| Late Pemian carbonate building-up developed at both, north and south, sides of Jiangnan old-land in the Middle Yangtze river Area. There are two types of reefs, Spongealga reef and compound coral reef, exposed in cili county, Chenxi county of Hunan Province, Chongyang county of Hubei province and Xiushuicounty of Jiangxi province. Sponge-alga reefs exist in the lower Daluockeng Formation (of the lower Changxingian stage), and compound coral reefs occur in the uuper part of the Xiamidong Formation (Wujiaping stage). In sponge-alga reefs there are abundant reef builders and dwellers, builders including calcisponges (identi-fied more 15 genera of shhinctoxzoans and inozoans), tabulozoans, hydrozoans, calcareous algae and bryozoans, and dwellers including brachiopods, bivalves, gastropods, foraminifers and crinoids. On the basis of the bio-microfacies analyses and shallowing-up sequences,a strati-graphic sequence franework isrestored taking Gaofeng area as a representative. The Xiamidong Formation is composed fo a highstand sysems tract (HST) and a lower systems tract (LST).A type 1 sequence boundary distinguished the Daluokeng Formation from the Xianmidong Forma-tion. Two shelf margin wedge systems tracts (SMW), sponge-alga reef and oolite band, exist in te Dauokeng Formation, and with a HST between them. The upper boundary of each SMW is the type 2 sequence boundary (Fig.3).Diageneses of carbonatte building up in the Middle Yangtze area are complicated with varous processes. Diagenetic recorders of rocks display that marine phreatic and vadoset, freshwater phreatic and vadose, mixing and deep burial environ-ment all exist in Late Permian carbonate rocks of the area. Porosity of rocks has regular change in stratigraphic sections. In Daluokeng section, for example, reef framestones and calcirudites usually have higher prosities. Oolites and oncolites have lower porosity but higher thav algal or foraminifer imestones. By restoring the original sediment thickmess we estimate te sea level change and subsidence of substrata. As showing in table 1, there are high values of relative sub-sidence ofsubstrata in each cycle from trasgression to regression. Finally, oribinal control con-ditions of Late Permian carbonate builking up and reefs are reefs are discussed in the paper. |
| Xu Guirong,Lao Xinmin,Huang Shiji,Wang Yongbiao,Lin Qixiang,Chen Linzhou,Xiao Shiyu.1996.On Original Conditions of Late Permian Carbonate Building-up in Middle Yangtze River Area[J].Acta Geoscientica Sinica,17(z1):120-129. |
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