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Late Devonian reefs and microbialite in Maoying, Ziyun County of southern Guizhou, South China—Implications for changes in paleoenvironment

Research paper by Jian-Wei Shen, Na Zhao, Ying-Jiang Mao, Yue Wang, Yongbin Jin

Indexed on: 05 Jul '16Published on: 05 Jul '16Published in: Palaeogeography, Palaeoclimatology, Palaeoecology



Abstract

There are Upper Devonian (Frasnian to Famennian) limestone outcrops in the Maoying area, north of Ziyun County, South China and they represent carbonate platform deposition with some patch reefs, as part of a shallow-water carbonate sedimentary formation in the Late Devonian nearshore environment. The Late Devonian carbonate deposition is, to the east, different from that in the nearby of Dushan County and around Buzhai village, Xiasi Town of Dushan County, but is, to the south, similar to that in Guilin area, northeastern Guangxi. According to the lithologic characteristics, Late Devonian carbonates in the Maoying area are divided into two groups composed of five lithologic sections, one reef limestone and one dolomite bed. The Late Devonian strata are cumulatively 530 m in thickness. Late Devonian reefs in the Maoying area were developed on a base of brachiopod- and bivalve-shell shoal packstone and grow into patch reefs in the interior of the carbonate platform. Patch reefs were developed in early Frasnian time. Reef-building organisms are dominated by massive and tabular stromatoporoids, Amphipora sp., Stachyodes sp., and coral Thamnopora sp., and brachiopods and algae accumulate between stromatoporoid skeletal frameworks. Three evolutionary stages of the Frasnian patch reefs, including a initial development stage, maturity stage and demise stage, can be recognized according to the sedimentary structures and fossil assemblage characteristics. The overlying Frasnian strata above patch reefs are well-bedded back-reef deposition and are mainly composed of Amphipora floatstone and packstone containing a few bulbous stromatoporoids and small fasciculate corals. Famennian strata are characterized by laminated limestone and fenestrate limestone that are intercalated with low occurrences of mudstone and argillaceous limestone. A microbialite bed was developed in the laminated limestone of Famennian nearshore carbonate platform deposition and consists of stromatolite and thrombolite framestone. It can be correlated, in horizon and age, with those microbial reefs and mounds in the Famennian offshore carbonate platform deposition in the Huanan Epeiric Sea (such as Famennian microbial reefs and mounds in Guilin), representing a biogenic carbonate formation characterized by microbial fabrics in a nearshore carbonate platform after the global Frasnian/Famennian biotic extinction event, which enriches the growth types of microbialites and their implicated environmental significance during Devonian critical environmental and climatic changes and major biotic event in South China.

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