The origin of Lower Permian Gufeng Formation cherts in the lower Yangtze area, eastern China

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Authors:Xia Bangdong; Zhong Lirong; Fang Zhong; Lu Hongbo
Author Affiliations:Primary:
Nanjing University, Department of Earth Sciences, Nanjing, China
Volume Title:Dizhixue Bao Acta Geologica Sinica
Source:Dizhixue Bao = Acta Geologica Sinica, 69(2), p.125-137. Publisher: Science Press, Beijing, China. ISSN: 0001-5717
Publication Date:1995
Note:In Chinese with English summary. 32 refs.; illus., incl. 5 tables
Summary:Cherts of the Early Permian Gufeng Formation in the lower Yangtze area are marked by bedded black rocks containing more or less clayey and organic materials, along with minor calcite in some samples. The thickness of the chert sequence ranges between 20 and 80 m, and the thickness of a single bed of chert generally varies from several cm to 30 cm. The chert beds usually alternate with very thin beds of clayey rocks, each only a few mm thick. Gufeng cherts can be identified as hydrothermal chert thanks to the following evidence: First, a heat source responsible for hydrothermal convection is present in this area. We discovered alternating beds of volcanic rocks and cherts; for example, there are at least 15 beds of volcanic rocks in the Gufeng Formation at Taochong, Fanchang County, Anhui Province. They are mainly intermediate-acidic tuffs with a bed of basic lava; their thickness varies from several mm to 104 mm. All the volcanic rocks have been argillized, which indicates that they underwent low-temperature hydrothermal alteration immediately after the accumulation of each volcanic bed. Second, there are several syngenetic faults transecting the crust of this area, which provided conduits for hydrothermal activity. Crustal extension along these faults resulted in the formation of a series of basins and uplifts inserted among the basins. Cherts were mainly deposited in the basins, whereas shallow-water carbonates up to 300 m thick accumulated on the uplifts. Third, geochemically the cherts are characterized by higher Fe and Mn content, slightly lower Al and Ti content, higher abundances of As, Sb, Bi, Au, Ag, Ga and Cr, lower total REE, a negative Ce anomaly, and slight enrichment in HREE. All these characteristics are important evidence for hydrothermal chert. [R.A.H.]
Subjects:Chemically precipitated rocks; Chert; Hydrothermal conditions; Lower Permian; Marine sedimentation; Paleozoic; Permian; Sedimentary rocks; Sedimentation; Structural controls; Anhui China; Asia; China; Far East; Fanchang China; Gufeng Formation; Taochong China
Coordinates:N310500 N310500 E1181000 E1181000
Abstract Numbers:96M/1172
Record ID:2012014643
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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