Citation: | SHI Jizhong, LU Jincai, WEI Jianshe, NIU Yazhuo, JIANG Ting, HAN Xiaofeng, XU Wei. Petrology, geochemistry and sedimentary environment of Permian siliceous rocks in Yingen-Ejin basin and its adjacent areas[J]. Geological Bulletin of China, 2018, 37(1): 120-131. |
The geochemical characteristics and depositional environment of Permian siliceous rocks were studied based on the petrological characteristics, major elements and rare earth elements. According to the test results, Hangwula sectional siliceous rocks' Al/(Al+Fe+Mn)values are 0.68~0.78, with an average of 0.73; δCe values are 0.89~0.94, with an average of 0.90; Erduanjing sectional siliceous rocks' Al/(Al+Fe+Mn)values are 0.50~0.67, with an average of 0.60; δCe values are 0.85~0.90, with an average of 0.88. In the Al-Fe-Mn triangular diagram, samples fall into biochemically-deposited area, which indicates a biochemically-deposited origin for these rocks. Hangwula sectional siliceous rocks' Al2O3/(Al2O3+Fe2O3)values are 0.78~0.86, with an average of 0.83; MnO/TiO2 values are 0.04~0.40, with an average of 0.16;(La/Ce)N values are 1.02~1.15, with an average of 1.10; Ceanom values are -0.041~-0.001, with an average of -0.029. Erduanjing sectional siliceous rocks' Al2O3/(Al2O3+Fe2O3)values are 0.82~ 0.91, with an average of 0.87; MnO/TiO2 values are 0.05~0.47, with an average of 0.24;(La/Ce)N values are 1.00~1.12, with an average of 1.06; Ceanom values are -0.058~-0.033, with an average of -0.045. All these geochemical characteristics suggest that these siliceous rocks were deposited in a continental margin setting where the sea water in the period of deposition was under an anoxic condition.
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Geological sketch map and tectonic units of Carboniferous-Permian strata in Yingen-Ejin basin and its adjacent areas
Composite column of Permian strata in Hangwula (a) and Erduanjing (b)
Al-Fe-Mn diagram for the siliceous rocks
NASC-normalized REE patterns for siliceous rocks in the Hangwula(a) and Erduanjing(b)
Diagram of Al2O3/ (Al2O3+Fe2O3) -Fe2O3/TiO2
Diagram of Al2O3/ (Al2O3+ Fe2O3) -(La/Ce)N