The Petrogenesis and Sedimentary Environment of the Bedded Cherts from Upper Permian Dalong Formation, Southwest Guangxi

Key words: 
• Upper Permian /
• Dalong Formation /
• cherts /
• petrogenesis /
• sedimentary environment

Abstract: The geochemical researches on the upper Permian cherts of the Dalong Formation in the southwest Guangxi have been conducted. 〖JP2〗And we have the following findings: the chert is rich in the terrestrial elements (for example Al, Ti etc.), and poor in hydrothermal elements（for example Mn, Fe etc.）, with high correlation between the terrestrial elements (R>0.90) and low correlation between the hydrothermal elements (R=－0.30); The correlation between the terrestrial elements (Al, Ti, Hf, Zr, Th etc.) and ∑REE is high (R=0.70～0.83); AlFeMn diagram shows that the cherts is nonhydrothermal type. The characteristics above confirm that terrestrial debris is one of the most important provenances. Considering the truth, the high content of the siliceous biodebris in the cherts, we prove that the cherts were formed by strong bio or biochemical sedimentation, with lets of terrestrial debris and little hydrothermal and volcanic material interfused. Ce/Ce*, (La/Yb)Shale, (La/Ce)Shale, Th/U, Ceanom, ∑REE and (La/Ce)ShaleAl2O3/(Al2O3 +Fe2O3) diagram make sure that the cherts are deposited on middleouter shelf in oxic conditions. 〖JP〗