Geochemical Characteristics and Environmental Implications of Middle Jurassic Shaximiao Formation, Western Margin of Sichuan Basin

Key words: 
• Sichuan Basin /
• Middle Jurassic /
• Shaximiao Formation /
• trace element /
• REE /
• paleoclimate /
• paleoenvironment /

Abstract: Trace elements and REE of sedimentary rocks contain abundant information of geology. Having a high sensitivity on hydrological changes of sedimentary environment, trace elements and REE can be used as an effective method on the study of paleoclimate and paleoenvironment during deposition period. Choosing the trace elements and REE measured value of 17 samples of middle Jurassic Shaximiao Formation of western margin of Sichuan basin. Results indicate that,  in the study area, both the Sr/Ba ratios of the upper and lower Shaximiao Formation are less than 1, which illustrate that there was a fresh water environment during deposition  of Shaximiao Formation. The characteristic values and ratios of trace elements and REE such as V,U,Mo,V/Cr,Ni/Co,U/Th,（Cu+Mo）/Zn,V/（V+Ni）,δCe,δEu,∑REE,La/Yb, suggest that the bottom water of the lake was moderate oxidation environment during the whole time    Shaximiao Formation deposition. According to the Sr/Cu ratios and the research findings before, we suggest that there paleaoclimate was warm and arid with cool interphases during the whole time of lower Shaximiao Formation， and after then it turned to worm and aridity again during the upper Shaximiao period， which is as the lower Shaximiao Formation, and the aridity strengthened gradually.