Keywords: 
• hydrothermal activity /
• source rock /
• Yuertusi Formation /
• Tarim Basin

Abstract: Based on geochemical analyses of Yuertusi Formation at Dongergou section of Tarim basin, trace elements and rare earth elements are used to probe paleoenvironmental conditions.Using δEu, Fe/Ti and (Fe+Mn)/Ti ratios for the interpretation of hydrothermal activity, Al/Ti ratios as paleoproductivity proxies and V/Cr, V/(V+Ni) and Ni/Co ratios as paleoredox proxies, the relationship of hydrothermal activity, paleoproductivity, paleoredox and total organic carbon was discussed. The data shows that Yuertusi Formation was deposited under dominantly euxinic conditions with a low paleoproductivity and that the lower part of the section experienced a strong hydrothermal activities. Although the hydrothermal activities improve the paleoproductivity of the lower part, the total organic carbon is low and ranges from 0.01% to 3.58% with an average of 0.64%. The middle-upper part of the section have a weak hydrothermal activities, but the total organic is high and ranges from 0.06% to 12.19% with an average of 8.95%. There are plenty of algal in the thin section of cherts related with hydrothermal activities. The study suggests that strong hydrothermal activities provided a lot of silica-rich fluid, which diluted the organic matter in the sediments and destroyed the formation of high-quality source rocks.