GEOCHEMICAL CHARACTERISTIC AND SEDIMENTARY ENVIRONMENT OF THE DEVONIAN NIQIUHE FORMATION IN NORTHERN DAXINGANLING RANGE

Based on the study of rock assemblage with geochemical analysis of clastic rock samples, the sedimentary environment of Devonian Niqiuhe Formation is researched. Lithologically, the Niqiuhe Formation includes quartz greywacke, siltstone, silty slate and slate. The high Al₂O₃ content(3.74%-17.13%), i.e. more clay mineral content, means the low maturity of clastic rocks, reflecting that the sediment is accumulated near the source. The geochemical analysis of rare earth and trace elements indicates that the detrital material is from feldspar and quartz areas. Eu is of obviously deficient, with δEu between 0.65 and 0.73. Ce is slightly abnormal, with δCe from 0.87 to 0.94. Tb/Yb value is 0.30-0.37. La/Th is in the range of 2.84-6.73. Th/U is 3.53-5.38. REE distribution patterns generally show rightward incline, with enriched LREE and flat HREE, which is similar to those of the typical upper crust source. It is concluded that the maturity of Niqiuhe Formation is relatively low, with a sedimentary environment of offshore shallow sea. The depositional system can be subdivided into fan delta and shore-shallow marine facies.