Redefinition of the Middle Devonian Kulumudi Formation in the South of Tiechanggou Town, West Junggar, Xinjiang and Its Geological Implications

The Devonian terrigenous clastic rocks are widespread in the south of Tiechanggou Town, West Junggar, Xinjiang. However, due to insufficient reliable fossil evidence, the age of sedimentary strata formation is controversial. According to rock stratigraphic correlation, predecessors considered it as the Middle Devonian Kulumudi Formation. Based on the analysis of the previous research results, the debris tuff horizons were sampled from this Devonian stratum and dated using LA-ICP-MS method. The analysis shows that the zircons are typical magmatic origin with oscillatory zoning; the weighted mean ²⁰⁶Pb/²³⁸U age of 379.3±5.0 Ma(MSWD=0.45) shows that the Devonian stratum in the south of Tiechanggou Town have a big time span, among which there are also the early late Devonian sedimentary stratum, rather than the middle Devonian previously considered in generalities. Therefore, it is more reasonable to define the formation age of Kulumudi formation in this area between the middle Devonian and the early late Devonian. On the basis of measuring stratigraphic section in detail, this paper further analyzed their rock assemblages and sedimentary facies. The result shows that the middle-late Devonian stratum characterized by terrigenous clastic rocks intercalated with a few pyroclastic rocks formed in shallow sea environment.