Geochronologic age constraints on the Middle Devonian Hujiersite flora of Xinjiang, NW China

The Hujiersite Formation of West Junggar, Xinjiang contain fossil plants that represent significant examples of Middle Devonian flora in North China. However, previous radio-isotopic age constraint for this fossil-rich formation is absent. The best-studied section of the Hujiersite flora occurs at a locality referred to as 251 Hill, which exposes numerous examples of fossil plants and information on depositional environment. In this study, we investigate the geological background of the 251 Hill section and collect two tuffaceous sandstone beds from a normal fault near the classic fossil outcrop. U-Pb ICP-MS analysis of detrital zircons from these samples gave a maximum depositional age of 385 Ma (Givetian stage) for the hanging wall and 380 Ma (early Frasnian stage) for the footwall of the upper Hujiersite Formation. This study thus reports a novel Givetian-early Frasnian age constraint for Hujiersite flora. This geochronologic constraint is consistent with previous age interpretations derived from biostratigraphic correlations.