Redefinition and Geological Significance of Jiamuhe Formation in Hala'alate Mountain of West Junggar, Xinjiang

Lithostratigraphic units established correct or not, which is related to the regional stratum sequence, the comparison of the stratum, the analysis and the structural evolution of the basin, is one of the most important research contents in the study of geology. Recently, regional geological survey of 1:50 000 scale in Hala'alate area confirmed that "Jiamuhe Formation" in West Junggar was not previously described sandwich-like interbedded volcanic rocks and continental clastic rocks, but constituted by the lower continental coarse clastic rocks and the upper volcanic rocks with regional angular unconformity relations, clear sequence, and obvious rock associations. The upper portion of volcanic rocks develops complete volcanic edifice including volcanic channel with aggromerate and subvolcanic rocks, strains and dikes intruded continental coarse clastic rocks, and volcanic eruption with basic lavas and tuffs angular unconformity contacted with continental coarse clastic rocks. Moreover, the lower portion of terrestrial conglomerate-gravel coarse sandstone has typical molasse features, containing plant and pollen fossils in Early Permian, such as Paracalamites stenocostatus, Lepidodendrales, and Striatoabietites. Based on Stratigraphic Guide of China and stratum lithostratigraphic standard, as well as the principle of formation's naming priority, we remove the continental volcanic rocks with typical volcanic edifice from initial Jiamuhe Formation (redefining as Baiyanghe Formation), to update a new Jiamuhe Formation only including terrestrial conglomerate-gravel coarse sandstone. The results provide significant evidence for the correct establishment of the stratigraphic unit, a reasonable regional stratigraphic division and comparison.