Xifangshan Fm

Aksu-Kalpin region. The Xifangshan Fm was named by Gao Zhenjia et al. (1986) and published by Lu Songnian and Gao Zhenjia in 1993. The naming section is located in the west part of Fangshan Mountain south of Yourmeinak residential area, north part of Aksu, Xinjiang Weiwuerzhu Zizhiqu (Xinjiang Uygur Autonomous Region). Lower formation of Qiaoenbulak Gr.

Synonym: （西方山组）

The formation consists mainly of gray green, dark gray feldspar quartz sandstone, lithic arkose and arkose with minor unstable interbeddings of pebbly sandstone, sandstone conglomerate and siltstone. The main part of this formation is in south Qiaoenbulak. The formation is 1266-1715 m thick, from Qiaoenbulak, Yourmeinak of south of Wushi County to west of Xifang and east of Yurtus mountains.

Well preserved microplants and trace fossils have been found in sandstone and siltstone, the former include Leiopsophosphaera sp., L. densa, Trematosphaeridium sp., T. holtedahlii, Taeniatum sp. etc; and trace fossils are Chondrites von sternberg and Planolites nicholson.

The formation is the typical deep-water debris flow sediments, basically characterized by lower maturity of lithological structure and composition, stable lithology, well developed sedimentary rhyme with the rhythmite thickness changing a lot from 1 to 3 4 cm. The lower part of the rhythmic horizons consists of sandstone, with siltstone at the top. Each rhythmic horizon has progressive bed (A) and horizontal bed (B), sometimes has micro cross-bedded and convolute bedded (C), but typical Bouma sequences (D) and (E) are not found. The progressive bed is commonly 50-100 m thick in the rhythmic horizons. The character of the rhythmic horizons belongs to gravity flow sediments of inner fan of submarine fan.