Qiulitag Fm

The type section of the Qiulitag Formation is Kokbuksanshan section, Artux City, Kizilsu Kirgiz Autonomous Prefecture, Xinjiang Uygur Autonomous Region (77°48’30”E, 39°56’54”N). The section was measured by the joint team of No. 1, 2 and 3 brigades of the No. 13 Geological Team of the Ministry of Geology of China in 1957. In the type section, the formation is 211 m thick. The Qiulitag Formation was first published by Zhang et al. (1959). The name is derived from Qiulitag Hill, close to Yin’gan Village, Kalpin County, Xinjiang Uygur Autonomous Region. Originally the formation was proposed as Qiulitag rock system in a 1957 manuscript by the joint team of No. 1, 2 and 3 brigades of No. 13 Geological Team of the Ministry of Geology of China and was published as Qiulitag Series by Zhang et al. (1959). Subsequently it was renamed Qiulitag Group by Compiling Group for Xinjiang Regional Stratigraphical Scale (1981) and Lower Qiulitag Subgroup (Cambrian portion) by Cheng (1990) respectively. The Qiulitag Group has been lowered in rank as Qiulitag Formation by Cai (1999).

Synonym: (丘里塔格组)

The Qiulitag Formation is a carbonate sequence. Lower part, belonging to Cambrian, consists of grey medium- to thick-bedded dolomite, containing s chert bands and lumps. Upper part, belonging to Ordovician, consists of thin-bedded brecciated limestone, greyish white, medium- to thick-bedded laminated limestone, and grey, thin- to medium-bedded, nodular argillaceous limestone.

The lower part of the formation yields trilobites belonging to Saukiidae, and conodonts Monocostodus sevierensis, Teridontus erectus, T. nakamurai, and T. reclinatus. Previously the Qiulitag Group used to be divided into two subgroups: the Lower Qiulitag Subgroup (Cheng, 1990), dominated by thick-bedded dolomite and the Upper Qiulitag Subgroup (Xiao, 1990), dominated by limestone with interbeds of dolomite. The Lower Subgroup was regarded to be Cambrian but lack any fossil evidence. The discoveries of trilobites, assigned to Saukiidae, from the upper part of the Lower Subgroup (Zhou et al., 1991) and conodont Monocostodus sevierensis of latest Cambrian in age (Cordylodus intermedius Zone) from the basal part of the Upper Subgroup (Zhang and Gao, 1992), reveal that the entire Lower Subgroup and the basal part of the Upper Subgroup should be Cambrian in age.