Torsuqtagh Fm

The type locality of the Torsuqtagh Formation is near the Torsuqtagh Hill, southern Mochaikhutuk Basin, Kuruktag. No type section was assigned when Norin erected the unit. An auxiliary section was proposed by Cai (1999) as representative section of the formation. The section is said to be located at about 4 km south of Wuleijizitagh in Qinggir Village, Yuli, Bayingolin, Xinjiang Uygur Autonomous Region (88°10’48”E, 41°31’24”N) and to be measured by Gao Zhenjia and Zhu Chengshun from Institute of Geology, Xinjiang Bureau of Geology and Mineral Resources in 1984. The Torsuqtagh Formation was named by Norin. (1937). The name is derived from Torsuqtagh Hills, about 25 km north of Xingdi Village, Yuli County, Bayingolin Mongolian Autonomous Prefecture, Xinjiang Uygur Autonomous Region. Originally it was called Torsuqtagh series by Norin (1937). Subsequently named formally Torsuqtagh Series by Zhang et al. (1959) and Torsuqtagh Group by Hu et al, (1965b). Finally it was lowered in rank as Torsuqtagh Formation by Xiang (1981b). This formation spans Cambrian-Ordovician boundary.

Synonym: （突尔沙克塔格组）

The Torsuqtagh Formation is a carbonate sequence, consisting principally of thick-bedded limestone, marlstone, edgewise conglomerate, crystalline limestone, intercalated with nodular limestone and minor chert, nodular chert and mudstone. Eastward, the formation changes in facies to dolomite and dolomitic griotte with interbeds of limestone. The thickness of the formation varies from 103 to 2620 m. In the type section, the Torsuqtagh Formation is 297.9 m thick.

The Cambrian part of the Torsuqtagh Formation in both southern and northern Kuruktag areas yields rich trilobites. The formation totally embraces seven trilobite zones. However, the southern area, with six zones, lacks the oldest zone of northern area whereas the northern area, with five zones, lacks two youngest zones of the southern area.

The trilobite zone in northern Kuruktag area are, from bottom up: 1, Buttsia-Acmarhachis Zone containing Acmarhachis sp., Ajrikina sp., Buttsia globosa, Clavagnostus sp., Dorypyge? sp., Eoshengia sp., Huzhuia sp., Hypagnostus brachydolonus, Meteoraspis sp., Parablackwelderia jimaensis, Phalagnostus sp., Proceratopyge coniformis, Prodamesella sp., Protaitzehoia sp., and Wanshania sp.; 2, Glyptagnostus stolidotus-Liostracina Zone containing Eoshengia sp., Glyptagnostus stolidotus, Liostracina sp., and Meteroaspis sp.; 3. Prochuangia Zone containing Aspidagnostus sp., Corynexochus cf. plumula, Homagnostus sp., Olenaspella sp., Paraacidaspis hunanica, Prochuangia sp., Proceratopyge sp., Pseudagnostus idalis, and P. vigilax: 4, Irvingella-Sinoproceratopyge kiangshanensis Zone containing Acrocephalaspina sp., Corvnexochus cf. plumula, Irvingella angustilimbata, Hunanaspis sp., Idamea sp., Koptura？sp., Neoagnostus sp., Olenaspella sp., Proceratopyge rectispinata, Sinoproceratopyge kiangshanensis, S. sp., and Yuepingia niobiformis; 5, Lotagnostus americanus-Hedinaspis Zone containing Charchaqia norini, C. sp., Haniwoides cf. varia, Harpides？sp., Hedinaspis regalis, H. sp., Innitagnostus sp., Jegorovaia sp., Ketyna sp., Lotagnostus americanus, Loulania kuruktagensis, L. sp., Micragnostus sp., Neoagnostus sp., Onchonotina sp., Pagodia sp., Pareuloma palmeri, Peratagnostus sp., Probilacunaspis sp., Proceratopyge fragilis, P. sp., Promacropyge sp., Proteuloma sp., Pseudagnostus sp., Pseudoyuepingia sp., Rhaptagnostus sp., Sinoproceratopyge grabaui, Trilobagnostus sp., and Westergaardites pelturaeformis.

The trilobite zone in southern Kuruktag area are, from bottom up: 1, Glyptagnostus stolidotus Zone containing Aspidagnostus sp., Glyptagnostus stolidotus, Peratagnostus sp., and Wanshania？sp. This zone yields also conodonts Gapparodus bisulcatus and Furnishina quadrata; 2, Glyptagnostus reticulatus Zone containing Glyptagnostus reticulatus and Pseudagnostus idalis. This zone yields also conodonts Prooneotodus rotundatus, P. tenuis, P. aff. tenuis, and P. terashimai; 3, Irvingella Zone containing Corynexochus cf. plumula, Peratagnastus sp., Proceratopyge fragilis, P. sp., and Pseudagnostus idalis; 4, Lotagnostus americanus-Hedinaspis Zone containing Charchaqia norini, Diceratopyge mobergi, Hedinaspis regalis, Jegorovaia sp., Ketyna sp., Lotagnostus americanus, Micragnostus orientalis, Neoagnostus sp., Onchonotina sp., Proceratopyge fragilis, P. rectispinata, Proteuloma huochengensis, Pseudagnostus communis, P. rugalis, Pseudoyuepingia sp., Sinoproceratopyge sp., Trilobagnostus sp., Westergaardites pelturaformis, and Wuhuia sp. This zone yields also conodonts Prooneotodus rotundatus, P. tenuis, P. aff. tenuis; 5, Lotagnostus hedini Zone containing Euloma sp., Lotagnostus americanus, L. hedini, L. cf. hedini, Niobella sp., Parabolinella latilimbata, P. sp., and Plicatolina sp. 6, Hysterolenus Zone (lower part) containing Borthaspidella anderssoni, Dividuagnostus cf. D. longa, Euloma sp., Hysterolenus asiaticus, H. oblongus, Leiagnastus sanduensis, Niobella sp., Proteuloma sp., Troedssonia sp. The Lotagnostus hedini Zone yields also conodonts Cordylodus proavus, Eoconadontus notchpeakensis, Proconadontus muelleri, P. serratus, Prooneotodus gallatini, P. rotendatus, and P. tenuis

[Figure: Some index fossils of the Torsuqtagh Formation, all from the Charchaq (Queerqueke) Mountain, Xinjiang Uygur Autonomous Region A, Glyptagnostus stolidotus Öpik, 1961, cephalon, from the Glyptagnostus stolidotus Zone; B, C, Lotagnostus americanus (Billngs, 1860), exoskeleton, from the Lotagnostus americanus-Hedinaspis Zone, C is dorsal view of the cephalon in B; D, E, Lotagnostus hedini (Troedsson, 1937), cephalon and pygidium, from the Lotagnostus hedini Zone; F, Westergaardites pelturaformis Troedsson, 1937, exoskeleton with librigenae missing, from the Lotagnostus americanus-Hedinaspis Zone, G, Charchaqia norini Troedsson, 1937, exoskeleton, from the Lotagnostus americanus-Hedinaspis Zone; H, I, Hedinaspis regalis (Troedsson, 1937), cephalon with left librigena missing and with 11 thoracic segments (H) and pygidium with 7 thoracic segments (I), from the Lotagnostus americanus-Hedinaspis Zone; J, Hysterolenus asiaticus Lu, 1959, pygidium, from the Hysterolenus Zone (lower part). All scale bars = 1 mm for A−E; 4 mm for F−J.]

Cai (1999) designated a section at Wuleijizitagh as auxiliary section for the formation. As noted by Cai (1999, p. 188), the section is located in Yuli County and was measured by Gao and Zhu (1984). However, a check on the Cambrian paper by Gao et al. in Gao and Zhu (1984) reveals these authors did not measure such a section but six other Cambrian sections, among which three sections embrace the Torsuqtagh Formation, all are more or less incomplete by lacking the upper or uppermost portion of Cambrian System. So far the author has not found where the Wuleijizitagh section was documented. To my knowledge it is possibly the Wuligezitagh section documented by Zhong and Hao (1990, p. 25) and commented by Lin et al. (2001). This section is located in the Yuli County (North Kuruktag area) and may be for the same Mongolian locality but translated into different mandarin characters. In addition, Cai (1999) noted the Wuleijizitagh section mentioned by him is in the Yuli County, but the geographical coordinate (88°10’48”E, 41°31’24”N), given by him indicates the location of the secion is outside that county. Probably the coordinate is incorrect, otherwise the section may be not in Yuli County. No thickness of the Torsuqtagh Formation is known for the auxiliary section as the Wuleijizitagh is questionable. However, the thickness of the formation in the Wuligezitagh section is measured 297.20 m thick (Zhong and Hao, 1990, p. 25−26), and in the section south of Baledigendabangtagh is 652 m thick (Gao et al., 1984, p. 5).