Bochatetag Fm
Type Locality and Naming
SW Tarim Basin. The Bochatetag Fm was named by the No. 13 Party of Geology, Ministry of Geology in 1957. However, the definition of the formation was modified by Ma Shipeng, Wang Yuzhen and Fang Xilian in 1991. The type locality is Mountain Tieklik on the north slope of western Kunlun Mts. Xinjiang Weiwuerzhu Zizhiqu (Xinjiang Uygur Autonomous Region).
Synonym: （博查特塔格组）
Lithology and Thickness
It is subdivided into three lithological members from bottom to top. First member, 140 m thick, is composed of thin platy limestone, laminated limestone. It is composed of grey thin-bedded, medium-thick bedded laminated limestone and grey-purple dolomitic laminated limestone, black-grey thin-platy microcrystal line limestone, intercalated with muddy dolomite and flesh-pink thin-platy microcrystalline dolomite. In the base there is grey, grey-brown calcareous slate, greyish sand-stone, grey-black sandy phosphorite, and the sandstone is of different-grained arkosic sandstone, intercalated with conglomerate, with vein quartz, chert rubble and dolomite boulders. Paleokarst funnels are seen. Second member is massive dolomite member of 40 m thick is composed of lithologically homogeneous grey-white massive microcrystalline dolomite. Third member is variegated chert-banded carbonate rock, 200 m thick. The lower part is dominated by grey, grey-black, thin-bedded limestone, worm-kalk dolomite and medium-thick-bedded chert-banded dolomite. The upper part consists of flesh-pink medium- to thick-bedded chert-banded dolomite. It is over 400 m thick.
Relationships and Distribution
Lower contact
The base of the lower member is in disconformable contact with underlying Bukatuwei Fm.
Upper contact
The top of the formation is in conformable contact with overlying Sumalan Fm, upper Jixian System, but locally it is in unconformable or disconformable contact with the Yushasi Fm of Sukuluok Gr of Qingbaikou System and the Upper Devonian.
Regional extent
SW Tarim Basin. The Bochatetag Fm is distributed in the area south of Yecheng County along the Xinjiang-Tibet highway and on its east and west sides. Westward it extends upstream in the Qipanhe River, while eastward it extends to the Tasihong River and Dilong River of Xinjiang Weiwuerzhu Zizhiqu (Xinjiang Uygur Autonomous Region).
GeoJSON
Fossils
Stromatolites are seen in first member and third member. The former include Stratifera, while the latter are the Gymnosolen, Boxonia and Parmites. Further more the third member yields rich microplants. According to Peng Changwen (1984, 1988), 10 and more species were recognized, predominated by Trachysphaeridium.
Age
Depositional setting
Additional Information
The crustal movement associated with paleokarst in the lower member is termed the Qipan uprising. According to Li Yong'an (1984), the paleomagnetic polarity of this formation was negative, and paleomagnetic pole position was located at 15.6°N, 25.6°E.