Oulongbuluke Gr

No type section was assigned previously for the Oulongbuluke Group, and an auxiliary section was proposed as representative section of the group by Sun (1997). The section is located on the south slope of Oulongbuluke Mountain (96°28’E, 37°16’ N), about 80 km west of the seat of Dalingha City and was measured by The Qinghai First Regional Geological Survey Team in 1978. In the type section, the group 965.22 m thick. The name of Oulongbuluke Group was first appeared in a 1958 manuscript by the Petroleum Exploration Team of Qinghai Bureau of Geology and subsequently the name was published in three articles in the same year and the same month respectively by Lu (1962), Mu et al. (1962) and the Qinghai Petroleum exploration Team (1962). The name is derived from Oulongbuluke Mountain in the west of Delingha City, Haixi Mongolian and Tibetan Autonomous Prefecture, Qinghai Province. Originally, both Lu and Mu et al. divided the unit into two units, called as the Lower and the Upper Oulongbuluke groups by Lu (1962) and as the Lower and the Upper Oulongbuluke series by Mu et al. (1962) respectively, but Qinghai Petroleum Exploration Team, Qinghai Bureau of Geology (1962) published it as undivided Oulongbuluke Series. Subsequently the No. 1 Brigade of Qimghai First Regional Geological Survey Team (1978) called the unit as Oulongbuluke Group, which is followed by Sun (1997) and herewith.

Synonym: （欧龙布鲁克群）

The Oulongbuluke Group is basically a carbonate sequence. The group is roughly divided into three parts. Lower part consists of dark grey, thick-bedded oncolite dolomite, grey, medium- to thick-bedded dolomite, intercalated with argillaceous sandstone and with a layer of phosphoric quartzose conglomerate of about 5 m thick at the base. Middle part consists of megathick-bedded false oolitic dolomitic limestone, thin- to medium-bedded limestone, intercalated with calcareous dolomite, fine-grained dolomite, edgewise conglomerate, and oolitic limestone. Upper part consists of thick-bedded brecciated limestone, thin- to thick-bedded limestone, intercalated with argillaceous striped limestone, megathick-bedded dolomite, intercalated with oolitic or edgewise conglomerate.

In the representative section, the middle part of Oulongbuluke Group yields trilobites Anomocarella sp., Blackwelderia sp., Iranoleesia quadrata, and Parakotuia sp.; the upper part yields trilobites Chuangia sp. and Parakotuia trancata. At Shihuigou, Haixi Prefecture, the upper part of the group yields younger trilobite assemblage with Changshania sp., Chuangia sp., Eochuangia sp. and Kaolishaia sp.