LATE PROTEROZOIC STRATA IN THE EASTERN SECTOR OF THE CENTRAL QILIAN MOUNTAINS

Late Proterozoic strata in the eastern sector of the central Qilian mountains are distributed in the area from Laoye Mountain to Nanmenxia in eastern Qinghai. The Diaogou Group of the Qing-baikou System may be divided into two rock formations:the lower rock formation（522. 42 mthick）and the upper rock formation（1250. 22 m thick）.The first member of the lower rock for-mation consists of alternating beds of pebbly sandstone,pebbly slate and slate,and its second member alternating beds of dolomite and siliceous rocks; the first member of the upper rock for-mation is represented by carbonaceous slate with limestone ,and the second member dolomite withlimestone. This system contains abundant microfossil plants and has a whole-rock Rb-Sr isochronage of 860 Ma, The lower rock formation of the Sinian System,more than 38.83 m thick,includestwo members : the first member consists of mud- and gravel-bearing dolomitic conglomerate（tillite?）,and the second consists of gravel-bearing dolomite, The upper rock formation of theSinian System, more than 310.30m thick,also contains two members: the first member is com-posed of carbonaceous,agrilla ceous and siliceous slate and barite-bearing argillaceous dolomite,and the second dolomite. The Sinian System contains microfossil plants,and its whole-rock Rb-Srisochron age is 606 Ma. The Sinian System is in fault contact with the overlying Middle CambrianMaojiagou Formation and the Qingbaikou System is in disconformable contact with the underly-ing Kesu’er Formation of the Jixian System;whereas the Sinian System and the Qingbaikou Sys-tem are in fault contact.