SEDIMENTARY FACIES,FACIES GROUPS AND THEIR EVOLUTION IN THE BAYAN HAR BASIN

According to vertical sedimentary sections of sedimentary facies and facies groups of Permian to Triassic age in the Bayan Har Basin, five substages of sedimentary evolution may be distin-guished.
1. Early Permian to Early Triassic substage. In the basin occur, from base upwards, the following facies groups: Carbonate platform slope→bathyal→abyssal plain→neritic and littoral facies groups.
2. Middle Triassic substage. The sediments from bottom to top of the basin may be divided into six facies groups in the following order: continental→littoral and neritic→slope→abyssal basin→slope→neritic and littoral facies groups. The depocentre of the basin lies in the Sertar-Lixian-Luhuo-Dawu zone.
3. Carnian substage(Late Triassic). The Carnian sedimentary facies groups are composed of neritic and littoral, slope and abyssal facies groups, constructing a complete sedimentary cycle sequence from transgression to regression. The sea water covered a maximum area during this period.
4. Norian substage(Late Triassic). The sedimentary sequences in the basin represent an overall regression sequence dominated by slope, littoral and neritic facies groups.
5. Rhaetic substage(Late Triassic). The continental and marine-terrestrial transitional facies groups have been recognized in the basin.