A research into the lithologic assemblage

sedimentary cycle

marker beds

and sedimentary evolution of the Benxi and Taiyuan formations as well as the regional geology reveals that the Benxi Formation was formed during the Late Carboniferous Benxi age.Its lower member consists of bauxitite and is equivalent to the ferrallite interval regionally and its upper member composes of sandstone and mudstone interbeded with thin coal and 1-3 local limestone layers and regionally corresponds to the Bangou member.The Taiyuan Formation can be divi-ded into three members.Its lower member is sandstone and mudstone with thin coal interbeds

regionally corresponds to the Jinci member

and its age is the Late Carboniferous.The middle member consists of coalbed

limestone and equivalent mudstone and regionally corresponds to the Maoergou member.The upper member consists of interlayering sandstone and dark mudstones with coal and 0-2 limestone interbeds and regionally corresponds to the Dayao member.The age of the upper and middle members is the early Permian.