Taiyuan Fm

The type section is located at Yumengou (formally mistaken as Yuemengou) of the West Hill, Taiyuan City, Shanxi. It was named by Weng Wenhao and Grabau in 1922.

Sandstone, Coal, Claystone and Limestone. A suite of marine-continental coal-bearing deposits, consisting of sandstone, shale, carbonaceous shale, coal seams and limestone. The formation at the West Hill of Shanxi includes the member from the bottom of the Jinsi sandstone to the Beichagou sandstone (also called the upper-layer Beichagou, or Nanyu sandstone, or Shangyeyu sandstone), intercalated with 4 layers of stable limestone (the Miaogou, Maoergou, Xiedao and Dongdayao limestones), 3 layers of stable sandstone (the Jinci, Nameless and Qiligou sandstones) and 5−9 layers of coal seams of unequal thickness, often intercalated with clay beds and siderite ore beds or nodules. Thickness 50−140 m.

It is 250 m thick at Hulusi of Helan Mt., 150−180 m thick at Peixian County of Jiangsu, and ~80 m north of Datong and south of Yuxian County-Yongcheng. Its lithology varies with the different sedimentation zones or environments: being dominated by coarse-grained clastic deposits intercalated with siltstone and mudstone and occasionally with 1−2 layers of marine mudstone and sandstone in the areas north of Junggar Banner, Datong and Tangshan in the northern basin, showing such features as complex compositions, multi-stage structures, great thickness, unstable distribution, etc.

Its coal-bearing potential is in reverse proportion with the grain size of clastic rocks: in areas with coarse-grained class well-developed, the coal seams are unstable and in small number, but the thickness of a single coal seam is great; in those with fine-grained clasts well-developed, they are stable and multiple in number, but smaller in thickness. In areas of the central basin, e.g. Linxian County of Shanxi, Fengfeng of Hebei, Feicheng of Shandong and Fengpei of Jiangsu, the number of limestone layers increases from 4−5 in the west to 10−14 layers in the east, and all the main coal seams are lying in the middle and lower parts of the formation. In the southern basin, the formation is dominated by limestone, intercalated with mudstone and thin coal seams, with minor coarse-grained clastic rock.

The formation contains abundant fossils, including fusulinids, corals, conodonts and plants. Among them the Fusulinids show various compositions in places. In the West Hill area of Shanxi, there are the two zones of Triticites simplex and Pseudoschwagerina in ascending order. The latter can be divided ascending into the Pseudofusulina pseudovulgaris, Dunbarinella nathorsti-D. nathorsti laxa, Schwagerina cervicalis and Pseudoschwagerina texana-Eoparafusulina obtusa subzones. In the Pexian area of northern Jiangsu, there is only the Sphaeroschwagerina zone, which can be divided ascending into the Rugosofusulina valida-Pseudofusulina firma and Boultonia gracilis-Schwagerina cervicalis subzones. In the areas such as Huaibei and Tangshan of Anhui, there is also the one Sphaeroschwagerina zone, which can be further divided into 2−3 subzones. In the Zibo area of Shandong, there is only the Pseudoschwagerina, which is divided ascending into 5 subzones. In northwestern Henan, there are ascending the Robustoschwagerina shanmianensis, Sphaeroschwagerina moelleri and Staffella zones. In the Junggar Banner of Inner Mongolia, there are ascending the Triticites-Oktaella and Staffella-Nankinella assemblage zones.

The formation contains three Coral assemblages, which are ascending: the Cyathaxonia orientalis-Lophocarinophyllum kousiense assemblage (found in the Jinci member), the Cyathocarinia maoergouensis-Amplexocarinia assemblage (found in the Miaogou and Maoergou limestones) and the Neokoninckophyllum tortum-Caninophyllum dobrolyubovae assemblage (found in the Dongdayao limestone).

The Conodonts consists of two assemblages ascending: (1) Streptognathodus elegantulus-Idiognathodus hebeiensis assemblage zone; (2) Streptognathodus elongatus-S. wabaunensis-S. fuchengensis assemblage zone.

The Plants belong to the early Cathaysia flora, consisting mainly of Neuropteris ovata, Lepidodendron posthumii, etc.

It is interpreted as a transgression succession on a coastal plain: When the formation was deposited, seawater transgressed to a large range, and later regressed gradually towards the south, southeast and northwest. Vertically, the marine-continental deposits gradually turned to continental deposits, and the climate from humid to arid. According to the variations of lithological features, grain size and thickness of the sedimentary rocks, it is inferred that the sedimentary environments from north to south were successively the alluvial fan, alluvial plain, distributary plain to tidal flat, and bay to littoral-neritic sedimentary systems. From the Yanshan Oldland to Daqingshan-Datong-Beijing it roughly belongs to the alluvial fan to alluvial plain sedimentary systems, and along Wushenzhao-northern Tianjin-Tangshan south of the line, it is of the distributary plain to tidal flat sedimentary systems, occasionally influenced by transgression. In the open range from south of the line to the Pingdingshan-Huainan areas, it is composed of tidal flat-bay-littoral plain deposits, and the southern part belongs to the epicontinental sea sedimentary system. In the bay area there is estuary-deltaic accumulation; in the open tidal flat zone are developed mixed sand-mud flat, sand flat and mud flat; in the littoral plain zone are also distributed longshore bar and distributary plain deposits.