A PRELIMINARY STUDY ON SEDIMENTARY ENVI- RONMENTS AND LAW OF COAL-BEARING FORMATION IN YANGQUAN,SHANXI

The Yangquan coal distrct is located in the eastern part of Shanxi. It's area is about 275 km² and coal resources are rich there. It is one of the main coal bases in China. The main coal-bearing formations in this area——Taiyuan Group and Shanxi Formation are of Permo-Carboniferous in age. The Carboniferous Taiyuan Group which consists mainly of grey and dark-grey limestones, argillites, sandy-argillites, sandstones, tuffs, tuffites and coal seams, is about 120m in thickness. It contains 4 -9 coal seams, and the Coal Seam No. 15 at the bottom of this group is the main mai-nable one. The Permian Shanxi formation overlaying Taiyuan Group in succession is about 65 meters in thickness and is composed mainly of grey sandstones, dark-grey sandy-argillites, argillites, carbonaceous shales and coal seams. There are some lens of limestones in the lower part of the formarion. Shanxi Formation contains 6 coal seams, the No. 3 of which in the main minable one. The present study shows that the coal-bearing series at the Permo-carboniferous in this district mainly consists of coastal plain, delta and interdelta deposits. The Lowe- Upper Carboniferous in this district like the Upper-Middle Carboniferous is also characterized by gulf depositions. The coal district is located at the northern margin of the gulf. The foreshore spread toward south as sea water regressed southward, and the kj sheet sandstone body deposited, above which siltstones deposited succesively at tidal flat and the Coal Seam No.15 was formed in the peat swamp. Since the Coal Seam No.15 was formed in the brackish-water swamp at the coastal plain, the swamp for the accumulation of coal materials was spacious and stable for a long time, thus the thick and stable coal seam was formed in extensive area. As the environment, in which the coal was formed, was influenced largely by sea water or brackish water, the ash content of the Coal Seam No. 15 is low and the sulphur content is high. After the Coal Seam No.15 had been formed, this region was transgressed by the sea and the "Sijieshi" limestone deposited, above which subsequently, an up- ward coarser deltaic deposition sequence was formed, and there occurred a sea invasion afterward, thus the "Qianshi" limestonewas deposited. Between "Qianshi" and "Houshi" limestones are interdelta deposits. The deposits between the top of "Houshi" limestone and the Coal Seam No. 8 are formed in the shallow water delta. The section from the Coal Seam No. 8 to the bottom of Shanxi Formation is represented by an intact series of delta deposits. Shanxi Formation is composed of delta deposits developed succesively from the top of Taiyuan Group, which is represented by the prodelta and delta-front deposits. The deltaic depositional series also underwent a process of construction-destruction-construction. The section from the roof sandstone of the Coal Seam No. 6 to the Coal Seam No. 3 is made up of destructional delta deposits. After the accumulation of the roof sandstone of the Coal Seam No. 3 , the delta was under the constructional stage and accumulated deposits of distributary river channel, natural levee, burst-fan, valley flat and flood lake. The Coal Seam No. 3 of Shanxi Formation was formed at an abandoned delta flower which is a main minable seam. The stable environment continued to exist for a long time, thus providing an ideal space for accumulation of the Coal Seam No. 3, which was formed in an extensive area. To sum up, all the above-mentioned suggests that the deposits of Shanxi Formation are not "pure continental" as considered by most geologists in the past.