THE PRELIMINARY STUDY ON THE SEDIMENTARY ENVIRONMENT OF TAIYUAN FORMATION OF UPPER CARBONIFEROUS IN PINGXI MINING DISTRICT OF QINSHUE COAL FLELD IN SHANXI PROVINCE

The Pingxi mining district is located in the eastern part of shanxi province and in the northeastern margin of Qinshue Field. It is a large one which is being built, its area is about 336.5km². The age of the coalbearing formation is Permo- Carboniferous.This paper probes into the sedimentary environment of Taiyuan Formation in this area. Taiyuan Formation is one of the main coal-bearing formations in this area, which mainly consists of grey and dark-grey limestones, argillites, sandy-argillites, siltites; light-grey and grey-yellow sandstones and coal seams, being about 120 mthick. By the analysis of vertical sequence, Hthologic characteristics, sedimentary structure feature of grain size distribution, trace elements, fossils, sand-body geometry shape and paleocurrent, Taiyuan Formation in this area is considered to be a set of the coal-bearing deposits represented by thd deltas, tidal flat and subtidal carbonate sediments, which occurred in the margin of Hua-bei Epicontinental Sea during the Late Carboniferous. The lower part of Taiyuan Formation is represented by sediments of a tidal system, while the middle and upper part of Taiyuan Formation are composed of sdeiments of the deltaic system. Two basic kinds of deltas have been recognized in this area, namely, high-construction lobate delta and high-destructive tide-dominated delta. There are three limestone seams in Taiyuan Formation, namely "Sijieshi" "Qianshi", and "Houshi" limestones, which are much like in lithologic characteristics and consist mainly of bioclastic micrites. The analysis of paleoenvironments shows that these limestones in this area are carbonate sediments formed in the subtidal low-energy zone.