GRAIN-SIZE DISTRIBUTION FEATURES AND SEDIMENTARY ENVIORNMENTS OF THE SANDSTONE BODIES OF CARBONIFEROUS-PERMIAN SYSTEM IN NORTH CHINA

On the basis of the grain size analysis of thin sections from the drills and exposures, the sedimentary enviornments of C-P of the region on the south of the line of Tangshan, Beijing and Taiyuan are mainly studied. The sediments and grain size in the studied region vary thiner and corser from the north to west, thicker and finer the north to east. The sediment is mainly from the Yinshan Old-land. The sorting of grain-size is medium or better. The values of standard deviation and skewness of grain-size put on Friedman's scatter diagram show a fluvial environment from Lower Shiqianfeng Formation to Upper and Middle Taiyuan Formation and a littoral enviornment from Lower Taiyuan Formation to Benxi Formation. According to the distribution features and change patterns of curves of frequency and probability of gain size, C-M patterns and parameters of grain-size (mean grain-size, standard deviation, skewness and leptokurtosis), some sedimentary sub-environments are determined such as braided channel on alluvial fan, braided channel of upper and middle river, braided-meandeting channel, meandering channel, delta and shore, tide flat and lagoon. By the sedimental models, the conclusion can be given as follows; the sedimentary environment is marine in the early Middle Carboneferous, shore and tidal flat and lagoon in the middle Middle Carboneferous, littoral delta in the middle Later Carboneferous, distributary plain of delta in the early Early Permian, meand-ring river on the north of the line of Zhengzhou-Puyang-Jinan and distributary plain of delta on the south of that in the later Early Permian, braided-meandering river on the north of the line of Zhengzhou-Xuzhou and distributary plain of delta on the south of that in the early Later Permian.