XISHA ARCHIPELAGO

Taking Huolinhe Basin as an example, this paper has discussed, according to the criteria required by basin analysis in sedimentation, tectonics and coal formation, the principles emoloyed in compiling paleoenvironmental map of coal measures of terrestrial facies, the choosing of map unit, classification of sedimentary environment, methodology of map compilation and the application and interpretation of the results. The unit for the paleoenvironmental map is equivalent to a bed deposited during a short time and can be distinguished from the overlying and underlying sedimentary beds by its composition, characteristics and genesis. Included in this paper are 18 paleoenvironmental maps of coal seams and their basal sandstone in the lower coal measures (200-600m in thickness) of Late Mesozoic Huoliuhe Group which consist of 5 coal sets and 9 main coal seams (equal to 9 coal-bearing cycles). The bases for the compilation of these maps are as follows;!) Different sedimentary environments have different macrocosmic environmental features including lithotype (lithof acies),vertical sequence,shape of the sedimentary rock bodies and lithogenetic index.2) Vertical variation of lithofacies results from horizontal shifs of neighboring sedimentary environments in accordance Walther Law. 3) Determination of the genesis of sandstone and/or conglomerate with bodies as a depositional fremework of a basin is the key to the analysis of other sedimentary environments. In compiling paleoenvironmental maps quite a few engineering control points are needed to distribute evenly in the basin. The general procedures for the compilation are: 1) Compilation of sedimentary section maps at certain intervals. 2 ) Analysis bof these maps and determination of map unit. 3) Compilation of lithotype distri-ution maps about successive beds. 4 ) Compilation of paleoenvironmental maps using the distribution maps as base maps and by comprehensive analysis of each bed's paleoenvironment. Determined in Huolinhe Basin are 8 different paleoenvironments the most important of which are shallow lacustrine, alluvial fan and swamp paleoenvironments. The others are lacustrine delta, river, fan delta and deep lacustrine paleoenvironments. The comprehensive analysis of the paleoenvironmental maps shows 1 ) Lithotype distributes and varies regularly during the formation of the lower coal measures.2) There is a distinct spacial zonation of sedimentary facies in the basin and 3 sedimentary facies zones change periodically in width as time goes by. 3) Generally speaking, the area and intensity of coal formation vary vertically from small (weak) to large (strong) and then vice versa. 4)Judging from the changing width of the alluvial fan norihwest of the basin, it can be co ncluded t hat at least 9 relatively intense periodic tectonic movements occurred in the basin in the formation of the lower coal measures.