The Yan′an Formation in the Ordos Basin is an important coal-bearing stratigraphic unit. In order to investigate its coal quality characteristics and coal-forming environment, in this study, by selecting coal and mudstone samples from the Yan′an Formation in the northern and southern parts of the Ordos Basin as research subjects, through analyses of major elements, trace elements and rare-earth elements of samples, and the industrial (proximate) analyses of coals, we have exploreed the quality characteristics of coals and the paleoenvironment of the coal-bearing strata in the Yan′an Formation. The results show that coals of the Yan′an Formation in the northern Ordos Basin are characterized with medium-high to high contents of volatile matter, ultra-low to low contents of ash, low to moderate contents of total moisture, ultra-low to low contents of fixed carbon, and ultra-low to low contents of sulfur. Paleoenvironmental indicators indicate that the intensive chemical weathering occurred under the predominantly warm and humid climate during the deposition stage of the Yan′an Formation in both the southern and northern parts of the Ordos Basin. The water system during the coal-forming stage of the Yan′an Formation of the northern Ordos Basin was mainly in oxic to suboxic environment, whereas that of the southern Ordos Basin was mainly in suboxic to anoxic environment. This paleoenvironmental difference between the northern and souther parts of the Ordos Basin was mainly controlled by the uneven subsidence of the basin during the Yanshanian orogeny. The coal and mudstone sediments of the Yan′an Formation in both the southern and northern parts of the Ordos Basin were mainly sourced from sedimentary rocks and granitic felsic rocks in the Yinshan and Daqingshan areas on the northern margin of the Ordos Basin, with the provenance in the continental-margin tectonic setting. This study is of important significance for exploring the coal-forming environments of the Yan′an Formation in the northern and southern parts of the Ordos Basin.
REN et al. (Thu,) studied this question.