Petro-chemical characterization and depositional setting of a late Permian high ash coal deposit, Central Mongolia

Abstract

Pan global Permian coal measures are unique in the evolution of the Earth, not matched in any period before or since. Middle and late Permian coal-bearing strata are widely distributed in Mongolia. In particular, a large concentration of transtensive coal-bearing sub-basins is located in southern Mongolia, some of which are well documented. However, the late Permian coal measures developed along the shores of the Mongol-Transbaikalian Seaway in central Mongolia, the focus of this contribution, has received very limited attention. This study focuses on the c. 420 m thick coal-bearing middle part of a c. 2,600 m thick Permo-Triassic succession in the Bayanjargalan district. The study draws on data from 38 drillholes, 3 km of trenches, mapping, petrological analysis of sandstone samples, analysis of macroflora, fauna and trace fossils, 82 coal quality samples as well as washability and ash XRD analysis from a 3t coal bulk sample. The unstable and wedge-shaped architecture of the coal seams strongly suggest a syn-tectonic influence on their development. Paleoclimatic indicators suggest the peat mire ecosystem developed during relatively cold - temperate climatic conditions. Peat-forming plants such as Cordaites, Rufloria and Koretrophyllites probably benefited from moist air currents along the seaway. Plant-arthropod interactions are reported from two sites, in particular DT228 and DT246 oviposition lesions, the latter being almost twice the size of a previous report from North America. Results from 82 proximate analyses returned consistent very high ash yields of 46.95% (db) and 43.45% (adb) from the 3t bulk sample, which are unusual for Permian coals in Mongolia.