Variability in coal facies as reflected by organic petrological and geochemical data in Cenozoic coal beds offshore Shimokita (Japan) - IODP Exp. 337

Elevated sulfur contents and high ash yields occur in the upper seams (cores 14R to 18R) whereas low sulfur contents and varying ash yields were determined for the lower coal seams (24R to 30R). The maceral composition and biomarker ratios of the uppermost seams argue for coal formation in a paralic environment and brackish, alkaline water conditions. In contrast, lignite samples from the lower part of unit III point to a limnic-fluviatile deposition. Conifers contributed significantly to peat formation in the uppermost seams (from cores 15R to 22R) and in the lowermost lignite seam. In all other samples, angiosperms are considered as the major peat-forming plants. The pollen and spore floras indicate rich angiosperm vegetation, however significant contributions from Pinaceae and Taxodiaceae are evident for all coals. Sporophytes have no dominant influence on the coal flora. Microbial activity in the peat is suggested for instance by higher concentrations of hop-17(21)-ene with increasing contents of hopanes or by low δ13C values of hop-17(21)-ene. The revealed changes in the environment during coal deposition highlight the importance of combined organic petrography, organic geochemistry and palynology to reconstruct palaeoenvironmental conditions.