Search

• Petrology, δ13C and gypsum of coal corroborate alternating dry and wet periods. • The fine-scale variability in the δ13C signature was controlled by plant type. • δ13C values positively correlated with angiosperm/gymnosperm and % gypsum. • A high δ13C spike caps each of the four longer-term cycles of peat deposition. • The atmosphere had a significant influence on the peat formation in the basin. Coal contains detailed long-term records of contemporaneous environment, climate, and subsequent diagenetic processes. Stable isotopes of carbon, petrological, palynological, and mineralogical analyses were carried out on a 28 m thick low-rank Miocene coal seam from the Mile Basin, Yunnan Province, China for the purpose of deciphering the palaeoclimate and sedimentary conditions during peat deposition. The coal is characterized by both pale and dark lithotypes. Palynological analyses show that both lithotypes are dominated by angiosperms, which is interpreted to indicate a moderately warm climate. The absence of Fagus and Taxodiaceae pollen suggests that there may have been dry periods during peat accumulation; in general, both Fagus and Taxodiaceae require a constant wet environment in order to proliferate. Organic petrography, δ13C, and gypsum concentrations corroborate that there were alternating drier and wetter periods within the palaeomire during peat accumulation. The fine-scale variability in the δ13C signature appears to be controlled by plant type. Angiosperm/gymnosperm ratios and Vegetation Index are directly correlated with δ13C isotopic values. Plant type, however, seems to be proximally controlled by water level. Angiosperms were more dominant during times of lower water table or less moist conditions, interpreted to correspond to less negative values of δ13C. The correlation of greater concentrations of gypsum with less negative δ13C values also supports drier conditions. However, in addition to the fine-scale variability, four larger scale cycles are defined based on less negative δ13C values. A less negative δ13C isotopic signature demarcates the top of each of these cycles, which represent spikes of lower water table and/or drier conditions. In addition, a general correlation of the δ13C variations in the studied coal seam with atmospheric CO 2 suggests that the atmosphere also had a significant influence on peat formation in the Mile Basin. Although the Mile Basin palaeomire accumulated over a long time, an integrated approach to its analysis has demonstrated considerable variation in palaeoclimate. Changes in wetness/dryness had a direct effect on the ecological composition of the palaeomire. These floral changes would not have only been restricted to the palaeomire but most likely had a regional influence. Thus, detailed analysis of coals can yield useful, insightful and practical knowledge on past regional palaeoenvironmental conditions, which can then be placed within a global context. [ABSTRACT FROM AUTHOR]