Search

Coupling carbon and nitrogen isotopes and petrography of coals and related intra-seam carbonaceous mudstone partings from basins in northern China provides insight into regional palaeoenvironments and palaeoclimate during the late Carboniferous–early Permian. The carbon isotopic composition (δ 13C coal , VPDB) of coal samples from the Taiyuan and Shanxi formations of Qinshui and North China-Bohaiwan basins ranges from −25.3‰ to −22.7‰, with an average of −23.7‰. The average δ 13C coal value is −23.6‰ in the late Carboniferous, −23.4‰ in the early Permian and −23.5‰ in the mid–early Permian. By contrast, equivalent early Permian coals in the southern North China-Bohaiwan Basin to the east were found to be significantly more negative at −25.2‰, likely as a function of regional aridity changes. Related δ 15N in coal seams ranges from +2.3‰ to +4.7‰, with an average of +3.7‰. Within the thick, economically important #15coal seam of the Qinshui Basin, δ 15N coal is significantly more negative than δ 15N in mudstone partings (avg. +7.1‰), implying that the coals underwent a stronger degree of microbial degradation during peat formation. δ 15N of mudstone partings varies stratigraphically, with significantly more positive δ 15N (+8.1‰, +8.3‰) for the lower partings and lower δ 15N (+4.8‰) for the upper parting. This may reflect varying degrees of microbial activity, but could reflect higher thermal maturity in the upper part of the seam as indicated in the coal rank profile. δ 13C coal in this region was used to calculate the carbon isotopic composition of atmospheric CO 2 (δ 13C a). Calculated δ 13C a ranges from −6.0‰ to −3.4‰, with an average of −4.5‰, which is more positive than the δ 13C a of modern atmospheric CO 2 (−8.5‰, Graven et al., 2017). Two δ 13C a excursions are noted: a positive one (magnitude 3.7‰) in the late Carboniferous and a tentative negative excursion (magnitude 6.0‰) in the mid–early Permian. The positive shift coincided with a sea-level transgression in the Qinshui Basin. The rise in sea level may have led to the burial of more terrestrial plant debris that decreased photosynthesis and enriched atmospheric CO 2 in 13C. More data are needed to understand mid-early Permian variation in δ 13C, as this could reflect a regional aridity or humidity effect rather than a global signal. Unlabelled Image • C and N isotope analysis of major coal seams in the Taiyuan and Shanxi formations. • Results compared with the existing terrestrial δ 13C org curve for northern China. • δ 13N coal offers insights on short-term environmental changes and microbial activity. [ABSTRACT FROM AUTHOR]