Stratigraphic distributions of biomarkers and carbon isotopes in coals constrain the Permo-Carboniferous climatic changes and floral turnovers in the north China block

Theintricate relationship between climate and vegetation dynamics, particularlyduring the late Paleozoic ice age marked by multiple icehouse-greenhousetransitions, is a compelling aspect in Earth's historical narrative. In thisstudy, we decipher the interactions between the Permo-Carboniferous climatefluctuations and floral turnovers within the North China Craton, based on thestratigraphic distributions of biomarkers and carbon isotopes from cored coalsin Huainan coalfield, North China. Our findings reveal that the changes inn-alkane, terpane, sterane, and polycyclic aromatic hydrocarbon (PAH)distributions result from a confluence of maturation, depositional environment,and organofacies effects. Molecular maturity-sensitive ratios align with thematurity stage determined by Rock-Eval pyrolysis and petrography, categorizingthe coals as high volatile bituminous A/B with a composite organic matterderived from terrestrial plants and marine algae. Notably, the18α-22,29,30-trisnorneohopane (Ts) to 17α-trisnorhopane ratio (Ts/(Ts + Tm)),as well as C₃₁–C₃₄ 22S/(22S + 22R) hopanes and C₂₉ 20S/(20S+ 20R) steranes ratios exhibit moderate correlations with %R_o, indicative of epimerization reactions induced bymaturation processes. The stratigraphic variations in pristane to phytaneratios (Pr/Ph), Pr/n-C₁₇, Ph/n-C₁₈, C₃₀ αβ/(αβ+βα)hopanes, and organofacies sensitive PAH indices collectively capture apaleoenvironmental shift from reducing to oxic conditions attributed to marineregression. The systematic changes in PAH concentrations and their maturityindices reflect condensation and dealkylation reactions during the maturationprocess. The δ¹³C signature manifests a negative excursion incoals of the Artinskian Shanxi Formation and a subsequent positive excursion inthe Capitanian Upper Shihezi Formation coals, respectively, reflecting changesin the δ¹³C values of contemporaneous atmospheric CO_₂ in response to regional aridity fluctuations. Copyright © 2023Elsevier Ltd. All rights reserved.