Paleo-Wildfires and Their Paleoclimatic Effects in Early Permian Coal in the Southern North China Basin.

Abstract

Paleo-wildfires can help elucidate the transition trends of Earth from "icehouse" to "greenhouse," thereby allowing us to forecast the current changes associated with wildfires of this era. In this study, the early Permian Shanxi Formation in the Pingdingshan coalfield, located south of the North China Basin, was selected as a study site. Based on data on inertinite content, inertinite reflectance, nine polycyclic aromatic hydrocarbons (PAHs), paleo-wildfires, and their paleoclimate effect during the early Permian coal formation were systematically analyzed. The inertinite content in coal in the study area ranged from 9.76 to 29.65%, with an average of 19.32%. Meanwhile, the average inertinite reflectance values ranged from 2.41-4.74%, with an average of 2.75%. PAHs in the study area were mainly tricyclic and tetracyclic; the contents of fluorene, phenanthrene, pyrene, bypyrene, benzo[b]fluoranthene, and benzo[e]pyrene were higher than those of other PAHs in the same stratum. The total concentration of PAHs varied widely between layers (3601-21,894 ng/g). The presence of paleo-wildfires was confirmed by the contents of inertinite and PAHs. It can be concluded that paleo-wildfires in the study area were dominated by surface fires at low and medium temperatures based on the combustion equation. The oxygen content in the paleo-atmosphere of the Early Permian Shanxi Formation in the study area was 24.29%, which provided the necessary conditions for the occurrence of wildfires.