Widespread paleowildfire records in the Middle-Late Pennsylvanian and their implications for environmental change during the late Paleozoic Ice Age

Abstract

The Middle-Late Pennsylvanian represents a peak “high-fire” period within the late Paleozoic Ice Age (LPIA), characterized by bidirectional feedback between paleowildfires, terrestrial ecosystems, and climate dynamics. To resolve interactions among wildfire regimes, vegetation evolution, and LPIA climate during the Middle-Late Pennsylvanian, this study integrates petrographic analysis of Benxi Formation coals (Middle Pennsylvanian) from the eastern Ordos Basin (4.0–44.6 % inertinite content, inertinite reflectance values of 1.78–3.08 %, and surface-fire dominance) with global Middle-Late Pennsylvanian inertinite databases. Results demonstrate that global fire intensified from Middle (15.2 % mean inertinite) to Late Pennsylvanian (23.7 %), with spatial migration of fire prevalence from Euramerica-dominated to North China-dominated alongside enhanced mid-high latitude burning. Elevated atmospheric oxygen levels (23.6–24.9 %) facilitated substantial greenhouse gas emissions from paleowildfires (238.1–297.7 Gt CO₂ in Middle Pennsylvanian; 92.9–185.6 Gt CO₂ in Late Pennsylvanian). Synergistic amplification of paleowildfire activity was driven by aridification, elevated atmospheric oxygen, fire-adapted flora expansion, and continental-scale floral restructuring (Cathaysian rapidly growing, resin-rich lycopods and thicker-cuticled pteridosperm leaves, Euramerican xerophytes, Angaran cordaites, Gondwanan glossopterids). Middle-Late Pennsylvanian ice cap dynamics were regulated by coupled wildfire-vegetation-climate interactions. During the Moscovian, wildfire and volcanic carbon emissions were counterbalanced by coal forest expansion, charcoal burial, and enhanced weathering, sustaining low pCO₂ and glacial conditions. Conversely, Kasimovian-Gzhelian wetland contraction, reduced weathering, and persistent wildfire/volcanic emissions elevated pCO₂, initiating widespread deglaciation. This study will enhance our understanding of paleowildfire patterns during the Middle to Late Pennsylvanian, and their relationship to LPIA climatic dynamics and floral evolution.