Widespread wildfires linked to early Albian Ocean Anoxic Event 1b: evidence from the Fuxin lacustrine basin, NE China

Wildfires are an important source of disturbances in the Earth’s system and are of great significance for understanding the interactions between environmental, atmospheric and vegetation changes over deep time. The early Cretaceous was a “high-fire” interval with frequent and widespread wildfires globally, but the timing and global significance of these wildfire events during this time remain uncertain. We undertook a multi-proxy study evaluating kerogen macerals, inertinite reflectance, and polycyclic aromatic hydrocarbons (PAHs) from mudstones to characterize wildfire activity in the Albian coal-forming Fuxin lacustrine Basin, and correlate these with (i) environmental and floral changes on land, and (ii) well-dated marine events including the early Albian Oceanic Anoxic Event 1b (OAE 1b), to consider their environmental and climatic significance. The presence of high inertinite contents demonstrate that multiple, widespread wildfire events occurred during the early Albian, which are correlated stratigraphically to the Kilian, Paquier and Leenhardt sub-events of the early Albian OAE 1b. Inertinite reflectance values ranging from 0.6% to 3.8%Ro show that wildfires in the early Albian were dominated by ground fires, with a smaller proportion of surface fires and almost no crown fires. Atmospheric oxygen concentration (pO2) levels, estimated from inertinite contents, attained ~25% during the early Albian, which exceeded the present atmospheric oxygen level of 21% and was able to support sustained combustion. Climatic conditions and frequent wildfire activity in the early Albian might have acted as an important control on vegetation distribution and diversification, which possibly further promoted the evolution of early angiosperms during the early Cretaceous. Wildfire activity resulted in the burning and destruction of both vegetation and soil structure, enhancing the post-fire erosion associated with intensified continental weathering under warmer and more humid conditions during the early Albian OAE 1b interval. These episodes of high wildfire activity correlate with high nutrients and organic matter levels in lakes and thereby contributed to eutrophication and anoxia in lacustrine and in contemporaneous oceanic systems.