Evidence for widespread wildfires and their environmental impact in the Late Cretaceous Canadian Arctic

Abstract

Wildfires are important in modern ecology but the complex interplay between wildfires and vegetation or climate is less well understood in ancient environments, in particular those of the Arctic regions. This includes the impacts of paleo-wildfires on surrounding marine basins by affecting sedimentation rates and nutrient input via soil degeneration and intensification of continental run-off. The Late Cretaceous was an important time of global climate shift, with the rise of angiosperm vegetation marking a turning point in global flora, and globally abundant wildfires due to high atmospheric oxygen levels and elevated temperatures. This study investigates Late Cretaceous samples from the Canadian Arctic Islands to examine the evidence for widespread wildfires and how these wildfires may have influenced or been influenced by contemporaneous climate and vegetation shifts. Organic geochemical, and organic petrological data show evidence of enhanced wildfires beginning in the Turonian, including increases in semi-fusinite macerals and pyrogenic PAH (polycyclic aromatic hydrocarbon) indicators of natural combustion. This increasing wildfire influence corresponds with a rise in broad-leafed Arctic forests, as evidenced by angiosperm-derived terpenoid biomarkers, with both wildfire and angiosperm abundances peaking in the Early Campanian. Additionally, geochemical and petrographic data shows a shift in the type of organic matter deposited over time, correlating to the evidence of increased wildfire activity. This study proposes that the distance between wildfire region and marine depocenter is assessed via a new provenance method based on the degree of photo-oxic degradation of selected PAH isomers upon airborne transport. The increasing effects of wildfires on the Arctic ecosystem over the Turonian-Campanian were likely driven by relatively warm temperatures, elevated atmospheric oxygen, volcanism related to the High Arctic Large Igneous Province (HALIP), and abundant fuel availability. Widespread wildfires are proposed to have fostered the expansion of angiosperm vegetation into the Canadian Arctic in the Late Cretaceous by allowing them to outcompete gymnosperms in post-fire regrowth. Intensified erosion and continental run-off associated with the destruction of the vegetation cover by wildfires is thought to have acted as a driving force in the increasing terrigenous organic matter deposition in the Sverdrup Basin during the Late Cretaceous. Taken together, the results of this study suggest that increasing wildfires related to global climatic conditions in the Late Cretaceous contributed to the expansion of angiosperm flora in the Arctic, and had a substantial impact on the deposition of sediments in the surrounding Sverdrup Basin.