Orbital-scale climate dynamics impacts on Gzhelian peatland wildfire activity in the Ordos Basin

Abstract. The Carboniferous, an important coal-forming period in geological history, was characterized by extensive vegetation and high oxygen levels. Numerous wildfire evidence suggests that high frequency of wildfire occurred at that time, specifically in peatlands. However, the control mechanisms for changes in wildfire activity in peatlands during this period are still not clearly understood. In this study, evidence from the Gzhelian in the Ordos Basin, such as the inertinite/vitrinite (I/V) ratio, indicated the existence of different frequencies of wildfire activity at that time. The CaO/MgO and CaO/MgO • Al₂O₃ climate indicators revealed that high-frequency wildfires mainly occur in warm and humid climates. Based on former age constraints, we deduced that orbital cycles (long eccentricity) controlled the climate influence on peatland wildfires during the Gzhelian. When eccentricity was high, abundant sunshine and frequent rainfall led to warmer and more humid peatlands. The latter environments were more favourable for vegetation development, leading to increased fuel loads, which in turn led to more frequent wildfires. Moreover, the Gzhelian global wildfire records, showed that evidence of wildfire during this period was mainly located in areas with abundant tropical vegetation, supporting the view that wildfire activity during this period was mainly controlled by the fuel loads. Although Hg could be produced by peatland wildfires, but our results show that Hg was mainly from frequent volcanic activity during this period.