Astronomically-forced wildfire control on high-latitude peatland carbon accumulation rate in the Middle Jurassic

Abstract

Peat has been a vital terrestrial carbon reservoir on Earth since the Devonian period, serving as a precursor of coal and impacting the global carbon cycle and climate change. The Jurassic is a typical greenhouse period in geological history, marked by the accumulation of numerous coal seams worldwide. However, the processes governing peatland carbon accumulation during this period remain poorly understood. In this study, we focus on the ∼60.9-m-thick No. B2 coal seam of the Middle Jurassic Xishanyao Formation in the high-latitude Junggar Basin, NW China. Time series analysis of natural gamma logging data reveals a sedimentation rate of ∼2.3 cm/kyr and a duration of ∼2.6 Myr for the coal seam. By considering the carbon loss during coalification, the carbon accumulation rates of peatland were 41.10–52.74 g C/m²·a, showing a gradually decreasing trend from the bottom to the top of the coal. The high inertinite content in the coal exhibits typical charcoal characteristics, indicating frequent peatland wildfires. The strong negative correlation between carbon accumulation rate and inertinite abundance suggests that frequent wildfires have reduced the carbon accumulation of peatlands. Spectral analysis indicates that peatland carbon accumulation rates may be regulated by wildfire activity linked to 405-kyr orbital cycles. This study offers novel insights into the influence of wildfire activity on organic carbon burial in the Middle Jurassic peatlands.