This paper is the result of coalfield geological survey engineering.
[Objective]Wildfire is an important part of the earth system. The greenhouse gases produced by combustion will have an impact on the climate and the biosphere. One way to obtain information about the potential long term influences of wildfires on ecosystems and the climate system itself is to study palaeo-wildfires.[Methods]A total of 56 Jurassic coal samples from 5 main coal seams were collected from Northern Ordos Basin. The samples were analyzed by macropetrography, microscope, scanning electron microscope in order to study the evidences of wildfire and their impact on the paleoclimate.[Results]The results showed that a great deal of charcoal has been found in the roof and floor of the middle Jurassic coal from Ordos Basin and the cell walls of charcoal observed under SEM were homogenized. The average proportions of inertinite in the coal samples ranged from 45.23% to 56.81%, and the reflectance of most inertinite in coal is less than 2%, which indicated that the frequency wildfires occurred during the peat deposition period and the fires type were dominated by surface and ground fires with low temperature.[Conclusions]According to a carbon emission model for modern forest fires, the total carbon and gas emissions from wildfires in peat swamps of the Middle Jurassic in Northwest China were calculated. The total carbon released from peat-swamp forest wildfires was at least 443 Gt, corresponding to emissions of CO₂, CO and CH₄ of 1377 Gt, 86.7 Gt, and 8.26 Gt, respectively. The large amount of greenhouse gases released by wildfires may lead to changes of the atmospheric, which may have accelerated the process of climate warming in the Middle Jurassic.
Highlights: Paleowildfire events occurred frequently in the early Middle Jurassic in Ordos Basin and the main types of wildfires were surface fires and ground fires; The total carbon released by wildfires in the early Middle Jurassic in Ordos Basin reached at least 443 Gt, which might have affected the paleoclimate.