Natural coal fires in the Kuznetsk Coal Basin: geologic causes, climate, and age

The paper summarizes data on the Pleistocene combustion metamorphic complexes of the Kuznetsk Coal Basin. Paralava and clinker samples are dated by 40Ar/39Ar incremental heating. The 40Ar/39Ar ages of the combustion metamorphic rocks permit reconstructions of the succession of renewed activity of ancient faults in the Salair zone and age estimates for the evolution of the present-day drainage network. Cross sections of burned rocks from the western margin and center of the Kuznetsk Basin are compared. The geologic factors of coal ignition risks are analyzed. On the western margin of the Kuznetsk Basin, paleofires occurred in steeply dipping thick seams with predominant crushed vitrain-clarain coal, which has a high oxygen and methane adsorption capacity. Highly denuded high-temperature combustion metamorphic complexes are most often localized in the arches of slightly broken anticlines. Oxygen was supplied to the coals during the Late Cenozoic renewed fault activity and the subsequent erosion of the sediments. The natural fires in the area were a result of external rather than spontaneous ignition. The depths of the paleofires (up to 200 m) indicate that they occurred in a warm and dry climate. In the center of the Kuznetsk Basin, dispersed fire foci appeared in seams of self-igniting coals with the erosion propagation of the current drainage network. The combustion metamorphic complexes here are partly eroded and consist mostly of clinkers with a low degree of alteration. The 40Ar/3(9)Ar ages and geological data indicate that the earliest large-scale combustion events on the western periphery of the basin occurred in the Eopleistocene (1.3-0.9 Ma). The oldest 40Ar/39Ar age of a coal fire episode (1.7 +/- 0.3 Ma) might be the upper age boundary of the altitude differentiation of topography, which corresponds to the renewed activity of the Tyrgan and Afonino-Kiselevsk faults. The later synchronous combustion events on the western margin (0.2 +/- 0.1 Ma) and in the center of the basin (0.13-0.02 Ma), most probably, occurred during the Kazantsevian interglacial, which gave rise to the present-day drainage network.