Spatial distribution pattern and sedimentary process of black carbon

Black carbon is direct evidence of ancient wildfires. However, its identification, genetic types, and sedimentary models have not been thoroughly investigated. This study takes the Triassic-Jurassic Haojiagou Section in the southern margin of Junggar Basin as example for analysis. We identified micro black carbon (micron level) and macro black carbon (mm level and above) in continental coal-bearing basins through field geological survey, float-and-sink experiment, sedimentology and coal petrological analysis. While micro black carbons were formed in situ from the incomplete combustion of organic matter in peatlands, most of macro black carbons underwent the process of transportation, whose spatial distribution followed sedimentary differentiation. They could be classified into 4 types: dispersed, aggregated, trunk, and mixed type. Wind and water flow were the main geological forces controlling black carbon deposition: dispersed black carbon was influenced by both wind and water flow; the aggregated type, such as concretion, lens-shaped, and fan-shaped black carbons, were closely related to channel migration and accommodation space changes; the trunk-type black carbon often distributed at the bottom of the river channel under the reducing accommodation space while mixed black carbon was formed by the superposition of different ancient fire intensities and gravity flow involving particle mixing. This analysis on spatial distribution pattern and sedimentary process of black carbon sheds new light on the reconstruction of the paleoenvironment and paleoclimate during ancient wildfires.