The formation of inertinite-rich peats in the mid-Cretaceous Gates Formation: implications for the interpretation of mid-Albian history of paleowildfire

Image analysis and standard point-count petrographic data are used to interpret the amount, source and variation of inertinite in coal seams of the mid Cretaceous Gates Formation, Rocky Mountain Foothills, northeastern British Columbia. Inertinite on average is abundant (between 40–60% by seam by volume, and higher in some zones), and within seams fluctuates cyclically. The inertinite is interpreted to be almost exclusively fire-derived, suggesting that fire was a relatively common occurrence in the original peat-forming wetlands. Inertinite enrichment in the Gates coals appears to have resulted from preferential destruction of vitrinite precursors by either low temperature decomposition processes or burning, rather than by formation of inertinite by a microbial process. The position of the Gates Formation depositional setting east of the rising Canadian Cordillera is interpreted to have resulted in overall drier conditions in the region, and periodic drought in the wetland settings. Cyclic variation in inertinite (vitrinite) composition within some of the seams is primarily attributed to climatic variations, although variation in subsidence rates could also have been responsible.