THE FORMATION OF INERTINITE-RICH PEATS IN THE MIDCRETACEOUS 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, nort heastern 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 excl usively fire-derived, suggesting that fire was a relatively common occ urrence in the original peat-forming wetlands. Inertinite enrichment i n the Gates coals appears to have resulted from preferential destructi on of vitrinite precursors by either low temperature decomposition pro cesses or burning, rather than by formation of inertinite by a microbi al process. The position of the Gates Formation depositional setting e ast 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) composit ion within some of the seams is primarily attributed to climatic varia tions, although variation in subsidence rates could also have been res ponsible.