Linking palaeo‐wildfire to depositional environmental and ecological dynamics of an Early–Middle Pennsylvanian fluvial‐tidal transition zone—Palynology and pyrolysis evidence

Abstract Pennsylvanian time was characterised by widespread transgressive depositional systems that spanned non‐marine to fully marine environments across the North American midcontinent. This study presents new palynological and Rock‐Eval pyrolysis data from 113 samples from five cores in the northern Forest City Basin within a depositional‐environment framework previously published which integrated a wide range of physical, chemical and biogenic attributes. A total of 153 palynomorph taxa were identified and we interpret depositional environments within a Palaeozoic hydrosere framework. Swamp forest assemblages are dominated by arborescent lycopods (~40%), sub‐arborescent lycopods (~15%) and ferns (~25%), with gymnosperms and sphenopsids each composing <10% of the population. Kerogen analyses reveal abundant charcoal, and the ratio of elongated to detrital charcoal decreases upwards from the Kilbourn Formation to the Swede Hollow Formation, reflecting both spatial and temporal changes in wildfire occurrence and charcoal transport processes. Rock‐Eval pyrolysis of 30 samples confirms dominantly terrestrial organic matter with Type III and Type IV kerogen. The prevalence of Type IV kerogen and abundant charcoal fragments point to frequent palaeo‐wildfires. Stratigraphically, the Kilbourn Formation represents the wettest interval, whereas the overlying Kalo and Floris formations record increased representation of fluvial floodplain and upland assemblages, indicating drier climatic intervals. The Swede Hollow Formation marks a partial return to wetter conditions, coinciding with renewed marine influence recorded by the Oakley Shale. Collectively, these results reveal that the Early–Middle Pennsylvanian landscape of the Forest City Basin was a complex mosaic of swamp forest, floodplain and fluvial upland environments influenced by climatic fluctuations, base‐level changes and periodic wildfire activity. The integration of palynological and geochemical data provides the first detailed reconstruction of ecosystem gradients and wildfire patterns across this midcontinent basin, highlighting its role as a key sediment transfer zone and ecological link between continental and marginal marine systems during Pennsylvanian time.