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Abstract Evidence of fire in the Middle Devonian remains globally scarce. Charcoalified mesofossils recovered from the Emsian–Eifelian Trout Valley and St. Froid Lake formations of Maine are direct evidence of wildfires proximal to the Acadian Orogen, formed as the Avalon terrane and the North American plate collided. These mesofossils include charred psilophytes, lycopsids, prototaxodioids, enigmatic taxa such as Spongiophyton, and coprolites. Here, fire combusted a senesced and partially decayed litter, and the intimately associated nematophytes, following a period of extended dryness. We envisage wildfires occurred during neap tide when exposure of the flora of this estuarine setting was prolonged. Herein we provide a reconstruction of this Middle Devonian landscape and its flora in which lightning generated by post-dry season storms ignited wildfires that propagated through an extensive psilophyte-dominated litter. 

Little evidence of macrofossil charcoal, a wildfire proxy, is recorded from upper Lower to lowermost Upper Devonian rocks. Coals of this age are few, and petrographic data indicate low volumes (<10% mineral-matter free) of charcoal. This paucity of data forms the basis of the “charcoal gap,” which is used to suggest an extended interval of abnormally low atmospheric oxygen (pO2). We reassess the current evidence for this hiatus using Emsian−Eifelian charcoal from the Trout Valley and St. Froid Lake Formations, Maine (northeastern United States), and integrate the microscopic charcoal record of dispersed organic matter. We conclude there is ample evidence of fire in the Middle Devonian. This interval is not innately of low pO2. Rather, it is one in which under-interpretation of available data has led to a perceived paucity of charcoal. This reconciliation indicates the Phanerozoic record of wildfire was substantially uninterrupted. Hence, we propose that pO2 achieved levels >16% and remained at such levels from the Silurian through the floral and faunal colonization of land and, from our current estimates, stayed as such until the present. 

Tournaisian-age failure of marginal lacustrine sediments, and their bulk collapse into an inland rift-basin lake in the Moncton Subbasin, Canada, led to the entrainment of rare, almost complete, three-dimensionally preserved non-woody trees. Preservation of these unique fossils from the Albert Formation was a consequence of contemporaneous seismicity. Synsedimentary structures include an array of soft-sediment deformational features and a field of cross-cutting sand boils indicating multiple seismic shocks >4.6 Mw. This tectonically controlled event, entombing trees whose novel growth form is both evolutionarily and ecologically transitionary and unlike other Paleozoic plants, is a one-off in the paleobotanical record. 

The earliest evidence of wildfire is documented from two localities: the early mid-Silurian Pen-y-lan Mudstone, Rumney, Wales (UK), and the late Silurian Winnica Formation, Winnica, Poland. Nematophytes dominate both charcoal assemblages. Reflectance data indicate low-temperature fires with localized intense conditions. Fire temperatures are greater in the older and less evolved assemblage. These charcoal assemblages and others, new and previously documented, from the Silurian and earliest Devonian are compared to box models of atmospheric oxygen concentration (pO2). Based on modern charring experiments, these data indicate pO2 is divergent from the broad trends predicted by the COPSE-revisited and GEOCARBSULFOR models. Sustained burns require a minimum pO2 threshold of 16%, or ~0.75 present atmospheric level. This threshold was first met and, our charcoal data indicate, was exceeded in the mid-Silurian and then, later in the Silurian, attained again repeatedly.