Late Triassic charcoal from Petrified Forest National Park, Arizona, USA

Fossil charcoal has been found in the Late Triassic Chinle Formation in Petrified Forest National Park, a location that is world famous for its silicified tree trunks. The material consists of charcoalified secondary wood, and has sufficiently well preserved plant anatomy to show it may be described as ‘araucarian type’, although it does display some minor differences from the anatomies described for the silicified gymnosperm trunks in the park. The presence of the charcoal proves that on occasion natural wildfires, most probably ignited by lightning, must have occurred in the Chinle Triassic palaeoenvironments, with resulting impacts on the biota of those times. It is currently impossible to estimate how often these fires occurred, as the incidence of charcoal here and in the whole fossil record apart from the frequency of ancient fires also reflects the preservation and burial conditions of the material. There is scant mention of Triassic charcoal in the literature, a notable absence given the abundance of charcoal that has been recorded in the Carboniferous, Jurassic, and Cretaceous periods. This lack of charcoal may support the theory that atmospheric oxygen levels were lower during the Triassic than in the Carboniferous.