TERRESTRIAL-MARINE LINKAGES: RECORDS OF DEVONIAN CHARCOAL, FIRE, AND PALEOATMOSPHERIC OXYGEN LEVEL

Fossil charcoal in the geologic record provides evidence for fire events that, in turn, may have implications relative to terrestrial ecosystems and atmospheric evolution. Much of the fossil charcoal record involves known terrestrial or near-shore environments and shows earliest occurrences of fire in the Pridolian (Late Silurian), with fire events increasing throughout the Late Devonian and into the Carboniferous. Reflectance analyses of charcoals from two well-established Upper Devonian (Famennian 2c) lowland sites (Red Hill, PA, and Elkins, WV) indicate that these fires were moderately hot (around 550^oC) and burnt mainly surface vegetation dominated by pre-ferns and lycopsids, rather than being produced by crown fires in forests. Charcoal from these fire events accumulated in lowland and near-shore environments, but may also have been transported by wind or water into basinal marine environments. Fragments of fossil charcoal have been identified in coeval marine black shales of the Appalachian and Illinois basins. Of note, is the observed increase in charcoal content up-section in the Late Devonian-Early Mississippian in several cores from Kentucky and Ohio. This charcoal has very similar reflectance distributions and is morphologically similar to that identified in the known terrestrial sites, and may provide a record of the expansion of land plants into more fire-prone niches. The occurrence of charcoal in marine black shales is significant in that it may yield a more continuous record of fire than is possible in many terrestrial systems. We suggest that inertinite (fossil charcoal) occurrences in marine shales, particularly marine black shales of Devonian and Mississippian age, can further constrain paleo-atmospheric oxygen levels and provide an important linkage between terrestrial and marine ecosystems. It is also likely that petrographic analysis of black shales of other ages may provide a similar wildfire record.