EVIDENCE OF FIRE IN THE TROUT VALLEY FORMATION OF MAINE AND IT'S IMPLICATIONS FOR THE MIDDLE DEVONIAN CHARCOAL GAP

Evidence of wildfires extends back to the Middle Silurian (Homerian), possibly even to the earliest Silurian (Rhuddanian), while evidence for this phenomenon is comparatively extensive in the earliest Devonian (Lochkovian-Pragian). The earliest Devonian charcoal preserves a diverse array of botanical taxa and demonstrates these fires, some well in excess of 600 ° C, were fueled by diminutive embryophytic plants and nematophytes. Famennian-age charcoal is well documented and a Late Devonian to Mississippian aged expansion in fire activity is inferred from charcoal in marine black shales. However, there are reports of a ‘charcoal gap” from the late Emsian through to the onset of the Frasnian based on an almost complete absence of charred material in this interval. The absence of charcoal is used to suggest atmospheric oxygen levels may have been depressed below the minimum required to sustain-and-propagate wildfire activity at this time.

Here we document evidence of charcoal from the late Emsian to early Eifelian Trout Valley Formation of Baxter State Park, Maine. These charred fossils, including psilophyte and lycopod remains, are preserved in a high rank, near meta-anthracitic setting, but can be distinguished from organic debris raised in rank by diagenesis (metamorphic origin). Criteria used to distinguish plants originally charred and deposited in the sediments include their isotropic character viewed by polarized, reflected light microscopy; in contrast, diagenetically altered organic matter exhibits anisotropic preservation. This charcoal record represents one small window in time in the ‘charcoal gap’ where atmospheric oxygen exceeded threshold values for combustion. Our data do not negate predictions made by mass-balance models over longer durations, but do indicate the search for other charcoal records during this time interval are worth pursuing.