Late Triassic charcoal and charcoal-like plant fossils from Petrified Forest National Park, Arizona
2006
Charcoal-like plant fossils, the majority of which appear to be wildfire derived, occur at several different horizons in the lower
part of the Chinle Formation of Late Triassic age in Petrified Forest National Park. The most common of these charcoal-like plant fossils are
small fragments of black woody material up to1 cm long that are found in situ in the formation. Less commonly, similar small fragments are
present on the surface of the formation at two localities where they were left behind as a lag deposit after the enclosing matrix had been
removed by erosional processes. Also, charcoal-like material occurs in some of the charred logs and stumps found in the formation.
Although there is some small doubt about the taphonomy of some of the material, it is possible that the unusual appearance and low
reflectance values of this ‘problematic’ material, may have resulted from later post-burial mineralization of charcoal. The quantitative
reflectance values of most of the in situ and reworked fragments ranges from 2.08-3.12% indicating moderate temperature paleowildfires. In
contrast, the reflectance results for a charred stump in the Blue Mesa Stump Field of 2.60-2.80% suggests low-temperature in-situ smoldering.
Because the phenomenon of smoldering stumps is commonly seen in modern wildfires this locality may represent the remains of an
ancient burnt forest.
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