A TURONIAN BURN SITE INDICATED BY CHARCOALIFIED AND PERMINERALIZED TREE BOLES

Because most fossil charcoal is allocthonous, it can be difficult to determine the exact locality of ancient wildfires. In the Moreno Hill Formation of New Mexico, an unusual assemblage of fossilized dicotyledonous wood pinpoints the location of a mid-Cretaceous wildland fire. Here, a large stump and nearby fallen log were found to contain both charcoalified and permineralized tissues.

The ~60 cm diameter stump is rooted in place and is almost entirely composed of black fusinite. Although the xylem structure of the fusinite is somewhat obscured, it is evident that the cell walls have been homogenized. The fusinite rapidly disintegrates when exposed to the elements. Embedded within the fusinite is a discontinuous half-cylinder of rounded pieces of permineralized wood.

A large log lies within 2 m of the stump in the same stratum. This horizontal log is permineralized, except for a layer of fusinite (several cm thick) on the underside. Raised ovoid lumps characterize the surface of the permineralized wood where it was in contact with the fusinite.

Both the stump and the lower part of the fallen log are emplaced in a mudstone that is overlain by a fine-grained sandstone. The wood histology, taphonomic context, and association of fusinite and permineralized tissues, indicate that both boles were burned. The rooted stump apparently burned underground during smoldering combustion; the included permineralized blebs are probably sections of sapwood that merely charred. The prostrate log appears to have lain on the soil surface and was only partially combusted. The lumpy configuration of the permineralized wood that was in contact with the fusinite resembles the characteristic 'crocodiling' texture commonly evident on freshly charred wood.

Although it is not clear whether the two sections of wood are from the same tree, the intact fusinite and in situ roots indicate that both boles remain in the positions in which they were burned, and were preserved by a flood deposit before the charcoal was eroded away. This discovery is intriguing because it represents a rare case in which the exact site and stratigraphic placement of an ancient wildland fire are evident.