Ultrastructural and Chemical Studies on Oligocene Fossil Wood from Bovey Tracey, Devon, UK

A specimen of Oligocene fossil wood from Bovey Tracey, Devon, UK, was examined using microscopical and chemical techniques. Although macroscopic examination clearly established that it was fossil wood, as opposed to fossil charcoal, both transmission electron microscopy and scanning electron microscopy of its fine structure revealed that the previously stratified cell walls were apparently homogenized; a characteristic previously taken to be diagnostic of fossil charcoal. This fossil thus represents the only known example so far of fossil wood which was definitely not exposed to charring or charcoalification, yet possesses homogenized cell walls. Examination of the fossil wood using solid state 13C nuclear magnetic resonance suggests that the specimen was depleted in carbohydrate carbon and enriched in aromatic carbon and carbon from non-carbohydrate wood components when compared with NMR spectra of native ligno-cellulose. It is suggested that conditions in the unusual deposition environment of a highly acidic freshwater lake, could have directly or indirectly resulted in the cell wall homogenization. The existence of this unusually preserved specimen suggests that the differentiation between fossil wood and fossil charcoal requires the use of a number of characteristics; fossil charcoal being recognised as possessing homogenized cell walls, three-dimensional anatomical preservation, high reflectance under reflected light microscopy, and macroscopical resemblance to modern charcoal. It is not suggested here that this material represents a transition stage between wood and non-pyrolysis fusain (e.g. degradofusinite), but rather that caution needs to be exercised when identifying the mode of preservation/fossilization of plant material based on a limited number of physicochemical characteristics