Analyses of petrified wood by electron, X-ray and optical microprobes

Abstract

Samples of petrified wood of different origins were analyzed by the use of the electron microprobe, capillary X-ray fluorescence microprobe, synchrotron capillary X-ray microprobe and optical microscope, applied in a microprobe manner. The main attention was given to the investigation of the ring structure of the petrified wood and the comparison of this with the ring structure of the living trees analyzed by much the same methods. The continuous X-radiation, applied in a microprobe manner, the distribution of the gray-scale representation of the secondary electron intensities and the characteristic X-ray signals, mainly from the light elements, were registered by the use of the electron microprobe method. The X-ray capillary microprobe detected the Rayleigh and Compton signals, scattered from microareas of the samples, and the characteristic X-ray signals, mainly from the heavier elements. In the synchrotron-based capillary microanalytical measurements, one of the most important results was achieved by the microprobe application of scattered synchrotron radiation. The emission and scattering results were supplemented by transmission measurements, where possible. All the methods proved to be complementary in the analysis of such periodic structures as tree rings. Both capillary microprobes were much more efficient in the detection of heavy elements and penetrated deeper than the traditional electron microprobe. Careful analysis of different signals indicated that some samples of petrified wood in the authors' possession, composed of silica of variable density, are the chemical negatives of the primordial living wood. This is the first such observation in the literature. Microdiffraction studies of the samples proved that polycrystalline α-quartz was the main matrix component of all these samples. The elemental analysis of the petrified wood gives important indications about the petrification processes. Comparison of the particular ring structure of the petrified wood with the ring structure of living trees shows great similarities. The widths of rings, density variations and density maxima are easily readable from the microanalysis of petrified wood. These parameters potentially can be exploited for the investigation of the biological, chemical, chronological and climatic information included in the fossilized tissues.