Optical Method for Characterizing Opaque Regions of a Fossil Thin Section
THE MICROSCOPE
2020, Volume 68:3/4, pp. 132–138
DOI
https://doi.org/10.59082/MSET6356
AUTHOR
James Solliday
ABSTRACT
Transmitted light microscopy, with brightfield, polarized and crossed-polarized methods of illumination, are often employed in the histological and morphological interpretation of fossil thin sections. These methods are quite sufficient for the carbonate-based regions of the section; however, iron-based areas are often completely opaque and block all transmitted light. In order to study and characterize this opaque region it is necessary to reverse the angle of illumination to expose the top surface of the obscured areas. This technique has rarely been applied to the analysis of fossil thin sections and thus justifies this study in order to determine if the method can be of value. Epi-illumination, which creates brightfield and darkfield epi-illumination (Figures 1–2), was found to characterize areas of the section that are obscured to standard light microscopy. In most cases, opaque areas respond with high reflectivity providing clues to its density and composition. Standard thin-section methods are sufficient as long as the exposed surface is polished and preferably no coverslip is applied. The specimen in this study is a thin section of a fossil, 50 μm thick, from the scapula of a Dimetrodon sp. from the Lower Permian period.