3-D OPTICAL (CLSM) AND CHEMICAL (RAMAN) IMAGERY OF PERMINERALIZED ORGANIC-WALLED FOSSILS

Two deficiencies have long hampered studies of permineralized (petrified) organic-walled fossils, (1) an inability to document accurately their three-dimensional morphology at high spatial resolution, and (2) a lack of means to analyze directly the chemistry of the coaly kerogen of which they are composed. These needs are met by two techniques recently introduced to paleobiology: three-dimensional confocal laser scanning microscopy (CLSM) and two- and three-dimensional Raman imagery.

Applicable to specimens in petrographic thin sections, cellulose acetate peels, or acid-resistant macerations, CLSM and Raman imagery can provide data at micron-scale resolution demonstrating a one-to-one match of three-dimensional cellular form and kerogenous composition in carbonaceous plants, microorganisms, and (relatively rare) animals permineralized in chert, calcite, or phosphate. Particularly useful for studies of Precambrian microbes and comparably minute Phanerozoic organic-walled microfossils, both techniques are also applicable to the investigation of megascopic fossils where they can provide insight into fossil structure and composition unavailable by any other means. Unlike standard two-dimensional optical photomicrographs, the digitized three-dimensional images provided by CLSM and by Raman can be rotated and visualized from multiple perspectives, such images of chert-embedded microscopic fossils being obtainable in thin sections to depths greater than 100 microns by CLSM, and greater than 60 microns by Raman.

Together, use of CLSM and Raman imagery can provide new information about the morphology, cellular anatomy, taphonomy, and geochemical maturity of permineralized kerogenous fossils, and Raman imagery can be used as well to characterize the mineralogy of the fossil-enclosing matrix and the spatial relations between such fossils and their embedding minerals. Because both techniques are non-intrusive and non-destructive, both can be applied to specimens archived in museum collections.