Elemental Relationships in Rock Varnish as Seen with Scanning Electron Microscopy and Energy Dispersive X-Ray Elemental Line Profiling

Authors

Robert Raymond Jr., Los Alamos National Laboratory
Steven L. Reneau, Los Alamos National Laboratory
Charles D. Harrington, Los Alamos National Laboratory

Abstract

The heterogeneous nature of rock varnish requires a thorough understanding of elemental and mineralogic compositions before chemical variability of rock varnish may be confidently related to varnish age or to past geochemical environments. Elemental relationships in rock varnish were examined using scanning electron microscopy in conjunction with an elemental line profiling routine using semi-quantitative, energy-dispersive x-ray analysis. Results of our analyses suggest: 1) variations in cation concentrations used in varnish cation-ratio dating relate more specifically to variations in detritus concentration within the varnish than to element mobility as defined by weathering indices; 2) Mn:Fe ratios may be a poor indicator of paleoclimatic fluctuations; and 3) the Mn-oxide phase existing in varnish is most likely a Ba-enriched phase rather than birnessite. An examination of data collected from elemental line profiling offers great potential for gaining insights into geochemical processes affecting the deposition and diagenesis of rock varnish and for testing hypotheses relating to its chemical variability.

Recommended Citation

Raymond, Robert Jr.; Reneau, Steven L.; and Harrington, Charles D. (1991) "Elemental Relationships in Rock Varnish as Seen with Scanning Electron Microscopy and Energy Dispersive X-Ray Elemental Line Profiling," Scanning Microscopy: Vol. 5: No. 1, Article 4.
Available at: https://digitalcommons.usu.edu/microscopy/vol5/iss1/4