ANALYSIS OF TURBIDITES BY SCANNING ELECTRON MICROSCOPY AND DIGITAL IMAGING

In the laboratory study of samples from a stratigraphic section of turbidites we have gained unique micropetrographic and microstratigraphic information by using the techniques of Scanning Electron Microscopy combined with those of Computer Imaging. A backscattered electron (BSE) detector produces images which clearly show the size, shape, and arrangement of the various grain components of the rocks; a microanalyzer provides whole-rock chemistry of different stratigraphic levels within the rock and the composition of individual mineral grains or parts of lithic grains; element maps show the distribution of chemical elements within the rock or within individual grains. Computer processing greatly improves the quality of the original images, allows enlargement of these images to enhance details, and allows us to assemble several individual images into one continuous image. The latter technique is especially useful in examining the detailed characteristics of a whole graded bed, the relationships between a single bed and the beds above and below it, or a sequence of several beds.

The samples used for the analyses are polished petrographic thin-sections or thick-sections cut perpendicular to the stratification. The BSE images are captured on film and digitized with a film scanner, or are taken directly into the computer with an A/D converter. We use Adobe Photoshop to process the images but there are many other software packages which work very well. There are also several program, including Photoshop, which can be used to assemble (stitch) adjoining frames into large mosaics or strips. Analysis of processed images can be carried out with software which produces gray-level histograms, "particle analysis" or techniques of stereology.