Mudrocks examined by backscattered electron microscopy

Abstract

The small size of many of the particles in mudrocks makes it almost impossible to image and identify them individually and in situ using conventional light microscopy. Partly for this reason, the petrography and genesis of mudrocks is poorly understood compared with sandstones and limestones. This deficiency presents a serious problem hi sedimentary geology, as mudrocks comprise almost two-thirds of the stratigrapnical column^1,2. We introduce here a new method of studying mudrocks, using backscattered electrons (BSE) in scanning electron microscopy (SEM). When thin sections or polished rock chip surfaces are examined with BSE, both atomic number (Z) contrast and topographic contrast can be obtained, providing much more detailed compositional and textural information than was previously possible. Used in conjunction with X-ray microanalysis, the new technique promises to revitalize mudrock petrology.