Microprobe aided mapping of areal element concentration and microporosity in chalk
By use of the autoscan mode of a microprobe on polished chalk surfaces, maps can be constructed representing areal concentrations of elements and areal distribution of microporosity. The maps presented herein are composed of 400 12×15 micron scenes, but maps composed of 10,000 scenes have been obtained.
The apparent porosity is derived by difference as 100 percent minus the sum of the chemical analysis. In the chalk samples used here the apparent porosity derived by this method is systematically lower than the porosity derived from mercury immersion of core chips and from logs, and consequently a correction factor has been derived. Low porosities determined using the microprobe are probably related to depth of beam penetration, which is comparable with the grain size of highly porous chalk.
The main advantage of the method described here is the direct linking of chemical data and microporosity on a millimeter scale.
KeywordsChalk Apparent Porosity Stylolite Areal Concentration Bulk Porosity
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