Porosity replacement-calcite dissolution

The most common origin of secondary porosity in sandstones studied is due to dissolution of plagioclase or else dissolution of carbonate that replaced plagioclase. Replacement of silicate minerals by calcite is not uncommon, and much of the plagioclase dissolution porosity may actually be replacement-calcite dissolution porosity. We know of no way to resolve this problem. For purposes of calculations, we assumed that plagioclase was dissolved. 

Not only is the shallowest formation (Fox Hills) plagioclase-rich, but it also has the most porosity attributable to plagioclase dissolution. The Codell Sandstone is highly argillaceous with low permeability, which has retarded the dissolution of framework grains. In all sandstones, secondary porosity attributable to dissolution of K-feldspar is limited to trace amounts. The third form of secondary porosity, which is dissolution of calcite cement and replacement, is sparse (maximum of 1.5vol%) and absent in most samples. Trace amounts of secondary porosity also formed by the dissolution of lithic fragments. 

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