Primary porosity in carbonate rocks consists of original pore spaces between and within grains during deposition. Secondary porosity is a modification of primary porosity as a result of subsequent physical and chemical processes after deposition. These processes are compaction, fracturing, solution, cementation, and inversions such as dolomitization and calcitization. Various physical and chemical processes affect porosity of carbonate rocks of the Carboniferous Windsor Group of Nova Scotia.

The Windsor Group is a postorogenic, molasse-type sequence of redbeds with perhaps a dozen, thin carbonate-sulfate blankets. Each blanket undergoes facies changes landward from shallow-marine biodolomicrite, through a high-energy facies of biosparite or oosparite, commonly to a low-energy, lagoonal biomicrite, and finally to intertidal and supratidal lithosomes. Facies 1 of Schenk is mainly biodolomicrites with relatively high grain densities, low natural densities, and high absolute porosities. Schenk's Facies II and III are chiefly biosparites or oosparites (locally dolomitic), with relatively low grain densities, high natural densities, and low absolute porosities. In general, absolute porosities of these carbonate rocks are directly proportional to their effective porosities.

Aragonite must have been the chief source material in these carbonate rocks. The depositional primary porosity of Facies I was nearly 80 percent and that of Facies II and III was almost 55 percent. The fundamental process in reducing the pore spaces is compaction, although it must be resisted by the presence of authigenic clay minerals. Other important processes that decrease the porosity are cementation and calcitization. Porosity increases as a result of dolomitization and solution in Facies I and as a result of solution in Facies II and III.