EXPERIMENTALLY-SIMULATED STYLOLITIC POROSITY IN CARBONATE ROCKS

An experimental program of stylolitic porosity development in stylolitic Atokan (Middle Pennsylvanian) limestones under simulated conditions of deep burial has shown that experimental dissolution preferentially occured and developed along existing styloties. The dissolution sequence was as follows: incipient pores following the traces of stylolites, grading into stylolitic lamellar pores, which enlarged eventually into non-fabric-selective channels. These stylolite-controlled conduits were surrounded by adjacent incipient-to-complete oomolds, enlarged oomolds, incipient-to-complete algal bioclast molds, enlarged biomolds, and halos of intercrystalline porosity to microporosity.
Trace element analysis (Mg, Sr, and Ca) of pore-fluid samples during early phases of experimental deep burial dissolution indicated that slightly less stable protions of carbonates enriched in Mg and Sr dissolved preferentially, as observed also in natural cases. Pyrolysis data indicate that stylolites concerntrated organic matter derived from inter-stylolite areas. This situation demonstrates the pressure-solution origin of stylolites.
Experimental stylolitic pore networks are similar in type, size, and geometry to natural stylolitic porosity. This preferential dissolution suggests that natural stylolites result from late (post pressure-solution dissolution, are not necessarily mechanically induced during stylolite formation as sometimes postulated, and act as effective conduits for secondary porosity generation in deeply-buried carbonate rocks