ABSTRACT

Stylolites are defined in terms of rock grain fabrics; aggregate stylolites and intergranular stylolites are differentiated. A classification of stylolites is given on the basis of the pure geometry of the stylolites themselves and on their relationship to the bedding plane.

Megascopic and microscopic observations on stylolite features from the Joppa Limestone Member of the Ste. Genevieve Limestone Formation (Upper Mississippian), the Downeys Bluff Limestone Formation (Upper Mississippian), from Cave-In-Rock fluorspar mines in southern Illinois, and from the Jefferson City Formation (Lower Ordovician) near Rolla, Missouri, are described and their interpretation discussed. Under the microscope, bituminous material, clay minerals, silica, dolomite, sulfides, and fluorite are observed near or within the stylolite seams. Dissolution, recrystallization (neomorphism), grain growth, grain orientation, pressure-twinning, pressure-shadows, micro-faulting and shearing, cavity filling, and geopetal features have been observed along stylolite seams.

Difficulties entailed in the mechanism of stylolitization by the pressure-solution theory and contraction-pressure theory are brought out. This study indicates that stylolites form during the various stages of diagenesis. Most frequently, stylolitization in tectonically and metamorphically non-affected carbonates is initiated during the early burial stage, that is, the stage of radiaxial and "dog-tooth" type cementation, and probably ends concordantly with the complete elimination of pore space by drusy mosaic carbonate. It appears that stylolites in tectonites are more the result of pressure-solution and recrystallization phenomena due to the physical factors involved rather than to the chemical factors.

It is proposed that in solving the stylolite problem, various diagenetic fabric and chemical changes should be considered.