The Mineralogy and Petrology of Upper Mississippian Carbonate Rocks of the Cumberland Plateau in Tennessee

The mineral assemblages of upper Mississippian carbonate rocks of the Cumberland Plateau in Tennessee, with only minor exception, obey the Gibbs Phase Rule, within the choice of chemical components that was made. These mineral assemblages are: dolomite, corrensite; calcite dolomite, corrensite; calcite, corrensite; calcite, chlorite-vermiculite; calcite, chlorite-vermiculite, montmorillonite containing mixed 10 Å layers. Compositional variation of the expandable chloritic minerals lies between the compositions of vermiculite and corrensite and is consistent with the topologic requirements of the ternary diagram showing CaO, MgO, Al₂O₃ of the system CaO, MgO, Al₂O₃, SiO₂, CO₂, H₂O. The mineral assemblages are the result of a mineral paragenesis adjusted to the bulk chemical composition of the sediment, including the originally trapped pore solutions. The compositional variations of the complex chloritic minerals are the result of adjustment to the same conditions that formed the mineral assemblages. The chemical composition of the sediments was determined, to a large extent, by chemical factors in the depositional environment, mainly salinity variations caused by evaporative concentration of normal marine water. Lithologies are clearly related to mineral assemblages, and lithologic associations determined from stratigraphic relationships are the same as those determined from similarity of mineral assemblages. These mineral assemblages may be the true equilibrium products or they may be metastable assemblages resulting from a temporary adjustment to the conditions necessary to nucleate dolomite either in the depositional environment or very shortly after deposition.