Interrelation of Mineralogy and Texture Within an Ordovician Lexington Limestone Section in Central Kentucky

Abstract

ABSTRACT Areal and stratigraphic data on the Ordovician limestone of the Kentucky Bluegrass region is increasing rapidly due to the cooperative Kentucky-Federal geologic mapping program. This study of the interrelations of mineralogy and texture of the Lexington Limestone supports the validity of the lithologic units used in the mapping program and establishes a centrally located reference. The Lexington Limestone has essentially no dominantly detrital units. The shale beds of the formation are more than 50 percent carbonate. The 255 foot thick section reported on here contains only 8 to 9 percent insoluble material. Authigenic quartz is widespread as silt-sized and larger particles. There is little if any subsilt-sized silica in these rocks. Detrital quartz is very sparse except for the bas l Curdsville Member. Illite is the only clay mineral group identified. A search for metabentonite proved negative although some admixture is probable. Pyrite is ubiquitous and amounts to units of percent of the insoluble residues. Dolomite is widespread, but minor in the formation. The limestones vary from micrite to coarse biosparite. The environment of deposition ranged from quiet to moderately agitated shallow water.