Petrography and Metamorphism of Sediments of Ouachita Facies

Abstract

Sediments of Ouachita facies extend in the subsurface from the Ouachita Mountains of Oklahoma and Arkansas to the Marathon and Solitario uplifts of extreme southwest Texas. Although these sediments have been subjected to strong dynamic metamorphism, the metamorphic grade attained is uniformly low. Sediments of Ouachita facies are essentially unaltered in some areas; elsewhere they range in degree of metamorphism as high as the biotite zone. Mineralogical change and cataclastic effects are key criteria for discerning the stages of progressive metamorphism in sediments of Ouachita facies. Metamorphic changes are most easily observed in shales and argillaceous sandstones; limestones and cherts react less conspicuously to metamorphic stress. The so-called schist of the Luling field, Caldwell County, Texas, and of some other deep wells along the Luling-Mexia-Talco fault system consists for the most part of metaquartzite, meta-argillite, phyllite, and slate. With two possible exceptions, these metasediments are restricted to the chlorite and biotite zones and are comparable in mineralogy and degree of metamorphism with sediments exposed in the more highly metamorphosed parts of the Ouachita Mountains of Oklahoma and Arkansas.