Stress Inferred from Calcite Twin Lamellae in Relation to Regional Structure of Northwest Arkansas

Distribution of stress within Carboniferous-age rock of northwestern Arkansas has been determined from dynamic analysis of calcite twin lamellae in gently deformed limestone. In the southern part of the area, compression axes are essentially normal to mapped east-trending fold axes that define the northern limits of the Ouachita orogeny. Farther north where this folding has not been recognized, a similar stress field is preserved in limestone. This relation shows that favorably oriented calcite crystals will twin very early under stress conditions that are insufficient to produce discernible fold forms.