The Dynamic Significance of Deformation Lamellae in Quartz of a Calcite-Cemented Sandstone

Abstract

In 3 specimens of macroscopically folded Oriskany Sandstone, deformation lamellae are profusely developed in quartz grains, and the calcite cement contains numerous twin lamellae on {0112} = e. Following the method used by Turner, axes of compression and tension were deduced from a statistical study of the pattern of calcite twinning in each specimen. The stress systems so deduced are symmetrically related to the geometry of macroscopic folding. Triaxial stress fields were obtained from samples from the limbs of an anticline, and a uniaxial stress field was determined from a sample from the axial plane of the anticline. The maximum and minimum stress axes, sigma 1 and sigma 3 , so determined lie within 10 degrees of the bedding and are perpendicular to the local fold axis; the intermediate axis, sigma 2 , parallels the fold axis. Quartz lamellae show strong patterns of preferred orientation also symmetrically related to the stress systems deduced from calcite twinning; they tend preferentially to develop in planes of high shear stress inclined at less than 45 degrees to the inferred axis of maximum stress, sigma 1 .