Origin and significance of microstructures in sandstones of the Martinsburg Formation, Maryland ( USA).

Abstract

Graywacke in the upper portion of the Martinsburg Formation occupies the core of the Massanutten synclinorium in Maryland. Rough cleavage, the psammitic equivalent of slaty cleavage in pelitic rocks, is well developed in many graywacke beds, but intracrystalline deformation may have been important in the modification of detrital grain shapes and hence to the development of cleavage. The cleavage developed during a phase of flattening that followed initial buckle folding. Veins, originally extension fractures, are intimately related to all microstructures indicating that pore fluid pressures remained high throughout much of the deformational history.-from Author