Bedding-Slip Movements in Fault Blocks Southwest of the Los Pinos Mountains, New Mexico

Brecciated zones occur along bedding planes in certain Pennsylvanian limestone cuestas which dip gently southwest off pre-Cambrian formations of the Los Pinos uplift in central New Mexico. The zones are thoroughly silicified and are confined to triangular blocks which are bound on two sides by normal faults of Basin and Range type. Breccias of the bedded zones capping the cuestas are continuous with similar silicified zones along the steeply dipping normal faults. The outcrops of these bedded breccias proved useful in locating the less evident breccias of the normal faults. The fault blocks are domed, and slickensides suggest that the brecciated zones along the bedding were formed by movements of beds upward toward the crest of anticlines during initial folding and by subsequent slipping of beds down dip. Silicification of the breccias was probably accomplished during the Tertiary.