FAULT-FOLD RELATIONS IN THE SHAWANGUNK FORMATION

Coeval strike-slip and thrust faults in the Shawangunk Formation are of Alleghanian age. Near New Paltz, NY the Shawangunk outcrops as a large faulted anticline. Here the formation is also exposed in streambeds which are situated in the hinge of an associated syncline. These fold trough exposures exhibit textbook fault-fold relationships.

Contractional structures are expected in a syncline hinge. Thrust and strike-slip faults are observed in this syncline hinge zone. Thrusts are oriented approximately parallel to the fold hinge lines. Strike-slip faults traverse the hinge at an acute angle.

Herein we document the characteristics and geometrical relations of the faults to the fold structure. Fault interactions are observed and inferred to have occurred during growth of the faults. Fault stress fields are studied and compared models of stress within a syncline hinge. Folding mechanism, bedding, hinge-localized conditions and relative timing of the origin of fold related structures are factors that affect the syncline stress model. Based on combined observations of stress and interaction we should be able to confirm that the faults developed coevally with the fold.