The Silurian Salinic Disturbance — newly discovered orogenic event in the northern Appalachians

Abstract

In northern New Brunswick the Silurian and Ordovician rocks have been affected by two regional deformation events. The first deformation is attributed to the Salinic orogeny. It took place during the late Wenlockian — early Ludlow (426—421 Ma) and produced tectonic folds with northwest striking axial surfaces. Evidence for cleavage and faulting coeval to this event is rare. The second regional deformation took place during the lower to middle Devonian (407—390 Ma) and is know as Acadian orogeny. The Acadian deformation overprinted the Salinic structures in the lower Silurian rocks but produced single fold generation in the upper Silurian rocks. Intensive cleavage and widespread faulting are related to the Acadian revolution. The refolds in the lower Silurian rocks are steeply plunging. The refolds are overprinted by the Acadian cleavage, while the Acadian folds are dextrally transected by the same cleavage. The kinematics of the Salinic deformation is not understood but it is known that the Acadian deformation was achieved during intensive dextral shear, which resulted in transecting cleavage and an echelon arrangement of Acadian folds with respect to the high-strain shear zones. Most of the faults in the northern Appalachians appear to be synchronous or to postdate the Acadian folding. The dextral shear was penetrative on a regional scale and resulted in numerous bedding parallel faults with hidden separation.