MICROFABRIC CHARACTERIZATION OF FOLDED PELITES OF THE WINDSOR TOWNSHIP FORMATION NEAR KUTZTOWN, PA

Meter-sized pericline structures in muscovite-rich pelites of the Ordovician Windsor Township Formation near Kutztown, PA, located on the foot wall of the Kutztown thrust fault, show evidence of several microfabrics, including parasitic folds, crenulation cleavage, conjugate kink-bands and pressure solution seams. These microfabrics record evidence of multiple deformation events, possibly related to the Taconic, Acadian, and/or Alleghenian orogenies. This study uses (1) mapping of microfabric attitude data in relation to the pericline structure to determine the direction of maximum compression for each deformation event; and (2) energy-dispersive spectroscopy (EDS) microanalysis, to determine whether pressure solution is responsible for the formation of a set of observed cleavage domains, or if they are solely caused by mechanical rotation, or a combination thereof.

The results show several distinct cleavages, one of which displays early-stage crenulations in the limbs of the pericline and conjugate kink bands close to the hinge zone of the fold. The inflection line of these crenulations is layer-parallel, linking them to the same deformation event that resulted in the pericline structure. The EDS analysis shows that some crenulations also form pressure solution seams oriented at ~45° to the crenulation fabric, and in one instance they contain a parasitic buckle fold, which is evidence for a prior or subsequent second deformation event.

The results presented show that several microfabrics observed in 3D pericline structures can be used to identify several deformation mechanisms and events recorded in the Windsor Township Formation.