AGE RELATIONSHIPS BETWEEN JOINT SETS IN THE EASTERN CATSKILL MOUNTAINS, NEW YORK, AND THEIR TECTONIC SIGNIFICANCE WITH RESPECT TO WNW SHORTENING IN THE HUDSON VALLEY FOLD-THRUST BELT

As part of an ongoing study in the central Hudson Valley, we at SUNY New Paltz are working to clarify the age of the Hudson Valley fold-thrust belt (HVB). The HVB’s oroclinal structure has led to uncertainty in assigning age constraints, evidence for both Acadian and Alleghenian deformation has been presented. It’s been shown that joints in a foreland of an orogenic belt delineate orogenic paleo-stress trajectories. For example, joints in the Allegheny Plateau of south-central New York have been used to delineate Alleghenian paleo-stress trajectories. Previous research conducted for our study has identified two primary joint sets in the eastern Catskill Mountains: Set A, oriented ~290°, and Set B, oriented ~020°. In addition, measurements of shear zones, and shallow west dipping beds were used to infer that this region experienced some WNW shortening, perpendicular to the NNE-striking HVB. This indicates that structures within the Catskill Mountains may have a cogenetic relationship with the HVB. It is hypothesized that Set A joints delineate Acadian paleo-stresses, while Set B joints delineate the later Alleghenian paleo-stresses. Thus, the HVB’s orogenesis may be accredited to Acadian events. Recently, collection of joint and shear zone orientations was continued on previously unstudied trails and roads. Additional bedding orientations were measured using point-elevation data on flood plain benches from digital elevation models in QGIS and Orient software. Emphasis was placed on the identification of cross cutting edge relationships between the joint sets. That is, Set A joints could be interpreted as Acadian in age if Set B joints are truncated against them. 605 joint orientations at 224 stations were taken, one new shear zone was identified, and several bedding orientation calculations were made. 31% of Set B joints were found to truncate against Set A joints. The shear zone was found to have a horizontal hanging wall displacement directed to 303°, while bedding on average strikes 191° and dips 02 west. These data are consistent with WNW shortening in the eastern Catskill Mountains, perpendicular to the HVB. The mutual cross-cutting joint relationships between Sets A and B does not clarify their age relationship. One hypothesis is that joint reactivation, possibly due to recent topography, has created this geometry.