STRUCTURAL AND STRATIGRAPHIC RELATIONSHIPS NEAR THE MARTINSBURG-SHAWANGUNK CONTACT
Field mapping near the Martinsburg-Shawangunk contact between Port Clinton, PA and Poughkeepsie, NY has resulted in a record of stratigraphic and structural relationships across this lithostratigraphic boundary. Of particular interest is the nature of the contact, along which evidence for stratigraphic conformity, unconformity, and fault contact exists.
Completed field work has confirmed many of the stratigraphic and sedimentologic descriptions of the Martinsburg and Shawangunk Formations reported in literature. Work to date suggests that the nature of the contact between these formations does not vary in a consistent manner along strike. From north to south, the angular unconformity of the contact varies from 21 degrees near Minnewaska State Park in southeastern New York to zero degrees around Bangor, PA. It then increases again to approximately 15 degrees at Lehigh River Gap, where there is also evidence of dip-slip faulting at the contact.
Methods for high-resolution digital mapping are currently being explored. These techniques employ high resolution (~ 1 meter / pixel) Lidar data and derivatives including slope, aspect, and hillshade topographic maps. These methods have the potential to reveal locations of interest prior to actual field-checking and may allow for digital measurement of structural elements.