SOLUTION ENHANCED FRACTURE KARST IN THE TRENTON GROUP CARBONATES, JEFFERSON COUNTY, NEW YORK

Systematic tectonic fractures are pervasive throughout the Paleozoic strata of the Appalachian Basin, including the northernmost region of the basin in the Tug Hill plateau of northern New York State. This region is mapped as underlain by the Middle Ordovician carbonates of the Black River and Trenton Groups directly overlying the Mesoproterozoic basement of the western Adirondacks. In turn, the carbonates are overlain by the Lorraine Group siliciclastic sequence that comprise the majority of the plateau. The region of western Jefferson County, New York, is characterized as generally flat, low relief terrain, that is more or less the top of the Trenton Group carbonates, blanketed with a thin veneer of glacial till. Under these conditions, the top of the Trenton Group has been exposed at the surface since the retreat of the Pleistocene glaciers between 14-10K years ago. The Trenton Group contains a dominant subvertical fracture set that strikes northeast, and a second conjugate set that strikes northwest. The northwest oriented fractures are linked to NW striking normal faults that form horst and graben at the scale of 100’s of meters. The throw on the normal faults is in the range of several meters, but in most cases less than a meter of total offset. Fault gouge consists of pulverized limestone and secondary deposits of clay. Throughout the western part of Jefferson County, the landscape is crisscrossed by shallow topographic lineaments that clearly parallel the major fracture sets. These lineaments are often filled with glacial sediments and post-Pleistocene soils. In the most cases, these lineaments are places where the bedrock contains gaps that are the result of dissolution along the pre-existing fractures. Cliff exposures on Lake Ontario reveal the extent of these dissolution features, projecting into the strata 10-15 meters and tracing into unaltered fracture zones. Through the use of remote sensing (imagery, LiDAR, etc. ), electrical resistivity imaging, and field survey and mapping efforts, it has been shown that there is a direct correlation between the NW trending lineaments and the enlarged faults that have been observed within the lakeside cliffs.