DEFORMATION OF THE UTICA SHALE DUE TO BASEMENT FAULTING AND UPLIFT OF THE ADIRONDACK MASSIF, NEW YORK

Situated between the Adirondack dome to the east and Lake Ontario to the west, the Tug Hill plateau rises about 500 meters from the lake shore to the highest point. The plateau flanks expose the Middle Ordovician strata of the Black River-Trenton Groups, and the Utica, Whetstone Gulf, Pulaski and Oswego Formations. These strata sit nonconformiably on the Mesoproterozoic basement of the Adirondack massif. Here we argue that the Adirondack dome uplifted in the Late Jurassic to Cretaceous, the overlying Paleozoic strata in the Tug Hill plateau experienced deformation, resulting in the regional 2-5 degree SW dip, displacement on minor faults and development of joints, but not all rock units experienced this deformation equally. Detailed structural analysis of all units demonstrates a geometric and most likely genetic relationship between deformation in the adjacent Adirondack basement (joint and fracture zones), and the occurrence of local and outcrop-scale faults in the overlying strata. With the uplift of the Adirondack dome, it appears that the stratigraphic units had different responses depending on structural competency and position, and thus had control on the development of joints and their intensity. The lowermost carbonate formations responded to the uplift by developing southeast striking normal faults and high joint density closer to the basement contact. Within the shale bearing rock units, the response was development of high density joints in addition to local fracture cleavage consistent with a less competent rock body. The overlying Pulaski and Oswego sandstone units were not as severely affected by joint development, but instead there was reactivation of pre-existing ENE striking joints as minor left lateral faults. It appears that the thick underlying shale of the Utica and Whetstone Gulf formations probably absorbed much of the joint forming stress through development of fracture cleavage and low-temperature plastic flow.