PRE-TACONIC FRACTURES IN THE TRENTON GROUP AND LITHOLOGIC CONTROL ON FRACTURE ORIENTATIONS, TUG HILL PLATEAU, NEW YORK

The Taconic clastic wedge, a prominent geological feature that outcrops throughout the Tug Hill Plateau, NY, records the depositional history of the Taconic orogeny. Underlain by Trenton carbonates, the clastic wedge comprises siliciclastics that coarsen upward from the Utica shale through the Oswego sandstone. This study examines detailed lithologic variation and the link to the development of fractures in extensive outcroppings along a 16.5 km traverse of Sandy Creek, Inman Gulf, Rodman to Barnes Corners, NY.

The exposures in the gulf include Trenton carbonates overlain by the Utica, Whetstone Gulf, and Pulaski formations. Thirty bed-scale stratigraphic sections were documented along with detailed joint orientation measurements at 80 locations. All joints systematically vary in strike along the traverse with progressive change in strike moving up stratigraphic section. The lower carbonates and lowermost Utica shale contain the greatest variation in joint set strikes with dominant NW and NE striking sets. This variation rapidly dissipates as joint strikes become more regular with two dominant sets appearing in the upper section of the Utica shale, growing more constrained moving up in section. The strike of the joints systematically vary showing formation scale refraction with strike migration to the north or east entering into formations with coarser clastic beds. While the Trenton carbonates display two dominant joint sets, these sets are significantly less pronounced in the overlying clastics.

This study highlights two interesting findings:

1. There may be joint sets in the Trenton Group that pre-date the deposition of the clastic wedge that are possibly associated with migration of the Taconic peripheral bulge that caused uplift and erosion prior to the rapid drowning of the carbonate shelf

2. The systematic migration of the strike of separate post-Taconic joint sets suggests lithologic/reheologic control on their orientation as the stratigraphic section varies from clay dominated rocks to coarser clastics. This relationship has been documented in several other gulfs that occur on the flanks of the Tug Hill plateau.