Fractures, Veins, and Faults: Deformation Characteristics in the Utica Shale, Mohawk Valley, New York State

Alex O’Hara
University at Buffalo, Geology Department Buffalo, New York United States
[email protected]

Brittle deformation characteristics in the eastern Mohawk Valley, New York State vary among outcrops as a function of stratigraphic and regional location within the Taconic foreland basin. Major structural variations within the formations of the Utica Shale include drag fold morphology on normal faults with an absence of fracture intensification domains, normal faults with accompanying fracture intensification domains, brecciated veins, and transtensional shear interpreted from vein-filled rhombochasms. Structural interpretations made from the deformation within the Utica Shale suggest a complex tectonic history of formation and reactivation of faults in the Mohawk Valley.

Fracture and vein measurements were taken from outcrop locations covering an area between Dolgeville and Schenectady for analysis of the diverse regional structure. Fracture and vein sets are observed striking parallel, sub-parallel, and orthogonal to major faults proximal to field sites. Veins observed in the field area exhibit Mode I opening in the western field area in the Indian Castle Formation outcrops with an increase in transcurrent motion in the eastern field area in the Flat Creek Formation outcrops. Right lateral and left lateral shear distribution varies between east-northeast, east/west, and west-northwest sets with vein counts peaking at 70° for right lateral shear and 290° for left lateral shear. The motion on these vein sets suggests the formation of conjugate shear zones with σ1 oriented east/west. Maximum east/west compression, in conjunction with the formation of fracture sets striking orthogonal to north/northeast striking faults, supports the hypothesis that normal faults were reactivated as thrusts within the Taconic basin.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects