THE INFLUENCE OF NORMAL FAULTS ON THE DEVELOPMENT OF POLYGONAL FAULT SYSTEMS, PENOBSCOT AREA, OFFSHORE NOVA SCOTIA, CANADA

Polygonal faults, small normal faults with a polygonal arrangement that form in fine-grained sedimentary rocks, can influence ground-water flow and hydrocarbon migration. Using well and 3D seismic-reflection data, we have examined the polygonal fault system on the passive margin of offshore Nova Scotia, Canada. In the study area, post-rift deformation includes both polygonal faults and larger normal faults. The larger normal faults strike approximately E-W to NE-SW. Growth strata indicate that these faults began to form in the Late Cretaceous (Wyandot Formation). The larger normal faults also offset younger strata, indicating that they continued to develop during the Paleocene-Oligocene. The polygonal faults affect the Paleogene Banquereau Formation, a fine-grained clastic sedimentary rock, and the Late Cretaceous Wyandot Formation, a fine-grained carbonate sedimentary rock. Thus, the formation of the larger normal faults and the polygonal faults were coeval, both developing during Late Cretaceous through Paleogene time. Unlike the larger normal faults, the polygonal faults have a wide range of strikes. The strike of many of the polygonal faults becomes increasingly orthogonal to the strike of the larger normal faults near the larger normal faults. Generally, the polygonal faults are poorly developed near the larger normal faults. We argue that the larger normal faults influenced the stress state around them and created stress-reduction shadows. These zones affect the strike of the polygonal faults and locally inhibit their development.