More recently, renewed effort has been devoted toward gaining an improved understanding of fracture arrays in Devonian rocks of New York State. Much of this work stems from petroleum exploration and concerns over the influence of urban expansion on groundwater systems. To date our work has centered in the Gowanda Shale and underlying Dunkirk Shale of the Canadaway Group and the underlying Hanover Shale at the top of the West Falls Group. Next summer we plan to work deeper into the sequence along the Lake Erie shoreline as well as higher into the more coarse-grained section of the Canadaway Group. We have gone through an evolution of thought regarding these structures.
Individual joints are very continuous and show little deviation in orientation along their strike.
We had considered that perhaps we were seeing evidence of joints produced by thermoelastic effects related to unloading within the contemporary stress field. As such, these fractures were initially considered to be neotectonic in origin and produced during the unroofing event that formed the Lake Erie Escarpment. Also, they are vertically extensive, extending locally for five or more meters up and down section. This latter observation suggests that the joints formed under high differential stress, something that would not be expected for shallow-formed neotectonic joint systems. One of the fascinating aspects of the ENE fractures is the fact that they do not propagate out of the Dunkirk into the underlying Hanover shale.