APPALACHIAN BASIN SALT IN THE SILURIAN SALINA GROUP: THE VIEW FROM THE MINES

Expansion of salt mines in New York and Ohio over the past three decades has provided an additional means to evaluate Silurian Salina Group lithofacies and structural fabrics within the Northern Appalachian Basin. Observations in the more laterally and vertically extensive mine workings complement the seminal geological analyses performed at these mines during the 1960's.

Our key observations are as follows: 1) Beneath the eastern Finger Lakes Region of New York, salt bed textures predominantly reflect tectonic shear; little evidence of true primary bedding appears to be preserved. 2) Tectonic signatures are still apparent in the Genesee Valley in New York based upon similar salt lithofacies to the eastern Finger Lakes Region and rock-in-salt features reported in the literature. 3) Tectonic signatures persist into northern Ohio, but primary depositional bedding in the form of halite-anhydrite rhythms becomes more apparent. 4) The regional decollement in the salt sequence that has been typically modeled as occurring at or near the base of the Salina F salt, actually is a multi-level phenomenon affecting the B salt, the D salt and the F salt zones. Instead of a single plane of slippage, each of the three major regional salt zones appears to have suffered deformation that varies locally in response to the lateral pinchout of specific salt beds. 5) Patterns of deformation in synjacent shales and dolomites suggests that "salt withdrawal basins" exist between regional anticlines in the Finger Lakes Region of New York. Roof rock above an observed withdrawal basin in one mine shows evidence of extensional deformation whereas compressional deformational features are clearly evident in the same roof rock stratum 4 miles to the south beneath a regional anticline. 6) Zones of thick salt in New York do not necessarily record original depocenters. Thick F-salt zones in New York are dominated by folded, faulted and brecciated sequences. Non-salt strata have been observed in drill cores to be "standing on end", thus exaggerating the original thickness of the local section. Lateral lithofacies trends in the non-salt strata and lateral termination/gradation of halite-dominated intervals into anhydrite/shale sequences (eastern basin margin) and anhydrite/dolomite sequences (western basin margin) are the best means to interpret paleogeography.