STRUCTURAL CONTROLS ON THE DEPOSITION AND STRATIGRAPHY OF THE CANADAWAY GROUP (UPPER DEVONIAN) IN CHAUTAUQUA COUNTY, WESTERN NEW YORK STATE

The Canadaway Group in Chautauqua County is comprised of black shales and interbedded grey shales, siltstones, and sandstones. The units of the Canadaway Group are distinguishable in the subsurface on well logs owing to differing gamma ray signatures and relatively sharp contacts. The black shales of the Dunkirk Formation and the Hume Formation (which persists into Chautauqua County contrary to previous interpretations) represent restricted basinal environments. Gray shale, siltstone, and sandstones were deposited farther up on the shelf of the westward prograding Catskill Delta complex. Gray shales of the Gowanda and Westfield formations represent a lower offshore facies. The siltier to sandier South Wales, Laona, Shumla, and Northeast formations record lower shoreface environments. Common hummocky cross-stratification indicates the predominance of storms during deposition of siltier and sandier units (e.g. Laona and Shumla). Canadaway grey shale units (Gowanda, Westfield, and Northeast formations) tend to thin eastward across Chautauqua County and the South Wales Formation thins westward. The Laona and Shumla formations display discontinuity throughout the subsurface; their distributions are irregular, and thicknesses are mostly controlled by local fault system reactivation. Correlation of well logs indicate significant changes in the elevations of stratigraphic units over short distances. In addition, some units display marked changes in thickness over short distances. These changes represent considerable offset across previously mapped basement faults (Jacobi, 2002). Reactivation of faults and syndepositional offset during the Famennian stage (Upper Devonian) produced paleotopographic changes which resulted in local formation of restricted basinal conditions and trapping of coarser siliciclastic sediments eastward. Recognizing these faults in the subsurface aids in small scale, local correlation.