The Whirlpool Sandstone (Medina Group), quartzose, white, clean, well-rounded, and well-sorted, is the basal Silurian unit in western New York. Its source was the Queenston delta some distance to the southeast. Sedimentary structures indicate that deposition occurred in a beach-shore face environment. Fragmented phosphatic marine fossils are found throughout the sandstone.

Erosion of Upper Ordovician sediments in western New York was minimal and involved only the uppermost green (reduced) portion of the Queenston Shale, which supplied lags of flat, green shale pebbles to the Whirlpool Sandstone. Soft sediment deformation and burrowing in the Queenston substrate (the transitional contact between the red Queenston Shale and red Grimsby Sandstone [Silurian] in Rochester, New York, immediately to the east of the area of Whirlpool deposition) suggest a short period of nondeposition or possibly mild erosion following the deposition of the Queenston Shale. Thus, the Ordovician-Silurian boundary in western New York is essentially conformable and signified only by an abrupt influx of clean quartz sand.

Petrographic analysis shows that the Whirlpool is a second or multicycle sandstone composed primarily of quartz grains originally derived from igneous and metamorphic terranes with only a minor sedimentary component. Because the sandstone is cemented by quartz overgrowths, usually in an advanced stage of development, primary porosity is reduced and the overall porosity of the Whirlpool Sandstone is low (less than 5%). Higher porosities are attributed to the development of secondary moldic porosity caused by dissolution of detrital quartz grains and their original calcite cement. These zones of higher porosity are the most prolific natural gas producing areas in the Whirlpool Sandstone when hydraulic fracturing is used.

End_of_Article - Last_Page 1174------------