Issues

ON COVER – Upper Ordovician Queenston Shale sharply overlain by the trough cross-bedded to hummocky bedded Whirlpool Sandstone. The Queenston has been interpreted as very shallow marginal marine to nonmarine tidal flats and alluvial plain muds; the Whirlpool, braided fluvial (lower unit) and shallow marine shoreface (upper unit). This outcrop in Lockport, Niagara County, New York, provides an excellent exposure of the Cherokee unconformity often associated with very late Ordovician Hirnantian glacio-eustatic sea level drop. Long considered to be the Ordovician–Silurian boundary, there is new evidence from biostratigraphy and carbon isotopes suggesting that the Whirlpool may also be of Hirnantian age. Photo by Andrea Sharrer.