Graptolite-bearing black shales in eastern New York have served as the standard of reference for Ordovician graptolite successions in North America. The Schaghticoke, Deepkill, and Normanskill shales do not include a continuous sequence of Early and Middle Ordovician graptolite zones, as previously thought.
The Schaghticoke Shale bears a fauna characterized by Dictyonema flabelliforme flabelliforme and Staurograptus dichotomous. An earliest Ordovician graptolite zone encompasses it.
Four zonal assemblages can be delimited in the Deepkill Shale. Two are latest Early Ordovician; one is earliest Middle Ordovician; the highest is Middle Ordovician and is separated from the others by a structural discordance and a faunal gap of one zone.
The Normanskill Shale bears graptolite assemblages typical of two zones and is of late Middle Ordovician age. It can be divided into four lithic members.
A lithic unit comprised of huge blocks of Normanskill Shale and other older formations in a black shale matrix, which bears graptolites typical of the Canajoharie Shale, overlies the Normanskill Shale on the eastern side of the Hudson River throughout Rensselaer County and the southern part of Washington County, New York. Its exposure belt may be the western limit of the “Taconic Klippe.” The unit separates apparent autochthonous from allochthonous portions of the Normanskill Shale.