PALEONTOLOGIC AND STRATIGRAPHIC REXAMINATION OF THE UPPERMOST SILURIAN STRATIGRAPHY OF EASTERN NEW YORK STATE: SOME NEW ANSWERS AND MANY MORE QUESTIONS

During the course of synthesizing paleontologic and stratigraphic data as a part of a project aimed at documenting the timing of large-scale faunal turnover events that occurred during the Silurian and Devonian periods in eastern North America, many interesting details came to light about this rather poorly understood interval in eastern New York State, in some cases clearing up previous misunderstandings and in other cases raising more interesting questions.

One of the main stratigraphic issues relates to the development of the Taconic Unconformity from south to north along the Catskill Front. In the south, near the tri-states area, there is a thick succession of middle to Upper Silurian units that sits in angular unconformity on the Upper Ordovician, whereas to the north near the Helderbergs, most all of these units have lapped-out against the unconformity. The precise nature in which these units thin, along with their internal facies relationships, has yet to be totally worked out. Additionally, further examination of the correlations between units in southeastern NY to age-equivalent units in central/western NY and in NJ/PA is necessary.

Recent work indicates a possible interval of transgression that resulted in a marine incursion eastward into the Hudson Valley during the deposition of the Shawangunk Formation resulting in the deposition of sedimentary ironstones similar to those found further west. Associated with these ironstones are marginal marine to open marine ichnofossils such as Skolithos and bilobed cruziana like traces. These fossil/sediment associations could provide a much needed stratigraphic tie-line between the eastern and western NY during this interval.

An examination of the invertebrate fauna of the Upper Silurian units in NY, PA, &NJ indicates a persistence of taxa from the mid-Silurian upwards into the Manlius Formation and its southern equivalents. This new finding suggests that the major faunal turnover from the Late Silurian Evolutionary Ecological subunit into the overlying Lower Devonian Helderberg Evolutionary Ecological subunit roughly coincides with the hypothesized placement of the Silurian/Devonian stage boundary within the upper part of the Manlius Formation.