TRILOBITE MOUNTAIN: THE REDISCOVERY AND REEXAMINATION OF THE PORT JERVIS FORMATION AND ITS FAUNA

The Tri-States region of southeastern New York State is unique in many ways, not least of which is the near-complete record of sedimentation through an interval in the mid-Early Devonian that, in almost all other localities in North America, is typically represented by the Wallbridge Unconformity that seperates the Tippecanoe from the Kaskaskia megasequences. In this area, the Lochovian-aged Helderberg Group carbonates and the overlying Pragian-aged Oriskany-Glenerie sandstones and carbonates, typically marked by a distinct unconformity, is separated by an argillaceous carbonate unit known as the Port Jervis Formation. This unit, missing to the north and south, provides a unique view into the transition interval between two major EE sub-Units in the Lower Devonian; the Helderberg Fauna below and the Oriskany Fauna above. Little is known of the full extent of the faunal composition of the Port Jervis Formation, but from lists prepared by workers in the early 1900’s, it is evident that this interval records somewhat of a gradational transition between the two faunas. However poorly understood the fauna of the Port Jervis Formation may be, the unit has long been known to contain a few beds with extremely abundant trilobite remains. W.W. Mather, who conducted some of the first geological investigations in this region as part of his study of the First Geological District of New York in the early 1800’s, named the ridge exposing the formation just west of the village of Port Jervis “Trilobite Mountain” for the rich fauna of trilobites discovered there.

The project, begun with an initial rediscovery of the famed Trilobite Bed within the Port Jervis Formation, aims to document as fully as possible the fauna of the Port Jervis interval in order to better understand the nature of the faunal turnover between the two EE sub-Units. Additionally, we will be tracing out the Trilobite Bed and prepare a detailed analysis of the preservation of this unique deposit. Although limited to a specific paleogeographic locality, the Port Jervis Formation provides an extremely important view into a dynamic period in Earth’s history in what is perhaps the most complete stratigraphic section for this interval anywhere on the North American continent. The stratigraphy of the ridge will be re-examined in order to provide an update to the formations found there.