ABSTRACT

BACKGROUND At the end of the Ordovician Period there was a major extinction event which coincided with a worldwide glaciation and, in New York State, with a major erosional episode that produced the Cherokee Unconformity at the Ordovician-Silurian boundary. The Silurian Period in New York begins, therefore, with a marine transgression, as the sea invaded the land following the melting of the ice sheets and the wearing down of the exposed land surface. The Silurian is a relatively shorter period than the Ordovician and, although most of the time sea levels were fairly high, there was a considerable variety of environments which are represented today by different rock types. The sea spread across New York from the west, laying down sandstones and shales derived from erosion of the land to the east. By midSilurian times, open sea covered most of the state and shales and sandstones gave way to increasing amounts of limestone. Increased tectonic activity rejuvenated mountains to the east which resulted in the sea floor becoming smothered with sand (in the east), shales (mid-state) and deep-water muds in the west. As the mountains wore down, so quiet-water conditions again prevailed and the later half of the Silurian Period in New York is represented with rock sequences predominantly carbonate in nature.