The depositional environments and geologic history of the Medina Group (Lower Silurian) and the Clinton Group (Lower to Upper Silurian) of New York have been interpreted from a regional subsurface study using approximately 250 gamma-ray logs and 125 sample logs. A sequence of paleogeographic maps illustrate the geologic history and depositional environments associated with this predominantly clastic, rock sequence.

Seven principal depositional environments are recognized on the basis of subsurface sedimentary facies. These environments are: (1) transgressive clastic shoreline, (2) stationary clastic shoreline, (3) progradational clastic shoreline, (4) shallow marine nearshore to deltaic, (5) transgressive shallow marine clastic shelf, (6) transgressive shallow marine carbonate shelf, (7) progradational shallow marine clastic-carbonate shelf. Subenvironments recognized within the stationary clastic shoreline include beach, bay, barrier, and open-marine.

The Silurian clastic rocks were deposited during an overall marine transgression that was interrupted by three major progradational phases. The orogenic episodes represented by these progradational phases steadily decreased in intensity. The sediment influx during the first progradational phase was large enough to produce a deltaic system that extended throughout New York. During the second progradational phase, the sediment influx was small relative to the first event, and subsidence probably increased from loading of the Grimsby sediments. The deltaic system that developed during this time was restricted to east-central New York. The final progradational phase represents an even smaller influx of terrigenous material; only a linear clastic shoreline developed in eastern New York. Th s phase marks the last major influx of terrigenous clastic sediments until Devonian time.

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