Catskill Formation
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The Devonian Catskill Formation (Dck) is the name given to a thick bedrock unit found in Pennsylvania and New York. It is at the top of the sedimentary rock sequence deposited in the Catskill Delta, known as the Catskill Clastic Wedge, which is a cyclical sequence of sandstones and shales thought to be deposited in a deltaic environment.
[edit] Formation
During the Devonian period, the Catskill Delta was formed by a series of river deltas and otherwise marshy terrain. This terrain was sandwiched between the epicontinental Kaskaskia Sea in central North America and the now-vanished Acadian Mountains. Erosion brought sediment from the mountain westwards into the sea, forming the deltas.
Eventually the Delta formation was buried and transformed into sandstone, which was then revealed in places when the Catskill and Appalachian Mountains were formed at a later date. This transformation and uncovering is the primary reason why the Catskill Delta is notable in the present; western Pennsylvania's petroleum was formed as a consequence. This was the first major oil region to be developed.
The Catskill Delta formation was once considered to be related to the Old Red Sandstone, but in actuality the two are only coincidentally similar. Both formed at approximately the same time, and under similar conditions: to the north of the Acadian Mountains were the Caledonian Mountains, and a similar region of marsh and river delta formed there.
