The

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

Catskill Formation or the Catskill

Clastic wedge In geology, clastic wedge usually refers to a thick assemblage of sediments--often lens-shaped in profile--eroded and deposited landward of a mountain chain; they begin at the mountain front, thicken considerably landwards of it to a peak depth, an ...

is a unit of mostly terrestrial

sedimentary Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...

rock found in

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

and New York. Minor marine layers exist in this thick rock unit (up to ). It is equivalent to the Hampshire Formation of

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...

West Virginia West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the Bur ...

, and

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

. The Catskill is the largest bedrock unit of the

Upper Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...

in northeast Pennsylvania and the Catskill region of New York, from which its name is derived. The

Pocono Mountains The Pocono Mountains, commonly referred to as the Poconos , are a geographical, geological, and cultural region in Northeastern Pennsylvania. They overlook the Delaware River and Delaware Water Gap to the east, Lake Wallenpaupack to the north, ...

of Pennsylvania are largely underlain by this unit as well. The rocks of the Catskill are predominantly

red sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) b ...

indicating a large scale terrestrial deposition during the Acadian orogeny. Many beds are cyclical in nature, preserving the record of a dynamic environment during its approximately 20 million years of deposition.

Depositional environment

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 North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

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 The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...

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 Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...

was formed as a consequence. This was the first major oil region to be developed. The Catskill was once considered to be related to the

Old Red Sandstone The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the northeastern seaboard of North America. It also exte ...

, 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.

Glacial Erosion

Though both mountain ranges were formed during the Acadian orogeny, the Catskill Mountains, unlike the Appalachian Mountains underwent glacial erosion. Much of what formed the Catskills as they stand today is a result of the

Wisconsin glaciation The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cor ...

which ended only about 12,000 years ago.

Signs of Glaciation

There are many signs of the

Glacial period A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

event which carved the current day

Catskill Mountains The Catskill Mountains, also known as the Catskills, are a physiographic province of the larger Appalachian Mountains, located in southeastern New York. As a cultural and geographic region, the Catskills are generally defined as those areas c ...

. These markers include: * Glacial Erratics such as the Devils Tombstone * Striations * "Dance Floors" such as

Pratt Rock Pratt Rock, also known as Pratt's Rock, is a rockface or other landform that includes a series of stone carvings in Prattsville, New York depicting the life of Zadock Pratt. Pratt was supposed to be buried in a tomb carved into the stone, but work ...

Terminal moraine A terminal moraine, also called end moraine, is a type of moraine that forms at the terminal (edge) of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, has been pushed by the front edge ...

Members

Eastern Pennsylvania

Towamensing, Walcksville, Beaverdam Run, Long Run, Packerton, Poplar Gap, Sawmill Run, Berry Run, Clarks Ferry, and Duncannon.

Central Pennsylvania

Irish Valley, Sherman Creek, Buddys Run, Clarks Ferry, and Duncannon.

References

External links

Depositional environments in the Catskill Clastic Wedge
{{Chronostratigraphy of Pennsylvania Geologic formations of New York (state) Geologic formations of Pennsylvania Devonian System of North America Devonian geology of Pennsylvania Devonian geology of New York (state) Devonian southern paleotemperate deposits Sandstone formations of the United States Shale formations of the United States Siltstone formations Deltaic deposits