Geology of Pennsylvania

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Pennsylvania's physiographic provinces
The Coal Region of Northeastern Pennsylvania has abundant anthracite coal, a high-value energy source.

The Geology of

geologic hazards and plays an important role in shaping everyday life in the state. From the southeast corner to the northwest corner of the state, the include: the Atlantic Plain Province province, the Piedmont Province, the New England Province, the Ridge and Valley Province, the Appalachain Province, and the Central Lowlands Province.[1]

A majority of the rocks in Pennsylvania exposed at the surface are

Mesozoic era.[2]

Pleistocene

glaciers have also repeatedly visited the state over the last 100,000 years. These glaciers have left some evidence and carved out much of the landscape of the northern tier of the state.[2]

A rock with high economic value from Pennsylvania is anthracite coal. Before mining began, there was an estimated 22.8 billion tons of anthracite in Pennsylvania. In 2001, 12 billion tons still remained in the ground, most of which was not economically feasible to mine.[3] American geologists recognized the importance of Pennsylvania's coal region and named the Upper Carboniferous Period the Pennsylvanian Period because of the abundance of coal in the state. Despite this, Celestine was proposed as the state mineral in 2002. The proposal however, was not approved by the state legislature.[4][5]

Pennsylvania is also home to the famous

Quaker State (now owned by Royal Dutch Shell) and Pennzoil
. Pennsylvania also has reserves of natural gas from both deeply buried source rocks and coal-bed areas.

Atlantic Coastal Plain

One of the smallest physiographic provinces in the state is confined to

Flash floods are becoming a local problem in the province.[2]

Piedmont

The Piedmont in Pennsylvania is divided into three distinct sections: the Piedmont Uplands, the Piedmont Lowlands, and the Gettysburg-Newark Lowlands. Much of the Piedmont is becoming urbanized and developed. Some of the best farmland in the state is in this region, specifically Lancaster and Chester counties.

Piedmont Uplands

The top plate illustrates the tectonic setting for the sediments of Pennsylvania

This section is characterized by the

deposition of sediment that would become the Wissahickon Formation during a rifting of Rodinia. Sea floor spreading continued until a passive margin developed along the new Iapetus Ocean and a beach strandline developed. These sediments eventually became the Chickies Formation.[8]

Siliclasitc and carbonate deposition continued through the Cambrian and into the Ordovician period. During the Taconic orogeny, more igneous intrusions and metamorphism occurred as the ancestral Taconic Mountains were pushed up. The sediments that were deposited in a sea between an island-arc and the Iapetus eventually were squeezed and deformed along a subduction zone. The sediments deposited in that sea are now located in the Great Valley section. (See below) The sediments placed from the rifting of Rodinia became the roots of the ancestral Taconics and went through their first wave of metamorphism during the Taconic orogeny. Additional waves of metamorphism continued up until the Alleghanian orogeny.[8]

Piedmont Lowlands

The lowlands are underlain primarily by more easily eroded rocks such as limestone, dolomite, and phyllite. These rocks are relatively younger in age than the surrounding uplands and are likely the result of a quiet stretch of shallow sea deposition. Some of the rocks deposited during this time are also found in the Great Valley section but have been separated by the Gettysburg-Newark Lowland section. Relief is low and generally never rises above 700 feet (210 m). Karst terrain is problematic in this section.[2]

Gettysburg-Newark Lowlands

This section is a bit misleading since there are hills as high as 1,200 feet (366 m) in this section. It is separated from the rest of the Piedmont sections due to the distinctive rock types found here. Also called the

dykes and sills later in the Jurassic as the Atlantic Ocean began to form.[9] Much of the rocks from this area have been eroded away, but the more erosion resistant diabase has left hills and small elevated regions throughout the section. The erosion patterns of these rocks played a pivotal role in the Battle of Gettysburg.[10]

Buckingham Valley

A small slice of Paleozoic rocks, mostly carbonates, exists in Buckingham Township. These rocks lie north of the Furlong fault which is an offshoot of the larger Chalfont fault.[11] Buckingham Mountain rises south of the valley and comprises quartzite. The other ridge is less prominent and is underlain by the conglomerates of the Stockton Formation. Karst is a localized problem in this area.

New England

A small and fragmented province in northeastern Pennsylvania called the

granitic rocks and quartzite of this area are highly metamorphosed and are Pre-Cambrian to Cambrian in age. Hills and ridges are locally steep and rounded at the top and form the hills around Reading, and to the south of the Lehigh Valley on South Mountain.[2]

Ridge and valley

This region in Pennsylvania, made famous by

Alleghenian orogeny. There are seven distinct regions of the province and they are listed below. Much of the drainage patterns in the province is trellis
.

South Mountain

South Mountain is the northern tip of the Blue Ridge Mountains. This region is characterized by broad flat ridges with deep narrow valleys. The rocks here are highly metamorphosed igneous and sedimentary rocks with some occasional dolomite. These rocks are Pre-Cambrian in age.[2]

Great Valley

The Great Appalachian Valley is a long broad valley that extends from Canada to Alabama. In Pennsylvania, the valley is known by three names: (listed from north to south) the

carbonate rocks are used for variety of purposes including, crushed stone, cement manufacturing, fertilizers, and coal-mine dust (reduces acid mine drainage)[12]
Karst features are problematic in the Great Valley.

Blue Mountain

The Lehigh Gap of Blue Mountain from its east peak

The Blue Mountain or Blue Ridge region, like the ridgelines to its north and west, is one of a series of near parallel ridges that run for tens of miles, and are equally likely to be called Ridge or Mountain. Hence Blue Mountain is not to be confused with the Blue Ridge Mountains but instead, represents the sharp

wind gaps" also exist. The rocks of the Blue Mountain section include mostly Silurian aged sandstone, conglomerate, siltstone, shale, and some limestone. Blue mountain is also known by the names Kittatinny Mountain (especially in New Jersey) and Hawk Mountain. One of the most prominent rock types of this section is the Shawangunk Formation, which is named after the Shawangunk Ridge
of New York state.

The sediments that comprise Blue Mountain were deposited as a result of the highlands that formed after the Taconic orogeny. The first wave of sediments were coarse, gray, and poorly sorted. (The Shawngunk Formation) This combination of depositional features means that the source area was relatively close and deposited in a moist climate. These sediments grade into finer reddish sands and silts, (Bloomsburg Formation) as the source area became more distant and/or less productive. The climate during this time was drier.[2]

Anthracite Upland

Arguably the most complex and most studied section in the

Mississippian
Period came from highlands located to the southeast. Waves of mountain-building occasionally brought coarser-grained sediments onto the plain. As the mountains eroded, the sediments became more fine-grained. As the highlands became more distant, or eroded, the sands would grade into silt or clay.

Since the

Pangea
was finally formed.

It would take 150 million years for the mountains of this area to achieve the shapes seen today. These mountains are steep-sided and valleys are canoe-shaped, largely due to the area's complex folded structure. Most of the coal being mined from this section is from the Pennsylvanian-aged formations. Along with the

Mazon Creek fossil field in Illinois, a tremendous amount of plant fossils has been studied from this area.[13] Landslides and acid mine drainage are two principal hazards of the area. In the past, underground mine fires have also been a threat. The Centralia Mine Fire
is located within this section of the Ridge and Valley province.

Anthracite Valley

Wyoming Valley and the Susquehanna River in Luzerne County

Detached from the rest of Pennsylvania's anthracite fields, this canoe-shaped valley is also known as the Wyoming Valley and is home to the cities of Scranton and Wilkes-Barre. The largest city in the Wyoming Valley is Scranton, with a population of 77,291. The whole structure of the section is a double plunging syncline with sharp mountain ridges on either side of the valley. The ridges meet just north of Carbondale. The North Branch of the Susquehanna River and the Lackawanna River flow through this valley. Large-scale coal mining and its accompanying industry and railroads have long been abandoned.

Unlike the southern and middle anthracite fields, the anthracite valley has been recently glaciated repeatedly. This action has left many talus slopes at the base of Moosic Mountains, and the soils often contain large boulders that make excavation difficult.

Susquehanna Lowland

This region has also seen its landscape altered by glaciation and the

fluvial processes of the Susquehanna River. Most of the ridges in this region are parallel to the streams that drain the area. The Susquehanna also cuts through many of the mountain ridges leading some to believe that the Susquehanna is an ancient river system that existed even before the recent continental glaciation. (Some speculate as far back as the Jurassic Period)[14]
None of the mountains in this section rise above 1,700 feet (518 m) and the river valley is as low as 250 feet (76 m).

Appalachian Mountain

Appalachian Ridge seen from Clarks Knob

Standard long, narrow, and steep-sided ridges with narrow valleys define the state in LANDSAT photos. Many of the valleys have karst features due to carbonate rocks that reside in them. Road-building generally follows the valleys and rarely cuts across the ridges. The Pennsylvania Turnpike used tunnels cut through the ridges rather than scaling the mountain tops. Mount Nittany, Tuscarora Mountain, Jacks Mountain, Wills Mountain, and Sideling Hill are five prominent mountains in this section. The section contains Cambrian- through Pennsylvanian-aged sediments all deposited into the

water gaps
through the mountain ranges, and has continuously presented new softer rocks in the valleys to be eroded away.

Appalachian Plateau

This is by far the largest province in the state, and most of the rocks in this region are not folded and faulted and sit relatively flat. However, parts of the Appalachian Plateau appear to be mountainous due to erosion caused by streams and glaciers. In western Pennsylvania, large bituminous coal fields exist in rocks with a similar age as the rocks in the anthracite region. Many of the folds in the province are high amplitude and stretch for miles. In glaciated sections, steep canyons developed and much of the terrain have many glacial features. The drainage pattern in this area is dendritic.

Glaciated Pocono Plateau

The

Catskill Formation are the predominant bedrock type in the Poconos. The elevation of the plateau is between 1,200 feet (366 m) and 2,300 feet (701 m) with only a few steep hills such as Camelback Mountain. Much of the rock sits in gently dipping horizontal beds, unlike the neighboring Appalachian Mountain section.[2]

Glaciated Low Plateau

Considered a part of the Pocono Plateau, this area lies to the north of the Poconos and contains many of the same types of rock. The local relief is less than that of the Pocono region and bounded to the southeast by the Delaware River. The

waterfalls, especially around the area of Resica Falls Scout Reservation. Dingmans Falls and Bushkill Falls are waterfalls within the Delaware Water Gap National Recreation Area, also a part of the Endless Mountains
region of Pennsylvania.

Glaciated High Plateau

Also an extension of the Catskill Mountains of New York, this section generally has higher elevations than the low plateau section as well as deeper valleys. Younger strata also outcrops in this area with a few minor coal beds. The uplands are rounded or flat along mostly broad hills. An excellent example of the escarpment that divides this section are Ricketts and Ganoga Glen located within Ricketts Glen State Park.

Deep Valleys

This section is home to the

Pennsylvania Bureau of Forestry
.

Allegheny Front

Snow covered Blue Knob Mountain (3,146 ft.) looming above the countryside

The

Blue Knob
, 3,136 feet (956 m), an unusual bulge along this symmetrical ridgeline. Streams that cut into the ridge are often shallow and steep.

Allegheny Mountain

For the ridge with the
Potomac, and Susquehanna Rivers, see Allegheny Mountain (Pennsylvania)
.

This section includes Pennsylvania's highest point,

Quecreek Mine Rescue and the crash of United Airlines Flight 93
.

Waynesburg Hills

Located in the southwest corner of the state, the Waynesburg hills are another major coal-producing area for the state. Much of the 64.4 billion tons of bituminous coal that is remaining in the state resides under these hills in near horizontal beds. The hills are narrow and steep-sided, with some deeper valleys.[3]

Pittsburgh Low Plateau

Another section that is a significant coal producer. It is similar to the Waynesburg hills section except for higher local relief and deeper valleys. Landslides and mine subsidence are common hazards.[3]

High Plateau

This section consists of high, broad, and flat uplands cut by sharp and shallow river valleys. Much of this area was not covered by the Late Wisconsinan glacier, but there is evidence of pre-Wisconsinan glaciers in the area. Along with the Endless Mountains, it is one of the most remote places in the eastern United States.

Northwestern Glaciated Plateau

This section has been influenced by glaciers and many of the valleys cut into the bedrock trend northwestward- in the direction of the retreating glaciers. There are many signs of glaciers including kames, eskers, kettles, and moraines. This section is home to Pennsylvania's largest natural lake, Conneaut Lake as well as one of the longest eskers in the state, West Liberty Esker.[15] Some of the drainage patterns have shifted and only a few of the streams flow into Lake Erie.

Central Lowlands

Along with the Coastal Plain Province, the smallest province in the state, the central lowlands are a part of the Great Lakes area and exist along a glacial escapement adjacent to Lake Erie.

Geologic features

The following is a list of Pennsylvania geologic features noted for their beauty and/or uniqueness.

Periglacial

Boulder Field at Hickory Run State Park

Glacial

Structural

upright=1.1Bear Valley Strip Mine, southwest of Shamokin in the Coal Region

Rock formations

See also: List of mapped rock formations in Pennsylvania

Pennsylvania has been updating its base geologic map last printed in 1980. New research has shifted the names of several formations and promoted or demoted many different sequences on the stratigraphic chart.

References

  1. ^ Sevon, W.D. (2000). Physiographic Provinces of Pennsylvania, Map 13. Pennsylvania Geologic Survey. Harrisburg, PA.
  2. ^ a b c d e f g h Schultz, C.H. ed. (2002) The Geology of Pennsylvania. Special Publication No.1. Pennsylvania Geologic Survey and Pittsburgh Geological Society. [1]
  3. ^ a b c d Edmunds, W.E., (2002), Coal in Pennsylvania (2nd ed.): Pennsylvania Geological Survey, Educational Series 7, p. 17.
  4. ^ Pennsylvania Geological Survey: Rocks and Minerals
  5. ^ Edwin, C., (2003). Celestine, the Proposed State Mineral. Pennsylvania Geology, Pennsylvania Geological Survey, Harrisburg, PA. V 33 n 1.
  6. ^ D. W. Greenman, D. R. Rima, W. N. Lockwood, and Harold Meisler, Ground-water resources of the Coastal Plain area of southeastern Pennsylvania (1961). 375 p., 22 pls.
  7. ^ Welcome to John Heinz National Wildlife Refuge at Tinicum
  8. ^ a b c Blackmer, G.C., (2005). Preliminary Bedrock Geologic Map of a Portion of the Wilmington 30- by 60-Minute Quadrangle, Southeastern Pennsylvania. Pennsylvania Geologic Survey, Open-File Report OFBM-05-01.0.
  9. ^ Faill, R.T. (2004). The Birdsboro Basin. Pennsylvania Geology, Pennsylvania Geologic Survey, Harrisburg, PA. V 34 n 4.
  10. ^ Smith, R.C. and Keen, R.C., (2004). Regional Rifts and the Battle of Gettysburg. Pennsylvania Geology, Pennsylvania Geological Survey, Harrisburg, PA. V 34 n 3.
  11. ^ Glaeser, J. D. (1966). "Provenance, Dispersdal, and Depositional Environments of Triassic Sediments in the Newark-Gettysburg Basin". Pennsylvania Geologic Survey, G43, Harrisburg, Pennsylvania.
  12. ^ Barnes, J.H. and Smith, R.C., II, (2001). The non-fuel mineral resources of Pennsylvania: Pennsylvania Geological Survey, Educational Series 12.
  13. ^ a b Oleksyshyn, J. (1982). Fossil Plants From the Anthracite Coal Fields of Eastern Pennsylvania. Pennsylvania Geologic Survey, Harrisburg PA, G72.
  14. ^ Inners, J. D., 1998, Rocks and ruins of the “Upper Grand”—An illustrated trail guide to the geology and historical archeology of Lehigh Gorge State Park: Pennsylvania Geological Survey, 4th ser., Open-File Report 98–03, 4 p., Portable Document Format (PDF).
  15. ISBN 0-87842-227-7

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