Geology of Delaware
Encyclopedia
The geology of Delaware
consists of two physiographic provinces. They are the Atlantic Coastal Plain
Province and the Piedmont
Province.
to Wilmington
. The unconsolidated sediments of the coastal plain range in age from Cretaceous
to recent. They consist of gravels, sands, silt, and clay, with varying mixtures of all four. The oldest layer, the Potomac Formation
also contains some scattered lignite
.
, Dewey Beach
, Bethany Beach
, South Bethany
, and Fenwick Island
. Headlands are located at Rehoboth and Bethany and one inlet, Indian River Inlet serves as the only "natural" access to Rehoboth and Indian River Bays. The other areas are known as bay barriers and provide the only separation from the Atlantic Ocean
from the lagoons.
Off shore there are two shoal
fields; Hen and Chickens shoal and Fenwick Island shoal. These two areas pose a hazard to boaters. The longshore drift
along the coast is generally north with a node just below South Bethany moving the sand south toward Ocean City, Maryland
. Further offshore, the Delaware River
paleovalley, which existed during the most recent ice age
, is filled with recent sediments scoured and re-deposited as sea level rose.
and Maryland
.
The rocks exposed in the Piedmont are metamorphic and igneous rocks that are approximately half a billion to 1.2 billion years old. The only Precambrian
rock unit is the Baltimore Gneiss. Cambrian
to Ordovician
rocks include Wilmington Complex, Setters Formation, Cockeysville Marble, and Wissahickon Formation
. Silurian
rocks include the Iron Hill Gabbro, Bringhurst Gabbro, and Arden Plutonic Supersuite http://www.udel.edu/dgs/Geology/geostrat.html. The cities of Wilmington
and Newark
lie at the Fall line
, where the northern margin of the younger Cretaceous
coastal plain sediments overlie the older Piedmont rocks.
is the primary source of information about Delaware geology and hydrogeology, such as surface and sub-surface geologic rock formations, extent and quality of aquifers, stream and groundwater monitoring, water supply, earthquakes, floods and droughts, coastal processes (tides, beach erosion), topographic mapping, state mapping and GIS coordination. DGS research and service activities are focused on five areas: (1) geology, (2) hydrology, (3) natural hazards, (4) the state geospatial framework, and (5) information dissemination. These efforts impact a wide variety of issues ranging from water resources, agriculture, environmental protection, and energy and mineral resources to economic development, land-use planning, emergency management, public health, and recreation.
Delaware
Delaware is a U.S. state located on the Atlantic Coast in the Mid-Atlantic region of the United States. It is bordered to the south and west by Maryland, and to the north by Pennsylvania...
consists of two physiographic provinces. They are the Atlantic Coastal Plain
Atlantic Coastal Plain
The Atlantic coastal plain has both low elevation and low relief, but it is also a relatively flat landform extending from the New York Bight southward to a Georgia/Florida section of the Eastern Continental Divide, which demarcates the plain from the ACF River Basin in the Gulf Coastal Plain to...
Province and the Piedmont
Piedmont (United States)
The Piedmont is a plateau region located in the eastern United States between the Atlantic Coastal Plain and the main Appalachian Mountains, stretching from New Jersey in the north to central Alabama in the south. The Piedmont province is a physiographic province of the larger Appalachian division...
Province.
Coastal plain
The coastal plain in Delaware is by far the largest province, encompassing all of the state south of the Kirkwood Highway from NewarkNewark, Delaware
Newark is an American city in New Castle County, Delaware, west-southwest of Wilmington. According to the 2010 Census, the population of the city is 31,454. Newark is the home of the University of Delaware.- History :...
to Wilmington
Wilmington, Delaware
Wilmington is the largest city in the state of Delaware, United States, and is located at the confluence of the Christina River and Brandywine Creek, near where the Christina flows into the Delaware River. It is the county seat of New Castle County and one of the major cities in the Delaware Valley...
. The unconsolidated sediments of the coastal plain range in age from Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
to recent. They consist of gravels, sands, silt, and clay, with varying mixtures of all four. The oldest layer, the Potomac Formation
Potomac Formation
The Potomac Formation consists of Lower Cretaceous to Upper Cretaceous strata located in Delaware, Maryland, and New Jersey, in the eastern United States.Flora found include large cycads....
also contains some scattered lignite
Lignite
Lignite, often referred to as brown coal, or Rosebud coal by Northern Pacific Railroad,is a soft brown fuel with characteristics that put it somewhere between coal and peat...
.
Atlantic coastline
Delaware has a 25 mile (40 km) coastline that includes the communities of Rehoboth BeachRehoboth Beach, Delaware
Rehoboth Beach is a city in Sussex County, Delaware, United States. According to the 2010 census, the population is 1,327, a decrease of 11.2% from 2000...
, Dewey Beach
Dewey Beach, Delaware
As of the census of 2000, there were 301 people, 161 households, and 83 families residing in the town. The population density was 876.6 people per square mile . There were 1,369 housing units at an average density of 3,986.9 per square mile...
, Bethany Beach
Bethany Beach, Delaware
Bethany Beach is an incorporated town in Sussex County, Delaware, United States. According to the 2010 Census Bureau figures, the population of the town is 1,060; however, during the summer months some 15,000 more populate the town as vacationers...
, South Bethany
South Bethany, Delaware
As of the census of 2000, there were 492 people, 253 households, and 170 families residing in the town. The population density was 948.6 people per square mile . There were 1,137 housing units at an average density of 2,192.1 per square mile...
, and Fenwick Island
Fenwick Island, Delaware
As of the census of 2000, there were 342 people, 178 households, and 126 families residing in the town. The population density was 994.5 people per square mile . There were 666 housing units at an average density of 1,936.7 per square mile . The racial makeup of the town was 99.42% White, and 0.58%...
. Headlands are located at Rehoboth and Bethany and one inlet, Indian River Inlet serves as the only "natural" access to Rehoboth and Indian River Bays. The other areas are known as bay barriers and provide the only separation from the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
from the lagoons.
Off shore there are two shoal
Bar (landform)
A shoal, sandbar , or gravelbar is a somewhat linear landform within or extending into a body of water, typically composed of sand, silt or small pebbles. A spit or sandspit is a type of shoal...
fields; Hen and Chickens shoal and Fenwick Island shoal. These two areas pose a hazard to boaters. The longshore drift
Longshore drift
Longshore drift consists of the transportation of sediments along a coast at an angle to the shoreline, which is dependent on prevailing wind direction, swash and backwash. This process occurs in the littoral zone, and in or within close proximity to the surf zone...
along the coast is generally north with a node just below South Bethany moving the sand south toward Ocean City, Maryland
Ocean City, Maryland
Ocean City, sometimes known as OC, or OCMD, is an Atlantic Ocean resort town in Worcester County, Maryland, United States. Ocean City is widely known in the Mid-Atlantic region of the United States and is a frequent destination for vacationers in that area...
. Further offshore, the Delaware River
Delaware River
The Delaware River is a major river on the Atlantic coast of the United States.A Dutch expedition led by Henry Hudson in 1609 first mapped the river. The river was christened the South River in the New Netherland colony that followed, in contrast to the North River, as the Hudson River was then...
paleovalley, which existed during the most recent ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
, is filled with recent sediments scoured and re-deposited as sea level rose.
Piedmont
The Piedmont Physiographic Region of Delaware only includes the hills of northern New Castle County, which rise to approximately 400 feet above sea level. The Piedmont extends into neighboring PennsylvaniaPennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
and Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...
.
The rocks exposed in the Piedmont are metamorphic and igneous rocks that are approximately half a billion to 1.2 billion years old. The only Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
rock unit is the Baltimore Gneiss. Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
to Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
rocks include Wilmington Complex, Setters Formation, Cockeysville Marble, and Wissahickon Formation
Wissahickon Formation
The Wissahickon Formation is a mapped bedrock unit in Pennsylvania, New Jersey, and Delaware. In Maryland, the term "Wissahickon" is no longer used and has since been divided into several units. It is named for the Wissahickon gorge in Fairmount Park, Philadelphia.-Description:The Wissahickon is...
. Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
rocks include the Iron Hill Gabbro, Bringhurst Gabbro, and Arden Plutonic Supersuite http://www.udel.edu/dgs/Geology/geostrat.html. The cities of Wilmington
Wilmington, Delaware
Wilmington is the largest city in the state of Delaware, United States, and is located at the confluence of the Christina River and Brandywine Creek, near where the Christina flows into the Delaware River. It is the county seat of New Castle County and one of the major cities in the Delaware Valley...
and Newark
Newark, Delaware
Newark is an American city in New Castle County, Delaware, west-southwest of Wilmington. According to the 2010 Census, the population of the city is 31,454. Newark is the home of the University of Delaware.- History :...
lie at the Fall line
Fall line
A fall line is a geomorphologic unconformity between an upland region of relatively hard crystalline basement rock and a coastal plain of softer sedimentary rock. A fall line is typically prominent when crossed by a river, for there will often be rapids or waterfalls...
, where the northern margin of the younger Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
coastal plain sediments overlie the older Piedmont rocks.
Geologic features
- Cape HenlopenCape HenlopenCape Henlopen is the southern cape of the Delaware Bay along the Atlantic coast of the United States. It lies in the state of Delaware, near the town of Lewes, Delaware...
DGS Special Publication 26 - Red Clay Valley DGS Special Publication 20
- Pollack Farm Fossil Site DGS Special Publication 21
- Carolina bayCarolina BayCarolina bays are elliptical depressions concentrated along the Atlantic seaboard within coastal Delaware, Maryland, New Jersey, North Carolina, South Carolina, Virginia, Georgia, and northcentral Florida...
s DGS Special Publication 24 shows Carolina Bays in Delaware
Delaware Geological Survey
The Delaware Geological SurveyDelaware Geological Survey
The Delaware Geological Survey is a science-based, public-service-driven Delaware state agency at the University of Delaware that conducts geologic and hydrologic research, service, and exploration for the benefit of the citizens of the First State...
is the primary source of information about Delaware geology and hydrogeology, such as surface and sub-surface geologic rock formations, extent and quality of aquifers, stream and groundwater monitoring, water supply, earthquakes, floods and droughts, coastal processes (tides, beach erosion), topographic mapping, state mapping and GIS coordination. DGS research and service activities are focused on five areas: (1) geology, (2) hydrology, (3) natural hazards, (4) the state geospatial framework, and (5) information dissemination. These efforts impact a wide variety of issues ranging from water resources, agriculture, environmental protection, and energy and mineral resources to economic development, land-use planning, emergency management, public health, and recreation.