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Site content related to keyword: "surficial geology"

GM16 Geologic Map of the Fairmount and Rehoboth Beach Quadrangles, Delaware

GM16 Geologic Map of the Fairmount and Rehoboth Beach Quadrangles, Delaware

The geologic history of the surficial units of the Fairmount and Rehoboth Beach quadrangles is that of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition related to sea-level fluctuations during the Pleistocene. The geology reflects this complex history both onshore, in Rehoboth Bay, and offshore. Erosion during the late Pleistocene sea-level low stand and ongoing deposition offshore and in Rehoboth Bay during the Holocene rise in sea level represent the last of several cycles of erosion and deposition.

Delaware Geologic Mapping Program (STATEMAP)


The Delaware Geological Survey has a continuing program to map the geology of the entire state at the detailed scale of 1:24,000. The STATEMAP component of the National Cooperative Geologic Mapping Program has contributed significantly to our surficial geologic mapping program. This work has resulted in not only new geologic mapping, but also the digital compilation of previous mapping. Products of this program include file formats that can be downloaded and printed from the web as geologic map products and imported into GIS software as georeferenced layers.

Delaware Geological Survey - US Geological Survey Stream and Tide Gaging Program

The US Geological Survey in cooperation with the Delaware Geological Survey through a State-Federal partnership program operates and maintains stream and tide gages throughout Delaware. The streamgage network is a component of the National Streamflow Information Program (NSIP), a program that provides real-time and long-term current and historical streamflow information that is not only accurate and unbiased, but also meets the needs of many users.

Nanticoke River Group


The Nanticoke River Group consists of the Turtle Branch and Kent Island Formations. The Nanticoke River Group consists of heterogeneous units of interbedded fine to coarse sand, clayey silt, sandy silt, and silty clay. Where the units are muddy, downstream of Seaford, the sequence consists of a lower fluvial to estuarine swamp to tidal stream deposits (coarse sand to gravelly sand with scattered organic-rich muddy beds) overlain by estuarine clayey silts and silty clays that contain rare to common Crassostrea (oyster) bioherms. The silts and clays are overlain by sands with clay laminae, to fine to coarse well-sorted, clean sand that are estuarne beach and eolian in origin. Upstream, the mud beds are rarer and restricted to the west side of streams and consist of organic rich clayey silt. Most of the stratigraphic section is dominated by clean, well-sorted sands.

Assawoman Bay Group


The Assawoman Bay Group consists of the well-sorted sands, silts, and clays of the Omar, Ironshire, and Sinepuxent Formations found adjacent to and inland of the Atlantic Coast of Delaware and Maryland. These deposits in Delaware and Maryland were named from oldest to youngest: the Omar Formation (Jordan, 1962, 1964), the Ironshire Formation (Owens and Denny, 1979a), and the Sinepuxent Formation (Owens and Denny, 1979a).

Kent Island Formation


Owens and Denny (1979) named the Kent Island Formation for deposits bordering the Chesapeake Bay found underneath lowlands that ranged in elevation from 0 to 25 feet in elevation but most of the land surface area is less than 10 feet in elevation. These lowlands are bordered by a scarp with at toe at approximately 25 feet. In its type area, the Kent Island Formation was described as consisting of thick beds of loose, light colored, cross-stratified sand overlying dark-colored massive to thinly laminated clay-silt. Pebbles as much as 10 cm (4 in.) in diameter occur in thin beds with the sand or as scattered clasts in both the sand and clay-silt. Locally, large tree stumps in growth position are encased in the clay-silt. Maximum thickness of the Kent Island was about 12 m (40 feet).

Omar Formation


The Omar Formation was originally described (Jordan, 1962) as consisting of interbedded, gray to dark gray, quartz sands and silts with bedding ranging from a few inches to more than 10 feet thick. Thin laminae of clay are found within the fine, well-sorted sands. Silt mixed with sand generally contains some plant matter and where dark in color could be considered organic. Sands contain wood fragments, some of which are lignitic.

Ironshire Formation


The Ironshire Formation was described by Owens and Denny (1979) as consisting of a lower loose, pale-yellow to white, well-sorted, medium sand characterized by long, low-angle inclined beds with laminae of black minerals. The upper portion of the units was described as consisting of light-colored, trough cross-stratified, well-sorted sand with pebbles and a few Callianassa borings. They described the Ironshire Formation near Rehoboth in a stratigraphic section which is now considered to be a part of the Lynch Heights Formation.

Sinepuxent Formation


Owens and Denny (1979) described the Sinepuxent Formation in Maryland as dark, poorly sorted, silty fine to medium sand with the lower part of the unit being fine grained with thin beds of black clay. The Sinepuxent Formation is described as being lithically distinct from the Omar and Ironshire Formations due to the presence gray, laminated, silty very fine to fine, quartzose, micaceous, sand to sandy silt. The base of the unit is typically a bluishgray to dark-gray clayey silt to silty clay. There are a few shelly zones within the Sinepuxent Formation in the vicinity of Bethany Beach (McDonald, 1981; McLaughlin et al., 2008). The Sinepuxent Formation is up to 40 feet thick.

Cypress Swamp Formation


The upper part of the Cypress Swamp Formation is a multi-colored, thinly bedded to laminated, quartzose fine sand to silty fine sand, with areally discontinuous laminae to thin beds of fine to coarse sand, sandy silt, clayey silt, organic silt, and peat. The lowermost 3 to 6 ft of the unit are commonly composed of thin beds of dark-colored, organic-rich, clayey silt with laminae to thin beds of fine sand and peat. Fine sand to fine sandy silt are present at the base of the unit in boreholes where the lower organic-rich beds are absent. Dark-colored, peaty, organic-rich silt and clayey silt with laminae of fine to medium sand as much as 4.5 ft thick are common within 5 ft of land surface, but may be absent in some locations. Colors are shades of brown, gray, and green where the unit contains visible organic matter, and orange, yellow, and red at shallow depths where the organic-rich beds are absent. Clay-sized minerals are a mixed suite that includes kaolinite, chlorite, illite, and vermiculite.

A Generalized Geologic Map of Delaware

Generalized Geologic Map of Delaware

The Delaware Geological Survey (DGS) has published the surficial geology of the state of Delaware at a scale of 1:100,000 for New Castle and Kent counties (Ramsey, 2005, 2007). Maps at this scale are useful for viewing general geologic framework on a county-wide basis, determining the geology of watersheds, and recognizing the relationship of geology to county-wide environmental or land-use issues. These maps, when combined with subsurface geologic information, provide a basis for locating water supplies, mapping ground-water recharge areas, and protecting ground and surface water. Geologic maps are also used to identify geologic hazards, such as flood-prone areas, to identify sand and gravel resources, and for supporting state, county, and local land-use planning decisions. Portions of Sussex County have previously been mapped at 1:24,000-scale.

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DGS releases new geologic map of Georgetown area

The Delaware Geological Survey (DGS) has published a new geologic map of the Georgetown area in eastern Sussex County entitled Geologic Map of the Georgetown Quadrangle, Delaware. Geologic Map No. 15 presents the results of research by Kelvin W. Ramsey of the DGS.

DGS Geologic Map No. 15 (Georgetown Quadrangle) Dataset

DGS Geologic Map No. 15 (Georgetown Quadrangle) Dataset

This vector data set contains the rock unit polygons for the surficial geology in the Delaware Coastal Plain covered by DGS Geologic Map No. 15 (Geologic Map of the Georgetown Quadrangle, Delaware). The geologic history of the surficial geologic units of the Georgetown Quadrangle is primarily that of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition of younger stratigraphic units. The age of the Beaverdam Formation is uncertain due to the lack of age-definitive fossils within the unit but is thought to be between late Pliocene to early Pleistocene in age. Refer to Ramsey, 2010 (DGS Report of Investigations No. 76) for details regarding the stratigraphic units.

To facilitate the GIS community of Delaware and to release the geologic map of the Georgetown Quadrangle with all cartographic elements (including geologic symbology, text, etc.) in a form usable in a GIS, we have released this digital coverage of DGS Geological Map 15. The update of earlier work and mapping of new units is important not only to geologists, but also to hydrologists who wish to understand the distribution of water resources, to engineers who need bedrock information during construction of roads and buildings, to government officials and agencies who are planning for residential and commercial growth, and to citizens who are curious about the bedrock under their homes. Formal names are assigned to all rock units according to the guidelines of the 1983 North American Stratigraphic Code (NACSN, 1983).

GM15 Geologic Map of the Georgetown Quadrangle, Delaware

GM15 Geologic Map of the Georgetown Quadrangle, Delaware

The geologic history of the surficial geologic units of the Georgetown Quadrangle is primarily that of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition of younger stratigraphic units. The age of the Beaverdam Formation is uncertain due to the lack of age-definitive fossils within the unit. Stratigraphic relationships in Delaware indicate that it is no older than late Miocene and no younger than early Pleistocene. Regional correlations based on similarities of depositional style, stratigraphic position, and sediment textures suggest that it is likely late Pliocene in age; correlative with the Bacons Castle Formation of Virginia (Ramsey, 1992, 2010).

DGS Cooperative and Joint-Funded Programs

The DGS is, by statute, the state agency responsible for entering into agreements with its counterpart federal agencies, including the U.S. Geological Survey, the USGS Office of Minerals Information (formerly the U.S. Bureau of Mines), and the Bureau of Ocean Energy Management, Regulation and Enforcement (formerly the U. S. Minerals Management Service), and for administering all cooperative programs of the State with these agencies. The DGS also works with many in-state and out-of-state partner agencies and organizations.

RI72 Geology and Extent of the Confined Aquifers of Kent County, Delaware

RI72 Geology and Extent of the Confined Aquifers of Kent County, Delaware

Ground water comprises nearly all of the water supply in Kent County, Delaware. The confined aquifers of the area are an important part of this resource base. The aim of this study is to provide an up-to-date geologic framework for the confined aquifers of Kent County, with a focus on their stratigraphy and correlation. Seven confined aquifers are used for water supply in Kent County. All occur at progressively greater depths south-southeastward, paralleling the overall dip of the sedimentary section that underlies the state. The two geologically oldest, the Mount Laurel and Rancocas aquifers, are normally reached by drilling only in the northern part of the county. The Mount Laurel aquifer is an Upper Cretaceous marine shelf deposit composed of clean quartz sands that are commonly glauconitic. It occurs at around 300 ft below sea level in the Smyrna Clayton area and is typically just less than 100 ft thick. Southward, toward Dover, it passes into fine-grained facies that do not yield significant ground water. The Rancocas aquifer is a Paleocene to Eocene marine unit of shelf deposits consisting of glauconite-rich sands with shells and hard layers. It occurs as high as 100 ft below sea level in northwestern Kent County and deepens southeastward, rapidly changing facies to finer-grained, nonaquifer lithologies in the same direction.

Old College Formation


Reddish-brown to brown clayey silt, silty sand to sandy silt, and medium to coarse quartz sand with pebbles (Ramsey, 2005). Rock fragments of mica or sillimanite quartzose schist are common sand fraction. At land surface, a gray to grayish-brown clayey silt is present. Sands are cross-bedded with laminae of muscovite or heavy minerals defining the cross-sets. Silty beds tend to be structureless, or in the gray clayey silt beds, heavily bioturbated by roots. No fossils other than pollen have been recovered. Pollen indicate a cold climate during deposition of the upper clayey silt unit (unpublished DGS data). Stratigraphic relationships indicate either slightly younger than or contemporaneous with the Columbia Formation. Ranges from 5 to 40 ft in thickness.

Delaware Bay Group


The Delaware Bay Group consists of transgressive deposits that were laid down along the margins of ancestral Delaware Bay estuaries during middle to late Pleistocene rises and highstands of sea level. The Delaware Bay Group was described in detail by Ramsey (1997). The Delaware Bay Group is comprised of the Lynch Heights Formation, the Scotts Corners Formation, and the Cape May Formation (undivided) in New Jersey.

Beaverdam Formation


Heterogeneous unit ranging from very coarse sand with pebbles to silty clay. Predominant lithologies at land surface are white to mottled light-gray and reddish-brown, silty to clayey, fine to coarse sand. Laminae and beds of very coarse sand with pebbles to gravel are common. Laminae and beds of bluish-gray to light-gray silty clay are also common. In a few places near land surface, but more commonly in the subsurface, beds ranging from 2 to 20-ft thick of finely laminated, very fine sand and silty clay are present. The sands of the Beaverdam Formation commonly have a white silt matrix that gives drill cuttings a milky appearance (Ramsey, 2001, 2007). This white silt matrix is the most distinguishing characteristic of the unit and readily differentiates the Beaverdam Formation from the adjacent clean sands of the Turtle Branch Formation. Interpreted to be a fluvial to estuarine deposit of late Pliocene age on the basis of pollen assemblages and regional stratigraphic relationships (Andres and Ramsey, 1995, 1996; Groot and Jordan, 1999; Groot et al., 1990). Ranges from 50 to 120 ft thick in the Georgetown Quadrangle.

Columbia Formation


Yellowish- to reddish-brown, fine to coarse, feldspathic quartz sand with varying amounts of gravel. Typically cross-bedded with cross-sets ranging from a few inches to over three feet in thickness. Scattered beds of tan to reddish-gray clayey silt are common. In places, the upper 5 to 25 feet consists of grayish- to reddish-brown silt to very fine sand overlying medium to coarse sand. Near the base, clasts of cobble to small boulder size have been found in a gravel bed ranging from a few inches to three feet thick. Gravel fraction primarily quartz with lesser amounts of chert. Clasts of sandstone, siltstone and shale from the Valley and Ridge, and pegmatite, micaceous schist, and amphibolite from the Piedmont are also present. Fills a topographically irregular surface, is less than 50 feet thick, and is interpreted to be primarily a body of fluvial glacial outwash sediment (Jordan, 1964; Ramsey, 1997). Pollen indicate deposition in a cold climate during the middle Pleistocene (Groot and Jordan, 1999).