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Geologic units in Delaware (state in United States)

Additional scientific data in this geographic area

Potomac Formation (Cretaceous) at surface, covers 26 % of this area

Potomac Formation - Variegated silts and clays with beds of quartz sand.

Lithology: silt; clay or mud; sand

Wissahickon Schist (Paleozoic) at surface, covers 14 % of this area

Wissahickon Schist - Dense micaceous schist, gneiss and migmatite.

Rancocas Formation (Tertiary) at surface, covers 14 % of this area

Rancocas Formation - Grayish-green and green, silty, glauconitic sand.

Lithology: sand

Mt. Laurel-Navesink Formation (Cretaceous) at surface, covers 7 % of this area

Mt. Laurel-Navesink Formation - Dark greenish brown and dark gray, highly glauconitic sandy silt and silty sand.

Lithology: silt; sand

Banded Gneiss (Paleozoic) at surface, covers 7 % of this area

Banded Gneiss - banded gneiss

Lithology: gneiss

Merchantville Formation (Cretaceous) at surface, covers 5 % of this area

Merchantville Formation - Dark gray to bluish-gray slightly glauconitic, micaceous silty, very fine sand.

Lithology: sand

Redbank Formation (Cretaceous) at surface, covers 5 % of this area

Redbank Formation - Reddish-brown, slightly micaceous and glauconitic, fine to medium sand.

Lithology: sand

Chesapeake Group (Tertiary) at surface, covers 4 % of this area

Chesapeake Group - Bluish gray silt with quartz sand and some shell beds.

Lithology: silt; sand

Unit C (Tertiary) at surface, covers 4 % of this area

Unit C - Grayish-green, clayey glauconitic silt and sand.

Lithology: silt; sand

Amphibolite (Paleozoic) at surface, covers 4 % of this area

Amphibolite - amphibolite

Lithology: amphibolite

Wenonah Formation (Cretaceous) at surface, covers 2 % of this area

Wenonah Formation - Gray and rust-brown fine to medium, micaceous, sparingly glauconitic quartz sand.

Lithology: sand

Arden Granite (Paleozoic) at surface, covers 1 % of this area

Arden Granite - granite

Lithology: granite

Gabbro (Paleozoic) at surface, covers 0.9 % of this area

Gabbro - gabbro

Lithology: gabbro

Magothy Formation (Cretaceous) at surface, covers 0.8 % of this area

Magothy Formation - White and buff quartz sand with beds of gray and black clayey silt.

Lithology: sand; silt

Unit B (Cretaceous-Tertiary) at surface, covers 0.8 % of this area

Unit B - Greenish-gray sandy and clayey glauconitic silt.

Lithology: silt

Port Deposit Granodiorite (Paleozoic) at surface, covers 0.8 % of this area

Port Deposit Granodiorite - granodiorite

Lithology: granodiorite

Bryn Mawr Formation (?) at surface, covers 0.7 % of this area

Bryn Mawr Formation - Red and brown quartz sand with silt, clay and fine gravel.

Lithology: sand; silt; clay or mud; gravel

Cockeysville Marble (Paleozoic) at surface, covers 0.5 % of this area

Cockeysville Marble - Dense, white crystalline limestone and dolomite.

Pegmatite (Paleozoic) at surface, covers 0.4 % of this area

Pegmatite - Pegmatite

Lithology: pegmatite

Quaternary Deposits Undivided (Quaternary) at surface, covers 0.3 % of this area

Quaternary Deposits Undivided - Undifferentiated gray to buff sand and gravel, gray to brown lignitic silt and clay, occasional boulders, and rare shell beds. Surficial deposits occur as intercalated fluvial sands and marsh muds (e.g. in upstream floodplain of the Wicomico and Nanticoke Rivers), well-sorted, stablized dune sands (e.g. eastern Wicomico County), shell-bearing estuarine clays and silts (e.g. lower Dorchester County) and Pocomoke River basin of Worcester County), and beach zone sands (e.g. Fenwick and Assateague Islands). Wisconsin to Holocene in age. Subsurface deposits of pre-Wisconsin age consist of buff to reddish-brown sand and gravel locally incised into Miocene sediments (e.g. Salisbury area), estuarine to marine white to gray sands, and gray to blue, shell-bearing clays (e.g. Worcester County).

Serpentine (Paleozoic) at surface, covers 0.2 % of this area

Serpentine - serpentine

Lithology: serpentinite

Mafic gneiss (Probably lower Paleozoic) at surface, covers < 0.1 % of this area

Mafic gneiss - Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to pCAmgp in places.

Anorthosite (Probably lower Paleozoic) at surface, covers < 0.1 % of this area

Anorthosite - Medium to coarse grained, light to dark bluish gray, predominantly plagioclase; local alteration minerals.

Lithology: anorthosite

Englishtown Formation (Upper Cretaceous, lower Campanian) at surface, covers < 0.1 % of this area

Englishtown Formation - Sand, quartz, fine- to coarsegrained, gravelly, massive, bioturbated, medium- to dark-gray; weathers light brown, yellow, or reddish brown, locally interbedded with thin to thick beds of dark clay. Abundant carbonaceous matter, with large lignitized logs occur locally, especially in clay strata. Feldspar, glauconite, and muscovite are minor sand constituents. Sand is extensively trough crossbedded particularly west of Mount Holly, Burlington County. In a few places in the western outcrop belt, trace fossils are abundant, typically the burrow Ophiomorpha nodosa. Unit is pyritic, especially in the carbonaceous-rich beds where pyrite is finely disseminated grains or pyritic masses as much as 0.6 m (2 ft) in diameter. Lowest part of unit is a massive sand that contains small to large, soft, light-gray siderite concretions. The Englishtown underlies a broad belt throughout the map area and ranges from about 45 m (148 ft) thick in the northern part of the central sheet to 30 m (98 ft) thick in the western part of the central sheet to 15 m (49 ft) in the southern sheet. Best exposures occur along Crosswicks Creek in the Allentown quadrangle and along Oldmans Creek. The basal contact with the underlying Woodbury Formation or Merchantville Formation is transitional over several meters. The age of the Englishtown in outcrop could not be determined directly but was inferred from stratigraphic position and pollen content. Wolfe (1976) designated the microflora of the unit as Zone CA4 and assigned it to the lower Campanian.

Lithology: sand; clay or mud

Trenton Gravel (Quaternary) at surface, covers < 0.1 % of this area

Trenton Gravel - Gray or pale-reddish-brown, very gravelly sand interstratified with crossbedded sand and clay-silt beds; includes areas of Holocene alluvium and swamp deposits.

Hornerstown Formation (lower Paleocene, Danian) at surface, covers < 0.1 % of this area

Hornerstown Formation - Sand, glauconite, clayey, extensively bioturbated, massive, medium-green in the shallow subsurface. Common to abundant microfauna in the subsurface are not present in outcrop. In the deep subsurface, the Hornerstown Formation consists of glauconite sand at base, overlain by a thin, laminated, dark-gray clay-silt that grades upward into a finegrained, clayey glauconite quartz sand. The formation is very thin and rarely exceeds 7.5 m (25 ft) in thickness. The basal contact with the underlying Kc4 cycle is difficult to place because both units are glauconitic sand; however, the basal Hornerstown contains dark-brown phosphatic debris. Less commonly the contact is marked by extensive burrows filled with glauconite sand that project downward into the underlying unit. Gamma logs from the Hornerstown have a very large gamma kick at the base of the formation. The age of the Hornerstown is early Paleocene (Danian) based on the presence of calcareous nannofossils (Chiasmolithus consuetus and Ellipsolithus macellus) and foraminifera characteristic of zones NP 3 and NP 4, and P1a to P1c (Chengjie Liu, Rutgers University, written commun., 1993), respectively.

Lithology: sand; clay or mud

Marshalltown Formation (Upper Cretaceous, upper and middle Campanian) at surface, covers < 0.1 % of this area

Marshalltown Formation - Sand, quartz and glauconite, fine- to medium-grained, silty and clayey, massive, dark-gray; weathers light brown or pale red, extensively bioturbated. Very glauconitic in basal few meters; glauconite concentration decreases upward so that in upper part of unit, quartz and glauconite are nearly equal. Feldspar, mica, pyrite, and phosphatic fragments are minor sand constituents. Locally, very micaceous (mostly green chlorite) with sparse carbonized wood fragments. Fine-grained pyrite abundant throughout formation. Local thin, pebbly zones with large fossil impressions occur in the middle of the formation. In the upper part of the formation, quartz increases to about 40 percent. Unit crops out in a narrow belt throughout the map area and forms isolated outliers in the central sheet. Best exposures are along Crosswicks Creek in the Allentown quadrangle. In the southern sheet, the Marshalltown underlies a narrow belt in the uplands and broadens to the southwest. Many Marshalltown exposures occur along Oldmans Creek and its tributaries near Auburn, Gloucester County. The contact with the underlying Englishtown Formation is sharp and unconformable. The basal few centimeters of the Marshalltown contain siderite concentrations, clay balls, and wood fragments reworked from the underlying Englishtown. Many burrows, some filled with glauconite, project downward into the Englishtown for about one meter (3 ft) giving a spotted appearance to the upper part of the Englishtown (Owens and others, 1970). The Marshalltown is the basal transgressive unit of a sedimentation cycle that includes the regressive deposits of the overlying Wenonah and Mount Laurel Formations resembling the overlying Red Bank Formation to Navesink Formation cycle in its asymmetry. Within the map area, only a few long-ranging megafossils occur in the Moorestown quadrangle (Richards, 1967). To the south, in the type area, Weller (1907) reported diverse molluskan assemblages indicating a Campanian age. More importantly, Olsson (1964) reported the late Campanian foraminifera Globotruncana calcarata Cushman from the upper part of the formation. No G. calcarata were found during our investigations. Wolfe (1976) assigned the pollen assemblage of the Marshalltown to the CA5A Zone considered to be Campanian. The Marshalltown has most recently been assigned to Zone CC 20-21 (Sugarman and others, 1995) of middle and late Campanian age (Perch-Nielsen, 1985).

Lithology: sand; clay or mud; silt

Mafic gneiss (Probably lower Paleozoic) at surface, covers < 0.1 % of this area

Mafic gneiss - Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to pCAmgh in places.

Bryn Mawr Formation (Tertiary) at surface, covers < 0.1 % of this area

Bryn Mawr Formation - High-level terrace deposits; reddish-brown gravelly sand and some silt. Age uncertain.

Lithology: gravel; sand; silt

Upland Deposits (Eastern Shore) (Quaternary) at surface, covers < 0.1 % of this area

Upland Deposits (Eastern Shore) - Gravel, sand, silt, and clay. Mostly cross-bedded, poorly sorted, medium- to coarse-grained white to red sand and gravel; boulders near base; minor pink and yellow silts and clays; (Wicomico Formation of earlier reports); thickness 0 to 90 feet, locally thicker in paleochannels.

Lithology: gravel; sand; silt; clay or mud

Pensauken and Bridgeton Formations, undifferentiated (Tertiary) at surface, covers < 0.1 % of this area

Pensauken and Bridgeton Formations, undifferentiated - Dark-reddish-brown, cross-stratified, feldspathic quartz sand and some thin beds of fine gravel and rare layers of clay or silt.

Lithology: sand; gravel; clay or mud; silt