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Geologic units in Delaware (state in United States)

[Additional scientific data in this geographic area]

Magothy Formation (Upper Cretaceous, middle and lower Santonian) at surface, covers < 0.1 % of this area
Magothy Formation - Sand, fine- to coarsegrained, locally very gravelly (pebbles less than 1.3 cm (0.5 in) in diameter) especially in updip areas, typically cross stratified, massive, horizontally bedded, light-gray to white, carbonized wood (several centimeters long) and colorless mica scattered throughout. Black to dark-gray, very carbonaceous clay is locally interstratified with the sand. No calcareous fossils were recovered from the Magothy Formation in the shallow subsurface. In the Freehold drillhole the thin basal bed of the Magothy is composed of quartz gravel (maximum clast diameter, about 2.5 cm (1 in)). The lower part of the formation above the gravel consists of thin-bedded white clay interbedded with fine- to coarse-grained, poorly sorted, thickbedded, light-colored, somewhat micaceous quartz sand. The interbedded clay becomes dark gray up section and the sand is slightly glauconitic and locally shelly. Quartz is the major sand mineral. Siliceous rock fragments, mica, and feldspar are minor constituents. In general, this formation appears to be fluvial near the base (upper delta plain) and gradually becomes more marine upward (shelf). The overall sedimentologic pattern suggests a net transgression during deposition of the Magothy with shelf deposits overriding a nonmarine (probably deltaic) facies. Downdip at Buena, Atlantic County, the Magothy is 22 m (72 ft) thick and is primarily a massive to finely laminated, dark-gray, woody clay-silt. Unit is as much as 55 m (180 ft) thick in the northern part of the central sheet and generally thins to the southwest. The age of the Magothy is best defined by pollen. Christopher (1979) placed this palynoflora in his Zone V of early and late Santonian age. He also recognized three assemblage zones within Zone V, the Complexiopollis exiqua-Santalacites minor Zone (lowest), the ?Pseudoplicapollis longiannulata-Plicapollis incisa Zone (middle), and the ?Pseudoplicapollis cuneata-Semioculopollis verrucosa Zone (highest). All three zones are present in the Magothy in New Jersey. The foraminifera Marginotruncana marginata and Rosita fornicata were collected from the Island Beach corehole at 550 m (1804 ft) and are indicative of the Dicarinella asymmetrica Zone. Because of the overall character of the foram assemblage it is probable that these fossils indicate a late Santonian rather than early Campanian age (H.J. Dowsett, written commun., 1992). The Magothy, therefore, is Santonian or older in age.
Lithology: sand; clay or mud; gravel
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
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
Gabbro (Paleozoic) at surface, covers 0.2 % of this area
Gabbro - gabbro
Lithology: gabbro
Merchantville Formation (Upper Cretaceous, lower Campanian) at surface, covers < 0.1 % of this area
Merchantville Formation - Sand, glauconite, locally has high quartz content, very clayey and silty, massive to thick-bedded, grayish-olive-green to dark-greenish-gray; weathers moderate brown or moderate yellow brown. Mica, feldspar, and pyrite are minor sand constituents. Very micaceous at base. Locally, has extensive iron incrustations in near-surface weathered beds. Fossil molds are mostly phosphatic. Fossils typically occur in siderite concretions. No calcareous fossils were found in outcrop. The Merchantville forms a continuous narrow to wide belt throughout the map area. The unit is about 6 m (20 ft) thick in the northern part of the central sheet, about 20 m (66 ft) thick in the Trenton area, and 12 to 15 m (39-49 ft) thick throughout the southern sheet. The formation is best exposed in the Trenton East quadrangle, mainly in the tributaries on the western side of Blacks Creek and south of Bordentown, Burlington County, where the entire thickness of the formation can be seen in gullies (Owens and Minard, 1964b). The basal contact with the underlying Magothy or Cheesequake Formations is sharp and disconformable. At most places, a reworked zone about 0.3 to 1 m (1-3 ft) thick is present at the base. This basal bed contains reworked lignitized wood, siderite concretions as much as 13 cm (5 in) in diameter, scattered pebbles and coarse-grained quartz sand and is burrowed. Most burrows project downward into the underlying formations. The Merchantville is the basal bed of a lower Campanian transgressive-regressive cycle that includes the overlying Woodbury and Englishtown Formations. Merchantville faunas were analyzed by Sohl (in Owens and others, 1977) who concluded that northern fauna represented deposition on a lower shoreface or in the transition to an inner shelf, whereas the southern fauna was a deeper water assemblage, probably inner shelf. Macrofossils occur as internal and external molds and include the ammonites Menabites (Delawarella) delawarensis and Scaphites (Scaphites) hippocrepis III. The Scaphites is of the type III variety of Cobban (1969) and is indicative of the lower, but not the lowest, Campanian. More recently, Kennedy and Cobban (1993), detailing the ammonite assemblage that includes Baculites haresi, Chesapeakella nodatum, Cryptotexanites paedomorphicus sp., Glyptoxoceras sp., Menabites (Delawarella) delawarensis, M. (Delawarella) vanuxemi, Menabites (Bererella) sp., Pachydiscus (Pachydiscus) sp., Placenticeras placenta, Pseudoscholenbachia cf. P. chispaensis, Scaphites (Scaphites) hippocrepis III, Submortoniceras punctatum, S. uddeni, and Texanites (Texanites) sp., concluded that the Merchantville is of late early Campanian age. Wolfe (1976) indicated that the Merchantville microflora was distinct from overlying and underlying units and designated it Zone CA2 of early Campanian age.
Lithology: sand; clay or mud; silt
Quaternary Deposits Undivided (Quaternary) at surface, covers 0.1 % 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).
Lithology: sand; gravel; silt; clay or mud; dune sand; beach sand
Potomac Formation (Upper Cretaceous, lower Cenomanian) at surface, covers < 0.1 % of this area
Potomac Formation - Predominantly clay to clay-silt, thinly laminated to thick-bedded, mottled red, white, and orange-brown, less commonly dark-gray and woody; interbedded with thin beds and lenses of very fine to medium-grained, massive, white to orange-brown, micaceous sand. Lithologies are typical of the shallow subsurface. Down dip, these lithologies interfinger with thin to thick beds of marine clay-silt, commonly glauconitic and locally shelly. Marine beds are most prevalent in the southernmost part of the southern sheet. Unit 3 was cored in its entirety at Freehold where it is approximately 75 m (246 ft) thick. In the core, the basal 6 m (20 ft) consists of red or mottled red and white clay interbedded with gravel and fine- to coarse-grained sand. The clay is pervaded by reddish-brown siderite. Most of the overlying beds consist of interbedded dark-colored clay, locally weathered to pale yellow or white, and fine- to medium-grained, light-colored sand. Layers that contain fine black carbonaceous material to large lignitized wood pieces are common in unit 3 in this core. At Toms River, the unit is about 60 m (197 ft) thick and consists of dark- to pale-gray clay, locally weathering to white or yellowish gray, and light-colored, micaceous sand. In general, the darker colored clay is more common in the upper part of the section. Locally, the sand has very small amounts of glauconite which may indicate some local marine influence during sedimentation. The age of unit 3 was determined from pollen in the nonmarine deposits and foraminifera in the marine sections. Typical forms found in Zone III in New Jersey are Ajatipollis sp. A, Tricolpites nemejci, T. vulgaris, Tricolporoidites bohemicus, Tricolporoidites sp. A, T. sp. B, and Tricolporopollenites sp. B (Doyle and Robbins, 1977). In the marine facies, Petters (1976) reports a planktic foraminiferal suite containing Praeglobotruncana delrioensis and Rotalipora greenhornensis. Both the pollen and foraminiferal assemblages suggest an early Cenomanian age.
Lithology: clay or mud; silt; sand
Mt. Laurel Formation (Upper Cretaceous, upper Campanian) at surface, covers < 0.1 % of this area
Mt. Laurel Formation - Sand, quartz, massive to crudely bedded, typically coarsens upward, interbedded with thin clay beds. Glauconite and feldspar are minor sand constituents. Muscovite and biotite are abundant near the base. Lower part of formation is a fine- to medium-grained, clayey, dark-gray, glauconitic (maximum 25 percent) quartz sand. Typically weathers to white or light yellow and locally stained orange brown by iron oxides. Small pebbles scattered throughout, especially in the west-central area. Locally, has small, rounded siderite concretions in the interbedded clay-sand sequence. Granules and gravel are abundant in the upper 1.5 m (5 ft). Upper beds are light gray and weather light brown to reddish brown. The Mount Laurel is 10 m (33 ft) thick from the Roosevelt quadrangle to the Runnemede quadrangle in the central sheet. Thickness varies in the northern part of the map area due, in part, to extensive interfingering of this formation with the underlying Wenonah Formation. Weller (1907) and Kummel (1940) recognized only about 1.5 m (5 ft) of the Mount Laurel in the north. In this report those beds are assigned to the overlying Navesink Formation. The interbedded sequence, the major facies in the north, ranges to about 4.5 m (15 ft) thick. These interbeds have well-developed large burrows (Martino and Curran, 1990), mainly Ophiomorpha nodosa, and less commonly Rosselia socialis. The Mount Laurel is gradational into the underlying Wenonah Formation. A transition zone of 1.5 m (5 ft) is marked by an increase in clay, silt, and mica into the Wenonah, especially in the west-central area of the central sheet. The oyster Agerostrea falcata occurs in the lower part of the formation. Exogyra cancellata and Belemnitella americana are abundant in upper beds in the west-central area of the central sheet (New Egypt quadrangle). The Mount Laurel Formation is of late Campanian age based on the assignment of Zone CC 22b to the formation by Sugarman and others (1995) and the occurrence of Exogyra cancellata near Mullica Hill, Gloucester County.
Lithology: sand; clay or mud; gravel
Bryn Mawr Formation (?) at surface, covers 0.1 % of this area
Bryn Mawr Formation - Red and brown quartz sand with silt, clay and fine gravel.
Lithology: sand; silt; clay or mud; gravel
Port Deposit Granodiorite (Paleozoic) at surface, covers 0.1 % of this area
Port Deposit Granodiorite - granodiorite
Lithology: granodiorite
Unit C (Tertiary) at surface, covers 0.8 % of this area
Unit C - Grayish-green, clayey glauconitic silt and sand.
Lithology: silt; sand
Pegmatite (Paleozoic) at surface, covers < 0.1 % of this area
Pegmatite - Pegmatite
Lithology: pegmatite
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 pCAmgp in places.
Lithology: mafic gneiss; paragneiss
Chesapeake Group (Tertiary) at surface, covers 77 % of this area
Chesapeake Group - Bluish gray silt with quartz sand and some shell beds.
Lithology: silt; sand
Amphibolite (Paleozoic) at surface, covers 0.7 % of this area
Amphibolite - amphibolite
Lithology: amphibolite
Serpentine (Paleozoic) at surface, covers < 0.1 % of this area
Serpentine - serpentine
Lithology: serpentinite
Arden Granite (Paleozoic) at surface, covers 0.2 % of this area
Arden Granite - granite
Lithology: granite
Unit B (Cretaceous-Tertiary) at surface, covers 0.1 % of this area
Unit B - Greenish-gray sandy and clayey glauconitic silt.
Lithology: silt
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
Merchantville Formation (Cretaceous) at surface, covers 1.0 % 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 0.8 % of this area
Redbank Formation - Reddish-brown, slightly micaceous and glauconitic, fine to medium sand.
Lithology: sand
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.
Lithology: mafic gneiss; paragneiss
Mt. Laurel-Navesink Formation (Cretaceous) at surface, covers 1 % of this area
Mt. Laurel-Navesink Formation - Dark greenish brown and dark gray, highly glauconitic sandy silt and silty sand.
Lithology: silt; sand
Potomac Formation (Cretaceous) at surface, covers 5 % of this area
Potomac Formation - Variegated silts and clays with beds of quartz sand.
Lithology: silt; clay or mud; sand
Cockeysville Marble (Paleozoic) at surface, covers < 0.1 % of this area
Cockeysville Marble - Dense, white crystalline limestone and dolomite.
Lithology: limestone; dolostone (dolomite)
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
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
Magothy Formation (Cretaceous) at surface, covers 0.2 % of this area
Magothy Formation - White and buff quartz sand with beds of gray and black clayey silt.
Lithology: sand; silt
Rancocas Formation (Tertiary) at surface, covers 3 % of this area
Rancocas Formation - Grayish-green and green, silty, glauconitic sand.
Lithology: sand
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.
Lithology: sand; clay or mud; silt; gravel; alluvium
"Glenarm Wissahickon" formation (Probably lower Paleozoic) at surface, covers < 0.1 % of this area
"Glenarm Wissahickon" formation - Lithologically similar to oligoclase-mica schist of the Wissahickon Formation (PZw), but also includes lenticular amphibolite bodies having ocean-floor basalt chemistry.
Lithology: mica schist; mafic gneiss; amphibolite;
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
Vincentown Formation (upper Paleocene, Selandian) at surface, covers < 0.1 % of this area
Vincentown Formation - Upper part, sand, glauconite (35-40 percent) and quartz (60-65 percent), fine- to very fine grained, very clayey and silty, massive, dark-gray, bioturbated, very micaceous. Lower part, sand, massive, less micaceous and clayey, dark-gray-green. The lower 4.5 m (15 ft) of the formation is a fine- to medium-grained, clayey glauconite sand. Locally, there is an accumulation of disarticulated calcareous shells along the contact with the underlying Hornerstown Formation. These shells are commonly the brachiopod Oleneothyris harlani or the mollusk Gryphaea dissimilaris. Where the shell bed is absent it is difficult to separate glauconite sand of the basal part of the Vincentown from the underlying Hornerstown Formation, which also is a glauconite sand. Gamma logs through this interval show that there is a small gamma spike along the contact between the glauconite sands. The grain size decreases and the formation is significantly more clayey downdip. At Allaire State Park, Monmouth County (drillhole Allaire-C), for example, the bulk of the Vincentown is a clayey, very micaceous, dark-gray, slightly feldspathic quartz sand. Large fossils, which are abundant in the near-surface beds, are absent. In addition, the basal glauconite beds tend to thicken somewhat downdip. Farther basinward, the bulk of the formation is an unfossiliferous, gray-green to locally tan clayey silt or silty clay. Locally, a thin- to thick-bedded glauconite sand occurs at the base. In the thickest downdip section penetrated at Island Beach, the Vincentown is mostly a pale-gray to dark-gray clay-silt. No megafossils were observed in the Island Beach core. On the basis of geophysical log interpretations in the deepest subsurface, this unit has a maximum thickness of about 38 m (125 ft). The age of the Vincentown is best indicated by calcareous nannofossils, which indicate Zones NP 5 to NP 9 (Bybell, 1992). Common nannofossils from Zone NP 5 are Chiasmolithus bidens, Ellipsolithus distichus, Fasciculithus tympaniformis, Scapholithus fossilis, and Toweius eminens. Common nannofossils in Zone NP 9 are Biantholithus astralis, Chiasmolithus bidens, Discoaster multiradiatus, D. salisburgensis, Fasciculithus involutus, F. schaubii, F. thomasii, and Lophodolithus nascens. The upper part of the Vincentown falls within the upper part of Zone NP 9 and therefore is late Paleocene (Selandian) in age.
Lithology: sand; clay or mud; silt
Wissahickon Schist (Paleozoic) at surface, covers 3 % of this area
Wissahickon Schist - Dense micaceous schist, gneiss and migmatite.
Lithology: mica schist; gneiss; migmatite
Wenonah Formation (Cretaceous) at surface, covers 0.4 % of this area
Wenonah Formation - Gray and rust-brown fine to medium, micaceous, sparingly glauconitic quartz sand.
Lithology: sand
Banded Gneiss (Paleozoic) at surface, covers 1 % of this area
Banded Gneiss - banded gneiss
Lithology: gneiss

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