The Yorktown Formation is a mapped bedrock unit in the

Coastal Plain A coastal plain is flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and a piedmont area. Some of the largest coastal plains are in Alaska and the southeastern United States. The Gulf Co ...

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and ...

and

South Carolina )'' Animis opibusque parati'' ( for, , Latin, Prepared in mind and resources, links=no) , anthem = " Carolina";" South Carolina On My Mind" , Former = Province of South Carolina , seat = Columbia , LargestCity = Charleston , LargestMetro = ...

. It is overconsolidated and highly

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

iferous.

Description

The Yorktown is composed largely of overconsolidated

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...

and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

with abundant calcareous shells, primarily bivalves.

Stratigraphy

The Yorktown

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

overlies the Miocene Eastover Formation, and conformably underlies the Pliocene Croatan Formation. The Yorktown was divided into members by Ward and Blackwelder (1980). These are in ascending order: Sunken Meadow Member, Rushmere Member, Morgarts Beach Member, and Moore House Member. The uppermost Tunnels Mill Member is recognized in Maryland only.

Notable exposures

*Type Section:

Yorktown, Virginia Yorktown is a census-designated place (CDP) in York County, Virginia. It is the county seat of York County, one of the eight original shires formed in colonial Virginia in 1682. Yorktown's population was 195 as of the 2010 census, while York Co ...

on southwest side of York River, York County *Carters Grove Bluffs, north side of James River *Moore House Bluff, southwest side of York River, York County (very close to type section)

Age

Hazel (1971) revised the age of the Yorktown from Miocene to Late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

to Early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typi ...

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of B ...

. The age was revised by Gibson (1983) to extend into the Middle Pliocene based on

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

. Further biostratigraphic work with ostracods and foraminifera was completed by Cronin (1991), which also summarized previous investigations.

Fossils

* Bivalves, including ''Glycymeris subovata'' (see Glycymerididae), '' Chesapecten jeffersonius'', ''Chesapecten madisonius'', ''

Mercenaria ''Mercenaria'' is a genus of edible saltwater clams, marine bivalve molluscs in the family Veneridae, the Venus clams. The genus ''Mercenaria'' includes the quahogs, consisting of ''Mercenaria mercenaria'', the northern quahog or hard clam, and ...

tridacnoides'', ''Panopera reflexa'', '' Chama'', ''

Ensis ''Ensis'' is a genus of medium-sized edible saltwater clams, littoral bivalve molluscs in the family Pharidae. ''Ensis'', or razor clams, are known in much of Scotland as spoots, for the spouts of water they eject while burrowing into the sa ...

'', ''Striarca'' and ''Noetia'' (see

Noetiidae Noetiidae is a family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its me ...

), '' Cerastoderma'', '' Dosinia'', '' Mulinia'', ''

Kuphus ''Kuphus'' is a genus of shipworms, marine bivalve molluscs in the family Teredinidae. While there are four extinct species in the genus,Maempel, George Zammit. "Kuphus melitensis, a new teredinid bivalve from the late Oligocene Lower Coralline L ...

'' (Shipworm), ''

Panope In Greek mythology, Panopea (Ancient Greek: Πανόπεια ''Panopeia'') or Panope (Πανόπη) may refer to various characters. The names mean 'panorama' or means 'of the beautiful husband'. * Panope or Poenope,Gaius Julius Hyginus, Hyginus, ...

'' (Geoduck), and the oyster ''

Ostrea ''Ostrea'' is a genus of edible oysters, marine bivalve mollusks in the family Ostreidae, the oysters. Fossil records This genus is very ancient. It is known in the fossil records from the Permian to the Quaternary (age range: from 259 to 0. ...

'' *

Gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...

, including ''

Crucibulum ''Crucibulum'' is a genus in the Nidulariaceae, a family of fungi whose fruiting bodies resemble tiny egg-filled bird's nests. Often called "splash cups", the fruiting bodies are adapted for spore dispersal by using the kinetic energy of fall ...

'', ''

Calliostoma ''Calliostoma'' is a genus of small to medium-sized sea snails with gills and an operculum, marine gastropod molluscs within the family Calliostomatidae, the Calliostoma top snails. Previously this genus was placed within the family Trochida ...

'', '' Busycon'', ''

Turritella ''Turritella'' is a genus of medium-sized sea snails with an operculum, marine gastropod mollusks in the family Turritellidae.Vos, C.; Gofas, S. (2013). Turritella Lamarck, 1799. Accessed through: World Register of Marine Species at http://www.m ...

'', and '' Crepidula'' *

Foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

, including the biostratigraphic marker species ''Dentoglobigerina altispira'' (see Globigerinida), ''Sphaeroidinellopsis'', and ''Globorotalia puncticulata''Dowsett, H.J., and Wiggs, L.B., 1992, Planktonic foraminiferal assemblage of the Yorktown Formation, Virginia, USA: Micropaleontology, v. 38, no. 1, p. 75-86. *

Scleractinian corals Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mo ...

, including '' Septastrea marylandica'', '' Paracyathus vaughani'' (see Caryophylliidae), and ''Astrangia lineata'' *

Ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typi ...

s *

Bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...

ns * Barnacles, including '' Balanus'' *

Worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wo ...

s *

Sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throug ...

s *

Bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s, including the large pelican ''

Pelecanus schreiberi ''Pelecanus schreiberi'' is a fossil pelican described by Storrs Olson from Early Pliocene (5.3 to 3.6 million year old) deposits in the Yorktown Formation of North Carolina. It was a large species with distinctive features suggesting that it rep ...

''. *

Whales Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...

, including the prehistoric sperm whale ''

Scaldicetus ''Scaldicetus'' is an extinct genus of highly predatory macroraptorial sperm whale. Although widely used for a number of extinct physeterids with primitive dental morphology consisting of enameled teeth, ''Scaldicetus'' as generally recognized ...

''.

Gallery

Image:coral_bivalve_Yorktown_Fm.jpg,

Coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and ...

growing on a ''Crepidula'' sp. (slipper snail) from the Yorktown Formation Image:Rushmere_Mbr_Yorktown_Fm.jpg, Rushmere Member of the Yorktown Formation, with abundant ''Chama'' bivalves Image:Sunken_Meadow_Mbr_Yorktown_Fm.jpg, Sunken Meadow Member of the Yorktown Formation Image:Balanus_Yorktown_Fm.jpg, '' Balanus sp.'' (barnacles) from Carters Grove Bluffs outcrop, growing on a bivalve

References

{{reflist Neogene geology of Virginia Neogene geology of North Carolina