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 ...
of
Maryland
Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), 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; ...
,
Virginia
Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the East Coast of the United States, Atlantic Coast and the Appalachian Mountains. The geography an ...
,
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 a ...
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 = G ...
. 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 soil texture, textur ...
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 part ...
with abundant calcareous shells, primarily
bivalves
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...
.
Stratigraphy
The Yorktown
unconformably overlies the Miocene
Eastover Formation
The Eastover Formation is a geologic formation in North Carolina. It preserves fossils dating back to the Neogene period.
See also
* List of fossiliferous stratigraphic units in North Carolina
This article contains a list of fossil-bearing str ...
, 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
The James River is a river in the U.S. state of Virginia that begins in the Appalachian Mountains and flows U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map , accessed April 1, 2011 to Ches ...
*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 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 means "less recent" ...
to Early
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58[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, typic ...](_blank)
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 Bio ...
. 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
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...
, including ''Glycymeris subovata'' (see
Glycymerididae
Glycymerididae, often misspelled as Glycymeridae, common names dog cockles or bittersweets, is a worldwide family of salt water clams, marine bivalve mollusks in the order Arcida. They are related to the ark clams. This family contains 45 ex ...
), ''
Chesapecten jeffersonius'', ''Chesapecten madisonius'', ''
Mercenaria 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 ...
'', ''Striarca'' and ''Noetia'' (see
Noetiidae), ''
Cerastoderma'', ''
Dosinia
''Dosinia'' is a genus of saltwater clams, marine bivalve molluscs in the family Veneridae, subfamily Dosiniinae Deshayes, 1853. The shell of ''Dosinia'' species is disc-like in shape, usually white, and therefore is reminiscent of the shell ...
'', ''
Mulinia
''Mulinia'' is a genus of small to medium-sized saltwater and estuarine clams, marine bivalve mollusks in the family Mactridae.
Species
Species within the genus ''Mulinia'' include:
* ''Mulinia cleryana''
* ''Mulinia coloradoensis'' – the Col ...
'', ''
Kuphus'' (Shipworm), ''
Panope'' (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 ...
''
*
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. ...
, including ''
Crucibulum'', ''
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 Tro ...
'', ''
Busycon
''Busycon'' is a genus of very large edible sea snails in the subfamily Busyconinae. These snails are commonly known in the United States as '' whelks'' or ''Busycon whelks''. Less commonly they are loosely, and somewhat misleadingly, called " ...
'', ''
Turritella
''Turritella'' is a genus of medium-sized sea snails with an Operculum (gastropod), operculum, marine (ocean), marine gastropod mollusc, mollusks in the family Turritellidae.Vos, C.; Gofas, S. (2013). Turritella Lamarck, 1799. Accessed through: W ...
'', and ''
Crepidula
''Crepidula'', commonly known as the slipper snails, slipper limpets, or slipper shells, is a genus of sea snails, marine gastropod mollusks in the family Calyptraeidae. This family includes the slipper snails (''Crepidula''), hat snails ('' Ca ...
''
*
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
The Globigerinina is a suborder of foraminiferans that are found as marine plankton. They produce hyaline calcareous tests, and are known as fossils from the Jurassic period onwards. The group has included more than 100 genera and over 400 spec ...
), ''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, including ''
Septastrea marylandica'', ''
Paracyathus vaughani'' (see
Caryophylliidae
The Caryophylliidae are a family of stony corals found from the tropics to temperate seas, and from shallow to very deep water.
Genera
*'' Africana'' Ocana & Brito, 2015
*'' Anomocora'' Studer, 1878
*'' Asterosmilia'' Duncan, 1867
*'' Auloc ...
), 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, typic ...
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
*
Barnacle
A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive ...
s, including ''
Balanus
''Balanus'' is a genus of barnacles in the family Balanidae of the subphylum Crustacea.
This genus is known in the fossil record from the Jurassic to the Quaternary periods (age range: from 189.6 to 0.0 million years ago.). Fossil shells withi ...
''
*
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 worm ...
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''.
*
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 a ...
, including the prehistoric sperm whale ''
Scaldicetus''.
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 secre ...
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
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...
Image:Sunken_Meadow_Mbr_Yorktown_Fm.jpg, Sunken Meadow Member of the Yorktown Formation
Image:Balanus_Yorktown_Fm.jpg, ''Balanus
''Balanus'' is a genus of barnacles in the family Balanidae of the subphylum Crustacea.
This genus is known in the fossil record from the Jurassic to the Quaternary periods (age range: from 189.6 to 0.0 million years ago.). Fossil shells withi ...
sp.'' (barnacles) from Carters Grove Bluffs outcrop, growing on a bivalve
References
{{reflist
Neogene geology of Virginia
Neogene geology of North Carolina