The Patuxent Formation is an

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

(

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

)-aged geologic formation of the

Atlantic coastal plain The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

. It is part of the Potomac Group.

Description

The Patuxent formation was first described by

William Bullock Clark William Bullock Clark (December 15, 1860 – July 27, 1917), was an American geologist. Early life William Bullock Clark was born on December 15, 1860, at Brattleboro, Vermont, to Helen (née Bullock) and Barna Atherton Clark. Clark had private ...

in 1897. The formation is primarily unconsolidated white-grey or orange-brown

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

and

gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...

, with minor clay and silt. The sand often contains kaolinized

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

, making it an

arkose Arkose () or arkosic sandstone is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose. Components ...

. Clay lumps are common, and sand beds gradually transition to clay. Sandy beds may be crossbedded, which is evidence of shallow water origin. Tolchester folio Maryland Plate I

The Patuxent is the basal unit of the Coastal Plain sedimentary formations and

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 o ...

overlies the crystalline

basement rocks In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The baseme ...

. This underlying unconformity is the subsurface equivalent of the Atlantic Seaboard

Fall Line A fall line (or fall zone) is the area where an upland region and a coastal plain meet and is noticeable especially the place rivers cross it, with resulting rapids or waterfalls. The uplands are relatively hard crystalline basement rock, and the ...

Notable exposures

The type locality is the upper and lower valleys of the Little Patuxent River and Big

Patuxent River The Patuxent River is a tributary of the Chesapeake Bay in the state of Maryland. There are three main river drainages for central Maryland: the Potomac River to the west passing through Washington, D.C., the Patapsco River to the northeas ...

in Maryland.

Economic value

The Patuxent is a notable

aquifer An aquifer is an underground layer of water-bearing material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...

in southern Maryland.

Age

Biostratigraphic dating by Dorf (1952) confirmed Early Cretaceous (

Neocomian In geology, Neocomian was a name given to the lowest stage of the Cretaceous system. It is generally considered to encompass the interval now covered by the Berriasian, Valanginian and Hauterivian, from approximately 145 to 130 Ma. It was introduce ...

) age.

Paleobiota

A diverse ichnofauna is known from the formation, comprising the trackways of dinosaurs, pterosaurs, mammals, turtles, and amphibians. Notably, a high proportion of these dinosaur prints appear to be from hatchlings, suggesting nesting sites were located nearby. The preservation of hatchling-sized dinosaur tracks is otherwise very rare in Cretaceous formations. A frog trackway from this formation provides the earliest known evidence of frogs moving by hopping. A particularly diverse trackway series deposited in a former wetland environment is known from the vicinity of

Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C., in Greenbelt, Maryland, United States. Established on May 1, 1959, as NASA's first space flight center, GSFC ...

. Very few vertebrate body fossils are known from this formation, which is thought to be an artifact of preservation. ''

Propanoplosaurus ''Propanoplosaurus'' is a genus of herbivorous nodosaurid dinosaur from the Early Cretaceous Patuxent Formation of Maryland, USA. Its type specimen is a natural cast and partial natural mold of a hatchling. Discovery and naming From 1994 on, R ...

'', a

nodosaurid Nodosauridae is a family of ankylosaurian dinosaurs known from the Late Jurassic to the Late Cretaceous periods in what is now Asia, Europe, North America, and possibly South America. While traditionally regarded as a monophyletic clade as the s ...

known from a single natural cast and mold of a hatchling, was found recovered from rocks belonging to the Patuxent Formation in Maryland. A single partial impression is known of a

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

(potential affinities to '' Paraelops''). Isolated nodosaurid scutes are also known. E. Dorf (1952) compared the flora identified in the Patuxent to that of the Wealden Flora in England studied by

Albert Seward Sir Albert Charles Seward FRS (9 October 1863 – 11 April 1941) was a British botanist and geologist. Life Seward was born in Lancaster. His first education was at Lancaster Grammar School and he then went on to St John's College, Cambridg ...

Pollen Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm ...

spores have been identified in the formation by G. J. Brenner (1963). Based on the Paleobiology Database and Weems (2021):

Ray-finned fish

Amphibians

Reptiles

Turtles

Dinosaurs

Based partially on Weems (2021):

Mammals

Along with an assemblage from Angola, the Patuxent comprises the world's largest known assemblage of Mesozoic mammal footprints.

Footnotes

References

* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. {{ISBN, 0-520-24209-2. Cretaceous Maryland Cretaceous geology of Virginia Aptian Stage Lower Cretaceous Series of North America Sandstone formations of the United States Claystone formations