The Patuxent Formation is a

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

of the

Atlantic coastal plain The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...

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 defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

and

gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifi ...

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

feldspar Feldspars are 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 ''plagioclase'' (sodium-calcium) feldsp ...

, 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. Quartz is c ...

. Clay lumps are common, and sand beds gradually transition to clay. Sandy beds may be

crossbedded In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The original ...

, which is evidence of shallow water origin. 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 typically prominent where rivers cross it, with resulting rapids or waterfalls. The uplands are relatively hard crystalline basement rock, and the coa ...

Fossils

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 onwa ...

'', a nodosaurid known from a single natural cast and mold of a hatchling, was found recovered from rocks belonging to the Patuxent Formation in Maryland. Fossil

stegosaur Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe, ...

tracks have been reported from the formation.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607. 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, Cambrid ...

Pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...

spores have been identified in the formation by G. J. Brenner (1963).

Notable exposures

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

Economic value

The Patuxent is a notable

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...

in southern Maryland.http://pubs.usgs.gov/of/2009/1088/ Curtin, S.E., Andreasen, D.C., and Staley, A.W., 2009, Potentiometric surface of the Patuxent aquifer in Southern Maryland, September 2007: U.S. Geological Survey Open-File Report 2009–1088, 1 map sheet.

Age

Biostratigraphic dating by Dorf (1952) confirmed Early Cretaceous ( Neocomian) age.Dorf, Erling, 1952, Critical analysis of Cretaceous stratigraphy and paleobotany of the Atlantic Coastal Plain:

American Association of Petroleum Geologists The American Association of Petroleum Geologists (AAPG) is one of the world's largest professional geological societies with more than 40,000 members across 129 countries as of 2021. The AAPG works to "advance the science of geology, especially as ...

Bulletin, v. 36, no. 11, p. 2162-2184.

Footnotes

References

* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. . Cretaceous Maryland Cretaceous geology of Virginia Aptian Stage {{US-geologic-formation-stub Lower Cretaceous Series of North America