Patuxent Formation

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Patuxent Formation
Stratigraphic range: Aptian
Patuxent Arundel Formation.png
. View at School House Hill, Baltimore County, Maryland showing the Patuxent Formation overlain by the Arundel Formation
Type Sedimentary
Unit of Potomac Group
Underlies Arundel Formation
Overlies Basement
Thicknessup to 250 feet (80 m)
Lithology
Primary Sandstone, claystone, gravel
Other Siderite
Location
Region Atlantic coastal plain
Country United States
ExtentMaryland, Washington D. C., Delaware, Virginia
Type section
Named for Patuxent River
Named byW. B. Clark, 1897 [1]

The Patuxent Formation is an Early Cretaceous (Aptian)-aged geologic formation of the Atlantic coastal plain. It is part of the Potomac Group.

Contents

Description

The Patuxent formation was first described by William Bullock Clark in 1897. [1] The formation is primarily unconsolidated white-grey or orange-brown sand and gravel, with minor clay and silt. The sand often contains kaolinized feldspar, making it an arkose. Clay lumps are common, and sand beds gradually transition to clay. Sandy beds may be crossbedded, which is evidence of shallow water origin.

Outcrop along railroad cut in Harford County Tolchester folio Maryland Plate I.jpg
Outcrop along railroad cut in Harford County

The Patuxent is the basal unit of the Coastal Plain sedimentary formations and unconformably overlies the crystalline basement rocks. This underlying unconformity is the subsurface equivalent of the Atlantic Seaboard Fall Line.

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 in southern Maryland. [2]

Age

Biostratigraphic dating by Dorf (1952) confirmed Early Cretaceous (Neocomian) age. [3]

Paleobiota

A diverse ichnofauna is known from the formation, comprising the trackways of dinosaurs, pterosaurs, mammals, turtles, and amphibians. [4] 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. [5] A frog trackway from this formation provides the earliest known evidence of frogs moving by hopping. [6] A particularly diverse trackway series deposited in a former wetland environment is known from the vicinity of Goddard Space Flight Center. [7]

Very few vertebrate body fossils are known from this formation, which is thought to be an artifact of preservation. [6] Propanoplosaurus , 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. [8] A single partial impression is known of a bony fish (potential affinities to Paraelops ). [4] Isolated nodosaurid scutes are also known. [7]

E. Dorf (1952) [3] compared the flora identified in the Patuxent to that of the Wealden Flora in England studied by Albert Seward. [9] Pollen spores have been identified in the formation by G. J. Brenner (1963). [10] [11]

Color key
Taxon Reclassified taxonTaxon falsely reported as presentDubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Based on the Paleobiology Database and Weems (2021): [12]

Ray-finned fish

GenusSpeciesLocationStratigraphic positionMaterialNotesImages
aff. Paraelops P. cearensisImpression of posterior portion (including caudal fin)A presumed elopomorph fish.

Amphibians

GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Anura indet.FootprintsA frog trackway. The earliest known evidence for hopping locomotion among amphibians. [6]

Reptiles

Squamates

GenusSpeciesLocationStratigraphic positionMaterialNotesImages
?Squamata indet.FootprintTentatively identified as a lizard track [5]

Turtles

GenusSpeciesLocationStratigraphic positionMaterialNotesImages
aff. Emydhipus E. ichsp.FootprintsA small-sized turtle track.

Crocodylomorphs

GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Crocodylomorpha indet. [13] Goddard Space Flight CenterFootprintsPreviously interpreted as pterosaur tracks. [5] [4] [7]

Dinosaurs

Based partially on Weems (2021): [14]

GenusSpeciesLocationStratigraphic positionMaterialNotesImages

Brontopodus

B. birdi

Footprints

A sauropod track, potentially made by Astrodon . Very small trackways are known presumably made by juvenile individuals, suggesting that these sauropods nested nearby. [14]

Sauropod Footprint.jpg
Caririchnium C. kortmeyeri (= Amblydactylus gethingi)FootprintsAn ornithopod track, potentially made by iguanodontids. [14]
Hadrosauropus H. leonardiFootprintsAn ornithopod track, potentially made by a primitive hadrosaur. [14] Caririchnium leonardii (dinosaur tracks) (Dakota Sandstone, Lower Cretaceous; Dinosaur Ridge, Colorado, USA) 45.jpg

Hypsiloichnus

H. marylandicus

Footprints

An ornithopod track. Potentially made by hypsilophodontids. Type locality of genus and species. [15]

Gypsichnites G. pacensisFootprintsA medium-sized theropod track. Track maker unknown. [14]
Irenesauripus I. glenrosensisFootprintsA large theropod track, potentially by Acrocanthosaurus . [14] Dinosaur Valley State Park - Track2.jpg
Nodosauridae indet.Goddard Space Flight CenterOsteodermA nodosaur scute. [7]
Ornithomimipus O. angustusFootprintsA theropod track, most likely by an ornithomimosaur. At least two different taxa (the smaller O. jaillardi and the larger O. angustus) are represented, of which one appears to have been made by a species identical or related to Arkansaurus . [14]
O. jaillardi
Propanoplosaurus P. marylandicusA partial body impression of a baby.A nodosaurid ankylosaur. Type locality of genus and species. [8] Propanoplosaurus restoration.png

Tetrapodosaurus

T. borealis

Footprints

An ankylosaur track.

Tetrapodosaurus borealis.png
Tyrannosauripus T. bachmani (= Megalosauripus sp.)FootprintsA small theropod track, most likely by a tyrannosauroid. Type locality of species. [14]

Mammals

GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Sederipes S. goddardensisGoddard Space Flight CenterFootprintsA small mammal track that had a temporary "sitting" posture in-between locomotion, reminiscent of modern small rodents. Only known fossil evidence of this locomotion type. Type locality of genus and species. [7]

Along with an assemblage from Angola, the Patuxent comprises the world's largest known assemblage of Mesozoic mammal footprints. [7]

See also

Footnotes

  1. 1 2 Clark, W.B. (1897). Outline of present knowledge of the physical features of Maryland (Report). Volume Series. Vol. 1. Maryland Geological Survey. pp. 172–188.
  2. Curtin, Stephen E.; Andreasen, David C.; Staley, Andrew W. (2009). Potentiometric surface of the Patuxent aquifer in Southern Maryland, September 2007 (Map). U.S. Geological Survey Open-File Report. U.S. Geological Survey.
  3. 1 2 Dorf, Erling (1952-11-01). "Critical Analysis of Cretaceous Stratigraphy and Paleobotany of Atlantic Coastal Plain" . American Association of Petroleum Geologists Bulletin. 36 (11): 2161–2184. doi:10.1306/5CEADBC6-16BB-11D7-8645000102C1865D.
  4. 1 2 3 Weems, Robert E.; Bachman, Jon M. (2015-10-02). "The Lower Cretaceous Patuxent Formation Ichnofauna of Virginia" . Ichnos. 22 (3–4): 208–219. doi:10.1080/10420940.2015.1063493. ISSN   1042-0940.
  5. 1 2 3 Stanford, Ray; Lockley, Martin; Weems, Rob (2007-05-30). "Diverse Dinosaur-Dominated Ichnofaunas from the Potomac Group (Lower Cretaceous) Maryland" . Ichnos. 14 (3–4): 155–173. doi:10.1080/10420940601049404. ISSN   1042-0940.
  6. 1 2 3 Weems, R. E.; Bachman, J. M. (1997). "Cretaceous anuran and dinosaur footprints from the Patuxent Formation of Virginia". Proceedings of the Biological Society of Washington. 110 (1): 1–17.
  7. 1 2 3 4 5 6 Stanford, Ray; Lockley, Martin G.; Tucker, Compton; Godfrey, Stephen; Stanford, Sheila M. (2018-01-31). "A diverse mammal-dominated, footprint assemblage from wetland deposits in the Lower Cretaceous of Maryland". Scientific Reports. 8 (1): 741. doi:10.1038/s41598-017-18619-w. hdl: 2060/20180004410 . ISSN   2045-2322. PMC   5792599 .
  8. 1 2 Stanford, Ray; Weishampel, David B.; Deleon, Valerie B. (2011). "The First Hatchling Dinosaur Reported from the Eastern United States: Propanoplosaurus marylandicus (Dinosauria: Ankylosauria) from the Early Cretaceous of Maryland, U.S.A." . Journal of Paleontology. 85 (5): 916–924. doi:10.1666/10-113.1.
  9. Seward, A. C., The Wealden Flora, 2 vols, 1894-95.
  10. Brenner, Gilbert J. (1963). "The spores and pollen of the Potomac Group of Maryland" (PDF). Maryland Geological Survey Bulletin. 27: 215.
  11. Brenner, Gilbert J. (1963-02-21). The Spores and Pollen of the Potomac Group of Maryland . Science. Vol. 143, no. 3608. p. 795. doi:10.1126/science.143.3608.795.a.
  12. Czaplewski, John J. "PBDB Navigator". paleobiodb.org. Retrieved 2025-01-28.
  13. Smyth, Robert S.H.; Breithaupt, Brent H.; Butler, Richard J.; Falkingham, Peter L.; Unwin, David M. (2025-05-19). "Identifying pterosaur trackmakers provides critical insights into mid-Mesozoic ground invasion". Current Biology. 35 (10): 2337-2353.E5. doi:10.1016/j.cub.2025.04.017.
  14. 1 2 3 4 5 6 7 8 Lucas, Spencer G.; Hunt, Adrian P.; Lichtig, Asher J. (2021-04-01). FOSSIL RECORD 7. New Mexico Museum of Natural History and Science.
  15. Stanford, Ray; Weems, Robert E.; Lockley, Martin G. (2004-01-01). "A New Dinosaur Ichnotaxon from the Lower Cretaceous Patuxent Formation of Maryland and Virginia" . Ichnos. 11 (3–4): 251–259. doi:10.1080/10420940490428797. ISSN   1042-0940.

References