Culpeper Basin

Culpeper Basin
Stratigraphic range:
Geologic map of Culpeper Basin from USGS, 1983
link to publication.
TypeRift Valley
Unit ofNewark Supergroup
Sub-units(Sedimentary units): Manassas Sandstone, Bull Run Formation, Catharpin Creek Formation, Midland Formation, Turkey Run Formation, Waterfall Formation
(Igneous units): Mount Zion Church Basalt, Hickory Grove Basalt, Sander Basalt
Area2,545 square miles, 4,096 square kilometers[1]
Thicknessup to 27,000 feet (8,230 m)[2]
Lithology
PrimarySandstone, Mudstone, Siltstone, Conglomerate
OtherBasalt, Diabase
Location
LocationWestern Piedmont of Virginia and Maryland
Coordinates39°05′43″N 77°42′16″W / 39.0953°N 77.7044°W / 39.0953; -77.7044
RegionVirginia, Maryland
CountryUnited States
Extent83 miles (134 km)[2]
Culpeper Basin (Virginia)

The Culpeper Basin is one of the Newark Supergroup's Late Triassic–Early Jurassic rift basins, exposed in Northern Virginia and Maryland.[3] Its development is tied to the initial rifting of the supercontinent Pangea (~201 Ma, across the Triassic-Jurassic boundary). Volcanism associated with the Culpeper Basin was part of a much larger event known as the Central Atlantic magmatic province (CAMP), one of the largest flood basalt eruptions in Earth's history.[4]

Geography

The Culpeper Basin lies just east of the Appalachian Mountains and extends from the Madison County—Orange County line in Virginia to Frederick, Maryland.[5] A diverse group of sedimentary rocks including siltstone, sandstone, and conglomerate within the basin were intruded by igneous rocks (primarily diabase), which caused thermal metamorphism at the contact with sedimentary rock.[6]

The Culpeper Basin is nearly continuous with the Gettysburg Basin to the north and with the Barboursville Basin to the south. The Groveton Member of the Bull Run Formation is exposed there.[3] The formation has produced disarticulated fish remains including isolated bones and scales.[3]

Geology

The Culpeper Basin preserves a series of both sedimentary formations and large basaltic lava flows associated with the initial rifting of Pangea. From oldest to youngest, these subunits are:[7][8]

  • Manassas Sandstone: Alluvial and stream sandstone and conglomerate, including the Poolesville, Tuscarora Creek, Reston, and Rapidan members. Footprints and fish are occasional found in these layers.
  • Bull Run Formation: Alluvial, stream, and playa lake sediments, including the Groveton, Balls Bluff, Haudricks Mountain, Mountain Run, and Leesburg members. Footprints are common in the Groveton Member, while body fossils sometimes occur in the Balls Bluff Member.
  • Catharpin Creek Formation: Alluvial sandstone and conglomerate, including the Goose Creek Member.
  • Mount Zion Church Basalt: This was the first eruption during CAMP volcanism, near the end of the Triassic.[8]
  • Midland Formation: Stream and lake sandstone and siltstone, equivalent in age to the Triassic-Jurassic boundary. Footprints and fish are occasional found in these layers.
  • Hickory Grove Basalt: This was the second outpouring of basaltic lava during the CAMP eruptions, near the start of the Jurassic.[9]
  • Turkey Run Formation: River, lake, and delta sediments
  • Sander Basalt: This was the final pulse of CAMP-related volcanic activity in the Culpeper Basin.
  • Waterfall Formation: Lake sediments, including the Millbrook Quarry Member.

A large body of diabase in central Montgomery County, Maryland, is known as the Boyds Sill,[10] named after the town of Boyds.

Fossils

In the upland Bull Run Formation, gastroliths (swallowed stomach stones) have been reported. They have been found in four different locations within the Bull Run Formation. These stones are interpreted as being eaten by herbivorous sauropodomorph dinosaurs to help them digest their food.[11]

Footprints are among the most common fossils in the Culpeper Basin. Footprints of theropod dinosaurs: Grallator and Kayentapus, Eubrontes, the small ornithischian Anomoepus, pseudosuchian/Aetosaur type reptiles like Brachychirotherium and Chirotherium, and crocodilian Batrachopus tracks have all been found.[12]

  • Jurassic diabase boulders in the Culpeper Basin northeast of Dulles Airport
  • Balls Bluff Siltstone with diabase intrusion, northern face of Luck Stone Quarry, Manassas
  • Limestone conglomerate of Leesburg Member
  • Another sample of limestone conglomerate
  • Sandstone from southwest the Boyds Sill in Montgomery County, Maryland
  • Unnamed stream exposing diabase of Boyds Sill, Hoyles Mill Trail, Montgomery County, Maryland

Footnotes

  1. ^ Pierce, Herbert A. "Open-File Report 03-056 -- Compartmentalization". pubs.usgs.gov. United States Geological Survey. Retrieved 29 December 2025.
  2. ^ a b Brezinski, David; Kavage Adams, Rebecca (5 February 2021). "EXPOSED TRIASSIC BASINS AS PROXIES FOR THE UNDERSTANDING OF BURIED RIFT SUCCESSIONS". Annapolis, Maryland: Maryland Geological Survey. pp. 1–88. Retrieved 29 December 2025.
  3. ^ a b c "Manassas National Battlefield Park," Hunt, Santucci, and Kenworthy (2006); page 64.
  4. ^ Marzoli, Andrea; Jourdan, Fred; Puffer, John H.; Cuppone, Tiberio; Tanner, Lawrence H.; Weems, Robert E.; Bertrand, Hervé; Cirilli, Simonetta; Bellieni, Giuliano; De Min, Angelo (1 March 2011). "Timing and duration of the Central Atlantic magmatic province in the Newark and Culpeper basins, eastern U.S.A.". Lithos. 122 (3): 175–188. doi:10.1016/j.lithos.2010.12.013. ISSN 0024-4937. Retrieved 14 December 2025.
  5. ^ Bedrock map and geotechnical properties of rocks of the Culpeper basin, Virginia and Maryland, Leavy, B.D., Froelich, A.J., and Abram, E.C. Miscellaneous Investigations Series Map I-1313-C. 1983. Map Scale: 1:125,000.
  6. ^ Geologic history and stratigraphy of the Triassic-Jurassic Culpeper Basin, Virginia, R. C. Lindholm. GSA Bulletin (1979) 90 (11_Part_II): 1702–1736. https://doi.org/10.1130/GSAB-P2-90-1702
  7. ^ Lee, K.Y.; Froelich, A.J. (1989). "Triassic- Jurassic Stratigraphy of the Culpeper and Barboursville Basins, Virginia and Maryland" (PDF). U.S. Geological Survey Professional Paper. 1472: 1–52. doi:10.3133/pp1472.
  8. ^ a b Weems, Robert E.; Olsen, Paul E. (1997-02-01). "Synthesis and revision of groups within the Newark Supergroup, eastern North America" (PDF). GSA Bulletin. 109 (2): 195–209. Bibcode:1997GSAB..109..195W. doi:10.1130/0016-7606(1997)109<0195:SAROGW>2.3.CO;2. ISSN 0016-7606.
  9. ^ Woodruff, L.G.; Froelich, A.J.; Belkin, H.E.; Gottfried, David (March 1995). "Evolution of tholeiitic diabase sheet systems in the eastern United States: examples from the Culpeper Basin, Virginia-Maryland, and the Gettysburg Basin, Pennsylvania". Journal of Volcanology and Geothermal Research. 64 (3–4): 143–169. doi:10.1016/0377-0273(94)00085-U. Retrieved 29 November 2025.
  10. ^ Fisher, G. W., 1964, The Triassic rocks of Montgomery County. In Geology of Howard and Montgomery Counties, Maryland Geological Survey, Baltimore, Maryland, 1964.)
  11. ^ Weems, Robert E.; Culp, Michelle J.; Wings, Oliver (30 May 2007). "Evidence for Prosauropod Dinosaur Gastroliths in the Bull Run Formation (Upper Triassic, Norian) of Virginia". Ichnos. 14 (3–4): 271–295. doi:10.1080/10420940601050030. ISSN 1042-0940. Retrieved 30 December 2025.
  12. ^ Weems, Robert (2018). "A SYNOPSIS OF THE VERTEBRATE FAUNA FROM THE CULPEPER BASIN (UPPER TRIASSIC-LOWER JURASSIC, MARYLAND AND VIRGINIA)". New Mexico Museum of Natural History and Science Bulletin. 79: 749–768.

References

  • Hunt, ReBecca K., Vincent L. Santucci and Jason Kenworthy. 2006. "A preliminary inventory of fossil fish from National Park Service units." in S.G. Lucas, J.A. Spielmann, P.M. Hester, J.P. Kenworthy, and V.L. Santucci (ed.s), Fossils from Federal Lands. New Mexico Museum of Natural History and Science Bulletin 34, pp. 63–69.
This article is issued from Wikipedia. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.