Bull Run Formation

Bull Run Formation
Stratigraphic range: Norian
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Layers of Balls Bluff Siltstone at a quarry near Manassas, Virginia
TypeGeological formation
Unit ofChatham Group
Sub-unitsBalls Bluff Member, Groveton Member, Leesburg Member, Mountain Run Member, Haudricks Mountain Member
UnderliesCatharpin Creek Formation
OverliesManassas Sandstone
Lithology
PrimaryMudstone
OtherShale, sandstone, siltstone, conglomerate
Location
Coordinates38°54′N 77°24′W / 38.9°N 77.4°W / 38.9; -77.4
Approximate paleocoordinates13°18′N 21°48′W / 13.3°N 21.8°W / 13.3; -21.8
RegionMaryland, Virginia
CountryUnited States
ExtentCulpeper Basin
Bull Run Formation (the United States)
Bull Run Formation (Virginia)

The Bull Run Formation is a Late Triassic (Norian) stratigraphic unit in the eastern United States.[1] It is part of the Newark Supergroup, exposed in the Culpeper Basin of Virginia and Maryland. Fossil fish bones and scales have been found in outcrops of the formation's Groveton Member in Manassas National Battlefield Park.[2]

The United States Geological Survey does not formally recognize the Bull Run Formation as a distinct formation,[3] but its validity has been promoted by some paleontologists.[4]

Geology

The Bull Run Formation includes several subunits:[4]

  • Balls Bluff Member (or Balls Bluff Siltstone): Fluvial (stream and river) sandstones and shales. The oldest and most widespread subunit of the formation. It is more common near the rim of the Culpeper Basin, where the dry lake deposits of the Groveton Member are less prevalent.
  • Groveton Member: Rhythmic playa lake shales and paleosols. Common in the central part of the Culpeper Basin, where it overlies the Balls Bluff Member.
  • Leesburg Member (or Leesburg Conglomerate Member): A conglomerate of limestone and dolomite fragments, outcropping in the northern Culpeper Basin above strata of the Balls Bluff Member.
  • Mountain Run Member[5] (or Cedar Mountain Member):[4] A conglomerate of greenstone fragments outcropping near Cedar Mountain in Culpeper County, Virginia.
  • Haudricks Mountain Member: Sandstones and metamorphic rock fragments outcropping near Haudricks Mountain in the Barboursville Basin.

The latter two members were once identified as a separate formation, the Tibbstown Formation.[6] However, later studies argued that they are merely local exposures where the Bull Run Formation takes on eroded rock material from surrounding mountains.[4] The Bull Run Formation is sometimes regarded as part of the Passaic Formation.[7][8]

Paleobiota

Distinctly rounded stones (possible gastroliths) are common in the Balls Bluff Member, while direct fossil material is more rare. The following vertebrates have been reported from the formation:[1][8]

Footprints

Trackways are abundant in the Groveton Member. The largest and most diverse footprint site in the formation is Culpeper Crushed Stone Company quarry near Stevensburg, Virginia. Footprints are also common in and around Manassas National Battlefield Park.[9][2][8]

See also

References

  1. ^ a b Bull Run Formation at Fossilworks.org
  2. ^ a b Hunt et al., 2006, p.64
  3. ^ Bull Run, National Geologic Map Database, Geolex — Unit Summary, USGS.
  4. ^ a b c d 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.
  5. ^ 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.
  6. ^ 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.
  7. ^ Weems, Robert E.; Tanner, Lawrence H.; Lucas, Spencer G. (2016). "Synthesis and revision of the lithostratigraphic groups and formations in the Upper Permian?–Lower Jurassic Newark Supergroup of eastern North America". Stratigraphy. 13 (2): 111–153. doi:10.29041/strat.13.2.03.
  8. ^ a b c Weems, Robert E. (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.
  9. ^ Weishampel et al., 2004, pp.517-607

Bibliography

  • 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
  • R. E. Weems. 2006. The manus print of Kayentapus minor: its bearing on the biomechanics and ichnotaxonomy of early Mesozoic saurischian dinosaurs. In J. D. Harris, S. G. Lucas, J. A. Spielmann, M. G. Lockley, A. R. C. Milner, & J. I. Kirkland (eds.), The Triassic-Jurassic Terrestrial Transition. New Mexico Museum of Natural History and Science Bulletin 37:369-378
  • Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (2004), The Dinosauria, 2nd edition, Berkeley: University of California Press, pp. 1–880, ISBN 0-520-24209-2, retrieved 2019-02-21{{citation}}: CS1 maint: publisher location (link)
  • R. E. Weems and P. G. Kimmel. 1993. Upper Triassic reptile footprints and a coelacanth fish scale from the Culpeper Basin, Virginia. Proceedings of the Biological Society of Washington 16(2):390-401
  • J. R. Smith. 1982. Dinosaurs in Virginia—evidence of two new genera. Lapidary Journal 36(6):1110-1111
  • R. Weems. 1979. A large parasuchian (phytosaur) from the Upper Triassic portion of the Culpeper Basin of Virginia (USA). Proceedings from the Biological Society of Washington 92(4):682-688


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