{{Short description|Geological formation in the United States}} {{Infobox rockunit | name = Bull Run Formation | image =Balls Bluff Siltstone (4802112634).jpg | caption =Layers of Balls Bluff Siltstone at a quarry near Manassas, Virginia | type = Geological formation | age = Norian<br>~{{fossil range|222|210}} | period = Norian | prilithology = Mudstone | otherlithology = Shale, sandstone, siltstone, conglomerate | namedfor = | namedby = | region = Maryland, Virginia | country = United States | coordinates = {{coord|38.9|N|77.4|W|display=inline,title}} | paleocoordinates = {{coord|13.3|N|21.8|W|display=inline}} | unitof = Chatham Group | subunits = Balls Bluff Member, Groveton Member, Leesburg Member, Mountain Run Member, Haudricks Mountain Member | underlies =Catharpin Creek Formation | overlies =Manassas Sandstone | thickness = | extent = Culpeper Basin | area = | map = {{Location map+ | United States#Virginia | relief = 1 | width = 250 | float = center | places = {{Location map~ | United States#Virginia | lat_deg = 38.9 | lon_deg = -77.4 | mark = Pink ff0080 pog.svg | marksize = 10 }} }} | map_caption = }}
The '''Bull Run Formation''' is a Late Triassic (Norian) stratigraphic unit in the eastern United States.<ref name=FW>[https://paleobiodb.org/classic/displayCollResults?geological_group=Chatham&formation=Bull%20Run Bull Run Formation] at Fossilworks.org</ref> 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.<ref name="nps-fish-manassas-64">Hunt et al., 2006, p.64</ref>
The United States Geological Survey does not formally recognize the Bull Run Formation as a distinct formation,<ref>[https://ngmdb.usgs.gov/Geolex/Units/BullRun_715.html Bull Run], National Geologic Map Database, Geolex — Unit Summary, USGS.</ref> but its validity has been promoted by some paleontologists.<ref name=":0">{{Cite journal |last1=Weems |first1=Robert E. |last2=Olsen |first2=Paul E. |date=1997-02-01 |title=Synthesis and revision of groups within the Newark Supergroup, eastern North America |url=https://www.ldeo.columbia.edu/~polsen/nbcp/weems.olsen.97.pdf |journal=GSA Bulletin |language=en |volume=109 |issue=2 |pages=195–209 |bibcode=1997GSAB..109..195W |doi=10.1130/0016-7606(1997)109<0195:SAROGW>2.3.CO;2 |issn=0016-7606}}</ref>
== Geology == The Bull Run Formation includes several subunits:<ref name=":0" />
* '''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<ref name=":1">{{Cite journal |last1=Lee |first1=K.Y. |last2=Froelich |first2=A.J. |date=1989 |title=Triassic- Jurassic Stratigraphy of the Culpeper and Barboursville Basins, Virginia and Maryland |url=https://pubs.usgs.gov/pp/1472/report.pdf |journal=U.S. Geological Survey Professional Paper |volume=1472 |pages=1–52 |doi=10.3133/pp1472 |url-access=}}</ref>''' (or '''Cedar Mountain Member'''):<ref name=":0" /> 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.<ref name=":12">{{Cite journal |last1=Lee |first1=K.Y. |last2=Froelich |first2=A.J. |date=1989 |title=Triassic- Jurassic Stratigraphy of the Culpeper and Barboursville Basins, Virginia and Maryland |url=https://pubs.usgs.gov/pp/1472/report.pdf |journal=U.S. Geological Survey Professional Paper |volume=1472 |pages=1–52 |doi=10.3133/pp1472 |url-access=}}</ref> However, later studies argued that they are merely local exposures where the Bull Run Formation takes on eroded rock material from surrounding mountains.<ref name=":0" /> The Bull Run Formation is sometimes regarded as part of the Passaic Formation.<ref name=":2">{{Cite journal |last1=Weems |first1=Robert E. |last2=Tanner |first2=Lawrence H. |last3=Lucas |first3=Spencer G. |date=2016 |title=Synthesis and revision of the lithostratigraphic groups and formations in the Upper Permian?–Lower Jurassic Newark Supergroup of eastern North America |url=https://www.researchgate.net/publication/309853816 |journal=Stratigraphy |language=en |volume=13 |issue=2 |pages=111–153 |doi=10.29041/strat.13.2.03}}</ref><ref name=":4">{{Cite journal |last=Weems |first=Robert E. |date=2018 |title=A synopsis of the vertebrate fauna from the Culpeper Basin (Upper Triassic-Lower Jurassic, Maryland and Virginia) |url=https://www.researchgate.net/publication/348579482 |journal=New Mexico Museum of Natural History and Science Bulletin |volume=79 |pages=749–768}}</ref>
== 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:<ref name="FW" /><ref name=":4" /> * Coelacanth scales (''Diplurus newarki'') * Phytosaur teeth and other isolated bones (''Rutiodon cf. manhattanensis'' or ''Machaeroprosopus'') * ''Semionotus sp.''
=== 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.''<ref name="dinosaurdistribution">Weishampel et al., 2004, pp.517-607</ref>''<ref name="nps-fish-manassas-64" /><ref name=":4" /> * ''Agrestipus hottoni'' * ''Anomoepus sp.'' * ''Apatopus lineatus'' * ''Brachychirotherium parvum'' * ''Chirotherium lulli'' * ''Eubrontes cursorius'' * ''Grallator tenuis'' * ''Grallator tuberosus'' * ''Grallator sillimani'' * ''Gwyneddichnium majore'' * ''Kayentapus minor'' * ''Rhychosauroides brunswickii''
== See also == * List of dinosaur-bearing rock formations ** List of stratigraphic units with ornithischian tracks *** Indeterminate ornithischian tracks
== References == {{reflist|2}}
=== 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 * {{citation |last1=Weishampel |first1=David B. |author2-link=Peter Dodson |last2=Dodson |first2=Peter |author3-link=Halszka Osmólska |last3=Osmólska |first3=Halszka |year=2004 |title=The Dinosauria, 2nd edition |url=https://books.google.com/books?id=vtZFDb_iw40C |publisher=Berkeley: University of California Press |pages=1–880 |accessdate=2019-02-21 |isbn=0-520-24209-2 |author1-link=David B. Weishampel }} * 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
Category:Geologic formations of Maryland Category:Geologic formations of Virginia Category:Triassic System of North America Category:Triassic geology of Virginia Category:Norian Stage Category:Mudstone formations of the United States Category:Shale formations of the United States Category:Siltstone formations of the United States Category:Lacustrine deposits Category:Ichnofossiliferous formations Category:Paleontology in Virginia
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