Midland Formation

{{Short description|Mesozoic formation in Virginia, United States}}

{{Infobox rockunit

| name = Midland Formation

| image =

| caption =

| type = Geological formation

| age =
Late Triassic to Early Jurassic,
late Rhaetian to early Hettangian

| prilithology = sandstone, siltstone

| otherlithology = shale, limestone

| namedfor = Midland, Virginia

| namedby = Lee & Froelich, 1989

| region = Maryland, Virginia

| country = United States

| coordinates =

| unitof = Meriden Group

| subunits =

| underlies = Hickory Grove Basalt

| overlies = Mount Zion Church Basalt

| thickness =

| extent = Culpeper Basin

| area =

| map =

| map_caption =

|period=Hettangian}}

The Midland Formation is a Mesozoic (latest Triassic to earliest Jurassic) geological formation in the Culpeper Basin of Virginia. It is a sedimentary unit which formed in a short period of time between the first two basalt flows in the basin: the Hickory Grove and Mount Zion Church basalts. The most common rocks in the formation are dark reddish interbedded sandstones and siltstones, representative of fluvial (stream) environments. Rare but fossiliferous calcareous shale and limestone also occurs, representing recurring lacustrine (lake) conditions. The Midland Formation is considered equivalent to the Shuttle Meadow Formation of the Hartford Basin, the Feltville Formation of the Newark Basin, and the Bendersville Formation of the Gettysburg Basin.{{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.researchgate.net/publication/40661805|journal=GSA Bulletin|language=en|volume=109|issue=2|pages=195–209|doi=10.1130/0016-7606(1997)109<0195:SAROGW>2.3.CO;2 |bibcode=1997GSAB..109..195W |issn=0016-7606}}{{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 }} Some sources prefer to classify the Midland Formation as part of the Shuttle Meadow Formation.{{Cite journal |last1=Olsen |first1=P. E. |last2=McCune |first2=A. R.|author2-link=Amy McCune |last3=Thomson |first3=K. S. |date=1982-01-01 |title=Correlation of the early Mesozoic Newark Supergroup by vertebrates, principally fishes |url=https://www.researchgate.net/publication/242164729 |journal=American Journal of Science |volume=282 |issue=1 |pages=1–44 |doi=10.2475/ajs.282.1.1 |issn=0002-9599|doi-access=free |bibcode=1982AmJS..282....1O }}

Based on conchostracan biostratigraphy, the Midland Formation is believed to contain the Triassic-Jurassic boundary near its base.{{Cite journal|last1=Kozur|first1=Heinz W.|last2=Weems|first2=Robert E.|date=2010-01-01|title=The biostratigraphic importance of conchostracans in the continental Triassic of the northern hemisphere|url=http://www.keuper.us.edu.pl/02_Keuper-literature/Kozur%20&%20Weems-2010_GSLondon.pdf|journal=Geological Society, London, Special Publications|language=en|volume=334|issue=1|pages=315–417|doi=10.1144/SP334.13|bibcode=2010GSLSP.334..315K |issn=0305-8719|s2cid=131224365}}{{Cite journal|last1=Lucas|first1=S.G.|last2=Tanner|first2=L.H.|last3=Donohoo-Hurley|first3=L.L.|last4=Geissman|first4=J.W.|last5=Kozur|first5=H.W.|last6=Heckert|first6=A.B.|last7=Weems|first7=R.E.|date=2011-03-15|title=Position of the Triassic–Jurassic boundary and timing of the end-Triassic extinctions on land: Data from the Moenave Formation on the southern Colorado Plateau, USA|url=https://www.sciencedirect.com/science/article/abs/pii/S0031018211000125|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|language=en|volume=302|issue=3–4|pages=194–205|doi=10.1016/j.palaeo.2011.01.009|bibcode=2011PPP...302..194L |issn=0031-0182}} A prominent shale layer containing Hettangian-age fossilized fish, the Midland fish bed, is present about 10 meters above the base of the formation. Though now flooded by a manmade lake, it was formerly well-exposed along Licking Run, just north of Midland, Virginia.{{Cite journal |last1=Baer |first1=Francis M. |last2=Martin |first2=William H. |date=1949-12-23 |title=Some New Finds of Fossil Ganoids in the Virginia Triassic |url=http://dx.doi.org/10.1126/science.110.2869.684 |journal=Science |volume=110 |issue=2869 |pages=684–686 |doi=10.1126/science.110.2869.684 |issn=0036-8075 |jstor=1677051|pmid=15396741 |bibcode=1949Sci...110..684B }}{{Cite journal |last1=Schaeffer |first1=Bobb |last2=McDonald |first2=Nicholas G. |date=1978 |title=Redfieldiid fishes from the Triassic-Liassic Newark Supergroup of eastern North America |url=https://digitallibrary.amnh.org/items/52d8aa67-6a45-4f02-b887-e7e3094c401d |journal=Bulletin of the American Museum of Natural History |volume=159 |issue=4 |pages=131–173}}{{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}} Plant spores,{{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.er.usgs.gov/publication/pp1472|journal=U.S. Geological Survey Professional Paper|volume=1472|pages=1–52|doi=10.3133/pp1472}} coprolites, and dinosaur footprints have also been recorded at nearby outcrops.{{Cite book |last=Olsen |first=Paul E. |title=Triassic-Jurassic Rifting and the Opening of the Atlantic Ocean |publisher=Elsevier |year=1988 |editor-last=Manspeizer |editor-first=Warren |location=Amsterdam |pages=185–230 |chapter=8. Paleoecology and Paleoenvironments of the Continental Early Mesozoic Newark Supergroup of Eastern North America |doi=10.1016/B978-0-444-42903-2.50013-0 |chapter-url=https://www.ldeo.columbia.edu/~polsen/nbcp/olsen_88.pdf}}{{Cite journal |last1=Olsen |first1=P. E. |last2=Kent |first2=D. V. |last3=Sues |first3=H.-D. |last4=Koeberl |first4=C. |last5=Huber |first5=H. |last6=Montanari |first6=A. |last7=Rainforth |first7=E. C. |last8=Fowell |first8=S. J. |last9=Szajna |first9=M. J. |last10=Hartline |first10=B. W. |date=2002-05-17 |title=Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary |url=https://www.science.org/doi/10.1126/science.1065522 |journal=Science |language=en |volume=296 |issue=5571 |pages=1305–1307 |doi=10.1126/science.1065522 |pmid=12016313 |bibcode=2002Sci...296.1305O |issn=0036-8075}}Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.