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.[1] 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.[2][3] Some sources prefer to classify the Midland Formation as part of the Shuttle Meadow Formation.[4][3][5]
| Midland Formation | |
|---|---|
| Stratigraphic range: Late Triassic to Early Jurassic, late Rhaetian to early Hettangian | |
| Type | Geological formation |
| Unit of | Meriden Group |
| Underlies | Hickory Grove Basalt |
| Overlies | Mount Zion Church Basalt |
| Lithology | |
| Primary | sandstone, siltstone |
| Other | shale, limestone |
| Location | |
| Region | Maryland, Virginia |
| Country |  United States |
| Extent | Culpeper Basin |
| Type section | |
| Named for | Midland, Virginia |
| Named by | Lee & Froelich, 1989 |
Based on conchostracan biostratigraphy, the Midland Formation is believed to contain the Triassic-Jurassic boundary near its base.[6][7] 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.[8][9][4][5] Plant spores,[1] coprolites,[8][9] and dinosaur footprints have also been recorded at nearby outcrops.[10][11][12][5]
Paleobiota
editColor key
|
Notes Uncertain or tentative taxa are in small text; |
| Paleobiota of the Midland Formation | |||
|---|---|---|---|
| Genus / Taxon | Species | Notes | Images |
| Anomoepus | A. scambus | Possible ornithischian dinosaur footprints.[10][11][5] | |
| Batrachopus | B. deweyii | Crocodylomorph footprints.[11][5] | |
| Darwinula | D. sp. | Freshwater ostracods (seed shrimp).[10] | |
| Diplurus | D. longicaudatus | A coelacanth fish.[8][9][5] | |
| Eubrontes | E. giganteus | Large theropod dinosaur footprints, up to 34 centimetres (13 in) in length.[11][5] | |
| Grallator | G. parallelus | Theropod dinosaur footprints.[10][11][5] | |
| G. tuberosus | Theropod dinosaur footprints, often given the name Anchisauripus.[11][5] | ||
| Ptycholepis | P. marshi | A ptycholepiform fish.[8][9][5] | |
| Redfieldius | R. gracilis | A redfieldiiform fish, the most common fish in the formation.[8][9][5] | |
| Semionotus | 'S. micropterus' group[4] | A semionotiform fish.[9][5] | |
See also
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Footnotes
edit- ^ a b Lee, K.Y.; Froelich, A.J. (1989). "Triassic- Jurassic Stratigraphy of the Culpeper and Barboursville Basins, Virginia and Maryland". U.S. Geological Survey Professional Paper. 1472: 1–52. doi:10.3133/pp1472.
- ^ Weems, Robert E.; Olsen, Paul E. (1997-02-01). "Synthesis and revision of groups within the Newark Supergroup, eastern North America". 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.
- ^ a b 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.
- ^ a b c Olsen, P. E.; McCune, A. R.; Thomson, K. S. (1982-01-01). "Correlation of the early Mesozoic Newark Supergroup by vertebrates, principally fishes". American Journal of Science. 282 (1): 1–44. Bibcode:1982AmJS..282....1O. doi:10.2475/ajs.282.1.1. ISSN 0002-9599.
- ^ a b c d e f g h i j k l 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.
- ^ Kozur, Heinz W.; Weems, Robert E. (2010-01-01). "The biostratigraphic importance of conchostracans in the continental Triassic of the northern hemisphere" (PDF). Geological Society, London, Special Publications. 334 (1): 315–417. Bibcode:2010GSLSP.334..315K. doi:10.1144/SP334.13. ISSN 0305-8719. S2CID 131224365.
- ^ Lucas, S.G.; Tanner, L.H.; Donohoo-Hurley, L.L.; Geissman, J.W.; Kozur, H.W.; Heckert, A.B.; Weems, R.E. (2011-03-15). "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". Palaeogeography, Palaeoclimatology, Palaeoecology. 302 (3–4): 194–205. Bibcode:2011PPP...302..194L. doi:10.1016/j.palaeo.2011.01.009. ISSN 0031-0182.
- ^ a b c d e Baer, Francis M.; Martin, William H. (1949-12-23). "Some New Finds of Fossil Ganoids in the Virginia Triassic". Science. 110 (2869): 684–686. Bibcode:1949Sci...110..684B. doi:10.1126/science.110.2869.684. ISSN 0036-8075. JSTOR 1677051. PMID 15396741.
- ^ a b c d e f Schaeffer, Bobb; McDonald, Nicholas G. (1978). "Redfieldiid fishes from the Triassic-Liassic Newark Supergroup of eastern North America". Bulletin of the American Museum of Natural History. 159 (4): 131–173.
- ^ a b c d Olsen, Paul E. (1988). "8. Paleoecology and Paleoenvironments of the Continental Early Mesozoic Newark Supergroup of Eastern North America" (PDF). In Manspeizer, Warren (ed.). Triassic-Jurassic Rifting and the Opening of the Atlantic Ocean. Amsterdam: Elsevier. pp. 185–230. doi:10.1016/B978-0-444-42903-2.50013-0.
- ^ a b c d e f Olsen, P. E.; Kent, D. V.; Sues, H.-D.; Koeberl, C.; Huber, H.; Montanari, A.; Rainforth, E. C.; Fowell, S. J.; Szajna, M. J.; Hartline, B. W. (2002-05-17). "Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary". Science. 296 (5571): 1305–1307. Bibcode:2002Sci...296.1305O. doi:10.1126/science.1065522. ISSN 0036-8075. PMID 12016313.
- ^ Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.
References
edit- Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.
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