Midland Formation Explained

Midland Formation
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
Unitof:Meriden Group
Underlies:Hickory Grove Basalt
Overlies:Mount Zion Church Basalt
Extent:Culpeper Basin
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.[1] [2] Some sources prefer to classify the Midland Formation as part of the Shuttle Meadow Formation.[3]

Based on conchostracan biostratigraphy, the Midland Formation is believed to contain the Triassic-Jurassic boundary near its base.[4] [5] 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.[6] [7] [8] Plant spores,[9] coprolites, and dinosaur footprints have also been recorded at nearby outcrops.[10] [11] [12]

Paleobiota

Paleobiota of the Midland Formation
Genus / TaxonSpeciesNotesImages
AnomoepusA. scambusPossible ornithischian dinosaur footprints.
BatrachopusB. deweyiiCrocodylomorph footprints.
DarwinulaD. sp.Freshwater ostracods (seed shrimp).
DiplurusD. longicaudatusA coelacanth fish.
EubrontesE. giganteusLarge theropod dinosaur footprints, up to 34cm (13inches) in length.
GrallatorG. parallelusTheropod dinosaur footprints.
G. tuberosusTheropod dinosaur footprints, often given the name Anchisauripus.
PtycholepisP. marshiA ptycholepiform fish.
RedfieldiusR. gracilisA redfieldiiform fish, the most common fish in the formation.
Semionotus'S. micropterus' groupA semionotiform fish.

See also

References

Notes and References

  1. Weems. Robert E.. Olsen. Paul E.. 1997-02-01. Synthesis and revision of groups within the Newark Supergroup, eastern North America. GSA Bulletin. en. 109. 2. 195–209. 10.1130/0016-7606(1997)109<0195:SAROGW>2.3.CO;2 . 1997GSAB..109..195W . 0016-7606.
  2. 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. en. 13. 2. 111–153 . 10.29041/strat.13.2.03 .
  3. Olsen . P. E. . McCune . A. R.. Amy McCune . 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 . 10.2475/ajs.282.1.1 . 0002-9599. free . 1982AmJS..282....1O .
  4. Kozur. Heinz W.. Weems. Robert E.. 2010-01-01. The biostratigraphic importance of conchostracans in the continental Triassic of the northern hemisphere. Geological Society, London, Special Publications. en. 334. 1. 315–417. 10.1144/SP334.13. 2010GSLSP.334..315K . 0305-8719. 131224365.
  5. 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. en. 302. 3–4. 194–205. 10.1016/j.palaeo.2011.01.009. 2011PPP...302..194L . 0031-0182.
  6. Baer . Francis M. . Martin . William H. . 1949-12-23 . Some New Finds of Fossil Ganoids in the Virginia Triassic . Science . 110 . 2869 . 684–686 . 10.1126/science.110.2869.684 . 0036-8075 . 1677051. 15396741 . 1949Sci...110..684B .
  7. 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.
  8. 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. 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. 10.3133/pp1472.
  10. Book: Olsen, Paul E. . Triassic-Jurassic Rifting and the Opening of the Atlantic Ocean . Elsevier . 1988 . Manspeizer . Warren . Amsterdam . 185–230 . 8. Paleoecology and Paleoenvironments of the Continental Early Mesozoic Newark Supergroup of Eastern North America . 10.1016/B978-0-444-42903-2.50013-0 . https://www.ldeo.columbia.edu/~polsen/nbcp/olsen_88.pdf.
  11. 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 . en . 296 . 5571 . 1305–1307 . 10.1126/science.1065522 . 12016313 . 2002Sci...296.1305O . 0036-8075.
  12. Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.