Midland Formation

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]

Midland Formation
Stratigraphic range:
Late Triassic to Early Jurassic,
late Rhaetian to early Hettangian
TypeGeological formation
Unit ofMeriden Group
UnderliesHickory Grove Basalt
OverliesMount Zion Church Basalt
Lithology
Primarysandstone, siltstone
Othershale, limestone
Location
RegionMaryland, Virginia
Country United States
ExtentCulpeper Basin
Type section
Named forMidland, Virginia
Named byLee & Froelich, 1989

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. Plant spores and fossil theropod tracks have also been reported from the site.[1][6][7]

See also

Footnotes
  1. 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.
  2. 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. doi:10.1130/0016-7606(1997)109<0195:SAROGW>2.3.CO;2. ISSN 0016-7606.
  3. 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).
  4. 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.
  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. 302 (3–4): 194–205. Bibcode:2011PPP...302..194L. doi:10.1016/j.palaeo.2011.01.009. ISSN 0031-0182.
  6. Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.
  7. 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.

References
  • 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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