Newark Supergroup

Newark Supergroup
Stratigraphic range: Triassic - Jurassic
Type Supergroup
Sub-units Chatham Group, Dan River Group, Chesterfield Group, Tuckahoe Group, Doswell Formation, Culpeper Group, Gettysburg Formation, Hammer Creek Formation, New Oxford Formation, Stockton Formation, Lockatong Formation, Brunswick Group, Portland Formation, East Berlin Formation, Shuttle Meadow Formation, New Haven Formation, Mount Toby Formation, Turners Falls Formation, Sugarloaf Formation, Fundy Group[1]
Location
Region East Coast, The Maritime Provinces
Country  United States,  Canada
Extent Nova Scotia, New Brunswick, Massachusetts, Connecticut, New York, New Jersey, Pennsylvania, Maryland, Virginia, North Carolina, and South Carolina
Type section
Named for Newark, New Jersey

The Newark Supergroup, also known as the Newark Group, is an assemblage of Upper Triassic and Lower Jurassic sedimentary rocks which outcrop intermittently along the United States East Coast. They were deposited in a series of Triassic basins [1]. The exposures extend from Massachusetts to North Carolina in the United States, with more still in the provinces of New Brunswick and Nova Scotia in Canada. It is named for the city of Newark, New Jersey.

Characteristics

New Oxford Conglomerate (Upper Triassic, York County, Pennsylvania); a unit within the Newark Supergroup.

The Newark Supergroup consists largely of poorly sorted nonmarine sediments; typical rocks are breccia, conglomerate, arkose sandstone, siltstone, and shale.[2][3] Most of the strata are red beds that feature ripple marks, mud cracks, and even rain drop prints; dinosaur footprints are common, though actual body fossils are very rare.[3] Some of the strata are detailed to the level of varves, with indications of Milankovitch cycles.[4] In preserved lake sediments, Semionotus fossils are especially common.[4]

The Newark sediments are extremely thick (up to 6 kilometers); they were deposited in a series of half-grabens that were themselves faulted into block mountains.[5] The beds dip to the east, while the faults dip westward.[5] The beds are intruded by numerous dikes and sills, indicative of considerable igneous activity; a superb example is the New Jersey Palisades sill.[5]

Formation

The Newark Supergroup's lithologies and structure are the classic hallmarks of a rift valley; the fault-blocking illustrates the crustal extension forces in play during the breakup of Pangea during the late Triassic Period.[2] The Appalachian Mountains had already been nearly eroded flat by the end of the period; the uplift and faulting that was the first part of the rifting provided new sources of sediment for the vast thicknesses deposited in the Newark Supergroup; the igneous intrusions are similarly diagnostic of a rift valley.[2][5] Coarse sediments were deposited near the eastern mountain front, while progressively finer ones were deposited farther west.[6]

Evidence suggests the climate at the time was subtropical and rainy, though divided between wet and dry months.[6] A few organic-rich deposits suggest patchy or intermittent swamps and lakes.[7]

Accumulation of Newark sediments within the rift basins continued from the late Triassic into the early Jurassic.[1][2]

See also

Notes

  1. 1 2 3 Luttrell, Gwendolyn W. (1989). "Stratigraphic nomenclature of the Newark Supergroup of eastern North America" (PDF). U.S. Geological Survey Bulletin. 1572: 1–136. Retrieved 30 June 2018.
  2. 1 2 3 4 Monroe & Wicander (1997), p. 602
  3. 1 2 Schuchert & Dunbar (1947), p. 108
  4. 1 2 Benton (1996), pp. 88–89
  5. 1 2 3 4 Monroe & Wicander (1997), p. 605
  6. 1 2 Schuchert & Dunbar (1947), p. 109
  7. ↑ Schuchert & Dunbar (1947), pp. 108–109

Bibliography

  • Benton, Michael J. (1996). The Penguin Historical Atlas of the Dinosaurs. London: Penguin Books.
  • Monroe, James; Wicander, Reed (1997). The Changing Earth: Exploring Geology and Evolution (2nd ed.). Belmont: West Publishing Company.
  • Schuchert, Carl; Dunbar, Carl (1947). Outlines of Historical Geology (4th ed.). New York: John Wiley & Sons.
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