Newark Supergroup

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The Newark Supergroup, also known as the Newark Group, is an assemblage of Late Triassic and Early Jurassic sedimentary rocks which outcrop intermittently along the United States East Coast; the exposures extend from Massachusetts to North Carolina, with more still in Nova Scotia. It is named for the city of Newark, New Jersey.

Characteristics[edit]

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.[1][2] 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.[5]

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.[6] The beds dip to the east, while the faults dip westward.[7] The beds are intruded by numerous dikes and sills, indicative of considerable igneous activity; a superb example is the New Jersey Palisades sill.[8]

Formation[edit]

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.[9] 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.[10] Coarse sediments were deposited near the eastern mountain front, while progressively finer ones were deposited farther west.[11]

Evidence suggests the climate at the time was subtropical and rainy, though divided between wet and dry months.[12] A few organic-rich deposits suggest patchy or intermittent swamps and lakes.[13]

Accumulation of Newark sediments continued from the late Triassic into the early Jurassic.[14]

See also[edit]

Footnotes[edit]

  1. ^ James Monroe and Reed Wicander, The Changing Earth: Exploring Geology and Evolution, 2nd ed. (Belmont: West Publishing Company, 1997), p. 602.
  2. ^ Carl Schuchert and Carl Dunbar, Outlines of Historical Geology, 4th ed. (New York: John Wiley & Sons, Inc., 1947), p. 108.
  3. ^ Schuchert and Dunbar, p. 108.
  4. ^ Michael J. Benton, The Penguin Historical Atlas of the Dinosaurs, (London: Penguin Books Ltd., 1996), 88-9.
  5. ^ Ibid.
  6. ^ Monroe and Wicander, p. 605
  7. ^ Ibid.
  8. ^ Ibid.
  9. ^ Monroe and Wicander, p. 602.
  10. ^ Monroe and Wicander, pp. 602,605.
  11. ^ Schuchert and Dunbar, p. 109
  12. ^ Ibid.
  13. ^ Schuchert and Dunbar, pp. 108-9.
  14. ^ Monroe and Wicander, p. 602.

External links[edit]