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.[2] Some of the strata are detailed to the level of varves, with indications of Milankovitch cycles.[3] In preserved lake sediments, Semionotus fossils are especially common.[3]

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.[4] The beds dip to the east, while the faults dip westward.[4] The beds are intruded by numerous dikes and sills, indicative of considerable igneous activity; a superb example is the New Jersey Palisades sill.[4]

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.[1] 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.[1][4] Coarse sediments were deposited near the eastern mountain front, while progressively finer ones were deposited farther west.[5]

Evidence suggests the climate at the time was subtropical and rainy, though divided between wet and dry months.[5] A few organic-rich deposits suggest patchy or intermittent swamps and lakes.[6]

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

See also[edit]

Notes[edit]

Bibliography[edit]

  • 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. 

External links[edit]