The Newark Supergroup, also known as the Newark Group, is an assemblage of Upper Triassic and Lower Jurassicsedimentary and volcanic rocks which outcrop intermittently along the east coast of North America. They were deposited in a series of Triassic basins, the Eastern North American rift basins, approximately 220–190 million years ago.[1][2] The basins are characterized as aborted rifts, with half-graben geometry, developing parallel to the main rift of the Atlantic Ocean which formed as North America began to separate from Africa. Exposures of the Newark Supergroup extend from South Carolina north to Nova Scotia. Related basins are also found underwater in the Bay of Fundy. The group is named for the city of Newark, New Jersey.
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.[6] The beds are intruded by numerous dikes and sills, indicative of considerable igneous activity; a superb example is the New Jersey Palisades sill.[6]
Depositional environment
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.[3] 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.[3][6] Coarse sediments were deposited near the eastern mountain front, while progressively finer ones were deposited farther west.[7]
Evidence suggests the climate at the time was subtropical and rainy, though divided between wet and dry months.[7] A few organic-rich deposits suggest patchy or intermittent swamps and lakes.[8]
Accumulation of Newark sediments within the rift basins continued from the late Triassic into the early Jurassic.[2][3]
The separate basins and sub-basins of the Newark Supergroup have historically been given their own geological formations by local paleontologists. However, a study by Weems, Tanner, and Lucas (2016) proposed that the formations of the Newark Supergroup should be defined on a regional scale due to their geological uniformity over eastern North America. From youngest to oldest, the regional formations proposed by this study are:[9]
Minor basins crop out in South Carolina (Crowburg, Wadesboro basins), North Carolina (Ellerbe, Davie County basins), Virginia (Scottsburg, Randolph, Roanoke Creek, Briery Creek, Farmville, Flat Branch, Deep Run, Scottsville, Barboursville basins), Connecticut (Cherry Brook Outlier), Massachusetts (Northfield and Middleton basins), and Nova Scotia (Chedabucto Basin).
Age
Until the late 1970s, the entire Newark Supergroup was assumed to be Triassic in age. A 1977 study of fossil pollen argued that the sediments actually range from the Ladinian to the Lower Jurassic.[13] Under this hypothesis, the Supergroup was deposited over the course of 50 million years.[1]
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