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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 64 (1980)

Issue: 4. (April)

First Page: 501

Last Page: 526

Title: Geology of New England Passive Margin

Author(s): James A. Austin, Jr. (2), Elazar Uchupi (3), D. R. Shaughnessy, III (3), R. D. Ballard (3)


The New England continental margin began to develop in the Middle Triassic, when rifting of Precambrian/Paleozoic terrane produced a complex arrangement of horsts and grabens. During the Late Triassic-Early Jurassic, these grabens were filled with terrigenous clastics, volcanics, and evaporites. When plate separation took place and seafloor spreading began approximately 195 to 190 m.y.B.P., the newly formed continental edge was uplifted and eroded, truncating preexisting rift structures.

As North America began to drift away from Africa, subsidence occurred along a series of normal faults now beneath the outer continental shelf. This "hinge zone" may represent the boundary between continental crust and a transitional zone of continental and oceanic crustal fragments.

Atop the faulted and subsiding crustal platform, thick sediments were deposited. The lower part of the drift sequence is an evaporite/carbonate unit of Early-Middle Jurassic age, and the upper part is a clastic wedge of Middle Jurassic to Cenozoic age. More than 80% of these sediments are Jurassic. Their total thickness may be as much as 13 km beneath the southeastern part of Georges Bank.

Beneath the outer shelf and upper slope is a Mesozoic reef/carbonate platform which was an effective sediment barrier until it was buried by prograding clastics in the early Late Cretaceous. Both the geographic position and steepness (5 to 8°) of the continental slope south of Georges Bank are a result of this carbonate buildup.

Emplacement of the drift sequence was disrupted by regressions during the Middle Jurassic, late Early Cretaceous, latest Cretaceous, late Eocene-Oligocene, late Miocene, and Pliocene-Pleistocene. The Middle Jurassic regression coincided with a westward jump of the Mid-Atlantic Ridge, whereas the late Early Cretaceous event was synchronous with the opening of the Bay of Biscay and the separation of Eurasia and North America. All of the more recent regressions were associated with continental glaciation.

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