The North Mountain Basalt

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Outcrops on the east shore of Cape Blomidon (here seen from the air looking west) consists of spectacular cliff exposures of North Mountain Basalt (gray) and underlying Blomidon Formation (red). The North Mountain Basalt is an immense tholeiitic lava flow sequence that covers most of the Fundy basin. It underlies the Early Jurassic age McCoy Brook Formation and overlies the, primarily Triassic age, Blomidon. The thin gray layer seen here between them consists of regionally extensive organic-rich mudstones containing pollen and spores that allow that the Triassic-Jurassic boundary lay within the uppermost couple of meters of Blomidon Formation. This paleontological information coupled with the U-Pb age of 202 MY (Dunning and Hodych, 1990), provides the most direct date for the Triassic-Jurassic boundary available.

Representative of one of the largest LIPs (Large Igneous Provinces), the North Mountain basalt is part of an gigantic flood basalt and intrusive complex of the same age (201-202 Ma) with a diameter of 4000 km sq, stretching from northern South America to France. This LIP may be associated with the initiation of seafloor spreading off the Southeastern United States (Withjack et al., 1998), while extension, but not seafloor spreading, accelerated around Nova Scotia.


Dunning, G. R. and Hodych, J. P., 1990, U/Pb zircon and baddeleyite ages for the Palisades and Gettysburg sills of the northeastern United States; implications for the age of the Triassic/Jurassic boundary. Geology v. 18, p. 795-798.

Fowell, S. J. and Traverse, A., 1995, Palynology and age of the upper Blomidon Formation, Fundy Basin, Nova Scotia. Review of Palaeobotany and Palynology. v. 86, p. 211-233.

Withjack, M. O., Schlische, R. W., and Olsen, P. E., 1997, Diachronous rifting, drifting, and inversion on the passive margin of Eastern North America: An analog for other passive margins. American Association of Petroleum Geologists Bulletin, in press.