|Latitude & Longitude (WGS84):||44° 42' 23'' North , 66° 48' 56'' West|
|Latitude & Longitude (decimal):||44.70639,-66.81577|
|Age:||At least Ma|
|Köppen climate type:||Dfb : Warm-summer humid continental climate|
All visitors to Grand Manan Island have to be aware of the extreme change in elevation of the tides. The difference between low tide and high tide can be greater than 6.6 meters (22 feet or more). Beach walkers can become stranded against high rock cliffs by the ocean during high tide and may encounter life-threatening conditions. Every island visitor should know when the tidal extremes occur and plan their exposure to coastal changes very carefully. Always review the current day's tidal predictions as every day the high tide times are different.
The geology has been described by McHone (2012):
The higher western 2/3 of the island has thick lava flows of Dark Harbour basalt, which are little changed from when they cooled at the end of the Triassic Period. They formed with the enormous “flood basalt” that underlies most of the Bay of Fundy, and which erupted 201 million years ago. The same lavas crop out along the south western shores of Nova Scotia, where they are known as the North Mountain Basalt. There as here, an abundance of interesting minerals have filled the cracks and bubbles left by gases boiling out of the cooling lavas. These include zeolite minerals chabazite, mesolite, stilbite, and heulandite, plus attractive quartz-related amethyst, agate, and many others. The Dark Harbour Basalt is divided into three sections, or members, something like a cake with many thin layers of frosting in the middle. At the bottom is the Southwest Head member, a single massive flow which forms cliffs up to 100 meters high along much of the western shoreline. As it slowly cooled in a huge lava lake, vertical columns formed from bottom to top. Overlying this colonnade, the Seven Days Work member is comprised of 12 to 14 lava flows each a few meters thick. The flows contain a variety of attractive minerals along the famous cliffs of their given name. Over that, a top-most member is named after Ashburton Head, where you can see another thick pile of massive lava something like the bottom member. The two upper members have been removed by erosion over much of the island. Beneath the basalt are two thick formations of Triassic siltstone and sandstone that total about 3 kilometers deep, called the Dwellys Cove and Miller Pond Road formations. They are equivalent to the Blomidon and Wolfville formations across the Bay in Nova Scotia. The top few meters of their shale and siltstone are exposed along the western cobble beaches, but we have yet to find any tracks or bones of dinosaurs in them, although it is worth looking!
The Mesozoic formations rest upon a surface of ancient metamorphic rocks,
which are poorly known where they lie buried deep beneath the Mesozoic rocks. But on Grand Manan, these “basement” formations are exposed in
the low-lying eastern third of the island. This is due to vertical movement along a great fault that runs from Red Point (where it is well exposed) northward to Whale Cove (where it is hidden), and far out beneath the sea in both directions. The ridge just west of our highway from Seal Cove to North Head is held up by Dark Harbour basalt along the western side of the fault. As it moved, the Mesozoic formations were eroded away on the up side to eventually expose our eastern “basement.” The Red Point Fault must have caused many Mesozoic earthquakes, but it has probably been quiet since then, so not to worry if you live near it!
The metamorphic formations are organized into the Grand Manan Group of Late Proterozoic age; the Castalia Group about 60 million years younger or Early Cambrian; and meta-plutonic bodies such as Stanley Brook Granite, Rockweed Pond Gabbro, and Kent Island Granite of the same two age groups.
Although originally they were igneous and sedimentary rocks like basalt, sandstone, and shale, the eastern formations have been metamorphosed into greenstone, argillite, schist, quartzite, and other types during Early Paleozoic mountain-building events. Many folds and faults have bent and
broken the formations in tortured-looking outcrops. One such fault can be seen at the north end of Pettes Cove, where it separates metabasalt of Swallowtail Head from schist of North Head.
With the help of several recent radiometric dates, the eastern formations are now known to range in age from about 618 to 535 million years, or latest
Ediacaran into Cambrian periods . This is of great interest to geologists who are trying to correlate the Grand Manan rocks with formations on the mainland of New Brunswick and elsewhere. Our eastern continent is assembled from sections of crust called terranes, which that have quite different rock types with different geological histories, and must have formed at other areas of the planet before being moved here via continental drift. The metamorphism displayed in our eastern rocks could only occur more than 5 km beneath the surface, while their faults, folds, and cleavages attest to dynamic mountain-forming events called orogenies, several of which occurred during the Paleozoic from 600 to 300 million years ago. Exactly which terranes and orogenies are represented on Grand Manan is still in dispute."
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33 valid minerals.
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McHone, J. G. and McHone, N .W., 2012, Grand Manan Geology: Excursions in Island Natural History: Stones2Gems Publications, Grand Manan, New Brunswick, 50 p.
McHone, J.G., 2011, Triassic basin stratigraphy at Grand Manan, New Brunswick, Canada: Atlantic Geology, v. 47, p. 125-137.