Maritime Rocks: A Southern Origin?
Multicoloured volcanic ash layers, Cape St. Mary, NS. Photo – Dr. Rob Fensome
The sediments, rocks and fossils that lie beneath Canada’s vast lands and oceans have many stories to tell. Uncovering these stories and what they mean is what scientists with NRCan’s Geological Survey of Canada (GSC) do best. In fact, for the past 175 years, explorers with the GSC and their provincial/territorial counterparts have played a major role in telling the geological stories of Canada: the discoveries are endless.
Perhaps one of the most fascinating geological stories about the Maritime Provinces is reflected by the amazing diversity of rocks found across the region, especially along the shoreline. This is in contrast to southern Ontario, for example, which is mainly underlain by large tracts of flat-lying limestone. The Maritimes are made up of parts of the Earth’s crust that originated in the Southern Hemisphere: indeed as far south as the South Pole. You read that right. It turns out that most of the older rocks of Nova Scotia and southern New Brunswick originated on microcontinents (what geologists call terranes) that were located in the “deep south” 400 to 550 million years ago. Such a fascinating geological history makes the region a modern-day geological playground according to GSC scientists at the Bedford Institute of Oceanography (BIO) in Dartmouth.
Microcontinents Ganderia, Avalonia and Meguma formed 500 million years ago near the South Pole. After 400 million, years they became parts of larger continents, and eventually, formed parts of the Maritime Provinces we know today.
Metamorphosed sedimentary Meguma rocks at Blue Rocks, NS. The light and dark bands represent the sedimentary layers deposited near the South Pole in a long-lost ocean. They have been deeply buried, folded and crinkled by tectonic forces and have subsequently been uplifted and eroded to their present-day position and appearance. Photo – Dr. Rob Fensome
Rob Fensome, a Research Scientist with GSC Atlantic at the BIO says that we know the latitude at which rocks originated because many of the iron-bearing minerals in them take on a magnetic signature that can be used, by way of sophisticated instruments, to determine the latitude at which they originally formed.
Sedimentary rock originally formed when southern Nova Scotia was a microcontinent, the Meguma Terrane, near the South Pole. Photo – Julie Root
The magnetic signature of the rocks isn’t the only evidence that the terranes of the Maritimes spent millions of years in the south. When the terranes amalgamated with larger continents, eventually to form the supercontinent Pangea, they continued to drift north as part of the larger entity. This is logical; if the region started out near the South Pole some 500 million years ago, it must have travelled to northern mid-latitudes, across the equator, since then. Apart from the magnetic data, evidence that this region crossed the tropics comes from the salt (at for example at Malagash, NS), potash (for example at Sussex, NB) and gypsum deposits (for example in the Windsor area of NS). Fensome notes that thick formations of such “evaporite” rocks, could only have formed in hot, dry tropical seas. A little later, geologically speaking, wet tropical conditions prevailed, leading to the deposition of peat in large bogs; with time, burial and compaction, the Maritimes’ coal deposits were formed. Such evidence confirms that the region crossed the tropics between about 375 and 275 million years ago.
Gypsum specimen - Gypsum is a mineral that forms in evaporating seas and in associated cracks in the crust. Gypsum comes in several varieties: this is an example of satin spar gypsum because of its fibrous texture. Photo – Julie Root
Gypsum cliffs at Sweets Corner, near Windsor, NS. Such thick evaporite deposits in the Maritimes are compelling evidence that a large part of the region crossed the tropics around 350 million years ago. Photo – Dr. Rob Fensome
From sandstone to volcanic rock to coal and beyond, there is a rich diversity of geology in the Maritimes with origins as far away as the South Pole. The long journey of these terranes over hundreds of millions of years make for interesting geological stories and discoveries in a small region. In the Maritimes, a scientist does not have to travel very far to uncover a whole new geological world.
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