Western newfoundland geo-museum
Mantle rocks, ancient continental land masses, evidence of oceans far removed, and barely explored sedimentary basins await discovery on this enchanting island in eastern Canada.
The Tablelands are made up of peridotite, an ultramafic rock that formed deep within the earth, in this case the upper mantle. These rocks were forced up during the collision of two tectonic plates. Peridotites are rich in elements that inhibit normal plant growth making the area rather barren. The weathered reddish-brown color is due to the high iron content while fresh surfaces are dark green from the high olivine content of the rock. Photo: Tom Smith
A museum is a place where objects of artistic, historical, and scientific importance are preserved. We go to museums to learn about and study our past. The British Museum in London and the Smithsonian in Washington, D.C. house many past accomplishments of man and how world events, both natural and manmade, have affected the world around us.
Western Newfoundland offers similar opportunities that attract millions of visitors to these great museums of the world: a unique chance to learn about the past. The global effects of plate tectonics abound here. The associated rifting and mountain building events have formed potential oil and gas basins and displaced rocks from deep within the earth over portions of these basins. All are beautifully displayed along the scenic coast of Western Newfoundland where visitors can explore World Heritage sites, coastal fishing villages, sail along steep-sided fjords, or simply enjoy a quiet walk on the beach.
Like most good museums, you must start on the ground floor; in this case Gros Morne National Park. Designated a World Heritage Site in 1987 because (from the park’s brochure), “The rocks of Gros Morne National Park and the adjacent part of Western Newfoundland provide some of the world’s best illustrations of plate tectonics, one of the most important ideas in modern science.”
An ancient continent can be seen along the cliffs of Western Brook Pond, where glaciers have exposed granites and gneisses 1.2 billion years old. Volcanic rocks exposed along the present-day shoreline give witness to a time when this super-continent Rhodinia split apart and a new ocean started to form. The limestone and quartzite exposed along the cliffs and mountain tops in the upper parts of Bonne Bay were deposited near the shoreline of this ocean. Finally, sediments that were deposited along the base of the continental shelf can be found along the northern shoreline of the park.
Deposition along this margin lasted into the early Ordovician, when forces inside the Earth changed. The ocean started to close and the tectonic events that followed created the park’s most obvious geologic feature, the Tablelands, which can be viewed from near the visitor’s center across Bonne Bay. These are some of the best exposures of mantle rocks anywhere, and also may be some of the most accessible. The rocks comprising the Tablelands were emplaced as a result of this ocean being subducted under the continental land mass and the eventual collision with Gondwana in the late Devonian. Large slices of rock, including those from the Tablelands, were scraped up and over the strata that bordered the continent of Laurentia.
The next ‘floor’ in this outdoor museum, actually along the coast just north of Gros Morne National Park, is devoted to petroleum geology and how it may relate to plate movements. Much of what is exposed at the surface are the allochthonous rocks that were shoved out of and over parts of the early Paleozoic Anticosti Basin. These rocks give the geologist a peek at what may be encountered below this allochthonous package into the less disturbed underlying rocks.
Knowing the location of the ancient plate boundaries and continental margins yields additional insight into the petroleum potential in the Anticosti Basin. From large gas discoveries off the coast of Labrador to the prolific Arbuckle and Ellenburger formations of Oklahoma and Texas and points in between, the ancient Laurentian margin is no newcomer to large oil and gas discoveries. All of the Cambro-Ordovician basins along the Appalachian and Ouachita mountains have production. Deep exploration is just beginning in the Anticosti Basin, one of the last largely unexplored basins along this margin.
No museum is complete without some relics from the past and the Parson’s Pond area (about 50 km north of Gros Morne National Park) is our next stop. Mr. Parsons skimmed oil from the lake that bears his name nearly two centuries ago to be used as a cure for rheumatism. Others seeking oil followed. In 1867, John Silver, using a steam powered drill, found “some oil and gas shows” in his 213m deep well. The 1890’s saw more attempts to find oil in the shallow strata around the lake when the Newfoundland Oil Company drilled a well down to 396m. Again, oil and gas shows were encountered and the company deepened the well, torpedoed (dynamited), and “pumped six barrels in a very short time”. The first 15 years produced less than 2,000 barrels. The company sold 900 barrels to St. John’s Gas and Light Company for $1,460 and subsequently went out of business in 1907.
For the next 100 years, various companies drilled more wells into the underlying shales near Parson’s Pond, encountering small amounts of oil and gas. At present, however, the first wells are being drilled through the allochthonous section and into the underlying Ordovician carbonate reservoirs. The Seamus #1 has been completed to a total depth of 3,160m and has encountered a hydrocarbon bearing zone that is to be evaluated later this summer. The drilling rig will soon start a second well in a planned three well program headed by Nalcor Energy Oil and Gas (a Crown-owned corporation) and their partners.
Who knows? The current drilling program could complete the link between the productive platform dolomites in Texas and Oklahoma to those of northeastern Canada, a link that started 600 million years ago.
It must be noted that one of the things that makes Western Newfoundland so unique geologically was its ancient location on the Laurentian margin. This margin was formed during the breakup of the super continent Rhodinia, which started about 600 million years ago (mya). Through much of the Cambrian and Ordovician periods Newfoundland formed a promontory or seaward continental projection along the Laurentian margin. The Laurentian continent included North America, Greenland, and parts of Scotland and Ireland. The margin of this continent can now be traced from offshore Labrador, Western Newfoundland, along the St. Lawrence Seaway, continuing south along the western Appalachian Mountains, west to the Ouachita Mountains of Oklahoma and Arkansas and on into south Texas. Pieces of this margin are also found in Greenland, Scotland, and Norway.
Thick sequences of platform carbonates similar to today’s Bahamas carbonate shelf were deposited along this margin in what is now called the Anticosti Basin in Western Newfoundland. Deep ocean basin sediments were deposited outward of the carbonate shelf. By early Ordovician, the dynamics driving plate movements changed and this ocean began to close. A series of tectonic events occurred that included the formation of volcanic island arcs and fore-arc basins and their eventual collisions with Laurentia until the super-continent of Gondwana arrived about 430 mya, at the start of the Acadian Orogeny that formed the Appalachian mountain range.
During the early stages of the continental collisions, huge masses of rock were transported and now lie on top of the platform carbonates. Rocks like the peridotites that form the Tablelands pictured above were thrust up from the mantle, as were sections of deep ocean and continental slope rocks. These are the allochthonous rocks (i.e. not in their original stratigraphic position) that now overlay the in-place (or autochthonous) margin carbonates, and are now the targets of recent oil and gas exploration.
As Larry says, “Western Newfoundland offers some of the best and most complete exposures showing the effects of plate tectonics. Outcrop exposures representative of an ocean opening and closing event are so well exposed and accessible, geologists refer to Western Newfoundland as the “Galapagos of Plate Tectonics” and in local circles as the “Eighth Wonder of the World”.
“It is no accident that earth scientists worldwide (Canadian J. Tuzo Wilson who refined plate tectonics theory, Newfoundland geologists Harold Williams and Bob Stevens who connected the geology there to a plate tectonics interpretation, and prominent plate tectonic researchers Marshall Kay and John Dewey, to name just a few) have been coming to our shores over the past forty years to view the rocks and test their theories or develop new concepts on plate tectonics.”
“Stroll along the Earth’s mantle, examine an ancient tropical shoreline or sleuth for fossils in deep water marine sediments – all just an afternoon adventure at Gros Morne National Park”.
Special thanks to Larry Hicks and Karen Waterman for the information and great field trip and to Sharon McLennon and the Greater Corner Brook Board of Trade for making it all possible.
|Article from GEO ExPro Magazine NO4 – 2010|