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Image 1 - 2: Trilobite Fossils on Mt. Stephen , near Field, BC
Image 3: The Burgess Shale with Field in the valley below
Field, BC & The Burgess Shale
By Alex Lausanne
Nestled in the Rocky Mountains in Yoho National Park lies the small town of Field, BC. Although Field only houses a small population of 169, it hosts a major UNESCO world heritage site in the mountains above – the Burgess Shale.
The Burgess Shale Formation is an outcrop of rock dating to 505 million years old and contains an amazing display of marine fossils. A hike up Mt. Stephen leads geology enthusiasts to an ancient underwater cliff of thousands of fossilized trilobites. These hard bodied organisms are very well-preserved. Fossils are usually formed underwater and offshore. Even more extraordinary is the preservation of soft tissue of marine organisms at the Walcott Quarry. It takes a unique combination of factors relating to sediment deposition to create fossils and especially rare circumstances for them to preserve for millions of years. The Burgess Shale is one of the oldest examples of soft tissue preservation in the world.
How did they come to be?
Around 708 million years ago (during the Late Pre-Cambrian) the supercontinent of Rodinia formed around the equator. This was followed by the Cambrian Explosion (542 million years ago) when most major animal life forms evolved. The Burgess shale represents the end of this mass evolutionary event. When Rhodina eventually split apart water rushed inland and filled, what is now, BC with sea water. Sea beds of clay and mud accumulated and trapped marine creatures, like trilobites, within these sediments.
Through time and tectonic shifting of the earth's plates, the dense Pacific Plate (modern BC) collided with the North America Plate and was forced underneath of the continental crust (modern Alberta). The underwater mountain features were scraped off and built up as massive sediment layers, appearing similar to the present day Grand Canyon.
The final formation of the Rocky Mountains began with the onset of the Ice Age 2.8 million yeas ago. The glaciers carved out the mountain valleys and continued to do so during subsequent glacial events, which exposed the incredible fossil beds we see today.
Thousands of years later, in 1886, the fossils were discovered by scouts during the construction of the Canada Pacifc Railway and eventually became designated a UNESCO world heritage site.
It should be noted that it is illegal to visit the Burgess Shale without a professional guided hike. Due to the significance of the site, as well as preservation concerns and issues with looting, hikers must pre-book a trip with Parks Canada or the Burgess Shale Geoscience Foundation. From experience, I recommend that it is well worth the visit! Not only are the fossils spectacular, but it is humbling to have such an amazing and unique UNESCO World Heritage site in BC's own backyard.
Thanks to our guide, Thomas Maguire, for a fantastic hike!
Posted 02 October 2016