The Science Behind the Burgess Shale
Scientists were stumped by how the fossils in the Burgess Shale were so well preserved up until a few years ago. It turns out that the type of rock the fossils were buried in typically builds up slowly over time – clearly was not the case for this instance. Scientists found that mud slurry from the oceanic floor buried these animals really quickly, preserving soft body parts when they would have decomposed otherwise. Because they were instantly buried, scavengers couldn’t eat away at the soft parts, and bacteria are not active at that level.
During the formation of modern day continents, tectonic plates smashed together and then drifted apart. This chaotic crust movement eventually would form the Rocky Mountains. During the Cambrian era, North America was shifting up from the equator, and the west coast was facing north. At this time, the coast was about where Calgary, Alberta is (where I live). The Burgess Shale quarry was underwater just below a huge cliff, which was also underwater at the time. The sea base was, of course, mud and periodically mud would rush into the quarry via storms and bury the inhabitants. The ocean basin filled with mud which formed shale; however the section was still underwater. Sections of the sea floor were crushed against each other; the result was older rocks being raised above younger rocks, and thus the Burgess Shale ending up “on top” so to speak. Western and central British Columbia formed by small islands and rocks colliding with the mountains holding the Burgess Shale, raising it further above the water.
The area has been greatly modified from its original state due to erosion, and the Burgess Shale is exceedingly hard to get to, being on top of fittingly named “Fossil Ridge” on the boarder of British Columbia and Alberta.