Welcome to my EarthCache!
An EarthCache is a special type of geocache where there is no container to find. Instead, you explore a unique geological feature and answer questions to claim your find, along with posting a photo. This EarthCache explores trace fossils, dolomitization, and how ancient animal burrows preserved within Tyndall Stone became one of Canada’s most recognizable building materials.
EarthCache Requirements
As with all of my EarthCaches, I’m not expecting PhD-level answers. Take some time to enjoy the site and learn something new. If you’re answering for multiple caching names, include a list of cachers with your answers so I can verify that you have completed the requirements for this EarthCache.
To log a find, please send your answers to the following questions via the link at the top of the page or email the owner:
Logging Questions
1. Describe two visible differences between the dark burrows and the surrounding light-coloured limestone.
2. Estimate what percentage of the stone surface is occupied by the dark dolomitized burrows and what percentage is occupied by the lighter limestone matrix.
3. Why are these features classified as trace fossils rather than body fossils?
4. Based on your observations, explain why magnesium-rich groundwater would have moved more easily through the burrows than through the surrounding limestone.
Photo Requirement: Take a photo of yourself, a signature item, geo-pet, or trackable item with the Tyndall Stone at GZ. Your face is not required to be in the photo, but it should be attached to your log.
Geology Lesson
The decorative stone at this location is known as Tyndall Stone, a fossil-bearing limestone quarried near the communities of Garson and Tyndall, Manitoba. It formed approximately 450 million years ago during the Late Ordovician Period, when much of central Canada was covered by a warm, shallow tropical sea located near the equator.
Tyndall Stone is one of the most recognizable building stones in Canada and can be found on government buildings, universities, museums, hotels, and office towers from coast to coast. While many people notice the distinctive grey patterns running through the stone, few realize that these markings are actually evidence of life on an ancient sea floor.
The light-coloured portions of the stone consist primarily of limestone formed from calcium-rich mud and the remains of marine organisms. The darker grey patterns tell a different story. These branching networks are fossilized burrows known as Thalassinoides. Long before the rock hardened into stone, organisms were moving through the soft sediment beneath the sea floor, creating tunnels as they searched for food or shelter.
Unlike body fossils, which preserve part of an organism itself, trace fossils preserve evidence of an organism’s activity. Tracks, trails, footprints, feeding marks, and burrows are all examples of trace fossils. The burrows visible in Tyndall Stone provide evidence that animals were actively living beneath the sea floor hundreds of millions of years ago.
One of the most fascinating aspects of these burrows is that geologists still do not know exactly what organism created them. Similar burrows are produced today by shrimp-like crustaceans, but those animals do not appear in the fossil record until hundreds of millions of years after these Ordovician burrows were formed. Despite decades of research, the identity of the original burrow-maker remains a mystery.
The dark colour of the burrows developed long after the tunnels were originally excavated. As the limestone became buried beneath younger sediments, groundwater rich in dissolved magnesium moved through the rock. The sediment within the burrows was less compacted than the surrounding limestone, allowing groundwater to flow more easily through these pathways.
Over time, the original limestone within the burrows was altered into dolomite, a carbonate mineral containing magnesium. This process is known as dolomitization. Because the dolomitized burrows differ in composition from the surrounding limestone, they appear darker and stand out clearly against the lighter background rock.
At this location, you can easily see how the burrow network branches, reconnects, and twists through the stone. What appears to be a decorative pattern is actually a snapshot of life beneath an Ordovician sea floor preserved for nearly half a billion years.
Tyndall Stone Components
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Feature
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Geological Origin
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Appearance
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Significance
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Limestone Matrix
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Calcium-rich marine mud
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Light grey to cream coloured
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Forms the majority of the stone
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Thalassinoides Burrows
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Ancient animal burrows
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Branching dark grey network
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Preserved trace fossils
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Dolomite
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Magnesium-altered limestone
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Darker grey colouring
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Created through dolomitization
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Marine Fossils
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Shells and skeletal remains
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Occasionally visible within stone
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Evidence of Ordovician marine life
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The striking appearance of Tyndall Stone is the result of biological activity, burial, groundwater movement, and mineral alteration working together over hundreds of millions of years. By studying these ancient burrows, geologists can learn about the behaviour of organisms that lived on the sea floor long before dinosaurs appeared on Earth.
AI Content Disclosure: Some of the descriptive text was created with assistance from AI tools. All information has been reviewed and verified by the cache owner for accuracy.
This cache was placed by a PROUD Platinum EarthCache Master.
