An unconformity is formed by geological processes and is when two connected rock masses vary in colour and texture. In some cases they can be a completely different stone altogether. The age between the rock masses can sometimes vary by hundreds of millions of years. This indicates that the deposition of the sediments may not have been continuous.
To be put in simple terms; an unconformity is a boundary between rocks which can be caused by one or more natural processes. This means there's a gap in the geological records.
The most common processes leading to unconformities are:
- Crustal deformation (caused by tectonic movements)
- Erosion
- Sea level variations
Multiple types of unconformities exist, including:
- Disconformity. An unconformity between parallel layers of sedimentary rocks, where layers above and below the boundary have the same orientation and is caused by erosion.
- Nonconformity. This exists between sedimentary rocks and metamorphic or igneous rocks when the sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock.
- Angular unconformity. Is an unconformity in which horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, resulting in angular discordance with the horizontal layers above.
- Paraconformity. Is a type of unconformity in which strata are parallel; no apparent erosion occurs and the surface of the unconformity resembles a simple bedding plane.
(https://www.eoas.ubc.ca/courses/eosc326/resources/Stratigraphy/unconformities-v2.htm)
Waterfall Creek is located within the Hallett Cove Conservation Park and is home to a prime example of an unconformity. The layers of rock were deposited between 3 and 600 million years ago.
This makes the area very popular among geologists as the age of the stone means it is significant to what the Earth was like millions of years ago.
Using the above information and by observing the place in question, answer the questions below to complete the EarthCache.
Logging Requirements:
Walk along boardwalk and face the given coordinates (you should be facing south) and answer the following questions:
- How many layers of unconformities can you see? What colours are these layers?
2. What type of unconformity do you think has occurred here? What led you to this conclusion?
(Disconformity, Nonconformity, Angular unconformity or Paraconformity)
3. What process do you think led to this unconformity? What led you to this conclusion?
(Crustal deformation, erosion or sea level variations)
4. Take a photo of you, your stamp or your personal item with the unconformities in the background.
Please send messages via Geocaching message centre or to my email, answers posted in the logs will be deleted.
You can log the find immediately, if answers are supplied to CO within 14 days.
Happy caching!
I have reached the GSA's highest level:
