Terrace Sands Fyshwick
This EarthCache will require a bit of field work to be able to put together a drawing, or stratigraphy diagram, to describe the exposed rocks at GZ. Plenty of parking just off the road however note will probably need to be on the on-ramp going northwards onto the Monaro Highway. As cachers do, I’m sure you may find other places to park and access the EarthCache site.
You will need a writing implement and some paper to complete the field work associated with this EarthCache.
Background to stratigraphy
Stratigraphy is the study of rock layers and their relative ages. In geology, the Law of Superposition suggests that rocks in the deepest layers are older than the rocks near the surface. Therefore rock layers can be thought of as pages in a history book that was written backwards with the most current events in the front and the most ancient history in the back. However, various geologic forces can disrupt rock sequence chronology.
When erosion removes layers near the surface, and later in time more layers are deposited over the exposed rock, an entire time period ends up missing from the sequence. These "missing pages" are called unconformities.
Tectonic forces like folding and faulting create especially confusing rock stratigraphy. Faults mix up rock sequences. Imagine taking a book, cutting it in half and gluing the right half on top of the left half. Now as you read down through the book you eventually encounter pages in the wrong order (first the right half and then much later the corresponding left half).
Folding occurs when rock layers are bent upwards and downwards like waves. When enough force squishes the folds, they can flop over on to each other in the same manner waves do as they approach a beach. When this happens entire portions of a rock sequence can be turned upside down. It's like cutting out the middle of your history book, flipping the cut section over and then gluing it back.
The site
This site is located at a road cutting on the western side of the feeder road across the Dairy Flats Road from Fyshwick to the airport. The cutting provides a good exposure of the regolith, the most recent rocks (albeit poorly consolidated) to be formed in the Canberra region from high- energy river flooding, fluvial processes and erosion. Age dates are uncertain but probably no older than 2-3 Ma.
The EarthCache
In order to log this EarthCache, you'll need to start at the given co-ordinates and walk approximately 50m northwards. Along the way observe and draw what you see into a diagram. You should see some differing layers of rock- for each layer note the colour and describe the type of rock. No need to go an examine the rock closely as we don’t want any damage.
Email the number of different layers you see, and their colour and composition. It is also preferable you email your drawing to me at sbthompson_1999@yahoo.com.
Feel free to log your find in anticipation- I'll let you know if there are any issues. Logs without the emailed answers may be deleted.
References:
http://www.nps.gov/brca/forteachers/paleoact5.htm
A Geological Guide to Canberra Region and Namadgi National Park Geological Society of Australia (ACT Division)
