An uncomfortable contact between two series of Precambrian rocks occurs at this reserve on the side of Old Mt Barker Rd Aldgate.
Ancient crystalline metamorphic rocks belonging to the "Archean" basement of the Adelaide region crop out along a small embankment on the west side Old Mt Barker Rd at GZ. At a higher level remnants of Algate sandstone are exposed. Thus at this earthcache location there is contact between ancient "Archean" rocks and the oldest and lowest member of the local Mt Lofty system from the Proterozoic eon.
"Archean" rock is grey coloured, medium grained, crystalline stone consisting of 80% feldspar and 20% diopsie and uralite. The rock contains stringers of dark iron manganese minerals. "Archean" rock is between 4,000 and 2,500 million years old.
Aldgate sandstone is estimated to be around 750 million years old is a similar coloured grey stone, which contains predominately fine quartz grains
Examine the stones at the listed coordinates. These are pieces of "Archean" rock. Compare this material with the stone at the secondary waypoint.
Please email your answers to the following questions.
Q1. What differences can you seen between the two types of rock, grain size, colour, texture?
Q2. The earthcache location is quarry. Why was the Aldgate stone used and the "Archean" rock not used?
Q3. Why are there no fossils in either of these rock types?
Any "Found it" logs for which answers have not been received will see that log discreetly deleted.