Ardrossan Cliffs EarthCache

The foreshore at Ardrossan is dominated by cliffs that rise up to 15m above the beach.  A variety of Pleistocene sediments are exposed on the cliffs.  Undercutting by wave action regularly causes large blocks to slump and tumble onto the beach.  The cliffs extend for several kilometres north and south of the town and are most easily accessable from the jetty carpark.

• The oldest and lowest unit forms the base of the cliff.  The 2 to 4m high unit is predominately sandy clays consisting of sand sized quartz set in a pale green matrix.  Some gravel beds are evident in this layer.
• The next layer or unit consists of coarse gravel containing clasts or fragments of rock, including granite, gneiss, limestone and ironstone.  The unit is up to 10m thick.  The layer is evidence of erosion and sedimentary deposition of rocks from a variety of sources.  Amongst the clasts is many Cambrian fossils, including  archaeocyathids, trilobites, molluscs and bryozoa.
• Overlaying the major unit is 1 to 2m of red alunite clay.
• At the top of the cliff is a layer or sand calcrete or limestone less than 1m thick.

1. Describe the interface between the lowest two lithological units.  Do you see a notch?
2. The cliff are red coloured but only one layer is a red clay.  Why are the cliffs red?

Acknowledgement:  Geological monuments of South Australia