Clay-rich Permian glacigene sediments underlying limestone cliffs, are responsible for rotational slumping.
Coastal cliffs north of Port Vincent show a stepped form. The shape of the cliffs is a result of differential seaward slip of blocks of Tertiary limestone sediments along a nonconformity with underlying Permian clays. Four separate steps can be recognised in the area. Each of the steps is defined by bench composed of the hard calcrete cap. A visit to the beach will reveal a layer of grey green gritty silts and clays, evidence of the slippery glaciofluvial sediments.
At the location the cliff consists of three distinct layers.
- Hard calcrete limestone
- Partially rotated Tertiary marl
- Permian glaciegien clay sediments.
Earthcache Tasks
- Find two of the calcrete benches. Estimate the change in height. How did you do this?
- Find a sample of the underlying clay. Describe the material. Does it feel slippery?
Acknowledgement: Geological monuments of South Australia