Cenozoic
unsettled sea levels
During the Cenozoic sea-level began to fall from the high levels experienced during the Cretaceous. A series of large coast-parallel dune complexes developed along most of the KwaZulu-Natal coastline. In Durban these now form the Berea and Bluff Ridges. In most areas deep weathering of old dunes has produced a dark red coloured sand called the Berea Red Sand.
| Berea red sand | Berea red sand 4x magnified |
In more recent times, fluctuations in sea-level have continued to shape the KwaZulu-Natal coastline. Recent coastal dunes contain economic concentrations of minerals such as ilmenite, rutile and zircon, which are mined near Richards Bay. Mineralogical studies indicate that the origin of the ilmenite is from the Jurassic Drakensberg Volcanics and from post-Karoo dolerites further inland. Rutile and zircon originated from the older basement granites and gneisses of the eastern Kaapvaal craton.
The ilmenite and rutile are smelted to produce titanium metal and white pigments (mostly for paint). The zircon is used for glazing on tiles and pottery, and as a metal alloy.
Titanium and zirconium rich minerals are significantly denser than common sedimentary minerals. As a result they became locally concentrated through their movement by wind and water through gravitational separation. This explains the dark areas on the beach.
(Source: Fockema P D, 1986 – The heavy mineral deposits north of Richards Bay)
During the last glacial period, approximately 18 000 years ago, the Earth was much colder and sea level was more than 100 metres below present. The coastline at that time would have been far out to sea and many of the larger rivers cut deep valleys along the coast. As the Earth warmed and sea-level rose, these valleys were infilled with unconsolidated estuarine muds and shelly sands. It is for this reason that many bridges along the coast require deep foundations to reach solid bedrock.
Beach Sand (coastal sediments)
Coastal processes
Beach sands represent the weathered and eroded remnants of rocks found inland. KwaZulu-Natal beach sand is characteristically brownish in colour, consisting mainly of more resistant minerals such as quartz and feldspar. Of major economic importance, the sands also contain abundant quantities of the minerals ilmenite, rutile and zircon which are mined near Richards Bay for titanium and zirconium.