ago, I got my hands on a leaflet all about the geology of
the Durban area and how our coast was formed.
came to the conclusion that my brain just didn't have the
capacity to absorb what I was reading. My informant Wade Kidwell,
in UKZN's Marine Geoscience Unit, arranged for me to chat
to his colleague Hayley Cawthra, who laid things out for me
in words of one syllable and gave me an invaluable article
by John McCarthy to read.
that, around 200 million years ago, there was a big continent
called Gondwana which was subject to terrific forces that
ripped the it apart. The various pieces of it became the southern
continents, including Antarctica, Australia, South America,
Africa, Madagascar and India, which drifted off in their own
fascinating discovery, for me, was that the Falkland Islands
started out in life adjacent to what became the coast of KZN.
They were really one piece of land, with the Falklands plateau
shearing away and moving off into the distance along the Agulhas/Falkland
Fracture Zone. It is actually still moving away from us at
a pretty nippy 6cm a year, thus steadily widening the Atlantic
newly formed Indian Ocean now along the KZN coast, the next
major event from 120-60 million years ago, was the Cretaceous
marine transgression, when the sea level rose to as much as
400m above present levels. The sediment deposited by the sea
during that period eventually turned to rock and, although
much of it has been eroded on the surface, layers of it still
underlie parts of Durban, including the city centre, Bluff
and the beachfront.
sea levels of the Cretaceous gave way to the Tertiary Marine
Regression when the sea level slowly began to fall due mainly
to to cooling of the oceanic crust. Since the last million
years or so sea levels have been up and down at least 5 times
due to the Pleistocene ice ages.
the height of an Ice age thick ice capes develop at the poles
lowering sea levels. During the most recent Ice Age about
18 000 years ago, sea levels reached about 120m below current
levels, meaning that Durban, if it had been around, would
have been about 15km inland.
this time, the features we know today as the Bluff and Berea,
were formed from sand dunes which became dune, or aeolianite
rock, through a process of lithification. This happened when
rainwater percolated through the sand, dissolving calcium
carbonate shell fragments which then dried into a type of
cement and stuck the sand particles together. The red sand,
found all over Durban, also known as Berea-type sand, is the
result of the weathering and oxidation of dune rock.
is pretty solidly grounded on a geological basement consisting
of layers of rock which are known as the Karoo Supergroup.
These rocks formed on the continent of Gondwana before it
Durban one can find the Ecca Group, which consists of dark
grey shales formed in an inland sea about 350 million years
ago. Underlying the Ecca shales are tillite of the the Dwyka
Group, which formed from rock material deposited by glaciers
300 million years ago. The tillite forms the huge cliffs on
either side of the Umgeni River and is quarried around Durban
Supergroup is cut by a number of faults. These include the
Springfield fault, which runs slap-bang across Jan Smuts Avenue
at 45th Cutting. It was apparently active during the breakup
of Gondwana but the good news is that it, and the other faults
in our area, are inactive. The area has been geologically
stable for 30 million years, and thank goodness for that.