Sterkfontein Caves - Part 6 Final

The caves form part of the Isaack Stegmann Nature Reserve and are owned by the University of the Witwatersrand.
They are open to the public from February to December each year, six days a week. Tours are conducted every half-hour.

Next to the caves is the Robert Broom site museum, housing exhibits of immensely ancient animal and bird life.

Bones and breccia in caves
Solution and roof collapses create entrances to the caves in the form of vertical shafts. Soil, rocks, bones and vegetation fell in from the surface – the animals and plants from which fossils formed did not actually live in the cave.

The bones which found their way into these shafts were often just fragments left by the activities of predators and scavengers around the shaft entrances. But sometimes – far less often – a whole animal would fall down a cavity to be fossilized in the infill. The famous australopithecine skeleton “Little Foot”, which was found deep inside a Sterkfontein grotto, is an example of this.

Over time, the material that fell into the shafts built up to form talus cones, which look like giant inverted ice-cream cones, on the cave floor. These formations were cemented by lime-charged water to form concrete-like breccia a type of rock. Bones within these talus cones were mineralized by calcium carbonate and stained with manganese and iron from the dolomite soil.

Sometimes floor collapses into lower caves or erosion by surface water disrupted the stratified layers, mixing deposits. This means that even if some deposits are deeper than others, they are not necessarily older than those nearer the surface.

The bulk of the Sterkfontein cave deposits were not disrupted in this way. The University of the Witwatersrand geologist Professor Tim Partridge classified the deposits from oldest to youngest as geological Members 1-6 from the Sterkfontein formation. The infills span a period from 4.2 million years ago to less than 200,000 years ago. The different infills have characteristic fossil and/or artifact (stone tool) content.

Sterkfontein Caves - Part 5

Many beautiful structures – including stalagmites and stalactites – form inside caves as carbonic acid carrying limestone, drips through cave roofs onto their floors. Structures inside a cave may take millions of years to develop.

Some of the geological structures which may develop inside a cave include:

Speleothem
“Speleothem: is a general geological term for a calcium carbonate deposit in a cave, including formations such as stalactites, stalagmites and flowstones.

Flowstones
Flowstones are speleothems on the walls and floors of a cave formed from a gradual flow of water over a relatively broad area.

Stalactite
The term stalactite comes from the Greek word stalaktos, which means “dripping” because these other-worldly formations “drip” from the roofs of limestone caves. Essentially, water reacts to carbon dioxcide to form carbonic acid. It then seeps slowly through the roof of the cave, depositing calcium carbonate which hardens and build up over time to form a stalactite.

Stalagmite
Stalagmites are corresponding formations on the floor of the cave to stalactites. Stalagmites rise from the floor in a build up of calcium carbonate over time, from mineral-bearing water dripping from the roof of the cave. The term stalagmite comes from the Greek word stalagma, to “drop”.

Column
Sometimes stalactites and stalagmites meet, forming a pillar or column of rock-hard calcium carbonate.

Helictite

A formation of calcium carbonate in a cave that grows in a twisted, curled fashion, like a helix (hence the name), seemly defying the laws of gravity.