WATERBERG GEOLOGY
The Secret to What Makes the Waterberg so Unique!
by Richard Wadley
Despite enjoying relatively good rainfall, much of the Waterberg plateau is marginal farming land, because of the poor nutrient quality of its soils. These in turn are derived from the rocks that make up the very old and complex geology of the region.
Around the foot of the plateau, from the west to the north-east, are groups of rocks (2.1-2.0 billion years old), which host the iron ore deposits around Thabazimbi, the platinum fields to the north of Mokopane and the tin and fluorite deposits along the southern base of the Sandriviersberge. Some of these rock types do produce quite fertile soils suitable for crop farming. By far the majority of the Waterberg, however, is formed from a very thick sequence of layered sedimentary rocks: sandstones, conglomerates and siltstones, deposited into shallow lakes or seas by long-lived river systems flowing from highlands far away to the north-east.
This process ended about 1.6 billion years ago. The erosion of these sandy rocks produced acidic, nutrient-poor soils, which support the biome we know as sourveld, unable to support large herds of domestic livestock or the sustained cultivation of subsistence crops.
It seems that for a very long time after the last of these Waterberg sands were laid down, this part of the African continent was stable and subject only to erosion, for the next rocks to be found today – those of the Karoo Group – are less than 350 million years old. Karoo lavas underlie the Springbok Flats to the south of Bela-Bela (where they weather to form black, clay-rich soils), and Karoo shales are found in the vicinity of Lephalale, where they host the huge coalfields being mined there.
If the acidic soils which make up the Waterberg plateau are too poor in quality to sustain subsistence agriculture, why is it that the region appears to be so well vegetated and even forested? The answer is that the plant species growing in the Waterberg are those which can tolerate the acidic soils.
When conditions for plant development and growth are unfavourable, nature responds unexpectedly by increasing the number (diversity) of species that attempt to survive in such an environment.
The result is that the Waterberg supports very wide biodiversity, possibly second only to the famous plant kingdom of the Western Cape (which also occurs on very poor, acidic soils derived from sandstones).
To find out more about Waterberg geology, and how its unique biodiversity formed and shaped its past, and will continue to do so in the future, have a look at Richard’s book “Waterberg Echoes”. The book is a fascinating study on the geology, history, archaeology, ecology and communities who make the Waterberg what it is.
