Tweefontein

The site

The site of Tweefontein is on a low ridge formed of Dwyka Group rock, situated in the middle of the Tankwa River floodplain. The river is currently dry, drained by a large man-made dam further to the east. Even if the Tankwa did not contain water at certain times in the past, the areas to the west and east collect rain run-off from the Cederberg and Roggeveld Mountains, especially in winter, offering more fertile land nearby.

During times of high-energy flow, cobble beds build up in the river channel
Source: Emily Hallinan
When the river has lower-energy, it deposits fertile alluvial sediments
Source: Emily Hallinan

Hunter-gatherers live by moving between places to make the most of different opportunities for food and water, especially as these fluctuate seasonally. The hill at Tweefontein would have been attractive to past people not only because of its proximity to water, but also because it gives good vantage for spotting animals on the surrounding floodplain. Stone tool-makers also needed a supply of stone. Tweefontein has easy access to large river cobbles right next to the site, as well as plenty of good quality rocks eroding from the Dwyka geology of the hill itself.

Tool-makers used hornfels cobbles carried by the Tankwa from further east
Source: Emily Hallinan
The Dwyka bedrock of the hill itself is made up of lots of knappable stone
Source: Emily Hallinan

Silcrete

In addition to these rocks that are local to the site, one of the interesting features of the tools at Tweefontein is the preference for silcrete, a type of rock from at least 10 km away. To a hunter-gatherer, this is not a huge distance and probably well within a normal daily range, but rocks are heavy and people tend not to carry them further than they have to. The transport of different types of stone away from their geological sources is important for helping archaeologists to understand how people moved around their landscapes.

Silcrete is a fine-grained sedimentary rock that forms in a hard duricrust near the soil surface, particularly in semi-arid regions with very seasonal rainfall. As groundwater evaporates in the dry season, silica grains that were held in solution harden and cement the sediments together to form a rock. This requires the presence of silica (quartz) grains, so silcrete forms on sandstone and quartzite bedrock like those of the Cape Supergroup.

An outcrop of silcrete on Cape geology
Source: Emily Hallinan
Silcrete is a fine-grained rock ideal for tool-making
Source: Emily Hallinan

We have found a number of different sources of silcrete in our surveys but they are restricted to Cape bedrock, giving us a minimum distance for their transport eastwards. In fact, our surveys have shown that MSA silcrete artefacts (including some that show Nubian technology) were carried at least 50 km into the Tankwa Karoo where they were lost or discarded. We think that people were transporting the rock to Tweefontein as a raw material rather than as finished artefacts because we found a lot of silcrete with cortex, the weathered outer rind of the rock, together with tiny pieces of knapping debris.

The weathered outer surface contrasts with the smooth inner rock on a silcrete raw material nodule
Source: Emily Hallinan
This point has been carefully knapped, leaving the red cortex on its upper surface. Was this an aesthetic choice?
Source: Emily Hallinan

Points

Another notable feature of Tweefontein was the number of pointed artefacts we found. Points that have been shaped on one face are called unifacial points and they are typical MSA artefacts. Specifically, they are the main tool type found during a period about 55-50,000 years ago known as the ‘post-Howiesons Poort’ (so-called because it follows the period known as the ‘Howiesons Poort’).

Numerous cave and rock shelter sites across southern Africa have layers that date to this time, including several sites in the Cederberg Mountains, close to the Tankwa Karoo. One of the difficulties of studying open-air surface sites like Tweefontein is that it is rarely possible to directly date the artefacts at the site since most scientific dating methods rely on artefacts being buried. However, a reasonable way of attributing an age to surface artefacts is to compare them to the typical tools and technologies that characterise different periods at dated, buried sites. Drawing comparisons with nearby sites based on typical unifacial points, distinctive newly-identified Nubian technology and the frequent use of silcrete, we suggest that Tweefontein dates to around 55-50,000 years ago.

Points similar to these from Tweefontein date to approximately 50,000 years ago at nearby cave sites
Source: Emily Hallinan

We have recorded over 150 points at the site, made in various different raw materials besides silcrete. It is unusual to find such large numbers of points (and point cores, discussed below) in one location, even if you take into account the very long period of time that they may have accumulated there for. One suggestion for why we have found so many at Tweefontein is that it was used by people as a workshop for making points that they then took with them elsewhere. Its situation in between the Cederberg and Roggeveld and the good supply of rocks make Tweefontein a strategic location for mobile hunter-gatherers.

What were people using the points for? Given the wide range of shapes and sizes at the site, they may have served different functions. Some might have been hafted for use as spears for hunting, but others may have been used as knives for butchery or other cutting tasks. New research as part of the TANKwA project will use cutting-edge digital methods to look at the variation in point shape and size to gain further insights into point technology at Tweefontein.

Points of different shapes and sizes made from chert and hornfels, with an illustration of how points might have been hafted
Figure by Emily Hallinan

Nubian technology

The most interesting aspect of Tweefontein is that many of these points were made using Nubian Levallois technology. While points were made using Levallois methods during the post-Howiesons Poort, the specific use of the Nubian method seems to be unique to the Tankwa Karoo and perhaps the wider Karoo area. So far, we have recorded 120 cores at Tweefontein and 11 in surveys of the surrounding area, confirming that this is not a ‘one-off’ phenomenon. We have published a preliminary report on the site and we are currently working on a full research article.

A Nubian core and broken point that fit back together, found a few metres apart
Figure by Emily Hallinan

One of our observations is that the cores made out of silcrete are much smaller than the cores made out of hornfels and other locally-available rock types. This tells us that because silcrete was harder to obtain, people were using as much of the material as they could. After making a point, they would repeatedly re-prepare their cores which made them gradually smaller until they were no longer any use. In contrast, hornfels was a much more expendable material so cores were larger when they were abandoned.

The smaller silcrete Nubian cores at the bottom were reworked more than the larger hornfels cores at the top
Figure by Emily Hallinan

Fantastic tools and where to find them…

Studying these artefacts both in detail at sites like Tweefontein and in our surveys of the wider landscape gives us a unique perspective on past hunter-gatherer lifeways. Stone tools and where we find them can help us to piece together how people moved themselves, tools and raw materials about a landscape. When we consider the present-day environment and set this within the context of past climatic change, we can begin to understand the different solutions that people found to adapt to seemingly challenging conditions.

Nubian technology is one of these technological solutions and the artefacts at Tweefontein give us the chance to study how it fits in at a local scale – within the Tankwa Karoo, at a regional scale – compared with similar time-periods in other parts of South Africa, and at a global scale – compared with similar arid environments separated in time and space. The TANKwA project will make these comparisons using new digital methods to begin to understand how and why people developed the strategies they did. These methods and our aims are outlined in the next section.

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