We think we found a fossil site – now what?

When we locate a potential site locality, we begin a process of exploration and evaluation to determine whether there is potential for further research at that locality. Our basic tools are a handheld GPS, a rock hammer, and a panga (or machete).

Field crew, 2nd trip: Andy with the GPS, Morris with the rock hammer, Kevin with the machete: Did the timer go off? is the camera working? did anyone hear a ‘click’?

The main objective of our project is to locate historic mining sites, and to evaluate whether they contain deposits and other features that are useful to us as palaeoanthropologists. We are looking for a variety of in situ (i.e., undisturbed) deposits including:

  • speleothem or cave formations, which can be sampled to obtain geological dates, and for stable isotopes which tell us about past climatic and environmental conditions;
  • cave infill sediments (derived from soil and other debris from both outside and inside the cave), which can tell us how the cave filled in, and also may contain evidence of the outside environment such as pollen;
  • fossil bone, including those of reptiles, birds, and rodents, as well as of larger animals including bovids, carnivores, primates, and of course, our own ancestors (hominids).

For some sites, the presence of such evidence can be quite obvious, especially if there are dense fossil deposits just waiting to be excavated. However, at other sites, it can take considerable effort to determine whether this evidence is present. Some sites are small and the deposits easily located, and others – especially when the mining activity was extensive – can be complex and more difficult to define.

One of the underlying objectives of this project is to consider what evidence at such sites can be used to answer questions of interest to palaeoanthropologists even in the absence of fossils. After all, when we find fossils (and especially those of hominids), we then use a battery of sampling techniques such as those above to obtain information about the temporal, environmental, and depositional context of that fossil. But since fossils are relatively rare in the geological record, we may be missing out on valuable information about past environmental conditions by passing over deposits in which hominid or other fossils are rare or even absent. This information could help us to refine our models about environmental and adaptive change during hominid evolution.

So, after that extensive preamble, what do we do when we think we have located a site? There are three basic tasks to complete: defining the limits and features of the site; mapping the locality; and evaluating the site’s potential for future research.

Defining the limits of the site involves exploration of the site’s geographical and geological features. We walk up and down hills, climb rock outcrops, and (carefully!) climb into mine shafts and trenches, looking for speleothem deposits, breccia and cave infill sediments, and fossils.

A miner’s trench exposing a lot of geological formation: Can anyone see any breccia up there?

One of the challenges in this work is being able to see the ground clearly in order to find features, breccias blocks, and of course, fossils. This is where the panga comes in handy!

Like most arid regions, many of the plants here have thorns. This site is overgrown with acacia trees and brambles. Keep repeating to self: ‘This is better than being stuck behind my desk at the universiity!’ (There is actually a nice cave infill deposit in this view… just to the right of the machete!)

The miner’s dumps are a great source of information about the deposits on the site. We comb the hills of rock, searching for fossils and other evidence of the nature of the underground deposits. Depending on what we find, we then have to search the mine trenches and chambers to determine where the blocks in the dump came from.

Fossils can be difficult to ID in the field. Observe the fossil braincase (below the knife to the right), and a vertebra (to the right on the edge of the block) of un-named mammals in this breccia block.

Finally, all of the features of the site are mapped using the handheld GPS, which locates each data point taken to within approximately 5 meters. For our initial fieldwork survey, this is good enough, but if we were to return for sampling or excavation we would use total station survey equipment and map the site with more accuracy.

Andy enters data points on the Trimble GPS at a small locality near Gondolin, North West Province.

The initial survey and exploration of a new locality can take several days, and also includes extensive photographic and written documentation; we also record information about the site on databases on the handheld GPS and a table PC. The final task is to sit in the shade and discuss what we have observed on site, and evaluate the potential for further work in the form of sampling or excavation.

Once we have completed this process of site survey and evaluation, we go back to the maps, head out to a new area, and begin the process again. All in a day’s work!

– KL Kuykendall

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Malmani Dolomites

To a large degree, our project is a field survey of the geological formation known as the Malmani Dolomite Subgroup, of the Chuniespoort Group of the Transvaal Supergroup. The Transvaal Supergroup is an extensive geological sedimentary rock sequence extending across much of the northern part of South Africa and into Botswana (Ericksson & Altermann, 1998). The Malmani Dolomites are just one rock formation in this sequence, and they are of interest to us because it is in the dolomites that we find the historic lime mines, and thus palaeocave fossil deposits. On the map below, the Transvaal Supergroup, including the Malmani dolomites, is indicated by the light blue-shaded areas in the north & central regions of South Africa. Geological dates for these rocks indicate that they were formed between 2.6-2.5 billion years ago, making them one of the oldest dolomite formations known.

Simplified Geology of South Africa: The Malmani Dolomites in blue in the north and central parts of the country – unfortunately, NOT at the coast!

Dolomite is a type of limestone rock that forms in warm, shallow seas from the slow accumulation of the remains of marine microorganisms and fine-grained sediment. It differs from other limestone rocks in having a higher magnesium content, and these dolomites are also characterised by fossils of algae formations that are known as stromatolites (see picture below). These materials contain high levels of calcium carbonate, and thus such rock formations are often referred to as carbonates.

Photo of stromatolite fossils (the clusters of concentric structures) in the roof of Sudwala Cave, Mpumalanga. These represent ancient algae formations in the sea at the time that the dolomite rock sediments were accumulating, roughly 2.6 billion years ago. 

One important quality of dolomite is that, over long periods of time, this rock is water soluble – ground water is a weak acid that will erode away the calcium carbonate matrix as it percolates through cracks and fissures within dolomite rock layers. This process eventually results in the occurrence of underground solution cavities, and when these break through to the surface due to erosion or collapse they form caves and sinkholes (see schematic below). Further percolation of groundwater through these solution cavities results in the precipitation of calcium carbonate to form various kinds of speleothem – the beautiful cave formations known as stalactites, stalagmites, and other structures. In addition, once the cave or sinkhole is open to the surface, it will begin to fill in with sediment, and if occupied by carnivores the infill will include animal bone. In South Africa, the ancient caves of this kind were open to the surface, and filling in with sediment and bone, between roughly 3-1 million years ago.

Idealised model of cave formation in dolomites (Martini, et al. 2003). The brick-like symbol indicates dolomite, and the differently-stippled symbols represent separate infill deposits over time.

Thus, over a period of millions of years solution cavities will form in the dolomites, break through to the surface as caves and sinkholes, and then fill in again with sediment and bone. The constant percolation of groundwater through the deposits will cement everything together in a calcium-carbonate matrix, and fossilise the bones. Finally, lime miners in the early 20th century blasted and excavated into the dolomite formations to retrieve the extensive cave formations (calcium carbonate, or ‘lime’), and in so doing often exposed the infill deposits containing fossilised bone. This attracted the attention of palaeoanthropologists who were interested in the fossil record of human ancestors and other mammals.

And that is why we are in South Africa surveying the Malmani Dolomite formation, looking for ancient cave deposits!

– KL Kuykendall

Boesmansgat, Mt. Carmel Farm, south of Kuruman: 12 June 2012

As we saw in the Gondolin region, a sinkhole is formed when the roof collapses on an underground solution cavity (or cave) in the dolomites. Sometimes these are very large, and may extend deep enough to fill with water, as at Boesmansgat south of Kuruman. This sinkhole does not hold any known fossil deposits, but it is an  excellent (and impressive!) example of the geographic and geologic features of the palaeocaves for which we are searching. It is thought that the water filling Boesmansgat is connected underground to another large water-filled sinkhole about 60km to the north – the Kuruman Eye – which supplies all the water for the local population.

View from the surface of Boesmansgat (roughly translates to “Bushman’s cave”)

Stagnant water fills the underground chambers of Boesmansgat

At least one diver has died trying to reach the bottom of the Boesmansgat sinkhole, which is 274 meters below the surface (some 337 meters when corrected for altitude) leading to the claim that this is the deepest and largest natural sinkhole in the world.

Our interest in Boesmansgat was to learn more about the occurrence of sinkholes on the farms in the area. With local farmers as our guides, we were able to visit several smaller sinkoles to inspect them for fossil deposits and ancient cave formations. We did find some small speleothem (calcite cave formations) occurrences, and one sinkhole led to a large underground chamber.

Surface of the sinkhole

Kristi photographs the sinkhole

Without proper equipment and safety gear, we could not fully explore the underground caverns on this trip, but in the main chamber at a depth of 10-15m we did find some rock breccia, speleothem formations, and recent micro-mammal bone — as well as one deceased tortoise that fell in to this ”animal deathtrap” and was lodged between the rocks! We could not see how deep the chambers extend underground, but there are at least two deeper tunnels that we will explore when we return on a later trip.

We have now learned that several more farms in this region also have sinkholes, so we will pursue those contacts and plan to return for a more extensive survey – in addition to lime mines, we are now also looking for sinkholes!

-KL Kuykendall

Wonderwerk Cave: 10 June 2012

Wonderwerk Cave is located in the Northern Cape province of South Africa, near Kuruman in the Kalahari Desert. The cave is a National Heritage Site and is open to the public for tours. Wonderwerk Cave has been studied extensively by archaeologists since the 1940s and has yielded quite a bit of material including Early, Middle, and Late Stone Age tools, decorative objects like beads, cave art, and possible evidence of the earliest controlled use of fire. The history of hominin use of the cave spans ~1 million years, with the cave art being relatively recent (~1000-10,000 years) and evidence of use of fire ~1 Ma.

The cave art depicts elephants, giraffes, ostriches, secretary birds, and various bovids. There is even a ‘chongololo’ (millipede)!

The cave has a long, low ceiling and extends back into the hill about 140 meters.

Excavations are still ongoing, and the majority of the cave is marked by an excavation grid:

View of the Kalahari from the hill above the cave:

-KL Lewton

Sinkholes: 7 June 2012

We’ve surveyed several caves in the hills near Gondolin. Most of these caves are visible from the surface as sinkholes, which are created when the roof of an underground chamber collapses. The walls of sinkholes can contain any number of geological formations including speleothem (flowstone and dripstone), breccia, sedimentary infill, and the rocks that comprise the regional geology, which in this area are dolomites.

Because caves are formed by erosional processes of underground water movement, vegetation is usually abundant at cave openings. Sometimes it’s so heavily vegetative that it’s difficult to see the sinkhole:

Andy and Kristi collect data at edge of sinkhole

But if you crawl in a bit (mandatory disclaimer: don’t do this at home) you can see the opening and the surrounding rock:

We also found a breccia dump outside this cave. Breccia is a conglomerate rock consisting of cave infill that forms when material–bones, rocks, and vegetation–falls into the cave. In South African fossil sites, the presence of fossils (hominin and other) in breccias is normally attributed to the action of carnivores (eg, leopards) that drag carcasses into trees to devour them without scavengers hanging around. Alternately, some animals might just fall into the sinkhole and subsequently die. The presence of this breccia dump outside the cave indicates that it was a historical lime mine. In the breccia we did find several small fossils, including this beaut:

My thumb for scale.

All in all, a successful day!

-KL Lewton

Project introduction

Since the 1920s, palaeoanthropological fieldwork in South Africa has focused on a handful of fossil-bearing cave sites mostly located in what is now known as the Cradle of Humankind. Our objective is to survey and inventory over 200 other historic mines located in the Malmani Dolomite system throughout the northern region of South Africa. We are using GPS and GIS systems to record the location of these sites and the presence or absence of fossiliferous sediments and other palaeontologically interesting features. Our ultimate goal is to discover new hominin fossil sites to further our understanding of Plio-Pleistocene human evolution.

Our first site visit of this field season was to Gondolin, a 1.7-1.8 Ma palaeocave located in the Northwest Province of South Africa that has previously yielded Paranthropus teeth and various fossilized fauna, including bovids (antelope), equids (horses), and one lagomorph (rabbit) (Adams et al., 2007). The good news is that our field test of our GPS equipment was successful! Part of the site documentation process includes photographic recordings of the site and its features. Here is a photo that demonstrates just how dense the fossils in bone breccias can be:

For more information about our field crew and project partners, please click on the “About” tab.

References
Adams JW, Herries AIR, Kuykendall KL, Conroy GC. 2007. Taphonomy of a South African cave: geological and hydrological influences on the GD 1 fossil assemblage at Gondolin, a Plio-Pleistocene paleocave system in the Northwest Province, South Africa. Quaternary Science Reviews 26:2526-2543.