Lime mines and fossil sites in South Africa

One of the well-known features of Plio-Pleistocene early hominid sites in South Africa is that they are all associated with historic lime mines – think of Taung, Sterkfontein, Makapansgat, and others. As mentioned in earlier posts, this association is one of the critical factors that we used to develop our method and implement this field project, and thus has great practical value to us in the field – find the old lime mines, and we might also find some nice fossils!

However, there is also a very interesting historical component to this association. Mining, primarily of gold and other precious metals, was a principal factor supporting the economic development of the early South African state in the late 19th Century. The lure of vast riches associated with mining attracted migrants from many parts of the Western world. Lime mining was important for many industrial uses, literally providing the mortar and cement for building new towns and factories, and it was also an important component in the extraction process for gold and other economically important metals.

Cemetery at Pilgrim’s Rest, Mpumulanga. The gravestone on the left (pointed pillar) is for a chap from East Dulwich, London.

Speaking of gold, there were several early ‘gold rush’ events in South Africa, including Pilgrim’s Rest (1873), Ottoshoop (1879), Barberton (1881), Kaapsche Hoop (1882), and finally the Reef goldfields on the Witwatersrand (1886) which led to the establishment of the city of Johannesburg – and to conflicts that contributed to the start of the second Anglo-Boer War (1899-1902). We have covered some of these geographic regions in our survey activities, and read a great deal of information about their history in our archive work.

Photo of a gold rig in the Ottoshoop area, from ‘Developments on the Malmani Goldfields’, The Mining and Industrial Magazine, Nov 8 1933.

The people we have met in all of these areas are very knowledgeable about their local history, and of the historical importance of these events, and we have also located additional documentation about mining history through our archive work at the Wits University Historical Papers Library, Council for Geosciences, and other sources.

One example is the lime kilns near Ngodwana in Mupumulanga Province. We located them through a reference in a geological textbook1, and later determined that there was an old lime mine nearby. Our local contacts informed us that the kiln site (see photos) had been an important distribution centre for lime extracted from many mines in the area prior to 1899, and after processing the lime was shipped out to other areas by railroad. With this information, we were able to locate six additional lime mines within a few kilometers of the kiln site, and there are likely to be even more! (While we did not find fossil deposits at any of these mines, we did find in situ clastic cave sediments, or ‘rock breccia’, and some very thick remnant speleothem deposits. Definitely worth some future sampling!).

The Ngodwana lime kilns, closed down around 1899, but used later as a citrus packing plant when lime mining was no longer lucrative in the region.

As it turns out, the geological formations in which the metallic ores occur – including gold, iron, and other mined resources – are closely related geographically to the dolomite formations of the Transvaal Supergroup. Thus, in the areas of our survey we have walked across other rock units in the Transvaal Supergroup such as quartzites and Banded Iron Formations (BIFS) [see previous posts], and encountered mines for resources such as gold, iron, and asbestos. In fact, some alluvial sources (i.e., those that have eroded out from original geological context and were redeposited elsewhere) actually occur in younger sedimentary context in dolomite regions. In both a geological sense, and historically, our observations in the field have led to a strong connection between the mines and our quest to locate new fossil localities in the dolomite formations. In learning more about mining history and practice in our study areas (focusing on lime mines, but requiring some understanding of more general issues), we believe that we will be able to refine our field methods to identify additional areas that hold strong potential to locate fossil sites. This is not a simple task, however, and will continue to be a focus of the research programme in the long term.

-KL Kuykendall

 

On field survey methods using handheld GPS

The previous post dealt with the various software packages we use for desktop mapping, ArcView, ArcCatalog etc. In this post we will look at the software we use to complete mapping tasks in the field.

ArcPad is a mobile version of ArcView and can perform many of the same functions as its desktop counterpart, but is designed for handheld devices used in the field. The main benefit in using ArcPad is the ability to combine map data with a GPS receiver on the mobile device. The GPS receiver, through various conversions, communicates with ArcPad to plot the location of the Trimble (and thus the person holding it) on the screen, relating it to the relevant map data.

After a few minutes to allow the GPS receiver to pick up a sufficient number of satellites, a crosshair appears on the screen indicating our location. As we work, the receiver will track our movements in real time and ArcPad will update our geographic position on the screen map, including point locations and shape files we have added. Thus, we can use the combination of the GPS position and the locations of the historic lime mines (stored in the handheld’s memory in Vector format) to guide us to the location of a specific mine, within an error range of a kilometre or so.


Image of ArcPad using GPS to plot a current position (crosshairs) on the Trimble Handheld. The points represent either historic mines or sites added to our database, depending on what colour they are.

Not only can we use existing files in the field, ArcPad also allows us to edit blank shapefiles and add data for new locations in the field, along with text-based attributes to describe relevant features of each location. This is another great advantage to mobile GIS. As explained in the previous post we use ArcCatalog to create blank shapefiles. Once these are loaded onto the handheld and opened in ArcPad we can use the GPS receiver to record our location and store it within the shapefile. This is how we add new locations to our database and record a more accurate location for any historic lime mines we find.

A major downside to using handheld platforms is that they do not have particularly quick processors. As such, using large raster data sets, like topographical maps, is tricky. It is possible to convert raster data to a size that ArcPad can handle, but this has limitations on the amount of data it can convert. Consequently only a very small section of a topographical map can be converted for use on the handheld. For survey work over large regions, this is not really useful.

Given the large scale of the project it has not been feasible, or deemed necessary, to perform this conversion over and over again for each of the regions we have visited. Rather we have mainly focused on using the digitised vector data to represent point locations and geological units extracted from the mining and geological maps for use on the handheld. This takes quite a bit of time to prepare but has provided invaluable information to us in the field. Once we have finished surveying for the day we download the shapefiles with the new location data on them onto our tablet PC and add them as new layers to ArcView. We can now view the points along with the topographical map, enabling us to view the new information in a wider context.

To summarise, ArcPad allows us to:

  • Know our exact location through the GPS receiver
  • View pre-existing Vector shapefiles like our historic mine location database and geological formations
  • Add new data blank Vector shapefiles with points or polygons captured using the GPS receiver
  • Upload the new information to our tablet PC viewing it in a wider context and with other relevant data like topographic maps

Without ArcPad and the GPS function of our handhelds relocating historic lime mines and plotting the accurate location of new sites for our database would be incredibly difficult. Using ArcPad and ArcGIS for mapping also has the added advantage of being able to connect directly to our project database in Microsoft Access and update our field data on daily basis. The next post on our survey procedures will deal with the database software and how we use both desktop and handheld-based software to record the sites we visit, and how all the components work together.

- A Reid

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

A little note on desktop mapping software

Previous posts have referred to some of the software we have been using on the project. So, we will explain a little bit about this software in a series of blogs dealing with the packages we use for different aspects of the project. The first of these is on ArcGIS and other PC based software we use for mapping.

ArcGIS is the main software package we use on the project, and particularly the ArcView and ArcCatalog components; we also make use of Quantum GIS (QGIS), GNU Manipulation Program (GIMP) and Google Earth.

An example of a project in ArcView showing  different sets of data (polygons of geological units) may be layered in their correct geographical position and displayed together.

As the project uses GIS to arrange and orient various kinds of data geographically, ArcView is the component we use the most. ArcView allows us to display different layers representing different types of data. It is crucial in planning and implementing the survey as it gives us access to all the relevant data for an area of interest and will allow us to analyse those data when the project has finished. These data (layers) consist of mine locations, geological formations, topographical maps etc.

In addition to ArcView, we have been using ArcCatalog to create blank shapefiles (A shapefile is a file format created by Environmental Systems Research Institute (ESRI) to store location data in vector format, i.e. polygons, polylines and points, along with attribute information). Point files are single locations and consist of X and Y, and sometimes Z, co-ordinates, along with space for any additional data we may want to record such as an observation or a type of feature. Polygon files consist of points and lines joining them together along with the information defining how they relate to each other. They are frequently used to record large features and because they are complete shapes, whether regular or irregular, once they have been drawn we can calculate the area they cover. This is particularly helpful when trying to determine the size of a site or a feature. We can also add relevant information to the polygon files in the same way that we can with point files.

We can also use ArcGIS to create a link between our maps and our database of sites. These sites can then be displayed in their geographical location with all the information we have recorded about them. This will be covered in more detail in a later blog post.

For map preparation, mainly cutting out relevant map features (e.g., the area of a geological formation) and changing the file format, we have been using the GNU Image Manipulation Program (GIMP) on a MacBook Pro, because the use of a mouse and a larger screen is much more effective than the pen and touch input on the tablet PC.

We have been using QGIS (a free, and highly recommended, GIS package) predominantly for converting file types. As it is an open source programme it offers a larger number of possible file extensions for conversion without the need for expensive extensions. This has proved especially beneficial with the final programme we use, Google Earth.

We have used Google Earth in a variety of ways. The shapefiles produced in ArcGIS for the geological formations and the mining locations have been converted to the .kml format that can be opened in Google Earth. This is extremely helpful when communicating with colleagues and other interested individuals who do not have access to a GIS package. Secondly it has assisted in pre-planning the areas to visit through zooming in close to the earth’s surface and establishing whether features of the lime mines we have plotted, and other relevant geography, can be visualised. It may also provide an excellent platform for further dissemination of results in the future.

Now that we have covered ArcGIS and our other mapping programs, the next blog in this series will tackle ArcPad.

- A Reid

On a brief little layover in Frankfurt…

There is a story about palaeoanthropology just about anywhere you might travel in the world. Our route to South Africa for the second fieldwork trip included what was to be a brief layover in Frankfurt, Germany, but which for me, became an unscheduled overnight stopover (more on this below).

Frankfurt is the home to the Senckenberg Research Institute and Natural History Museum, which is a prestigious research centre that includes in its diverse research programmes both fieldwork and laboratory research in palaeoanthropology. Senckenberg was once home to the distinguished German palaeoanthropologist G. H. R. von Koenigswald. During his career, which spanned from the 1930s to his death in 1982, von Koenigswald conducted research into human origins in many parts of the world. He recovered fossils now recognized as Homo erectus in Java, including the Modjokerto juvenile calvarium, and some of the very robust Sangiran material. In the 1950s, von Koenigswald visited South Africa to study the hominid fossils from sites such as Sterkfontein and Swartkrans, and later, he also published with the late South African palaeoanthropologist Phillip V. Tobias (…and thus, some links in this blog to our South African fieldwork project…).

Aside from his scientific pursuits, von Koenigswald lived through some incredible experiences. During World War II, he was taken prisoner (in Java) by the Japanese, and spent the war years in a POW camp. In fact, he was presumed dead by many, and as a result some of his fossil finds were initially described by Franz Weidenreich. After the war, the two great palaeoanthropologists resumed work together, and proposed that the taxa Pithecanthropus (named for the Javanese fossils) and Sinanthropus (named for the Chinese fossils) should be merged because of the similarities displayed by these two assemblages. Later, all such material was incorporated into Homo erectus, as it is now known.

Today, the Senckenberg Research Institute remains a world-renowned centre for palaeoanthropological research in Africa, Europe and Asia. Further information about their projects and researchers can be found here: http://www.senckenberg.de/root/index.php?page_id=898

Unfortunately, during my journey to South Africa, I was not able to visit the Senckenberg Institute or museum. Though we were only scheduled for about a 2 hour layover, I was not allowed to continue to South Africa by the customs officials at the Frankfurt Airport because I did not have any clean, blank pages in my passport! I was told that South Africa has a ‘very strict’ policy about this, and that I would have been turned me away on arrival in Johannesburg. So I spent the night in Frankfurt, and the next day visiting the US Embassy in order to obtain an insert of 10 clean, blank passport pages. (I just want to add that I did have five pages that appeared to have space for a customs stamp, but all had already been stamped at other ports-of-call).

The next day, everything was in order, and I was on my way to South Africa, a bit irritated over the delay, but still excited to get to the field. An expensive lesson in travel preparation, to be sure.

- KL Kuykendall

ps. Andy Reid made it all the way to Joburg as scheduled…!

Geology maps: where is that dolomite?

Apart from the two historic mining maps we have acquired, a substantial amount of our information has come from 1:250,000 maps of the bedrock geology. These provide the geological characteristics, and the location, of the underlying rocks in any area of South Africa. Because the types of caves we are looking for form in dolomite, locating areas where this rock is present is one of the main factors in determining our survey strategy.

The geology maps have been treated in the same way as the historic mining maps, utilising only the information relevant to the project and converting that information into a usable digital format. However, unlike the mining maps, on which the digital information is characterised by a point, the information we require from the geology maps relates to the region (including the size and shape) occupied by a lithological unit of bedrock.

Geology base map. An example section of a 1:250000 geological map showing areas of dolomite in different shades of blue (map published byDepartment of Mineral And Energy Affairs, Republic of South Africa 1981).

 

In order to convert this map information from Raster to Vector formats, we trace around the edges of the bedrock formations we are interested in, save them as a polygon (instead of a point), and then add the lithological information as an attribute of the feature. Not only does this kind of digitisation help in establishing areas to investigate but it also has a number of other advantages.

Geology map with polygons.  In this figure, the blue areas denoting a dolomitic lithological unit have been overlain by a traced polygon using ArcGIS and are now represented by different colours to indicate different attributes the rock unit might have, such as including interbedded chert, quartzite, or shale (map published byDepartment of Mineral And Energy Affairs, Republic of South Africa 1981).

The first advantage is the reduction in size of the file from a large scanned map which may be as much as 390 Megabytes per file to a few Kilobytes of data. This is helpful not only when trying to use the data on a handheld computer but also for storage on the device, since we can fit many more polygons than scanned maps on a 4 Gigabyte memory card. The second advantage of digitising in this way is that we can select the only data that are  relevant to the project and its aims. We can ignore all the other geological formations which do not hold the appropriate characteristics and only digitise those that we need. This again saves space on the memory cards but also saves time, both in the tracing of the geology and in locating regions appropriate to the project in the field.

Geology polygons. This figure shows how the digitisation of the geological formation looks when the area is loaded onto the handheld computers. The pink and orange colours represent the (dolomite) geology and the green background represents the Vector outline of the main provinces of South Africa.

The “Identify” function on the GIS software (ArcPad) we use on the hand-held computers can be used to call up the attributes of any of the Vector layers  once defined. The GPS function on the handheld also enables us to determine our current field position relative to the geological formations (polygons) and to the mines (points). This helps us to avoid spending a lot of time driving around searching in the field!

This is the final step in the digitisation process to prepare the maps for the field. The next blog in this series will deal with some of the hardware and software we are using in more detail.

- A Reid

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