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Addo Elephant National Park

Geology

The Addo Elephant National Park encompasses a unique and complex bit of earth history covering about the last 500 million years. This includes the more recent events during the evolution of planet Earth, which is estimated to be about 4,5 billion years old.

Before we start, one must remember that we live on a dynamic planet, which is permanently changing and evolving. The earth has a radius of about 6300 km and is covered by a 40 km thick crust. The surface crust is continuously being driven by convection currents in the underlying mantle. This causes the crustal plates (continents and oceans) to move relative to each other, a process called “continental drift”. Crustal plates can drift (float) from the warmer tropics to the colder pole regions, all the time changing the way in which a landscape evolves. The combination of earth processes and climatic conditions has a significant impact on the final landscape appearance.

The Oldest Rocks – Peninsula Formation Quartzitic Sandstone

The easiest way to describe the geological evolution of the Park is to start with the oldest rocks and work our way towards the present. Our story begins when Africa was joined to a number of other continents to form a super continent called “Pangea”. We (South Africa) were stuck in the middle of this land mass and our landscape was, therefore, very different to what one sees today.

The oldest rocks encountered in the Park occur as small islands in Algoa Bay. The Bird Island complex comprises Black Rock, Stag, Seal and Bird Islands and occurs about 10 km south of the Woody Cape cliffs. These rocky islands are made up of quartzitic sandstone of the Peninsula Formation, which forms part of the Table Mountain Group, which in turn forms part of the Cape Supergroup. This is the same formation that occurs along the Port Elizabeth beachfront (Summerstrand) and on Table Mountain in Cape Town.

The Peninsula Formation rocks were formed about 500 million years ago (during the Ordovician Period) in a shallow marine beach environment. A large trough (basin) developed within the Gondwana landmass due to tectonic (crustal plate movement) activity. This basin filled with silica-rich sands, which have re-cemented to form relatively pure (clean) quartzitic sandstone. Quartzitic sandstone is very hard and forms the very prominent landscapes in the Eastern Cape Province. The Cockscomb Peak in the Groot Winterhoekberge is an excellent example of how weathering-resistant quartzitic sandstone is relative to the surrounding, softer bedrock material.

Witteberg Group Rocks

A gap in the geological record of about 100 million years occurs to the next geological unit (this gap is referred to as an “unconformity”). The Witteberg Group rocks of the Cape Supergroup comprise quartzitic sandstone, sandstone and shale and were deposited about 400 million years ago during the Devonian Period. These rock types make up the Zuurberg mountain range to the north of the existing Addo Elephant National Park. Witteberg Group rocks have been grouped into two smaller subgroups, the lowermost one referred to as the Lake Mentz Subgroup and the upper unit called the Kommadagga Subgroup. Both of these stratigraphic units were named after places from the Eastern Cape Province. The Lake Mentz area is now called Darlington Dam.

The Devonian Period coincides with the evolution of the first land plants and marine fish. These would have both been fairly primitive specimens, with the zoological record dominated by marine invertebrates. The Witteberg Group was deposited in a tidal flat environment. The quartzitic sandstone and sandstone rock types would have been deposited in the intertidal zone, where clean sands were being reworked by marine action. The darker (and softer) shale was formed within the mudflat environment.

Glacial Dwyka Group Tillite

A very significant marker horizon occurs on top of the Witteberg Group rocks. During the Carboniferous Period (about 300 million years ago), Africa (as part of Pangea) was located at much higher latitudes and experienced colder climatic conditions. Southern Africa, as we know it today, was an ice sheet dominated by glaciers during these times. These ice sheets migrated towards the south and south-west from what is today Zimbabwe and Botswana. En route these ice sheets ripped up pieces of rock from the floor of the glacier and carried a multitude of rock types over thousands of kilometres.

Inevitably, the continents moved to warmer latitudes, resulting in climatic warming. The ice sheets began to melt and released all of the rock material that had been consumed by the glacial fronts. In modern glaciers, the dumping of material from retreating glaciers is called “terminal moraine”. This terminal moraine during the Carboniferous Period became cemented to form a rock type called “tillite”. Tillite is a grey-brown, fine-grained rock mass with numerous small foreign clasts of various rock types and colours. Many of the clasts are polished (have a smooth surface) due to the friction when they were picked up by the moving ice sheets.

The tillite deposits in our end of the world are referred to as the Dwyka Group rocks of the Karoo Supergroup. The Dwyka Group occurs as a horizontal band along the northern edges of the Zuurberg mountain range and along the southern shores of Darlington Lake. This lithological horizon is an indicator horizon, which separates the Cape Supergroup rocks to the south and the Karoo Supergroup rocks to the north. Dwyka Group rocks are fairly easy to spot in the veld, as they weather to form an irregular landscape that looks like tombstones – so called “tombstone weathering”.

Ecca and Beaufort Sediments of the Karoo Supergroup

The Dwyka Group is overlain by the Ecca and Beaufort Group rocks, of the Karoo Supergroup. These rock types occur in the Darlington Dam area, in the northern part of the Greater Addo Elephant National Park and cover a period of between about 250 and 300 million years (Permian Period). The Karoo landscape represents a significant climatic warming after the Dwyka glaciation. Karoo Supergroup sediments were deposited into a large inland sea (with an inlet where present day East London is), with northwards flowing rivers depositing sediment into a massive basin that extends into Zimbabwe and Botswana. The huge mountain ranges to the south of the Karoo Basin were probably larger than the present day Himalayas and were undoubtedly the source of all the sediments that form the present day Karoo landscape.

The Ecca Group sediments were deposited in a marine origin within the inland Karoo Sea. This stratigraphic unit comprises sandstone, shale and mudstone. Interestingly, the Ecca coincides with the evolution of large forests (conifers) and the first reptiles. The large forests gave rise to the significant coal reserves that occur in the eastern part of South Africa at present. Some of the smaller formations within the Ecca Group were named after places within the Eastern Cape Province. These include the Ripon Formation (named after a railway siding south of Cookhouse) and the Waterford Formation (named after a village south-east of Jansenville.

The Beaufort Group depositionary history represents a change from marine to fluvial (riverine) environments. The Beaufort landscape was characterised by large meandering river channels in a fairly flat land surface. The climate would have been fairly hot, with terrestrial vegetation restricted to a narrow green belt along the riparian habitats flanking the drainage channels. The remainder of the Karoo landscape would probably have been fairly dry and arid. Only the Koonap Formation of the Beaufort Group occurs within the boundaries of the Park, around the northern fringes of Darlington Dam.

Beaufort Group rocks are very important from an anthropological point of view. Beaufort times are characterised by the emergence of the mammal-like-reptiles, which are the precursors to the dinosaurs. These animals comprised both carnivores and herbivores and dominated the Beaufort landscape during the Permian Period.

Mesozoic Algoa Basin

The Mesozoic Algoa Basin represents a very significant geological event along the south-eastern coast of southern Africa. The Algoa Basin extends along the Algoa Bay coastline from Bethelsdorp in the south-west to the Sundays River mouth in the north-east. It probably extends even further beneath the surface cover material to the Woody Cape cliffs area. It extends inland along what is called a “panhandle” to the Erekroonspoort area, about 25 km east of Jansenville.

Towards the end of the Triassic (about 230 million years ago) the Pangea mega-continent began to break apart. Two new super continents began to form, namely the northern Laurasia and the southern Gondwana. The compressional stresses associated with splitting of the land masses caused the folding of the Cape Supergroup rocks along the southern margin of southern Africa, to form what is today known as the Cape Fold Belt. The further break up of Gondwana into Africa, South America and a host of other land masses also resulted in the formation of half-graben faults along the south-eastern margin of the present-day coastline. These half-graben faults formed deep basins, which subsequently began to fill with sediments.

The breaking up of the continental land mass initially resulted in what we call Suurberg volcanics. These are extrusive (igneous rocks that flow across the surface) rocks derived from great depth and associated with volcanic activity due to crustal tectonics. The resulted Suurberg Group rocks comprise basalt, tuff, and breccia. The Suurberg Group is made of the Coerney and Slagboom Formations (named after a river about 25 km east of Kirkwood) and a farmstead about 17 km north-east of Kirkwood, respectively. The Suurberg Group is named after the Zuurberg mountain range. An excellent basaltic outcrop occurs in a small quarry to the north-east of Tembani, within the Nyathi Concession area.

During the Jurassic Period (about 140 to 190 million years ago) torrential streams eroded the quartzitic sandstone highlands and deposited extensive boulder beds and gravels. The resultant red-coloured conglomeritic Enon Formation (named after the small village of Enon to the north of Port Elizabeth) is a very prominent horizon along the southern foothills of the Zuurberg Mountain range. The Mimosa quarry to the north-west of the Mimosa farmstead is an excellent outcrop of the Enon Formation conglomerate. The quarry was apparently used to source the quartzitic sandstone material used to construct many of the gravel roads within the present Addo Elephant National Park.

The Kirkwood Formation sedimentation began towards the end of the Jurassic Period (about 140 to 150 million years ago). The Kirkwood Formation represents an accumulation of fine-grained sediments under fluvial conditions. The resultant mudstone and subordinate sandstone also contains foliage and wood fossils. The fluvial deposition began to filled the Algoa Basin and was followed by marine ingression to form the Sundays River Formation. The Sundays River Formation contains numerous marine fossils, such as ammonites, belemnites, bivalves and gastropods (shells). From oldest to youngest, the Enon, Kirkwood and Sundays River Formation are collectively referred to as the Uitenhage Group.

Extensive oil exploration was undertaken throughout the Uitenhage Group rocks during the 1960’s by Soekor (South African Oil Exploration Corporation). It was during this exploration exercise that the highly visible cut-lines were cleared throughout the Addo region and today represent highly disturbed transects within the Valley Thicket. It is interesting to note that some of the exploratory boreholes in the Colchester area proved Algoa Group sediments in excess of 2 km. These oil exploration drives apparently revealed minor, but insignificant, reserves of oil and gas.

Interestingly, local press releases during the first quarter of 2003 stated that oil exploration had recommenced within the Mesozoic Algoa Basin. This may prove successful if one considers that the economically viable reserves encountered in the Mossel Bay area (Mossgas) is derived from very similar geological environments.

The northern part of the present Park (including the rest camp) is underlain by sediments of the Sundays River Formation. Further to the south, the Park is underlain by sediments of the Kirkwood Formation. These formations appear very similar in surface outcrop and generally comprise reddish and greenish-grey coloured mudstone, which weathers to reveal a very slippery, clayey material when wet. This material is also very problematic from a construction point of view, as it swells when it gets wet. Much structural damage has been caused to dwellings in the region, where inadequate precautionary measures have been taken when building. The Addo brickfields used to use the clays of the Kirkwood Formation to make clay bricks.

Tertiary Alexandria Formation

By the end of the Cretaceous Period (about 80 million years ago), the present configuration of the Southern African coastline was established. The evolution of the landscape from this time onwards was dictated to to a large extent by fluctuating sea-levels. You will understand that climatic cooling results in more seawater freezing in the polar regions, which will correspond with a dropping of global sea level. By the same token, sea level rise will be associated with global warming.

One such sea level rise from about 20 to 2 million years ago, resulted in the flooding of the Eastern Cape coastline to form the marine Alexandria Formation. This formation has deposited 10’s of kilometres inland of the present coastline and has resulted in a fairly level wave-cut platform. These levels occur in about three different heights (each representing a different sea level), each formed during a still-stand followed by further lowering of sea level. The maximum landward extent of the raised sea level resulted in the development of the Grassridge Platform, which occurs at heights of 245 - 320 metres above mean sea level. The shoreline of this sea level curved inland from the vicinity of Port Elizabeth to Paterson and Port Alfred. Under the water of the fluctuating sea levels, were deposited the sediments of the Alexandria Formation.
The lower Coega Platform occurs further seawards, at an average height of about 200 metres above mean sea level. This Platform ends inland against a former cliff line that is exposed near the N2 highway in the vicinity of the Coega salt pans, between Colchester and Port Elizabeth.

The Alexandria Formation near Colchester would form part of the Coega Platform, whilst the same formation within the Addo Elephant Park near Addo Heights, would form part of the older Grassridge Platform.

The Tertiary Alexandria Formation generally attains a maximum thickness of about 13 metres near Colchester and comprises calcareous sandstone, coquinite (cemented shell-rock) and quartzitic sandstone gravel. The Tertiary Period (65 to 2 million years ago) also coincides with the rise of the mammals. Dinosaurs became extinct at the end of the Cretaceous Period (about 65 million years ago) and small quadrupeds and flowering plants dominated the landscape.

The Alexandria Formation is easily discernable within the current Addo Elephant National Park and stands out as a white-coloured band near the upper portions of the hills. The best outcrop within the Park would be at the Zuurkop Lookout, where this material was previously mined to produce the white coloured material used to surface the gravel road in this part of the Park. In 3-D it should be remembered that this formation represents a fairly flat sea-level deposit, so it extrapolates as a thin disk into the landscape beneath the overlying cover material such as at Addo Heights. This cover material is known as the Nanaga Formation in the Park.

Aeolian Nanaga Formation

During each still-stand of sea level, a coastal dunefield was deposited. This process still occurs today along the existing coastline of Algoa Bay. The resultant ancient dunefield cordons formed during the Tertiary Period have been preserved as rolling hills of the Grassridge and Nanaga areas and called the Nanaga Formation. This aeolian (wind deposited) deposit attains thicknesses of up to 250 metres and extends from Paterson in the north, down to Woody Cape in the south.

This formation obviously gets progressively younger towards the coast, as the sea level receded. The formation generally comprises semi- to well-consolidated calcareous dune rock (sandstone). A good outcrop would be the road cutting along the N2 highway about 5 km north of the Nanaga intersection. The Nanaga Formation is very prominent as fine-grained red sands, which form the high-lying topography in the Park, such as at Addo Heights.

Recent (Quaternary) Deposits

Recent (the Quaternary Period covers a time scale from about 2 million years ago to present) geological evolution and geomorphologic evolution of our region is highly complex and driven by climatic variation and associated sea level fluctuations. Of interest would be a coastal marine formation called the Salnova Formation. This formation generally occurs at a height of about 20 metres below sea level and comprises calcrete with quartzitic sandstone boulders and shell material. Salnova Formation outcrop occurs near Cannon Rocks, in the extreme eastern part of the proposed Greater Addo Elephant National Park. It also occurs near the Coega River mouth, to the south of the Park.

Another aeolian formation along the coastal zone includes the well-consolidated Nahoon Formation. This calcareous sandstone formation attains thicknesses of up to about 50 metres and has had a significant effect on the weathering rates of the Eastern Cape Province coastline. These aeolianites (dune rock) typically protrude has coastal headlands into the sea, producing Kwaaihoek near Boknes (Diaz Cross), Bushman’s River Mouth, Bats Cave (Great Fish River), Nahoon Point (East London) and Flat Rocks (Port Elizabeth). In the Park, this formation is responsible for the very scenic Woody Cape Cliffs.

The most recent of all geological formations is the aeolian Schelm Hoek Formation. This comprises wind- blown sand adjacent to the present day coastline and is still being deposited at present. The Schelm Hoek Formation is included as the Alexandria dune sea in the south-eastern part of the Park. This formation includes an older generation vegetated dune and a younger generation, non-vegetated sand dune. The migration of non-vegetated Schelm Hoek Formation has been retarded to a certain extent by the infestation of Australian wattle species. This is especially noticeable along the eastern side of the Sundays River mouth.

Geomorphology

The land that rose above the level of the sea that cut the marine platform (Alexandria Formation in the Park) was drained by various rivers. Along these rivers, cycles of erosion worked their way into much of the interior of southern Africa, giving rise to the African Erosion Surface (African Land Surface). This surface exists at different altitudes and developed over the last 100 million years (since the Mid-Cretaceous Period). They are capped by hard silcretes and, in the Park, characterised by Grassy Fynbos vegetation. These African Land Surfaces are clearly visible along the upper reaches of the Zuurberg mountain range in the Park.

The geomorphological evolution of the area included in the Park still continues today. Inland remnants have been preserved for many millions of years, but bear testimony to prolonged but still continuing fluvial (river) processes. The marine processes are still shaping the coastline, be it the deposition of sand in the Alexandria dune sea, or the erosion of the Nahoon Formation along the Woody Cape cliffs.

It should be remembered that all river systems attempt to erode the surrounding landscape down to sea level. Geological processes such as sea level change and tectonic activity prevent this strategy from ever being realised. It is, nevertheless, important to remember that erosion still continues (as does deposition) and the morphology of both the inland and the coastal region continues to evolve.

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  • Addo incorporates the largest coastal dune field in the southern hemisphere

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