HYPOTHESISING THE HIGHLY FRACTURED DEFUSE SOUTH AFRICAN TRANSVAAL AQUIFER
MIKE BUCHANAN (2005)
Hampshire, United Kingdom.
IUCN WCPA Task Force on cave and Karst.
Cave Research Organisation of South Africa - CROSA
In this document I explore the probability of a vast undermanaged
subterranean cross border, sedimentary karst hydrological system . This will be referred to as The South African Transvaal Aquifer (SATVLA) for the purpose of this document. The naming will be subject to governmental influence due to the nature and size of the SATVLA upon acceptance.
This hypothesis can be considered the first ever attempt at describing the karstic system which makes up the subterranean hydrology of the Limpopo River catchment and drainage basin.
The SATVLA can be construed as one of the world’s largest subterranean sedimentary karst aquifers, after the Edwards Aquifer in the United States of America. This system has many notable karst basin features. Including a conforming sedimentary periphery, inwardly directing geologic strike angle towards the central basin. The slope angle of the karst varies between ten and fifteen degrees - A well defined, buried karst basin around and beneath The BIC. Inclusive of a well-developed, deep-seated hot spring network within the central basin is also evident (Bella Bella, Grobelarsdal etc lowest basin point amsl).
The SATVLA hosts the world’s oldest Neoarchaen dolomitic geology, including a one of a kind complete, magmafic, lopolithic infill of economic importance called the Bushveld Igneous Complex (The BIC).
“The Neoarchaean-Palaeoproterozoic Transvaal Supergroup geology was laid down during the Archaean geologic era which spans the period of time 2800 to 2500 million years ago; the period being defined chronometrically and not referenced to a specific rock section level. Oxygenic photosynthesis first evolved in this era and was accountable for the oxygen catastrophe which was to happen later in the paleoproterozoic era 2.4 mya from a poisonous buildup of oxygen in the atmosphere, produced by these oxygen producing photoautotrophs, which evolved earlier in the neoarchean era.” (1.Wikipedia encyclopedia).
From this, the stratigraphic subdivisions within the Transvaal Supergroup have been delineated. They are consolidated into five distinct groups, some containing various stromatolitic and oolitic assemblages throughout the sedimentary sequence. The lowest non sedimentary layer (Chuniespoort - Black Reef Quartzites) containing no known fossil remnants, stromatolites or oolites.The delineated sedimentary stratigraphy within the Malmani Dolomite Subgroup are named - the Oaktree, Monte Christo, Lyttelton, Eccles, and Frisco Formations
2. Description and history
The SATVLA is undoubtedly one of the worlds largest subterranean groundwater bearing dolomitic karst aquifers. Consisting of a multitude of separate intercommunicating porous sub systems via fractures and interbedded chert. All located in one dynamic mega groundwater system with a shallow stratigraphic strike angle. Thereby, low flow hydrologic gradient. This high altitude, highly fractured, diffuse groundwater karst system consists of an average conformity of 1500 - +- 3000 meters thick and is calcium magnesium carbonate or dolomite with blatant surficial karstification (CaMg(CO3)2). The dolomite incorporates stratified, interbedded silicate chert (fossiliferous interbedded chert) which provides a well defined base for dolomite karst land-form development.
The interbedded chert (Mohs scale 6-7*), has a higher density and Mohs hardness rating code than the dolomite (3-4). Silicate Chert is considered as a biologic stromatolitic remnant of the Archean development of this once inland sea, lake or water body. No one is quite sure how dolomite came to being. Many speculate that it was either laid down as dolomite due to the acidic constituency of the atmosphere many millions of years ago or the dolomite was once limestone that had a unique transformation which gave it the magnesium carbonate either by volcanic super-heating or meteoric impact. All concepts will be discussed latter.
*The Mohs scale was devised by Friedrich Mohs in 1812 and has been a valuable aid to identifying minerals ever since. (2. Andrew Aldern Geologist).
Karst aquifers are vitally important because they provide fresh potable water (this being a small part of the systems production). Twenty five percent of the earth’s human population depends on karst systems for drinking water. They are also seen as sites of natural habitat for numerous specialist feeders. Like bats, which remove vast quantities of invertebrates from these environments in their diet. Aquifers and their vulnerability to contamination by pollutants are reasons to seek conservation and an improved understanding of how karst systems work.
The primary reason for this hypothesis, is to explore the disparity between current anthropogenic interactions within this under managed resource. This is seen to be one of the largest threats to the under managed subterranean karst aquifer system. It is common knowledge internationally that the BIC is the world’s most economically viable geology, providing a large percentage of the world’s quality platinum and palladium as well as many other valuable heavy metals. Some of the most advanced deep mining technology is used to recover gold from it's contact periphery. This history is one of the prime reasons for a conflict of this nature to exist, challenging the balance between mineral resource over-exploitation and environmental sustainability. Gold was discovered in Johannesburg, South Africa in the late 1800’s and its demand grew rapidly because of mining technological advancements and the vast availability of valuable gold deposits around Johannesburg. Most major cities around the world evolved along an economically navigable river or coastal plain, Johannesburg has none of them. This city was founded and established because of its gold. It is 5500 ft above mean sea level (amsl). This phenomenon has a vast bearing on the understanding of complications facing the SATVLA which will be discussed latter.
The SATVLA is detailed in Council for Geosciences geological maps from as early as the beginning of the 1900’s. This was merely indicated as a dolomite belt. The nature of which was not quite understood at this stage. This belt was detailed as a surface exposed geology that happened to be on the contact of Johannesburg’s (JHB) viable granite dome which is the source of all the gold, Uranium, Lead (Pb), Molybdenum, zinc etc. More recently the sediments are well documented and defined throughout and under the BIC. The sedimentary dolomite belt border extends from Mogale City (was Krugersdorp) in the south and follows an oval pattern toward the northwest, toward the mining town of Ventersdorp , broaching the Botswana border. It takes a turn to head back out of Botswana in a northeasterly direction towards Thabazimbi, on towards Mokopane (Potgietersrus) Northwest Province of South Africa. It narrows superficially and creates part of the great South African, Drakensberg Escarpment heading down towards the Mozambique border, skirting the border by a few hundred kms. Then doubles back to the Johannesburg area culminating at the now world famous Cradle of Humankind World Heritage Site, Sterkfontein caves and surrounds (CHK WHS). The SATVLA karst lends itself to the creation of the CHK WHS, due the nature of the sedimentary karstic processes that were laid down some 2300 million years ago.
Some speculated that three to four billion years ago a vast inland sea had developed, possibly prior to the development of Gondwanaland Land, when the world had only one super continent. This inland sea bore testament to the earliest evolutionary phases of macro life and possibly some of the first living organisms that were starting to adorn our earth; Prokaryotic life, cyanobacteria or blue green algae grew into what we know as stromatolites. These biologic fossils can be witnessed in the stromatolitic ensemble that makes up the Transvaal Supergroup sedimentary succession today.
As volcanic activity and the natural cooling processes were settling down after earth’s evolution, the earth had a rapidly changing atmosphere which was much more acidic than today. Due to volcanic action and cooling processes the atmosphere would have been sulphurous and full of dust and ash from the changing earth. We can see this happened in the content of the most basal layer of the SATVLA. It is merely a thick layer of sediment that has no visible life forms encapsulated it (Nanobacterium cannot be ruled out). As atmospheric dusts settled on the inland sea, it sank to the sea floor and overtime grew to many hundreds of meters thick, encapsulating some of the most important events that occurred during our earth's evolutionary processes. This is well conveyed in the book written by Mc Carthy and Rubidge called The story of Earth & Life. ISBN: 1 77007 148 2.
The SATVLA is believed to have developed around two thousand three hundred million years ago as an inland sea prior to the Gondwanaland split. This hydrologically sound system was upset some 1300 million years ago when great intercontinental tectonic movement caused volcanic, or a succession of volcanic events to take place, which in turn caused a warping or uplifting of this sedimentary sea. This changed the nature of the sea into geology that no longer was filled in by water but which was replaced by molten magma. Geologists have identified a number of different events that helped this process along, hence the variable economically rich mineral resources that are found within the BIC. The BIC filled in the SATVLA Sea basin remnant and was primarily responsible for eluding many geologic/hydrologic authors for centuries.
The size of the SATVLA is still not quite understood. However if one ponders the possibility that the area depicted on the Geosciences map is roughly 500 km by 250 km without incorporating other extra periphery based dolomitic land-forms that could have been, or are hydrologically connected and communicating, the SATVLA size could jump considerably, i.e. The Ghaap Plateau certainly, possibly and not ruling out the Namib karsts or western Botswana karst! However, for this document I shall focus on the sediments that have now been irrevocably buried by the BIC.
The surface fluvial catchment area has historically been recorded as the Limpopo basin.
3. TIMELINES - According To Geological History
1) TVL SEQUENCE laid down 2,300 million years ago. The Cango and UK limestone’s are +- 200 million years old with substantial conduit cavern development I.E. karstification. A clear indication that the SATVLA had well defined karstic and conduit formation prior to the BIC formation.
2) BIC formation started 2,054 billion years ago
3) Vredefort ASTROBLEME 2,023 million years (huge fracturing took place at this time)
4) Pilanesberg Volcano/s 1 300 million-year-old
5) The Tswaing/Soutpan Meteor Crater 200 000 years ago (again, huge fracturing of the karst and associated dykes would have prevailed,responsible for the mammoth collapse of all Pretoria region caves. The reason why they all demonstrate substantial instability and collapse)
6) Gondwana split 100 million years ago, possibly responsible for the uplifting of the southern side of the SATVLA
4. Limpopo Basin profile
Statistics and background information: -
• Catchment area: Around 413,000 km²
• Rainfall: Average 530 mm per annum. Range: 200-1,200 mm
• Evaporation: Average. 1,970 mm per annum. Range: 800-2,400 mm per annum)
• Runoff: 5.5 x 109 m³ per annum or 13 mm per annum
• Water transfers: Water is transferred into the basin under 6 separate transfer schemes
• Population: 14 million
(Information provided by the Department of Agriculture, South Africa)
The Limpopo River Basin
“The Limpopo River flows over a total distance of 1,750 kilometers It starts at the confluence of the Marico and Crocodile rivers in South Africa and flows northwest of Pretoria. It is joined by the Notwane River flowing from Botswana, and then forms the border between Botswana and South Africa and flows in a northeasterly direction. At the confluence of the Shashe river, which flows in from Zimbabwe and Botswana, the Limpopo turns almost due east and forms the border between Zimbabwe and South Africa before entering Mozambique at Pafuri. For the next 561 km the river flows entirely within Mozambique (the Limpopo flood plain) and enters the Indian Ocean about 60 km downstream of the town of Xai-Xai. The Limpopo river basin is almost circular in shape with a mean altitude of 840 m above sea level. It lies between latitudes 22°S - 26°S and longitudes 26°E - 35°E. The total surface area drained by the basin is estimated at about 415,000 sq km.”
“The Limpopo basin covers almost 14 percent of the total area of its four riparian states - Botswana, South Africa, Zimbabwe and Mozambique, and, of the basin’s total area, 44 percent is occupied by South Africa, 21 percent by Mozambique, almost 20 percent by Botswana and 16 percent by Zimbabwe.”
“In the southern (South African) portion of the basin, the Bushveld Igneous Complex forms an extremely important geological feature, and contains a very large proportion of the region’s mineral wealth. The geological features of this area consist mostly of basic mafic and ultramafic intrusive rocks, accompanied by extensive areas of acidic and intermediate intrusive rocks. At the southern and eastern periphery of this area, large dolomite and limestone formations occur, accompanied by extensive mineralization along their contact zones.” (4.Information from the Southern African Research and Documentation Centre)
What is not mentioned in virtually all publications is that the BIC covered the SATVLA’s sediments some 2,054 million years ago. This happened as a result of various volcanic eruptions and magmafic oozing taking place over a 750 million year period. The molten magma slowly filling in the TVL basin, thus obscuring the (karst) groundwater resource potential for many years to come.
5. Bushveld Complex
“The Bushveld Complex is largely igneous in origin and occurs in the northeastern region of the Province, from Brits and Rustenburg in the east to north of Zeerust and Swartruggens into Botswana. Of the three suites making up the Complex, only the peripheral mafic intrusive phase occurs in the North West Province. This consists of four main layers: the upper zone of gabbro, olivine, diorite to grandiorite with some anorthosites and magnetites. The main zone of 5 200m which consists mostly of gabbros, which gives rise to topographic features such as hills. Below this is the critical zone consisting of norites, anorhosites, pyroxenites and chromites, below which is the basal zone mostly of pyroxenite and peridotite. Platinum and chromite from this zone is mined extensively in the Rustenburg / Brits region. “
The Bushveld Igneous Complex (BIC)
“The Bushveld Igneous Complex (BIC) is the world's largest known layered intrusion and has an estimated area extent of 182,000 km2 .The BIC is an enormous, champagne glass-shaped body 370 kilometers across, with its center buried deep beneath younger rocks but with its rim exposed. It is composed of a series of distinct layers, three of which contain economic concentrations of platinum group elements (PGE). The principal PGE-bearing reefs are the Merensky Reef and the Upper Group 2 (UG2) Reef, which occur around the Eastern and Western sides ("limbs") of the BIC. A third PGE-rich layer, the Platreef, is found only on the Potgietersrus limb at the north-eastern edge. “
“The BIC contains an ultramafic to mafic unit (the Layered Series), up to 9 km thick, which outcrops as eastern, western and northern lobes surrounding a felsic core of largely granitic rocks. The Merensky Reef, which is the best known and most commonly exploited platiniferous horizon in the complex, can be traced for at least 240 km along strike and is estimated to contain 60 000 t of platinum group metals in its upper 1 200 m, as well as significant resources of cobalt, copper and nickel. The pyroxenitic Platreef horizon, north of Potgietersrus, is a wide zone containing PGE mineralisation, along with nickel and copper. Of major economic importance is the UG2 (Upper Group 2) chromitite horizon that is being increasingly exploited for its PGEs, particularly in the eastern lobe of the Bushveld Complex. This represents an even larger resource of PGEs than the Merensky Reef. The BIC also contains almost 70% of the world's reserves of chromite as well as significant resources of vanadium.” (North West Dept. Agriculture, Conservation and Environment, Mafikeng)
The entire BIC is underlain by Archean sediments which host many billions of Terra liters of subterranean groundwater, some geothermal by nature. The slow moving young groundwater finds its way through the documented Transvaal dolomite sediments from its exposed periphery. Following the the ten degree strike angle circumferentially. Flowing towards the deepest most central points, where this low flow emanates in the form of highly valuable fossiliferous groundwater, older than 20 000 years in age (J. Talma CSIR - Warmbaths/Bella-Bella). Which is being exposed to intensive, irresponsible Government sanctioned anthropogenic interactions, in the form of unsustainable, deep heavy metal mining, within and around the BIC. Inclusive of inputs from industrial and agricultural pollutants without authoritative knowledge backed check. All as a result of past ignorance around the true nature of this vast low flow hydrology. "The Compartmentalisation Theory".
There was never tight confined compartmentalisation as described and documented historically by many notable Key Opinion Leaders and geohydrological authors. Simply, a vast volume of groundwater moving slowly in terms of geologic time and permeability varying exponentially at depth. Within one vast, highly fractured, defuse, mega Archean - Proterozoic Karstic Groundwater System that requires immediate remediative intervention without further delays.
THE SOUTH AFRICAN TVL AQUIFER and B.I.C.
Click on picture for large imageWith associated impacting events. A modified Council for Geosciences map with insert by Buchanan
1. Wikipedia encyclopedia - http://en.wikipedia.org/wiki/Transvaal_Basin2. Andrew Aldern Geologist - pachamamatrust.org/f2/1_K/SGl_geology/Aa_INTRO_KSGl.htm
3. Mc Carthy and Rubidge The story of Earth & Life. 2005 - ISBN: 1 77007 148 2.
4. The Limpopo River Basin - www.sardc.net/imercsa/Limpopo/objective.htm
5. The Bushveld Igneous Complex (BIC) State of environment report 2002 - www.nwpg.gov.za/soer/FullReport/industrial.html