Romancing the Stone

GeoZone Photographic Competition

2011-01-23T07:40:00.007+02:00

GeoZone GeoServices is running an inaugural photographic competition and is open to anyone with an interest in the geotechnical and engineering disciplines. We therefore invite everyone to send in their best images of any geological, mining, geotechnical or engineering subject. With any luck this will become an annual event and we can attract some good prize money and increase the number of categories.

Roger and Pat de la Harpe of Africa Imagery fame will be judging the competition, and should their image be selected as a potential winner it may well be included in the Africa Imagery image bank. If Africa Imagery sells on the image a royalty fee will be paid out use of the image. So send in those great images and with any luck, you might grab the prize money.

Please send images of no more than 1 MB to geologist@netactive.co.za. Should your images be shortlisted we will require larger files and if possible the RAW images. Please download the competition application form at http://www.geozone.co.za/GeoZone_Geotechnical_Photography_Competition.htm.

Happy snapping, and may we take the opportunity to wish you the best of luck.

Rules:

* Closing date for entries is 30 April 2011

* The results will be announced on 15 May 2011

* The judges decision is final and no negotiation will be entered into with regard to the prizes.
* By entering your agree to incorporation of your images into the Africa Imagery image bank and allow GeoZone GeoServices to post your images onto the GeoZone site.

Dinosaur Footprints in Lesotho

2011-01-05T09:00:00.007+02:00

We were in Lesotho just before the new year, mostly to get away from the usual humdrum of suburban life, but also to take in magnificent mountain scenery, geology, the spectacular Maletsunyane Falls, and look for dinosaur footprints. We met with success in all departments, and had a laugh too. The Land Rover behaved itself - in fact went like a dream up those impossibly long, steep mountain passes which was a relief to say the least. I had given her a stern talking to a few months back - any more breakdowns and trouble from you and you are out on your ear - new owners, perhaps even the scrap yard for you if you don't buck up your ideas. So she seems to have taken note and with any luck the truculence of the last 18 months has come to an end. But on to more serious things - mostly dinosaur footprints. With a bit of help from the Lonely Planet guide, the GPS, and the local Basotho lads we found the most magnificent dinosaur footprints under a rock overhang. It is perhaps a bit of an indictment on the geological community that one has to find out information on such significant things as dinosaur fossil tracks from an Australian published travel guide. Well done to Lonely Planet, Nil points to the geologists. But now we hope to rectify this, so if you want to go see them, here are the co-ordinates: S28 54.151 E27 59.864 or if you prefer: S28.90252 E27.99774 or S28 54 09.1 E27 59 51.9.

They must be at least 10 metres up and under the overhang, and the ones at the entrance to the cave are closer and more impressive. That said, they are very well preserved and it looks as if there was a whole herd of them galloping around in the sediments. We are considering ways of jugging up and taking casts at the moment - will need to revisit my rope access skills.

2009-04-15T21:09:00.004+02:00

After a couple of technical glitches and a shed load of hard work www.geozone.co.za went live. We have taken a two pronged approach, so if you are interested in geotechnical issues, please follow the links through to the relevant portion of the site. Otherwise click through on the Romancing the Stone image and come explore the world of geology with us. www.geozoneonline.com. For information on our workshops and safaris go to www.oldcanvasexpeditions.com.

2009-04-04T17:29:00.004+02:00

www.oldcanvasexpeditions.com

2009-04-04T17:05:00.005+02:00

We had a very succesful trip about a month ago when we journeyed with Roger and Pat de la Harpe to Bonamanzi Game Reserve, and then through to Clarens to scout out venues for various workshops. Bonamanzi is located right on the shores of Lake St Lucia and the World Heritage Site of Isimangaliso forms their northern boundary, so they are perfectly positioned in terms of birding, photographic and drawing and painting safaris. The views out of what is the largest wetland in Africa are phenomenal, and then there are the delights of the reserve itself. Accommodation comprises delightful, air conditioned thatched chalets, all with en-suite bathrooms, set in beautiful, thorn tree studded parkland with warthog and nyala wandering freely through the camp. Some of the classes will be held in a beautiful, semi-enclosed deck overlooking an African waterhole where the water lilies splash their colour across the languid waters and frogs serenade one another late into the night.

Dinners are served beneath the star-studded heavens, where cathedrals of candles and a huge camp fire throw flickering, golden shadows across enchanted faces. Delicious food, chilled drinks and convivial company are a given, and time is marked by the slow wheel of the Southern Cross through the African sky.

We reluctantly left Bonamanzi and headed inland to the second highest town in South Africa - Clarens. Again a very successful couple of days, for we found dinosaur remains, explored the Golden Gate National Park from a geological point of view and looked into the possibility of taking participants over the highest road in Africa to the Letseng Diamond Mine. Letseng is the highest diamond mine on Earth and has produced four of the twenty largest diamonds ever discovered.

We approached the mine to ask them if they would take tours and they have agreed to do this, so this is a huge feather in Old Canvas Expeditions' cap, and an exciting addition to our workshop. We have also organised flights along the Eastern Escarpment to take in the second highest waterfall in Earth - the Tugela Falls - the towering buttresses of the Drakensberg/uKhahlamba World Heritage Site, and the vast Post Gondwana Landscape which stretches out to the east.

Certainly experiences not to be missed and we would urge everyone to come on one of our safaris. As we say, more than just a game drive. Go to www.oldcanvasexpeditions.com for more information.

Romancing the Stone Workshop

2009-04-04T16:51:00.007+02:00

Well, it has been a long hard slog but we have managed to break the back of it. Yesterday we went live with our new website, www.oldcanvasexpeditions.com. Now Old Canvas is the provider of some of the top specialist safaris in Southern Africa. More than just a game drive is our slogan and that is exactly what we hope to achieve.

Old Canvas Expedition's flagship geology workshop is out of the town of Clarens in the Eastern Free State - at an altitude of 1800 metres it is the second highest town in the country. The beautiful sandstone cliffs which surround the town and provide the magnificent backdrops for which it is famous, are fossilised sand dunes, harking back to a time 180 million years ago when the area was a desert, the realm of dinosaurs and small mammals.

Gondwana was stilled joined; a vast supercontinent including Africa, India, Australia, Antarctica and South America. Incontestable forces began to play out at the end of Gondwana times, and the supercontinent began to tear itself apart. As these ruptures took place, thousands of metres of red hot, incandescent lavas flooded out onto the Gondwana landscape, burying all in a fiery embrace.

Walking through the town of Clarens gives no inkling of this cataclysmic history, but looking south one can see the blue Maluti Mountains - a remnant of those thousands of metres of lava which burned everything before it. Dinosaur bones protrude out of rocky road cuttings, the ancient desert dunes lie preserved in the cliff faces, faults form large dislocations in Earth's crust and dykes traverse the landscape for tens of kilometres, once feeder pipes to the overlying basaltic outpourings.

We will marvel at the geological history of the region and the story of both wandering continents and wandering dinosaurs. We will drive the highest road in Africa to the Letseng Diamond Mine - the highest on Earth and the source of 4 of the 20 largest diamonds ever found. On the final day we will fly past the Tugela Falls, the second highest on Earth at 947 metres and enjoy views of the Drakensberg. This range is a proclaimed World Heritage Site - the uKhahlamba. From the air we will also be able to see the post-Gondwana landscape and the phenomenal gorges that the eastward-flowing rivers have cut into the ancient African bedrock.

Join us then on a journey through 300 million years of Earth history, witness the breakup of Gondwana, the outpourings of lava and see the highest diamond mine on Earth. Perhaps the highlight will be to fly along the Eastern Escarpment past the Tugela Falls and the towering ramparts of the Drakensberg.

These are experiences which cannot be missed, and so we invite you to journey not only to one of the most picturesque towns in South Africa with its art galleries and restaurants, but on a journey down through the aeons, to a time when dinosaurs once ruled the Earth and Clarens was at the heart of a vast continent called Gondwana.

The Ancient of Days - Barberton

2008-12-22T05:57:00.011+02:00

Romancing the Stone

There is a piece of land on South Africa’s eastern escarpment so ancient that it beggars the imagination. We as humans work on another time scale entirely - our short lives are measured in decades and a time span of 2000 years seems so very very long ago. Five million years spans all of human evolution and even those numbers seem improbable. So to now tell you that rocks which underlie this piece of land have been dated at 3 538 000 000 years might indeed stretch your imagination. That number does indeed read as “three billion, five hundred and thirty eight thousand million years”. Whew! To set our own lives against this kind of timescale makes them appear entirely insignificant, and the history of mankind not much more so. But there is worse to come – they have discovered ancient gneisses in the Slave Province of Canada 4 billion years old, and a single zircon crystal from Australia has been dated at 4.3 billion years. But this is no dent to our national pride – we are still up there with the front runners and Barberton remains an earth scientist’s Mecca.

It is one of the few places on Earth where the Archaean (rocks of 2500 million years and older) is so well preserved and so easily accessible and at one stage we held the record for the oldest rocks on Earth. But let us not indulge in hubris here, remembering the insignificance of our allotted three score and ten years when compared against the background of this vast sweep of geological time.

The Barberton Mountain Land is characterised by rugged topography and deeply incised river valleys. It is shaped roughly like a giant ice-cream cone, with the mandatory cherry on top located at Badplaas and Komatipoort forming the tip of the cone (well, almost). It extends from the high African hinterland down to the Lowveld, including a portion of northwest Swaziland in its sweep.

The towns of Steynsdorp, Havelock, Horo, Kaapmuiden, Louw’s Creek and of course Barberton have the honour of being founded on this veritable Methuselah of the Earth’s crust and those who walk on it are treading on hallowed ground. Moving swiftly from the realm of the metaphor to that of the mundane, the limits of the zone and its simplified geology are shown in the accompanying figure.

To peer through the swirling mists of the deep abyss of geological time in an attempt to unravel what went before is an almost impossible task. To have remnant samples from this deep abyss preserved relatively unaltered is a gift in the process of unravelling the complexities of Earth history.

Without boring you unduly with lessons in geology, suffice it to say that the earth is in a constant state of flux. Mountains are thrust upward and then ground down by the inexorable mill of erosion. The crust beneath the ocean basins is created by fire at the mid-oceanic ridges and is then carried away towards destructive plate margins on massive convection cells at a rate ranging from 2.5 (the rate at which your finger nails grow) to 15 cm per year. There is no hurried agenda to the slow grind of Earth’s workings – she has all the time in the world to crank the workings of her machine. On average, oceanic plates will last no longer than 100 million years - they will be carried back down into Earth’s mantle along subduction zones – known as destructive margins - the most famous of which is the Ring of Fire encircling the Pacific. Similarly mountain ranges such as the Alps and the even mightier Himalaya were thrust skyward approximately 65 to 40 million years ago – the mountain building process in these regions is still ongoing. But they are being worn down by the agents of erosion, and in 100 million years will be reduced remnants of their former glory, nothing more than a detritus of sand and mud. Throw another hundred million years into the pot and there will be little left of the world which we currently know.

Two hundred million years may seem an immense span of time, but considering how crust, both continental and oceanic, will doubtless be destroyed and recycled in this time, then to have a 3.5 billion year remnant preserved right here in our own back yard is miraculous indeed.

The Barberton Mountain Land is indeed a remnant – a remnant adrift in a sea of granite, cast to the sharks of time and erosion, leaving her chewed and frayed around the edges. Two geologist brothers, Viljoen and Viljoen, wrote a paper in 1969 titled grandly “The Geology and Geochemistry of the Lower Ultramafic Unit of the Overwacht Group and a proposed new class of igneous rocks Komatiite, Upper Mantle Project.“ This if course all sounds very esoteric to most of us, but one has to read a little between the lines to understand the significance of what they had found. Some of you might remember in the mid 1990’s the discovery of a 90 kg, cowlike animal called a Saola in the jungles between Vietnam and Laos. This was the first land vertebrate of this size to be discovered for more than fifty years. Well, the discovery of a new type of igneous rock in the Komati Valley, and an extruded lava at that, was perhaps the geological equivalent of the discovery of the Saola, although it didn’t get anywhere near as much coverage in the popular press. The exciting thing is that the chemistry and mode of occurrence of this rock shed light on the geological conditions prevailing during the formation of Earth’s crust way back then, which until this discovery had been open to nothing but pure conjecture. Appropriately this rock was called a komatiite and several other occurrences have since been found elsewhere on the planet’s face, but it was here near Barberton that this ancient rock type was first brought to the attention of the geological world.

And what were conditions like 3.5 billion years ago? Well, we must add a little more flesh to the geological skeleton, otherwise we will be getting ahead of ourselves. Sitting on top of the ancient komatiites is an accumulation of volcanic lavas, limestones and shales. These rocks make up the Onverwacht Group, the first of three broad subdivisions of the geology of the Barberton Mountain Land. Overlying the Onverwacht is the Fig Tree Group; a sedimentary pile of material laid down in submarine conditions. Finally all is overlain by the Moodies Group which comprises quartzite (metamorphosed sandstone), sandstone and shales with occasional volcanic lavas.

The interpretation of conditions prevailing in the Archaean has been made based on studies of the BML and other greenstone belts around the world. Mantle heat flows were higher then than now. The chemistry and mineralogy of the komatiites indicate that they were erupted at relatively high temperatures compared to those associated with the eruption of younger basaltic lavas. Richard Fortey in his recent book titled Earth: An Intimate History, sums things up beautifully, describing prevailing Archaean conditions thus: “The nascent masses of continental crust had not yet congealed to their present size. Instead, smaller rafts of lighter rocks formed the nuclei of what would become more stable continental areas..…. The sea – and there was certainly an ocean – was whipped up by storms, reducing all land newly elevated by tectonics to sedimentary waste. Slabs of oceanic rock were covered with sediments derived from the rapid weathering of the protocontinents. Unprotected by any cloak of plants, the wind and rain worked fast upon the naked rocks. This was a world of tempests and flash floods, of jagged crags and dunes. Clays and grits, the mucky progeny of erosion, slumped down into deep water. Volcanic rocks were erupted over the sea floor….. Buoyed up by their less dense composition, the growing continents bobbed onwards, as would rafts of cork on a mill pool, while heavy ocean crust was created and then destroyed in the early cycles of plate tectonics.”

These interpretations of the processes which formed these ancient greenstone belts might quicken the pulse of earth scientists everywhere, but these events took place so far back in Earth’s history to be almost irrelevant to most of us here in the early part of the 21st Century. But two really important conditions prevailed which do affect us all. Firstly sedimentary structures in the form of sand ripples within the sandstones of the Moodies Group indicate deposition on tidal flats, and to have a tide, we must have a moon. So this is the first evidence of for the existence of the moon in orbit early on in our geological history. Secondly, and perhaps most importantly, on pondering our origins and our significance on this small blue planet of ours, it may be useful to remember that some of the first evidence of unicellular life occurs within the Onverwacht and Fig Tree Groups. Spheroidal or rod-shaped micro-organisms formed algal mats called stromatolites – a form of blue-green algae which changed the world forever. Back then the atmosphere was almost devoid of oxygen with hydrogen sulphide and methane being the dominant gases. Blue green algae, stromatolites included, added via the process of photosynthesis oxygen to the atmosphere, molecule by tiny molecule to create an atmosphere which sustains us all. But the evolution of life must have predated the deposition of the Fig Tree sediments and currently it is thought to have occurred around 3.2 billion years ago.

Having said all that, other than being of interest in terms of the origin of life and the fact that the moon was winging its elliptical path around our Earth 3.5 billion years ago, what other relevance does all this have to our lives? Well, internationally, Archaean Greenstone belts, as they are also known, are home to many of the world’s gold mines.

The four operating in the Barberton region are have the romantic names of Sheba, Consort, Fairview and a somewhat more down to earth name, Agnes. Gold was discovered in the headwaters of the Blyde Rivier in 1873 by “Wheelbarrow” Patterson which led to a gold rush and the founding of the town of Pilgrim’s Rest. The largest gold nugget (perhaps the term boulder would be more appropriate here), discovered in 1875, weighed in at 8.02 kilograms. But the gold rush days soon passed by when gold was discovered in the Witwatersrand gold fields 12 years later.

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Vredefort Impact Site - Ground Zero

2008-12-22T05:43:00.004+02:00

Romancing the Stone

Wandering through the long grass around the village of Vredefort, Free State, South Africa, the casual observer would not have the slightest inkling that this is Ground Zero of the largest meteorite impact on Earth. Low quartzite ridges provide the topographical interest with valleys in between. From the air the picture becomes somewhat clearer; as a series of concentric topographic ridges with intervening valleys become apparent, best developed in the northwest of the area. In geological parlance this is a “dome” – an approximately circular area of Earth’s uplifted crust, dipping away from the centre, and in our case 80 km in diameter. To explain the enormity of this event a little stratigraphy is necessary at this point and perhaps a good analogy is a multicoloured cake. The adventurous chef has placed pink sponge at the base, and then covered with alternating layers of chocolate and vanilla sponge. The pink represents the ancient granite which underlies 1000’s of square kilometres of real estate around the dome, and the alternating coloured sponge layers the younger sedimentary cover. At Vredefort the layers of the cake are stood on end, with the pink granite sponge protruding through the overlying layers. Returning to the scale of the real world, this is the equivalent of 20 km thickness of rock being upturned and the granite punching through to the surface. This is, to use an overused but appropriate word, awesome. Back on the ground, evidence of some kind of cataclysmic event having occurred here is to be found in the form of two rock types known as pseudotachylite and granophyre. Shatter cones and spectacular fracturing the rocks also are witness to this event. Tachylite is a form of glass found in volcanic environments, which the material in the dome resembles, although this is clearly not a volcanic environment, hence the prefix ‘pseudo’. Pseudotachylite is almost ubiquitous throughout the dome and occurs in veins from less than 1 mm to up to 100 metres thick. The Vredefort granophyre, a brecciated rock, has as part of its composition a glassy matrix indicating instant melting and rapid cooling. In fact both of these rock types are the product of shock-induced melting. The granophyre occurs as large dykes, several kilometres long and many metres wide with a composition different to any other known rock and containing fragments of extraterrestrial material. Then there are the shatter cones – concentric, conical structures the result of the almost instantaneous shock wave so intense as to shatter and melt hard, competent rock. And in the process to overturn a thickness of 20 km of granite and lithified material.

The 80 km diameter of the dome represents only the uplifted, central part of the impact crater and by extrapolating from other known impact craters on the Earth and the moon, a figure of 300 km diameter for the Vredefort crater is arrived at – the largest impact crater on Earth. As a student in the late 1980’s there was much speculation as to its origin, and geologists, being essentially romantics at heart, adopted the meteorite impact theory. However, absolute, conclusive evidence was lacking but thanks to the careful work of Uwe Reimold and his team from the University of the Witwatersrand, conclusive evidence was provided to sustain this theory, enough for it to be declared a World Heritage Site in 2005, as Earth’s oldest and largest meteorite impact crater. How old is it? Just over 2 billion years, which is just under half the age of Earth. Fortunately life was still in its infancy then and the impact, although cataclysmic, did not cause the damage that better known and more recent collision events had on the biosphere.

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The Age of the Earth - Episode 3

2008-12-21T19:36:00.006+02:00

Newton then swept away Descartes’ imprecise theories with his Principia – the laws governing the motions of the heavenly bodies were now defined in minute detail. However his seems to have wasted his intellect and the latter years of his life trying to tie the history of ancient kingdoms and biblical chronology into the record of astronomical events – eclipses and the arrival of comets – but with extremely limited success.

Isaac Newton

His friend Edmond Halley then came up with the theory that the age of the Earth could be estimated by the amount of salt in the sea. By measuring the rate of increase of the sea’s salinity, and assuming that salt had been washed into the oceans at a constant rate, it would be possible to work backward to a time when the seas contained no salt at all, which would then give the age of the Earth. In 1715, this was a fantastic idea, but no one, least of all Edmond Halley, knew how to measure increases in salinity year on year, and he concluded that the observations would need to be made a century apart to be meaningful. However Methuselah, in spite of his famed longevity, was no longer alive, so this was impossibility.

Georges Louis Leclerc Buffon was the next to estimate the age of the Earth. He was well connected with the French court and had the ear of several of the crowned heads of Europe. Clever, hard working, and somewhat eccentric, he proposed the idea that the Earth’s age could be estimated by the rate at which it cooled.

Georges Leclerc Buffon

He heated up metal spheres and then estimated the rate of heat loss as they cooled, and then extrapolated this to the larger Earth, settling on the age of 75 000 to 168 000 years. This was a quantum leap from the 6000 year old theory and he nearly got excommunicated for his troubles. Being a politically astute animal, he recanted his heresies but then proceeded to repeat his assertions for the rest of his days.

Charles Darwin, apparently unhappy with creating controversy, but brave enough to do so anyway, suggested that the Earth was 300 million years old. This date proved so contentious that he actually withdrew it from his Origin of the Species. The great Lord Kelvin, who towered over Victorian science like a colossus, took Darwin to task for some of his assertions, and declared that the Earth cold be no older than 24 million years, which were downward revisions of an original figure of 400 million. However, in spite of Kelvin’s phenomenal intellect, he was not aware of the invisible heat source deep with the Earth – radioactivity – which drives the engine of our planet. Radioactivity is a concept to which we have become accustomed to thanks to the popular press, nuclear power and its use in the medical field. But is Kelvin’s day it was still unknown, and it was thanks to the pioneering work by Marie and Pierre Curie that radioactive material was first recognised and isolated. Earnest Rutherford then provided the world with an explanation of how it all worked, and of the energies released in the process – which then provided a mechanism for keeping the interior of the Earth at elevated temperatures. Other great names of nuclear physics come from this time – Bohr, Heisenberg, Thompson, Chadwick and of course Einstein. The properties of the atom and the elements became increasingly understood as well as the chemistry and isotopes of radioactive elements.

This understanding of radioactive half lives became fundamental to the dating of rocks, Professor Arthur Holmes of Durham University took up the cudgels and pioneered the methods which are used to this day. The technique was based on Rutherford’s 1904 work, when he discovered that atoms decay from one element into another at a rate predictable enough to allow them to be used as clocks.

Arthur Holmes

Holmes measured the rate of decay of uranium to lead, and used this to calculate the age of the Earth. In spite of a lack of funds and sophisticated equipment, he announced in 1946 that the Earth was at least 3 billion years old. His methods met with praise, but his date was not. But he was far closer to the mark than Kelvin had been.

Building on Holmes' pioneering work, Clair Patterson of the University of Chicago took up the challenge. The problem with dating the Earth is that one needs rocks almost that old, and these are rare thanks to the ongoing cycling of crust due to plate tectonics. In addition one needs uranium-bearing crystals within these rocks. Patterson made the assumption that if all the lead on Earth came from radioactive decay, then it would be easy to find the age of the Earth. The more lead a rock contained, the older it had to be. In reality all the lead on Earth did not come from uranium and it was impossible to separate out the ‘primordial’ lead – that which had been around from the creation of the Earth, from that derived from radioactive decay. To sidestep this thorny issue, another brilliant assumption was made, that meteorites were left over building material dating back to the early days of the solar system, and thus their lead content would be the same as that of the early Earth. Perhaps more importantly they contained no uranium to upset the clock. None of the lead in meteorites then would have come from radioactive decay. Harrison Brown, Patterson’s doctoral supervisor said this to him:

“Pat, you just go in and get an iron meteorite – I’ll get it for you. We’ll get the lead out of the iron meteorite. You measure its isotopic composition and you stick it into the equation. And you’ll be famous, because you have will have measured the age of the Earth.”

Clair Patterson

It took Patterson 7 years to build a completely lead free laboratory and to obtain a result, which dated the Earth at 4550 million years. After three hundred years we had at last a date for the beginning of the World. And that figure still stands to this day.

The Age of the Earth - Episode 2

2008-12-21T18:13:00.012+02:00

Firmly entrenched and supported by the church, Ussher’s date seemed impregnable. However, some sceptics put forward their own versions. A French Calvinist and lawyer, La Peyrere in 1641 postulated that there had been people on Earth before Adam. This was heresy and of course was banned by Cardinal Richelieu, the prime minister of France. Essentially a pragmatic and fair man, he however realised what effect La Peyrereses manuscript might have in France. La Peyrere kep this freedom, but he did not desist with his theories, eventually in 1655 invoking the wrath of the Catholic Church. He was arrested, interred and forced to recant his heretical views – in short he got off lightly. Enter another player on this grand stage – a Jesuit missionary, Farther Martino Martini, who was carrying out missionary work in China.

Martino Martini

On telling the Chinese that mankind had been destroyed by God in a great deluge, they greeted his pronouncements with great hilarity and disbelief. Their own history stretched well beyond the so-called date of the Flood, and they had records to prove it. A reversal of roles took place, with Martini realising that the ancient Chinese chronology posed a serious challenge to the authority of the bible. In 1654 he returned to Europe, where he published an account of Chinese history, receiving of course the usual disbelief and hostility which marked all other controversial ideas perpetuated at the time. However arrest and persecution was out of the question as Martini had returned to China to further his missionary work. Europe continued her dyed-in-the-wool approach, but slowly thinking was evolving, with crucial intellectual shift away from biblical textual authority towards an enquiry based on scientific principles. Throughout Europe the cry was the same: rocks, not books were believed to hold the secrets of the past. And indeed they did, and still do, and it was left to the natural philosophers to prove the age of the world.

One of the more interesting notions of the 17th Century was that the Earth had been created fully formed; flat, beautiful, unblemished, with no disease, famine, mountains or deserts to blemish her perfect face. A golden age had existed before the Flood, and age when all God’s blessings were poured out onto the world – in short a perfect God had created a perfect world. But now things were in decline – the Earth had become old and wrinkled, volcanoes and deserts were carbuncles and scars on the face of the Earth. An old prophecy that the world would last only 6000 years was being confirmed by nature. The thinking was that the Earth had run most of its days, and doomsday was not far off, perhaps only 350 years in the future (taking of course the date of 4004 BC as the day of creation).

However this idea of an ageing Earth brought the notion of a world in flux and a constant state of change to the fore, and it was Rene Descartes who lead the break with the literal interpretation of the bible. Reason was the reason de etre. Paris, 1625, and our clever and sociable Descartes had become the leading light of Parisian intellectual life – a time when libertine free thinkers were making their mark. Caution was always necessary and a weather eye was kept open for gathering storm clouds in the direction or Rome. One Giulio Vanini, a ‘heretic’ doctor, had had his tongue cut out before being strangled and burned six years before for voicing some anti religious views. Inevitably the storm broke and Descartes moved to Holland, a country which has always had a tradition of tolerance and liberalism which endures to this day. He began his philosophical treatise, The World, which was to be a completer revision of philosophy which he eventually published in 1641.

Rene Descartes

However it was a watered-down version of his original manuscript as it was a bad time for liberal thinkers. Galileo had recently been arrested and forced to recant his heretical views that the Earth went around the Sun. Descartes’ view of the world was essentially that a few simple laws governed the universe, and these laws were what created the complex world around us. The world had the same relationship to God as a clock had to the clock maker – once it had been carefully constructed and set in motion, there was little more involvement from the creator. His ultimate achievement was to remove God from the day to day running of the world. Until then the belief was that God was intimately involved in the day to day, minute to minute running of the world. God may have created the world, but it was then governed by the laws of nature.

To be continued.......................

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The Age of the Earth – Episode 1

2008-12-21T14:52:00.004+02:00

All this frantic subdividing and classifying based on rock types and fossil assemblages allowed for a systematic assessment of the order of the ancient strata. Relatively, those early geologists knew which rocks preceded others, but no one had the faintest idea how old they were in absolute terms. Which brings us to some of the other great controversies of the geology which raged from 1650 to the middle of the 20th Century. Two thousand years ago the idea that the world might have a starting point was inconceivable. Most of the ancients believed that the Universe had existed forever, and that recurring cycles of creation and destruction were part of the clockwork which was so evidently displayed in the endless cycling of the heavenly bodies overhead – clear manifestations of the cyclical machinations of the Universe. The Hindus believed that the shortest cycle, the Maha Yuga, lasted 4320 000 years. A thousand Maha Yugas made up one Kalpa, and two Kalpas completed a single day in the life of Brahma. After this, eveyone was reincarnated and the cycle repeated.

Similar ideas were manifest in ancient Greece, and Plato suggested that the length of a cycle was defined by the time it took for all the planets to return to their same relative positions in their orbits, which they had occupied at an earlier time. This time period of 36 000 years was known as the magnus annus – the great year. However just one civilisation in the ancient world ascribed to a different idea – that the heavens and the Earth had been created by God, and that there was a beginning. This Jewish notion was adopted by Christianity, and with the concept of a beginning now firmly planted in the thinking of the Christian world, it was only a matter of time before someone attempted to set a date to it.

The most influential was Bishop Ussher who set it at 6 pm on Saturday, October 22, 4004 BC. We may well pour scorn on this date but there are those who still subscribe to this improbably precise reckoning and it may still be seen in the margins of some old bibles printed around the turn of the last century. Bishop Ussher was no fool mind you. The genealogy of the book of Genesis, the biblical account of creation of the world, runs to 21 generations. Precise dates of the lengths of the lives of the various protagonists are also given, and by totting up the numbers on can arrive at a precise date of creation. This is exactly what Ussher did. No one was more qualified than he, having learned Latin as a boy, and after joining Trinity College in Dublin in 1593, he pursued the date relentlessly, teaching himself Hebrew and Greek so as to better understand the ancient texts from which he was working. He built up Trinity College’s library into what was probably the largest collection of learned works in the world at the time – a total of 4000 volumes. He himself owned 10 000 at the end of his life. He had access to the libraries of London, Cambridge and Oxford, and rubbed shoulders with the free thinkers of the time – Frances Bacon and Ben Jonson.

In 1624 at the age of 44 he was appointed Bishop of Armagh, the most senior position in the Church of Ireland. Issues of which version of the Bible to use in determining this date – for example the Greek-derived Septuagint Bible used by the Orthodox church gave dates which stretched back almost 1000 years earlier than the Hebrew-derived Bible. Adding to the difficulties was the fact that different nations had different ideas as to how long a year actually was, and different dates for the beginning of the year. In addition, astronomical records were used to help tie down dates. For example the date of the birth of Christ was based on the following account:

“As for the other Mathias who had stirred up the sedition, Herod had him burnt alive, together with his companions. And that very night there was an eclipse of the moon.”

The thinking was that Jesus must have been born before this date, and that the great astronomer Keppler leant his weight to this argument, opting for the date of March 14th 4 BC, which is in fact the accepted year of Jesus’ birth today. Ussher’s consulted far and wide, had agents in the Near East buying up ancient texts, and devoted his entire life to the quest. Secular problems also intruded into his world, including rebellion in Ireland and dodgy political connections in England which led to his arrest during the English Civil War. If Cromwell was ready to behead King Charles I, what qualms would he have about severing the head of a mere bishop? Ussher managed to weather these storms to the extent that he was given a state burial by Cromwell, so esteemed was he in Irish and English society. Certainly he was a formidable scholar and made maximum use of the resources available to him, and although we can look on at his date with faint amusement, we must remember that he was a product of his age.

The 4004 BC date may have fallen into obscurity if it hadn’t been added to the bible by a bookseller and printer, Thomas Guy. In 1675, in a simple marketing ploy to boost sales, Guy added the date into the margins of his bibles, which worked fantastically, making him a rich man. The subtle twists of fate are in fact quite breathtaking, for Thomas Guy bequeathed his fortune to Guy’s Hospital – an institution which has provided medical care for over 300 years. In 1701, the date received the official blessing of the Church of England.

The Origins of the Science of Geology

2008-12-21T14:14:00.016+02:00

Romancing the Stone

Humankind has had an intimate association with the Earth from the first tentative footsteps of those early hominids to our current insatiable need for minerals and fossil fuels. Undoubtedly our early ancestors were aware of geological deposits, whether they were a source of flint for hand tools or clay for cave paintings or body adornment. Once the origins of the science stretch way back into the early history of man. Adobe to build dwellings or the source of ochre for cave paintings may have been the first venture into sources of materials for the use of mankind. Later stones and clay would have become important as building materials or for brick making. Certainly the ancient Egyptians were using bricks in their less ambitious constructions. And to deny that there was no understanding of the local geology when it came to the quarrying of stone for the Egyptian pyramids would have been naive indeed.

Herodotus, 484 to 426 BC, made many significant geological observations, speculating about the effect of earthquakes on landscapes, but ascribed their causes to Poseidon. Pliny the Elder (AD 23 to 79) lost his life tramping around the slopes of Vesuvius during the eruption that destroyed Pompeii. His reasoning was that earthquakes were a result of Earth’s resentment against those that mutilated and plundered her for gain. Christianity put scientific enquiry literally into the dark ages due to an all encompassing theory for the cause of everything, and besides it was thought that the Earth was a very young place, doomsday was nigh, and therefore the study of the machinations of the planet would be a pointless exercise. Inconsiderately doomsday did not arrive which got some individuals wondering about the natural world. In addition the increasing preoccupation during the Middle Ages with alchemy kick started a scientific process which continues to this day. Leonardo da Vinci, Nicholas Copernicus, Galileo Galilei, brave and brilliant philosophers and scientists all, drove some of the first nails into the coffin of ignorance, holding high the light of knowledge for those who would see.

However the first real attempt on a treatise on geology was made by Scottish farmer James Hutton in an inaccessible 1795 tome titled ‘A Theory of the Earth with Proofs and Illustrations.’ He might have passed into geological obscurity if it wasn’t for a certain John Playfair who rewrote the book on Hutton’s death, making it possible for mere mortals to grasp the concepts that Hutton had so obscurely written about. At that time natural philosophers were divided into two camps – the Neptunists, who believed that everything on Earth, including sea shells on lofty peaks, were due to rising and falling sea levels, and the Plutonists, who noted that volcanoes and earthquakes continually changed the face of the planet and that seas were not the agents which the Neptunists believed. Plutonists also raised difficult questions such to the whereabouts of all the water during periods of tranquillity, a period we are experiencing now.

Hutton’s insights threw some light on the matter, thanks to his keen eye and a close identification with the land thanks to his farming background. He observed the formation of soils, and their erosion and transport to other locales. He realised that over time this erosion of the high ground and the infilling of the lows would leave a planet smooth and devoid of topography. However everywhere he looked there were hills and mountains, particularly so in his native Scotland. He realised that there had to be some process that renewed and uplifted the landscape the keep the cycle going. Those pesky fossils on the mountain tops had not been deposited by floods, but had been lifted there, along with the mountains themselves. Heat within the Earth was the driving force of all this activity, or so ran the thoughts of Mr Hutton. Interestingly some of these thoughts have only been vindicated in the last 40 years or so. More importantly however was the idea that these processes required immense periods of time – far more than anyone had as yet ever conceived.

At the same time, down south, William Smith was building canals and draining bogs for a range of clients as part of the expanding infrastructure driven by the Industrial Revolution. During his daily work he uncovered a myriad of fossils, and realised that each succeeding geological bed or formation had its own particular assemblage of preserved organisms. Spending huge amounts of time and money, he travelled widely across vast swathes of England and to some extent Scotland, mapping the various outcrops of the various strata wherever he went. His exertions damaged his health had his finances to the extent that he even spent time in a debtors gaol, and perhaps even more galling for him, his work was discounted and ridiculed by the supercilious aristocrats who had formed the Geological Society of London in 1807.

However an examination of the map that Smith produced and now hangs in the Society’s headquarters in London reveals his genius. His map shows in amazingly accurate detail the geology of the British Isles and was the first ever geological map. Singlehandedly Smith had mapped out what the British Geological Survey, with hordes of geologists and government funding, couldn’t really improve on except by adding detail. And in a true Hollywood ending, Smith was eventually accepted and then lauded by the Society, and was granted a pension in his latter years, putting off forever the spectre of a debtor's prison and a difficult retirement.

Charles Lyell then enters the stage. He had managed to wade through chunks of Hutton’s book, and was eternally grateful to Playfair for rewriting the work into something approaching readable. Lyell was the most influential geologist of his century, which was a time incidentally when the world was in thrall to all things geological. Geology was the central science and the older Royal Society was in danger of being eclipsed by the upstart Geological Society as the premier scientific society of the country, which at that time also meant the world. So popular was the science that when Charles Lyell travelled to America to lecture, 3000 people showed up to be enlightened on ponderous subjects such as marine zeolites and seismic perturbations in Campania. Back home, modern, thinking men would venture forth to do fieldwork dressed in top hats and dark suits, except for a Reverend Buckland of Oxford who preferred an academic gown. Lyell produced his masterpiece, The Principles of Geology, which built on the works of Hutton of a previous century and made his reputation. Charles Darwin carried a copy of his book on the Beagle voyage, writing afterwards “the greatest merit of the Principles was that it altered the whole tone of one’s mind, and therefore that, when seeing a thing never seen by Lyell, one yet saw it partially through his eyes.”

Between the time of Hutton and Lyell there arose another controversy that followed on from the great Neptunist-Plutonist debate. New lines were drawn between the Catastrophism and Uniformitarianism camps. The former adhered to the idea that the Earth was shaped by cataclysmic events – floods, mainly, while the latter camp believed that changes on Earth took place over immense periods of time. The Catastrophists found that their theory worked in well with the Noachian deluge and therefore did not fly in the face of any biblical beliefs. Lyell was a Uniformitarian and his influence remains right down to the present day. As an interesting aside however, rude Catastrophist brickbats still whizz down the passage of 2 centuries to strike at the very heart of Uniformitarian belief. These brickbats comprise meteorite impacts which are widely believed to have brought to a close the Cretaceous Period and the demise of the dinosaurs, and have been invoked as the cause of a number of other extinctions in Earth history.

Because the Brits were the most active in the early years of the science, British names were assigned to the geological time scale. The Devonian Period is named after Devon, the Cambrian after the Roman name for Wales, and the Ordovician and Silurian after ancient Welsh tribes, the Ordovices and the Silures. However other names began to creep in from practitioners elsewhere – Jurassic from the Jura Mountains of southern France, Permian from the Russian province of Perm while the Cretaceous was named by a certain J.J. d’Omalius d’ Halloy of Belgium.

Initially the geological time scale was divided into 4 spans – Primary, Secondary, Tertiary and Quaternary. The Tertiary is the last surviving member of this initial subdivision, although Quaternary does get a period outing. Lyell introduced additional units known as epochs or series to cover the period since the end of the Cretaceous. These were the Pleistocene, meaning ‘most recent’ Pliocene, the ‘more recent’, Miocene, ‘moderately recent’ and Oligocene ‘but a little recent.’ Nowadays geological time is divided into four great chunks known as eras – Precambrian, Palaeozoic, Mesozoic and Cainozoic, which in turn are divided into Periods which some of you may be familiar with, viz., Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, and Cretaceous. (Camels Often Sit Down Carefully Perhaps Their Joints Creak is a useful acronym for remembering them).

Romancing the Stone

Ground Zero - Vredefort Dome Meteor Impact Site

2008-12-03T10:12:00.000+02:00

Winging its way in at 70 km per second from somewhere in the asteroid belt, the meteorite, at 15 km in diameter is the largest and deadliest object to ever strike Earth. At ground zero the destruction is unimaginable, as a concentric shock wave propagates outwards at supersonic speed for a distance of over 300 km. The ground heaves, and where there was once solid rock, now there is molten glass, where there was once stable atmosphere, there is now a column of dust and ejecta towering thousands of metres into the afternoon sky. Ejecta and ash billow in vast, debris laden clouds, casting a doom-black pall across the land. The sun, as if bending down to look onto the face of the Earth, gazes impassively at her blighted face, while hot winds toss the dark clouds across the crimson disk before going out with the light.

Wandering through the long grass around the village of Vredefort, Free State, South Africa, the casual observer would not have the slightest inkling that this is Ground Zero of the largest meteorite impact on Earth. Low quartzite ridges provide the topographical interest with valleys in between. From the air the picture becomes somewhat clearer; as a series of concentric topographic ridges with intervening valleys become apparent, best developed in the northwest of the area. In geological parlance this is a “dome” – an approximately circular area of Earth’s uplifted crust, dipping away from the centre, and in our case 80 km in diameter. To explain the enormity of this event a little stratigraphy is necessary at this point and perhaps a good analogy is a multicoloured cake. The adventurous chef has placed pink sponge at the base, and then covered with alternating layers of chocolate and vanilla sponge. The pink represents the ancient granite which underlies 1000’s of square kilometres of real estate around the dome, and the alternating coloured sponge layers the younger sedimentary cover. At Vredefort the layers of the cake are stood on end, with the pink granite sponge protruding through the overlying layers. Returning to the scale of the real world, this is the equivalent of 20 km thickness of rock being upturned and the granite punching through to the surface. This is, to use an overused but appropriate word, awesome. Back on the ground, evidence of some kind of cataclysmic event having occurred here is to be found in the form of two rock types known as pseudotachylite and granophyre. Shatter cones and spectacular fracturing the rocks also are witness to this event. Tachylite is a form of glass found in volcanic environments, which the material in the dome resembles, although this is clearly not a volcanic environment, hence the prefix ‘pseudo’. Pseudotachylite is almost ubiquitous throughout the dome and occurs in veins from less than 1 mm to up to 100 metres thick. The Vredefort granophyre, a brecciated rock, has as part of its composition a glassy matrix indicating instant melting and rapid cooling. In fact both of these rock types are the product of shock-induced melting. The granophyre occurs as large dykes, several kilometres long and many metres wide with a composition different to any other known rock and containing fragments of extraterrestrial material. Then there are the shatter cones – concentric, conical structures the result of the almost instantaneous shock wave so intense as to shatter and melt hard, competent rock. And in the process to overturn a thickness of 20 km of granite and lithified material.

The 80 km diameter of the dome represents only the uplifted, central part of the impact crater and by extrapolating from other known impact craters on the Earth and the moon, a figure of 300 km diameter for the Vredefort crater is arrived at – the largest impact crater on Earth. As a student in the late 1980’s there was much speculation as to its origin, and geologists, being essentially romantics at heart, adopted the meteorite impact theory. However, absolute, conclusive evidence was lacking but thanks to the careful work of Uwe Reimold and his team from the University of the Witwatersrand, conclusive evidence was provided to sustain this theory, enough for it to be declared a World Heritage Site in 2005, as Earth’s oldest and largest meteorite impact crater. How old is it? Just over 2 billion years, which is just under half the age of Earth. Fortunately life was still in its infancy then and the impact, although cataclysmic, did not cause the damage that better known and more recent collision events had on the biosphere.

The Carbon-Silicate Cycle.

2008-12-03T07:34:00.005+02:00

A recent study by scientists at Columbia University have come up with an interesting method of removing atmospheric carbon, the aim being to reduce greenhouse gases and global warming. When CO2 comes into contact with peridotite, a rock commonly found in the Earth’s mantle, but more rarely at surface, it is converted into inert and solid minerals such as calcite. The Sultanate of Oman has vast quantities of peridotite exposed at surface and geologist Peter Kelemen and geochemist Juerg Matter claim that the naturally occurring process can be supercharged to grow underground minerals that can permanently store two billion tons of CO2 emitted by human activity every year. Source –Reuters/IOL Timothy Gardner

Al Gore has been campaigning for reductions in greenhouse gas emissions, and the Kyoto Protocol expires in 2012, and yet we are no closer to getting any meaningful reduction in greenhouse gas emissions. However I am not going to take up the climate-change cudgels at this stage, but will dwell rather on an amazing system which, over the long term, ensures that Earth’s climate remains within certain limits which keeps our planet habitable – the carbon-silicate cycle. We might be able to negatively influence climate over the space of centuries or even decades, but if we look at the issues from a geological point of view, these human-induced perturbations in the grand sweep of geological cycles are inconsequential, and will not affect the long-term fecundity of the planet. We may however suffer tremendously during these short-term perturbations – an increase in 5 degrees will make vast portions of our planet uninhabitable. Our distorted sense of importance as a species causes us to fret about our future on Planet Earth, but if we can accept that our predominance might be nothing more than a lucky roll of the evolutionary dice, and that the survival of the human species is inconsequential to future of the planet, then we can to some extent stop worrying about our supposed role in the grand scheme of the universe. Whether we like it or not, we will ultimately go extinct, but life in a myriad of different forms will continue through to the sun’s ultimate supernova. But let us move on from philosophy and speculation to some hard facts concerning our immediate environment and how Earth’s climate is kept within those all important limits. Most of us are aware of continental drift and plate tectonics, where Earth’s crust is recycled by subduction of plates along the plate margins. The sinking plate descends into the fiery interior of the Earth where it is melted, and its constituent elements returned to the rock cycle via volcanic action. One of the most important elements in this cycle is calcium, used widely by organisms, including humans, to build shells and bones. Add some carbonic acid to the mix and one gets the formation of calcium carbonate – CaCO3 – the most prevalent form being limestones.

Limestones are one of the most common sedimentary rocks and generally represent ancient coral reefs preserved in the geological record. The development of coral reefs sequestrates vast quantities of atmospheric carbon for millions, sometimes billions, of years until the limestones get caught up in the tectonic mill or become exposed to the agents of weathering and erosion. The more CO2 there is in the atmosphere, the faster limestone formation will occur, provided there is sufficient calcium available. Question is, what is the source of the calcium? It is derived from igneous, sedimentary and metamorphic rocks brought to the surface by volcanic action due to plate tectonics. The same eruptions that spew CO2 into the air deliver the chemical necessary to remove it, thereby keeping things in balance. Wow!

Now we need a source of the carbonic acid. The weathering of silicates – feldspars and micas – in common rocks such as granites and sandstones produces calcium, silicon, water and the all important carbonic acid. Now, as we have already seen, the more CO2 there is, the faster limestone forms, thereby removing the same CO2 from the system. Similarly the higher the concentration of CO2, the warmer the planet gets – an unfortunate fact which we are discovering to our cost. This leads to increase in evaporation which leads to increased rainfall and associated increase in weathering. The greater the amount of weathering, the greater the formation of carbonic acid, which in turn leads to faster limestone production. This of course speeds up the removal of the CO2 from the atmosphere, ultimately cooling the planet. Cooling then reduces the rate of weathering, carbon levels rise and Earth warms once again. What a wonderful, self regulating, fantastic, system! But it takes more than a few decades or centuries to smooth out the variations in atmospheric carbon. Cold comfort perhaps to know that ultimately the high carbon levels in the atmosphere will be removed by the carbon-silicate cycle.

For those who want to know more on the doomsday predictions for Earth, get the book The Life and Death of Planet Earth by Peter Ward and Donald Brownlee. An interesting read, although nothing to be alarmed about as real trouble is only coming some way into the future.

The Coal Reserves of Mozambique

2008-12-03T07:25:00.000+02:00

The day dawns cool but even in the early light the sky is burnished brass and the sun a red orb through the Mopani and Baobab trees, heralding the scorching temperatures to come. Not that one wakes to the sounds of the bush – the cockerels have been crowing since 04:30, the guinea fowls chirruping not much after that, and a generator has been thumping away in the neighbouring driller’s camp since 5 a.m. Six a.m. finds us nursing cups of tea around the fire, talking shop as one is apt to do in these environs, and contemplating the day’s work ahead. Home is tent town, but actually quite civilised – there is a beautiful grass-thatched lapha, open to the four winds, with a concrete floor, dining table, DSTV and a couch and an adjacent kitchen tent. Fridges and freezers whirr away while the periodic clunk of the ice maker as it dumps another load of ice into its frigid innards punctuates the morning. Concrete paths lead to tents, the shower block or to garages, coresheds and stores. Seven p.m. and everyone goes their way – to the core sheds, to the drilling rigs, to the ‘office’ to beaver away in proving the vast reserves of coal which underlie this entire region and outcrop at surface in the river bed not 30 metres from the camp. This is our source of fuel for heating up the donkey boilers for our hot water. All that is required is a wheel barrow and a pick to dig the coal out, and a bit of legwork to push it up to the shower block. This might almost be construed as a free lunch.
The coal reserves of Tete Province have been described as the largest unexploited coal reserve in the world. Deposited in ancient forests over 300 million years ago, they have lain essentially unsullied until now. Evidence of ancient life lies everywhere, not least being the coal, but in places one can see the distinctive imprints of Glossopteris leaves fossilised in the ancient sandstones. Glossopteris was the Gondwana tree, found across India, Southern Africa, Australia and Antarctica, which made up the majority of the biomass from which the coal was derived. A number of exploration concessions have been granted to Australian, India and UK based mining houses and the race is on to get the first Mozambiquan coal out of ground and to the port. Which is a logistical nightmare in itself, as the bridge over the Zambezi at Tete has been officially condemned thanks to a Russian commander driving his tanks over the structure, exceeding its design loads and damaging it forever. Then there are the terrible roads down to Beira to contend with, which can only get worse as they fall to pieces due to the excessive loads of coal trucks. But the reserves need to be proven which is what brought me to Tete Province and the life of a coal geologist.

Occasionally we make it up to Songo, which is the town adjacent to the Cahorra Bassa Dam and 25 km distant from our life in the bush. Higher, cooler, and relatively civilised, it overlooks the amazingly beautiful Zambezi gorge. The dam is awesome and the lake stretches back 250 km. The bream straight out of the lake are delicious and one of the highlights of life in the vicinity of Songo. But there is not much time to go sightseeing or fishing, and we spend all of our time not more than 2 km from the camp. A morning walk out into the Mopani woodlands and baobabs is welcome relief from the tedium of the camp, and a climb into the ancient granite hills to the north of the concessions reveals vast tracts of Africa, punctuated by Baobabs and the ubiquitous power lines which hum south-eastwards towards South Africa.

And that is why it has been a while since my last missive – stuck in the bush without easy access to emails and the internet, and without much spare time for that matter either. But it was an interesting few weeks and certainly Mozambique is in many ways the land of opportunity.

High Water

2008-07-24T16:06:00.000+02:00

Coral fronds wave gently in the ocean currents, occasionally more agitated by the passing of a larger swell nearing the shoreline. Brightly coloured fish, swimming in vast schools, dart amongst the coral heads while their larger counterparts swim sedately along the drop-offs, silhouetted against the deep blue of the ocean depths. Eels lurk in the caves and overhangs, making occasional forays out into clear water on the never-ending quest for prey. The reefs are encrusted with star fish and sea urchins and the long tentacles of crayfish protrude from beneath the rocky overhangs. In the upper sunlit zones ammonites jet their way through the water, their large, squid-like eyes taking in the details of their watery realm, their tentacles trailing behind them as they propel themselves through the warm, blue seas. Sharks proliferate, circling in schools near the surface, or hunt in solitary stealth in the deep blue vastness of the oceans. A plesiosaur swims by, momentarily blocking out the darting rays of the sun as it surfaces and surveys the airy world above the waves. Out on the sand banks between the reefs marine snails or gastropods and bivalves make their living on the sandy substrate.

These are Cretaceous seas, the time period stretching from 142 to 65 million years ago. It is more famously known for its dinosaurs – Tyrannosaurus Rex, Triceratops and Brachiosaurus to name just three – but life here in the oceans was no less prolific, with coral reefs covering vast areas of shallow oceans. Global sea levels were elevated during this period thanks to high global temperatures and much of the low-lying regions of the continents were inundated by ocean. The term Cretaceous, which has been assigned to this geological period, derives from the Greek for chalk. Coral reefs are made up predominantly of calcium carbonate, and over time they may become preserved in the geological record as limestones and chalk beds, perhaps the most famous of which are the White Cliffs of Dover. Here in South Africa a narrow seaway had formed along the eastern margins of the continent due to the ongoing movement of the tectonic plates. Blue, tropical seas encroached upon the land from just south of Durban to north of the Mozambique border, and regions of the Eastern and Southern Cape coasts. Boreholes drilled into the Cretaceous sediments in Durban harbour and Richards Bay reveal thick accumulations of shells and other marine organisms. One doesn’t need to drill boreholes at St Lucia, as the Cretaceous is exposed along the lake shores and at Hell’s Gate. Fossil ammonites occur in abundance here and a fine example is to be found outside the entrance to the offices at Charters Creek. Ammonites ranged in size from a few centimetres across to massive specimens up to 1 metre in diameter, but to our eternal loss, the ammonites went extinct, along with the dinosaurs, at the end of the Cretaceous, and the only surviving member of the species is the nautilus – that beautifully spiralled shell which graces the shelves of tourist shops across the world.
Cretaceous rocks form reservoirs for the entrapment of oil, and much exploration has taken place along the South African coastlines since 1965. Although much of the drilling has been unfruitful in terms of oil, the borehole data has been highly instrumental in understanding Cretaceous geology. Gas reserves were found off Mossel Bay and these are currently being exploited, while ongoing exploration for oil continues on the continental shelf.
The idea that the dinosaurs were wiped out by a massive meteor impact has become part of popular culture. It is one of those cataclysmic, apocalyptic endings which we as a species seem particularly fond of, which is perhaps the reason for its mass appeal. Geological theory is based on the theory of Uniformitarianism, whereby the processes which make our world take place over millions of years, and that the processes in operation today were similar to those of the past. In the early days of the science there was a protracted battle between the Uniformitarians and the Catastrophists, who ascribed to the theory that the Earth was created by a series of catastrophic events. The Uniformitarians won in the end, but the notion of a catastrophic impact leading to the demise of the dinosaurs and marine life is part of the Catastrophist creed, and it is irony indeed that, 150 years later, geologists had to accept the role of catastrophes in the geological evolution of the Earth.

The supposed site of the impact which ended the Cretaceous Period is the Chicxulub Crater in the Yucatan Peninsula of Mexico. The jury is still out to some extent whether this is the smoking gun of mass extinction, but it is accepted that some catastrophic event, or a series of them piled one on top of the other led to the extinctions.

A Fiery Embrace

2008-07-24T15:25:00.001+02:00

Incandescent, red hot lavas pour out from a myriad of fissures in the Earth’s crust. The flowing, rumbling mass spreads over the landscape, consuming all in its path. Scattered trees form paltry obstacles to the inexorable advance of the lava front, bursting suddenly into flame to add to the mind-blowing display of fireworks. Ponded water in the desert depressions is vaporised in hissing clouds. Dinosaurs dart hither and thither, but always away from the lava front, but their efforts to escape will ultimately be in vain. Ejecta spew skywards from the fissures, filling the air with molten bombs. Ignimbrites – hot ash clouds which vent from some of the fissures fill the air, and the ash falls back to Earth, accumulating in layers which are then buried by subsequent lava flows. It is a 160 million old Dante’s Inferno visited upon the Earth.

We are almost at the end of Karoo times. Gondwana is under stress due to increased mantle activity beneath the continent, leading to uplift and rifting. Tensional stresses cause the crust to pull apart and out of these fissures pour millions upon millions of cubic metres of molten, incandescent lava. At the end of this volcanic event a thickness in excess of 2000 m of material will have flowed out across the Gondwana landscape, burning and burying everything before it in a fiery embrace. These kinds of outpourings are aptly known as flood basalts, and have occurred in a few localities around the world. A walk up, or down Sani Pass will reveal the evidence of this cataclysmic event. The lava flows are quite easy to make out, as their bases are marked by pipe amygdales. We are all familiar with the shaken can of cola – once the can is opened the cola comes pouring out with its attendant mess. Lavas behave similarly – their origins are the deep bowels of the Earth, and on reaching the surface where temperatures and pressures are low, the dissolved gas and fluids are free to expand and escape from the molten rock. Close examination of many of the Drakensberg Basalts will reveal round, white nodules within the greater groundmass of basalt. These are amygdales. At the bottom of the flows, most probably due to the chilling effect of the cooler material below, long pipe amygdales formed which rose up through the molten material, before being eventually frozen into the surrounding rock once temperatures had fallen sufficiently. In places it is possible to work out the direction of flow of the lava, as the pipe amygdales are dragged in the direction of flow. Pahoehoe (pronounced pa-ho-ee ho-ee) lavas also occur. A Polynesian word used to describe the ropy, rumpled texture of fresh lavas, particularly well known from the Hawaiian Islands; these same textures are also preserved in the 160 million year old lavas of the Drakensberg. If you are observant, and possibly know what you are looking for, there is an horizon of welded tuff about half way up the pass on the left hand side. This once was red-hot volcanic ash which fell to Earth and became welded together to form the ash horizon.

The next big question of course is how all this lava got to the surface through all the underlying rock. Well, scattered throughout KwaZulu-Natal and much of the Karoo for that matter are thousands of dolerite dykes, which were the feeder pipes which carried the molten lavas upwards to be extruded on the surface. These dykes now form areas of elevated relief around the Midlands, as well as boulder beds – sometimes there are more boulders to be seen than soil and vegetation. Fantastic examples are to be found on the road towards Nqutu, Rorke’s Drift and Insandlwana. Some of these dykes also cross cut the basalts themselves – carrying lava ever higher in the volcanic pile. In addition to the vertical dykes are horizontal sills, which intruded along the bedding planes before solidifying. Many of our koppies and hills are now capped by dolerites which form a hard, erosion resistant layer which protects the underlying softer sediments from erosion. Some of these dolerite bodies are of significant size. The Quarry at Hilton is a fairly large hole in the ground, and that hole used to be hard, unweathered dolerite. It makes a fine aggregate for both concrete and road building and dolerite bodies of the size of Hilton’s have significant commercial value.

The Drakensberg owes its existence then to tensional forces in the Earth’s crust which rang the death knell of the supercontinent Gondwana. Over two thousand metres of lava were poured out onto the planets face, destroying everything in its path, and covering much of Southern Africa. The Drakensberg and the Lesotho Highlands are nothing but a remnant of a far larger accumulation of basalt.

Reptiles of the Great Karoo

2008-07-24T14:53:00.000+02:00

Fifty million years on, and the Karoo Sea is but a hint of its former self. In its place is a giant lake fed by a number of northward flowing rivers draining from the high Cape Mountains which shimmer through the heat haze far to the south. Along the river banks vegetation grows in abundance thanks to a plentiful supply of silt, water and the hot climate. On the flood plains between the rivers vegetation still grows abundantly although not with the same profusion of that along the river banks. Vegetation comprises mosses, ferns, glossopterids and gymnosperms which grow in profusion along the river channels, while in the more arid flood plains, more glossopterids and gymnosperms dominate. For the most part the rivers remain confined to their channels, but during the wetter, winter months when torrential rains lash the high Cape peaks to the south, the rivers rise and overflow onto the low-lying plains in an all encompassing flood, bringing water and nourishment to the arid areas between the rivers. Insects and beetles rattle through the undergrowth while cockroaches scratch in the leaf mould. And where there was little animal life in this ancient world until now, things have changed, for rooting between the plants and wading in the shallows are herds of strange creatures with shovel-like heads and tusks protruding downwards from the rear of their mouths. This is Lystrosaurus, a beast with a long robust body and short legs - a clumsy and inelegant creature. They wade and forage, chomping their way through vast amounts of vegetation while some work their shovel-like heads as spades, burrowing into the river banks to make shelters from a hostile world.

Gondwana has continued its inexorable wanderings from the southern high latitudes to warmer climes. Ongoing sedimentation over millions of years has filled the Karoo Sea to the extent that only a large lake remains, fringed with primitive vegetation. The Cargonian highlands to the north have been eroded down and become covered by younger sediments of the Karoo Basin. The only significant topography now comprises the Cape Mountains far to the south, which due to the ongoing processes of erosion have produced billions of tonnes of sediment which has filled the basin. Fossil trees show growth rings which indicate changing seasons and possible droughts. Desert roses, so typical of arid conditions, are found within the fossil sands of the Beaufort Group. The flood plains are home to a passing parade of reptiles which are the forerunners of the dinosaurs and ultimately mammal life, and Lystrosaurus but a latecomer on the stage of reptile evolution. One of the most amazing things about the rocks of the Karoo Supergroup are their level of preservation. Often rocks of this age get caught up in the tectonic mill, or are subject to erosion which destroys the record of Earth history which is written therein. The Karoo is internationally famous in palaeontological circles for its abundance of pre-dinosaur fossils. They preserve an almost unbroken record of 80 million years of vertebrate evolution and record the progression of life from primitive reptiles to the transitional stage between reptiles and mammals. These rocks also record the largest extinction event which has ever occurred in the history of life. The end Cretaceous extinction which led to the demise of the dinosaurs is more famous, thanks to popular movies and media coverage, but was nothing compared to the end-Permian event which shook the very foundations of life, when an estimated 96 percent of all life was extinguished. This event took place 251 million years ago and no one has yet come up with a watertight theory as to the reasons for this extinction, but changes in Earth’s atmosphere due to volcanic activity, a major meteorite impact, or drop in sea levels due to an ice age which exposed organic sediments leading to sudden oxygen depletion of the atmosphere have been postulated. For whatever reason, life was almost snuffed out. No longer was there any vegetation to slow the transport of sediment and the meandering rivers which fed our great lake were replaced by a myriad of sand-laden drainage channels which spread over the flood plains. Lystrosaurus survived the extinction event and not only are its remains found in the rocks of the Karoo, but also in Antarctica, additional evidence for the great landmass of Gondwana. Ongoing northward drift of Gondwana led to increasingly arid conditions. Local swamps were scattered here and there, but over time a vast desert formed in the centre of Gondwana, far from the oceans and possibly in the rain shadow of the towering Cape Mountains. Massive sand dunes formed which are now preserved as the golden cliffs of the Clarens Formation, so spectacularly displayed as the little Berg and at the Golden Gate National Park.

We are currently putting together a fortnightly news letter on all things geological, so if you wish to subscribe please email me on geologist@netactive.co.za

The Karoo Sea

2008-07-24T14:48:00.000+02:00

This is swampland on a giant scale. Teaming, pushing, living, scrambling forest grows riotously along the muddy banks of lagoons and stinking back swamps. Trees, club mosses, cycads and ferns compete for space, water and light, while those that have seen their days out collapse back exhausted to the forest floor, to be rapidly colonised by fungi and bacteria. Beetles scramble through the leaf litter or fly ungainly through the canopy, while cockroaches scuttle and scratch in the leaf mould. In the creeks and backwaters amphibians populate the mud flats and dark pools, while out on the sunny waterways fish leap and squadrons of giant dragonflies keep station above the languid waters.

Times have clearly moved on from the icy grip of the Dwyka Ice Age. Gondwana has wandered northwards and South Africa now finds itself at approximately 30° south where temperatures are more conducive to life, which has seized the day, colonising the land to form vast subtropical forests along the northern rim of an ancient sea. But now we need to step back a little and look at the geological processes which have led to this change of circumstances. We have looked at the great ice age known as the Dwyka glaciation of 300 million years ago, but now we must take our focus off KwaZulu Natal for a short time and look at what was going on in South Africa as a whole. Many of us will have travelled through the passes of the Cape Mountains and wondered at the spectacular folding which characterise this mountain chain. These mountains began to form approximately 330 million years ago during the late stages of the Dwyka glaciation. The mountains formed the southern boundary of an ancient sea which covered the majority of Southern Africa – bearing in mind of course that we were part of a larger supercontinent. This sea had a low tidal range and is thought to resemble the modern Black Sea - open to the larger ocean, but without the dynamics of a full-blown ocean. To the north, stretching from the Northern Cape through Gauteng to Mpumalanga, were the Cargonian Highlands – a range of hills which defined the northern limits of this sea. Our Dwyka ice sheets have been bumping and grinding their way southward across these northern highlands before being cast adrift as icebergs on the turbulent waters. As the ice scoured the landscape, Gondwana continued to drift northwards, ultimately bringing us to warmer latitudes and creating conditions conducive for the burgeoning of life.

With decreasing latitude, the ice melted, to be replaced by southward flowing rivers which began to drain the Cargonian highlands, depositing vast quantities of sediment along the northern margins of the Karoo Sea to form large, meandering deltas. Like deltas everywhere, they supported the forests and swamp life where today’s narrative began. The trees that dominated these deltas were a Gondwana classic known as Glossopteris - the distribution of this species another nail in the coffin for the naysayers of continental drift and plate tectonics – it is found in South America, South Africa, Australia, India and Antarctica, strong evidence indeed for the supercontinent of Gondwana. Glossopteris, ferns, horsetails and club mosses thrived within these vast deltas, to the extent that thick accumulations of wood and organic matter were unable to rot and were buried and ultimately converted to coal. These deposits form our coal reserves of KwaZulu-Natal and the Highveld.

The southern margins of the Karoo Sea were characterised by deep water and a narrow littoral, set against the towering peaks of the Cape Mountains. Small, fast flowing rivers typical of mountainous regions deposited their load along a narrow littoral on the southern margin of the Karoo Sea. Every so often some of this accumulation of sediments would slump into the depths to form large, fan like deposits on the sea floor called turbidites, and these may still be seen fossilised in the hills of the Eastern Cape. But this is treatise on the local geology, so we will stay focussed on what is in our backyard. The accumulation of sediment in the Karoo Sea continued for in excess of 150 million years, eventually filling the basin. Karoo rocks have the widest distribution across the subcontinent and reflect the changing latitude and depositional environments as the basin began to fill. It is an ongoing tail of evolution and change and we will continue with the Karoo story in the next article. However any journey inland from Pietermaritzburg will traverse sediments once laid down either on an ancient sea floor or on the swampy margins thereof, where verdant forests thrived in a magnificent outburst of life. Karoo rocks extend to the crest of van Reenen’s Pass and beyond – a truly magnificent heap of sediment which reflects in part the geological history of a subcontinent.

Romancing the Stone

2008-07-18T03:17:00.000+02:00

From Hilton’s lofty viewpoint one can almost imagine the blue smudge that is the Indian Ocean out towards the east, particularly after rain when the visibility is at its best. I often marvel at the amazing altitude difference between the City and the misty heights and how comfortable we are with the 500 m ascent which many of us make on a daily basis. This may be partly due to a long and familiar association with this ‘Hill’ which defines to some extent our town and which we effortlessly beetle up and down thanks to the internal combustion engine. However there is more to all this than initially meets the eye and it is an interesting but fairly obscure fact that the African hinterland, and Southern Africa in particular, has an average altitude of 1000 m. This is significantly higher than areas underlain by similar geology elsewhere on Earth, where average elevations of 300 m are the norm. Consider too that the highest point in Southern Africa, Thaba Ntlenyane, is located approximately 160 km from the coast. The descent from Southern Africa’s highest point to the littoral is therefore abrupt – from 3300 m to sea level over a horizontal distance of 160 km – this is nothing less than phenomenal and is almost unheard of except in very mountainous terrains. Question is, why? Current thinking has it that Southern Africa is elevated due to ongoing mantle-plume activity beneath the subcontinent which initiated the break-up of the supercontinent of Gondwana approximately 160 million years ago. In lay person’s terms, this ‘hot spot’ beneath the Earth’s crust has led to a localised upwelling of buoyant, molten material (the mantle plume) which in turn has led to upward bulging of the overlying crust and associated elevated topography. Ongoing tensional stresses in the Earth’s crust due to continental rifting led to the formation of seaways (the infant Indian and Atlantic Oceans) on the Southern African continental margins. This resulted in faulting and the stepping down of the landscape from the original land surface of the interior (what is now the highland regions of the Drakensberg) to the ocean margins.

As our Dusi paddlers can attest, the Umsundusi and Umgeni Rivers flow through some spectacular, steep-sided valleys and the same can be said for the rest of the rivers of the province – Umkomaas, Umzimkulu, Umhlatuze and the great granddaddy of them all, the Thukela. The existing rivers, originally flowing on a high altitude plain prior to Gondwana breakup, then took the most direct route to the newly formed Indian Ocean, cutting down through the ancient bedrock to the sea to form the spectacular kloofs and valleys which we know so well. The verdant growth of Strelitzia and Acacia and the unique ecosystems of these valleys are a direct result of this remarkable geological event. From the lofty viewpoint atop Town Hill one gets some inkling of the spectacular scenery of the Umsundusi and Umgeni Valleys, but for some real mind-blowing scenery, follow the Comrades Marathon route to Durban and keep your eyes peeled for views of the Valley of a Thousand Hills out towards the east. Perhaps even more spectacular vistas are to be had on the road from Hillcrest to Inanda Dam where a stop on the edge of the escarpment prior to the descent to Kwa Ngcolozi will reward you with some of the finest views in Africa.

In the following weeks we will venture forth on a geological journey, beginning on the edge of the great ocean basins, then on to the fiery birth of the Drakensberg, down through the age of deserts, temperate swamps and dinosaurs, ice ages and ultimately to the ancient exposed bones of the Earth – the remnants of an ancient Himalayan-sized mountain chain which once straddled our province. Earth history is writ large in our own back yard – 300 million year old glacial pavements where the ice ground across the landscape are to be found just outside of Pietermaritzburg; glacial deposits lie dumped by retreating ice everywhere; 160 million year old lava and ash flows outcrop lie in the cuttings of Sani Pass, the body imprints of crocodile-sized amphibians lie preserved in the Karoo mudstones outside Estcourt, and Durban’s Berea is part of an ancient cordon of sand dunes which accumulated when sea levels were higher than they are now. We walk, in a sense, on hallowed ground, where the history of the Earth is recorded in the rocks beneath our feet, affecting us all in a myriad of ways. Our prosperity and survival is intimately entwined with the underlying geology – it provides us with metals and fossil fuels vital to modern life, forms the substrate on which we found our structures, and soil, the residue of the aeons, nourishes our crops.

A Grue of Ice

2008-07-17T19:43:00.002+02:00

Glacial Striations - Hopewell Farm, KZN

From Zululand in the north to the shores of the Southern Cape in the south are to be found accumulations of a fine grained, bluish grey rock containing ground down lumps of granite, sandstone and other rocky debris. This might all seem esoteric and of little relevance to us, but perhaps if I were to tell you that these piles of bluish-grey rock represent nothing less than fossilised deposits of glacial till, perhaps you might sit up and take notice. Glaciers? In Africa? Well yes, but not last week, not last century, but 300 million years ago. At that time we were still part of the supercontinent of Gondwana, drifting through the polar-regions, with conditions not much different to those which Antarctica is currently experiencing.

However, no one was around then to observe this, so what evidence is there to prove that we were in the grip of prehistoric ice age? Many of the geologists who mapped the strata of South Africa a hundred years back were from European schools and hence were familiar with modern glacial tills which occur in northern Europe. The effects of the inexorable milling of the landscape by ice sheets during the last European ice age are no different to those experienced here 300 million years ago, except that our deposits have had time to consolidate and lithify. I would imagine that they were more than a little surprised to find evidence of glaciation whilst sweltering under the African sun. At that time there was no mechanism to explain to our pioneering geologists how the climate got to be so cold, but there was no refuting the evidence. We have the benefit of hindsight now that the theory of continental drift has become hard geological fact, but back then the very idea of wandering continents had not even been suggested. To have put forward a crackpot theory that the immovable earth had been part of a larger ancient continent, and moreover that this continent had once been centred on the South Pole would have led to derisive laughter at best or questions as to the state of their sanity at worst.

The fine-grained groundmass which makes up the bulk of the rock is fossilised rock flour – a pulverised matrix ground into being by the overbearing weight of tonnes of ice juddering across the ancient continental surface. Our local outcrops of Dwyka Tillite contain countless millions of fragments of Natal Group Sandstone and Granite Gneiss, torn from the underlying substrate by the bulldozing and grinding ice.

Perhaps even more spectacular are the occurrences of striated pavements in a number of places around the province. When they opened up the foundations for the new Geography building at the then University of Durban-Westville, they found a striated pavement with grooves gouged into the hard underlying sandstone - grooves made by the bedload of the glacier as it ground its way across the sandstone substrate. Other local examples occur on top of the Natal Table Mountain and on the Hopewell Farm near Thornville. Dropstones – boulders rafted out on ice floes and then deposited into the sea floor muds - can be seen in the road cuttings on the Table Mountain – Nagle Dam Road.

So much for the direct evidence of glaciation, the question now remains as to how they worked out that Southern Africa was drifting around down there in the high latitudes. Well, it was found that, as lavas pour out onto Earth’s surface, which they have been doing for 4.6 billion years, the iron in their minerals aligns itself with the prevailing magnetic poles. As the rock cools the iron is frozen into that orientation and preserved for geophysicists to analyse millions of years later. Some of you might have noticed when driving up Sani Pass, round uniform holes drilled in the lavas in the road cuttings, evidence that the geophysicists have been there before you. Careful note is taken of the orientation of the sample in the field before it is removed from outcrop. Back in the laboratory the specimen is then reorientated to its original field position, and then the orientation of the iron is measured. This then tells our geophysicist in which direction the magnetic pole once lay, relative to our rock sample. Thousands of these measurements have been plotted onto base maps, and over time a pattern has emerged polar wanderings throughout Earth history.

So on a continental scale, vast ice lobes ground southwards across the ancient face of our continent, scarring and adding character to our African landscape. Vast deposits of tillite may be seen from the Dwyka River in the Cape to the far north of Zululand and are evidence of continental wanderings and an ice age which has us in its frigid grip 300 million years ago.

The Natal Group Sandstone

2008-07-17T19:32:00.000+02:00

Standing on the edge of the precipitous cliffs, with the views to the distant krantzs and the cool winds tousling the hair, one cannot help but be moved by the magnificence of the scenery, or wonder how this all came to be. The rocks on which you stand are the result of a complete change in the geological conditions which had prevailed during the formation of our Himalayan-sized mountain range which we visited two weeks ago.

Six hundred million years have flitted by since our mountain chain was thrust up into the teeth of icy gales and snow. Inexorably the agents of erosion have ground down the high peaks of our mountain range into nothing more than mud and sand – transporting the detritus in rivers to be dumped ignominiously in some forgotten backwater, their magnificent provenance forgotten. All that remains of our high peaks is a level plain, floored by ancient granites and gneisses, with localised hills adding some interest to the landscape. It is difficult to grasp the concept of time – geologists glibly refer to millions of years or hundreds of millions of years, so to put this into some kind of perspective, the Alps were formed 60 million years ago and are still subject to the compressional forces as Africa continues to drive forward into the underbelly of Europe. Six hundred million years is sufficient time therefore to reduce a mountain range from towering peaks into nothing more than thick accumulations of sediment dumped in the low-lying regions of the Earth.

Crustal forces had changed from collision to tension since the days of our mountain building episode, and tensional stresses had begun to accumulate to the south of the supercontinent of Gondwana. These tensions began to tear apart the greater landmass to form rift valleys identical in many aspects to the well known Great Rift Valley system of East Africa, the rifts extending along the southern, western and then more latterly the eastern coasts of Southern Africa. Bear in mind though that Africa did not exist at this time – it was centrally located within Gondwana and I use the name only to give some kind of geographical reference to our journey. The rifting process continued long enough to develop valleys deep enough and wide enough for the southern ocean to inundate the existing landmass, forming a seaway which has been called by geologists as the Agulhas Sea. This new ocean, with marine life, currents and waves not unlike our own, became a great repository of a thick pile of sediment – sand, mud and gravel - which were deposited in the depths, recording the vagaries of ocean currents, floods and storms over the millennia. In the Cape the sediments attain a thickness of 8 km or more in places.

Here in KwaZulu Natal, rivers carried sand and detritus southwards towards our local arm of the Agulhas Sea, whereupon they were dumped into deeper water, to be reworked by ocean currents. The climate was apparently semi arid at this time, although there must have been enough rain to fill the rivers and transport the sediments to the coast. If you are able to read the rocks, almost any outcrop of the Natal Group Sandstone shows evidence of strong currents and ripples, indicating transport in river systems way back in the Ordovician. Moving ‘upstream’ around Melmoth and Eshowe the original stream valleys, dating back nearly 500 million years, are still to be seen, choked with boulders and gravel derived from the weathering of the surrounding mountains. These ancient palaeo valleys can be seen if one takes the Jameson’s Drift or Middle Drift roads from the northern rim of the Thukela Valley.

Ongoing accumulation of sediment continued until, with the passage of time, those tensional stresses in the crust which had lead to rifting were reversed and the whole accumulation of sediments were squeezed, folded and uplifted into what is now the spectacular scenery of the Cape Fold Belt. The sediments here in KwaZulu-Natal were spared the vice-like embrace of this tectonic mill, but were uplifted nonetheless, to form the magnificent scenery of Kloof Gorge, the rim of the Valley of a Thousand Hills, the Kop at Kranskop and the spectacular Oribi Gorge. Next time you are driving from Pietermaritzburg to Durban, the cliffs on your left just after the Shongweni off ramp and before the toll reflect an environment where rivers carried vast accumulations of sediment into an ancient sea, 490 million years ago.

Although not as dramatic as the mountain building event which preceded it, the formation of the Natal Group Sandstone was a significant event in our geological history and was the substrate on which the Gondwana Glaciation took place when South Africa (as part of the larger Gondwana landmass) found itself at the South Pole.

The Ancient of Days

2008-07-17T18:40:00.000+02:00

White, snow-capped peaks project jaggedly into the blue rarefied air of the jet stream, which draws out long plumes of snow from those high summits. In the valleys below the snow-flanked shoulders of the mountains, glaciers brood, grinding and plucking the encompassing rock which holds them in their icy realm. Further downslope, fast flowing rivers, milky with the rock flour derived from glacial mills above, cascade seaward through valleys strewn with sand and boulders. These sediments are the debris of the aeons, carried here by inexorable action of water and ice. There are no birds or animals, no plants or trees; the only sound the roar of the rapids which is occasionally punctuated by the crash of landslides, or the muffled thunder of avalanches falling from the snowfields above. This is primal world set in a time when life was in its infancy and a mountain range of Himalayan proportions straddled an ancient supercontinent called Rodinia. Forming part of the inner core of this mountain range were rocks which now find themselves, 1.1 billion years later, exhumed and exposed to the glare of the African sun, the footfalls of Nguni cattle and the impetuous ebb and flow of our mud-laden rivers.

How do we know this? Geologists, plying their trade in the Alps, Rockies and then the Himalaya, had dissected and described the rock types which underlay these massive mountain ranges. Geologists here at home realised that the rocks exposed in the Valley of a Thousand Hills or in the valleys of the Thukela or Umkomaas had uncanny resemblances to those found in more modern examples. It was therefore no great conceptual leap to realise that the geological processes which formed the Alps and the Himalaya were identical to those which created the granites and gneisses which underlie our province. By inference, the rocks of what is known as the Natal Metamorphic Province, had their origins in the roots of an enormous mountain belt. The modern-day Himalaya is the result of India colliding with greater Asia due to plate tectonics and in a similar vein our ancient range formed 1.1 billion years ago, as Ur and Atlantica, two relatively small continents, collided with a larger continent known as Nena (acronym for North America-North Europe) to form Rodinia. I can hear you gasp, but if one accepts that the Himalaya and the Alps are the result of continental collision, then an ancient mountain range here in KwaZulu-Natal caused by the same mechanisms is not in the realm of fantasy. Collisions of this magnitude throw mountains up to great heights, but also carry crust to great depths, sometimes up to 70 km or more, where temperatures and pressures melt, cook and torture the buried sediments into metamorphic rocks which at first glance belie their origins.
Some fine examples of the original core of our ancient mountain range are to be found in the valley of the mighty Thukela. Augmented by a myriad of tributaries, this river has cut down through the younger geological cover to exhume the ancient bedrock of our province. Fantastic folding may be seen in the road cuttings on the southern approaches to the steel bridge at Jameson’s Drift. Granites and gneisses are exposed in the river beds of most of our rivers throughout the province and provide a competent substrate for socketing the foundations of our dams which have become essential to our urban life. One particularly distinctive rock type, called ‘augen’ gneiss, is to be seen in the road cuttings on the descent to Nagle dam via the abattoir road. The term ‘augen’ describes perfectly the large, eye-shaped feldspar crystals which ‘schiller’ in the harsh sunlight. The more adventurous might continue the drive to the dam and negotiate access to the spillway below the diversion weir. Blasted out of the living rock, the gneisses exposed in the floor of the cut are classic examples of a high- grade metamorphic rock. Light and dark banding characterise the rock mass and closer inspection will show this material to be melted, contorted and stretched into tight, convoluted folds under those immense pressures and temperatures which we discussed earlier.
It is here then, in the deep tectonic mill that our rocks found themselves 1.1 billion years ago – contorted and melted into the gneisses and granites exposed in our province’s river beds. Since then, those towering peaks have been ground down by the inexorable action of a billion years of rain, wind and ice, to leave only a remnant of a once magnificent, Himalayan-sized mountain chain which stretched for hundreds of kilometres across a now disintegrated supercontinent. So next time when you stand on the crystalline basement of our province, be aware that snow clad peaks, towered above your head, 1.1 billion years ago.