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Sunday, January 23, 2011
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Wednesday, January 5, 2011
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.
Wednesday, April 15, 2009
Saturday, April 4, 2009
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.
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.
Monday, December 22, 2008
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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