Falklands Fossils Unlock Their Secrets

PS: Most of the fossils in the Falklands are from a unit of rock called the Fox Bay formation and this was a sandstone/shale unit that was laid down about 400 Million years ago. In [Stone, Philip] geological jargon, that's the [Stone, Philip] Emsian stage of the Devonian period.

PS: Way before the break-up. They were laid down at a time when Gondwana was quite a large, stable continent. These particular 400 Million-year-old fossils are found all along the Pacific shoreline of Gondwana. So, you get the same fossils from the Ellsworth Mountains in Antarctica through the Falkland Islands, right through South Africa and to some parts of Northern Argentina, across into Brazil and way up into Bolivia. They are the same fossils and in the same rocks that were on the Pacific coast of Gondwana at the time.

PS: Yes. If [Stone, Philip] you want to talk in terms of present day oceans, [Stone, Philip] but in terms of 400 Million year-old geography[Stone, Philip] , it was the coast of the [Stone, Philip] Gondwana continent which [Stone, Philip] now forms the margin of the Pacific, really.

PS: There are some later ones, but there are also, curiously, some earlier ones. To my mind, the earlier ones are the most fascinating because they actually are older than the oldest sedimentary rocks in the Falkland Islands. And, you find them in lumps of limestone that are contained in [Stone, Philip] a tillite formation. Tillite is an ancient glacial deposit[Stone, Philip], [Stone, Philip] so let's go back again to Gondwana.

Think of it as a big, huge continental mass. At about 300 million years ago, the Earth went into one of its periodical ice age [Stone, Philip] phases . And, because Gondwana was fairly well down in the Southern Hemisphere, a lot of the area was subjected to glaciation[Stone, Philip] . [Stone, Philip] The ice sheets extended out from the polar area in what is now East Antarctica and spread out from there [Stone, Philip] to flow across into Southern Africa and the Falkland Islands[Stone, Philip] .

Bear in mind that all the continents are joined together so we are not talking about such huge distances as we would be now. But as the ice sheets spread out, they brought with them bits of rock from what is now East Antarctica and dumped them at the end of the ice sheets in places like the Falklands and South Africa.

So, in the Fitzroy Tillite, which is the name given to [Stone, Philip] the Falklands' fossilised glacial moraine, and the [Stone, Philip] Dwyka Tillite, which is the equivalent in South Africa, you find all these exotic bits of rock which can be matched up with an original home back in what is now Antarctica [Stone, Philip], the Trans-Antarctic Mountains in particular.

One of the most curious [Stone, Philip] examples is the limestone. There is no limestone in the Falklands[Stone, Philip] ' rock succession, no limestone at all. But you do find lumps of it in the Tillite and those lumps, in some cases, carry fossils. And the fossils are of weird, extinct things called [Stone, Philip] archaeocyathids. They are little creatures, rather similar to a primitive sponge. [Stone, Philip] Think about [Stone, Philip] a loofah, the kind you use to scrub your back[Stone, Philip] , and scale it down till it's about 2cm long. That's the kind of [Stone, Philip] creature it was. [Stone, Philip] It consisted of two cones, one inside the other with cellular structures joining [Stone, Philip] them [Stone, Philip] to leave a hollow space in the middle. These things lived about 500 million years ago. As I said, they were entirely extinct before the oldest sedimentary rocks in the Falklands were laid down so they are wholly exotic as far as we are concerned. Those are the oldest fossils we have found but they are not in place any more. They have quite a complicated[Stone, Philip] distribution history.

There are younger [Stone, Philip] fossils too, just a little bit later than the glaciation. When the Ice sheets retreated, the area currently occupied by the Falklands and its adjacent areas in South Africa became a huge fresh water inland sea. In that inland-sea, things lived and fish swam. There were cool, temperate forests around the edge of the inland [Stone, Philip] sea.

But for all that, we[Stone, Philip] have only found one animal body fossil in Lafonia[Stone, Philip] , the part of the Falklands where there are rocks of this age. It's a tiny [Stone, Philip] pair of bivalve shells. [Stone, Philip] We have nothing else at all. There must have been a lot of soft-bodied, slimy things [Stone, Philip] crawling around because the trails they made are all over the place. [Stone, Philip] Some rock surfaces in Lafonia are just covered [Stone, Philip] in crawling traces and browsing traces. In a similar way we can deduce that there were fish swimming around in the sea because some of these fish swam close to the bed of the lake and their fins and tails trailed in the ground and made the most delightful, meandering traces along the seabed. You can still see these things. They are beautifully preserved in places. So we can deduce that there were lots of soft, slimy things crawling [Stone, Philip] about [Stone, Philip] and that there were fish swimming around, probably eating the soft, slimy things[Stone, Philip] , but as far as actual body fossils are concerned, we have one, precisely.

What we do have from Lafonia is wood. Lots of wood drifted out into the lake, sank and some of it became petrified[Stone, Philip] when the cellular structure in the wood was replaced by silica [Stone, Philip] once it was buried. [Stone, Philip] You also get lots of impressions of plant stems and leaves and all sorts of things like that.[Stone, Philip] Some of them are delightful[Stone, Philip] . The fine definition [Stone, Philip] of detail [Stone, Philip] that is preserved[Stone, Philip] is quite staggering.

PS: There are two different stories here, I think. First of all, the North and South Poles of the [Stone, Philip] Earth have switched at various times, so that North became South and South became North. This has happened on a fairly regular basis. In terms of the last 20 million years, we actually have quite a good record of polar reversals. You can build up quite a good time-scale based on when North was North and when North was South.

But superimposed on that, of course, is the concept of polar wandering. [Stone, Philip] Continents are drifting and are not fixed in place. They move around and so their position relative to the pole changes through time. [Stone, Philip] So, not only are the poles switching but the continents are changing their positions relative to the poles.

Now, the switching of the poles will have no affect whatsoever on animal life and fossils, as far as [Stone, Philip] we can tell, anyway. But the moving around of the continents relative to the poles is, of course, crucial because if a continent drifts slowly into more tropical conditions, different kinds of life will evolve and thrive there. If, on the other hand, like East Antarctica when Gondwana broke up, the [Stone, Philip] continental block drifted away with all of its plants, animals and its thriving life forms[Stone, Philip] into polar conditions - they were doomed. The [Stone, Philip] whole [Stone, Philip] lot would die out

FINN Comment: To help understand fossils that have been discovered in the Falklands, Dr. Stone has co-authored a pamphlet entitled "Fossils from the Falkland Islands." It is on sale at the Mineral Resources Department in Stanley for £2.00.[Stone, Philip] - also from Capstan, Pink Shop, Museum.