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A Walk in the Ice Ages

24 May 2012

At the small coastal village of Happisburgh in Norfolk recent erosion and cliff falls have caused large pieces of the face to fall away taking houses and outbuildings with it. An alarming amount of cliff has disappeared in a few years, obvious by the gas and water pipes that hang loosely outside the cliff face and the steps up to the top that are stranded on the beach yards away from the cliff face they once provided a means to climb. Coastal defence in this part of Norfolk has been abandoned – and people have lost their homes. However, it is worth taking a stroll down to below the cliffs which appear to be comprised mostly of a very dry and sandy sedimentary section intermingled with a variety of clays and dark brown silty material. The silt layer appears to be the remains of the sediment at the bottom of a lake that formed after one of the Ice Ages – the inference being that it belonged to an interglacial period. The silt, in effect, had once been a thick layer of mud lying on the bottom of the lake. The dimensions of the lake are unknown and it could have stretched far out into what is now the North Sea. What is even more intriguing is what actually lies on the beach – the remains of a forest once buried by all the sediments that have collapsed and been swept away by the tides. The idea we live on a stable piece of the continent is perhaps an illusion – it might just be shifting sand (as at Happisburgh). Stone tools have been found in the forest layer in a recent excavation undertaken by the British Museum (see www.britishmuseum.org/research/research_projects/featured_project_happis…).

Plant remains, mammal fragments and insects and stone tools have been dug out of the beach and you can actually poke your fingers into the sand and encounter wood from tree stumps and roots that are said to date back over 700,000 years ago. The geology at Happisburgh is that it was at the time an ancient river channel and the sediments consist of gravels, sands and estuarine silts laid down by an early course of the river Thames, emptying into the North Sea somewhat further north than it does today. The ancient forest, on the other hand, is not just below the last Ice Age but the third Ice Age back, the Anglian, and the evidence of the three Ice Ages are above the tree stumps in the sand and the silt, clearly disseminated in the layering process. The Anglian reached further south than the other two, later, Ice Ages, and apparently had the ability to shift huge massive blocks of chalk, churning up the chalk bedrock (dating back to the Dinosaur Age) and moving it in large sections that can clearly be seen in some sections of the cliff face, with sand and silt above and below. The chalk blocks are clearly separated from the chalk bedrock and lie incongruously within the Ice Age levels.

The Happisburgh beach deposit, the forest layer, is actually something like 26 metres above the chalk bedrock – so a lot went on between the forest deposit and the dinosaur age. We might at this point ask what has happened to the geology inland which is bereft of material above the chalk bedrock of the Downs, the Chilterns and the Weald. A bit of clay and flints here and there is nothing, although the London clay deposit is substantial and must include the period of the forest layer. However, on some Norfolk beaches you can actually walk on the chalk bedrock – it might be littered with flints left behind by erosion but the chalk is there in place of the sand (and very peculiar). This is where wave action has washed away the overlying layers and the chalk has remained resistant as it absorbs water. Even more dramatic is the disappearance of the geology across Bedfordshire, the Vale of Aylesbury and the Vale of the White Horse. In these locales it is the Jurassic era that lies at the surface – what happened to all the later periods, including the chalk that belongs to the Cretaceous? Going further north, to Yorkshire, the Lake District, and Scotland, even older rocks lie at the surface, and the geology is reputedly sheared from the face by glaciation. These regions were at one stage deep under an ice sheet. We can see what happend on the Canadian Shield – the bedrock is devoid of geology, wiped clean. Norfolk was at the edge of the Anglian ice sheet and its geology has survived as a result of that – but it is very fragile. Why the geology disappeared from locations to the south is not adequately explained as they would have been unglaciated – although that is a moot point. It is a fascinating subject and obviously other processes could well have been at work.

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