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Peterborough Geology: May 2012
Notes from talks given by Dr Jonathan Larwood and Dr Colin Prosser at the Geology Field Days on April 30 and May 1.Colin and Jonathan both work for Natural England, which is a national organisation that deals with Geological Conservation. They also are both involved in GeoPeterborough, a partnership in the Peterborough area to raise awareness of Geology.

Dr Larwood lecturing the group

Jonathan started his talk by showing the relevance of Geology. It is the science and study of how the earth was formed. Some geology is ‘in your face’ and iconic. Some examples are the Grand Canyon, Mount Everest, which is more recent active geology than the Grand Canyon. The jagged high peaks of Mount Everest are not eroded like British Mountains.   Volcanic activity is seen through the geological record and Krakatoa shoes that geology can be dangerous. Geology also relates to things found in rocks, the fossil record. This is the study of how life evolved and changed around us, and some of that is also iconic, such as the skulls of dinosaurs.

British geology is also iconic, such as the white cliffs of Dover. The chalk is widely spread around the coast. The North West highlands of Scotland have rocks that are 400 million years old. Ben Nevis is 4400 ft high, the tallest mountain the British Isles. The Giants Causeway is evidence of volcanic activity in the rock record and is igneous rock. Originally a lava plateau 1.8 million across the basalt columns of the Causeway are striking and found also in Norway and on parts of the West Coast of Scotland.

Dr Prosser lectures the group

Here in Britain we have our own dinosaurs, such as the plesiosaurs found in the brick pits of Peterborough and in Dorset. This is all evidence of changing life and sea levels. Britain is one of the most diverse places in the world for its geology. It has a complex geological history due to being on the edge of a continent, meaning it has existed in a more challenging environment than in the middle of a plate. The oldest rocks in Britain are found in Scotland. The rocks around Peterborough date from 160 million years old, and are slightly tilted from west to east. 3 types of rock dominate the area, clay, gravel and limestone.

Limestone – Lincolnshire Limestone from the middle Jurassic. This was deposited in a shallow warm sea such as the Bahamas today. This limestone is full of ooliths, small circular grains of sand less than 1mm in size. They have rings of lime cement around them. Limestone influences habitats, such as Barnack Hills and Holes.

Clay is found to the South and East of Peterborough. This is also Jurassic in origin, at 140 million years od. At this point rising sea levels would have put Peterborough under the sea. The clay is extracted and used to make bricks. Marine reptiles are found in this clay.

The gravel is much more recent, having been deposited 200,000 years ago. It is part of a complex sequence of sediments associated with changing environments. In the Ice Age large sheets covered the land, 2 km thick over Peterborough. When these retreated sediments were dumped onto the land. The Ice Ages had periods of extreme cold and also more temperate times. During the temperate times there was temporary occupation by early man in the landscape and rivers in the area. The river terraces contain gravel. Ferry Meadows was a site of gravel extraction.

Fen characterised the East of Peterborough over the last 10,000 years. This is a sign of warming climates, at certain points Peterborough was close to the coast. Since this type of landscape developed there has been more permanent occupation of people due to less extreme temperatures. Geology isn’t just the history of earth but allows us to understand why things go on around us.

There is a long association between man and geology, from the cave systems of early man through the stone ages, Bronze and Iron ages. All early stages of man are defined by what man was doing with rock. The ability to work stone set us apart from animals. Technology allowed us to dominate the eco systems, and early man was quick to put up stone structures.

Geology influences the character of areas. It is why you recognise places. It is a vital resource and aspects such as cost and ease of extraction influences local stone use. When the railways came to Peterborough in 1845 it brought national stone to the city. Local stones were in use from the Roman period, who brought their own masons with them 2000 years ago. They used Barnack stone. Other local stones include Alwalton marble and Collyweston Slate. With the railways came Welsh slates, granites and decorative marble. Once used the quarries can be restored to new habitats as end uses.

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