Sea level rise is a result of global warming which may affect many areas around the world: The Netherlands, The Maldives and Bangladesh are countries in particular which many predict will suffer most if sea levels continue to rise; many areas of the UK may also be in danger. The flooding of these areas will have big impacts around the world, but is sea level rise anything new? As this article shows sea level rise is not an event unfamiliar to our county. The Jurassic period in particular was an era which experienced changing sea levels, affects of which can still be seen today.

 

                

                                             Oxford?

 In the Jurassic period, 206 to 144 million years ago, Oxford was covered by a shallow sea which would have looked more like a scene from the Caribbean than the "dreaming spires" of Oxford city. The shallow tidal sea, commonly referred to as the Oxford Shallows, stretched between Lincolnshire and Dorset covering the Oxford area. The shallow stretch of water was only around 10 meters in depth and would have included a network of small islands.  Along the coast poorly drained swamp lands would have been common and home to a variety of dinosaurs, which have literally left their footprint on our county. Footprints of these dinosaurs can actually be seen in Ardley Quarry in Oxfordshire, a site claimed to be the most important dinosaur pathways in the UK and a recommended visit.

 As the Jurassic period continued into the middle Jurassic there was a significant fall in sea level, resulting in the formation of many depositional environments including salt marshes and coastal lagoons. As a result, vast amounts of materials were deposited during this time including rich muds, limestones, silts and sands; rocks which make up the bulk of the county. The limestone formation in particular is important; it was formed by the chemical precipitates of calcium carbonate from organisms known as ooliths. Ooliths still grow today in water less than 5m deep in areas with strong currents and this helps us understand what the conditions were like over Oxford during the middle Jurassic period.

 Due to its formation, the limestone in the Oxfordshire area is referred to as the oolithic limestone and is separated into two types: inferior oolite and greater oolite. Many of us probably pass the inferior oolite rock around Oxfordshire on a regular basis. The inferior oolite has been used as a building stone in many picturesque villages and towns of the Cotswolds, as well as the Oxford colleges and great buildings such as Blenheim Palace. The limestone has a yellowish-white colour on extraction which weathers to a lovely honey colour, evident throughout Oxford. However, due to limestone's chemical composition (calcium carbonate), it is easily dissolved by acid rain and modern pollutants, a major problem for the beautiful old buildings of Oxford. Many of the limestones found in Oxford also contain rare dinosaur skeletons and other vertebrates, including flying reptiles and early mammals and this once again gives us an insight into Jurassic Oxford.

 Towards the end of the Jurassic period, the upper Jurassic, Oxfordshire experienced another change in sea level. The Oxford shallows began to deepen and in all over 300 feet of Oxford clay was deposited. The Oxford clay underlies Oxford and now forms a belt of low country which stretches from north Wiltshire to Peterborough.

                           

     The Oxford collages would not look the same if not for the

                                  county's geological past

 

By Larisa Vircavs