"Geology" West Lulworth Favorite Tip by toonsarah

Favorite thing: The Lulworth Coast is part of the Dorset and East Devon World Heritage Site known as the “Jurassic Coast", although in fact the rocks that are exposed here date from the Triassic, Jurassic and Cretaceous time periods. There are 185 million years of the earth's history in just 95 miles of coastline, which explains why this coastline is considered significant enough to have been awarded World Heritage Site status.

The Lulworth section stretches for 5 miles between White Nothe in the west to Worbarrow Bay in the east. The five types of rock at Lulworth are between 150 million years old and 65 million years old. The geology is important as it reveals the environment and creatures living at that time. The fossils within the rock are history set in stone.

To look at Lulworth Cove today is to look at a geology lesson brought to life. Here limestone forms a massive bastion against the sea, and this perfect horseshoe bay has developed where a stream breached the limestone allowing the sea to enter the valley and hollow out the softer clays lying behind it. Behind this again, chalk forms a resistant cliff at the back of the bay.

The science bit! (adapted from several websites):
The Jurassic Coast was formed over eons of time spanning three prehistoric periods: the Triassic, Jurassic and Cretaceous. In the first of these this area was part of a super-continent called Pangaea. This landmass divided to form the continents of the modern world. Dorset lay within the arid centre of the super-continent and was a hot desert region. During this period the first dinosaurs evolved, as did the very first mammals. Fossils of some of these creatures can still be found here.

Pangaea started to break apart during the Jurassic Period. The Atlantic Ocean opened to the west of Britain and the Americas drifted away from Europe. The Earth was relatively warm and sea levels here rose and fell in a series of cycles, depositing deep water clays, followed by sandstones and finally shallow water limestones. These today hold fossils of ammonites, molluscs related to the modern squid. But the reptiles were the “top predators” on land, sea and in the air. Dinosaurs walked the Earth and the dominant carnivores in the seas included ichthyosaurs, plesiosaurs and crocodiles.

During the Cretaceous Period, America continued to drift away from Europe, and the Atlantic started to become a recognisable ocean. Early in the Cretaceous, the environment of this area was similar to the modern Gulf of Arabia, with lagoons covered by salt flats. Mid-way through the period earth movements deep under south-west England titled the rocks to the east. Then a vast sea developed over the area, and within its clear, warm waters billions of microscopic planctonic organisms thrived. It is their skeletons which sank to the sea floor to form today’s pure, white chalk. This is also the time when some of the largest and most fearsome dinosaurs walked the Earth and is also the period when the first flowering plants evolved.

Update August 2008: thanks to VT member kokoryko for helping to make my explanation more accurate