Kimmeridge Bay: A Marine World

An International Name

The rocks at Kimmeridge Bay were once the floor of a deep, tropical sea rich in pre-historic life.  They formed in the Jurassic period, 155 million years ago.

The cliffs and foreshore contain a very thick sequence of Kimmeridge Clay.  The rock layers are like the pages in a book and the fossils they contain tell a story on each page.  Each rock layer provides a window allowing us to look back through geological time.  The sequence of rocks here provides such an excellent record of this part of the Jurassic that geologists have adopted Kimmeridgian as the term for rocks of this age all around the world.

Important fossils have been found in the Kimmeridge Clay, but they need an expert eye and time-consuming preparation.  Hammering is strictly forbidden here and you may only collect loose fossils from the beach.

Rocky Ledges

Harder bands of limestone within the Kimmeridge Clay create a series of rocky ledges that run out to sea.  As a result, the Bay boasts some of the most accessible marine wildlife in the UK.  The stone ledges make it easy to view life on the shore an in the shallow waters, and there is safe snorkelling for the more adventurous.  Kimmeridge Bay is part of the Purbeck Marine Wildlife Reserve, managed by the Dorset Wildlife Trust.  The Trust runs the Fine Foundation Marine Centre in the bay, providing an exhibition, aquarium and a programme of events.

Oil in the rocks

BP's ‘nodding donkey' on the cliff top has been producing oil since 1959.  The oil formed in rocks that were laid down on a stagnant sea floor.  The rocks were buried and organic matter within them was ‘cooked' to form oil and gas.  More oil lies in the northern part of Purbeck, and under Poole Harbour.  This is the Wytch Farm Oilfield - the largest onshore oil field in the UK.  It is difficult to see the carefully landscaped oil wells.

The geology of an oil field

Oil fields form where the structure of the rocks creates a trap for oil generated in the rocks below.  At Kimmeridge the oil is held in the layer of rock called the Cornbrash Limestone which can also be found around Osmington Mills.

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The Jurassic Coast: A Mighty Tale

A light-hearted python-esque animated film by Tim Britton.