The Cretaceous World (140-65 million years ago)

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 the World Heritage Site was similar to the modern Gulf of Arabia, with lagoons covered by salt flats known as sabkhas.  Conditions became more hospitable, with lush swamps populated by dinosaurs.  Mid-way through the period earth movements deep under south-west England titled the rocks tot he east.  Then, as the Atlantic Ocean and Mediterranean expanded, a vast sea developed over the area.  Within the clear, warm waters billions of microscopic algae bloomed, and their skeletons sank to the sea floor to form the pure, white Chalk.

The Great Unconformity

The ‘Great Unconformity', a time gap between rocks of different age, runs right across the World Heritage Site.  The rocks were tilted east in the Mid-Cretaceous, and then eroded by seas and rivers.  There was little erosion in the east of the Site but in the west, all the Jurassic and  Lower Cretaceous rocks are missing and the Upper Cretaceous rocks lie directly on the eroded surface of the Triassic.  So the walk through time is a little more complex: because both the oldest and some of the youngest rocks in the site are found in East Devon.

Cretaceous Life

The Cretaceous is 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.  The end of the Cretaceous is critical to the shape of the modern world (though not recorded in the World Heritage Site).  A mass extinction took place which brought to an end the reign of the reptiles as the dominant life on Earth.  The dinosaurs, great marine reptiles and the ammonites were amongst the species which became extinct.  The world that would follow saw the present style of life on Earth emerge, dominated by mammals, flowering plants and grasses.

The earliest Cretaceous rocks in the World Heritage Site are the Purbeck Beds, perhaps the most complex rock sequence within the entire coast.  They contain a wealth of fossils including dinosaur footprints and the microscopic teeth of mammals.

Chalk

The Chalk is the youngest Cretaceous rock in the World Heritage Site and is found throughout the area.  Animals such as the sea urchin burrowed in the sediment of the Chalk sea floor.