The formation of a geological spectacle
The rocks of the World Heritage Site are laid out from oldest to youngest moving west to east. This is a little unusual because these layers of rock would have originally formed one top of the other, and if they had stayed like that we would have to drill deep into the Earth to see them. Something truly epic must have happened to allow us to see these layers in continuous sequence along the coast.
250 – 100 million years ago – rocks are continuously laid down as the Earth's crust in this area slowly sinks. The layers record the Triassic, Jurassic and the beginning of the Cretaceous period.
100 million years ago – Massive earth movements tilt all the layers of rock gently to the east lifting up rocks in the west and exposing them to erosion. The exposed rocks are stripped away revealing Triassic and Jurassic rocks that have been buried for millions of years.
100 million – 65 million years ago – The sea floods across this 'erosion surface' and new rocks form on top recording the rest of the Cretaceous period (this is the Upper Greensand and Chalk).
65 million years – 10,000 years ago – erosion and sea level change carve into the rocks, slowly creating the coast we see today. The cliffs dissect the tilted layers of rock allowing us to follow them in sequence. Erosion carves down into the landscape stripping away the youngest Cretaceous rocks, leaving only a few high cliffs where they can still be seen. (photo of golden Cap or Dunscopmbe cliff)
The Great Unconformity
The 'Great Unconformity' is a time gap between rocks of different ages and runs right across the World Heritage Site. It was created when the layers were tilted and eroded 100 million years ago. The late Cretaceous rocks lie directly on the eroded surface of the Triassic, Jurassic and early Cretaceous. 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.