Worbarrow Bay and Mupe Bay

The geology of Worbarrow Bay and Mupe Bay is very similar and they almost mirror one another, with the mirror being where the two bays meet at Arish Mell Gap. They both consist of Upper Chalk, Middle Chalk, Upper Greensands, Gault, Lower Greensands, Wealden Beds, Purbeck Beds and Portland Stone that have been subject to complex folding. All the sediments have been tilted vertically, around 45 degrees for Worbarrow and 60 degrees for Mupe. In effect both the cliff sections have been buckled upwards to form a horseshoe shape with the bottom of the horseshoe hidden from sight deep beneath the ground. The cliff sediments have also been twisted horizontally. This is why the Chalk is found at the back of the bay, while the Portland Stone and Purbeck Beds take the brunt of the seas at the front, forming the peninsula of Worbarrow Tout in the east and the Mupe Rocks in the west.

Worbarrow Tout

Worbarrow Tout consists of 150 million year old Portland Limestone and 147 million year old Purbeck Beds. It was originally part of Gad Cliff to its east, but erosion from the sea is working hard to turn the outcrop into an island. It’s pointy shape and steep angular layers of rock clearly demonstrate the complex folding to affect this area caused by tectonic pressures when the continents of Africa and Europe collided around 30 million years ago, forming the mountain range of the Alps. This area is in the heart of the MOD’s Lulworth firing range, the large number boards mark the firing zones.

The Great Unconformity and The Cretaceous Blanket

The sediments which make up the Jurassic Coastline were deposited in the following order, Triassic, Jurassic and Cretaceous, with the oldest rock, the Triassic sitting at the at the bottom of the pile. Part way through the Early Cretaceous Period the sea levels dropped and the layers of rock were tilted to the East by earth movements. Overtime the exposed rocks were eroded before sea levels rose again, depositing more Cretaceous sediments. The combined tilting and erosion explains why the Jurassic Period is completely missing in East Devon and why areas of cliff all along the coastline are capped with Cretaceous rocks which are millions of years younger than the sediments laying directly beneath them.

Gad Cliff

Gad Cliff is one of the most spectacular cliffs along the Jurassic Coastline, consisting of Purbeck Beds and Portland Limestone on top of Portland Sand over Kimmeridge Clay. Its jutting angles are evidence of the immense tectonic forces at work which effected so much of the geology around this part of Dorset when the continents of Africa and Europe collided around 30 million years ago, forming the Alps. This cliff section represents the most Northerly impact ripple from that event.

Rock Pools

The rocky out crop of Worbarrow Tout provides some rock pooling opportunities arount its base. Be sure to time your visit with low tide.

Pink Sea Fans

The rocky seabed off Worbarrow Tout is the most easterly location along the south coast for colonies of a rare type of coral called the Pink Sea Fan. The slow growing coral is a protected species and individuals are being monitored by divers to learn more about their growth characteristics.

Flowers Barrow

Overlooking the bays of Worbarrow and Mupe on the top of the chalk at 160 meters above sea level is Flowers Barrow, an extensive Iron Age hill fort. Originally the site covered an area of around 20 acres, about a third of which has since collapsed into the sea due to cliff falls and coastal erosion. Along with Dorchester’s Maiden Castle and Blandford’s Hod Hill, Flowers Barrow was one of many hill forts occupied by the local tribe, the Durotriges, which were taken and occupied by the 2nd Roman Legion, Augusta, after the invasion of 43 AD. The views from the top on a clear day are outstanding. A more modern hill fort stands on the cliff edge overlooking Worbarrow Bay in the form of a concrete WW2 pillbox.