Ancient seabeds at Southerndown

Glamorgan Heritage Coast at Southerndown, seen from the viewing point in Dunraven Park on the clifftop

When I visited Dunraven at Southerndown on Christmas Day (see blog post here) I did say I would tell you some more about the cliffs of the Heritage Coast itself. So here goes.

Dunraven Castle is on a headland between two beaches. The tip of the headland is called Witches Point. The beach on one side is hard to reach, but looks good in pictures taken from the Dunraven viewing point, while the other is a popular beach for families, dog walkers – and BBC TV filming.

I love the ripples in the rock of this wave-cut platform on the beach to the south

These Southerndown cliffs are made up of layers of sedimentary rocks, laid down as the calcium skeletons of marine creatures, mud silt and sand at the bottom of ancient seas. Over millions of years they solidified into limestone, shale and pebbly conglomerate.

The oldest rocks here are hard, grey Carboniferous limestones, now found at sea level. These were laid down in a warm, shallow sea 300 million years ago when what is now Wales was just south of the equator.

Although there is some sand, this beach is hard to reach

This crust was folded, fractured and eroded over the next 100 million years during the Variscan orogeny, a time when the southern land mass of Gondwana slowly collided with the northern land mass of Laurussia to create the supercontinent of Pangea.

You can see the layers of sediments in the nearest cliff

Coming back over the headland you reach the main Southerndown beach, an area called Dunraven Bay. There is car parking here.

Back over to Dunraven Bay

Around 200 million years ago, in the Triassic and early Jurassic periods, this area again lay underneath a warm, shallow, equatorial sea.

New deposits included a red Triassic conglomerate and a creamy white Jurassic limestone known as Sutton stone. Overlying these, the “Southerndown beds” consist of blue/grey limestones with thin shale partings in between.

An outcrop half-way along Dunraven Bay beach

Beyond the beach is Witches Point or, in Welsh, Trwyn y Witch – there are lots of grey pebbles but plenty of sand when the tide is out

The beach doubled as Bad Wolf Bay (in Norway) in Doctor Who – the place where the Doctor and Rose said goodbye in the episode Doomsday. I cried! If you want to watch the parting again it’s on YouTube.

David Tennant as the 10th Doctor and Billie Piper as Rose Tyler on the beach

It’s a very atmospheric place

At low tide, Triassic deposits dated at 250 million years, can be seen extending for 300 metres out to sea.

At the other end of the beach you can walk out a way on a concrete path

Away from the sea you can see the clear layers in the cliffs, but don’t get too close as they are crumbling…

Broken slabs of limestone under foot

The cliffs show the layers of limestone and shale

Most of these rocks have been known as “Blue Lias“, a particular geological formation of a certain date with thick beds of limestone and thin layers of shale between. Lias is an old word for limestone. The Jurassic cliffs around Lyme Regis in Dorset are also “Blue Lias”.

Minerals such as lead sulphide and barium sulphate were deposited in the limestone layers around 200 million years ago – and I wonder if that is why there is a yellow tinge to the cliffs?

A closer look

This part of the beach was used for another Doctor Who setting. The 11th Doctor, Matt Smith, was here with Amy Pond (Karen Gillan) and River Song (Alex Kingston) in episodes The Time of Angels and Flesh and Stone…

The Tardis on the beach – or alien planet Alfava Metraxis in Doctor Who

The Jurassic rocks are rich in fossils. Shells of bivalves and ammonites, fragments of crinoids, corals and pieces of carbonised fossil wood are quite common. There is now a display to show people what to look for…

The information reads: The fossil remains of Gryphaea arcuata or ‘Devil’s toenails’ are very common along the Glamorgan Heritage Coast. These extinct marine oysters lived in large colonies on the muddy sea bed in the warm, shallow waters of the Jurassic period. The shells consist of two articulated parts: a larger, gnarly-shaped shell (the ‘toenail’) and a smaller, flattened shell (the ‘lid’). The larger, curved shell has prominent growth bands.

A sample of ‘devil’s toenails’

Here are some I picked up along the coast at St Donat’s many years ago

The information reads: The Jurassic period had a warm, humid climate, which allowed lush jungles to cover most of the landscape. Conifers were the dominant land plants and in this area there seems to have been an abundance of trees in the ‘Araucariaceae’ family. Araucaria trees still grow in the wild in central Chile and you may even have one in your garden. You might know it better as the Monkey Puzzle tree!

A fragment of fossil tree

The information reads: Ammonites, with their typically ribbed spiral-form shell, are perhaps the most widely known fossils. These creatures lived in the seas from 240 million years ago, until they became extinct 65 million years ago along with the dinosaurs. The name ‘Ammonite’ originates from the Greek ram-horned god called Ammon. Today their closest living relative is the nautilus, found in the Pacific Ocean, which belongs to the same family as the squid, octopus and cuttlefish.

A fragment of a large fossil ammonite

There’s still life on the beach…

I rather liked this seaweed…

…a closer look – I’m pretty sure it’s a Fucus, probably Fucus spiralis, although not very mature and not very twisted – not enough bladders to be Fucus vesiculosus and not serrated enough to be Fucus serratus

And so we return to the present day at Southerndown – but with 300 million years of life on Earth on display, what better setting could there be for a Time Lord like the Doctor and his companions…

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