STRANGE circular structures discovered on the seafloor at Weymouth Bay have provided new insights into the geology of the Jurassic Coast.

These new images have been obtained by Dorset Wildlife Trust's (DWT) Dorset Integrated Seabed Survey – also known as DORIS.

DWT has organised a lecture about the discovery, which will be led by Dan Bosence, Emeritus Professor of Geology at Royal Holloway University, London.

During the talk DWT's living seas policy and evidence manager Peter Tinsley will give an introduction about the DORIS project, which DWT says has effectively 'peeled back the sea' revealing the seabed off the county's coast for the first time.

Mr Tinsley said: "It is hard to think back to how little we used to know about the seabed before DORIS.

"Most of our information came about from point sources – a grab sample or a dive.

"Even on a good day a diver can only see about ten metres in any direction, so it would take an awful lot of dives – and many of them very similar – to fill in the gaps."

The large circular structures discovered in the Purbeck Limestone have not previously been seen in any of the coastal cliffs or quarries from Durlston Bay to Portland, despite more then a century of geological research.

Professor Bosence will discuss their possible modes of formation and the geological implications of these explanations.

The DORIS project, which started in 2008, was made possible following a major award from Viridor Credits, the Landfill Tax Communities Fund.

DWT, working in collaboration with the Maritime and Coastguard Agency, the Channel Coastal Observatory and the National Oceanographic Centre, Southampton, set out to map natural seabed features.

It started with a full cover, high resolution multi-beam sonar survey, which revealed the shape of the seabed - detailed down to less than one metre resolution. Then, in 2009, geologists worked to match the new data to previous grab samples from divers and remote cameras.

Championing the efficiency of DORIS, Mr Tinsley said it gave them an insight into every ledge, large boulder and sand-wave.

"Perhaps the biggest surprise was just how much of the seabed geology was visible," he added. "The strong tidal currents keep most of the seabed clear of overlying sediments, and that's what makes it so fascinating."

The talk, organised by the Destination Kimmeridge Partnership, will be held at The Etches Collection Museum of Jurassic Marine Life, Kimmeridge, at 2.30pm on Sunday, September 23.

A suggested donation of £4 on the door is requested.

Visit or call 01929 481044 to find out more or reserve your place.


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