Sunday, 13 May 2007

Volcanoes and Coral Reefs in South Gloucestershire

Yesterday I spent my day looking at lava which flowed over the Tortworth area about 425 million years ago when this bit of the Earth's crust was about 30 degrees south of the equator.

Later we moved into a warm, shallow sea where I collected about 20 little horn corals, Pycnactis (as illustrated), only about 3 cm long.

Of course, I was on the Bath Geological Society's field trip, mentioned in my post of 6th May. It was an excellent trip, very well researched and organised. It was led by an expert on the geology of the area, a member of both the Bath Geological Society and of the Avon RIGS Group. The leader's car boot was full of beautiful specimens he had collected previously from the sites. He had specimens of all the creatures shown in the cartoon - the tabulate 'chain' coral, Halysites, trilobites, crinoids and brachiopods. The sea was teeming with life but there was virtually nothing on land; no trees, no flowers, no grass and certainly no animals. At least the rocks would have been well exposed.

Thursday, 10 May 2007

Geology of the Hot Springs, Bath

Have you seen the article about the hot springs in Bath in 'Geoscience in South-West England', Journal of the Ussher Society?

Click here to view it.

There are lots of interesting articles in this Journal so it's worth scrolling through the website.

Tuesday, 8 May 2007

Dinosaurs of Gloucestershire

Have you seen the new posters produced by the Gloucestershire Geology Trust? (in the Publications section)

There are 7 in total, all A2 size.

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Sunday, 6 May 2007

New RIGS sites in South Gloucestershire

Recently the only known exposure of the early Devonian (Downtonian) Thornbury Beds in the outskirts of Thornbury has achieved RIGS status. It is a small roadside stream bank showing the maroon sandstones typical of this formation. They are about 410 million years old and were deposited in desert conditions when 'Britain' was at about 23 degrees South.

A second recently identified RIGS site is near the castle and Parish Church where a low cliff displays the Triassic Dolomitic Conglomerate as a series of clastic flows fining from south to north. Some of the clasts are boulders 1 metre across. You can imagine the power of the flash flood that moved these. It's called 'Thornbury Rock' not to be confused with the sugary stick. It is about 230 million years old and was deposited when 'Britain' was again in desert latitudes at about 23 degrees North.

A third RIGS is in the Tortworth Inlier and is of the Silurian Wenlock Limestone. It's in a ditch 2m x 1m but it does have very good fossils, including stromatolites (algal mats). This limestone is about 425 million years old and was formed in a warm sea when 'Britain' was at about 30 degrees South. This site is on private land and will be visited by members of the Bath Geological Society on their field trip on 12th May.