Geology Blog

 Deadmaids Quarry, Mere, Wiltshire,      Saturday 2nd September,   Bath Geological Society

Bath Geological Society is organizing a major geoconservation event to clean up the face of this important exposure and would welcome any assistance that BNS members can give. It will also give an opportunity to see rocks that are not exposed in the Avon Area. The whole face is obscured by ivy, grass and brambles. Parking is at the back of the trading estate just next to the location. Bring gardening gloves, secateurs, loppers hard hat and eye defenders will keep out the debris. Bringing a packed lunch is recommended.

Deadmaids quarry just to the west of Mere is an S.S.S.I. for the only clear location showing the junction between Upper Greensand and the Lower Chalk. This site is of importance both for the Chalk and for the Upper Greensand units of the Cretaceous. The quarry provides the finest available section in south west England of the Upper Greensand/Chalk transition as developed in the area to the north of a shallow area in the Cretaceous sea known as the ‘mid-Dorset Swell’. The unique and highly fossiliferous ‘Popple Bed’ is well exposed above the Chert Beds, and is of importance for the rich and diverse assemblage of fossil bivalves, gastropods, ammonites, brachiopods and echinoids which it contains, mainly as phosphatised casts. This is a key locality for study of the palaeontology of the lowermost part of the Chalk (the Cenomanian Stage) in Britain

See: www.thegcr.org.uk/SiteReports.cfm?Step=3v for more information about the location.

If you have any queries concerning the trip please contact Isabel Buckingham at isabelbuckingham@btinternet.com or tel 01985219313. A location plan and travel directions can be found on the Bath G.S. website

Saturday 7th October, Ogmore and Southerndown

Dr. Geraint Owen, Swansea University

Mesozoic rocks unconformably overlie Upper Palaeozoic rocks in the Vale of Glamorgan. The rock units and their relationships are superbly exposed along the spectacular Glamorgan Heritage Coast. Highlights include richly fossiliferous Carboniferous Limestone and Blue Lias (early Jurassic); marginal facies of the Mesozoic that developed close to upstanding areas of Carboniferous Limestone and are preserved adjacent to unconformities in the form of wadi breccias and rocky shoreline deposits; a variety of styles of unconformity; and impressive folds and faults.

Meet at the car park at the south end of Ogmore-by-Sea village (SS 869 734) and later move to the car park at Dunraven Bay. There is plenty of parking available but with pay-and-display fees at Ogmore and a toll at Southerndown. Strong footwear and packed lunch will be needed. For further information, including time of meeting please contact the Bath Field Trips Secretary admin@bathgeolsoc.org.uk (01249) 813628 or 443019

Thursday 7 to Sunday 10 September 2017

This September, the Alfred Gillett Trust is hosting a free pop-up exhibition of fossilized ichthyosaurs found in Street as part of the national Heritage Open Days initiative. From 7-10 September, the public can view the fossils and learn about how they were found and what they tell us about the local environment.

19 large ichthyosaur fossils will be on display, as well a selection of smaller fossils found in the local area. Known as ‘sea dragons’, ichthyosaurs were dolphin-like marine reptiles that swam in the warm seas which covered Somerset around 200 million years ago. Street is known internationally for the quality and quantity of the fossils found in the local Blue Lias rock.

The fossils were found in local quarries in the 19th century by Alfred Gillett, a cousin of the founders of Clarks the shoemakers. Clarks family members were also interested in the fossils which were being discovered in the area, and this impressive collection gradually developed. First displayed in Glastonbury Town Hall in 1880, the fossils were soon moved into a purpose-built Geological Museum in Crispin Hall in Street, which was opened in 1887.

Noted geologists and academics visited the collection to study them, along with tourists and residents in the locality of Street. Such was the importance of the collection and the affection held for the fossils in the area that the newly formed Street Urban District Council chose the ichthyosaur as their symbol in 1894. It is still used today by local societies and associations.

The fossils were finally taken off public display in 1978 when they were moved into storage for conservation. Now, for the first time in nearly 40 years, locals and visitors alike will get a chance to come face-to-face with the famed sea dragons. The exhibition will be open to the public from Thursday 7 to Sunday 10 September from 10 am to 5 pm. Entrance is free, but donations towards the care and future display of the fossils would be gratefully received.

For more details ring the Alfred Gillett Trust 01458 444060.

MENDIP ROCKS FESTIVAL 2017         

This year’s Mendip Rocks Festival will run from 30 September to 31October 2017. There will be a full programme of events and visits of interest to BNS members. Too many to list here but please see the websites of Somerset Earth Science Centre and The Mendip Society. These two organisations are jointly organizing this year’s event.

 

Geology section Field Meeting  31 May 2017

We had a very pleasant evening stroll on Clevedon beach, with a good turn out of 12 BNS members together with Professor Susan Marriott and Dr Shaun Lavis from the University of the West of England and the Geologists’ Association. Being in such a public place, rather than tucked away in a quarry, even meant that other beach users came to ask what we were looking at, with three young, potential geologists, also engaging with us.

After investigating the main fault by the pier, with its associated mineralisation, we studied the unconformity between the rocks of the Lower Carboniferous Avon Group and the lacustrine limestone facies of the Triassic Mercia Mudstone Group.  We were looking at micro/macro scale geology, with miniature faults, folds and slickensides showing well along the beach. There was so much to see that we only covered about 100m of beach.

We saw lead, copper and iron minerals and a few fossils, especially some very delicate undamaged crinoid stems.

Thanks to Richard Ashley for organising the session, David Moore for producing maps to include in the handouts and the other members whose expertise contributed greatly to what we have learned about the geology of this compact and very interesting area.

Geology section Field Meeting to Watchet  Saturday 25th June 2016

Ten of us assembled and first we visited the museum. There were many artefacts associated with the history of the town on display including the famous incline railway – used to export iron ore from the Quantocks to South Wales from the harbour.

We visited the station. The waiting shelter had more historical photos and we inspected the Jubilee Wall which was built by children using exemplars of the rocks, minerals and fossils of the area – all identified on an attached chart. We then set off along the cliff path towards Heliwell Bay.

Steps led down to the beach where the tide was retreating – always approach this area on a falling tide as many tides reach the cliffs. On the right of the steps was a gully which followed the line of the separation between the Red Mercia Mudstone – Triassic and the undifferentiated black mass of the Charmouth Mudstone – Jurassic. This separation is marked by the Helwell Bay / Doniford fault. This is a normal fault with an upthrow of 200 metres, bringing up the Charmouth Mudstone from the upper part of the Lower Lias which is the highest part of the Jurassic rock sequence exposed on the Somerset coast. There are further, more recent Jurassic rocks out in the Bristol Channel, which is an ancient rift feature in which a great thickness of sediments has built up. To the left of the gully were Triassic rocks which had been severely contorted by their proximity to the fault. There were also circular holes in the cliff which we took to be left after evaporites had weathered out. The colouration of the strata meant that the throw of the many small faults could be clearly seen.

The main fault cannot be clearly delineated as it brings together two soft mudstones, but the gully and a line of mud and sand stretching across the bay gives a good general indication. South of this fault could be seen the low cliffs of Liassic strata of the amioceras semicostatum zone. Adjoining the beach were shales and limestones that contained small and large examples of Amioceras sp. and Coroniceras sp. The larger ones reached 32 cm in diameter. There were several beautiful examples.

The succession could be followed across the beach as the dip is about 18 degrees to the NNE.This succession went from the Red/Green/Grey Triassic Mercia Mudstone Group up through the Grey Blue Anchor Formation, the Westbury Formation of the Penarth Group followed by the Lilstock Formation, Cotham and Langport Members. The top, surface rocks on the foreshore are the shales, mudstones and limestones of the Jurassic Lower Lias. We found zone Ammonites from the Psiloceras planorbis to the Arietites bucklandi ( conibeari subzone ) as the tide retreated.

As we walked across the foreshore, we saw part of the cliff that was covered in green moss. Closer inspection revealed that water was oozing out of the cliff face and depositing a tufa layer on the surface of the cliff and on the moss. This showed that the water had dissolved calcium carbonate from the rocks as it passed through. The drop in vapour pressure as it emerged allowed the degassing of the dissolved carbon dioxide resulting in a drop in the carbonate carrying capacity of the water and so it deposited it on the surfaces it traversed.

A very interesting day covering the Triassic and Jurassic succession with excellent explanations and interpretations from Richard with lots of fossils to find on the foreshore.

Proposed Excavation of Temporary Exposure in the Lower Lias

Simon Carpenter has plans to excavate a temporary section through the rarely exposed Charmouth Mudstone Formation during the month of September. It is hoped to arrange a visit for BNS members to the excavation but if any member is interested in helping either practically or financially please contact Simon. Tel: 01373 474086, email simonccarpenter@gmail.com

Report on Geology Field Trip to Trendlewood Woods and Badgers Wood, Nailsea and Backwell, Sat 14 May

Rocks, fossils, a cave, orchids, bird song and sunshine – what more could we have asked for?

Nowhere Wood is an old quarry, now a small nature reserve providing an oasis of calm in the middle of Nailsea. It ceased being worked about 100 years ago and now has a good stand of mature trees which are home to a wide variety of birds which were singing loudly. The best sighting was a Great Spotted Woodpecker.

The Pennant Sandstone rock exposure shows good examples of river bed dune structures (cross bedding), some small faults and some fossil wood. This rock bed is over 600m deep and stretches all across Southern England. It was formed from material eroding from Volcanoes somewhere to the South East, some volcanoes!! The rock was quarried for use in buildings and paving in Bristol and Nailsea. This is the best surviving exposure of the Pennant Sandstone in the Nailsea Coalfield. Further details may be found on the relevant page on the Avon RIGS blog:-

http://avonrigsoutcrop.blogspot.co.uk/2013/01/trendlewood-quarry-nailsea.html

We then moved onto Badgers Wood in Backwell, managed by Backwell Environmental Trust,  www.backwellenvironmenttrust.org. This has been the site of small and large scale quarrying of Clifton Down Limestone and the reserve is now a wooded area with many small rock outcrops. There is a small cave, opened up during quarrying, with very unusual formations of crystals in the walls. We postulated that these were probably formed by Hydro-Thermal action and subsequently surface water has entered and dissolved some of the limestone. Adjacent was a fantastic face of limestone which had formed by a blue-green algal colony, the stromatolites growing through each succeeding layer of limestone, giving a very fine laminated appearance. The visible exposure is around 2 metres high, so consider how many thousand (million?) years that a stromatolite colony lived for. And there are still living examples in tropical seas today.

We also discovered a fantastic specimen of fossil colonial coral, Siphonodendron martini. These corals have daily growth bands, interestingly indicating that a year was 391 days long in Carboniferous times, so we are slowing down.

Walking up to the rim of a large quarry which ceased operating only in 1999 we passed Early Purple Orchids and Lords and Ladies, happened upon a white tailed bumble bee.

We then decamped to a pub for a late lunch and a drink, so all round a very interesting, varied and enjoyable field trip, enjoyed by 8 BNS members and 2 WEGA guests. Thanks to Richard for leading us on the right paths (most of the time) and for his depth of knowledge and clear explanations. David

29 April 2016

Report on Geology Field Trip to Sully Island. Sat 23 April.

This trip was laid on by Bath Geological Society. There was a great turnout of 28 people of whom 10 were BNATS members. The trip was led by Professor Maurice Tucker (Bristol Uni. and BGS) who extensively studied this area when he was a Professor at Cardiff Uni. some years ago. He in fact first identified the dinosaur footprints which are found at Bendrick Rock, and which we visited. The best specimens were lifted and are now in Cardiff Museum, to protect them from “collectors” and the ravages of the sea. We even had on the trip, one of the guys involved in removing them, he said his back still hurt!

Most of the rocks we looked at were deposited when this was the edge of an inland sea which stretched to south of Paris. There is a lot to study in a small area and we saw some great examples of faulting, conglomerates, and of course the dinosaur footprints.

David

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