Newbury Geology Society

24/04/2024

March was the group’s first trip of the year and was also our annual weekend away. This year we visited North Norfolk. After an early breakfast at Kings Lynn Premier Inn on Saturday morning we met Tim Holt-Wilson, a local geological expert, who gave us an introduction to the purpose of the field meeting weekend. Tim explained Saturday would mainly be spent looking at rocks of the Lower Cretaceous and Sunday we will be looking much younger exposures from the Pleistocene and Holocene
Our first site was Ling Common in the Leziate Beds of the Sandringham Sands Farm formation. Dating to c135Ma they comprise unconsolidated fine to medium-grained, cross-bedded quartz sands which are acidic, so no fossils were found. Some geodes and boxstones were found. Sitting on the sands was a large boulder. Tim explained this was a remnant of a Pleistocene silcrete layer (similar to a sarcen). This was quartzite and is known locally as “silver carr” or “Leziate quartzite”. Few of these blocks remain in situ as most have been quarried and used in local buildings.
Next, we took a short trip to St Laurence Church, Castle Rising where we could see the “silver carr” blocks used in the construction of the church. Tim also pointed out several blocks of Carstone in the walls. An iron cemented pebbly sandstone, c110Ma, it was also well used in buildings in the area.
Continuing eastwards our third site was at the old railway cutting at Wolferton. Here we viewed the Dersingham Formation c126Ma, a rhythmic succession of thinly interbedded, fine-grained sands, ferruginous sandstones, silts and clays, resting on the Sandringham Sands Farm Formation (seen earlier). The junction of the two was obvious due to the colour change.
The fourth site of the day was Hunstanton Cliffs, a biological and geological Site of Special Scientific Interest. It is also Geological Conservation Review site. The sea cliff, up to 18 metres high had a distinct colour contrast between the exposed strata, from the rusty brown Carstone Formation at the base of the exposure, the brick red of the Hunstanton Red Chalk Formation and finally the white and grey colours of the Ferriby Chalk Formation, at the top of the exposure. The Carstone c110Ma, was deposited in a high energy, shallow sea, near shore environment with some cross-stratification observed. The Red Chalk c101 Ma, with red colour coming from iron pigments, was very rich in fossils (including ammonites and belemnites). The top of this bed and the base of the overlying white chalk showed signs of bioturbation. The Ferriby Chalk c99Ma, extends to the top of the cliff and is approximately 10 metres thick. It contains brachiopods, belemnites, bivalves, echinoids and ammonites.
Our final stop of the day was at Holme-next-to-Sea Nature Reserve. The site where Seahenge was discovered in 1998 and is now preserved and resides in Kings Lynn Museum. Here we could view a sequence of Holocene deposits. Walking across the beach to the sea we saw a layer of peat over a layer of clay. Tim explained this peat formed during the Bronze Age c0.4Ma, in a mixed freshwater marsh and woodland environment. At the back of the beach was a retreating dune complex and beyond that a salt water marsh.
After a quick refresh at our accommodation, we all met for an excellent group dinner at The Nelson, Clenchwarton.
Sunday morning started grey as we made our way to West Runton our final location of the weekend. Walking onto the beach Tim pointed out the sequence with Chalk (marine c90Ma) at low tide level, overlain with Wroxham Crag (marine c3Ma-1.5Ma), concreted, orange, iron rich sands, gravels and pebble deposits containing clays on the foreshore and then the Cromer Forest Formation (marine and estuary) topped off with superficial deposits in the cliff . We were particularly interested in the West Runton Freshwater bed dating between 720,000 and 650,000 An internationally famous “Type Site” for the “Cromerian Interglacial Period”. Forming a dark bed at the base of the cliff up to a maximum of 2 metres thick it is highly fossiliferous and rich in the remains of plants and trees (seeds, cones, wood, fungi and pollen) Various mouse, vole and deer species, spotted hyena, horse, duck, goose, wolf, wild boar, bear and extinct species of rhino, giant deer, giant beaver, big cat and macaque monkey have also been found in this deposit. The most famous of these being the West Runton Elephant. Standing 4.8 metres high it was about 85% complete and is the most complete set of bones of a steppe mammoth that has ever been unearthed in the world.
Above this were thick yellow and brown sandy deposits known as the Contorted Drift comprising fine layering of different types of sediments. Some were made by the outwash streams, created when the glaciers melted, others from wind-blown sands during intensely dry and cold periods. Some of the fine layers are twisted into strange patterns, by the weight of the huge ice sheets above pushed and contorted the deposits. These are the best Ice Age sediments to be seen in the whole of the UK.
Also, of note under Wood Hill Tim pointed out rafts of chalk hundreds of metres long which have been thrusted and folded by ice moving from the north north west, raised up to 40m above beach level and incorporated within the Contorted Drift. These are some of the most spectacular glaciotectonics in Europe. Tim also mentioned areas of the sea bed have been mapped as to where these chalk rafts originated.
We had hoped to move on to East Runton beach to see the flint Paramoudra but with the tide not cooperating and time getting on we thanked Tim for an excellent weekend and left for home.

29/02/2024

Dr Herbert Charles "Leslie" James 26th September 1940 - 1st February 2024

The group's geologist sadly passed away earlier this month. Les taught so many of us, bringing geology to life on many field trips and in classes, over two decades of the Newbury geology group. He was as characterful as he was knowledgeable. He will be missed.

19/10/2023

September marked the start of the group’s 2023/2024 program of trips. Fourteen members made the trip meeting at Flaxley Schoolroom Village Hall, Gloucestershire. Here we met Dave Green, a local geologist and expert who was to lead us on a 3 mile walk to examine a major fault in the area.
Our first stop was Flaxley Quarry. Here we could see the junction of the Aymestry Limestone and the Lower Ludlow Shales. Dave pointed out that the Aymestry Limestones were slightly overturned. A few fossils were observed in the quarry, mainly brachiopods and an interesting nautiloid.
Moving on we started to climb the ridge towards Mugglewort Wood. Halfway up we stopped to view the landscape. Dave pointed out the ridge we were on was the Aymestry Limestone. It stood out because the strata were dipping to the west and erosion of softer material had formed the crests. A short distance to the east the next ridge was the Wenlock Limestone and the vale between, the softer Ludlow Shales. Beyond this Dave pointed out the Blaisdon fault, running approximately along the hedge line. Running north to the Malverns and south toward Bristol the area to the east of the fault had subsided approximately 2km since the Permian and the fault was the western edge of a large grabben. We were standing on Silurian rocks c425 million and the other side of the fault were Triassic Mercia Mudstones c225 million. Beyond the Triassic we could see the Lias of the Jurassic and the Cotswold scarp beyond.
A little further up the slope Dave showed us a view to the west from our ridge across the older Raglan Mudstone Formation.
Walking on we joined the old Ross on Wye to Gloucester railway line. Dave asked the group to look out for a point where the colour of the rocks in the embankment changes. When it was pointed out the rocks changed from grey to red Dave explained we were now standing directly on the Blaisdon Fault. On inspection of the embankment which had become overgrown we were just able to identify the Mercia Mudstone rocks and Wenlock Limestone either side of the fault and evidence of drag folding of the fault.
During a break for lunch the group held is AGM. Neil gave a summary of the group’s activities during the last year and that work was ongoing on the next year’s programme. Jackie explained the accounts summarizing that the finances were in a good state with no liabilities and a small balance in the account to cover contingencies.
We returned to Flaxley and made our way north to Hobbs Quarry. It produced burning lime and there is an old kiln standing nearby. Classic exposures of Silurian Wenlock limestone were left once quarrying ceased. The series of algal and coral reefs have major visual impact and are called 'ballstones' because they have a circular cross-section. These are unbedded, very fine-grained limestones deposited by calcareous algae. Drapes of bedded limestone overlay the reefs and were formed about 400 million years ago when the region was under warm seas.
By now the rain had arrived so we thanked Dave Green for an excellent day and returned home.

08/04/2023

Anglesey Weekend March 2023

Initially planned for March 2020 the group finally made it to Anglesey for its annual weekend away trip. A great deal of thanks goes to Mike and Helen who planned the itinerary but could not be with us this year.
Led by Neil we met near the old Mermaid Hotel at the southern end of Anglesey. Neil gave the group a brief explanation of the geological formation of Anglesey before we took a short walk to view some of the youngest geology on the island from the Quaternary, a section through a drumlin. Formed of glacial till under the ice, these elongated hills have their long axis parallel with the direction of the ice flow and can vary greatly in size. The glacier side is always high and steep, while the lee side is smooth and tapers gently in the direction of ice movement. There is much debate over their formation. The two favourite theories being subglacial sediment deformation and erosion associated with catastrophic meltwater flooding under the ice.
Travelling north along the west coast our next stop was the beautiful Llanddwyn Island. After a long walk across the beach, we first encountered pillow lavas. Basalt erupted on the ocean floor at a constructive plate margin. The rapidly cooling magma forms a skin, cooled margin, when in contact with cold water creating pillow shapes, then as they settled the higher pillows moulded around those beneath. Between the pillows we could see red jasper, greyish quartz, lime-green epidote, minerals precipitated from sea water. Moving on to the northwest of the island we examined the agglomerates on the cliff face. Comprising angular fragments of lava ejected by volcanic activity angular fragments in a fine tuff matrix. Heading south past the ruined church of St Dwynwen to the concrete causeway we saw exposures of the Gwna Melange. A melange is a breccia lacking in clear internal bedding and consisting of a chaotic mixture of clasts of varying compositions and sizes in a fine- grained matrix. We also saw a good example of a dolerite d**e cutting through the melange.
After a brief stop for lunch at Porth Trecastell we ventured onto the beach to look at the exposures of the Penymynydd schists which date back to the pre-Cambrian. They were wrinkled and also faulted, as would be expected in ancient rocks. On one side of the fault there were black Graphitic schists.
Just a few hundred metres along the coast we stopped again at Porth Nobla. Here the main interest was to view glacial till and a large picrite erratic. Late Pleistocene glaciers flowing across Anglesey from the north-east carried material from as far away as Scotland and the Lake District. Whilst Snowdon is just a few miles away the Welsh ice only reached the Menai Straights before being forced south by the Irish Sea Ice. The picrite erratic probably came from a few miles away to the north east.
Our next stop was Porth Dafarch. The bay was predominately pre-Cambrian mica-schists of the South Stack group. The tide was rising fast, but we just had time to get close to a Paleogene dolerite d**e. This d**e was one of many formed by tectonic processes that split the ancient continent of Pangea approximately 65 Ma.
Our final site of the day was at South Stack lighthouse. Before tackling the 300 or more steps toward the lighthouse we had time to visit the excellent RSPB café where a few members were very lucky to get a sighting of a chough. Below the lighthouse was a large anticline. On the steep right-hand limb of the syncline there were a cascade of minor folds of the thinner beds of greywake. Further down the steps we came to a window where we could look back to view the cliff. Part of the Monian Super Group the South Stack Formation is the lowest this group consists of bedded alternating sandstones and siltstones, including some massive quartzites. These are turbidites, clastic sedimentary rocks deposited by turbulent underwater currents laden with debris in a marine sedimentary basin.
In the evening several of the group met at The Inn at The Bay, Trearddur for an evening meal and to discuss the days offerings.

Day 2 to follow.

22/03/2023

Interesting interview with earthquake scientist, James Jackson, an Emeritus Professor of Active Tectonics at the University of Cambridge recommended listening from a member.

How studying processes that shape the planet’s surface can help us become more resilient.

07/03/2023

February’s trip took the group to Buckinghamshire where we examined rocks from the Middle and Upper Jurassic. We met at Thornborough Bridge on the outskirts of Buckingham where Tim, our leader for the day gave us an introductory talk on the classification of limestones. With our newfound knowledge we made our way to the bridge to try and classify the stone. Constructed from Blisworth Limestone, possibly from the nearby Coombs Quarry the bridge dates from the late 14th century and is the last surviving medieval bridge in Buckinghamshire. Viewing the stone in the bridge we saw evidence of its formation, ooliths, shells and cross-stratification that shows the movement of water currents in the sea that deposited these particles. Areas of the bridge had been repaired using blocks of Portland limestone which weathers to a much lighter shade.From the bridge we walked across the fields to Coombs Quarry which was used for building stone and rock for lime burning from Roman times until the end of the 19th century. The exposures here are part of the Great Oolite Group. Tim gave an explanation of the sequence in the quarry and with the help of the information boards the group set about trying to identify the different layers. The face consisted, Blisworth Limestone at the base laid down in a shallow sea environment. Above this the Blisworth Clay deposited in a shallow brackish to fresh water close to the shoreline, and overlying this the Cornbrash formation a return to marine conditions. The Cornbrash was only visible in one part of the quarry thanks to a fault.
Before leaving the area we had a quick look at two Romano British burial mounds just north of the bridge which date to around 200 AD. A burial site for high status Britons the mounds were excavated in 1839 for the Duke of Buckingham and the finds were sent to the Cambridge Museum of Archaeology.
In the afternoon we visited the village of Brill sitting on one of a number of hills sitting above the clay vales. Tim explained that these hills are only present because of the resistant capping provided by the Whitchurch Sandstone (Lower Cretaceous) and the equally hard underlying Purbeck and Portland beds (Upper Jurassic). Locally sourced clay from the Whitchurch Sand Formation provided raw material for Brill’s brickmaking and perhaps, Brills most famous export Brill pottery dating from 13th Century to the mid-1800s. Evidence of these workings could be seen in grassed over pits such as the ones observed near the Windmill. We took a short walk around the village to see evidence of these rock used in the buildings.

24/01/2023

Our first trip in 2023 on a cold January day took us to Oxford University Museum of Natural History for a look behind the scenes.
The museum opened in 1860 and is now Grade 1 listed. Designed by the Irish architects Thomas Deane and Benjamin Woodward, it is a striking example of Victorian neo-Gothic architecture, the building's style was strongly influenced by the ideas of 19th-century art critic, John Ruskin. Ruskin believed that architecture should be shaped by energies of the natural world, and thanks to his connections with a number of eminent Pre-Raphaelite artists, the Museum's design and decoration now stand as prime examples of the Pre-Raphaelite vision of science and art.
Our guides for the visit were Eliza, Head of Earth Collections, palaeontology and Duncan, Collections Manager Earth Collections, mineralogy. We split into two groups and Duncan led our group to mineralogy. Containing over 30,000 mineral specimens of global provenance with some dating back to 1600s. Duncan showed us several examples including some from the moho and a piece of continental crust dating 4.03 billion years old. We then moved upstairs where we examined samples from meteorites and the fascinating Corsi Collection of Decorative Stones comprising 1,000 polished slabs collected in the early 19th century by Roman lawyer Faustino Corsi which was purchased for the museum in 1827.
It was time for the groups to swap and we joined Eliza for the remainder of the tour. The palaeontology collection includes one of the world’s most important collections of Middle Jurassic dinosaurs. It features around 400,000 fossils, ranging from the Archean, ~2.7 billion years ago, to the end of the Pleistocene, 11,700 years ago. Eliza gave us some history of the early days of the museum and controversy that surrounded it at the time. Important figures featuring in the collections include, William Buckland, Mary Anning and William Arkell to name a few. We then examined several fossils including a Megalodon tooth and the lower jaw of the carnivorous dinosaur Megalosaurus, nine metres long in life and weighing about a tonne. Megalosaurus became the first creature to be named a ‘dinosaur’, in 1824.
After the tour had finished there was time for members to have lunch at the café before spending some time look at the exhibits in the main hall.

18/11/2022

A bumper 22 members made the trip to Riddlesdown Quarry, Croydon on Sunday. Here we were very lucky to be led by Rory Mortimore, one of the leading chalk specialists in the UK. Riddlesdown is one of the last remaining quarries in the London area and provides an excellent resource for engineers working on projects like HS2 and the Thames Sewer to understand problems that they may encounter.
After an introduction on how chalk was formed, we moved to the quarry face in the southwest corner where the youngest rocks, the New Pit Formation are exposed. A blocky, white firm to moderately hard chalk with numerous marl seams. Rory pointed out several beds of the Glynde marls. It was explained the marls were a volcanic ash. Moving up the sequence Rory picked out the Southerham marl near the base of the Lewis Nodular Chalk which he described as an important marker bed which can be identified in most of the chalk regions.
We then moved to the centre, the main face of the quarry to view the Lewes Nodular Chalk. This chalk is mostly composed of hard to very hard nodular chalks, with interbedded soft to medium hard chalks. In this face we observed prominent marker beds including the Lewes Marl and underlying tabular flints.
Finally, we moved to the viewing point to view the Seaford Chalk, a firm white chalk with flint seams. Rory pointed out the Bar End/Rochester Hardground, the boundary between the Seaford and Lewis Nodular Chalk. The top of the Seaford chalk appeared castellated caused by dissolution pipes into the chalk with fills of Clay-with-flint, red brown clays which also cap the top of the quarry.
This closed a very informative morning and the group warmly thanked Rory for joining us for the morning.
In the afternoon we visited Chislehurst caves. Over 22 miles of tunnels and caverns the caves date back to the 9th century. The tour focused mainly on the history of the caves but geologically they are cut in the Seaford chalk. In some areas in the roof of the caves the Bullhead Beds, at the base of the overlying Thanet sands were visible. We also saw an ammonite cast approximately 700mm in diameter.

21/10/2022

On Sunday the group made the long trip the North Somerset. The morning was spent at St Audrie’s Bay. At the base of the steps, we observed the gently dipping sequence of late Triassic and early Jurassic rocks. The cliffs were made up of alternating red/green beds of Mercia Mudstones which reflect the relative levels of oxygen in the environment as it changed from terrestrial to marine. It was explained that cyclic repetition of the beds was probably caused by the Milankovic Cycle, changes in the earth’s orbital movements. Further west along the bay the sequence continued into the Lower Lias of the Jurassic. Here the junction between the Triassic/Jurassic boundary was once proposed as a candidate World Stratotype section for the base of the Jurassic, a “Golden Spike” due to the presence of an early ammonite, Psiloceras Planorbes. We did not find this point on the day.
In the afternoon we travelled to Kilve beach to look at the structural geology. Faults can be traced across the beach and into the cliffs almost giving a 3D impression of the structure. It was explained that the Bristol Channel was a rift basin formed about 200 million years ago by plate tectonic forces. It was here that many ideas of fault geometry were built and tested. Even today the area is heavily used by students and industry professionals to enhance their own knowledge of fault systems. Three main episodes are responsible for sediment accumulation. The Jurassic mudstones have excellent oil source rock potential. However, the interbedded limestones posses very poor reservoir potential. In the 1920s there was a short-lived attempt to extract oil from the shales of the Lias at Kilve. An experimental retort was built but volumes did not prove commercial. Large amounts of capital were raised and no doubt a few got very rich (it’s been called a scam) and very many lost their shirts.
Other items viewed on the day were various ammonite fossils and mud volcanoes. These structures are thought to have formed on the sea floor by sediment-laden water forcing its way to the surface driven by pressure and/or methane.

06/10/2022

Living over 200 million years ago, Scleromochlus helps to show how ancient reptiles took their first steps towards flight.