At the April meeting Prof. David James gave a talk entitled: Some Structural and Mineralogical Problems in the Corris Slate Belt
The talk centred on the area known as the Corris Slate Belt. This is an area between Dinas Mawddwy and Towyn which is on the slope of the Harlech Dome. The rocks are Upper Ordovician /Lower Silurian in age and are formed from deep water turbidites. The rocks form a homocline with a NE-SW trend. Two of the formations i.e. the Narrow Vein and the Broad Vein contained sufficient pure mud that workable slate was produced when metamorphosed. The narrow vein being of a higher quality of slate. At the base of the Broad vein lies the Nod Glas formation which is a characteristic black hemipelagic mudstone deposited in deep oxygen-poor conditions by quiet settling of suspended mud particles from the overlying column of seawater.
Prof. James then went on to point out that the anticlines in mid-Wales peter-out into this inclined belt. He then posed the question : “were the folds formed with the belt roughly horizontal and then tilted down to the south or did the folds develop on a homocline that already existed?”
He went on to suggest that during the deposition of these rocks the Bala - Tal y Llyn Fault (Bala Lineament) was active and downthrowing to the south.
Results from various studies actually suggest this to be the case. Metamorphic studies do suggest that there was movement of the fault during sedimentation. Measurements show that with increasing burial there was an increasing low grade metamorphism from the Dolgau Mudstones to the Nod Glas. But as the Bala fault is crossed the degree of metamorphism is reduced. This shows that by the time these rocks had metamorphosed the Bala fault had downthrown the sequence to its south against the sequence to its’ north before the final phase of Acadian heat.
Paleo-current studies also support this idea. If you observe the palaeocurrents i.e the distribution of the sandstones, their transport direction, the deep water passages and thickness in the sequence you can work out when the fault was quiescent and when it was moving.
Sediment was found to flow towards the fault and flow along the fault thus showing that the fault was moving.
Further it can be found that the area contains two basins. The main turbidite basin in central Wales and a smaller basin which is the Denbigh Trough and the dividing line being the Bala lineament.
He went on to discuss the 1923 paper by WJ Pugh. Here he pointed out that the axis of the Corris anticline was anomalous for which Pugh had suggested torsion had occurred in the axis.. This area became known as the “Corris Appendix”. Prof. James went on to show that unlike the surrounding area where the strike of the cleavage is axial planar the cleavage goes straight across the “appendix”. This suggests that ,if correct, the Corris anticline must be compound as it has an axial planar cleavage in one part but predates the cleavage in another. But this is irrational.
The dip on the anticline is shallow on one side but steep on the opposite limb. This has suggested the presence of faulting. The problem with the “appendix” can be resolved by the presence of a low angle reverse fault on the eastern portion of the anticline. Others had suggested the presence of a fault but had suggested that the fault was vertical but by going underground into the Garnedd Wen mine prof. James viewed the fault which did prove to be of a low angle. This fault can be traced approximately parallel to the bedding for some distance when it then merges with a second fault.
Before any folding occurred there was a syn-sedimentary slide off the Bala lineament which produced thickening in the hanging wall. So the Corris anticline was developed when the hanging wall sequence was backthrust over the footwall sequence during the Acadian deformation
Prof. James went on to explain what he described as a geometrical puzzle and mapping problem at Aberllefenni where there is a repetition of the Narrow Vein.
The geological structure at Aberllefenni is again affected by faulting, which causes repetition of the Narrow Vein outcrop on the south of the valley. Therefore on the northern side by Foel Grochen there is only one outcrop of the Narrow vein but on the southern side of the valley the vein is repeated. Both Pugh 1923 and the BGS 1995 have presented ideas of what happens to cause the repetition but Prof. James suggests that they are both wrong. They suggested that the faulting is vertical and the fault displaces the rocks to the north as a downthrow but Prof James argues against this idea. He suggests the apparent downthrow to the north is the result of the bedding dipping more steeply than the fault plane.
He then made the prediction that the fault should come down into the valley and then climb out. So he went on an excursion into level one at Ceunant Ddu to find the fault. The fault was in the location that he predicted, showing Prof. James to be correct.
He ended with discussing scams that had occurred in the area when coal and gold where suggested to be present, shares bought and sold on speculation only for neither to be present.
A very interesting and informative talk.
Sunday 13th April 2025
At the last meeting Prof Burek gave a fascinating talk about forensics used in the untangling of the case regarding Ötzi the Iceman a 5,300-year-old glacier mummy recovered at the Tisenjoch (South Tyrol Italy) in 1991.
The talk commenced by prof. Burek describing the history of the development of forensic science in general and that of geoforensics in particular.
One of the fundamental principles in forensic geology was devised by Dr Edmund Locard (1877-1966) when he became interested in dust being transferred during a crime. It was Locard who suggested that whenever two objects come into contact, there is always a transfer of material and it was this idea that led to the fundamental idea that every contact leaves a trace. He also set up his own police lab in his attic in Lyon in 1910. The science developed over time as methods and technology has improved and now forensic geologists are routinely used on cases.
Geoforensics (forensic geology/forensic geoscience) may be described as follows:
The application of geoscience information and methods to investigations which may come before a court of law.
It’s boundaries are not clearly defined
Mainly concerned with rocks, sediments, minerals, soils and dusts and also man-made materials where natural materials are an essential part eg. cement or bricks.
Can cover air and water
Geoscience is often used in environmental forensic cases.
Its main uses being in identifying material for a match and to indicate timing of an event. The purpose of a forensic geologist at a crime scene is to collect geological samples which may include samples of, for example, minerals, soils, sediments, rocks, or natural building materials (e.g. sand, gravel, building stone and slate) or material that is derived from geological raw material (e.g. glass, bricks, concrete, plaster board or tiles).
The body of Ötzi was found by two German hikers in 1991, whilst walking in the Ötztal Alps near the Austrian and Italian borders. His removal from the ice was difficult which led to some damage of the corpse. His remains were delivered to the Institute of Forensic Medicine in Innsbruck, Austria. He was moved to Italy where he was kept in a freezer at the South Tyrol Museum of Archaeology in Bolzano, Italy.
Not much research was done on the remains for about 25 years, after which forensic experts were brought in to unravel the mystery. Unlike mummies from dry climates, the organs, tissues, bones, and skin of this “wet mummy” were intact, right down to the contents of his stomach, which allowed a very detailed study to be undertaken.
The findings showed that he was about 45 years old, 5’3’’-5’5” tall, weighed 50kg, and suffered from arthritis: gallstones and whipworms. He had old wounds consisting of a frost-bitten little left toe and broken ribs. He also had very fresh wounds of a badly cut right palm inflicted less than 48 hours previously. He had 61 tattoos from head to foot which were the oldest tattoos ever found by about 2000 years. These were located in areas of joints and spine and may have been at acupuncture treatment points. Pollen analysis discovered 30 different types of pollen in his gut. These findings suggested that he died in spring or early summer. That in the 2 days before he died, he had traveled from an elevation of 6,500 ft down to the valley floor at about 5,000 ft, and then back up into the mountains at 10,500 ft. He had consumed ibex meat, einkorn wheat, fatty bacon or cheese, and flowering plants in one meal, and red deer meat and grass or cereal in another. His last meal was eaten about 30 minutes before he died. In 2001, a CT scan revealed a flint arrowhead in his left shoulder, and a puncture at the same spot was found when his coat was examined. This led to his death. Thus he was murdered.
Recent DNA analysis has revealed that Ötzi had dark skin and dark eyes. They also found that 92% of his ancestry comes from early Anatolian farmers who migrated out of modern-day Turkey about 8000 years ago. This is the highest percentage of Anatolian heritage yet recorded in an ancient European from Ötzi’s time. DNA also shows that he is most closely related to the inhabitants of Sardinia. He had a copper-bladed axe which was new technology that required special skills to extract and process the metal. This discovery drove our understanding of the Copper Age back by 1000 years.
The use of multi-disciplinary forensic techniques shows just how even the most coldest of cases can sometimes be unravelled.
Saturday 15th March 2025
Dinosaurs and Deserts in Wales by Cindy Howells palaeontology curator National Museum of Wales.
If you are hoping to find fossils of dinosaurs or perhaps fossil trackways in Wales then in you have to travel to the SE of Wales to the Mesozoic rock outcrops that possibly contain them. The area is a narrow wedge situated between Cardiff and Porthcawl.
The first evidence of dinosaurs in the area was found in the form of footprints. A block consisting of a footprint trackway was found by TH Thompson in 1879 in a local churchyard Newton, near Porthcawl. He was a naturalist and recognised the similarity of these footprints to some recently described ones from America. He then worked in conjunction with prof.Sollas (1849 - 1936) from Bristol, to undertake further investigations of the footprints.
They not only concluded that these were dinosaur footprints but observed the similarity between these footprints and those made by flightless birds. In one experiment they persuaded an Emu to walk across wet cement to show the similarity. That was ingenious as it is the earliest idea of linking dinosaurs to birds. The prints were tridactyl, bipedal with a long central toe suggesting a Theropod dinosaur. The trace fossil itself is known as Anchisauripus.
Not only are Theropod tracks found in south Wales but bones from theropods have also been found. For example, in 1898 a fossil jaw was found by stonemasons in Bridgend and in 2012 a finger bone was discovered at Lavernock Penarth. Both of which were found in deposits of Rhaetian age (208.5-201.3 mya)
In 1879 another block of stone revealed fossil Anchisauripus but also two completely different sorts of prints. These latter prints are known as Eosauropus and will have been made perhaps by a Sauropodomorph dinosaur.
As footprints differ depending on the thickness, grain size and moisture content of the mud when they are made it is difficult to always get a really good impression of the foot that made it. But one was found by a four year old girl whilst out walking with her father during Covid lockdown, from which one could see the shape of the muscle pads, the joints and the claws. This was recovered and is now in the museum. On studying the fossil it was found that there was in fact two prints which showed that it was moving so that now the stride-length can be determined from which other measures can be deduced.
Another series of prints found by the public in 2023 occur at Penarth in redbeds similar to that which occurs at Bendricks bay. These have a very consistent stride-length but these prints are eroding very quickly.
If you go inland to the Carboniferous limestone quarries near Bridgend you will find Triassic material filtered down in fissures in the Carboniferous limestones. Here can be found bones of various creatures eg. The mammal Morganucodon oehleri. But also other finds.For example, In 1952 dinosaur bones were also found within these cave sytems eg. Pantydraco caducus a herbivore.But in 1921 they re-examined a few bones and found that they were in fact the bones of a theropod dinosaur known as Pendraig
In 2014 at Lavernock bone material was found after a rock fall which has been identified as a theropod dinosaur and has been named Dracoraptor. Therefor south Wales has a diverse fauna of dinosaurs and other reptiles covering 20 million years
A summary can be seen in the table below:
If you would like to see fossil footprints then the SSSI site of Bendricks Bay Barry is a good site to visit. Here there have been found at least four different types of footprints.The National Museum of Wales in Cardiff also has footprints on display.
An interesting talk by Cindy Howells on the fossils that can be found in Wales.
Tuesday 19th November 2024
The October talk was by member Roy McGurn.
Summary by Roy
The talk was inspired by a field trip led by Tony Crimes, a leading trilobite expert in 1970 to the Nant Ffrancon valley. In particular Tony was a leading specialist in trilobite tracks, commonly attributed the ichno-genus Cruziana, amongst others.
Cruziana,Vale do Pônsul, Penha Garcia, Portugal by Correia PM Wiki Commons
Until this time trace fossils had been more of a curiosity, as mainstream fossils were more useful for dating, still very much an objective in geological research. Trace fossils are usually found quite separate to body fossils, so correlating the two is difficult, as different modes of preservation are at play.
A trace fossil may have more than one causal animal, Cruziana has been identified in the Triassic, long after trilobites became extinct. One animal may also be responsible for several trace fossils, depending on it's behaviour.
What trace fossils tell us is how the animal behaved, culminating in the stunning walking with dinosaurs films. In this instance Tony was able to say what a trilobite was doing - resting, starting or finishing swimming or feeding and burrowing. How they moved and the prevalence of juveniles etc in the population. It is assumed, for example, that juveniles were pelagic.
That year Tony had chaired an international conference on trace fossils with a Prof Seilacher of Tubingen under the auspices of the Liverpool Geological Society. Together with Richard Fortey possibly the modern triumvirate of trilobite men.
The main sites are 2000 ft up the sides of Cwm Cuenant, a daunting field trip today probably classifying as a rock climbers "scramble" or worse. However a "debris" field behind a cottage, Ty Newydd, can be quite productive of actual fossils.
Friday 20th September 2024
The talk covered two field trips run by Chris Darmon at Geo Supplies in Sheffield. (Text and photos by Chris Simpson)
The first trip was to the Mull of Kintyre and the adjacent islands of Islay and Jura, which all lies between the Great Glen fault and the Highland Boundary fault. The second trip was to the Ayrshire coast, which is part of the Midlands Valley (Central Lowlands) terrain. These trips covered adjacent terrains, and enabled contrasts and comparisons to be made.
The Highland Boundary fault runs just south of the Mull of Kintyre. The basement for the whole of the Grampian terrain is the Rhinns complex – but it is only seen on the surface on Islay.
Typical “pink” gneiss of the Rhinns complex seen at Portnahavan.
(The scale is an A6 field notebook)
The commonest rocks on the surface are Dalradian schists which are seen from Islay in the west to Fraserborough on the east coast of Scotland. The degree of metamorphism is variable, but often low. This means that residual sedimentary features can be seen.
Dalradian schists at the side of Loch Caolisport. Original shale bed between two original sandstone beds.
(The scale is an A6 field notebook.)
Kiel Point at the southern tip of the Mull of Kintyre is a localised resistant rock standing out from its surroundings. It is a volcanic agglomerate within a volcanic pipe. The matrix is volcanic ash, and the clasts are pieces of the original country rock. The volcano came up through an area of Devonian sandstones.
Kiel Point standing above the coast road
A closer view of the exposed rock face.
Devonian sandstones on the beach close to the plug show mechanical disruption. A micro-fault is visible.
(Scale is an A6 field notebook)
The Midlands Valley (Central Lowlands) is a rift valley which was mainly filled by a variety of sedimentary rocks, but also shows evidence of widespread volcanic activity.
The North Ayrshire region has a base of Old Red Sandstone rocks with some volcanics: basaltic lava flows and 2 sets of dykes, Tertiary and Permo-Triassic. Further south, there is an ophiolite complex at Ballantrae.
A lava flow on the Eastern bank of the Firth of Clyde just south of Hunterstone
Columnar jointing is evident on the exposed rock faces.
At the beach south of Largs.
There is a dyke on the right which has come through conglomerates.
Pillow lavas on a beach south of Ballantrae.
The lava is vesiculated.
Ailsa Craig lies about 8 miles out from Girvan. We had a day trip there, landing and walking over the eastern side of the island, and then sailing right round. It is a Tertiary granitic inclusion, around 60Ma, formed at the time of the sudden opening of the Northern Atlantic Ocean. Similar intrusions are present on Arran and in Northern Ireland. It is an unusual intrusion because many of the cliffs show prominent pseudo-columnar jointing.These are not regular columnar joints and often only have three faces and are the result of the intersections of different joint faces.
Multiple doleritic dykes are also present.
The eastern coast of Ailsa Craig where previous quarrying took place.
The western side of the island with tall sheer cliffs
The vertical dyke in the centre is darker than the surrounding granite; and shows columnar jointing at right angles to the jointing seen in the rest of the cliff face.
