Thursday 16th May 2019
At the last meeting Prof. Neil Glasser gave a highly informative talk on the MAGIC-DML project ( of which he is part) which is a collaborative project between Sweden,UK, US, Norway and Germany and is researching the glacial history of the Antarctic ice-sheet and how it has changed over time. The area chosen for the research is Dronning Maud Land (DML) area of Antarctica which is largely covered by the East Antarctic ice-sheet. There were two field seasons in 2017 and 2018 with Prof. Glasser attending in 2017.
The ice in Antarctica is very thick ( with a mean of 2.16km and a maximum of 4.7km) such that only the peaks of the highest mountains protrude through the ice. These areas are known as nunataks. Ninety per cent of the world's ice (29 million cubic km) and approximately 80 per cent of its fresh water, is locked up in the Antarctic ice sheet. If all the ice were to melt, the level of the world's oceans would rise by nearly 60 m.
Nunatak Antartica - creative commons
MAGIC-DML stands for Mapping, Measuring, Modelling Antarctic Geomorphology and Ice-elevation Change in Dronning Maud Land (DML). (Queen Maud Land is a c. 2.7 million square kilometre region of Antarctica claimed as a dependent territory by Norway.)
Mapping- Firstly the area has to be mapped and this is done using methods such as the Geographic Information System (GIS) and Google Earth. This allows the researchers to understand the landforms they are going to survey.
Measuring - Involves using Cosmogenic nuclide testing to determine how long the surface of the rock has been exposed. This helps in determine past ice-sheet extent and the rate of recession.
Cosmogenic particles are produced when elements are bombarded by high energy particles ( cosmic radiation) that enter the atmosphere from outer space. These particles can interact with silica and oxygen in quartz ( in a process known as spallation) to produce isotopes of 6Be and 26Al. Other isotopes produced are 36Cl, 14C, 21Ne, and 3He. Thus the assumption is made that there is a constant rate of production so that the the accumulation in the rock is proportional to the length of time exposed and the rate of decay of the isotopes. The isotopes are measured using an accelerator mass spectrometer.
Samples can only be taken from the top of the rock exposure as the high energy particles cannot penetrate into the depths of the rock and any disturbance to the rock from weathering could affect the results. So the field worker has to be very careful in choosing the correct sample.
Modelling - The aim is to produce numerical models of past ice-sheet behaviour which can help predict what might happen in the future.
Next month will be the evening field trip which this year is to Middletown quarry. This will be on Wednesday 19th June 6-8pm.
Friday 26th April 2019
At the last meeting David Lockett gave a very interesting talk on the FISH ( Fossils In SHropshire project). The grant funded project commenced in 2016 with the aim of digitising geological collections at the Ludlow museum.
The museum holds in the region of 250,000 specimens which are important both nationally and internationally. Of this number there are 41,500 specimens of fossils, rocks and minerals with the greatest number being that of the fossils. The Shropshire mammoth remains found at Condover in 1986 is an example of a nationally important find.
Silurian Eurypterid taken for the project
But why digitise the specimens?
- the large number of specimens cannot be physically on display.
- it allows dissipation of information.
- there are not many museums digitising their specimens
- 3D models of fossils is not really undertaken
- produces images that can be used for identification purposes
- as the collections are viewed prior to digitisation often new and unusual specimens are found.
The equipment used is based upon a 35mm DSLR camera, macro and zoom lenses, LED lighting and computer software. The 3D virtual models are obtained by photographing all sides whilst the specimen is rotated on a turntable.
They have had help from the BGS in the form of a white light scanner to scan some of the more important specimens from which a 3D model can be made.
The second half of the talk consisted of David showing images from specimens relating to each time period of the geological sequence.
The talk was extremely interesting and the images superb. If you are interested in following this project then here is a link to their website
Tuesday 16th April 2019
At our March indoor meeting on Wednesday the 20th, guest speaker, Prof. Michael Rosenbaum, gave us a talk on "Elan Valley dam construction and the Birth of Engineering Geology.”
As a result of rapid industrialisation and urbanisation of the area in the 1860s and 70s, the populace in Birmingham was largely housed in crowded tenements in insanitary conditions. Shared privies were the rule with seepage into the shallow wells owned by the water companies. The only surface water resource was the diminutive and polluted river Rea which now flows through a ditch underneath Digbeth.
Water was very short and rationed, with drinking water sold from a pony and trap. Water-borne diseases such as cholera and typhoid were rife and something had to be done to improve the health of the workforce.
The then mayor, Joseph Chamberlain, a self made man who had made his fortune as a screw manufacturer, took action. He forcibly bought up the water companies and appointed Robert Rawlinson as consultant.
Providing an adequate clean water supply was fraught with difficulty. With no adequate local river or aquifer, water would have to be found at a distance and transported. Looking at the significant rivers surrounding Birmingham, going north, the Trent was of poor quality, the Derwent required an aqueduct and pumping, in the west the Severn was too low and the Teme had too many people and high quality farms requiring compensation. The Wye was low and people in Hereford would object, so although distant, the The Elan, with the Claerwen, were selected as most suitable. They had a large catchment area with a high rainfall and enough elevation to avoid pumping.
Caban Coch Reservoir Elan Valley ( Colin Price Creative Commons)
In 1890 an act of parliament was obtained and Mansergh was engaged as engineer who designed the Elan scheme with a dam at Caban Coch where the valley was constricted. Much of the local stone was called "Cyclopian" as it contained large hard cobbles and could not be accurately shaped. Accordingly, the construction of the dam was with a core of rough irregular local stone blocks, set in concrete with an Ashlar facing of accurately cut stone ferried in from a distance. This was one factor which caused a 50% cost overrun.
We were shown a remarkable 1892 photograph of Mansergh heading a group of the "great and the good" geologists and engineers on a viewing field trip. It included Prof. Topley (Surveyed the Weald), Prof. Boyd Dawkins, Thomas Hawksley (engineer for the Vyrnwy dam), perhaps showing an early merging of geology and engineering disciplines into engineering geology.
Members were treated to an interesting evening, being given an insight into the basic structure of an iconic local heritage site.
The next meeting will be on Wednesday 17th April when Daniel Lockett will give a talk on the FISH (Fossils in Shropshire) project.
Thursday 28th February 2019
At our indoor meeting on Wed 20th February, Bob Loveridge, Research Fellow in the School of Earth and Environmental Sciences at the University of Portsmouth, gave a talk on 'Flying reptiles at Buckingham Palace', including how a team of researchers did their giant pterosaur spectacular for The Royal Society's 350th Anniversary and how they took pterosaurs to meet the Queen at Buckingham Palace.
Pterosaurs were flying reptiles, best imagined as "flying crocodiles". Finds in the early 19th century were generally described as avian, including "bird bones" described by Gideon Mantell and finds by Dean William Buckland of the first UK specimen. In 1828 Mary Anning uncovered a complete specimen, albeit as a jumble of bones. It was Cuvier who first reconstructed the skeleton and recognised them as flying reptiles.
Pterosaur reconstruction Sommerring 1812 - Wiki Commons Image
They were famously popularised by Conan Doyle when he published "The Lost World" in 1912 and have remained popular ever since.
Pterosaurs evolved in the Triassic and developed into many forms from the size of small birds to the giants with enormous wings and long necks and heads in the Cretaceous. They sported bizarre head crests the purpose of which is obscure. They could have been for maintaining heat balance or for sexual display. (It is established that they had sexual dimorphism.)
The largest, Quetzalcoatlus, was some 40ft long, with a three metre neck and head, the largest ever flying animal, comparable to a Spitfire! It probably fed on small fish and there is some controversy over how they flew, but it does look as though they were capable of powered flight.
The skeletal structure was somewhat bat-like, with the skinny wings supported by an extended fourth finger. Unlike birds, on landing, they took up a quadruped position.
One recently discovered, now in the Kimmeridge Museum, is named Cuspicephalus scarfi after Gerald Scarfe due to its resemblance to Scarfe's iconic charicature of Margaret Thatcher!
As part of the celebration of the 350th anniversary of the founding of the Royal Society, the team from the University of Portsmouth built a flight of life sized flying pterosaurs which 'flew' (suspended on wires) above the Southbank Centre in London.
In addition to celebrating the founding of the oldest scientific society, it was an opportunity to learn more about how these animals flew and walked. The models were built on a lightweight frame with assistance from Griffon Hoverwork and were fabricated from foam with a hairy textile covering. The eyes comprised finials from B & Q, suitably painted.
To demonstrate the size of these animals, with help, Bob unfurled a scale drawing of one wing which went two thirds the length of the auditorium. (The whole animal would not have fitted in the room.)
The models were also exhibited at Buckingham Palace as part of the Queen's 80th birthday celebrations when they were enjoyed by her, other members of the Royal Family and by many schoolchildren invited for the occasion.
Bob was thanked for showing us models, books, drawings and fossils and giving a memorable talk with a difference.
The next meeting will be on Wednesday 20th March when Professor Michael Roenbaum wiii give a talk entitled: "The Elan Valley Aqueduct and the Birth of Engineering Geology."
Monday 28th January 2019
Twenty six members attended the AGM which was followed by a talk on Anglesey's geology based around the geology observed during the club's annual summer weekend. The weekend was led by Dr. Charlie Bendall.Below is an outline of David's talk.
The standard view of Anglesey geology, based on the detailed work of Edward Greenly in 1919, dates from long before plate tectonics was understood. There has been much controversy about the exact chronological order of the main units, and whether they might perhaps be “upside down”.
Since 2007, some Japanese scientists, working with Brian Windley of Leicester University, have put forward a new view, where the Anglesey rocks are seen as a classic example of what happens when an ocean plate is subducted under a continental plate. The main components, including an accretionary complex, extensive mélange, an exhumed blueschist, an ophiolite sequence, and continental margin sediments, are exactly what one sees in other parts of the world where an ocean plate has been subducted. An example is the San Francisco region - as was well illustrated in Chris Simpson's recent talk to our group. As Chris pointed out, one of the key features of such a scenario is that the older units are on top, with the younger units thrust underneath - the opposite of the usual stratigraphic order!
The “Japanese” analysis is summarised in the following diagram by Professor Shigenori Maruyama, taken from my photo of the GeoMôn geopark information board at Llanddwyn Island:-
GeoMôn geopark information board at Llanddwyn Island
To summarise the story, around 680Ma, an oceanic plate was being subducted under Avalonia, leading amongst other things to the magmatism of the Malvern Hills. Subduction was building up an accretionary complex corresponding to the Gwna Group. The accretionary process continued over a long period of time until at least the early Cambrian.
The accretionary complex mainly consists of ocean plate sediments scraped off the descending plate by the overriding continental plate. It typically comprises a succession of small units thrust one under another in succession. Each unit, or “horse”, represents a slice of seafloor. Each typically encapsulates, at the base some pillow basalt from a mid-ocean ridge, capped by bedded chert and sometimes limestone, with possibly mudstone and turbidites on top. The units are particularly well exposed over the entire Llanddwyn island, where the Japanese scientists have mapped out 23 “horses”, which they believe represent over 7,800m of seafloor shunted into an accretionary deposit only about 300m thick.
At the core of the subduction's accretionary process is a deep oceanic trench, with a particularly steep slope on the continental side. In many situations, material tumbles down this slope, creating a chaotic mixture of various rock types, mostly derived from previously accreted seafloor, with components ranging from kilometre-scale chunks down to small pebbles. This is the famous Gwna Mélange. As I understand it, it's more likely to be the result of an ongoing process, rather than being produced by a single, huge, catastrophic event. The mélange can be seen on the north coast of Anglesey, and less dramatically at the southern tip of Llanddwyn island as well as the famous example on the mainland at the southwestern tip of the Lleyn peninsula.
Gwna mélange
Returning to the detailed story of the subduction, it is thought that at around 620-600Ma or perhaps earlier, Avalonia advances to the point where a mid-ocean ridge gets subducted. Although the exact effect of such an event is unclear, it is suggested this led to the creation of the Coedana granite within the continental crust at the edge of Avalonia.
Around 575-550Ma, a ductile wedge of the accretionary complex, a few kilometres thick, gets subducted, recrystallised under blueschist conditions (high pressure but relatively low temperature), and then is squeezed back to a higher level, possibly assisted by a shallowing subduction angle. In this way, the Blueschist Unit is formed.
After the emplacement of the Blueschist Unit, the accretionary process continues, with conditions producing mélange becoming more prevalent.
During the final stages of the subduction, in the Cambrian, continental margin sediments corresponding to the New Harbour Group, and subsequently the South Stack Group, are underthrust more-or-less intact into the base of the accretionary complex. This underthrusting leads to doming of the already accreted complex, causing a fragment of the western margin of Avalonia containing the Coedana granite to become separated from the rest.
At some point after the New Harbour Group turbidites were emplaced, a deep slice of ocean crust was thrust within it - as a so-called “dismembered ophiolite”.
After subduction had largely ceased, magmatism continued into the Ordovician, resulting in the igneous rocks of North Wales. And there the subduction story ends.
In a later paper from 2013, Windley and others show that the Anglesey story is far from unique. For at least 3.8 billion years, the Earth has experienced a remarkably consistent process of sea floor spreading, subduction and accretion at continental margins. Other examples are to be found in Greenland, Central Asia, Japan, and the previously mentioned California coastal range. A further example is nearer at home in the southern uplands of Scotland, where an accretionary complex was formed on the margin of Laurentia as the Iapetus Ocean was being subducted. All of these examples show very similar rock types and structures. It appears that the overall process is a major factor in the creation of continental crust. It is even suggested it has played a part in plate tectonics being a major heat loss mechanism on Earth since the early Precambrian.