Cymdeithas Daeareg Gogledd Cymru
North Wales Geology Association
Programme :
2018-19
at a
Glance
Which way to meetings?

Wednesday February 21st 2018
Monitoring subsidence related to relict salt mine, Marston, Cheshire.
Speaker: Cathrene Rowell, Keele University

Wednesday March 28th 2018
Epic seafloor off North Wales.
Speaker: Katrien Van Landeghem, Bangor University

Sunday July 29th 2018
Field Meeting: Pen yr Henblas Quarry, Halkyn
Leader: Chris Twigg

Sunday August 19th 2018
Field Meeting: Benllech, Red Wharf Bay
Leader: Jonathan Wilkins

Wednesday October 10th 2018
Multibeam sonar: Revealing the hidden marine geology of Wales.
Speaker: Michael Roberts, CAMS, Bangor University

Wednesday December 5th 2018
Annual Members' Meeting

Saturday TBA 2019
Annual General Meeting


Wednesday
February 21st 2018
Monitoring subsidence related to relict salt mine, Marston, Cheshire.
Speaker: Cathrene Rowell, School of Geology, Geography and the Environment, Keele University
Meeting Room, Pensychnant, Conwy.
Location details and map: Contact/Find

Meeting to commence at 19:30h

The Cheshire Basin contains >4.5km of Permo-Triassic red beds, including the Mercia Mudstone Group (MMG) which accumulated in playa and tidal-flat environments. The MMG is the host to two major halite formations: The Northwich and Wilkesley Halite formations, which have been commercially exploited. Both rock salt and brine has been extracted from mainly two horizons of the Northwich Halite Formation in the Cheshire Basin in various locations, and rock salt is still mined in nearby Winsford, Cheshire.

canal subsidence Surface subsidence resulting from salt mining and brine pumping in Northwich, and the surrounding areas in Cheshire, has occurred since Medieval times. This has varied in severity, with evidence of subsidence ranging from topographic depressions to catastrophic surface collapse from the mid-18th Century onwards.

To detect, characterise and monitor areas susceptible of subsidence, near-surface geophysics has been applied. A section of the Trent and Mersey Canal, in Marston (Northwich), crossing 3 abandoned salt mines has been the focus of long-term microgravity surveys for >10 years. The data collected over this period shows consistent, deepening negative anomalies at the margin between the Adelaide and Old Marston relict mine workings, as opposed to over the mines themselves. By correlating microgravity data with mine plans, boreholes and sedimentary logs, 2D gravity models have been produced: the anomalies are interpreted as upwardly propagating voids, and associated collapse material. A void feature at the point of the microgravity excursion has been confirmed by intrusive investigations. Further investigation of the canal water depths and the underlying silt accumulation on the canal floor has been undertaken, in addition to water / sampling and analysis, to ascertain any connection to underlying mines and potential canal collapse. This study further demonstrates the importance of time-lapse microgravity surveys to facilitate the identification and monitoring of at-risk areas, with a view to mitigating the risk of catastrophic surface subsidence.

Cathrene Rowell is studying for her PhD at Keele.

Wednesday
March 28th 2018
Epic seafloor off North Wales shows rapid ice retreat during the last ice age. The fate of West-Antarctic ice?
Speaker: Dr. Katrien Van Landeghem, School of Ocean Sciences, Bangor University
Meeting Room, Pensychnant, Conwy.
Location details and map: Contact/Find

Meeting to commence at 19:30h

antarctic science cruise A spectacular 2100 km2 seafloor image dataset collected on behalf of Celtic Array Ltd between Anglesey and the Isle of Man reveals the geomorphology and subsurface geology of a wide, submerged glacial landscape. With this data, we investigated how the Irish Sea Ice Stream advanced and retreated about 20,000 years ago (during the last ice age). This ice stream was the largest of its type to drain the interior of the former British-Irish Ice Sheet, and this study thus provides a conceptual model of how large ice streams retreat and cause the instability (even collapse) of large ice sheets. Why is that so interesting or important? Some ice streams in West Antarctic Ice Sheet are currently also unstable and there are concerns that their retreat can cause an onset of rapid collapse of parts of this massive ice sheet. That in turn would cause a huge global sea level rise (in the order of metres), and warrants our greatest attention.

Katrien is a lecturer and researcher in the School of Ocean Sciences at Bangor. Her current research includes sand dredging, sediment transport, shipwreck sites and the future of the Antarctic Ice Sheet. She is an engaging speaker and this talk will appeal to anybody with an interest in the special area we call the Irish Sea. N.B. This sea has equal claim to be Scottish, English and Welsh, and it matters to all of us! Her image (left) bears an uncanny resemblance to the view of the Carneddau from the Menai Strait during chilly times, don't you think?

Sunday
July 29th 2018
Field Meeting:
Pen yr Henblas Quarry
Leader: Chris Twigg and Tom Hughes, NEWRIGS
Based on the Pen yr Henblas Quarry, Pentre Halkyn

This field trip is a follow up to Tom Hughes short article in Newsletter 97, and to the brief "taster" visit a number of us made to the western quarry high wall last summer.

Pen yr Henblas Quarry"Pen yr Henblas quarry is of regional geological importance because it has excellent exposures of the Lower Carboniferous Pentre Chert and Cefn Mawr Formations. There is also exposure of the regional unconformity between the Pentre Chert and the underlying Cefn Mawr Formation".

There is a lot to see here, in spectacular exposure. The site is an abandoned quarry, with open public access, and opportunity to park nearby. In the quarry itself, there are the usual precipitous walls, spoil heaps etc, but it is only a short walk from the car park area, into the quarry, and this should not be considered an arduous trekking visit.

Please note hammering should only limited to breaking up existing fallen debris (there is plenty of it). As well as the usual brachiopods and corals there have been a number of sharks' teeth, and a coelacanth jaw recovered from this quarry.
News hot off the press: Chris Twigg has promised to bring along the coelacanth jaw!

Once we have finished fossicking in the quarry, there are plenty of interesting outcrops of Carboniferous Limestone, and old mining archaeology in the surrounding landscape to walk about in.

Please contact Keith Nicholls to register your interest.

Image ©Dave Dunford. Geograph.org.uk #4418887

Sunday
August 19th 2018
Field Meeting:
Benllech, Red Wharf Bay/Traeth Coch
Leader: Jonathan Wilkins
Based on the upper shore of Red Wharf Bay, nr Benllech, Anglesey

Carboniferous Karstification

Trwyn Dwlban

This meeting is designed to appeal to members who do not relish arduous upland or subterranean rock exposures; instead we take to the traditional Welsh seaside for a look at the Carboniferous Limestone of south-eastern Anglesey.

Cyclic sedimentation is well-known in this formation, where thick beds of limestone are interrupted periodically by mudstone beds representing deeper water. However, emergence of the limestone surface due to lowered sea level allowed the development of a Carboniferous karst surface which has been exposed to modern view as a result of erosion. Subsequent to the development of the karst surface, renewed sedimentation as the relative sea-level rose once more resulted in sandstones being deposited into the features of the karst surface. The modern exposure of these features include in-filled pipes and isolated sandstone columns where limestone has eroded from around them. It is claimed that these exposures are unique in the British Carboniferous!

Join us for a very gentle rocky-ramble, whose maximum elevation is around 5 metres and whose maximum length is around 1000 metres, depending upon where you park your vehicle. Full facilities are available in nearby Benllech, and we have checked that low tide is at mid-day.

Please contact Jonathan Wilkins by email or telephone to register your interest.

Image ©Jonathan Wilkins (not Geograph this time).

Wednesday
October 10th 2018
Multibeam sonar: Revealing the hidden marine geology of Wales.
Speaker: Dr Michael Roberts, CAMS, Bangor University
Meeting Room, Pensychnant, Conwy.
Location details and map: Contact/Find

Meeting to commence at 19:30h

skerries sonar image For the last six years a team of researchers and technical support staff from Bangor University have been undertaking numerous surveys of the marine environment off the coast of Wales. The data and resultant outputs are now providing fascinating new insights on marine processes operating over a range of spatial and temporal scales. This talk will include images and 3-d models illustrating a range of marine geological features including previously unseen and unknown rock outcrops and sedimentary bedforms.

It is hoped that this informal presentation will be of great interest to the audience and stimulate further discussion on how best these new insights can contribute to better understanding the marine geology of Wales and geological/sedimentological processes in general.

Dr Michael Roberts is R&D Manager in the Centre for Applied Marine Studies at Bangor..

Wednesday
December 5th 2018
Annual Members' Meeting.
Speakers: Richard Birch, Gary Eisenhauer, Jonathan Wilkins
Meeting Room, Pensychnant, Conwy.
Location details and map: Contact/Find

Meeting to commence at 19:30h
We are pleased to announce that extra refreshments of a potentially seasonal nature will be available to help the party swing. skerries sonar image

Gary Eisenhauer: Cwmorthin Quarry 2018
A video presentation gathered at this year's field meeting in Cwmorthin Quarry. Inaccessible to some, and not the 'cup-of-tea' of many members, Gary thought that this might be a suitable introduction to the dark and esoteric world of slate-working.

Richard Birch: Trilobites & their Relatives
A short, fascinating film on the 2017 conference of the same name in Tallinn, Estonia. Filmed in high-definition, it highlights a couple of the most interesting presentations, and explores this beautiful city and country, including a few of its birds, wildflowers and Ordovician marine reefs.

Rob Crossley: Lesotho kimberlites & diamonds
A unique opportunity to see inside the ultra-secure world of kimberlite-pipe diamond mining. And why we thought Penmaenmawr quarry might be able to teach them a thing or two.....

Jonathan Wilkins: Geology and Seaweed
More light-hearted than the accompanying films, but with a real science core, this presentation highlights the complex and intriguing links which can be discovered in the coastal ecology of western Ireland. Jonathan has not yet mastered the moving image, so only static shots will be provided. Health-warning: contains images of rocks, seaweed and tractors.

Saturday
TBA 2019
ANNUAL GENERAL MEETING and
Speaker: Dr Cathy Hollis, University of Manchester
Location TBA

Annual General Meeting commences 10:00h
Refreshments at 11:00h
Lecture to commence at 11:30h
The Great Orme: Limestone exemplar.
Abstract to follow.

Cathy is a Reader in Petrophysics & Production Geology, University of Manchester (since 2007), where she co-ordinates Carbonate Research within the Basin Studies Group. She is a carbonate sedimentologist, specialising in diagenesis and pore system characterisation, with over 15 years postdoctoral experience, primarily within the oil industry.