Two Nick Chidlaw Field Courses 

Nick Chidlaw has asked me to help publicise two 1-day field courses he would like to run in June. 

One is a repeat of the Mendips course which featured earlier in the year. Details of that can be found HERE. The admin details of the June course are given below.

The other course is a walk in North Somerset, looking at Variscan folding and thrusting.

Here is what Nick has written about the courses.

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Note that the two courses are to run on the same weekend, but are independent of each other  - you can choose to enrol on one or both, according to your interests and availability. Both courses are in the same general geographical area, which may be suitable for anyone who's home is located elsewhere; they could decide to attend both courses and arrange accommodation between the two. 

Saturday 11th June   A LINEAR WALK IN NORTH SOMERSET: Variscan folding and thrust faulting 

Image: Google Earth oblique view in the area of the village of Clapton in Gordano, near Portishead. In this area, strata of early Carboniferous age have been thrust-faulted onto the top of younger late Carboniferous strata, along the extensive Clevedon Thrust.  In the Vale of Gordano, the thrusted rocks have been eroded into several remnants, forming 'klippen' . The purple dot marks a location where the strata in the klippen are exposed.    

Sunday 12th June   ASPECTS OF MENDIP GEOLOGY: Early Carboniferous open shelf seas, Late Carboniferous rivers, metalliferous mineralisation in the Jurassic

Image: former opencast lead mine working exposing early Carboniferous strata at Ubley Warren on the Mendip plateau. 

Each course would run 10.00 am - 5.00 pm. Course fee is £30.00 per person.

No prior knowledge of geology or the study area is assumed.  Attendees will be covered by insurance during the duration of the course. 

If you / anyone else you know would like to attend, please forward a cheque to me at the address below. If you would prefer bank trans, I can send you details. 

8, Silver Street,

Dursley,

Glos.

GL11 4ND.  

There is a handout for both courses that those enrolled would receive in advance, so they can read up about what will be covered and be in a good position to get the most out of each day when it runs. The handouts contain numerous colour images; due to printing costs, I can email you a Word Doc with the coloured images in that you can print out yourself and bring the printout to the course; otherwise I can post you a black and white printout, which is perfectly serviceable. 

Do let me know if you would like to receive the Word Doc which you would print out in colour yourself. 

If you wish to have the black and white printout instead, do let me know and provide me with your postal address, so I can send this to you a week or two before the course is due to run.    

Viability Deadline

The deadline for the minimum number of enrolments for each course (10) is Thursday 12th May. If the minimum of enrolments for each course is reached by 12th May, arrangements for that course will be able to continue. If not, the course(s) will be cancelled and fees returned soon after. For each viable course, enrolments can continue up to 1 week (Saturday 4th June) before the course dates. 

Please see details below. I hope the courses are of interest and to hear from you soon. 

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A LINEAR WALK IN NORTH SOMERSET: Variscan folding and thrust faulting 

In the Bristol- Mendip area, the present day landscape represents partially-exhumed landforms of Late Triassic age. This course looks at these landforms and underlying geology in the Portishead area. Rocks of Triassic age form a veneer over older ones: these latter, once horizontally-lying, became rucked up into folds, and dislocated along extensive  thrust faults, during the Variscan Orogeny some 300 million years ago.  Exposures of Early and Late Carboniferous, and Triassic strata are examined, both inland and on the coast, and Quaternary deposits in the Vale of Gordano are discussed. The walk is about 5.5 miles in length, beginning on the Cadbury Camp ridge to the south of Portishead, and ending on the sea front at Woodhill Bay, Portishead.  A lunch break is included, as is an afternoon break at the Windmill Inn above Woodhill Bay. 

Covid consideration

This course involves vehicle sharing. We meet at Woodhill Bay, Portishead, leaving most vehicles there, and drive in the minimum of vehicles to the start point of the linear walk on the Cadbury Camp ridge.  Drivers are returned at the end of the day to their vehicles left at the walk start point.  I have run this course more than once before in 2021, indicating there are people who consider car sharing to be safe; to help this safety, in the vehicles we wear masks, and ensure hands are sanitised before and after travelling,. Driving with open windows is a further precaution. It is appreciated that views on the risk of catching covid vary greatly between people, and that only those who consider vehicle sharing (with precautions mentioned above) will consider enrolling on the course.

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ASPECTS OF MENDIP GEOLOGY: Early Carboniferous open shelf seas, Late Carboniferous rivers, metalliferous mineralisation in the Jurassic 

The Mendip Hills, rising to 325m above sea level, and located in the counties of Somerset and North Somerset in the west of England, are underlain by mostly sedimentary rocks and mostly of Devonian, Early Carboniferous and Triassic age. They record deposition as the British crust moved slowly northwards from the southern tropics, across the equator, and into the northern tropics. Rivers laid down deposits during Devonian times, and in the Carboniferous, marine environments were present, followed by coal forests on delta and river plains. At the end of the Carboniferous, about 300 million years ago, the British crust was involved in a major plate tectonic collision, known as the Variscan Orogeny: the once-horizontally lying Devonian and Carboniferous strata were pushed up into a series of enormous dome structures elongated east - west, producing a mountainous terrain. By Mid Triassic times, about 240 million years ago, the mountains had been much worn down and coarse bouldery and sandy deposits were being laid down in wadis and valleys, eventually building up to bury the Mendip area. In the following Jurassic period, more sediments were laid down on top, in marine environments. In Middle Jurassic times about 170 million years ago, crustal stretching opened fissures in the Mendip area, up which hot metal-bearing fluids rose from deeper in the crust, cooled and crystallised. The metals included lead ore, of much importance subsequently to mankind. The nature of the ore deposits enabled the first large scale workings (opencasting by the Romans) to be highly productive, but later in time the ores were found to become more scarce at depth. Historic mining records refer to the ore occurring as 'stones of lead', and uncertainty of what exactly this meant was finally resolved by Mendip cave explorers in the 1980's.  

This course examines evidence for the shallow tropical sea at extensive exposures in the rocky dry valley of Burrington Coombe, and discusses the lead mineralisation at Ubley Warren on the Mendip plateau (no lead ore can be seen in exposures now); the final part of the day visits the Deep Leap Reserve on the Hills above Wells, where Late Carboniferous sandstones equivalent in age to the Millstone Grit of the Pennines can be examined.    

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