Sunday, 26 June 2011

Linear Geological Walk: Dartmoor to Bolt Tail

Linear Geological Walk: Dartmoor to Bolt Tail to be led by Dr. Nicholas Chidlaw
- This is a privately-arranged trip and does not involve any other organizations (e.g. a University) – no question paper at the end!!
- Dates: Sunday 11th – Tuesday 13th September inclusive. Three-day format.
- Reason for these specific dates: on the 2nd day, we cross the River Erme at low tide c. 1 pm using the established ‘South West Coastal Path’.  On the 3rd day we cross the River Avon by small passenger ferry (available only until end of September). Saturday 10th September can be used as a travel day to get to the start point of the walk, but those in work will need to take holidays Monday 12th, Tuesday 13th (and possibly Wednesday 14th if home area is some distance from the field area).
- Reason for ‘linear walk’ format: very effective way of studying landforms and underlying geology in areas where there is plenty of change in these aspects; a fuller understanding of the landforms and geology can be gained by walking a route essentially at right- angles to the grain of the ‘country’ rock and examining exposures en route. This is a format that has been tried out with adult ed. students at Bristol University, is popular and has worked well. Idea is that you carry your overnight belongings etc in a rucksack – contents would be lightweight and kept to a minimum. Water bottles can be replenished each night. Pubs / caf├ęs are included for short breaks during each day.
- The proposed walk crosses the ‘grain’ of part of the Variscan Orogenic Belt in South Devon: beginning near the S end of Dartmoor, and working south to the coast at Bigbury Bay, then along the coast to Bolt Tail west of Salcombe.
- Geology covered: Hemerdon Ball Granite (offshoot of Dartmoor Granite), metamorphic aureole / metallic mineralization around margin of the latter; deformed basinal metasediments (mainly turbidite sandstones and slates) and interbedded mafic bodies; major strike-slip fault of the Start-Perranporth Line; mica schists and hornblende schists of the Start Complex (possibly lateral equivalent of part of the Lizard Complex).
- Logistics: 3 day walk. Approx total distance walked 15 – 20 miles; many stops en route to examine geology / landforms. Vehicles would be left at a secure location (arrangement made in advance) near the beginning of the walk. Coach / minibus and driver arranged in advance to pick up field party at a stated location and return to the secure parking location. B&B accommodation to be arranged in advance: in / near Yealmpton (end of 1st day); in /near Ringmore / Bigbury village (end of 2nd day).
- Tuition fee: £69.00 per person.  Cost of hired coach / minibus and driver would be divided between attendees and paid in advance. There is a small charge for the Avon passenger ferry which is paid on the day of the crossing.
- Attendees would be insured against accident for the duration of the trip.
If you find the proposal of interest and are able to attend, please let me know, sending in your tuition fee by Sunday 24th July. In order for the trip to be viable and to work effectively, enrolled numbers will need to be a minimum of 10, and a maximum of 20.
I will contact those who have enrolled shortly after Sunday 24th July, to inform them whether the trip can be put on or not; if the former, arrangements will need to be made soon after for overnight accommodation, and transport (see below); if the latter, cheques will be returned to those who have sent them in shortly afterwards.
Contact: Dr. Nicholas Chidlaw.

Wednesday, 15 June 2011

Mini Ice Age within 10 years?

US solar physicists have announced that the Sun appears to be headed into a lengthy spell of low activity, which could mean that the Earth – far from facing a global warming problem – is actually headed into a mini Ice Age. Will we be ice skating on the Thames by 2025?
Click here to read more.

Sunday, 5 June 2011

Book review - Exe Valley

Hugh Prudden of the Somerset Geology Group has reviewed this new book as follows:-
The Quaternary of the Exe Valley and adjoining areas: Field guide.
Basell, L.S., Brown, A.G. and Toms, P.S. (eds).  2011. 
Quaternary Research Association.  
The Guide was produced to accompany the Field Meeting to the Exe Valley and adjoining areas 4-7 April 2011.The recently published field guide is an important contribution to our knowledge of the Quaternary of Somerset.  The following chapters are of particular interest for Somerset readers: -
The archaeological context of the Exe Valley and adjoining areas. (Basell, L. and Brown, T.) This chapter summarises the context, chronology, typology and raw materials of artefacts, and draws together the present state of knowledge.
Quaternary fluvial sequences and landscape evolution in Devon and Somerset (R. Westaway). This is a complicated chapter based on shoreline flats, river terraces and karstic features plus magmatic underplating.  Figure 3.3 shows there to have been an estimated post-Ipswichian uplift of 11-12m around Burroughbridge rising to 13-14m around Weston-super–Mare and the Mendips.
The Haldon Gravels Although in Devon this is a tightly argued assessment of the gravels on Haldon and is highly relevant to the wide spread of early Tertiary gravels on the Blackdown Plateau.
The Devil’s Punchbowl (S. Harrison).Visitors to Exmoor will be aware of the cirque-like feature above Winsford. It has been suggested that this was indeed the site of a small cirque but some of us wondered if non-glacial, as opposed to periglacial, processes could account for the features.  However, Stephen Harrison has researched the landforms and sediments in more detail and has added more supportive detail to his original suggestion that the evidence points to a cirque glacier.  Read the account and visit the site to see what you think. It may be relevant that recent research has suggested that the surface bedrock of Lundy in the Bristol Channel became exposed following deglaciation between 40-30 ka.  The presence of the nearby Irish Sea Ice Stream at a relatively recent date might explain increased snowfall and what seem to be fresh glacial landforms. Chard Junction Quarry and the Axe Valley gravels (Basell et al.) There are very few workable gravel resources in Somerset compared with Dorset except to the south of Chard in the Axe Valley; the Jurassic limestones are rapidly worn down and the clays are a non-starter.  However, there are considerably quantities of durable Cretaceous chert and flint outcropping on the sides of the Axe Valley together with a smaller contribution of Tertiary gravels from the Blackdown Plateau. These gravels are unlike the terrace staircases in most of our rivers; they from a stacked sequence resulting from erodible bedrock, high rates of sediment availability and periglacial transport.  Palaeoliths have recently been found in situ and optical age estimates give an intrinsic measure of reliability and a weighted mean age of 326+/- 22 ka.  The stacked gravels include periglacial structures at several levels; at the time of the field visit an excavated horizontal surface showed narrow vertical fissures filled with fine material as part of polygonal structures; it was like walking on the tundra!.
The Middle Pleistocene Deposits and Archaeology at Broom. (Horsfield et al.) The Broom sites are some 3km SW of the Chard Junction pits and were worked in the 1930s. C.E. Bean made valuable records and collections of Lower Palaeolithic hand axes at the time. This chapter summarises the stratigraphy, sedimentology and age of the deposits. Of particular interest is the Broom Member (Broom Gravel Member and Broom Sand and Silt Bed); the Bean archive suggests the association of the majority of artefacts with land surfaces contemporary with the Broom Member.  Recent pollen samples indicate a regional vegetation of boreal forest, with tree stands interspersed with wide expanses of open country and ericaceous heath.
The Doniford gravels (Basell, et al.) This is perhaps the most useful exposure for the general geologist as it has open access and is well-exposed.  The cliff is subject to erosion but this maintains a clear face.  It lies just to the east of Watchet harbour.  We owe much to the Wedlakes for their collections and observations together with those of C. Norman.  OSL samples do form a stratigraphically consistent time-series spanning from 65+/- 5ka to 25 =/- 3ka. These gravels are associated with periods of hillslope recession, mass wasting and periglacial solifluction which contributed to the gravels we see today.  It was a time of shallow braided rivers choked with rock debris.  The widespread angular unsorted head on lower valley sides is evidence of mass wasting; come the next glacial phase doubtless the head would be on the move again.
The geological setting and landform evolution of the Exe Valley and adjoining areas. (Brown, et al.)
This is a broad brush overview of the structure, topography, bedrock geology and superficial deposits.  It is thought–provoking.
Get your copy today from:
Quaternary Research Association.

Members £15: non-members £20.
Please note that on November 3rd Professor Tony Brown and/or Dr. Laura Basell will be talking to the Bath Geological Society about this new research.

Saturday, 4 June 2011

Recent landslip affecting A46 in Gloucestershire - June 14th

The Western Regional Group would like to invite you to a Geological Society evening lecture on Tuesday 14th June, where Jonathan Merrick of Atkins and Gloucestershire Highways will be presenting a case study (including investigation techniques and preventative options) of a recent landslip which affected the A46 in Gloucestershire.
The lecture will start at 6.30pm, but please feel free to come and have a few sandwiches and a chat with colleagues from 6.00pm.  There is no charge for the event and non-members are welcome.  
The lecture will be held in the S H Reynolds Lecture Theatre (Room G25), Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol BS8 1RJ.