Saturday - Llanmadoc, Gower: south limb of South Wales syncline
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The Loughor Esturary from Cwm Ivy,
looking towards Burry Port |
The drive to Llanmadoc from Hereford took a tad longer than anticipated (might have been something to do with the breakfast break in the Clydach Gorge) and, despite an early start, Jan and I only just arrived in time - always a bit of a rush then as there are forms to be filled in, fees to be collected etc. Our leader, Stephen Howe from the National Museum of Wales in Cardiff, was already there along with some 10-12 geologists from OUGS Severnside branch and the SWGA. Without more ado they set off up Llanmadoc Hill while I decided to do my own thing for the day as I thought the 6 km walk was possibly going to be too strenuous for my back/hip and I didn't want to hold them back.
A stroll down Cwm Ivy
Libby (Jan's middle-aged King Charles Cavalier) and I decided to head down the lane to Cwm Ivy: there was plenty for her to sniff and I enjoyed the bluebells though I didn't sniff them with quite the same devotion as she did. After a few hundred metres we reached the hamlet of Cwm Ivy and, rather than exploring the Nature Reserve, made our way through a gate onto National Trust land and on down the lane. This led down towards the coast path (confusingly the signs pointed to left and right with no indication of where you might end up... bit like the South Circular... also !) and some interesting looking rocky tors.
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Cwm Ivy Tor: an exposure of
Carboniferous Limestone (Dinantian) |
Cwm Ivy Tor is an exposure of Oxwich Head limestone: on the southern limb of the South Wales Coalfield syncline, the beds dip steeply north, towards the estuary. At one time it was on the coast but now sand has accumulated and cut it off from the sea.
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| Bluebells |
The wildflowers, particularly the cowslips on the limestone soils, were beautiful but the increasingly strong, chilly wind as we approached the coast eventually drove Libby and me back up the hill to the car park where we waited for the others to return.
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| Cowslips |
The following day we were due to meet Geraint Owen at Llansteffan at 10am so Jan and I had booked a campsite near there at Llangain, a few miles south of Carmarthen. This was a 45 mile drive from Llanmadoc and hailstorms made it an interesting one! No problems finding the campsite which, apart from no light in the loos, was comfortable enough - and not muddy: a bonus!
Sunday: Llansteffan; north limb of South Wales syncline
A pretty village, with its own ruined castle, which sits in an out-of-the-way position on a promontory between two estuaries. We met up in the car park: some people from the previous day and some newcomers, put all our wet weather gear on, and then found a convenient shelter to sit in while Geraint briefed us on what we were going to be seeing.
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| Sheltering from the rain - Geraint is actually under cover too ! |
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| Geraint tells the story |
There's a good Geologists' Association leaflet on this area - a nice walk of about 1 km each way along a level beach and I'd assumed Geraint would be following this (since he had written the leaflet... well you would wouldn't you?). However we were obviously lined up for the super-deluxe, extended version which began with a pleasant walk through the woods below the castle (and above the cliffs), around the headland before heading down a set of steps onto the beach. No - down a set of steps, across some interestingly slippery rocks, onto the beach...
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| Right hand end of the exposure |
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| Left hand end of the exposure |
At this point I wimped out again: hip and back problems mean I'm not as agile as I'd like to be and the party looked as though they were taking it very gingerly over the aforesaid slippery rocks at the foot of the steps so, once again, I did my own thing, went back through the woods and headed along the beach below the cliffs where I was able to do the first couple of field stops on Geraint's leaflet. I skimmed over the 'head' at Stop 1 (dating from the last Ice Age) and went on to see the Old Red Sandstone sandstones, mudstones and particularly the palaeosols at Stop 2. I was keen to look at these to compare them with those at Portishead which I knew quite well.
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| Close up of tectonics in the central section |
The strata were dipping a bit north of east at about 22 degrees. At least I think so - I've not quite got to grips with the clinometer app on my phone yet. Either side of the sandstone there were beds of red shale; halfway up the limestone sequence there was a considerable amount of thrusting which had repeated beds in one section in a mini duplex (Field sketch opportunity alert!!!).
A little further along, and stratigraphically below the sandstone, was a series of red shaley beds deposited as alluvium on river floodplains with grey/beige patches which represent calcrete formed in palaeosol in a warm, dry climate.
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| Beds of red shale with beige/grey patches (see lower right side) which formed in calcrete rich soils. And yes, I know these look as though they are dipping to the left (west) but that's within the beds - a bit of cleavage maybe - and the actual beds themselves dip to the right (east) |
I continued on around the base of the cliffs but the sand became increasingly squidgy - too much water/not enough sand? - and eventually I turned around and made my way back. Geraint told me later that the squidginess is due to an inordinate amount of air in the sediments decreasing their density but they aren't quicksands. Good. Well the group walked back across them and I don't think we lost anyone so I guess they aren't!
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| Nine soggy geologists and a dog make their way over the 'no they aren't quicksands' back to Llansteffan |
Lunch and a cafe was indicated; the hot chocolate was good and we warmed up a bit (its May remember) and decided that a slightly reduced group would continue to Amroth - only half an hour around the corner, though Philip (the one with the local knowledge) did take us the 'pretty way'.
Amroth - somewhere around the middle of the syncline
For me this was the best of the weekend so I was really glad we went on. We reached the beach by a comfortable walk along the prom and down a concrete slip across the pebbles. From here a short walk across the sand led up to some superbly exposed folds.
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| Folds in Lower Coal Measures (Bashkirian). These have to be an exceptional teaching locality: for starters that faulted fold needs sketching! |
I avoided walking along strike on the bedding planes to the cliff exposures as the gently sloping surfaces were pretty slippery but none-the-less saw some good geology.
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| The faulted fold - go on, dare you - do a field sketch! |
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| Examining the coal seam close up |
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| The bed below the coal has limonite nodules and fine, irregular black line which are probably roots |
Something that was fascinating was to see two contgrasting palaeosols on the same day: the oxidised version with calcrete at Llansteffan, and the reduced version with limonite at Amroth. Add to that some beautiful structures and it was a day to remember despite the rain!
