18 April 2021

Structural Recce

The easter break is over, and soon we will be going back into the field with the students again. One of our upcoming trips is to Traeth Lligwy; a beach on Anglesey where Old Red Sandstone is exposed. I had been there for a recce a long, long time ago, but for some reason I had never actually done the trip. And it seemed that the last time, things didn't quite work out for some reason. So we wanted to go and have a look before we would go there with the students, to check we know exactly what to do with them and where. Just show them the lithology? Let them measure it? Something else?

We were supposed to go on a Wednesday, but one of us had forgot to put that in the diary, so we had to move to Thursday. That was fine; the weather was equally nice. So I drove up and walked onto the beach. Dei would already be there with a GPS. He was already measuring the lithology; the sandstone beds and finer beds, which are really clearly seen in outcrop, have been deformed, and you can measure strike and dip of the beds over the width of the beach, and get a clear idea of what is going on. So when I found him I joined him. We were a bit confused; there are also fault zones in the lithology, and they complicate everything. And sometimes you think there might be one without being able to detect it, because the inclination of the beds just changes in strange ways.

After a while Jaco appeared too. As this is a sedimentary environment, this is his cup of tea. No microfossils for me, and no geophysics for Dei! We went through the whole section together. Some of his confused us; we had an article about this very section, but we couldn't match up will do so in the field with what we saw in the article. That is unusual!

We figured we would ask the students to indeed measure the inclination of the beds over the width of the beach. Maybe they would get an idea of the overall structure that way. But we will make sure we also have some time for looking at the lithology. It has all been deposited in an arid environment in the Devonian. You get to see channels, and channel overspill, and surface processes, and material affected by the surface processes then ripped out again by a flash flood and redeposited in very messy layers. A lot to look at!

I think we can pull this one off. And I really hope we have the same kind of weather when we get there with the students!

I think this beach has been eroding; this access ramp is only milddly fit for purpose

Dei with his GPS on the red sandstones

The deformation of the beds

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