At the moment there is a good exposure on the shore of the Nevern estuary, on the north side, to the west of the Riverslee boat house. SN 056401. It's just above HWM, and a bit messy, but it shows the LGM /Devensian till overlying a somewhat chaotic layer of churned flaky slope breccia.
The soil at the top of the section has all been sliding down the slope from the footpath above -- so I would say it is in a secondary position and tells us nothing about the real stratigraphy.
The "churned" layer of slope breccia is most likely to be the equivalent of the slope breccias to be found beneath fresh till all around the Pembrokeshire coast. In some places the breccia is churned, but most often it is not. We can put this down to either to the rapid flow of a saturated horizon, or -- lore likely -- severe permafrost conditions with very active frost heave processes operating.
Around A and B in the photo we see abundant rounded pebbles and gravelly debris, and I'm rather certain these are incorporated patches of raised beach material that have come from nearby. There are no clear exposures.
The till is typical for this area, incorporating pebbles and cobbles of all shapes and sizes (including some that are well rounded) and many lithologies. I haven't been able to do a proper analysis, but the till characteristics and the mix of pebbles seem to tie in pretty well with the exposures of till on the foreshore of the estuary to the west of this exposure. As I have mentioned before, there do seem to be quite high concentrations of Palaeozoic sandstones, quartzites and shales than in other exposures to the west of here on the Cardigan Bay coast -- and this might indicate that Welsh ice, rather than the ice of the Irish Sea Glacier, may have been dominant at one stage in the glacial history of the area.
No comments:
Post a Comment