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Wednesday 22 July 2020

The Mill Bay samples

I just wanted to put on the record the approx positions of the sampling sites I visited some years ago when I gathered rock samples for Rob Ixer and Richard Bevins.  The above map is Fig 1 reproduced from the seminal paper by Richard Thomas and others:

THOMAS, R G, BARCLAY, W J, MORRISSEY, L, WILLIAMS, B P J, and ALLEN, K C. 2006. Enigma variations: the stratigraphy, provenance, palaeoseismicity and depositional history of the Lower Old Red Sandstone Cosheston Group, south-central Pembrokeshire, Wales. Geological Journal, Vol. 41, 481-536.

I have marked two sampling points on the map.

MB 1 and MB2 came from Mill Bay, close to the bend in the coast. So there is no doubt that they represent one of the facies of the Mill Bay Formation.  The other point shows a sampling point (MB3) near Whalecomb jetty.  Richard Thomas thinks that the junction between the older Mill Bay Formation and the newer Lawrenny Cliff Formation lies about 60m south of the jetty.  So I think that when I took that sample I inadvertently sampled the Lawrenny Cliff Formation sandstone near its base -- this explains the slight differences between this sample and Samples MB1 and MB2.

Nonetheless, it's fairly clear that the 3 samples are all closely related, and that they are very different from the supposed "Altar Stone" samples analysed by Ixer and Bevins and reported in their recent paper.

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