It is important that you access this field trip on a laptop or desktop PC. Click images to enlarge.
We are taking a short side trip on our route from Derby to South Wales.
Explore the area in Google Maps. View the outcrop (an old quarry) in Streetview, looking east from Leach Green Lane. It is obscured by houses and vegetation. Fortunately I visited it when I was a student, back in the early Anthropocene, and it was much more accessible then.
Field evidence
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| Views of the quarry face. Note that health and safety was much more lax in those days! Just above the climber's head in the left photo, note a sharp contact across the quarry face between the Lower Ordovician Lickey Quartzite Formation (below - light-coloured) and the Lower Silurian (Llandovery) Rubery Sandstone Formation (above - brown). | |
The significance of this location is that it exposes rocks of similar age to those we will see on the Cardiganshire coast later today. However, the sedimentary facies are very different.
The unconformity surface is broadly horizontal on a small scale, but highly irregular when seen close up - see the Black Country Geological Society web site. Hollows on the unconformity surface contain pebbles of Lickey Quartzite. Clearly the Rubery Sandstone was deposited on a hard, rocky surface. Llandovery age brachiopods have been found attached to this surface. The Rubery sandstone is well sorted and shows evidence of bioturbation. The evidence suggests it was deposited in a very shallow, nearshore marine environment.
Handout: refer to the handout for today, which contains essential diagrams and information. Don't forget to use the information in the Field Guide too. Both are available in Course Resources.
Thin-section evidence
You have met the Rubery Sandstone before, in Rocks, Minerals and Gemstones. The photograph below is a photomicrograph of this rock, in thin section A200. It is a quartz arenite. The rock was impregnated with blue resin before the thin section was made, to show the porosity more clearly. In spite of the high porosity, it is a very hard rock, due to the presence of a syntaxial quartz cement. This makes the grains look more angular than they really are - they are mostly rounded.
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Heading to Wales....
Now sit back in your comfortable seat on the virtual coach, and enjoy the scenery as we drive to West Wales. Use the information in the Field Guide to observe and make notes on the geology en route. We will cross the border into Wales just east of Middletown: Google Maps
Our next location in about 3 hours time - much less if you are travelling virtually - will be New Quay.
This page is maintained by Roger Suthren. Last updated 29 April, 2020 10:48 AM . All images © Roger Suthren unless otherwise stated. Images may be re-used for non-commercial purposes.
