The GCSE and A Level geology students travelled to the Somerset coast with the ambition of working out what Britain was like during the Carboniferous Period (300 million years ago) and the Triassic (230 million years ago).
First we visited Middle Hope to examine the gently dipping Carboniferous strata. The youngest layer in the sequence was easily identified as a massively bedded limestone with abundant crinoid, coral and brachiopod fossils. Things got harder quickly, however, as the upper surface of the limestone appeared baked and pitted with pebbles and the next layer appeared missing… After two hours of squinting, measuring, umming, ahing, head scratching, scribbling and much consulting of the guide book, we concluded, correctly, that what we were looking at was the emergence of an undersea volcano which had repeatedly and violently erupted in pyroclastic eruptions, submerging and killing the life on the seafloor. In between each eruption the sea life re-emerged and flourished, before being incinerated again. Finally, the sequence was capped with a spectacular basaltic lava flow with well developed pillows, and calcite filled amygdales indicating a very shallow ocean (so the gas could escape).
We ate a much deserved lunch looking out over the Severn Estuary towards Cardiff. Many thanks to Mrs Middleton for making a spectacular giant sausage roll.
We then ventured to Clevedon, a beautiful 19th Century seaside town complete with Pier. Our objective here was to make a geological map, a task made more tricky by the complex geological structures on show. We made short work of the steeply dipping Carboniferous Rocks, ignored the small but interesting fold structures as they were too small to map, and then puzzled at the way the strata suddenly seemed to become horizontal. This could only mean one thing: an unconformity. Standing on an unconformity is a profound experience, and nevermore so than on this one as the exhumed landscape is exactly as it would have been 230 million years ago in the Triassic, with the waters of a drylands lake lapping against the steeply dipping Carboniferous Rocks. We then came up against the most difficult geological structure of the day, a steeply inclined normal fault complete with another unconformity on the other side, this time between much older Devonian river sediments and a Triassic Conglomerate. We struggled to understand this without recourse to the guidebook, but finally managed to complete the map. Most spectacular of all was the mineralisation in the fault and the presence of a beautiful pink fault breccia all stuck together with the dense mineral barytes.
This was a great day and reminded us all of why we love geology. The rocks were diverse, the structural features profound and the weather mercifully fine. We look forward to the next trip.
Finally, many thanks to the Secondhand Uniform Shop who very kindly funded the trip and the geography department who leant us the equipment.
