The Bristol and South-West Regional Group were recently treated to a wonderful tour around the rocks and landscapes of the local area by Elizabeth Devon, who thoroughly entertained the 50-strong audience with a visual presentation par excellence.
Speaking with obvious enthusiasm and gentle humour, Elizabeth guided us through ten snapshots of the Bristol area over the past 400 million years, each one chosen to highlight a different environment of the South-West over time, and each one impeccably backed-up with geological evidence. Many of the audience were amazed at the small details of climate, flora and fauna which a geologist can extract from the rocks beneath our feet!
After outlining the general geology of the British Isles and explaining the processes by which all these successive layers of rock were deposited, Elizabeth first took us back 380 million years to the Devonian period, during which time Bristol sat in a flood plain close to a tropical sea, with nearby volcanoes making the environment exceedingly hazardous. A far cry from today, not in the least as we were at a latitude close to 45° south! We advanced to the Lower Carboniferous, as rainforests sprang into existence, and our seas filled sharks, then onwards to the Upper Carboniferous and through to the Early Triassic, now a mere 246 million years ago. By now, Bristol was now 13° north, and the land was hot and arid. Flash floods were common thanks to seasonal rainfall, and the reptiles roamed the land.
In the Late Triassic we were once again submerged but, as we reached 160 million years in the past, our climate had become Mediterranean, we were 35° north and surrounded by warm, shallow seas. However, hazardous tropical storms wracked the west country, volcanoes churned off our coasts, and dinosaurs roamed freely. By the time we arrived in the Upper Cretaceous, global warming had run rampant, and the lack of polar ice caps had plunged Bristol once more under water thanks to sea levels 400m higher than we are used to today! Speeding up as we neared the end of our journey, the Miocene and Pliocene had given rise to dangerous mammals in our mild, warm climate, and the Bristol Channel had opened up, along with the North Atlantic Ocean.
Our last stop, 20, 000 years ago and 51° north, saw Bristol sitting on huge tundra plains, just south of a huge ice sheet and suffering from very cold, arctic winters. Homo sapiens had colonised the land, and survived by hunting the mammoths, reindeer and woolly rhino that meandered across the frozen landscapes. Back to the present day, Elizabeth also showed us possibilities for the near future, as the temperature – and attendant water levels – continue to rise.
What made Elizabeth’s lecture so enjoyable, besides her clearly extensive knowledge, were her excellent illustrations of the climactic conditions in every epoch she chose, bringing home the likely reality of what she described. She had also gone out of her way to find local examples of each and every rock she described – thanks to her, it is now possible for audience members to look at many a local landmark building and find signs indicating climate, river currents, and local lifeforms from millions of years in the past, all within the walls of the buildings we pass each and every day!
With the summer approaching, perhaps an upsurge of amateur geology will be gripping the local SCI?
Derek Gillespie
Honorary Recorder
Bristol and South-West Regional Group
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