The Geology of Radnorshire by Joe Botting

//The Geology of Radnorshire by Joe Botting

The Geology of Radnorshire by Joe Botting

The third Radnorshire Society lecture of the 2018 season took place at Llandewi Village Hall on Friday October 19. It followed the AGM of the Society’s Field Section. The guest speaker was Joe Botting of Llandrindod Wells, who was introduced by the Society’s Secretary Dr. Colin Hughes. His lecture was entitled “The Geology of Radnorshire”. Joe is a specialist in paleontology, and spent two years as guest scientist at Nanjing Institute of Geology and Palaeontology (China). He started his talk by saying that geology in Radnorshire is unique, and the best place to study some aspects of the fossil record. Interest in the subject goes back a long way, and he referred to the magnificent 1839 book “The Silurian System” by Roderick Impey Murchison, a copy of which was on view after the lecture. He noted that the names of major geological periods, (Cambrian, Silurian and Ordovician), have Welsh connections due to pioneering geological work in Wales. Although nowadays modern tools are used, the old tools like hammers and chisels are still not out of place.

Joe spoke of the time scale of rocks, mentioning that Radnorshire was mostly Silurian, but that there were also the Ordovician and Devonian periods represented (together with some ancient Precambrian rocks). The area of Radnorshire he concentrated on was that of the ‘Builth Inlier’: a fossilised volcanic island sequence preserved in the area between Builth,Llandrindod and Llandegley. He described the many changes in land/ ocean structures, and different layers of rock. In 1699 Edward Llwyd made the first description of trilobites, based on fossils found near Builth. Since then there has been centuries of work in the inlier, but only recently have the most important discoveries come to light, with Llandegley Rocks being a unique paleontological site. Ash deposited by the volcano and washed around in a shallow lagoon preserved the remains of delicate starfish, sea urchins and other creatures. The area has more varied evidence of such creatures than anywhere else in the WORLD, including over 15 species of sponges that are not preserved anywhere else. Another site preserves the oldest known holothurians (sea cucumbers) which were found within a bed of mud deposited just after an ash layer. These rarely found fossils of animals which had dies out millions of years ago show extraordinarily well-preserved fine detail when viewed microscopically.

Perhaps most important of all the sites, Llanfawr Quarry, near Llandrindod Hospital, is famous for trilobites, although admittedly they are the standard ones. However, there are also hydroids that resemble the living C124462376 orymorpha nutans at Llanfawr, together with other soft-bodied animals. Joe spoke about the numerous types of sponges found and groups found here, in an ecosystem that resembles some modern deep-sea faunas.

After the events of the Builth Inlier, the rocks still tell an interesting story. There are sandstone layers in the Elan Valley from an Ice Age in the latest Ordovician: cause of the second-greatest mass extiniction event. Slightly older rocks near Nantmel preserve abundant shells and other fossils, most of which disappeared during the crisis. During the Silurian, life recovered as thick sequences of siltstone were laid down. At the Pales Meeting House Quarry, for example, Silurian fossils are typical planktonic graptolites and nautiloids, plus occasional complete (exceptionally well preserved) crinoids. At the end of this period, the continent of Avalonia (including Wales) collided with Laurentia (North America and Scotland), forming huge mountain ranges.

Much has happened since, but the land surface we see now was sculptured by the current Ice Age, which has lasted a mere two million years. During this period, pre-existing valleys were deepened, new ones carved out, and the landscape rounded.

The speaker concluded by reaffirming that both Llandegley Rocks and Llanfawr Quarry are unique and of world significance. Overall, he stressed that Radnorshire is unique and very special, something the large enthralled audience of Society members and guests readily agreed with.

Dr Botting’s presentation was well illustrated by photographs and specimens which he brought along.

2018-11-18T16:23:56+00:00
Show Buttons
Hide Buttons