Thursday 15th September 2016
At the August meeting David Pannett ( Shropshire Geological Society) explained how many of the landscape features observed in the Severn Valley are the result of glaciation. He explained how glaciations have occurred a number of times in the past 2-2.5 million years. The last of these being the Devensian from about 120,000 to 11,000 years BP.
The ice from these glaciations have given rise to many features to be found in the landscape, including moraines, kettle holes, outwash basins and river terraces. The origin of these features was explained. He took us on a trip up the Nant-y-Llyn valley to Pistyll Rhaeadr explaining the stepped profile of the valley, the corries and the classic hanging valley that is Pistyll Rhaeadr.
The talk was interesting and informative.
The next meeting will be on 21st September when Dr. Sara Metcalf will give a talk entitled: Mesozoic Mammals.
Monday 15th August 2016
Our next event will be on Wednesday the 17th of August, where guest speaker David Pannett from the Shropshire Geological Society will present his talk “Glacial Features in the Severn Basin”
Sunday 31st July 2016
At the last meeting Dr. Chris Simpson presented a snapshot of the geology to be found on the island of Cyprus. The main focus of the talk was the Troodos Ophiolite. Ophiolite is a fragment of oceanic crust and the underlying upper mantle that has been uplifted and emplaced onto continental crust.
The Troodos ophiolite was created during the complex process of sea-floor spreading and formation of oceanic crust and was emerged and placed in its present position through complicated tectonic processes related to the collision of the Eurasian plate to the north and the African plate to the south.( Geological Survey department cyprus) It is seen as the most complete, intact and studied ophiolite in the world.
With many good photographs Dr Simpson worked his way up through the stratigraphic column of the ophiolite commencing with the ultramafic rocks like harzburgite composed of olivine and orthopyroxene. Harzburgite along with dunite are interpreted as a “mantle sequence”, which represents residue from partial melting of the upper mantle. The next sequence was the layered gabbro with massive gabbro above. The gabbro is a residual of magma. During the slow cooling, the heaviest minerals lie in the depths, thereby creating the darker coloured gabbro, with light-coloured varieties in the higher layers. At higher levels and in small pockets, the products of this different crystallisation are to be found, known as plagiogranites or granophyre.
Above this is a sheeted dyke complex. They are pathways through which molten basaltic magma rose from the mantle to the seafloor where it solidified as a pillow lava. Some of the magma did not reach to the surface and solidified as dykes, consisting of dolerite. Above these are the volcanic rocks consisting of pillow lavas and lava flows. Basalts predominate in the pillow lavas and are characterised by large spherical to ellipsoid pillows. Their crust is glassy due to the rapid cooling but the insides of the pillows is honeycombed due to sudden expansion of gases in the lava.
The geology along with the wonderful weather makes Cyprus a lovely and interesting place to visit.
The next meeting will be held on 17th August when David Pannett will give a talk entitled: “Galcial Features in the Severn Basin.”
Wednesday 8th June 2016
Our next event will be on Wednesday the 15th of June where guest speaker Dr. Chris Simpson will give his talk “Cyprus Geology: a snapshot”
Monday 23rd May 2016
This month we had a talk by Jack Davies on “Reflections on Geomorphology”. It was much more than an investigation of the development Britain's geomorphology, more a geologist's life story. Starting with childhood freedoms exploring Britain by cycle, through student days, to theses typed in DS with multiple carbons, he had developed a deep understanding of the development of landforms and an appreciation of the uniquely diverse geology of the British Isles.
He described, from a personal perspective, the landforms resulting from the Cretaceous transgression of Wales, followed by Mid Tertiary uplift and the removal of the chalky deposits, with the initiation of drainage and erosion. Stripping back of the Mesozoic cover revealed a wave-trimmed peneplain, with superimposed radial drainage cutting down to the Palaeozoic rocks beneath.
Mid Tertiary uplift elevated the Welsh High Plateau and later negative changes in base level produced the Middle and Low Peneplains with consequent adaptation of drainage.
Later Pleistocene glaciations produced the 400ft, 300ft and 200ft platforms
It was a refreshing approach with no Powerpoint!
The next meeting will be on Wednesday 15th June when Dr Chris Simpson will give a talk entitled: Cyprus Geology: a snapshot