Sunday 8th April 2018
Evening Meeting Wednesday 14th April 2018- "Creataceous Fossils Araripe Basin Brazil" - Bob Loveridge
Twenty three members attended the last meeting when Bob Loveridge (Visiting Research Fellow University of Portsmouth) entertained us all with a superb talk on the Crato Formation of the Araripe Basin of Brazil. The Araripe Basin is located in a forested cirque in the north central part of the Chapada do Araripe, a large tableland in north-eastern Brazil. The Crato Formation ( Late Aptian in age) is 50-60m thick and is composed of a series of rock types with the basal unit of micro-laminated limestones, the Nova Olinda Member, yielding spectacular fossils which earns the formation its status as a Fossil Konservat Lagerstätte. There is a huge number of fossils all of which are exceptionally preserved and includes insects, arachnids, vertebrates and plants.The Chapada do Araripe is now a UNESCO GeoPark and collecting fossils is illegal without a permit but the area continues to be used for extraction of the limestone for buildings and roads which is leading to it’s destruction.
The fossils are preserved by pyrite/geothite which is thought to be due to pore waters permeating the specimen and envelopment by bacteria which create a covering over the outside of the carcass causing a micro-environment in which mineralisation of tissues can occur i.e. “bacterial sealing”.
The talk was accompanied by superb photographs and SEM pictures of the fossils but also by the escapades that Bob and partners undertook in order to study them.
The next talk will be on Wednesday 25th April when Andrew jenkinson will give a talk entitled: “Rocks along the Cut” - looking at rocks along the Montgomeryshire canal.
Wednesday 21st February 2018
Evening Meeting Wednesday 14th February 2018 - "The Origins of Atoms" - Dr. Geoff Steel.
We all have seen and been taught about the Periodic table of elements but how many understand how these elements came into being. Geoff's talk went a long way in helping in this understanding.
The first lighter elements were formed by Big Bang nucleosynthesis. The Big Bang being the cosmological model that best explains the origin of the universe. During the first second following the Big Bang, a wide range of events were occurring including cosmic inflation, elemental particle formation, the formation of baryonic matter, collisions between elementary particles, decreases in particle energies and temperatures. Between one second and three minutes after the Big Bang temperatures cooled to about 109K at which Big Bang nucleosynthesis could occur. This led to the production of protium (1H), deuterium (2H), tritium (3He), helium (4He), and some Lithium (7Li) but no heavy elements were formed. The heavier elements had to wait until later to be formed by Stellar Nucleosynthesis.
Most stars produce energy by fusing hydrogen to form helium, with the release of energy. The outward flow of energy (thermal pressure) released balances the collapsing force of gravity, and this stabilizes the star's size. As helium increases in the core it reduces the rate of hydrogen fusion which in turn decreases thermal pressure and the star starts to contract. Depending on the initial mass of the star Helium can fuse to form carbon nuclei which leads to the formation of a carbon core via a process known as the Triple Alpha Process. This increases thermal pressure of the core to a point where it will overcome gravity and the size of the star increases giving rise to a red giant. If a star had sufficient mass, though, eventually enough carbon would accumulate so that the temperature and density reach a point where carbon nuclei could be fused into Neon nuclei. This carbon burning core would be surrounded by two outer shells, the innermost burning Helium, and the outermost burning hydrogen. This pattern of the central core collapsing and increasing temperature continues until a further round of fusion occurs and more shells form. How many shells are eventually formed is dependent on the initial mass. Eventually iron (56Fe) will be formed but the average binding energy per nucleon has now reached maximum so there can be no more energy-generating reactions, all reactions are required to be endothermic. The star therefore undergoes gravitational collapse. The star then enters a runaway phase leading to the development of a supernova explosion which in turn can lead to the production of even higher elements via a process involving neutron capture.
Finally Geoff explained that the abundance of lithium, beryllium and boron in the universe is thought to be due to the process of Cosmic Ray Spallation. This refers to the process where interstellar collisions between very energetic cosmic rays and interstellar nuclei causes the heavier nuclei to break up forming smaller nuclei. During the collision there is expulsion of a large number of protons and neutrons from the object hit. Cosmic Ray Spallation not only occurs in deep space but also in the earth's upper atmosphere and crustal surface.
The next meeting will be on March 14th when Bob Loveridge will give a talk entitled: “Cretaceous Fossils of the Araripe Basin, NE Brazil”
Friday 19th January 2018
Evening Meeting and AGM - Talk by Bill Bagley - "The Wonders of Calcite"
Eighteen members attended the first meeting of the year despite the wind and rain. The AGM was followed by a very interesting talk by Bill Bagley in which he gave an overview of the mineral calcite. Bill took us through the processes of formation including a short video clip of the rare type of volcano producing carbonatite i.e. Doinyo Lengai volcano in Tanzania. With photos he explained calcite's structure and colour variations. That the most common crystal forms are scalenohedra, and rhombohedra and calcite readily cleaves into rhombohedra. It may also occur as prismatic crystals. The crystals may be tabular, acicular, prismatic and platy. Calcite can occur as crystals, stalactitic, massive, earthy, as aggregates or in geodes. The colour of calcite can vary from colourless through white, yellow, brown, reddish, bluish to black. It is also one type of mineral that shows birefringence.
The talk, along with the numerous impressive specimens that Bill brought from his own collection made for a very interesting evening.
The next meeting will be on Wednesday 14th February when Dr. Geoff Steel will give a talk entitled “The Origin of Atoms”
Wednesday 1st November 2017
The next meeting will be on Wednesday 17th January. This will be the AGM followed by a short talk by Bill Bagley entitled: The Wonders of Calcite.
Thursday 12th October 2017
At the last meeting Tony Thorp gave an illuminating talk on geological thin sections, the history and practicalities.
It was Henry Clifton Sorby (1826-1908) whose work laid the foundations of microscopical petrology which became the cornerstone of geology. A man of independent means, he took an interest in microscopy and following in the footsteps of William Nicol and sir William Brewster he learned to make transparent sections of specimens like teeth and bones for observation under a polarising microscope. Of greater importance was the fact that he made thin sections of rock and was the first person to appreciate it's value. His thin sections were 0.03mm (30μ) in thickness which is now the standard.
Tony went on to explain the use of the polarising microscope and the property of birefringence. In other words, as polarised light passes through a thin section the different minerals both refract and often re-polarise the light, so that light waves leaving a section are no longer aligned. By inserting a second polariser at 900 to the first all lightwaves that have not been re-polarised will be cut off and appear black. But any that were re-polarised will give a strong colour. Hence the patterning seen when observing a section.
Finally advice was give on how to make your own sections at home. I should add that Tony's ingenuity on achieving this was remarkable.
At the next meeting Michele Becker will give the ins and outs of bricks and brickmaking.