Lectures

Lecture Programme 2014-2015

Our varied programme of illustrated lectures runs from October to Easter.  Speakers and topics are carefully chosen to provide interest for both the amateur and professional geologist.

These meetings also provide an informal opportunity to chat to other members, and to gain advice from local experts on visiting geological localities.  Each year, a celebrity lecture is given by a geologist of international repute, who is invited jointly by the Society and the Geological Society of Glasgow.  At the annual Fellows' Night, members can give accounts of their own geological interests, specimens or travels.  

Lectures are usually on Wednesday evenings at 7.30 pm. These meetings are open to the public, there is no charge, and visitors are most welcome. Tea and biscuits, also at no charge, are served following the lecture in the Cockburn Museum of the Grant Institute.The lectures usually take place in the Hutton Lecture Theatre in the Grant Institute of Geology, on the University of Edinburgh's King's Buildings campus.
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15 October Prof John Parnell University of Aberdeen
Evidence for a deep biosphere in the geological record

29 October Dr Maarten Krabbendam BGS Edinburgh
Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion (or: How to make a cnoc-and-lochan landscape)

12 November Dr Simon Cuthbert University of the West of Scotland
Eclogites and the fate of subducted continental margins

26 November Prof Colin Ballantyne University of St. Andrews
Catastrophic landslides in Scotland and Ireland: timing, causes and implications


10 December, 7:30 pm Fellows’ Night & Social Evening
BGS, Murchison House, Edinburgh
This meeting is a chance to meet other members of the Society informally, with a series of short talks given by members, followed by a wine and cheese reception, expertly selected by John Mendum. (Soft drinks will be available.) Booking for the event is not required and tickets will not be sold in advance, but those wishing to stay for the Reception are asked to pay £6 on the night.

15 October Prof John Parnell University of Aberdeen
Evidence for a deep biosphere in the geological record

A significant part of Earth’s biomass lives in subsurface habitats down to several kilometres depth, below both oceans and continents. This deep biosphere is readily evidenced today in microbial isolates from drill cores, but proving that it has persisted from deep geological time as an intrinsic aspect of life on Earth is more challenging. The talk will explore the available evidence in the geological record. Demonstration of a long-term geological record of the Earth’s deep biosphere emphasizes that life on other planets is also likely to include a deep biosphere, which may be the dominant habitat. As a subsurface habitat does not depend upon surface liquid water, this substantially extends the number of planets that could support life.

29 October Dr Maarten Krabbendam BGS Edinburgh
Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion (or: How to make a cnoc-and-lochan landscape)

Vast areas previously occupied by Pleistocene ice sheets have a rough landscape of knolls and lake-filled rock basins, the ‘cnoc-an-lochan’ landscape or ‘landscape of areal scour’. These landscapes are invariably underlain by gneiss or granitoids. These landscapes are interpreted to be formed either by strong glacial erosion, or by stripping of regolith from an older deeply weathered landscape.

We analyse the ‘cnoc-an-lochan’ landscape of the NW Highlands of Scotland, its relation with bedrock structure and remnants of regolith. We compare the landscape with: i) an adjacent sandstone terrain , which shows widespread till cover; ii) a gneiss terrain in a non-glacial, arid setting (Namaqualand, South Africa), which is very similar to the ‘cnoc-and-lochan’ landscape, including abundant rock basins.

The rough gneiss landscape in Scotland and Namaqualand is close to the old bedrock—regolith contact. The roughness is caused by deep joints providing a highly irregular surface area for weathering to proceed. The contact represents a significant jump in bedrock physical properties. Glacial erosion (and aeolian erosion in Namaqualand) is simply an efficient way of stripping regolith, but not very efficient in eroding hard, unweathered bedrock.

Glacial gneiss terrains are the result of a multistage process: 1) Long term weathering, forming a deep, irregular weathering front; 2) Stripping of regolith by glacial erosion during the first glaciation(s), resulting in a rough landscape, broadly conforming to the old weathering front; 3) Further modification of exposed bedrock by glacial erosion, especially in areas of fast ice flow.

Except in areas of high palaeo-ice flow, glacial erosion during the last glaciation(s) was low, so that little sediment was produced and deposited. Little sediment was produced, explaining the lack of subglacial deposition in gneiss terrains. The presence or absence of glacial till is thus strongly predicated by underlying bedrock lithology. Much of the gneiss-dominated bed of the Greenland Ice Sheet probably comprises a similar landscape with similar roughness.

12 November Dr Simon Cuthbert University of the West of Scotland
Eclogites and the fate of subducted continental margins

Eclogites are spectacular red and green garnet + clinopyroxene rocks formed by metamorphism of basaltic rocks at pressures normally experienced in the mantle. First described by Hauy in the 18th century they are now known from subduction and collision zones and mantle-derived xenoliths in  kimberlites. Eclogites and related high-pressure metamorphic rocks preserve abundant information about processes at destructive plate margins. Mafic oceanic crust to undergoes wholesale conversion to eclogite during subduction but, paradoxically, eclogites are often found within continental gneiss terrains whose low density might be expected to prevent subduction. These will be the main focus of the presentation. Some of these rocks contain metamorphic diamond and other unusually dense minerals such as coesite, indicating burial to depths in excess of 150km. Frequently found outcropping beside eclogites are garnet-bearing peridotites – bodies of sub-continental mantle that have been introduced tectonically into the eclogite-bearing crust. Such "ultra-high pressure" eclogite-bearing terrains tell us that continental crust can be subducted quite deep into the mantle when continental margins follow oceanic lithosphere into a subduction zone. Their return to the surface also presents us with some interesting tectonic challenges. We will explore these fascinating rocks with examples from around the world, and with some recently published computer models of collision tectonics. For the skeptic of all this grandiose story-telling, just come and look, because eclogites are, quite simply, very beautiful rocks found in beautiful places!

26 November Prof Colin Ballantyne University of St. Andrews
Catastrophic landslides in Scotland and Ireland: timing, causes and implications

Scottish and Irish mountains contain over 700 major postglacial rock-slope failures (RSFs). Dating of 31 RSFs shows that they occurred over the period 18.2 ± 1.2 to 1.7 ± 0.2 ka, but were 4.6 times more frequent during the Lateglacial period than during the Holocene, with peak RSF activity 1600-1700 years after ice-sheet deglaciation. This time lag is inferred to represent deglacial stress release leading to progressive failure plane development, and ultimately to spontaneous kinematic release or failure triggered by some extrinsic mechanism. The timing of most RSFs coincides with maximum rates of glacio-isostatic recovery, suggesting that earthquakes were important triggers of rockslide release. The prevalence of ‘pre-last glaciation’ RSF scars lacking runout debris demonstrates that rockslides made a major contribution to the sediment budget of former ice sheets and glaciers, and suggests that the erosive role of Pleistocene ice sheets has been over-emphasised: perhaps glaciers mainly ‘clean up the mess’ left by landslides.

  

 

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