Lecture Programme
Lecture Programme
11th October 2012
Dr Steve Jones, Birmingham University
The relationship between the Greenland-Scotland Ridge, the Iceland Plume and Northern Hemisphere glaciation
8th November 2012
Dr Jim Morrison, Geological Society of Glasgow
North Atlantic opening - an introduction
13th December 2012
AGM and Presidential Address
Miss Margaret Donnelly
Geological journeys10th January 2013
Dr Jon Mound, Leeds University
The complex and dynamic inner core
14th February 2013
David McInroy, BGS Edinburgh
Formation of the Rockall microcontinent: a result of pre-Palaeogene extension in the NE Atlantic region
14th March 2013
T. Neville George Medal lecture
Professor Jenny Clack, Cambridge University
Populating Romer’s Gap: rebuilding terrestrial ecosystems after the end-Devonian mass extinction
18th April 2013
Dr David Chew, Trinity College, Dublin
Measuring Palaeozoic time by isotopic dating
9th May 2013
Members’ Night
Lecture Summaries
11th October 2012
Dr Steve Jones, Birmingham University
The relationship between the Greenland-Scotland Ridge, the Iceland Plume and Northern Hemisphere glaciation
Opening and closing of oceanic gateways between continents can influence global climate. For example, establishment of the Antarctic circum-polar current, following separation of Antarctica from South America and Australia, helped to allow growth of the Antarctic ice sheet. This talk will look at how a gateway in the North Atlantic Ocean near Iceland has affected oceanic circulation. Evolution of the Icelandic gateway influenced the onset of the Northern Hemisphere Glaciation and possibly other periods of global climate change.
At the head of the North Atlantic, between Scotland and Greenland, lies an important hub in the global oceanic circulation system. Here, warm Gulf Stream water that has flowed north near the ocean surface cools, sinks and returns southward along the seabed. This Atlantic circulation system carries warmth from the tropics to the Arctic, and changes in the circulation system can change the temperature gradient between the equator and the North Pole. The position of the circulation hub near Iceland and the strength of the circulation are both affected by the Greenland-Scotland Ridge, a shallow sill straddling Iceland where the sea floor rises to a depth of only several hundred metres.
The elevation of the Greenland-Scotland Ridge has fluctuated over the past 60 million years in response to three controls. First, the ridge is a hotspot track, built from the large volumes of magma formed when unusually hot mantle within the Iceland Mantle Plume rises up beneath the Mid Atlantic Ridge plate spreading axis. Secondly, like all young oceanic plates, the Greenland-Scotland Ridge subsides gradually as it spreads away from the mid-ocean ridge. Finally, the temperature of the Iceland Mantle Plume has fluctuated over time. The consequent waxing and waning of mantle convective support of the Greenland-Scotland Ridge has, from time to time, restricted or even cut off the connection between the main Atlantic and the ocean basin to the north. Oceanic crust south of Iceland preserves an excellent record of these mantle temperature fluctuations in the form of topographic features known as V-Shaped Ridges. Recent research cruises have clarified the long-held notion that V-Shaped Ridges are generated as pulses of hotter and cooler mantle flow outward from Iceland beneath the plates.
The Northern Hemisphere Glaciation began during the Pliocene (c. 3 million years ago). The preceding period was the most recent period in Earth’s history in which global average temperatures were similar to those projected for the end of this century; however, state-of-the-art global climate models have great difficulty in reproducing the Pliocene warm period. The new data from the North Atlantic V-Shaped Ridges indicate that the most recent patch of cool mantle within the head of the Iceland Mantle Plume was positioned beneath the Greenland-Scotland Ridge lock-gate during the Pliocene. With cooler mantle beneath, the lock-gate would have been relatively low and allowed the strong Atlantic oceanic circulation that kept the high latitudes warm. As the cool mantle moved towards its present position, the lock-gate rose, oceanic circulation was inhibited and the Arctic ice expanded. It seems likely that the global climate models cannot reproduce pre-Northern Hemisphere Glaciation conditions because they do not yet correctly represent the Icelandic oceanic gateway.
8th November 2012
Dr Jim Morrison, Geological Society of Glasgow
North Atlantic opening - an introduction
For more than a billion years, until the beginning of the Palaeogene, Scotland and NW Ireland were plastered against the edge of Laurentia. When Pangea began to break up, the movement of Africa away from South America marked the start of Atlantic opening. About 150 million years later the mid-Atlantic Ridge had reached the position of the Azores Triple Point.
From there, the ridge continued to grow to what is now the Charlie-Gibbs Fracture Zone (well seen on Google Earth) and continued between Labrador and West Greenland. At this point, something dramatic happened and the ridge switched to the east of Greenland and continued, splitting Britain and Ireland from North America during Palaeogene times. This gave rise to the familiar British and Irish Palaeogene Province and eventually to Iceland.
Palaeogene opening occurred between Greenland and, not Ireland, but the Rockall-Hatton Bank (or microcontinent). This is partly underlain by Rhinnian basement and has moved away from Ireland by pre-Palaeogene extension.
13th December 2012
AGM and Presidential Address
Miss Margaret Donnelly
Geological journeys
The oldest rocks in Scotland occur in the Lewisian Complex of the Northwest Highlands: the Scourian gneisses of the Outer Isles are dated at 2.75 to 3.12 Ga, and show greater affinities with the east coast of Greenland than with the Scottish mainland. The Lewisian Complex records a series of metamorphic events, followed by the emplacement of the Scourie dykes at c. 2.4 and at c. 2.0 Ga. Subsequently, the lengthy Laxfordian deformation took place, possibly from 2.1 – 1.5 Ga; juvenile rocks of Laxfordian age are also found – on the Rinns of Islay, c. 1.79 Ga. The later Grenville orogeny, c. 1.2 Ga, also left its mark on Scotland in the Glenelg-Attadale Inlier, and then the mainly fluvial Torridonian sandstones and the mainly shallow marine Moine were deposited between c. 1.2 – 0.9 Ga, the latter from the south in, possibly, a separate basin. There followed traumatic events – the “Snowball Earth” of at least two major glaciations, between c. 800 and 650 Ma; the Port Askaig Tillite is our own excellent example. The Iapetus Ocean opened c. 600 Ma as evidenced by the Tayvallich volcanics, and closed in the Grampian orogeny c. 470 Ma. Much later the opening of the Atlantic, c. 55 Ma, gave rise to our Tertiary Igneous Province. This talk will focus on a selection of memorable field trips, including the Outer Isles, Northwest Highlands, Glenelg, Islay, Ardnamurchan, Mull and Skye.
10th January 2013
Dr Jon Mound, Leeds University
The complex and dynamic inner core
[Joint lecture with Astronomical Society]
It has been over 75 years since the discovery of the Earth's solid inner core, and for much of that time it has been viewed as a relatively inert and uniform sphere of iron and nickel. However, over the past decade the vast improvement in the quality and coverage of seismic observations have revealed a surprising amount of structure within the inner core. This internal structure points to the existence of dynamic processes that are constantly reshaping the inner core. Does the inner core rotate faster than the rest of the Earth? Is half of it melting? Does it affect the generation of the Earth’s magnetic field? There is still much to learn in the decades to come.
14th February 2013
Dr David McInroy, BGS Edinburgh
Formation of the Rockall microcontinent: a result of pre-Palaeogene extension in the NE Atlantic region
Prior to Early Eocene sea floor spreading in the North Atlantic, a number of pre-Palaeogene extensional phases affected the Rockall region, offshore NW Europe. The area is underlain by crystalline basement terranes, assembled in Palaeozoic times during the Caledonian Orogeny. A number of poorly constrained late Palaeozoic to Mesozoic extensional phases substantially thinned the continental crust, leading to the development of sedimentary basins such as Rockall Basin and Hatton Basin, separated by basement highs such as Rockall High. Although the basin stratigraphies are poorly calibrated due to a lack of well control, several regional studies suggest that significant rift episodes affected the Rockall area during Permo-Triassic and Jurassic times, with the main phase of rifting during the Cretaceous.
T. Neville George Medal lecture
Professor Jenny Clack, Cambridge University
Populating Romer's Gap : rebuilding terrestrial ecosystems after the end-Devonian mass extinction
At the end of the Devonian, a mass extinction changed the faunal composition of terrestrial and freshwater faunas. The following 20 million years is a fossil-poor interval known as ‘Romer’s Gap’. This interval, the Carboniferous Tournaisian stage, saw the re-establishment of fully terrestrial ecosystems and the evolution of terrestrial tetrapods. Unfortunately, almost no fossils were known that could document these events. Now, for the first time anywhere, abundant fossils of tetrapods, arthropods, and fishes from this interval have been found – in Scotland. My talk introduces the finds and their significance, and the research planned to investigate this crucial stage in Earth history.
18th April 2013
Dr David Chew, Trinity College, Dublin
Measuring Palaeozoic time by isotopic dating
Precise absolute age dating of sedimentary sequences is extremely important in establishing the timing and duration of many geological processes, including climatic fluctuations or rates of evolutionary change. This presentation will consist of two case studies from Carboniferous sequences in NW Europe (Ireland, England and Belgium).
The first case study employs precise U-Pb CA-TIMS zircon dating (the “gold standard” in Palaeozoic timescale calibration) of Carboniferous volcanic layers. These air fall tuffs are interspersed within glacio-eustatic sedimentary sequences with high-resolution biostratigraphy. These data are used to constrain the onset of Gondwanan glaciation and duration of Gondwanan glacial–interglacial cycles. The second case study involves dating sedimentary rocks by two relatively new isotopic methods (Re-Os dating of black shales and U-Pb dating of diagenetic xenotime). These methods are applied to the same sequences dated by the U-Pb zircon method, and allow us to determine the suitability of the Re-Os black shale and U-Pb diagenetic xenotime chronometers to dating older, fossil-free sedimentary units.