What is your favourite place to do field work?” is the question Dave Schumaker at Geology News is asking as last this month’s Accretionary Wedge.

I am extremely lucky having a job that allows me out into the field occasionally, even if at the minute it is just down the road. In my top five I would have to include the Atacama Desert of Chile, Iceland, Colorado and the Alps but at number one has to be the Spanish Pyrenees.


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I’ve been many times, as a postgraduate demonstrator and lecturer on undergraduate field courses and twice as a field assistant to a Ph.D. student. However, I’ve not been back in a long time, so apologies in advance for the scans of twenty year old slides.

The Spanish Pyrenees is a classic place to teach geology. The Spanish side (unlike the French side) is arid so there is excellent exposure, and, unlike the Alps, they are not too high and much of the geology is accessible from the roadside (with a suitable loose definition of road).

The geology shows a superb interrelationship of sedimentation and tectonics with the sediments eroded from the high Pyrenees being progressively deformed as the mountain front advances.

Riglos

Riglos 2

Turbidites

The variety of geology is also stunning from vertical bedding to trace fossils.

Vertical bedding

trace fossils

The local cuisine is excellent with chorizo, pyrenean mountain cheese and local wild boar washed down vino tinto. The only exception to this is breakfast (sweet cake is not my favourite at the best of times) but we did manage to train a cafe owner in Jaca in the art of bacon and egg butty making.

Of all the places in the Spanish Pyrenees I think my favourite has to be the Ordesa National Park. From the olistostromes at Torla to the climb up to Monte Perdido is the most spectacular walk I have ever done. The views from the top are absolutely breathtaking.

cylindro

ordesa

One day I shall return.

 

One of the latest geoblogosphere memes is animals in the field.  It was started over at Clastic Detritus, originally with domestic animals but this has been more loosely interpreted by subsequent geobloggers.

I’ve been out on Cannock Chase over the weekend working on a geotrail. Here are a couple of the local inhabitants.

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Timber!

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Oct 252008
 

Geotripper started this meme here.

Being no dendrologist I’m not up to much insight but here are some favourites from my photograph collection.

South of Three Shires Head in the Peak District, Carboniferous Millstone Grit in the background.

A Rowan above Grasmere in the Lake District.

A Silver Birch at Innominate Tarn in the Lake District.

My Acer, at our old house, with Norwegian granitic pegmatite sample to the left.

 

Callan over at NOVA Geoblog has asked for examples of geological analogies in something he says is between a meme and an accretionary wedge. At the time of writing, the contributions to this thin end of the accretionary wedge have come from:

My favourite analogy regards geology itself. I liken it to being given ten pieces from a thousand piece jigsaw and being asked what the picture is. You have to examine each piece you have incredibly carefully, describing it in detail. You have to decide where you pieces might fit in the overall picture (sky, land, water …) and also how the pieces might relate to each other. You have to make educated guesses based on what you have seen before. You can go and explore down the back of the sofa and if you are lucky you will find an eleventh piece. This will possibly confirm your interpretation, but more likely require you to completely re-evaluate what little information that you have. However, how ever hard you look, you are never going to find all the pieces and you are going to have to use all your experience and skill to get a reasonable approximation too what is going on.

Beyond the obvious like volcanoes and champagne bottles, the only other analogy I can think of straight away is one a former colleague used to use. He used to say that gneissose fabrics were like the result of stirring porridge with a spanner. No, we didn’t have a clue what he was on about either!

Mineral Meme Redux

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Sep 102008
 

Callan and Nova Geoblog has subverted the Minerals Meme with the question …

Which five minerals do you think are the most important ones to know, and why? In other words, if you had to introduce a non-geologist to just five of the earth’s multitudinous building blocks, which ones would you choose to share, and offer a justification for each.

You can see Callan’s favourite five here and Kim at All My Faults list is here. Like Kim, I’ve tried not to look at the previous posts until I’ve finished my five.

1. Perovskite

From the 660km spinel to perovskite transition at the upper/lower mantle boundary down to the core/mantle boundary at 2900km the Earth’s lower mantle is dominated by perovskite (or at least the pyroxene enstatite with a perovskite structure). By my calculations, the lower mantle comprises about 55% of the Earth by volume, making this the Earth’s commonest mineral.

My Ph.D. was on deep earthquakes so I developed a keen interest in mantle structure and mineralogy.

2. Olivine

For similar reasons, olivine has to be one of the fundamental minerals, dominating the upper mantle. I also think that it is also one of the most vibrant when seen under the microscope in cross-polarised light. I’d better add a passing reference to spinel here. As much as I’m interested in mantle minerals, I don’t want to waste all my five.

3. Iron

Whilst the outer core is liquid and not technically a mineral, the inner core is solid. There is some evidence from the seismic anisotropy of the inner core that it (or maybe the inner-inner core) is crystalline iron, possibly even a single crystal!

4. Quartz

Quartz is probably the most logical choice. Being stable, it is a common component of igneous, sedimentary and metamorphic rocks are found pretty much everywhere. If there is one mineral that is common at the Earth’s surface, this is it. Passing mention should go to feldspars, not quite as common due to their being less stable but again found in many igneous (even more than quartz), sedimentary and metamorphic rocks.

5. Calcite

Calcite is important not only as the main constituent of limestone but because it locks up so much CO2 from the atmosphere. If we didn’t have calcite, our atmosphere would be full of CO2 from volcanoes and we would be a greenhouse planet like Venus.

OK, lets see how I compare
Callan has 1. Quartz, 2. Clays, 3. Olivine (+spinel +perovskite), 4. Plagioclase, 5 Ice.
Kim has 1. Quartz, 2. Calcite, 3. Pyrite, 4. Clays, 5. Olivine

I suppose it is unsurprising that we come up with similar lists. I suspect that my geophysics / seismology background makes me think a little ‘deeper’, but we are all on pretty much the same wavelength.

Not too sure about ice though. Sure it is technically a mineral but it smacks a bit too much of geography.

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