Britain's Largest Meteorite Impact

 geology  Comments Off
Mar 292008
 

Geologists at Aberdeen and Oxford have reinterpreted the Stac Fada Member of the Torridonian Stoer Group, previously believed to be a volcanic mudflow deposit, as a fossilised ejecta blanket from a meteorite impact about 1.2 billion years ago near Ullapool in Northwest Scotland. The unit bears the chemical signature of extraterrestrial origin including high iridium levels.


[Image from Waters 2003]

This unit presents a superb opportunity to examine an ejecta blanket deposit from an impact into a wet substrate. I don’t know of any other terrestrial examples.


[Image from Waters 2003]

The unit is up to 20m thick, unbedded and poorly sorted with angular clasts.


[Image from Waters 2003]

The rock also contains devitrified volcanic glass.

I have no insight to offer here. As a geologist, particularly one with an interest in planetary geology I’m fascinated by it and hope to get to see it one day.

Geology article abstract
http://www.gsajournals.org/perlserv/?request=get-abstract&doi=10.1130%2FG24454A.1

Aberdeen University Press Release
http://www.abdn.ac.uk/mediareleases/release.php?id=1275

BBC News Story
http://news.bbc.co.uk/1/hi/sci/tech/7314329.stm

Waters DJ, 2003. Rocks of N.W. Scotland
http://www.earth.ox.ac.uk/~oesis/nws/nws-a98-st1.html#field

[Hat-tip Ole]

 Posted by hypocentre at 23:07

Getting Stuck (and Unstuck)

 fieldwork  Comments Off
Mar 112008
 



Following Silver Fox‘s tales of getting stuck in the mud, reminds me again of my time doing fieldwork in the Atacama Desert and getting a jeep stuck. On the other occasion we managed to get a jeep stuck it was in one of the few rivers in the place and at about 3500m altitude when we had been visiting one of the sulphur mines in the ‘foothills’ of the Andes above the Salar de Atacama. This time we had two 4x4s and it was the other one that managed to get bogged down to the axles in the stream bed when trying to cross it.

Although we had two vehicles we had no tow rope. We did, however, have a tyre which had burst a few days earlier and replaced with a spare. We burnt this and then braided the steel reinforcing wire into a very short tow bar. It was too short, however, to join the two tow balls on the jeeps back to back as one was low down, and the other higher.

We then took the two vehicle jacks. We then jacked the back of the sunken vehicle up as far as we could, placed a large rock next to the first jack, placed the second jack on it and raised the back up further. Then two large rocks were placed next to the second jack and the process repeated. Rocks were also placed under the wheels to stop the whole lot sinking back down as everything was on softish sand.

It was quite a sandy area generally and suitable rocks had to be lugged a considerable distance, not easy at that elevation. Eventually we managed to get the tow balls level and with much heaving and spinning of wheels eventually got the jeep out. That was the only time I got queezy from altitude sickness on the whole trip, with all that exertion, despite going up to nearly 6000m in Bolivia.

 Posted by hypocentre at 23:54

Do Geologists Have A Death Wish?

 fieldwork  Comments Off
Mar 062008
 

I’m a little late on posting about the current meme permeating the geoblogosphere, started by Geotripper and Chris Rowan, do geologists have a death wish?

A lot of the posts have involved photos of geologists playing with still glowing lava flows but being of the cowardly persuasion I don’t really have many tales to tell.

Two incidents though do spring to mind from my younger, more reckless days. The first was doing geology many years ago in the Atacama desert in northern Chile. It was my last day before having to fly home and my co-geologist and I decided to have one last look at a particular area. Instead of the meticulous planning that had gone with the rest of the fieldwork we just went for it. With only a single vehicle, no food and very little water we just turned off the pan-american highway and headed out across the desert, without telling anyone where we were going, aiming for a distant mountain. We had no maps, only a landsat image and compass to navigate by and this is in the days before GPS. The inevitable happened and we got the four-wheel drive irretrievably (for us) bogged down in the soft sand. Nothing for it but to walk out of the Atacama Desert with no real idea of exactly where we were or where nearest settlement was. After about 20km of walking on a compass bearing we picked up a road which fortunately lead to a small village. We found a bar where we did a reasonable attempt of re-enacting the bar scene from ‘Ice Cold in Alex’. We then cadged a lift to the nearest military base and persuaded the army to come and dig the jeep out.

The Atacama is a superb place to study geology – it’s so good they signpost it from the side of the road.

The other occasion is from a time working as a field assistant in the Spanish Pyrenees. We decided to climb Monte Perdido but I didn’t have any crampons and had to borrow an ice axe, something I had never used before. Most of the climb was fine but the last 100m was hard ice. Just near the top I slipped and learned to use the ice axe first go – otherwise I would have ended up in France several hundred metres below!

The views from the top were spectacular though, as seen here with recumbent fold of El Cylindro in the foreground and the high Pyrenees in the background.

I don’t think it is a death wish, but good geology can be in some risky places. It should be all right though as long as you take the right precautions!

 Posted by hypocentre at 23:30
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