Friday, March 30, 2007

The great North Sea impact crater vs. salt withdrawal basin debate

That title doesn't quite roll off the tongue...oh well.

A debate is currently going on (or at least now making it into the news) regarding the origin of a conspicuous feature found in the subsurface of the North Sea.

Here is the original BBC article.

Geologists from the oil exploration company BP discovered a circular structure about 3 km wide and 1 km deep in the subsurface about 130 km off the coast of England. Some are claiming it to be an impact crater while others have some other thoughts.

Two studies by Dr Stewart and Mr Allen (of BP), the latest of which mapped the structure in 3D, concluded that it was the result of a space impact.
But, University of Edinburgh geology professor, John Underhill, has examined some of the data and disagrees.
"I decided to throw a more regional view at it, and ended up finding a whole load of these features with very similar cross sections," he said.
It turns out that Underhill's approach has either uncovered a field of impact craters...or perhaps there's an alternative explanation.
[Underhill] says that the swarm of structures is the result of movement of a thick layer of salt of Upper Permian (248-256 million years ago) age that lies below the whole area.
Granted, I've never worked the North Sea...I have worked on projects in the subsurface of the Gulf of Mexico, which is also influenced by the flow of salt, and it can produce a fantastic and wild subscape full of nearly circular minibasins. It seems that this explanation is a pretty good one, especially with this little tidbit:
"The key observation is that every single syncline is exactly coincident with where the salt has thinned or withdrawn," [Underhill] said.
But, the ones who discovered the original feature in question still disagree.
Dr Stewart is un-moved. He points to a 300m-high central peak, or nipple, in the centre of the inner bowl, typical of impact craters.
Alas...the debate is interesting enough to draw other researchers into it. The only real way to settle this is to drill, sample, and look for evidence of impact in the rocks (e.g., shocked quartz).

Hmmm....what are the chances BP will pay for that?

Thursday, March 29, 2007

Giant sandy bedforms seaward of the Golden Gate Bridge

High-resolution sea-floor mapping done in 2004 and 2005 by the US Geological Survey (USGS) and Cal State Monterey Bay (CSUMB) reveals a field of gigantic sand waves just west of the Golden Gate of San Francisco Bay.

More than 40 large sand waves were mapped, with crest-to-crest lengths of as much as 220 meters and heights of as much as 10 meters. Although the tidal range is not huge here, the narrowness of the Golden Gate straight augments the tidal force significantly (tidal currents > 2.5 m/s). Note in perspective bathymetric images how the area directly under the bridge (blue/purple colors) is kept clean of sediment.

Here is a short synopsis from the USGS's website.

Here is an article from the San Francisco Chronicle from last summer.

Check this out for another submarine view of San Francisco Bay.

Tuesday, March 27, 2007

Nature to launch a geoscience journal

Not sure if this has been blogged about yet.

I was pleasantly surprised this morning when I stumbled upon news that Nature is launching a specialized journal called Nature Geoscience in January 2008.

Here's their description of it:

Launching in 2008, Nature Geoscience will be a monthly multi-disciplinary journal aimed at bringing together the most significant research across the entire spectrum of the Earth Sciences. Published monthly, in print and online, the journal's content will reflect the core subject disciplines and other related areas with direct links to Earth Sciences.

In addition to primary research, Nature Geoscience will also publish review articles, news and views, research highlights about important papers published in other journals, commentaries, book reviews and correspondences.

Nature Geoscience will take an interdisciplinary, integrated and balanced approach to all areas of geoscience and foster the exchange of ideas between scientists involved in different disciplines. Nature Geoscience will be an invaluable resource for all researchers who are active in the process of discovering and developing an understanding of the Earth, environmental and planetary sciences.

I subscribe to the general Nature journal and enjoy it quite a bit...especially their review articles for the technical papers outside of my field -- like in genetics, quantum physics, astronomy, etc. But, there's typically only about one or two Earth science-related papers per issue (if that). I'm actually quite surprised it took this long for Nature to get this going considering how important the disciplines of Earth science are to the scientific community.

Will this be a good thing for the science? Any thoughts?

Giant selenite crystals

Some of you may have seen these photos....they have been circulating via e-mail over the last few weeks.

Pretty amazing....probably the largest selenite (CaSO4·2H2O) crystals found, i'd imagine. Miners discovered them in Naica Mine, Chihuahua, Mexico. Note people for scale in photos.

From the perspective of a guy from Buffalo at a Tragically Hip concert in San Francisco

This story is from the perspective of a guy from Buffalo at a Tragically Hip concert in San Francisco.

Really...the only way to see these guys is in a small (and famous) music club in San Francisco and not in a giant arena in Calgary. Don't get me wrong...I love 'em...but they are better suited to the smaller room. This is, by far, the most concentrated collection of Canadians in San Francisco tonight -- maybe the most all year?

In the bathroom between the opening band and The Hip, a voice calls out "Who's from Vancouver, eh?" -- this is answered by "Go Canucks!" from the opposite corner and, slightly overlapping in timing, "Go Leafs, Go" from right next to me in a clear combative tone. A couple more Crown and Coke's and I would have added in my own $0.02 and screamed something clever like "Buffalo rules...wooo". The 'wooo' is pretty standard really...seems trite, but how can you leave it out. C'mon.

The Canadian national anthem was 'sung' outside the club afterwards by competing packs of drunks waiting for their friends. It was beautiful...I wanted to pull the sweater over this guy's head next to me and start beating the crap out of him...but in a fun and friendly way. The kind of fun fight where the involved parties make sure to take care of their eyeglasses beforehand and do so with a giant and somewhat maniacal smile on their face. Although I never did find my friends -- the guys who flew down from Calgary just for this show -- and they now have my coat from the coat check, dammit.

Even though they didn't play 'Naughtical Disaster'...the Sabres have clinched a playoff berth. All is well.

once in a while...I stray from geo worries, it's just a random post

Sunday, March 25, 2007

Photographic summary of recent Patagonia field work

I am putting together a post about the general geology of the region of southern Chile we work in, what we are working on exactly, etc. but is taking a lot longer than I'd like.
As most of you out there who do relatively long stints of field work you know how it is getting your non-geology life back in order when you get home.

In the meantime, here a some photos and superficial information about them, and anecdotes from this year's session. (Click on photos for hi-res versions).

The above photo illustrates one reason why we travel so far to look at sedimentary rocks -- the exposure. Much of the stratigraphic section we are investigating is shale/siltstone, which does not typically create great outcrops. In this area, however, the recent glaciation has 'cleaned up' the mountainsides giving us a glimpse of these strata. You'll notice in the bottom portion of this exposure an odd lens-shaped area....this section is riddled with deep-sea mass wasting deposits (slumps, slides, debris flow deposits, etc.). The interior of that lens-shaped area is chaotically folded and deformed (syn-sed, soft deformation). There are very few places in the world where this kind of syn-sedimentary deformation is this well-exposed. The photo below is zoomed in a bit. Note the discordant strata in the lower half.

For this particular study area we were lucky to be able to stay in a nice little puesto...a glorified shack where the gauchos stay when they are in the area tending to sheep (see below). Not that I dislike camping...but when working, it is nice to come back to a roof and wood-burning stove in the evening. Plus, being able to drive to the puesto allows us to bring additional supplies (i.e., wine).

Up until this year, all of the work i've done in this area has been near, but outside of the national park boundaries (Torres del Paine). A new student is starting a project looking at the structure and thermal/exhumation history of the fold-thrust belt. This requires going further west into the more deformed part of the belt and thus towards the Patagonia ice cap (the 3rd largest continental ice sheet after Antarctica and Greenland, I believe). As you can imagine, accessibility is a major issue....the roads/trails within the park remain the best way to access a lot of these rocks efficiently, safely, and cheaply. So...the bonus is the spectacular scenery. The photo below is from our campsite early one morning...if you've ever read anything about this area you've no doubt seen this image. It is, by far, the most iconic image of this massif...called Los Cuernos (or 'horns').

The light rocks are the granitoid laccolith rocks intruding into the dark shales of the sedimentary sequence we are studying. The sed sequence is Upper Cretaceous...the laccolith is Miocene...I promise I'll get a post going putting all this random geo-info into some context. By the way, the water in the foreground is essentially sea level and the top of those peaks are nearly 3,000 m (10,000 ft). A little bit of relief.

Another day we were sampling along a trail that led to Glacier Grey. We, of course, had the proper permission and paperwork for sampling in the park, but still got many curious (and some dirty) looks from tourists along the trail. I suppose we may have been ruining their solitude by hammering away....but, hey, tough break. But most people were simply curious and once they find out we are scientists they will ask questions about the area. This photo below is a view of the glacier during our lunch break.

The geologic map of this area that we have is from the late 1970s. Note the two rock 'islands' at the glacier front...the bigger one to the right and the much smaller to the left in the photo above. The smaller one is not on the 30 year old map...the glacier has retreated that much.

After this work, me and one other guy set out for an excursion to a rather remote area in an area northeast of the park (again...I will post about the geography/geology more properly sometime soon). I've been working in this area for 4 years, but this was the first time to this particular area. It required being horse-packed in and camping for 10 days. Essentially, a gaucho guide takes us in, drops us off, and then comes back on a specific day to retrieve us. I shot this photo (see below) of the gaucho leaving the canyon we were in after dropping us off. He was much more efficient in traveling once he got rid of the two gringos (not necessarily master horseman) and all the supplies.

This was one of the harder areas i've worked physically. We couldn't really get too close to the outcrop we wanted to work on with the horses due the the ruggedness of the canyon we were in. So, we had a 5 km cross-country hike every day to the rocks (about 4 hours). By the end of the excursion we were not only in better shape but had found a good network of game trails that made the commute not so hard on our bodies.
Now that I'm sitting comfortably at home and not cursing my blistered feet and shaking a fist angrily at the weather gods, I can say it was worth it. The sedimentary sequence we were investigating in this area is important to the overall understanding of the basin fill because it is the record of delta progradation that eventually constructs the shelf and fills in the deep-water foreland during the latest Cretaceous. So, in a short sequence we saw turbidites intermingling with hummocky cross-stratification (wave-base) and deltaic deposits. This is another student's research, so I'm not gonna steal his thunder by posting too much about it....stay tuned.

On a nice day, we got this view from the top of the outcrop (photo above). The tops of those mountains in the distance (to the west) is the Patagonia ice's a few km thick in that area...or something like that.

Stay tuned for a post with more geology and context for all of this.

Friday, March 23, 2007

Where on (Google)Earth #6?

This is one of the prettiest deltas I've found exploring around GoogleEarth....

Good luck.

Thursday, March 22, 2007

Back from field work safe and sound

Yet another field season in Patagonia...and i've made it out alive and relatively unscathed. Although there's little to no jet lag involved with the journey from Patagonia to California, it is 24 hours of traveling and if you're like me and can't sleep on planes (what a drag!) feels about as bad as jet lag.

I will blog more about it and post some photos soon...this weekend I hope. There are a lot of great posts out there in the geoblogosphere that I'd like to catch up on too...and Highly Allochthonous has moved to Scienceblogs...congrats.

Here's a photo from this year of us on one of the more beautiful days I've experienced down there. That's the torres of Torres del Paine in the background. A lot of tourists travel a long way and never see them because they'll be shrouded in clouds for days at a time.

Thursday, March 08, 2007

still in the field

We are in town right now (Puerto Natales, Chile) to resupply, get a shower, and sleep in a bed for a night. There are a bunch of internet cafes in this town because it is a jumping off point for backpackers and such (mostly Europeans) traveling around Patagonia.

The weather has been the usual...either really nice (60s F and sunny) or completely miserable (30s F with snow or rain). I either feel ridiculous carrying so many articles of clothing in my day pack when its nice or wish I had more to wear when its cruddy.

Probably the most exciting thing to happen so far this that I finally saw a puma! They are essentially the same species as a mountain lion in North America but a bit bigger I think. They are around and probably see us all the time, but are timid and difficult to actually see. Today, we saw one cross the dirt road we were driving. I was happy to be in the car...the thing was big and muscular. It could kill and eat me without much trouble if it wanted to. Luckily, they are fairly well fed in this region...plenty of sheep and guanacos (and turistas).