christie at the cape

No Longer At The Cape

2010-06-14T20:05:00.000+02:00

Well it's been a while since I blogged here - or anywhere - and since I'm no longer "at the cape" I'm retiring this blog. Maybe I'll pick it up again in the future. Anyway thanks for following and all your comments over the years, it's been fun. I'll add a contact email to my profile in case anybody wants to contact me with questions about any of my posts but won't check back here anymore.

Cheers,
christie

Naukluft Mountains

2010-03-14T09:32:00.001+02:00

We're 225kg richer in Namibian fault rock and we have a lot of stories to tell... now it's time to write.

Thanks Bandile, Zach and Åke for a great field campaign.

new frontiers in rock packing

2010-03-05T12:30:00.002+02:00

hello from windhoek. We have just packed our rocks (wrapped in plastic bags) in steel 20-L paint buckets and filled the gaps with expanding insulation foam. any bets on whether this will work? not sure if it will kick off properly inside the bucket. not sure if it will withstand the motion of the rocks in the truck south. if it works as well as it appears to - we have revolutionized the preservation of structural rock samples which so often I have lost to mechanical weathering along the way home...

Geological terminology I hate.

2010-01-03T04:38:00.000+02:00

Geological terminology is always evolving. The meanings of old terms can change through time. Early suggested terms may turn out to be inaccurate and may be replaced, or may become more or less specific in their usage. Nevertheless, old habits die hard. Certainly the use of certain terms help us establish or test identity or affinities - scientific jargon at large plays important roles in social relationships.

4. Basement
"Basement" is the ultimate relativistic term. It describes the rocks one is not interested in talking about. If you write a paper about soils, the recent sediments underneath may be the "basement". If you're writing about those sediments, the granite underneath those may be the basement. Basically it means whatever is older or under or around or near the rocks one is actually interested in. My friend Mike, who loves ice and lichen and moss and squirrels and everything else more than he loves rocks, gave me another variation on "basement" the other day when I accidentally picked him up on the Golden Gate Bridge: "underburden". Nice.

3. Subduction channel
Apologies to my good friend Åke, but this one has to die. The "subduction channel" refers to the area between the subducting lithosphere and the overriding plate in a subduction plate boundary, where sediments are subducted and variably deformed and metamorphosed and de-watered. It is generally seen as a tabular region - not linear - so it isn't the shape of a channel. The term also causes confusion due to some people suggesting models where material flows only downward through this "channel", while others invoke backflow within the "channel" to help uplift metamorphic rocks which record very deep conditions. Both camps use the term "channel" and neither one is describing a 1D feature. I'm just confused by this. Finally, in a channel, the flowing media flows in one direction relative to the walls of the channel, right? But in a "subduction channel" the flowing stuff (subducting sediments) moves in a direction and rate intermediate between the upper and lower walls. It's a shear zone. Not a channel.

2. Pseudotachylyte (or pseudotachylite)
Aside from having two spellings (-yte is older and therefore preferred although it is counter-intuitive most of the time and looks weird with 2 "y"'s so close to each other), the term "pseudotachylyte" is an example of defining something by what it is not, instead of what it is. Pseudotachylyte is a glassy rock formed by either seismic or impact-related melting of any rock (but in practice is restricted to silicates). It does not therefore include a whole suite of other glassy rocks (igneous, melt cortices on meteorites, etc), so it is not a good descriptive term, but requires an interpretation of how the thing formed. Finally, tachylyte is an igneous glassy rock similar to obsidian. So pseudotachylyte is something that could be mistaken for tachylyte but is not. Oh yah, and there are other very fine grained, dark coloured fault rocks (e.g. ultramylonite, ultracataclasite) that can't be distinguished from pseudotachylyte without some serious microscopy. So it's not useful as a field term either. Fail.

1. Pan-African
As far as I can devise from the literature, the term Pan-African refers to nearly any geological event (mostly magmatic but also metamorphic, deformational, etc) occurring during a period of approximately 250 million years (roughly 750-500Ma) anywhere in Africa or continents formerly associated with Africa. My dear colleagues who advocate the use of this term tell me the exact meaning can be deduced from the context of the specific location or events being discussed which makes this term actually less useful than not using any term at all. I can think of no good reason to use "Pan-African" at all unless one is trying to obscure the problem of massive dating errors or giant uncertainty about tectonic events. THIS ACTUALLY HAPPENS.

ok just to make me sound a little less cranky, here's a comment left by somebody called NJ on Kim's blog a while ago that makes me totally happy:

"You'd better wait. My desk is totally Franciscan right now and I have no idea where to start looking.

Or:

"He completely Franciscaned his first draft and his advisor wouldn't even read it."

Hollister - the Creeping Calaveras Fault

2009-12-19T16:52:00.001+02:00

Every region has its particular strengths and weaknesses with regards to the type of geology which is easily accessible for student field trips. In the areas surrounding UCT, we have some seriously awesome geology but there are at least two things my students have to accept without seeing any really clear direct evidence in the field:

plates really move
plates really subduct.

Since I have a student from UCT with me in San Francisco this week for the AGU meeting (who gave a badass poster presentation by the way), it's a good opportunity to fill some of these gaps. We took an afternoon drive down to Hollister and San Juan Bautista to see some evidence for recent fault creep offsetting sidewalks and walls.

Hollister is positioned just north of the split where the Calaveras Fault branches from the main strand of the San Andreas Fault. The Calaveras Fault is creeping through Hollister, but rates vary along the fault in space and time from 3-18mm/yr (http://funnel.sfsu.edu/creep/SiteTable.htm).
(Map from http://quake.usgs.gov/recenteqs/)

My student is clearly excited by this right-lateral bulge in a garage wall.

Tension gashes where the fault crosses the street at a high angle and disappears straight under the middle of a house.
wonky sidewalk
another wonky sidewalk
seriously wonky sidewalk, and the steep small hill on the left of the photo is a pressure ridge
wonky sidewalk
more tension gashes in the street
carly will be creeping to your right as you look at this photo.

It's cool to see how different sidewalks and houses of different ages have accumulated different amounts of offset. We also couldn't help noticing new skirting and lots of concrete repairs which presumably addressed the larger offsets. Also - in some places the total offset was accommodated by narrow strands (usually ~ 1m wide) but in others, the deforming zone seemed to be much wider (10m). Seems like this depends on local soil conditions as well as the rigidity of the surface features. Sometimes it is wide under a sidewalk and sometimes all the strain seems to accumulate on one joint between sidewalk panels, as in the last photo.

Today we are off to Ring Mountain with Åke to see some evidence for #2.

Stromatolites in the Naukluft Nappe Complex

2009-09-30T16:55:00.004+02:00

Finally back in CT for a while. Lots to post but more to catch up on. Here are some cool stromatolites in dolomites of the Naukluft Nappe complex. There's a thin layer of sand over the top of the carbonate bed. I wonder what this represents. Was it a wave that washed sand between the bioherms? Did it kill them? I didn't see the beds above. Isn't it incredible how the sedimentary record is a stack of discrete moments - not a continuous record. Just snapshots.

I love being a geologist because I can hike up a cliff on a dry hot windy day in southern Africa, watch a meerkat shading himself with his tail, scare a herd of Hartman's Mountain Zebra up the slope ahead of me, then sit on this 550-million year old warm shallow sea and imagine a tropical, tectonically active world owned completely by algae and possibly some ediacaran fauna - no shells, no teeth, no fish, no birds. Must have been a quiet and peaceful world.

First Fold 2009

2009-09-14T00:06:00.005+02:00

The traditional "First Fold" picture - see 2008 and 2007). I just can't get enough of this cool folded bed in the lower Prince Albert Formation.
This class was fun - and every one of them was pretty keen in the field! Also did their chores without nagging! Truly a first on both counts. It was a nice one to go out on - my last trip to Laingsburg, at least as a lecturer at UCT.

It was a big year for transitions - as Dr. John Rogers, our sedimentologist with whom I have taught this part of the field course for the last 4 years, will be retiring at the end of this year.
We were lucky to have the two new guys (our replacements) accompanying us for the trip, in a kind of hand-over. It was great to be in the field with them and see all the energy and interest and excitement they will bring to the department. They both saw a lot of research potential in the area too - I hope some of their plans will turn into future Honours projects for these students!

As you can see, they worked well together in the field. All the groups did. I haven't seen their final maps yet but I have a feeling they will be good.
Every year I change it up a little bit - we usually do a "structure training day" and a "sedimentology training day" before they start mapping on their own. This year it went particularly well. I decided to focus directly on field methods instead of rehashing the structure topics we discussed in the classroom. We practiced sketching from afar and ground-truthing the sketch, and talked a lot about scale and planning where to go. Here's an example of a student with his field sketch of a faulted anticline thrusted over a faulted anticline. That peaky Prince Albert Formation sure does take up a lot of the strain in this part of the fold belt.

Here we are on the last day - the last day, for me, of formal teaching at UCT. Pretty sad about that but also looking forward to the next phase of my life.

The Cake Practical

2009-08-19T17:43:00.003+02:00

The theme of this month's Accretionary Wedge blog carnival is "Time to Think Out of the Box", in terms of approaches to teaching. I thought I'd contribute an activity I've been running in my classes which comes directly out of a box - a cake mix box.

We spend a lot of time in my Honours tectonics class (that's equivalent to a senior seminar in Tectonics in the states) talking about the lithosphere.

We discuss and in some cases, calculate:

the flexural thickness (relatively thin, <10km>
thermal definitions (thickness varies, but temperature is really a proxy for rheology),
definitions based on a sheared layer (high seismic anisotropy) separating the lithosphere from the asthenosphere,
more abstract definitions based on calculated rheologic transitions (using more complex proxies than just temperature)
discussion expanded this year to include looking at sub-continental lithospheric mantle which has been a stable geochemical reservoir for a very long time.. therefore not likely communicating with the convecting mantle (shout out to my colleague Steve), a distinction which is obviously important and in some places observable but was previously not on my radar.

However, for the students to really grok* this they have to have a good grasp on the concept that the same material can behave both as either an elastic or ductile solid under different conditions of pressure and temperature. There begins the search for an analog material.

The Cake Practical

As it turns out, cake deforms elastically at low stress and non-recoverably (let's call it viscous) at higher stress. This is a ~~cheap~~ tolerable proxy for Maxwell behavior. I bake some thin sheet cakes - from an ordinary cake mix - each pair of students gets about 100cm² piece of 3cm thick cake. The technical staff of the department was kind enough to provide me with a few "core samplers" = pieces of 1" pvc, about 2" long, with a nice bevel cut around one end to sharpen it for cutting into the cake. They also need an ordinary metric ruler and a watch or cell phone with a stopwatch.

The students cut as many sample cores from the cake as they can. This leads to a bit of waste, invariably eaten, thereby increasing the general level of ~~blood sugar~~ excitement in the room.

Fernando shows his glee at performing rheological experiments
on rock analog materials. Photo: William Cheng.

I give a bit of a talk about elastic at low stress, viscous at higher stress rheologic models and remind them that elastic deformation is linearly related to stress by the Young's modulus:

σ = E * e
where σ is stress in Pascals, E is the Young's Modulus in Pascals, and e is the linear strain (change in length / original length).

They are also reminded that viscosity is the relationship between stress and strain rate, not linear strain, by the relation:

σ = η * ε

Where η is the viscosity in Pa*s and ε is the strain rate in s^-1.

We assume a Maxwell rheology wherein:

σ = η ε + E e

and also assume that if we do experiments at very low stress, viscous strain negligible (all strain is elastic) and therefore set η ε = 0 at very low stress. This enables the students to isolate the Young's modulus (E).

Load is applied by placing other food items (of labeled mass, e.g. small cans and jars) on top of the cake cores. The students measure the surface area of contact and calculate applied stress.**

The students are asked to design and execute experiments to determine:

the Young's Modulus

Cake sample after elastic rebound (there's a bit of a delay there - hysteresis loop?)
Photo: William Cheng

This turns out to be amazingly reproducible. For my cake this year, everybody seemed to get a result between 5-8 kPa. Or, since the concept of significant figures doesn't seem to have taken hold, 6449.33352 Pa.... that's another issue.

the elastic limit

100g jar of capers produces about 1.2 kPa load on the cake core.
Amazingly, at 50% shortening the cake core still rebounds elastically.
Must be all those eggs I put in.
Photo: William Cheng

This parameter is bracketed by increasing the load on the sample until the sample no longer rebounds elastically to its original height after the load is removed. For the cans and jars I brought, all groups bounded the elastic limit at between 100g capers and 400g organic kidney beans. With our cake core samples this is between about 1-6 kPa. Next time I would get more intermediate weights.

the viscosity (for deformation above the elastic limit)

Under the 400g can o' beans, the cake has gone viscous and very little rebound is
observed. No conch shell or painted stick reported either...
(Photo: William Cheng)

The viscosity is the most unreliable part of this experiment, mostly because the students have to estimate the timescale of deformation and that timescale is very short. Perhaps larger pieces of cake would address this....

Anyway this prac gets good reviews. The discussions of the lithosphere seem to go well afterwards, although I will let you know for sure after the exams in October. I have used the same concept for a more open-ended inquiry and had students investigating the shear modulus by sheathing the cores in plastic wrap and shearing them, investigating the temperature effects by freezing them and microwaving them [don't tell the boss I broke into his lab for a little N₂ (liq)]. Obviously no amount of temperature increase is going to allow dislocation glide in chocolate so the metaphor rapidly breaks down. However - I never have to clean anything up with this lab... except wiping a few crumbs from the table tops.

Hoping someone out there will improve on this or suggest improvements... leave me a comment if you have any ideas!

*I was introduced to the Grok concept by my algebra II teacher in high school who made us chant (daily) the quadratic formula "so that if any of you two reproduce, your children will be born knowing it". Well, Mr. Steiger, x equals the opposite of B plus or minus the square root of B squared minus four-A-C over two-A.

** Yes I'm aware that the labeled weight on the can only refers to the food inside and does not include the weight of the container. Trust me this is not the largest source of error here and anyway, saves time and hassle when the students have only a short time to complete their experiments.

I should be more aquatic myself

2009-08-03T05:06:00.003+02:00

You know what? I know I'm going to be eating crow about this for the foreseeable future but I've changed my position about the Aquatic Ape Hypothesis. I just watched the Elaine Morgan
TED talk.

In a nutshell, Elaine Morgan has been arguing for decades (from outside the academic mainstream, which may be important in this case) that the major phenotypic differences between humans and chimpanzees are the characteristics we humans share with aquatic mammals. These include hairlessness and the subcutaneous fat layer which no other primate possesses. She also notes that apes, which are all capable of walking upright when they feel like it, always walk upright when entering the water.

She makes other points which I can't independently verify, that all hairless terrestrial mammals (e.g. elephants and rhinos) have aquatic forebearers (save the naked mole rat, a freak by anyone's measure) and that breath and diaphram control is common to aquatic animals but otherwise unknown in apes. This control gives us the power of speach.

I've read her arguments before and there wasn't anything new in the TED talk that I hadn't heard already. So I googled around a bit to see if she was under-representing the strength of arguments made by her detractors. Most of the arguments I found rely either on the lack of fossil evidence to support the theory, or on logical arguments which don't seem to me to be significantly stronger than those in favor of the aquatic ape.

Evolutionary change can occur when a fortuitous coincidence of environmental pressures with the occurence of a mutation in some population which directly affects the likelyhood of survival relative to those pressures. It also occurs when random mutations which don't affect the likelyhood of survival are also prevalent in the selected population - so it is not reliable to look at a single characteristic and deduce a past environmental pressure. In the long term, traits which advance survival or reproductive success are most likely to survive. However, the rate of mutations is such that this model is never run out to its conclusion. No organism exists, or is likely to ever exist, which is perfectly adapted to its environment at the time we observe it. The disadvantage to survival caused by the occasional appendicitis is not sufficient to cause the next generation to be born without an appendix. The reproductive struggles introduced by the upright human pelvis are likely a more significant challenge to survival than the appendix. But these are accomodated by cultural means, or technology, and have clearly not affected the survivability of the species. In short: the logical arguments made on both sides of the aquatic ape hypothesis so far fail to produce a unique conclusion, only explore what could have been possible.

So. Is it possible that a semi-aquatic hominid existed in our lineage, which could have perservered long enough in the lakes of the East African Rift to adapt some characteristics common to aquatic mammals, although not our nearest ancestors? Logical arguments could be resolved by adequate data from the fossil record.

The hominid fossil record is painfully scarce (relative to other more numerous, longer lasting species). In order to be fossilized, an animal has to die in the right place at the right time. On the savannah, animals are dismembered, desicated, and the bones dry and crack in the sun. There is almost no potential for preservation. Fossil beds from which we understand the record of terrestrial animals come from environments where rapid burial in sediment can take place - lakes and rivers - where we know that terrestrial and aquatic animals gather together. Hominid fossils are also found primarily in lake sediments but this does not really address where they lived, only where they died. Even so, it is not possible from the fossil remains that have been found to determine soft tissue characteristics such as identifying the emergence of a subcutaneous fat layer in our hominid ancestors.

So... Dad... although I am unwavering in my opinion that when discussing scientific theories, "interesting" and "likely to be true" are mutually exclusive - I am no longer hostile to the Aquatic Ape Theory. This has mostly to do with a recently developed appreciation for the scarcity of the hominid fossil record, and therefore the higher degree of uncertainty, than anything else. Now I'm going to the pool.

Some advice if you are looking for a grad school program

2009-08-02T00:45:00.001+02:00

Greetings all. As the application season is coming around soon, I've been getting a lot of questions lately about how to find the right graduate school or project. So here are some comments about the criteria I think are important... and how to go about looking for the right match. This is by no means a comprehensive set of instructions, more like an incomplete list of FAQ...

APPROPRIATE PROJECT
You best find something that turns you on right from the beginning. You're probably going to hate it at some point, sooner or later, and you'll need some serious motivation to help you get through the low spots. You should be interested in both the BIG QUESTIONS and the PIDDLING DETAILS of your project.

The project ought to be the right scale for the degree you are seeking (MS or PhD) or have the potential to scale up or down if needed. It ought to afford you the opportunity to learn some specific skills or get experience which will make nice bullets on your CV.

THE RIGHT GROUP FOR THE PROJECT AND FOR YOU
The adviser, and members of the research group, should be experts in the background of your intended research projects. Someone should have those specific skills that you intend to learn. It is common for a student project to require a skill which is not currently in the group repertoire - something the student can learn and then contribute to the group. This depends on the past experience of the student.

Adviser personal skills and attitude toward advising can affect the quality of life for a newby grad student to a great extent - take a look at the rest of the group and ask current students privately about the group dynamics. However, keep in mind that graduate students are nearly always disgruntled. It's a point of pride. After a campus visit or two, you will easily pick out happy/functional groups and... other groups. There are sometimes sad mismatches of adviser and student style/personality. Learning about the group dynamics can help you avoid these.

Think about how you enjoy spending long hours. If you are fascinated by the outer core, but hate math, you may be out of luck because most people who study the inner core are seismologists and modelers. Even if you don't know exactly what topic you want to study, but have an idea of what you enjoy/are good at, you will have a better chance of finding the right project for you.

STARTING THE SEARCH
Use a search engine to find journal articles that interest you. Google the authors. Nearly everybody teaching at a university has a website that includes a summary of their research, publication list, and past student projects. I googled about 50 people and narrowed down 12 to email directly. I have no idea if these are typical numbers. Ask your professors for advice. If you are able to, go to conferences! GSA and AGU are great places to shop programs/advisors/projects and distribute your CV. Watch the ads in EOS and GSAToday

When emailing potential advisors:

Learn what you can about the advisor/group and write a personalized email showing that you have done your homework. I immediately delete emails of inquiry which make clear that the student has not looked at my webpage and is not interested in anything I do. Ironically, anything that says "Dear Sir" will get a response - A strongly worded response.

Keep it short. One paragraph is plenty. Be focused and organized. Include a sentence or two summarizing your background and offer a CV on request or a link to your CV download (do not attach it to the first email as you might end up in the spam folder, and it's presumptuous). Clearly state why you are interested in this particular person's research. If your interests are broad, you may write to more than one member of a department. It is expected that you are shopping around.

Don't kiss ass. Don't alter your email so strongly for different targets that you look like you're kissing ass or being fake - people do talk, especially people in related fields. Keep your CV short (1 page is usually plenty) and if you have job experience which is not related to your application, just summarize it briefly (e.g. no list of babysitting references here!)

Edited to add: read FSP's post before you send that email!

FINDING FUNDING

In the USA - finding funding is usually a joint effort between advisor and student.

Students typically support their education by some combination of grants, teaching assistantships, research assistantships, and loans.

Grants/Fellowships: can come from the Univ, Advisors' grants, or any number of private institutions. Potential advisors will have knowledge of appropriate opportunities in your field. These could be for direct support (living, tuition) and/or research expenses.

-- NSF Graduate Research Fellowship. This money follows the student even if they switch universities, advisors, projects for 3 years. quite competitive and lucrative. Obama just tripled the number of Fellowships!!! applications open in August 2009.

Most of the advisors' grant money comes directly or indirectly from the National Science Foundation, or in some fields, DOE or other agencies. Many of these grants are written with some student support in the form of TA or RA positions. Expect to be asked to work ~20hrs/wk and receive adequate compensation for tuition, health insurance, and a small living allowance. FYI that 20hrs is a completely made up number and has almost nothing to do with your workload in practice.... (see above reference to graduate student disgruntlement).

In South Africa...
If you are South African, you can apply for an NRF bursary. This is something like R35 000/yr for MSc students and R60 000/yr for PhD. Not enough to get by in Cape Town but maybe in some other cities it's enough? I'm not sure. Many students get support from an employer and nearly everyone supplements that with demonstrating (TA) jobs. There are other pools of money available specifically for scarce skills development (including geology) and for previously disadvantaged populations (everybody but white males who had citizenship or permanent residency before 1994, varies whether white females are still considered disadvantaged. But that's another topic for another post.)

In any case, your supervisor will have more insight on funding opportunities and again, it should be a joint effort between student and supervisor to get the money together.

AND NOW SOME UNSOLICITED ADVICE...
Don't be afraid to apply overseas for your graduate studies. It's a great stage of life to try out living in a foreign country, as your life is relatively institutionalized so it's not as lonesome as moving somewhere entirely on your own. There are additional challenges - funding is often earmarked for citizens of that country, there are issues with translating transcripts and qualifications... but it's an excellent chance to spend a few years building relationships/support networks in the international community. In particular, for South African students it's a chance to get a world view in your field in a short period of time, during which somebody (your supervisor) is officially committed to supporting you and your development as a scientist. You can bring those relationships back to your home country, but it's far more difficult to develop them without investing the time overseas. When so much research funding is available through international collaborations with Europe or the US, those connections can help support you through subsequent decades of your career.

Alright i'm off the soapbox... did I forget anything?

Corona Heights Fault

2009-07-05T15:02:00.000+02:00

Emily found this fault by searching the internet for local slickenline photos and landing at Andrew's site, geology.about.com. What did we do before the internet? The fault outcrops in the Castro Area (Corona Heights) where a post-1906 aggregate quarry has been repurposed for a playground and pet cemetery. The relatively recent exposure of the fault allows excellent preservation of the slip surface itself.

The fault is a thin breccia zone (less than a meter) with an anastomosing network of highly polished, slickenlined surfaces within the breccia zone.

Nils admiring his reflection in the fault surface. Seriously it is so so shiny. I've never seen anything like it. Twice now I have gone out to the Marin Headlands Terrane (same cherts) to look for fault surfaces and see if I can find anything similar. Can't. Went the second time because it was too foggy the first time and I worried I might have missed it.
Emily and Amir worked on a big normal fault in southern Oregon which had a similar fault rock structure - thin, superfine-grained polished slicked core, thin breccia zone with pinch-swell structures, rapidly dropping off to undeformed bedrock on either side of the fault. That thin breccia zone probably takes up a lot of deformation and accomodates the roughness on the polished slip surface. (See Sagy, Brodsky and Axen (2007) in Geology; it's available here.)

Here's Emily getting a grip on "Layer II", that granular layer which must break or flow in order for slip on these uneven, anastomozing polished surfaces to occur. Her hand is on that ~ 40cm layer of breccia in between two slip surfaces.

The texture of the polished surface is truly remarkable. You can see some rounded fragments of chert - which are green, while the local rock is all red chert. They are embedded in a translucent super fine-grained silica matrix. You can see through it. It is positively glassy (in a descriptive sense; I have not examined it for molecular structure). It has beautiful tensile cracks which are generally perpendicular to local slickenlines - and rotate as the slicks rotate and the fault surface undulates. Truly amazing.

OK what you can almost see in this photo are tiny round white spots in the superfine silica layer - they are lensoid fractures in the silica. I have some theories about what this stuff is and what the tiny fractures mean. But I have apparently been too far out on a limb lately (at least for some reviewers) so I will just ask you, on the off chance that anybody is still reading this blog...
1. What is the shiny, transluscent silica and how did it form?
2. Why does it have tiny lens-shaped fractures inside?

Probably the way I worded those questions leads toward my ideas about the answers... but ... anyway...

Flying over Greenland

2009-06-30T20:48:00.000+02:00

On the plane from Heathrow to San Francisco, Nils and I sat across the aisle from an Icelandic glacial geologist on his way to vacation to Hawaii. When we flew over the east coast of Greenland I had to wake Nils up and make him look out the window! So amazing.

Medial moraines where two glaciers flow together:

A beautiful long fjord:

Tidewater glaciers calving

Field of bergs:

Winners

2009-06-29T20:04:00.002+02:00

The Art of Subduction took 3rd place at the annual Geological Society of South Africa Western Cape Branch Quiz night.

Nice job team.

Fun with Folds

2009-06-24T13:45:00.004+02:00

BrianR at Clastic Detritus posted a great photo of some disharmonic folds in bedded strata. Here are some more!

I particularly like the chocolate-tablet layers visible on the top of this outcrop.

Rock of the Week #10

2009-06-11T07:11:00.000+02:00

1. What are the sedimentary structures in this rock?
2. What can they tell you about the depositional environment?
3. Why is this rock reddish in colour?

Solution to Rock of the Week #9:

This is a SKARN – that is, a contact metamorphic rock produced when magma intruded low-grade country rock. This sample comes from the Birch Creek Pluton in the White-Inyo Mountains of California. The older rock here was a Cambrian (530Ma) carbonate and shale marine platform sequence. The intrusion of granitic plutons (80Ma) transferred heat and Si-rich fluids into the sedimentary rocks, causing metasomatism and metamorphism. This was a moderate-sized pluton and the zone of contact metamorphism around it is about 600m thick. This sample was taken ~200m from the pluton where temperature reached about 500°C. It contains garnet, dolomite, calcite, fluorite, epidote, and quartz and is classified as a Ca-Fe-Si skarn.

1. (1 pt) 2 minerals?
: 1 point if 2 of the above listed minerals are given.

2. (1 pt) Rock name?
: 1 point for skarn (only).

3. (2 pt) How did it form?
: 1 point for contact metamorphism or metasomatism.

A paradigm switch on the simple seds

2009-05-30T13:22:00.000+02:00

Sedimentology, when I was an undergraduate student, was kind of seen as the easy course. Structural geology was the bottleneck course that you'd have to be insane to take before your junior year (See exhibit 1: insane undergraduate seen here in final throws of thesis preparation at which point I was sleeping under the poster printer in the computer lab to the chagrin of the academic staff who found this horribly embarrassing.)

Don't get me wrong, Sedimentology was a lot of work and rigorous work at that. In particular, I credit Sed with really helping me develop my field observation and writing skills. But I think we thought it was easy because it was accessible - it's geology's first line in a lot of ways. You can see an outcrop and look around you and see the depositional setting at the same time. I was reminded of this when my brother visited last year and we were on a beach watching each wave lay down a thin, well-sorted layer of course white sand. All around the beach were beautiful outcrops of Ordovician Peninsula Formation - the fluvial/marginal marine pile of ... massive and laminated well-sorted coarse white sand. I couldn't resist pointing this out and I saw the Principal of Uniformitarianism spontaneously pop into my brother's pointy social scientist head. Sedimentology, more than some other fields, includes opportunities for accessible discoveries like this for introductory geology students and anybody else who's not old and jaded about little obvious things like the Age of the Earth. In other words, seeing seds in the field can give people an easy entree into the paradigms of geology... and everything that logically follows from something as profound as Uniformitarianism. These moments do not require someone to be able to conceptualize Deep Time or visualize things way beyond human scales in order to see Geology in Action. Teaching structure and tectonics involves a lot of convincing students to suspend the tangible world for a minute and imagine things NOBODY HAS EVER SEEN and convincing them that some gnarly rotten outcrop of blueschist 1000's km from Cape Town is enough evidence to suggest that these things are REAL and HAPPENING RIGHT NOW far below the earth's surface on continents they have never visited.

So... Let's just say that for years I labored under the impression that field sedimentology was somehow light weight science. I see it now in some of my students as well. Most of the textbooks make it clear that if you can just identify some sedimentary structures that the depositional environment will be uniquely determined and then you just put together some transgression/regression model and you're done. There are obvious complications (e.g. the afore mentioned Peninsula Formation - if the structures are fluvial, why does it have the grain composition and size distribution characteristic of aeolian sandstones?) but it's always possible to work up a story of reworking during environmental changes to get around some of that.

So it turns out of course that South African geology has given me yet another paradigmal smack down (is that a word?). In yet another installment of the IBD but not really chronicles, there are mystery environments recorded in the Cape Supergroup rocks that surround us here in the Cape for which there is no conveniently adjacent depositional model with which to compare.

Take the Peninsula Formation for example. It's nearly all quartz. Like upwards of 98% SiO₂. It is bedded on a scale of on order 1-10m. It is regionally extensive over 100s of km (1000s if you include comparative formations in South America, which we should). It is incredibly well sorted with regards to grain size and rounding. The crossbedding shows bars and meanders and shoals and maybe some lagoons. It's been through the Permo-Triassic Cape Orogeny which involved a lot of (now extremely hard to detect) layer-parallel thrusting so aside from the section 400m from my house on Table Mountain, nobody can really be sure how thick it is - but it's really thick. (Exhibit 2: Sandstones so thick you have to take a cable car from the base of the section to the top).

So... moving on to the "easy" sedimentology part... How do you make a huge sand sea (or erg) of perfectly sorted and rounded quartz sand? On today's earth: wind. Dry, hot or cold, and plantless ergs occur on every continent in specific climate zones. So we have analogs - but they are not the only possibilities. Here is an exception to Uniformitarianism - in the Ordovician there were no land plants anywhere. So environments existed then for which we have no analogs on earth - places where sediment was unconstrained by vegetation which could have occurred everywhere and not just in places of extreme climate.

Issue 2: the sedimentary structures. We can imagine a case where a wind-sorted erg was re-sorted by rivers and shallow seas by sea level rise or continental subsidence. The Ordovician southern world was a very cold place, and Africa resided at more southerly latitudes than it does today. Or - a situation where a windy sandy desert provided sediment to a subsiding margin where the sand was sorted by rivers and surf as it accumulated along the coastline. Maybe the overlying units can provide more of a clue.

To be continued....

On the topic of scientific dissent

2009-05-11T01:31:00.000+02:00

There is a buzz going around the blogosphere in the wake of press releases on a new paper coming out which challenges the asteroid impact correlation with the K-T extinction event.

This seems like an opportunity to point out that the whole search for a "smoking gun" in extinction events is probably off-target: All the largest extinction events in earth's history seem to be a result of positive interference between multiple factors which change the habitability of one or more environments on earth. In the case of the K-T event, the longer-term carbon cycle perturbation associated with the flood basalt eruption of the Deccan Traps in central India (68-60Ma) coincided with the Chixulub impact in Yucatan, Mexico (64.5Ma) as well as the increasing domination of the plant world by angiosperms (flowering plants) which may have been less edible to the terrestrial herbavores. Several other events, both fast and slow, have been suggested to correlate temporally with the end-Cretaceous extinctions.

WHY DO WE NEED A SMOKING GUN? Clearly this is a multiple-whammy event. Every K-T paper seems to have to take a side. From my reading it appears to me that a long (multiple-million-years) decline in biodiversity (caused by plate tectonics and climate effects such as volcanism and plate reorganization in latitude and coast-line length) was punctuated and probably accentuated by spikes in volcanism rates (CO₂ increases) and at least one big asteroid impact. Without the combined effects of ALL of these driving factors, the extinction event would have been less pronounced, or the biota would have had more leeway to recover. Maybe the "everybody's right" approach isn't as headline grabbing.

Anyway, the more interesting discussion growing out of all this is the topic of scientific mavericy: the role of a scientist or group of scientists who argue against the generally preferred interpretations.

The Lab Lemming and my perennial favorite, Female Science Professor have each written superior posts on the topic. FSP in particular highlights the intrinsic value of minority opinions to the overall debate, while acknowledging the erroneous effects of the popular media's tendancy to highlight "both sides" of a "debate" by digging out a quote from some dinosaur who thinks the world is flat.

There are ways for non-experts, including science journalists to tell the difference! And we ought to hold them accountable for this!

The paper which triggered these discussions (Press Release here) reports some new stratigraphic work in the Yucatan area which IS INCONSISTENT with one of the key attributes of the hypothesis that the Chixulub Impact ALONE was responsible for the mass extinctions of the K-T boundary. The stratigraphy records both the extinction event and the impact event and they are NOT PRESENT IN THE SAME STRATIGRAPHIC LEVEL, suggesting that they did not occur at the same time.

This is a key piece of data, which is important to the ongoing conversation on the relative role of different factors which caused the extinction. The community of scientists who promote the idea that this impact directly led to the extinctions will have to somehow explain or discredit this data or their case for their model will be weakened. Although there will be moments of drama (and for us, a "dramatic moment" involves somebody standing up in a dark conference room and telling somebody else they are wrong.... ooooo drama), people are right now in their offices reviewing their own data sets and hypothesizing new explanations or new narratives that incorporate the new data along with all the existing data. Science will go on. So will the debates about the dinosaurs' extinction.

This does not make the authors of this study some kind of gadfly harbingers of doom, shooting poison darts into the currently dominant hypothesis. I beg of you, journalists and general public -- do not mistake the give-and-take of ideas, data and hypotheses in the scientific sphere for intellectual cage wrestling. Disagreeing does not have to lead to drama between scientists... it's part of our daily lives and we enjoy the process of working out the details to find concensus or narrow the points of contention. If you are married to or dating a scientist, you may experience the great joy of this process as an integral part of your personal life.

Fully Equipped Field Geologist

2009-05-03T13:01:00.006+02:00

Alright I'm a bit behind the curve here... but ever since The Lost Geologist posted a photo showing all the bells and whistles comprising the field geologist's kit, the world of geobloggers has been weighing in. (Also see... Geotripper, Hypocentre, Kim, the Ethical Palaeontologist, Johannes, Silver Fox, etc...)

Over the years I've developed some very climate and duration specific field kits. I hate to carry anything I don't need and I hate to be overloaded as to be uncomfortably hot. I also hate to run out of water and/or food.

Always have:
1. No Belt. I wear pants or shorts with many deep pockets. In those: Brunton Compass (I have one for S and one for N-hemisphere field work) Rite-In-The-Rain field book, at least 2 mechanical pencils, fatty eraser, many fine-tipped sharpies in multiple colours, a few big black sharpies for marking samples. Can't have enough sharpies. (often: cell phone, gps, whistle)

2. Handlens(s) on a chord around my neck.

3. At least twice the water I think I will need. Two or more pieces of fruit which are waste-free (I eat apple cores and orange peels rather than leave them in the field or carry them home. Thanks to Eric Thompson for long ago convincing me of the edibility of citrus peels). To keep this light as possible, I have knit some water bottle slings which I will use in place of carrying a pack if the water is all I'm bringing.

4. Map board - still using the Hilde Schwartz-style boards from UC Santa Cruz which are made from two pieces of plexiglass (one with a 1.5" bit cut off from one side), duct tape, and binder clips. Put the topo maps +/- aerial photos in here. I'm still looking for a replacement for standard binder clips which does not affect my compass, as I do end up taking measurements on the map board pretty often.

5. Peanut butter and jelly sandwiches in zip-lock baggies (also twice as many as I think I could possibly need; these roll over every day if I don't eat them. They keep just fine, even improve with age(?), they're high energy, and there's no need to wash out the ziplock between pb&js.

6. Camera. Currently rocking the Canon EOS 1000D. Always with spare battery and SD cards.

Hot Weather Kit: Photo by Taufeeq Dhansay, Near Monapo, Mozambique (2008)

----That's it for the "always" items. ---

7. Hammer and heavy plastic bags, duct tape, and super glue for sampling - The way I do field work often involves several days of structural measurements at one outcrop or small area - normally then I do all the data collection and then set aside a day for sampling at the end. That way I don't a) smash anything I should have measured or b) take unneccessary samples before I understand the full picture. This has been a pretty important adaptation to my field plan because as a structural geologist who works on brittle rocks I NEED REALLY BIG ROCK SAMPLES and when rocks cross borders in Africa, they often have to go through customs with a certified currier company. This means I pay by the kilo. I want fewer, bigger, better samples.

----Matters of personal style---

When mapping in arid and semi-arid environments, I wear running shoes ("takkies") with short cotton socks. I hate being too hot more than I hate getting my legs all scratched up in the blasted fynbos. I wear SPF40 super waterproof sunscreen everywhere but somehow end up burned anyway.

When mapping in cold wet places, I wear NO COTTON WHATSOEVER not even underwear. Synthetics and wool only. In Alaska I often wear extra-tuffs while mapping in the field but I'm not sure this is the best way to go.

Hair: Always with the dual-braid configuration. Fits best under hats.

Hat: My SeaHawk Air hat has been my standard since 02. However, I lost it when it blew away in sub-gail force winds while I was sitting on top of a really fantastic sycline-axis koppie with a crinkly little bit of Prince Albert Formation in a sea of Dwyka diamictites. I got SeaHawk to send me another and it's almost as good. Finally, Sila talked me into getting a proper 360-degree brimmed floppy hat and it's ... alright. But I feel like such a dork.

Pants: Dork score increasing here: I wear zip-offs these days. Specifically, Convertable nylon pants from Cape Storm. They have kick-ass pockets with zippers so i don't lose keys. They look terrible because there is some bunchy elastic at the back for some odd reason. I don't care. They are light-weight and seemingly bulletproof, even in the face of elephant-skin weathering (also known as tareponts weathering to the Poleta crew).

Kit for Alaska field work: Photo: Asuka Yamaguchi, June 2006

---- Also, things that live in my backpack forever ---
knife
15m of good strong 3mm nylon line (good for clothesline if nothing else)
a powerbar or two of unknown antiquity
ziplock baggie of extra TP (also of unknown antiquity)

Ha ha I'm looking for pictures of myself in the field and I realize something that's present in nearly every photo but I completely forgot to add to the list:

Students. Not technically required for every field campaign but they sure do make it more fun. That's me in the green. Laingsburg field trip 2008. (not sure who took this picture.)

Fire on Devil's Peak

2009-04-13T18:51:00.002+02:00

2am on 18 March - I got home from cutting rocks in the Stellenbosch geology department to find my neighborhood being evacuated.

It burned fast through the fynbos but as everything is built of cement, nothing else caught fire near my house. Now there are pink and white lillies growing in the ash. Rumour has it they only bloom after a fire.

Suck it Bobby Jindal

2009-03-27T07:36:00.002+02:00

Lahars at the Drift River Tank Farm, Mt. Redoubt, Alaska. Photo from AVO.

The "IBD Effect" and a trip to Ring Mountain

2009-03-09T10:40:00.008+02:00

I keep finding geologically interesting spots in South Africa. There is a never ending supply, actually. However, often times when I ask around to find out what kind of work has been done in one of these areas, I get an answer to the effect of, "It's been done". In the Saldania Belt, represented locally by the slate belt that underlies the Cape Town area, a lot of people told me "It's been done". Digging into the literature and archives of theses from the local universities, I found several pieces of really nice work. Some of them emphasized the structures in the area. But to my mind, there is actually a *giant hole* in the literature when a few theses, fewer than 10 journal articles, and a sprinkling of unpublished conference abstracts are considered "DONE" for an orogenic belt or accretionary complex (the literature is ambiguous as to which this is). After finding this phenomenon at several different localities around South Africa, my friend Jodie and I christened it the "It's Been Done Effect" or IBDE, which sounds like "Ibid". Get it?

In terms of the local slate belt, my friends at the survey agree it needs some more attention so I got a few students together and we're going for it. Peeling off the coastal belt of the Malmesbury Group for scrutiny. Hoping to get started asap with a mapping day starting at the Sea Point Contact. Starting where the last thesis left off... and importing an old friend with a global slate belt habit for help!

My beloved Franciscan Complex has suffered a bit of the IBDE. It was such a hot topic a few decades ago that people tend to think that It's Been Done. In fact, there are a lot of secrets still hidden in the Franciscan and a lot of unanswered questions. Only a small but hardcore loyal following still works on it (often as a pet project without substantive funding). As such, I took some visitors there during AGU - subduction people from New Zealand - California's geologic evil twin, in some ways - whom I thought would adequately appreciate it.

Ring Mountain has low grade sandstones and shales on the lower slopes. On top there is a plate of ultramafic rock. In between the two there is a complete mess. Sheared serpentinite melange in green, purple, white, yellow and black wraps around blocks and boulders of strange metamorphic rocks.

Here's a blueschist boulder with some intense folding of the internal foliation.
On its outside surface, the reaction rim between the silicate minerals of the boulder and the ultramafic serpentinite matrix breeds an actinolite and talc-rich reaction zone (green) wrapping the glaucophane-rich blueschist (violet).

Another boulder clast contains epidote-garnet zones where fluid has entered? or departed? along fractures in the blueschist rock. Sorry met friends, I don't know which. Can I use a lifeline? I'm going with departed.

Here's what reminded me to finally post these photos: One of my fellow members of the underground Ring Mountain club mentioned fucsite on Facebook. Is this it? I'm talking to you Naomi.

My camera took a crooked picture of me with VT and AF. Perhaps it's because it was distracted by the metamorphic block it sat on:
"Wakabayashi Block", in tribute to another die-hard Friend of the Franciscan.

Coincidence:

2009-03-09T09:23:00.003+02:00

Richard Firestone will be giving a talk on Tuesday at the Peninsula Geological Society meeting at Stanford on evidence for supernova-related impact events correlated to Cenozoic climate events and extinctions. And that's his real name! Or so I assume...

My dad will be there to ask him some insano questions afterwards, like, "how do your results affect the aquatic ape hypothesis?" Other than that, I'm sorry to miss it. Details here.

Sri Lanka is more beautiful than I imagined

2009-01-24T09:26:00.003+02:00

No time to write something clever, but the people have made their demands for more photos. By "the people" I mean one anonymous comment on my last post which I suspect came from my husband, who was there when I took the photos.

Sila bodysurfing at Mirissa.

Mirissa Beach has a lot of hotels and bars.

Ram's Surfing Beach guest house, Midigama:

A green river in Colombo

Temple of the Sacred Tooth Relic, Kandy. The tooth was reportedly recovered from the Buddha's funeral pyre in India and secretly taken to Sri Lanka because the Buddha had said Buddhism would be safe there. The tooth is under that good tooth there. The white/red building on the lake is actually the police station. And the little rectangular island was built by a king to house his harem.

The island in Matara where 4 monks live:

Buddhist +/- Hindu "devale" near the tooth relic

Terraced tea plantations seen from the train, near Nanu Oya. The Hill Country is a giant zen garden. The rows of tea bushes wrap around trees and boulders. The plantations are so ancient and contoured to the landscape that they seem to have always been there.

Train riders wave at me. We were in the last 2nd class car and behind us in the first 3rd class car the Tamil tea pickers were singing and drumming for hours across the Hill Country.

Best breakfast ever: roti and dahl with strong sweet milk tea in Ella.

Garnets and lots of them. It's a granulite-facies world up there. This is the ONLY fresh rock I observed during the entire trip.

Coconut plantations along the coast between Weligama and Midigama

Water buffalo preparing the rice paddies near Peradeniya Junction. The egrets always attend the buffalo.

Patient buffalo calf tied nearby:

Buddhist shrine at the train station in Ella, while Sila watches a dog eat hot curry out of a crumpled piece of newspaper

For some reason, Sila loves billboards in Sinhalese.

Street scene near the airport outside Colombo. Hop a ride anywhere in a tuk-tuk but negotiate your price BEFORE you get in.

Brahman calf checks the surf at Lazy Lefts, Ram's Surfing Beach, Midigama.

A silent monument to 2004 tsunami victims on the south coast

there will be MORE photos.

Proof Of Nerd

2009-01-21T17:40:00.000+02:00

Sri Lanka is a Holy Paradise

2009-01-21T09:44:00.002+02:00

A few snapshots until I have time to do a proper post or a few...

Lazy Lefts at Ram's Surfing Beach, Midigama:

Dancers at the Kandyan Cultural Centre

The temple elephant at the Temple of the Sacred Tooth Relic, Kandy

Tiered gardens among the tea plantations, Nanu Oya

Couple of cold Lion Lagers.

Geology is boring - Punk kid.

2009-01-05T06:39:00.003+02:00

DATELINE: Yesterday on the beach in front of Ons Huisie, Klein Baai, Cape Town:

Punk Eight-year old Kid: Hey what are you looking for in the rocks?

Me: We're geologists so we study rocks.

PEYOK: That must be boring.

Me: It might sound that way at first but the more you learn about it, the more interesting it gets.

PEYOK: Hm.

Me: The whole history of South Africa and how it got here is hidden in these rocks.

PEYOK: Whatever. (runs away)

mini field trip to the Rodeo Cove Thrust

2008-12-30T03:40:00.000+02:00

Calling all Franciscan lovers out there - where are you? Are we going extinct? I am busy recruiting for our cult.

The Franciscan is the accretionary complex along the coast of California which preserves records of Mesozoic subduction: the wedge edge of the more famous Sierra Batholith-generating subduction zone. The Farallon Plate subducted under North America for over 100 MY until its tail edge hit the coast (with the Pacific Plate behind it) and the San Andreas Fault was born. While it was active the Farallon Trench subducted, offscraped, underthrusted and underplated a huge amount of marine sediment and a bit of igneous oceanic crust, mostly in discrete fault-bounded packets = terranes.
In the Marin Headlands, just north of San Francisco's Golden Gate Bridge, you can see the contact between two terranes (white teeth) where an ocean-island seamount (Bonita Terrane) was thrust northeastward over a stack of greenstone-chert-sandstone nappes (Marin Headlands Terrane). Within those nappes of the Headlands Terrane, one major fault outcrops on the beach (black teeth): the Rodeo Cove Thrust. Also, it's frickin beautiful out there on Cronkite Beach and there's a really sweet hostel out there. Field trip planners take note.

The "Cron" is probably the most accessible, adequate surf spot in southern marin. The beach is pebbly and composed almost entirely of chert/ jasper in many colors of red, green, black, gray and orange, aka carnelian (apparently orange chert gains some kind of metaphysical significance?)

The beach divides the sea from the Rodeo Lagoon - happy birds. The bridge out to the beach makes it feel like you're leaving Marin behind.
My dear friend Francesca wrote an amazing paper about the Rodeo Cove Thrust*. Sadly she was not able to guide us on this field trip because she was needed in Italy to make soap out of olive oil. I am not making this up. Anyway, Francesca described the intense veined zone in the thrust:

The kiwi delegation checks out the veined zone, comparing it to kiwi veined zones:
At the top of the veined zone, a small, fault-bounded slab of pillows. VT observes that pillows are all nearly the same size, except for some rhyolitic pillows she has seen. I experience the dual sensations of the elation at realization that there is a such thing as a rhyolitic pillow and disappointment that my Geolutions list for 2009 is already full. Where are these rhyolitic pillows of unusual size?

A close-up look at the perlitic texture on the surface of the pillows. This texture forms when volcanic glass slowly hydrates and develops nano, then micro crystals over time. Glass is an uncomfortable state of being for cations and anions. This is evidence that the outside of the pillows were once glassy.

South of the pillows: greenstone cataclasite. Yummy. It's right about here that this old Mesozoic thrust fault is cross cut by a steep, NW-striking smectity gougey fault zone. The San Andreas is right off the beach. I think this young fault is part of the SAF. But this cataclasite... old or new? A bit of both maybe.

Coming next: Ring Mountain.

*Meneghini, F. and Moore, J. C. (2007) Deformation and hydrofracture at seismogenic depths: The Rodeo Cove thrust zone, Marin Headlands, California. Geological Society of America Bulletin 119 1-2, 174-183, DOI: 10.1130/B25807.1

Coupla Christmassy Pictures for ya

2008-12-25T06:15:00.002+02:00

Red chert clast in a greenstone cataclasite

Garnets in blueschist with epidote?

And remember: axial tilt is the reason for the season. Have a good one whatever your reason.

Long night flight - back to the action

2008-12-24T20:33:00.005+02:00

I flew back to the US for the AGU spectacle and holidays with the family. On the plane, I read Kinabo et al. (2008)'s paper in Tectonics which includes some interpretations of aeromagnetic surveys over the Okavango Rift in NW Botswana (Figure 4c, below).

These images show the magnetic susceptibility of the subsurface geology. I think that it's basically a measure of how strongly the material responds to a magnetic field - so it relates to the amount of magnetic minerals in the rocks as well as the exact minerals present and their alignment. Anyway like so many geophysical data sets, it can be used for purposes that are not really related to magnetics, like looking for changes and patterns in rocks in a more general sense: mapping. In this case Kinabo et al. have interpreted the purple-red WNW-trending features as Jurassic dolerite dykes (common in this part of the world) and the NNE-trending lines as faults offsetting them. This is reasonable and consistent with everything I know about the region and I believe they are correct. However I couldn't help noticing that the clouds over Frankfurt, Germany also contain Karoo dykes offset by normal faults:
Excuse the sarcasm, what's wrong with me? It's flippin Christmas.
Just trying to express my trepidation about "mapping" by tracing "lineaments" and making guesses about what they really are. I have extreme discomfort about doing this kind of mapping myself but my local experts assure me that I still have a lot to learn. In theory, educated guesses are just fine (as in Kinabo et al. (2008)). However, if there are real geologic surprises in that data set you'd have to be pretty careful and pretty insightful to find them. Anyway if it leads to a ground-truthing campaign in the northern Kalahari, I'm all over it.

Cold: ice pack in Hudson Bay. Hot: the baby blanket I'm knitting for Mini MacStammer the Vth (not the child's real name).

We flew in twilight across the Canadian shield. My photos didn't come out so well but I could see the shapes of the 3 billion year old rocks poking up in roche moutinees through the patterned ground between snowy frozen lakes. It looked cold and very windy and isoclinally folded with a WSW-ENE trend to everything.

Getting ahead of the sun we finally broke into California in the late afternoon. The clouds opened in front of the sea and I saw what I had been waiting for - the active margin. The Crystal Springs Reservoir in San Mateo:
Funny that the wikipedia article on the reservoir mentions that it "... lies in a rift valley created by the San Andreas Fault". This is technically true, although it might be more accurate to say "IS THE SAN ANDREAS FAULT" (see USGS page for proof).
We did the customary spin around the bay, revealing an intersection of the SAF with the coastline - the mouths of both Tomales and Bodega Bays (west Marin County).

Sunset over the Salinian Plate: Point Reyes

And on to the big party!
(Slugs breakin it down, Thirsty Bear Pub, San Francisco. Looks seismic doesn't it. I frickin love San Francisco.)

New Year's Geolutions

2008-12-15T04:03:00.010+02:00

I have been in South Africa for 2+ years now and seen very few of the BIG SOUTH AFRICAN THINGS I meant to see. So I'm suggesting a new meme for you geobloggers out there to follow up on Geotripper's list of the 100 things we all "ought" to see.

What are 10 things you have never seen before, which you hope or plan to see in 2009?

Here are my ten GEOLUTIONS for 2009:
1. Wolfberg Cracks/ Wolfberg Arch Cederberg Mountains, South Africa
2. Etosha Pan, Namibia
3. Any really big wall of San Bushman Paintings
4. Coarse Kyanite schist in the Monapo Complex, Mozambique
5. The Vredefort Crater with the mega-pseudotachylyte breccias, shatter cones, the works.
6. Jeffrey's Bay aka JBay, the world-famous SA surf spot
7. Gems in Sri Lanka
8. Forest elephants in Addo National Park
9. The Bushveld Layered Igneous Intrusion
10. Triassic therapids in the Beaufort Formation, Karoo Basin...

Also for good measure (and a spin), 5 things I want to find or see evidence for (or against, as it may come). These are research goals, or ideas, as well as hobbies, or wishes for my students, etc...:

1. Incipient westward propagation of the Okavango Rift across the Botswana-Namibia border
2. Fluidized granular flow of very thick (meter or more) gouge layers in shallow crustal faults
3. Tectonic environment of the deformation of the "Saldanian belt"
4. Syn-crystallization shearing of the pegmatitic ijolites of the Mazeripane Suite, Mozambique
5. Tectonic fabrics in the Cape Granite Suite - timing, spacing and source.

Finally, how about 10 things that should be on the top 100 List? I totally concur with Geotripper's reticence to rewrite the list himself, as it is politically sticky and never unbiased. But for the sake of it, what would you add?

1. A famous "big wave" e.g. Maverics or Dungeons, breaking.
2. A glacier calving into the sea
3. Pink sand beaches (e.g. Bahamas)
4. Singing beaches or dunes
5. Walk across and observe a metamorphic aureole
6. Experience an earthquake
7. See the snowball earth stratal assemblage (e.g. diamictites+carbonates)
8. An earthquake damaged area, e.g. Earthquake Park in Anchorage
9. A Bore tide
10.Hear the sound of waves in a fjord.

I wonder why we geologists emphasize the fast/rare things on this list, instead of the slow/common things... which are more truly special to observe...

Apologies for missing the geobloggers dinner on Weds, I was too jetlagged/overwhelmed to stay so I went and worked on my talk in bed.

11. Hoping i get another chance to meet Kim Hannula

New Lows Achieved.

2008-12-15T03:12:00.005+02:00

Two things I said I would not do: join facebook; do a blog meme. Today I did both. Anybody want to come over and give me a tattoo or a makeover or something? Just so I can become totally unrecognizable to myself.

This one is pretty fun. Geotripper is responsible for this. Following Chris Rowan's lead, I'll post a photo where possible. Bold ones are CHECKED OFF. Italicized are checked off sensu lato.

1. See an erupting volcano
(erupting what? if steam and gas, YES (Yellowstone). if magma, NO.)
2. See a glacier (unID'd glacier near Whittier, Alaska)

3. See an active geyser such as those in Yellowstone, New Zealand or the type locality of Iceland
4. Visit the Cretaceous/Tertiary (KT) Boundary. Possible locations include Gubbio, Italy, Stevns Klint, Denmark, the Red Deer River Valley near Drumheller, Alberta.
(according to my field books, I saw it in the Elk River Basin, WY. However, I don't recall this.)
5. Observe (from a safe distance) a river whose discharge is above bankful stage
6. Explore a limestone cave. Try Carlsbad Caverns in New Mexico, Lehman Caves in Great Basin National Park, or the caves of Kentucky or TAG (Tennessee, Alabama, and Georgia)
7. Tour an open pit mine, such as those in Butte, Montana, Bingham Canyon, Utah, Summitville, Colorado, Globe or Morenci, Arizona, or Chuquicamata, Chile.
8. Explore a subsurface mine.
9. See an ophiolite, such as the ophiolite complex in Oman or the Troodos complex on the Island Cyprus (if on a budget, try the Coast Ranges or Klamath Mountains of California).
10. An anorthosite complex, such as those in Labrador, the Adirondacks, and Niger (there's some anorthosite in southern California too).
11. A slot canyon. Many of these amazing canyons are less than 3 feet wide and over 100 feet deep. They reside on the Colorado Plateau. Among the best are Antelope Canyon, Brimstone Canyon, Spooky Gulch and the Round Valley Draw.
12. Varves, whether you see the type section in Sweden or examples elsewhere.
(Smith College - Paradise Pond!)
13. An exfoliation dome, such as those in the Sierra Nevada.
14. A layered igneous intrusion, such as the Stillwater complex in Montana or the Skaergaard Complex in Eastern Greenland.
15. Coastlines along the leading and trailing edge of a tectonic plate
16. A gingko tree. (Smith College again!)
17. Living and fossilized stromatolites (Glacier National Park is a great place to see fossil stromatolites, while Shark Bay in Australia is the place to see living ones)
18. A field of glacial erratics Smith college rugby field! also freshies in Alaska and fossil in South Africa
19. A caldera Long Valley! Yellowstone! Haleakela!
20. A sand dune more than 200 feet high Namib Desert, Sossusvlei
21. A fjord (unknown fjords in Kenai Mts, Alaska; photo by my colleague francesca)

22. A recently formed fault scarp Lone Pine, CA
23. A megabreccia Death Valley
24. An actively accreting river delta
25. A natural bridge Natural Bridges Beach, santa cruz!
26. A large sinkhole
27. A glacial outwash plain Alaska
28. A sea stack
29. A house-sized glacial erratic
30. An underground lake or river
31. The continental divide
32. Fluorescent and phosphorescent minerals
33. Petrified trees fossil ridge Y-stone, also in Anza Borrego but just pieces
34. Lava tubes Bend, OR and hilo
35. The Grand Canyon. All the way down. And back.
36. Meteor Crater, Arizona, also known as the Barringer Crater, to see an impact crater on a scale that is comprehensible
37. The Great Barrier Reef, northeastern Australia, to see the largest coral reef in the world.
38. The Bay of Fundy, New Brunswick and Nova Scotia, Canada, to see the highest tides in the world (up to 16m)
39. The Waterpocket Fold, Utah, to see well exposed folds on a massive scale. I think the Cape Fold Belt qualifies for this one:

40. The Banded Iron Formation, Michigan, to better appreciate the air you breathe.
41. The Snows of Kilimanjaro, Tanzania,
42. Lake Baikal, Siberia, to see the deepest lake in the world (1,620 m) with 20 percent of the Earth's fresh water.
43. Ayers Rock (known now by the Aboriginal name of Uluru), Australia. This inselberg of nearly vertical Precambrian strata is about 2.5 kilometers long and more than 350 meters high
44. Devil's Tower, northeastern Wyoming, to see a classic example of columnar jointing
45. The Alps.
46. Telescope Peak, in Death Valley National Park. From this spectacular summit you can look down onto the floor of Death Valley - 11,330 feet below.
47. The Li River, China, to see the fantastic tower karst that appears in much Chinese art
48. The Dalmation Coast of Croatia, to see the original Karst.
49. The Gorge of Bhagirathi, one of the sacred headwaters of the Ganges, in the Indian Himalayas, where the river flows from an ice tunnel beneath the Gangatori Glacier into a deep gorge.
50. The Goosenecks of the San Juan River, Utah, an impressive series of entrenched meanders.
51. Shiprock, New Mexico, to see a large volcanic neck
52. Land's End, Cornwall, Great Britain, for fractured granites that have feldspar crystals bigger than your fist.
53. Tierra del Fuego, Chile and Argentina, to see the Straights of Magellan and the southernmost tip of South America.
54. Mount St. Helens, Washington, to see the results of recent explosive volcanism.
55. The Giant's Causeway and the Antrim Plateau, Northern Ireland, to see polygonally fractured basaltic flows.
56. The Great Rift Valley in Africa.
57. The Matterhorn, along the Swiss/Italian border, to see the classic "horn".
58. The Carolina Bays, along the Carolinian and Georgian coastal plain
59. The Mima Mounds near Olympia, Washington
60. Siccar Point, Berwickshire, Scotland, where James Hutton (the "father" of modern geology) observed the classic unconformity
61. The moving rocks of Racetrack Playa in Death Valley
62. Yosemite Valley
63. Landscape Arch (or Delicate Arch) in Utah
64. The Burgess Shale in British Columbia
65. The Channeled Scablands of central Washington
66. Bryce Canyon
67. Grand Prismatic Spring at Yellowstone
68. Monument Valley
69. The San Andreas fault
70. The dinosaur footprints in La Rioja, Spain
71. The volcanic landscapes of the Canary Islands
72. The Pyrennees Mountains
73. The Lime Caves at Karamea on the West Coast of New Zealand
74. Denali (an orogeny in progress)
75. A catastrophic mass wasting event
76. The giant crossbeds visible at Zion National Park
77. The black sand beaches in Hawaii (or the green sand-olivine beaches)
78. Barton Springs in Texas
79. Hells Canyon in Idaho
80. The Black Canyon of the Gunnison in Colorado
81. The Tunguska Impact site in Siberia
82. Feel an earthquake with a magnitude greater than 5.0. Loma Prieta!
83. Find dinosaur footprints in situ Dinosaur Tracks, MA
84. Find a trilobite (or a dinosaur bone or any other fossil)
85. Find gold, however small the flake
86. Find a meteorite fragment
87. Experience a volcanic ashfall
88. Experience a sandstorm
89. See a tsunami
90. Witness a total solar eclipse
91. Witness a tornado firsthand.
92. Witness a meteor storm, a term used to describe a particularly intense (1000+ per minute) meteor shower
93. View Saturn and its moons through a respectable telescope.
94. See the Aurora borealis, otherwise known as the northern lights.
95. View a great naked-eye comet, an opportunity which occurs only a few times per century
96. See a lunar eclipse
97. View a distant galaxy through a large telescope
98. Experience a hurricane
99. See noctilucent clouds
100. See the green flash

Score: 42 sensu stricto
ps. I did post a bunch of rock pictures on facebook though.

goin to the BIG SHOW!

2008-12-11T19:03:00.003+02:00

Folks, I am about to get on the plane to go to AGU in San francisco and I can't remember the last time I was so excited. I got all the Christmas shopping done, cleaned the house for the housesitter (although he is my student and I did leave him a six-pack so who's complaining). I downloaded all the session info.

I used to think GSA was so much better than AGU. People wear field-fashion there and bring rocks to their posters for goodnessakes. Now I think they're just different. I like going to GSA when I want to reconnect with my geology roots and especially for teaching/education recharge. I like to go to AGU when I want to stretch myself quantitatively and party with everybody I ever knew in geology, ever, while spending a month's income on food and drink!

I like to give a talk when I want a lot of people to hear what I have to say. I like to give a poster when I want to hear what a lot of people have to say to me. Also talks are nice when you're flying from overseas, and say, not ready to go to print yet.

This year my needs/wants are perfectly aligned with my AGU/talk. There is a lot I love about being in South Africa but one of the drawbacks is a small community of very busy scientists working on very different things. In order to have the real exciting science discussions and challenging collaborations, I have picked up some very new and strange research directions. Now I have some great stuff going on and some very interesting people to work with on it. But I miss the energy and intensity of a being at a pumped-up research institution where everybody is jazzed about science all the time. Also, there are so many people available to talk to that questions get opened and answered all the time. Heavy trading on the ideas floor.

Bring on the BIG SHOW! I want to see all you friends of kodiak at thirsty bear on Tuesday night. I want to talk about SUBDUCTION and ACTIVE FAULTS with a beer in front of me that is made of BEER INGREDIENTS and not CORN! Ahhh the brew pub options within 3 blocks of Moscone center trounce the entire ~~nation of South Africa~~ subsaharan Africa.

If you're at AGU and you make it to Friday Afternoon I hope you'll check out my talk. Yahooo!

Eric was here.

2008-11-21T13:28:00.004+02:00

My brother was here.

Whoops, wrong photo, sorry: Eric enjoys the view at Blouberg Beach. Eric, Sila and I checked out Shipwreck Trail in Cape Point National Park.

Unfortunately Eric had to ruin it by stealing a sandwich from a nice lady.

Visitors are Fun.

2008-11-04T12:15:00.000+02:00

For those of you considering a visit to Cape Town, get on with it already! Visitors are Fun! When Visitors arrive I go out to Eat! I see the Sights! and I do ridiculously short field trips to Far-Away Turbidites!

I have had three "reunions" recently as a result of the AAPG meeting - two with blogosphere "colleagues" (Jeannette and Chris), and one with an an actual real-world acquaintance, the notorious Daniel Minisini. These visitors are very intrepid - Chris circumambulated Cape Town to see the Sea Point Contact on his own, and gave an excellent talk in our department. Jeannette found her way (taxi-wise) to campus on her own for Chris's talk, and brought me an amazing and unexpected present without sticking around long enough to be compensated by a trip to above-referenced turbidites. Come back Jeannette! Anyway, watch your mailbox.

Daniel materialized a few days after the meeting was over. Daniel is one of the "crazy Italians" who held court in my grad school lab at UC Santa Cruz - there were always one or more around during the 5.5 years I was there - We were part of some Appeninic exchange program! Daniel probably inspired the most mayhem during his tenure (excepting our RESIDENT Italian, Stefano, the undisputed Maestro of Mayhem).

I won't tell you what happened on Friday because... um... it's blurry.

On Saturday we made lots and lots of food and went swimming with penguins. Can you see how this photo is weirdly funny?
On Sunday, we drove to Laingsburg to see turbidites. Yes, the Laingsburg, which is 3.5 hrs away from Cape Town. We spent an hour or so pondering weird sedimentary structures in the Laingsburg Formation.

We also visited my favorite folds at the "LilyPad Pond". Can you see how this photo is also weirdly funny?
We had the chance to follow up on rumors from past students that there was a cave on the "Whale Back" doubly-plunging anticline that had Bushman paintings. We found them. Small and perfect (but potentially NSFW).
You be the judge.

We stopped at Matjiesfontein for a beer on the way home and arrived in CT at 11pm.
On Monday Daniel and Sila went surfing and hiked all over Cape Point and we cooked another HUGE dinner.
On Tuesday Daniel and Sila are climbing Table Mountain (via Platteklip Gorge) and then ALSO climbing Lion's Head.
On Wednesday I need a nap.

Landmarks

2008-11-03T19:01:00.003+02:00

Next week my first generation of advisees (BSc Honours students) will turn in their theses. In keeping with the tradition in which I was raised, I'm having a dinner party for them. Tacos.

In another, perhaps more poignant benchmark moment, when they say:

"Hey, what's the time?"

and I say:

"It's time to get ILL!"
"Hey what's the time! It's time to get ILL!"

They don't get it.

They are all getting CDs for graduation presents. You know, to make me feel younger.

Anybody hear me on this one?

Lazy post - funnier than me anyway

2008-11-03T18:37:00.002+02:00

FSP I love you. That's Female Science Professor to those of you who don't currently substitute her in your mind into the vacuum of lady-scientist role models at your institution.

FSP has written of a recent search to fill a tenure track position as her cat in the fall of 2007.

FSP has just announced that happily Kitten X has been awarded tenure and promoted to Associate Cat X.

For those of you involved in/subject to either of these processes I think you will enjoy this.

Rock (photo) of the Week

2008-10-23T09:42:00.002+02:00

Special treat today folks. We have a reader submission for rock (photo) of the week. This means somebody besides Mom reads my blog. It also means I'm not 100% sure what the hey is going on in this picture, only that there are lots of things going on. The first thing is that somebody is gonna need a bigger hammer to get this done right.

So what's up folks? What do you see in this Rorschach Ink Blot of an outcrop?

I want to recognise Elisabeth for authorising the use of this photo for you to analyse. See what I did there? Just finished this book, which I enjoyed very much. So much that I have been making a bunch of word nerd puns since I read it.

I would like Elisabeth to recognise that her institution stole the world's greatest university president from my institution. No hard feelings though.

Some people we met in Mozambique

2008-10-21T16:40:00.003+02:00

I've had this post in the "draft" folder for a while, trying to decide what to write about these photos. But I think they are expressive enough on their own. Nampula Province, Mozambique, July 2008.

Carrots and brains

2008-10-10T15:36:00.002+02:00

I made these! I fought the snails.

My lithops are turning themselves inside out for spring. Absorbing their old leaves and making new ones. Resurfacing like Venus. Looks like brains.

You know what else is cute, but I don't have a picture? My students had a slumber party on the roof of the geology building last night.

Sockeye Salmon Pattern for Knitters

2008-10-07T16:15:00.000+02:00

Sure, I publish. I publish knitting patterns!

This pattern "Sockeye Salmon" is available on Ravelry.com

See pattern here
or

buy now

Link will remain in the sidebar - in case you're not sure but you want to buy it for somebody!
If you're not a Ravelry user but would like to purchase the pattern, leave a comment or email me and I will contact you.

100% of proceeds go to the Cordova District Fishermen United Scholarship Fund which supports continuing education for fishermen and their families.

I present you the Sockeye Salmon, prototype #1

running up Turnagain Arm, Alaska :

He's got character.

He now has two more prototypes to spawn with (here posed in mid-flop

among my chili plants)

The final pattern incorporates the head from the front right salmon with the body

and fins from the left front salmon below.

Dwykacious Injectites

2008-09-30T18:35:00.002+02:00

The famous Dwyka "Tillites". As previously ranted on this blog, these are not lithified tills! They are glaciomarine. As proof, I offer the drop pebble. Isn't he cute. (top of photo is stratigraphic top)

The Dwyka Group contains one formation, the Elandsvlei Fm., making it the city and county of San Francisco of geologic Groups. Sorry if that's too corny for you. The whole package is matrix-supported, laminated and massive diamictites. The massive ones are ridge-formers in the field area and the laminated ones are valley-formers. They are informal called "coarse" for the ridge formers and "fine" for the valley formers but I actually think the difference is in cementation rather than grain size, possibly having to do with more abundant clays in the "fine" laminated units prohibiting silica circulation. The matrix is glacial rock flour, a very fine sediment (quartz/felspar ground down to clay-size particles) which is unique to glacial erosion.

Anyways, along some of these facies-boundaries we have channel sands. These are often called "eskers" but they are not true eskers as this is not a ground moraine.
Super TA Nic perched on the stratigraphic top of one of these channel sands - the dip is to the left on the photo at about 40*S and Nic is sitting on the top of the deepest part of the channel. Original vertical thickness is about 2m and the sand body tapers to the foreground and background (these represent the edges of the channel). This particular channel deposit has a nice coarse, well-rounded conglomerate around the edges - like a gravel bar? The matrix of the conglomerate is greenish-gray rock flour, resembling the rock into which the channel cut.

Here's where things get even better (and by "better" I mean "more structurally interesting"). See that long spindly (~15cm thick) sandy arm reaching gently UPSECTION from the sandstone channel? IT'S A SANDSTONE INJECTITE! If you look carefully at the photo (click to enlarge if you need to) you will see that the lamination in the gray-green matrix is going roughly across the photo while the dyke cuts upsection (and up-photo) to the left.

Injectites usually form when a porous, saturated sediment is overlain by a less porous sediment. The overlying rock acts as a seal and doesn't allow the water to escape from the porous sediment. Pressure increases as the sediments are buried and eventually the porous rock can become very "overpressured", with the trapped water in the pores carrying the weight of the rocks above. This is an unstable state and can only persist as long as the overlying seal rock can withstand the pressure! Eventually, the sealing rock fails - usually along a planar or curviplanar fracture - this occurs when the overpressure reaches a greater magnitude than the weight of the rock, or some kind of disturbance (earthquake, passing landslide or debris flow) triggers the failure. The high pressure fluid/sediment mixture escapes its former captivity by injecting outward and upward along the fractures. When the pressure is released, the water is free to move off but the sediment is left behind in the fractures, forming "injectites" or "sandstone dykes".

The injectites are found in a particular stratigraphic horizon in the Dwyka Group (2c/3f contact for those of you in the know) where small sandy bodies are common. The sand is coarse, well-sorted and nearly pure quartz (C. Herbert pers. comm. last week in the computer lab). Injectites are curviplanar with roughly parallel surfaces (although they sometimes undulate out of phase). Thickness varies from about 25cm to 3cm in the several examples Nic and I ~~stumbled upon while looking for faults~~ fortuitously discovered. The outer surfaces of the injectites are very smooth and polished. They are now quartz cemented and weather out relative to the finer-grained, less well-cemented rock flour matrix.

The outer wall surfaces of the injectites have a very distinctive texture - I don't know if it has a name, but it's something like flute marks but sort of braided looking.... Can anyone help me out here? Has this been described before? Perhaps my dear friend the "former" geologist can help.

Have I ever told you that you can't un-geologist yourself? It's like finding out about santa claus carter. Your world has rocks in it and that makes you different... forever.

Eh hem, excuse me. Anyway, the anastomosing flutes are about a centimeter to 3cm in wavelength, with high amplitude (~0.5x wavelength) and vary quite a bit in length. Sources say that the famous Panoche Hills injectite complex in central California may show similar clastic-dike-margin-textures... but on a larger scale...

The geometries fo the injectites can be rather complex - they are even sorted with coarsening towards the center - reflecting increased flow velocities with distance from the conduit walls. Here's Nic again sitting on what is either a) a folded injectite or b) the complex branching/intersection of multiple injectites - Somebody should find out!
What can these surface textures tell us about viscosity and velocity of injectites, strength of sediments, and fluid pressure in the ancient sub-glacial-icey seas? Somebody should find out! Who should that somebody be? I'm hoping one of my future honours students....

In case you doubt that these sandstone channels are submarine, I present you... the drop-boulder. I'm sorry, so sorry for this but each time I look at this picture I think of Cornwallis.

More on the rock chip bug

2008-09-16T14:08:00.003+02:00

Throughout my life as a geologist I have known a lot of folks who are torn between geology and biology... SuperNaturalists? Geobiogists? "Slug-cutters"? That one's from Andy Duncan who has a rivalrous relationship with zoologists who vie for his barstool.

One of these friends ended up sawing the heads off frozen timber wolves and grinding up extinct bird parts and putting them in a geology machine. Another ended up shipwrecked somewhere in the Inside Passage communing with Orcas and "dropped out" to go to vet school, via cattle ranching. Another dropped geology altogether (or so she says) and become a kayak guide and forester (but there are still a disproportionate number of rocks at her house). Anyway we've got one here, not sure what adventures she will get up to in the future but she right away sent me another example of the rock chip bug. He has a name! And it is Pamphagidae!

This little guy was caught in the grey limestones of the Cango Inlier near Outshoorn in the Cape Fold Belt. (Recall that I recently described his long-lost cousin in this post). The astute student also notes that she's seen them in suits matching red weathered dolerite in the Karoo. Looks like it's a pan-south-african bug.

So thank you to the sharp-eyed geobiogist who sent me this photo ( I make it a practice not to post students' identifying details unless they explicitly authorize me to, UCT geologists will know who she is anyway).

Ptygmatic Folds in the Prince Albert Shales

2008-09-13T13:31:00.000+02:00

The first exercise I do with the students when we begin working in Laingsburg is to have them run around just outside the field station and find a fold. Luckily this is not so hard as the Prince Albert Formation here is wrinkled like a raisin. I have some theories about this.

Sorry for the crap outcrop photo - should have taken the advice about
"morning vs. afternoon shots".

The Prince Albert Formation is early Permian in age and directly overlies the Dwyka Group diamictites dating from the Carboniferous-Permian Gondwanide glaciation. The paleo-latitude is about 70°S. I have a massive pet peeve about people calling the Dwyka Group "tillites" because that term clearly implies terrestrial origin and the rocks are very clearly submarine. The first person to describe the rocks (Alex du Toit in 1929) may not have known this but the very detailed work of JNJ Visser in the 70s and 80s made very clear the glacio-marine origin. If there's any doubt, please see: dropstones everywhere throughout the sequence. So don't say "Dwyka Tillite" to me unless you want to hear more about that. But I digress! I'll return to the Dwyka in future posts because I'm finding it more and more fun. Rock flour is weird.

Anyway, the Prince Albert Formation overlies the mudcracked glacial muds at the top of the Dwyka. It has a few meters of grayish pink shales/siltstones, followed by a few more meters of chestnut brown shales/siltstones, and then a few more meters yet of black shales/siltstones with blue phosphate nodules (and at least one 8-cm thick black chert bed, discovered by my students this year! Shout out to Klipdrift Group!). I'm being vague about thickness because nearly everywhere we see the Prince Albert in the Laingsburg area it is majorly folded and faulted and we actually have no clear idea how thick it should be. Looks like it was the preferential site for accomodating strain in the stratigraphic sequence. I would guess it is related to the big hard massive Dwyka diamictite below, and the relatively deformable Ecca Group turbidites above - those two strain very differently and the Prince Albert had to squish around to make up the difference. That would be the technical term of course. You see - this is how I check whether my students are plagiarising my blog.

Anyway, you can see in the photo above that some beds make nice concentric folds and others make parallel folds (see different shapes within the little syncline on the right). On this local scale, the thin yellowish ash beds flow into the hinges to accommodate the different shapes of adjacent folded beds. I think the Prince Albert Formation on a regional scale is doing the same thing the yellow ash beds are doing on this outcrop scale - flowing toward the hinges.

Maybe you need a refresher on folding mechanisms? Check this one out.

Do you see the amazing cleavage refraction?

Our class rep, also known as "the ginger kid" (in his own mind at least)
is impressed by the faulted folds.

The style of folds varies between the pinkish grey, chestnut and black members of the Prince Albert, I think as a function of viscosity variation in the strata. In the basal pinkish-grey member, there are lots of fine clayey shales and a few "siltstone" beds which are pretty hard and quartz cemented. This results in a thin stiff layer in a low viscosity matrix - the necessary condition for... (drum roll please)... PTYGMATIC FOLDS!

Carried away at the Pizza Place

2008-09-12T01:18:00.002+02:00

This is what can happen if you mark cross sections and eat pizza and there are crayons on the table. Particularly if you keep thinking about what you wish the cross sections would look like...

A word about ecotones in the Klein Karoo

2008-09-09T12:34:00.001+02:00

OK I have never pretended to be a biologist in spite of a growing fixation on succulents, but there are a few concepts from biology that just seem REALLY IMPORTANT and stuck with me somehow.

The first is the "ecotone" - basically the line marking the edge of the area where a species is successfully living (actual definition is more systemic) - so maybe i don't know the right term but I'm trying to say, the edge of the world for a particular species.

For example, anybody ever driven the Extraterrestrial Highway? Otherwise known as NV state route 375? It was laid out to skirt the Joshua tree ecotone - literally - on one side (south) of the highway there is a semi-geometric grid of Joshua Trees as far as the eye can see. On the other side.... none.

Why do I like this idea so much? It's pleasantly mathematical - as in calculus plus binary - somehow asymptotic to one, then zero. It has a pleasing physics sensation like quantum mechanics - can't see the line when you're looking at it? And in a geological sense - to which it is often correlated, any way - it reminds me of the brittle-ductile transition. A hard and distinct theoretical boundary - but more often than not, shifted or curved by strain rate, temperature, moisture, other mysterious factors.... easy to describe in the abstract, hard to pinpoint in the field. LOVE IT LOVE IT LOVE IT***.

This absolutely beautiful, Georgia-OKeefeish, [absolutely cuter than any foram] pink Aloe plant reminded me of the ECOTONE concept. Succulent people - please name it ??? This beauty and her blushing sisters were found on one hill, in one mapping area, facing one way, on one formation. Literally about 50m³ of real estate, bounded by changes in slope, strike or lithology. Beyond that - another subspecies of different colour, size or shape. To a girl from the California Chaparal this explodes my little mind. Even the plants here are on geologic time.... and the geology? on astronomic time I think. Billions instead of millions. I know I left nothing for scale but that aloe is about a meter across.

Two formations down section - we found this little beast. He is in the lower Prince Albert siltstones, which are pink. OK this section is often madly folded and thickened but the stratigraphic thickness is about 10m. Maybe 15m. Above that: Dark brown siltstones and shales. Below: green glaciomarine diamictites. Literally this guy crosses geologic boundaries and his whole life plan for camoflage is over.
I'm desperately sorry I don't have a photo, but THERE IS A DARK BROWN ONE EXACTLY LIKE HIM IN THE NEXT UNIT UPSECTION. again, a perfect match to the chippy opally silty rocks.

*** You know what i got a lot of crap for recently? "ILOVEITILOVEITSOMUCH".
Turns out this is just more evidence that Americans are flakey. but you know what? IDO FRICKIN LOVE IT SO MUCH. It's that great to be here and see these things. No time for post-colonial understatement.

It's that Field Mapping time of year again

2008-09-09T08:30:00.001+02:00

Hey folks I'm back from Laingsburg again with the 2nd year field trip. Every year it seems to get better and better as the sedimentologist and I iron out the plan and I get to know the field. This year's class seemed particularly keen and that makes it even more fun of course. And since they've let me know they found this blog, I'll say they were also clever and good looking, and don't forget to turn in your course evaluations kids. Anyway.

Here's the now traditional "first fold photo" (see 2007 first fold photo). Always a bit of a step up learning about trend and plunge and remembering strike and dip. This year I had an extra prac during 2nd year structure and we used it to do some mock mapping exercises. Seemed like it helped. We were forced by the weather to do things a bit differently this year because it snowed/sleeted on our first day of instruction. What the hey? this is not why I moved to Africa, to field map under ice. At least, not Quaternary ice...

Anyway I'm going to try to arrange some more inclement weather for next year because that was the only day the students complained about the mapping conditions. Awesome.

I digress for a moment to show you a cute tiny angulate tortoise. What could be cuter?

We return to customary annual photos with the "giant pencil cleavage fencepost" installment for 2008 (see 2007 giant pencil cleavage fencepost). This beauty makes use of the Laingsburg Formation turbidite sands.
Sunrise on the last morning in camp:
Time to rise and shine!
more hard core geology posts to come!

Mineralogy MacGyver

2008-08-17T13:35:00.003+02:00

What do you do when you're out in the field and you really really wish you could positively identify a particular mineral? There are ways of doing this which are no longer taught - involving powders and torches and things like that - I never learned these methods, these days we just take the rock home and make a thin section.

We were in northern Mozambique looking at what appear to be charnockitized gneisses - which should by definition contain pyroxene - normally orthopyroxene. However, the thin sections we made last year just had clumpy biotite - maybe replacing opx? But without finding any remnant opx we couldn't be sure if it had ever been there, or if all the patchiness we could see in the rock was just clumpy biotite. We crushed up some of the gneisses, which wasn't too hard to do because they have a nice "sugary", recrystallized annealed texture and readily fall into angular "sand". Some of the grains had a greenish smokey luster - possible orthopyroxene? Or just ugly looking feldspars? Or quartz with some micro inclusions? If only we could see the birefringence of the mineral grains we could readily pick out the opx - which has higher birefringence - from the feldspar and quartz, which have similar, low birefringence.

Birefringence is the effect when light passes through a crystal more quickly in one direction than in another, effectively splitting light like a prism. The strength of this effect varies with the wavelength of light as well as with the properties of the crystal. The birefringence of different minerals is a characteristic feature that can be used to identify them. To see this effect, geologic microscopes use two polarizing filters. Full-spectrum light is passed through a polarizing filter and then through a thin section of rock (30-microns is the usual thickness for this slide). Then the light passes through a second, polarizing filter perpendicular to the first one and through to your eye.

Two polarizing filters at right angles to each other will block all light - so if there is no rock slide in the path of the light, or if there is just glass or some other isotropic material in the path of the light, you will see nothing at all. However, a birefringent rock sample will take the oriented light and twist it - allowing some of it to pass through the second filter. The colour you see will change depending on how strongly the mineral "twists" the rays of light.

So what to do in the field with no slide, no microscope, no way to estimate the birefringence of these mineral grains? Kosuke came up with an answer - like geologist MacGyver. He used the polarizing filters from his camera lenses - mounted them on an incandescent head lamp (torch) and put the mineral grains in between. He then carefully rotated the top filter so that it blocked out all light except for what was passing through the mineral grains. Voila! A field petrographic microscope!

Did it work? Sadly, not really. The problem was, of course, that all the mineral grains had different diameters and therefore the path of light through the minerals wasn't constant. As the colour you see is a function of the length of path as well as the properties of the crystal, we couldn't keep this factor constant and were left with uncertain results. However, it was a pretty good exercise (and a lot of fun) and a reminder of the basic principles of geology which we sometimes take for granted.

You know what? Identifying rocks is pretty hard. Very few minerals come in only one color or shape, and a little bit of weathering or deformation can change the appearance of a rock pretty drastically. Geologists and geology students have to learn a whole range of criteria which change from place to place and rock to rock. It's a lifetime effort to learn to identify rocks, accelerated by seeing as many rocks as one possibly can but one can never hope to see them all.

In accretionary wedges - my "specialty" (if I have one, that is) - low temperature metamorphism and high strain can result in all the rocks looking pretty much the same - it can be very difficult to tell an igneous rock (eg. basaltic ash from the ocean floor) from a sedimentary one (e.g. volcaniclastic greywacke). It's hard to tell students that the first basic thing we tell them about rocks - that there are 3 types (igneous, metamorphic and sedimentary) might be the last thing you figure out about a particular rock sample. Some day when I have the time I'd like to teach myself some of those old techniques for identifying minerals without a microscope - I'm sure they would come in handy.

Penguin party

2008-08-12T18:03:00.002+02:00

Got away the other day to go down to Boulders Beach and visit my favourite Cape Town attraction: baby penguins. The activities of the colony of African penguins (formerly known as Jackass Penguins thanks to their hilarious goofy honking call) put to rest any concerns about penguin reproductive struggles and hardship you might worry about if you've seen March of the Penguins.

The biggest hardship these penguins seem to suffer is itchy molting.

In fairness, it does look pretty uncomfortable.

It's great when guests give you the excuse to enjoy your town. Thanks Kena and Hwakong!

Can you thank a reviewer?

2008-08-05T22:38:00.003+02:00

Maybe this is a rookie question - most certainly it is - but when you learn very much about your own work from sending a paper off to review, is there an appropriate way to acknowledge someone who spent more time (and expertise) working on your paper than the co-authors have done? A way to thank a reviewer who has acted as an advisor?

Answer: Don't send off a chapter of your thesis to a journal.

Answer #2: If it's not rejected outright, on the basis that it is just a chapter of your thesis, and it takes a very long time to rewrite and re-review same, feel lucky, and improve.

ps. Will I outgrow the stage when I need this kind of help?
Answer #3: Only if I publish only where I am comfortable - not a near term option, given my recent research activities.

pps. Can I write a review which is simultaneously direct, stringent, rigorous and supportive? Especially when I am sent a paper to review which is clearly a chapter of somebody's thesis?

Answer #4: I must work on this point.

Contrite Post

2008-08-05T22:34:00.002+02:00

I think I forgot how to blog when I was away for so long. In my defense: it's hard to come back to work. It's time to move from this law-forsaken neighborhood. And: my head and heart are exploding with exciting geologic problems. So much so that I must advise students on them and write them up for publication. I'll be back soon. -c

¡Acuñas!

2008-07-16T09:39:00.002+02:00

You might wonder what the locals in rural Nampula province think about a bunch of geologists stomping around their villages asking "Pedras? Aqui? Mais pedras?"

They think we are frickin nuts.

Field Fantastic!

2008-07-16T02:29:00.002+02:00

Just back from Mozambique and covered in red dirt - I have only one question for you tonight:

What happens when a Pan-African pegmatitic granite intrudes a mid-crustal shear zone in the middle of the construction of Gondwana?

Answer: one of two things:

Those would be augen formed from entrained feldspar crystals in the intruding magma, or,

Those would be rafts of mylonite floating in a granite.

Snowball Earth Strata near Kogelfontein

2008-07-08T06:18:00.000+02:00

Some time ago, in the middle of an igneous field trip no less, we were out on the coast of Namaqualand near the Kogelfontein igneous complex. The Kogelfontein rocks are Cretaceous, which to a South African is pretty much Yesterday, or in other words, that piddly small part of the geologic time scale that nobody bothers to learn. Did I mention that my students don't learn the Phanerozoic part of the time scale? And similarly, I never learned the other 80% of the time scale? Remind me to chalk that up on my list of SA-USA translation problems in English. I do feel like I've been accepted to some degree, with all my idosyncracies, because people don't correct me anymore when I say "Al-U-Min-Um"**. But I digress... it is a blog after all.

Anyway we took a detour to see this incredible outcrop of interbedded black turbiditic shales and clean, beautiful white marble. Yes, shales (sedimentary) and marble (metamorphic, or should I just say recrystallized).
This assemblage, Neoproterozoic* in age, is a key assemblage in the Snowball Earth story - a story better told by other outcrops in other places, perhaps, but there's evidence for it here if you accept it as such. The story goes that at 600Ma (give or take), the earth experienced a total glaciation - most of the continental landmass at the time was at high latitudes, close to the poles, and as earth cooled and entered the glacial period the continents were completely covered by ice sheets. If you're familiar with the concept of albedo - the reflectivity of the earth - you will know that rocks will absorb light and heat from the sun and re-emit it all as heat, warming the atmosphere. Ice, on the other hand, will reflect the majority of that energy back to space, and will not do the nice turn-light-into-heat action that bare land can do. The bare land bit is important here, because this is hundreds of millions of years before plants, or fungi, or any of those great heat collectors working for us today emerged onto land. So a planet with its land mass covered in ice is a very cold planet indeed, and has lost its means for warming itself from the sun's heat.

As the story goes, tectonics was still chugging away under all that ice, warming the oceans from mid-ocean ridge volcanoes and supporting tiny islands of bacterial life. The combined effect of the geothermal heat and the CO2 from volcanoes and life was eventually enough to break the cycle of cooling, and the planet warmed again. As land began to see the sun, the warming sped up and the oceans warmed up very quickly.

One of the fascinating things about CaCO3, that is marble, that is the most common mineral form of CO2, is that it is reversely soluble - that is, it dissolves more easily in cold water than in hot. That's the opposite of most everything, sugar, salt, most other minerals... So when the oceans were cold, there was a lot of CO2 dissolved in them. When the oceans warmed up quickly, all that CO2 was no longer stable in the dissolved state and CaCO3 - limestones - precipitated on the seafloor all over the world. We usually associate limestones with warm shallow places - coral reefs, etc. - but in the late-Neoproterozoic warming, limestones were forming everywhere, even in the very deep sea. Enter the outcrop at Kogelfontein.

The black shales here are deep water deposits (again, or so the story goes) that are very rarely found in association with limestones, anywhere in the rock record. Here they are together, repeated at least a couple of times: a shale, a limestone, a shale, a limestone. Or is it?

Here's trusty TA Duane pointing out the reason for the repetition. The reddish rounded lump he's standing on is the long thin hinge of an isoclinal bedding parallel fold - the axial plane of the fold lies in the plane of bedding.
The fold is ultimately doubly-plunging - it rounds off at both ends like a big sausage (that would be wors in local parlance) but there are others along strike. And in between, some beautiful evidence of tectonic interference with the stratal succession: shear foliations in otherwise sugary marbles, and strange little cuspate-lobate structures on ptygmatic folds (not sure what that folded bed is). That ZA 50-center is the size of a US quarter.

Here's a shot down the axis where a quartz-rich bed is desperately trying to maintain its radius of curvature in spite of the drag:

So the moral of the story is: earth warmed up, and here we are. Whether these marine seds actually provide anything more than circumstantial evidence for Snowball Earth and catastrophic warming of the oceans is still under debate. The other moral of the story is: don't measure section in an accretionary complex***.

*Neoproterozoic is about 1Ga -> Cambrian, for those who share my timescale bias problems.
** as opposed to "Al-Yu-Min-E-Um"
***I don't really know if it's an accretionary complex. It's supposed to be an along-strike equivalent to the Malmesbury Group down here in Cape Town. But that's an axe to grind for another post.

Happy Tunguskaversary!

2008-06-30T22:43:00.001+02:00

It's the Centennial of the mysterious Tunguska Explosion, which flattened something like 80 million trees in Siberia on 30 June, 2008 (Click the link to see Andrew's summary of the whole story). Most people agree now that this was caused by an asteroid or comet blowing up as it entered the atmosphere - but not until it was only a few km above the surface of the earth. "Impacts" such as this leave no crater, and no trace at all if over the ocean. Maybe there are a lot more dangerous impactors entering the atmosphere than we know about! the Sandia super computers who have calculated that the asteroid or comet which exploded was much smaller than previously thought. The drawback to this, of course, is that the frequency of smaller objects is greater (see this NEO size frequency diagram). Party on!

Mineral Party Tricks at the Orange River

2008-06-27T07:21:00.000+02:00

To tell you the truth, I never thought much of fluorite. Seems too cutesy to be the favorite mineral of anybody serious. I mean, the formula is dead simple (CaF2) and the name is practically a giveaway for it anyway. It comes in all kinds of luminous colors, any color you want, and cleaves into darling little double-pyramids. Yah, it's pretty, and puppies are cute. Tell me something interesting.

Even in this abandoned mine - really just a half-dug-out vein about 1.5m thick - it's cute. Look at that bright purple and pale green. Fluorite does look great in those black light mineral displays - it fluoresces, it phosphoresces... and some specimens can also thermoluminesce...
My opinion on fluorite changed when my students showed me what you can do with it (but only at night, while camping, and in possession of a mad excess of messy, less pretty handfuls of fluorite chips).

When nobody's looking, toss a handful or a few bigger chunks into the campfire. Best if it's a little low to the coals and not too bright. A few minutes later, long enough for anyone who saw the toss to forget about it, small points of turquoise glow fade into view among the coals. They grow brighter and brighter and then POP! Like a little popcorn kernel the crystal explodes in a tiny shower of blue sparks. A whole handful is enough to emit quite a POP, too.

Geological Spouse

2008-06-18T18:23:00.000+02:00

"Why do I always have to be 'For Scale'?"

Groot Winterhoek Reserve, Western Cape, South Africa, December 2007.

And what do you want to be when you grow up?

2008-06-14T20:22:00.002+02:00

In the fall of 2000, I went to the GSA Meeting in Reno. I was 6 months out of college, 6 months into wage slavery under an egomaniacal boss in an environmental consulting firm. I knew I didn't want to stay where I was, but didn't really have a good idea of the transition from undergrad to graduate student, hadn't been a particularly good undergrad anyway. I remember a vague sense of disappointment from some professors when I put rugby ahead of school (time and time again). On the rugby team I was the leader, the decider, director of all things! In the classroom I was one of many, and not calling all the shots.

I didn't have any sense of the incremental pathway between a bad case of senioritis and professorship. I knew I wanted to chase my own ideas, regardless of the fact that I didn't have any! Without of view of that path, I never pictured myself walking it.

At the GSA meeting I met a new kind of character, one I had read about in John McPhee but didn't really see on the East Coast where I went to school. The old crusty cowboy kind, dirt in the beard, leather boots molded to his feet, plaid western shirt, plus or minus big lump of turquoise on bolo, belt buckle or pinky ring. I've always referred to them as GreyBeards, although some are neither grey nor bearded. This character is a bit of a composite, clearly. Here's my portrait of one, gruff, sh*t-talking, "good ol days" wildcatting, tall-tale telling, swaggering example (before his time, even): Don Foss in the field in 2001:

He's somewhere between Jules Verne and Deadliest Catch, if you get the picture. My composite character hovers somewhere between mining exploration and academia, with plenty of distrust for both sides. He is a desert rat. He has nemeses who look just like him. He might have an axe to grind about how things are done these days. He probably has a beard, or at least a mustache. He does not respond to attempts by Eager Young Geologists to charm him with their enthusiasm, but might be easily flattered if he is recognized by the same. He is 100% geologist, everywhere, all the time. He knows no other life.

In that last bit, I found a model, an identity. It explained, in so many ways, why even though I felt sooo far away from college (6 months, but a very transformative 6 months) I was having difficulty performing basic social functions, such as hiking and chatting. Or driving. Past road cuts. Or bidding a remediation job at a very well known archaeo-Olympic Tahoe ski resort without asking the age and mineralogy of the tills into which the UST were leaking. Geological details had moved from facts I had to cram for a test to welcome, necessary diversions to keep me entertained during increasingly repetitive jobs.

I iconocized a cast of males, many-post retirement, in part because of their pride in being a bit "dying breed", a bit TOO FIELD for even the GSA meeting. God forbid they ever meet the dark matter of AGU. But I digress. At the same meeting, I ran into peers I had known in college. Some of them were graduate students, presenting their first posters. I weighed myself against them, competitively. Sure, my grades were lower, but hadn't I helped her when she totally bottomed out on Norm Calculations? Hadn't I helped (another) her when we studied all night for the paleo exam? Yes, I had. I was just as good. So why did I feel so inferior?

I applied for grad school. I got one rejection, some serious wine-and-dining, and one tenuous, not yet funded option at a school I hadn't meant to apply to, in a subject which had been my weakest in college. STRUCTURE - A subject I had somehow understood to be the web in which all my other subjects were suspended but just couldn't get my head around at the time. But in a brief interview with a potential advisor (of which I did many, and so should you) I met somebody who presented the most interesting questions I had heard, in a fascinating field area, with deep global relevance for fundamental processes in HOW FAULTS WORK.

This potential advisor was not my iconic character in the sense I understood it - he was young (or so he looked!) and quiet. None of the bluster and pushy dictation of project (amazing project! big money and big papers!) I heard at other universities. But he asked me some pretty hard questions. Not about what i knew, but about what I wanted to know.

The project took me to new places, more meetings, new people. Realized that my iconic old men were probably rolling out the GB persona for GSA meetings, as much as I was rolling out my best "promising young student" persona. My icon morphed from a bearded old grump into something much wider and deeper. Best yet, I finally found the female side.

My first discovery was at the same Reno GSA all though I didn't recognize it at the time, I can still picture her so clearly. Long straight grey braid down her back, middle part. Corduroy skirt, birkenstocks, wool tights. Festooned with what must have been a brutally heavy thick beaded necklace of picture jasper, or some similarly non-precious ROCK. She was nearly hidden among a crowd of plaid dusty men in bolo ties. Bingo. The "Grey Braid". Many of these women are not "grey" in terms of being "old". I mean to say that they are venerable, they have a sense of history, and some are every bit as crotchety as the Grey Beards, whether old or young.

Once I picked up on this phenomenon I started watching for more women like her, and there they were. At a local society meeting I met an incredible retired USGS geologist with brightest red hair, wearing a sparkling gold ruffled blouse with a full slab of Green River Shale with a fish in it around her neck. My new fashion icons were generally younger than the original Grey Beards, maybe because there aren't as many women geologists in their post-retirement era at GSA, certainly there were fewer field geologists in their generation. I met a volcanology prof at a neighboring college - the first woman at the UofO volcanology field trip. She had a rattle snake skin on her office wall. She had dispatched this huge specimen by throwing her bowie knife through its neck while it menaced some not-so-supportive (male) fellow students. Hell yah! The Grey Braid mythology grew.

I met more and more women who struck me as heroes of geology. Of women in geology. My kind of geology. My kind of women. My reluctantly glamorous field camp mentor who did volunteer autopsies at the Nairobi zoo and carried her baby on her back to dinosaur digs. A USGS mapping geologist who carries a whip in the field and takes no prisoners. The great gun-toting field geologist women of Alaska, who move easily between tectonics and petrology, geochronology and geomorphology, present and past as if they can see the whole Great Land in four dimensions before them at any time and place. One while wearing a brightly colored vest she quilted herself.

These women all have striking stories behind them. Stories of finding their own way into doing the field geology they love, often through very circuitous paths, often making great sacrifices by leaving the straight-and-narrow career path. Each of them eventually created a niche for herself- maybe not perfect niche, but a balance between career and family and love that works.

I want to write a book about these women. Or rather, I want someone who can write to do it. I want it to be a big portrait book, like an art exhibit book, with beautiful photography of these women in all their non-precious jewelery, pyritized ammonite-wearing splendor. As a model I suggest Alison Owing's Hey Waitress! The USA from the other side of the Tray. I've been a fan of Alison's writing for some time, she writes these incredible anthologies of portraits which vary deftly from funny to profound, intertwining the stories to produce a portrait of a group of women without smoothing over the individual faces.

Why are the portraits so important, and why am I obsessed with Grey Braid fashion? Because it asserts so strongly the geologistness of these women, and the womanliness of these geologists. It represents a collective turning-of-the-back to mainstream ladies clothing, the clothes are functional, machine washable, there is almost a pioneer sensibility about the corduroy and wool. Layered on top of this functionality is a feminine flamboyance expressed in wacky color and irrepressibly geological, often uncomfortably heavy accessories. This look is every bit as vital and expressive as any form of fashion, and a good deal more individual than what my students are wearing these days.

In case you missed my birthday.

Charnockites.... what?

2008-06-13T05:20:00.000+02:00

Hey geoblogosphere, help me out will ya?

I'm a brittle fault person by trade. Now I'm working on a project in the middle crust... slow, squishy and unfamiliar territory. Big mineral grains are nice though... I can identify them in hand sample! They fill a thin section! In most of my field areas, I was identifying minerals primarily through x-ray diffraction. So this is a nice change I suppose.

So here's the scene. The protoliths are a TTG suite - tonalites, granodiorites - metamorphosed at amphibolite facies. Luckily for us, the biotite foliation is pre-syn folding... which means it is sometimes axial planar but often folded. Leucosomes abound; they are solid albite+/-quartz. There are some gorgeous folded meta-dikes of nearly straight amphibole - most likely primary basaltic dykes into the TTG suite - which I am planning to use as strain markers. Here's one in a quarry in the middle of Nampula, Dr. Micheque for scale:

Outcrop here is limited to isolated, steep-sided mounds of rock (inselbergs), it's a common geomorphology in the subequatorial Gondwanaland. There are many inselbergs around Nampula, with completely flat land in between. I have questions about that as well... but I'll save those for another post. Anyway, one of the inselbergs has a unique zone crosscutting it, a networked zone of kspar-qtz-mt veins with a smoky, greenish patchy alteration zone around them (Lee-anne Rudd, Hons 07 and trooper extraordinaire, for scale). What you see looks like wet patches on a jointed rock, but I assure you, at 40° in blazing sun, there is no water here, you are seeing the greenish alteration zones:
Here's a closer look at the thing. The edges of the blocks in the network are sheared, the biotite foliation is curved into the boundaries - implying some rotation of the blocks. (excuse the white chalky patches, which are hammer blows):

Previous descriptions by previous workers called this a charnockite zone. This led me to a big literature search on charnockite (which I never, I swear it, heard of as an undergraduate). I found basically that charnockite is a sparcely defined facies? or rock type? resulting from (rock containing hydrous mafic minerals) + (CO2) -> (rock containing orthopyroxene) + (k-rich, volatile-rich melt). Basically, the idea is that if rocks with a little bit of water in them are flushed with CO2 at high enough temp, the hydrous minerals will dehydrate and the water will cause partial melting of the less refractory minerals, in this case biotite. (More recent work has pointed out that the fluxing fluid need not be CO2, but it needs to be thirsty for water). This fit well with our field observations and we were happy. Until we got home with the rocks. And found no opx, anywhere. Worse yet, our samples from the general background look exactly the same in thin section as the samples from the green patchy alteration zones. No textural difference, no change in mineralogy, even some (scanty, preliminary) microprobe work didn't turn up any difference between the green greasy-looking patchy rock, and the ordinary biotite gneiss. Hmmm.

From a geochemical standpoint, WTF? How can something so obvious in outcrop disappear in thin section? Luckily we have a new secret weapon on board, a metamorphic petrologist who knows THERMOCALC, knows migmatites, would prefer pelites but will help us out anyway.

From a structural standpoint (my standpoint), looky here. We have a network of veins of (I don't know what), at roughly 90° angles. This network occurs in a narrow linear zone about 20m wide. It clearly accommodated the flow of some reactive fluid. And take a look at the meta-basaltic dikes in the blocks in this zone:

Clearly, and this is a new level of wishywash for me, this is a "locus of strain" here in this zone.

Now we come to the question: Falling back on my old friend the Mohr Circle, I would say that 90° fluid conduits are a sign of hydrofracture. Can that be true? Slow, ever so slow hydrofracture in which the opening of joints is accommodated by volumetric strain in the blocks between joints? More importantly, can I use these folded dikes as passive strain markers? And people, what are charnockites? Truly? Do they require CO2, or low aH2O magma, or what? And how do I find out?

* just so you know, that is not my compass. I'm a brunton girl to the grave.
** theres been a lot of chatter lately about appropriate use of the geoblogosphere. Allow me to push the limits here by asking for your opinions on current research.

Barbarians Attach Rowe

2008-06-11T21:36:00.001+02:00

This is what it looks like when Rowes visit you at the airport. Yooo HOOOO!

Alaganik Slough

2008-06-09T09:52:00.003+02:00

Alaganik Slough is only a short drive outside Cordova. We drove out one evening just before sunset with our friend Craig to check it out. Fishing just outside the Copper River Delta along the sand bars, you can only see that a vast flat area stretches inland with mountains on all sides. I was really looking forward to seeing the delta from inside.
There are lots of moose on the delta this time of year, and they are big ones!
The willows were flowering and attracting all kinds of pollinators,

...such as these surprisingly huge but herbivorous mosquitoes...

The Canada geese are here in full force:
The hooligan (aka euchalon, aka smelt) are running and got caught all over the banks of the slough at low tide. I don't know much about hooligans but these must be spawned out I suppose... they are known as candlefish because they are so oily that they can be dried and lit like a candle for stinky winter illumination. We watched some eagles taking them out of the river but they looked pretty bored. Obviously they are waiting for the big payday when the salmon run kicks into high gear.

The delta is unbelievably rich in color.

Rock of the Week #9

2008-06-04T06:49:00.003+02:00

Here's a real beauty. In my low-grade, brittle line of work I don't often get to admire such prettiness in my sample collection. But I digress...
1. Name two of the many minerals present in this rock.
2. What is the name of this rock type?
3. How is this rock type formed?

Once again if you can answer 1. you can figure out 2, which should lead to 3. Both cut slab and weathered side are shown - sorry for the saw marks. The third photo is the most true to colour.

Solution for Rock of the Week #8:
This is a fine-grained, blueschist facies metabasalt from the Franciscan Complex, California, USA. It was collected at the Russian River, California where it was lying as a large knocker (exotic block) in a tectonic mélange. Mineralogy is glaucophane+garnet+epidote+albite+pyrite, consistent with an overall composition of hydrated basalt.

1. (1 pt) Rounded red mineral?
: 1 point given for garnet.

2. (1 pt) Fine-grained matrix?
: 1 point for glaucophane or sodic amphibole.

3. (1 pt) Rock name or metamorphic grade:
: 1 point for blueschist.

Rock of the Week #8

2008-05-28T06:34:00.001+02:00

EDITED *** WHY DIDN'T YOU GUYS TELL ME I HAD THE FOSSIL WRONG? THANK GOOD NESS FOR STUDENTS (NOW GLOATING STUDENTS). The Rock of the Week #8 contains a Receptaculid. It is maybe a green algae or maybe an echinoid but definitely not a bryzoan!!! Excuse me please. Receptaculids are most prevalent in early ordovician so early Paleozoic is still the correct answer.

For my birthday week, my very favouritest rock type. Note that I had to massively screw with bright/contrast/saturation to make these photos look like the rock really looks! Maybe I shouldn't take pictures of rock of the week after dark in my office while pretending to prep for tomorrow's early lectures. Hm.

Anyway:
1. Name the rounded reddish mineral.
2. Based on the colour (and any crystals if you can find them), what mineral comprises the very fine-grained matrix of the majority of this rock?
3. Rock name or metamorphic grade?

Solution to Rock of the Week #7:

This is a fossiliferous Ordovician (520-430Ma) Kanosh Formation limestone from Crystal Peak, Utah. It is almost completely composed of fossil material, so it would be called a biosparite or biomicrite (Folk classification) or a biograinstone (Dunham classification). Due to the large amount of broken shelly material, this rock is also called “hash”, in this case “brachiopod hash”. There is a wide variety of fossils in the rock, including the very large bryzoan and numerous brachiopod shells. Crinoid stem sections are present as well as lots of little very thin bits looking like fingernail clippings – I think these are part shed exoskeletons from trilobites. This assemblage is consistent with deposition on a shallow marine shelf. The prevalence and diversity of brachiopods, as well as the abundant trilobite fragments suggest lower Paleozoic, as brachiopod diversity and trilobite abundance never fully recovered after the end-Ordovician extinction. As such, this type of assemblage is sometimes called “Cambrian-type” assemblage.

1. (1 pt) What is large fossil?
: 1 point given for bryzoan.

2. (1 pt) Rock type?
: 1 point for either fossil hash, biosparite, biomicrite, or biograinstone.

3. (1 pt) Age:
: 1 point for b) early Paleozoic.

Succulent of the Week - Aloe dichotoma

2008-05-26T12:48:00.003+02:00

The beautiful and iconic Quiver tree gets its common name from the indigenous practice of using the hollowed out spongy branches to store arrows. Its original name is Choje (San) and the Afrikaans speakers call it Kokerboom (which means... that's right... quivertree.) These trees, in their natural habitat, seem to have this ethereal air of permanence about them. Although some sources on the web suggest that they are threatened by habitat destruction, I think I can say with certainty that the area I visited has seen very little expansion of human land use for a very long time.

I did hear, anecdotally, that mature specimens are dug up and shipped to places like Dubai and Palm Springs for exotic landscaping. The tree aloes are very slow growing, and it is not possible to grow them in captivity to this size on the timescale of a Dubai construction project. There are rumors of people buying whole tracts of land just to deforest them for export, and the survival rate of the trees in shipment is not fantastic. This is just heartbreaking as this landscape is such a slow and old place, it's easy to imagine that a few greedy people could destroy it very quickly and recovery might never happen.

The species name "dichotoma" refers to the usual 2-pronged branching style. Given that some of the examples I photographed seemed to have more than two branches from some joints, it might be the Bastard Quiver Tree (Aloe pillansii), although that doesn't seem quite fair.

Here's a social weaverbird colonial nest in a large Quiver tree:
These beautiful examples were spotted near NousWells in the Northern Cape, not far off the N7 (if you consider "not far" enough space to get completely stuck, lost, separated from the other vans, without cell phone reception, and running out of beer and ice).

Gittin the Fish - How it works

2008-05-25T00:16:00.004+02:00

First you get the net onto the boat. The net is 150 fathoms x 5 fathoms. On top there is a float line and on the bottom there is a lead line. We stacked it on the dock on a tarp and pulled it off with the net reel.
It goes over the bow roller and through the fairleads, which slide back and forth to help wind the net evenly on the reel.

Next you go to the cannery (our relationship is with Copper River Seafoods thus far in the season) or the tender boat and get some chipped ice into the fish hold. The ice lasts quite a while actually. We have a big snow shovel on board for moving the ice around. Note stylish double-funnel day marker.
Then you wait. And you check the Fish & Game website to see whether ADF&G is going to announce an "opener" - usually 12 hours long this early in the season - when you can fish.

Fast forward to putting the net in the water. You tie a big orange buoy to one end and throw it over the bow roller. The bow roller has a hub like a 4wd hub on a pickup. You lock the hub, turn on the bow roller to spin seaward and idle backward for a few minutes while 900' of net rolls off the bow. That's why its "drift net" fishing.
Then you "soak the net" for a while - maybe 15 minutes at first just to check whether you are in the fish. When you're pretty sure you're in the fish, you might leave it an hour or more. You can even drop your end of the net on a second buoy and putter around to the first end to check for fishies.

When you're ready to pull the net, you just turn on the net reel and wind it in. This is a red net so the mesh size is about 5 inches, just the size to catch a sockeye (red) salmon around the gills. They can see the net in clear water but they get frustrated and try to swim through it anyway. When a fish comes over the bow roller you stop the real and paw through the net to "pick" the fish out. Sometimes they get pretty wrapped up and tangled.
You ease the fish out of the net. Those blackish lines on its back are from the net. You see those on fish at the market and you know it was caught in a gillnet as opposed to some other method. Some are dead in the net but most come onto the boat alive and the squirm around and slime you while you work. Raingear is key. You can see my black raincoat is covered with silver scales. Then you reach under the gillplate and pop the artery in there to bleed the fish. This helps preserve the meat.
Sometimes you get lucky and another species, like this king (chinook) salmon will get tangled in the net. Obviously he can't get his head through it but sometimes just his teeth or nose will get caught. Often times one person can stand next to the net roller with a big dipnet watching for kings to make sure they don't fall out when the net comes out of the water. This one was just barely caught but he got pulled over the bow roller and flew into the boat! He's about 19 lbs, a little smaller than average. We sold him for $6.70/lb. You can buy him for about $25/lb.

Here they are on ice in the brailer bag. The bag will get picked up by the crane on the tender boat and weighed and we will get a little ticket that says how much fish we delivered and what kind. Straight to a market near you.

Cordova by day... and later in the day.

2008-05-24T08:26:00.005+02:00

Sila and I watched a huge sea otter lolling on the dock during the stormy days we arrived in Cordova. A few hours later, the sun came out and the sea otter gave birth. We called the baby Meep because he squeeked like a toy every time his mama turned him over and over to wash and fluff him.

During the storms, Alaska Department of Fish & Game called the first "opener" for Thursday May 15 on the Copper River Flats. Due to the foul conditions, we waited it out. We were glad of that - abet a little sheepish - because the average catch per boat was ~12 fish and we had calculated we needed 13 to pay our round-trip fuel to the Flats. Over the sunny weekend following, professional net menders like Lisa here were really busy on the docks - everyone anticipating the BIG ONE opener on Monday the 19th. Oh yah, and every next opener is gonna be the BIG ONE.

Here's Cordova Harbor as we first saw it when we pulled into town. It's really a tiny harbor compared to some, but it is home to most of the south-central Alaska gillnetting fleet - usually in the 30' range - so they pack a lot of boats in that small real estate. The town is cozily wrapped around the harbor and has an old-towny feel from its turn-of-the-century spruce sided buildings with big carved wooden signs. Like many wet towns in Southeast Alaska, most of Cordova's storefronts have deep awnings and you can walk around town without getting too wet.
Here's a view from K-float where we docked, looking up to town. And that's pretty much it! You can almost make out the little ski hill above town. They have a chair lift! It was recycled from Sun Valley, Idaho.
Bustling "business district" of First Street, Cordova: picture of cuteness.

And with this view of busy Second Street we conclude our tour of the Business District. Do note that every home and business in Cordova has an absolutely a$$-Kicking view.

Here are a couple of cute houses between the harbor and the cannery row . . . Cordova is an Obama Town.

The old Canneries line the waterfront north of the small boat harbor. Whether active or "historical", they all share the extremely tall, precariously old and rotty looking piling complex from which ice is lowered to boats in big plastic totes or by shooting out of a large hose. More on that later. The docks are well above high tide and maybe even above local tsunami potential. The corregated exteriors hide thoroughly modern processing, smoking and freezing facilities as well as kids from all over the world who come to the Alaska canneries to work for the summer.Not all of those piers are seeing action these days... I think that is somebody's vegetable garden half way down this grass-covered dock but I was too scared of the rotty wood to find out.

The USCG Cutter and buoy tender Sycamore was on hand for the opening of the season, launching random safety checks on the fleet. These fishermen are generally pretty conscientious, and NOBODY wants to miss a day of fishing on account of being short a fire extinguisher or other violation. Hilarity prevailed however, because the marine suppliers in town were universally out of at least the following items:

day markers (a black marker in the shape of two cones point to point); required to be shown when fishing during daylight hours.
hand-held breathalizers (one for every person onboard required to be produced by captain in case of accidents while underway) ; and
the REPORT ALL INJURIES placard that must be displayed in every boat.

The auto parts store, fortunately, had a really large supply of black funnels which were readily formed into a day marker with black electrical tape - maybe not typical but probably legal? An internet search turned up the detailed text of the REPORT ALL INJURIES placard and carefully Sharpied substitutes appeared on bulkheads across the harbor. As for the breathalizers - everyone is waiting for reinforcements from Anchorage.

When the sun started setting on the harbor that clear beautiful evening, the snowy mountains around Cordova lit up with alpenglow. The harbor was like a mirror. Here are a few favorites.

Next post: the fishies.

I was worried I wouldn't like fishing

2008-05-24T08:24:00.002+02:00

turns out I frickin love it.

20lb King Salmon, Kokenhenik Bar, Copper River flats, 19-May-2008

Rock of the Week #7

2008-05-21T06:24:00.002+02:00

Here's a fun one I collected Long Ago.
1. What is the large fossil (meaning the big round thing on the right side of first photo)?
2. Name this rock (any appropriate classification scheme is OK.)
3. Multiple choice. This rock is:
a) Proterozoic
b) early Paleozoic
c) late Paleozoic
d) Mesozoic
e) Cenozoic
f) Quaternary (modern)

Solution to Rock of the Week #6:

This rock is only 500 years old! It erupted from Panum Crater, a small rhyolitic cone in the Mono-Inyo chain in California’s Long Valley Caldera. Legends among the local Inyo tribe of the Native Americans reveal that the eruptive event was observed by local residents. The Mono-Inyo volcanics are about 76% SiO2, with only rare phenocrysts, producing pumice and obsidian. Both are glassy products but with variable bubble contents. The pumice (like this sample) can be very low density! It can be found floating on nearby Mono Lake. Nobody can resist picking up huge rocks of pumice and lifting them over head.
Here's an example from Tulane's 2002 trip.

1. (1 pt) What is rock?
: 1 point given for pumice.

2. (2 pt) How did it form?
: 1 point for volcanic.
: 1 point for rhyolitic or dome or crater.

Succulent of the Week - Faucaria tuberculosa

2008-05-19T12:06:00.000+02:00

This funny little beast is another Eastern Cape native. The gaping leaves of Faucaria give it the common name "Tiger's jaws".

This guy was pretty compact when I brought him home. After several weeks on a mostly "bright shade" windowsill, he seems to be opening up a bit. It's truly amazing to watch succulents adjust to their surroundings over the course of weeks... in both shape and colour.
Although it is fall, I'm afraid the 'bright shade' situation might not be bright enough to encourage this little guy to flower. According to Dr. Internets, it is a good beginner's succulent because it is not as particular as some as far as watering schedule, is less rot-prone and can recover from rot if clean cuttings are salvaged. In addition, it tolerates a wide range of sun conditions and enjoys occasional fertilizer but grows well without it. It's the pet snake of succulents.

in search of Columbia Glacier

2008-05-18T05:10:00.006+02:00

Prince William Sound truly is one of the wonders of this world. Can't say we were blessed with good weather during our crossing - but it is gorgeous and sunny as I write from Baja Taco in Cordova, looking out over the blue harbor and snowy mountains - and hundreds of bowpickers.

En route from Whittier to Cordova, we stopped in Columbia Bay behind Glacier Island to try to get a look at Columbia Glacier. There were a lot of icebergs behind Glacier Island and we had to idle up the bay and drive from the bow to watch for ice. There were a lot of happy otters though.
At the mouth of Columbia Bay, there ice fields got so thick that we couldn't get into the bay. We took a side route into Heather Bay and Sila dropped me off in the mud on Moraine Spit. I clambered between the tide-stranded icebergs and mud and tried to get a clear view to the glacier.

The receding tide had left all kinds of strange icey forms on the spit, in shades of blue and white.

With matching seagulls.

Fresh water falling on the sea and flowing off the melting bergs was frozen into a thin sheet of shore ice - which fell also on the falling tide and broke over the rocks on the shore:

In case you ever doubted that ice is hexagonal, look deeply into your screen for gorgeous evidence of volume diffusion creep in glaciers:

We never did get a look at the mighty Columbia. It has receded miles from where it is shown on the 1960's marine charts.

Shrimping at Ester Island

2008-05-14T23:34:00.003+02:00

We left the pot in about 400' of water overnight:

When we pulled it up all the cat food was gone from the tins.

But we got our breakfast:

Rock of the Week #6

2008-05-14T06:18:00.000+02:00

Anyone who's seen this before in the field will no doubt recognize it instantly. For the South African students though.... I have encouraged them to use google, and a certain locality name is actually written on the rock. We'll see how they fair!

1. Rock type
2. How did it form?

Solution to Rock of the Week #5:

This rock is a Jurassic slate from the Merced Falls Formation in the Sierra Nevada foothills, California, USA. The slates were deposited in a Jurassic-age subduction trench and accreted to the western margin of North America in the late Jurassic. They are very low grade metamorphic (sub-greenschist) and are dominated by the “slaty cleavage” formed by pressure solution. The empty cubic holes are missing diagenetic/metamorphic pyrite phenocrysts which most likely oxidized to goetite and washed away. Astute observers might have seen very small strain shadows preserved around the cubic grains in the form of fibrous quartz. This particular hand sample comes from the axial region of a tight fold. In the axis, the cleavage is perpendicular to bedding (which can be seen on one end of the sample. This causes the rock to break at 90° angles, creating a “pencil structure”.

1. (1 pt) What is rock?
: 1 point given for either shale, mudstone or slate.

2. (1 pt) What is missing from those cubic holes?
: 1 point for either pyrite or phenocrysts.

3. (1 pt) shape:
: 1 point for mentioning “pencil” or “fold axis”.

Succulent of the Week - Crassula argentea cv. gollum (??)

2008-05-12T11:57:00.002+02:00

Some succulents are apparently easy to hybridize, and lots of strange freak plants are produced for the pet trade. When I bought this tube-wormy, translucent plant I had no idea what it was, and it doesn't seem to resemble any of the naturally occurring species very closely.

Dr. Internets tells me that this little guy will grow up to a small "tree succulent" with woody stems and clusters of finger-like leaves at the ends, looking remarkably like the whole plant looks now (e.g. this photo). Wonder how long that will take?

If I had known it was a cultivated hybrid instead of a "real plant" I think I wouldn't have bought it. Am I becoming a succulent snob? In spite of its decidedly non-deserty appearance, it seems to do just as well with long dry periods as my other pets.

Scenes from Homer

2008-05-09T20:03:00.002+02:00

Spending a couple of beautiful days in Homer Alaska before the fishing season opens -
It's a late spring here and still a few feet of snow at our place up on the ridge. It's been a whirlwind of trying to get ready and still spend time with family and friends.

View from the spit road on a clear day

Caption this photo:

Beach combing in Seldovia

Boat ride with the nieces

Microfaults in marble in the 191Ma Seldovia Metamorphic Complex -a tiny glaucophane-bearing sliver along the Border Ranges Fault at Seldovia Bay.

Rock of the Week #5

2008-05-07T06:04:00.001+02:00

Ah, finally a "structure rock".
Here are the questions:
1. What is this rock?
2. What is missing from the little cubic holes?
3. Why does the rock have that rectangular-prism shape?

Hint for the online audience: the words "Merced Falls" are written on the rock, this wouldn't give anything away to the south african students but I had to tell you anyway.

Solution to Rock of the Week #4:

Thanks to Johann Diener for the interesting rock!

1. (1 pt) 2 minerals?
: 1 point given for either feldspar or pyroxene.

2. (1 pt) Rock type?
: Komatiite.

3. (1 pt) Locality:
: any komatiite locality acceptable, e.g. Barberton Belt.

Nouswells, Northern Cape

2008-05-05T10:57:00.001+02:00

A few weeks ago I went on the third year Igneous field trip to the northern cape and southern Namibia. What an incredible part of the world. We drove north through Springbok, South Africa on the N7 and left the highway in a terrane of rounded granite "koppies" in a sea of red sand. The sun went down on us while the vans got increasingly stuck in this sand.
Here's the first time we got stuck... Turns out flash flooding a few weeks before had washed soft sand across the old sandy tracks in this desolate area of sheep herding. The ground surface was marked by mini-deltas, braided stream channels, and all kinds of tiny miniaturized flood features in the fine sand. We ended up leaving the vehicles in disarray all over the desert and hiked in the last couple of kilometers to the campsite.

In the morning, Chris handed out some aerial photos and we sent the students off into the desert while the instructor team got started on the digging out process.

Due to the mid-day heat, we started them out early in the morning and had them return to camp for lunch/siesta and back out for more mapping in the afternoon. This was the first time for me mapping in an essentially all-intrusive landscape. There was enough diversity in the intrusive suites that it's not too hard to tell them apart in the field. In contrast to mapping bedded rocks however, structures are often obscured and it's almost impossible to predict what you might see at the next outcrop since you have no "initial shape" model to work from. That means you have to actually visit every outcrop you can find. This makes things a bit slower...
Here's an intrusive contact between medium-grained pink granite (top) and porphyritic adamelite (bottom). The adamelite is easy to identify because it has those big squarish feldspar crystals. The intrusive contacts here are "soft" like this - and irregular.

The country rock to all these intrusives is the Orange River Volcanic Suite. These were generally some gritty, blackish-green actinolite metabasalt and some metasediments. Here's a quartz-talcy shear zone with a sheath folded quartz vein!!!! Props to Johann the metamorphic petrologist who found this and showed it to me!!

Here's the class checking out some of the amphibolites in the ORVS:

Duane caught this crazy beetle out of the air. They buzz around slow and lazy making a mini-helicopter sound.

Here's an awesome fault surface in the ORVS. The rock here is a quartz porphyry - maybe - but it might be a metasomatic product. The thin darker pink layer on the surface of the outcrop is a cataclasite layer, and the rounded quartz grains get stretched out into ellipsoids with increasing flattening toward the cataclasite layer - and oh yes, I got a gorgeous big oriented sample.

Succulent of the Week - Euphorbia meloformis

2008-05-05T10:57:00.000+02:00

As a non-botanist, I find Euphorbia the most difficult genus to get a handle on. Euphorbia come in all kinds of shapes and sizes. The common characteristic is a milky, toxic sap. Of course I don't want to cut the plants to try to identify them. The only one I was familiar with before this obsession with succulents struck me was the Poinsettia. Which is not exactly succulent.

This cactus-like stem succulent Euphorbia meloformis is one of my new favorites.
It's native to the Eastern Cape. Two weeks after I brought it home, I discovered tiny scale insects living among the stems, apparently sucking the supposedly toxic sap. I borrowed a very nice tweezer from the mineral picking students and removed most of them. I think the plant looks happier now, if it is possible for Euphorbia meloformis to look happy. Its unapologetic fatness is somehow happy.
I like the radial symmetry which in this individual has grown into a helix-like shape. These pictures were taken after the peak of its bloom but I have high hopes for next year.

Rock of the Week #4

2008-04-30T08:30:00.002+02:00

1. Name two minerals present
2. Name this rock type
3. Give an example of a locality where this type of rock can be found:

I'll give you a hint: that's not actinolite!

And the solution to Rock #3:

Copper minerals are fun because they are bright coloured, and the colour can tell you what mineral it is (at least, it is a more reliable indicator than with most other minerals). The best-known copper minerals have distinctive colours (for example, deep bright/dark green stripes for Malachite, deep blue-violet to blue-black for Azurite).

This rock is from Francistown, Botswana, and is mostly quartz. In this rock, light blue-aqua colour is characteristic of chrysocolla [(Cu,Al)2H2Si2O5(OH)4 •nH2O]. Chrysocolla forms in the oxidation zones of copper ore bodies. The lighter coloured, massive greenish-yellowish crust on the rock has a distinctively different colour and fizzes vigorously in HCl. It is either the unusual mineral rosasite [(Cu,Zn)2CO3(OH)2], which also occurs in the oxidation zone of copper/zinc/silver deposits (such as the Francistown locality), or it is a calcite crust with unknown copper minerals in. You will get a point for either answer as I am not sure myself!

Thanks to Catherine Curtis for the interesting rock!

1. (2 pts) blue-green minerals?
: mention of copper (1 pt)
: chrysocolla, rosasite or calcite (1 pt)

2. (1 pt) How was it formed?
: Oxidation or precipitation from water got a point.

AWARDS OF THE WEEK:

FIRST PLACE: Shirley Whitmore for:

1. Mildew
2. Left in a moist area

The “awards of the week” seem to be turning into the “most sarcastic of the week”, and Shirley certainly has the lead!

Please note that I am going off to sea for a month so May's RoW will be auto posted. Please don't be discouraged from commenting however! I'll be checking in when I can.

Succulent of the Week - Pleiospilos nelii

2008-04-28T18:18:00.000+02:00

Pleiospilos - another "split-rock" type succulent, this time from the Klein Karoo region of South Africa. It is sometimes mistaken for a Lithops due to its similar habit (small, stone-like, 2 leaves at a time, flowers from the crack ), but it is not closely related. Pleiospilos are sometimes called the "liver plant", and my elliptical specimen certainly looks a bit like a liver. Like the lithops, these guys do quite well with no water at all. Even for a whole year. I will water it monthly though the fall, and not again until spring. I've moved it to my office windowsill where there's a bit more sun but they are not so cold tolerant. Maybe I need to start knitting some cozies for these pots? I wonder.
The new set of leaves is forming in the center - assuming I don't overwater, these will grow as the old set shrinks and is eventually resorbed by the plant. I'm wondering if this also means an effective 90° rotation of the long axis every year - cool. I will mark the pot and wait to see.

I think the split rock succulents are generally my favorites because they remind me of plate tectonics. A bit of heat, a bit of water.... and wait... total recycling and overturning of the whole body of the plant/planet, at centimeters per year. Yup - these succulents have about the same strain rate as the tectonic plates. If only the world would crack open and produce a giant daisy-like flower... well, I guess somebody already thought of that.

I'm going on vacation - if you can call commercial fishing a vacation - so the Succulents of the Week will be auto-posted through May. I'll check in from fish-stinky internet/laundry mat/postoffice/bar/rent-a-shower facilities periodically so feel free to leave comments, I'll get back to you.

Rock of the Week #3

2008-04-23T08:10:00.000+02:00

Sorry, I am getting a bit behind on RoW. That's just as well, and I think I will keep the blog a week behind the student competition as they could always find this and use your guesses! And they are in direct competition for geology stickers so we can't have that.

Due to the general troubles with the first two rocks of the weeks (both online and in the office) I decided to try something a bit more accessible to students and internet viewers this week. I present:

And the solution to last week's rock:
This rock is a partially-serpentinised harzburgite from the Franciscan Complex (Ring Mountain), California, USA. Harzburgite is a rock of “depleted” mantle origin. The rock comes from an ophiolitic unit which was thrust over the complex during the Jurassic. The original mineralogy of the rock would have been about equal amounts of pyroxene and olivine. You can still see the grains of dark green pyroxene but the olivine has reacted with seawater to form serpentine (antigorite) and talc. Metallic looking bits come from weathered sulfides and oxides. These minerals weather easily, leaving the surface of the rock rough and yellow in colour.

1. (1 pt) Minerals?
: Pyroxene, serpentine, magnetite

2. (1 pt) Rock name?
: peridotite or harzburgite got a point

3. (1 pt) Tectonic environment?
: ophiolite or subduction zone got a point.

AWARDS OF THE WEEK:

FIRST PLACE: Pia Vigletti for
performing experiments on the rock, even though results are inexplicable

RUNNER UP: Anonymous person for
“Moon rock, that’s why it smells like cheddar”

Succulent of the Week - Hoodia gordonii

2008-04-22T12:02:00.002+02:00

Wild in Namaqualand! This week's Succulent of the Week was spotted during the third year mapping trip in wild bloom. I haven't blogged about this trip yet, too busy not finishing marking the third year papers, but I'll get around to it one of these days.

This outlandish looking beast is best known for it's overhyped, not FDA-approved popularity as an appetite suppressant. Therefore, it is commonly poached and is now endangered in its native habitat, northwestern South Africa and southern Namibia. Perhaps if it adapted to camouflage better... but where could it hide?

Aha! inside another bush. Those flowers are truly amazing. They do have the stapeliad quality of stinking like dead meat, but they are weird and pale in the bright desert sun with one big, flat, nearly monochrome petal. In the buds before they open, they have the same star-tear drop shape as my little stapeliad in my office.
The long purple pods are the seed pods - these will dry and split and tufted seeds will blow out across the desert. Judging from the locations I saw blooming Hoodia all over the area, it doesn't seem to matter much where they land. They grow in dry sand, cracks in rock, edges of piles of sand, dry rivers, middle of dirt roads gone unused... everywhere. Feel lucky to have seen it in bloom, even if the occasion was presented by the necessity of piling out of the van to push it out of a sand pit.

Oddly enough - just a day after I started working on this post I went to the garden store, and look what I found:
My own little Hoodia! Wonder how long until it makes big pink flowers? Years and years I imagine.

More on Plagiarism

2008-04-21T19:56:00.003+02:00

Yesterday I posted about the issue of students plagiarizing from blogs, which, judging from the response, is clearly a touchstone issue for a lot of us in the business. The comments mostly centered around discussing the criteria for appropriate use of blogs (and similar sources) for students.
Andrew has taken to the next level with his comment:

"Christie, you've probably been plagiarized before. What's different this time is that a colleague informed you--but why did they do so? Did they ask you to change your practices? What do they do at their school? This is a separate discussion from the one you've chosen to feature. What do you expect of your peers? Can teachers be 'bad teachers' "

I should clarify here that the colleague who contacted me did not ask me to take down the material, or to stop blogging about local field trip areas. His words:

"Your blog should include a warning -- "NOT TO BE USED FOR UNDERGRADS ASSIGNMENTS" !"

He's right - and so timely considering the discussions going around - rather than complaining about use/misuse I can take steps to address inadvertent cases by giving some instruction for appropriate use when I post potentially useful information. You'll see from the warning I chose to put up that I didn't follow the letter of his recommendation. I do think undergrads can use this information for assignments, according to principles of appropriate use. I don't know the details of the field assignment at Neighbor U.

In answer to Andrew, you're right, I probably have been plagiarized before. My initial response to hearing about it from a colleague was a bit embarrassed - wondered if I had done something wrong. Glad to have been reading all the recent discussion about blogging because it helped clarify my opinion that the internet really has changed everything about information and intellectual property, as well as propriety - and our societal expectations haven't adapted to address that. Asking my students not to google a topic when they have been assigned to read about it would be even more hopeless than asking them not to download Heroes from a mirror site in Thailand. But I digress.

At my institution we are able to use Turn-It-In, a service which compares submitted text to millions of print and web sources and simply highlights identical strings. I then go through and visually review each string. I did an informal experiment in which I read a paper first and circled suspicious areas. Turn-it-in identified the same trouble spots, but saved me a lot of time by identifying the source. This service has taken a lot of criticism for various reasons - one being the presumption of student guilt. Since professors have been manually comparing sources to check for plagiarism since the dawn of papers, I think the writing and the checking should move into the internet age together. I am not swayed by any of the arguments against using the service.

My undergraduate institution had a very strict honor code. I left with a very polarized view of plagiarism and people who committed it.

In my current position, I realize that plagiarism is probably much more common than I previously thought, and that there are subtleties that can cause students to cross the line without evil intent. For example, I busted a student last year for a "mash-up" essay - basically interleaving complete sentences from two or three sources into semi-coherent paragraphs. When I confronted the student about this, he/she replied that this approach was necessary because he/she didn't understand the material but was trying to patch it together to complete the assignment. He/she was genuinely horrified to be accused of plagiarism and had honestly wanted to do the right thing. The concept of synthesis - of taking information 100% from other sources but phrasing it in such a way as to make it your own - was not there.

In response, I developed a handout on writing - probably too long to be read by many students in full! But I am comforted to know that when a student is in violation, I can at least demonstrate that they were specifically given a definition of the "mash-up" and told that it was not appropriate. At a school which has no liberal arts component, sometimes students are expected to learn this by osmosis but in my opinion, it is much more effective to teach them explicitly how to write scientific papers. Subsequent results have been much better and the students are motivated to follow my guidelines. So in answer to Andrew's "Can teachers be bad teachers?" I think I would hesitate to use the word "bad", but maybe we fail our students when we assume prior knowledge that they don't have. And that includes failing to give them clear instruction on our expectations.

This situation is not really a test case for all these subtleties, because the student who plagiarized was so blatant that there is no way it could have been inadvertent, and the colleague who contacted me made a simple request that I agreed with: to suggest guidelines for appropriate use when publishing information that could be used in many ways.

(c) 2008

*Click here to download my writing handout in Word format. Anyone may use any part or the whole document for any teaching purpose, no attribution is necessary. It is somewhat poorly organized anyway so I will fix that for next year.

on tv

2008-04-21T11:20:00.002+02:00

I will be appearing on SABC2's Hectic-nine-9, a "teen-tween" show in the 4pm timeslot, on Wednesday 30 April to talk about studying earthquakes. After watching some show clips on the website, I think I can safely say that "hectic" refers to wildly enthusiastic, highly styled young presenters gesticulating madly during incredibly fast and short scenes. I hope the 2 hrs of rehearsal and makeup (!) are enough to get me to tween-speed.

Bad Students! No!

2008-04-21T02:37:00.002+02:00

I just received word that a 3rd year student at a nearby university turned in significant portions of my Sea Point Contact field trip post for his/her own field trip report to the same locality. Fool! No pity for plagiarizers!

As a new grad student I once googled some suspicious-looking text strings in a student's New Idria field report and discovered that a recently graduated student had posted all of his school projects on his website for some reason. Naturally the student failed and I wrote to the blogger and asked him to take the material down or password-protect it. At the time I felt this was a fair course of action because the material he posted was an exact model of what we were asking students to do.

Now what about geoblogging? Field trip blogging? There's been a lot of buzz lately about whether it is ethical to critique or comment on peer-reviewed papers in the blogosphere, where the public often has access to the critique but not the original paper. In my opinion, anything that's published becomes public information and commentary is free. However, some discretion is advised, because these blogs are often written by people who carry some kind of official authority on the topic and there is a fine line between the "official word of the scientific community" and some casual spouting off by somebody who writes the "official word" as their day job. The discussion made me think about my flip language on this blog and my tacit assumption that if nobody comments, nobody reads it. Not true, eh? I suppose I could check my stats on blogger or something.

Anyway, I would like to think that somebody might be interested in the geologic information I post, as I am interested in others' posts, particularly field experiences, research questions, etc. but I am HORRIFIED that students might misuse this material. Almost worse is the thought that students or anybody else might inadvertently use blogs over more reputable sources. Students:

(I'll spare the rest of you for now, but any students who want to hear it, drop me an email.)

I am not going to stop blogging about field experiences and interesting problems. I can't anticipate every assignment that might be set at every university (although I could have anticipated this particular one, had I thought about it) to avoid writing something that might be utilized by an unscrupulous person. I will however, add a threatening copyright notice.

It's in the sidebar.

What else can be done? Anything?

(c) 2008 C. D. Rowe

Succulent of the Week - Titanopsis

2008-04-17T11:16:00.002+02:00

Why would this cute little thing get a name like Titanopsis calcarea? I might be going nutso, but after I took these photos I gave everything its monthly watering. Now, a few days later, the Titanops is almost as wide as the pot. How did that happen. Feed me Seymour. Maybe it will shrink back to its previous size as it dries out again.

The name means "looking like limestone" and I will admit there's a certain resemblance to the Rock of the Week #1. This guy is native to the Karoo and according to Dr. Internets, the leaf shape and colour can vary considerably with moisture, specific regional origin, etc. I bought this one for its almost reptilian skin - blue-green leaves and the enlarged cells on the edge of the leaves look like scales. Godzilla.
Yo mama was a stegosaurus.

What I've seen recently besides my honours students all day every day

2008-04-15T20:14:00.002+02:00

Green Point Stadium - under construction for World Cup 2010.Experimenting with lino printing.

Now back to prepping for my practical exercise tomorrow - turns out nobody remembers how to add or multiply vectors, today's prac was a slog.

Why the Brunton Compass is the Most Important Tool

2008-04-11T08:08:00.010+02:00

Sometimes I forget that this is a blog and not a private diary. Ishmael reminded me by asking about some of the jargon in this post. Ishmael asks:

"What's a fault thrust? Why is compass direction important in describing features? Why does my brain hurt so?"

I'm just going to focus on question #2, as I think google can answer #1 and probably #3 has something more to do with Tony's Navigational Hazzard (sic) than with geology.

ORIENTATION OF STRUCTURES
Why do we measure the orientation of geologic features?
1. It helps us group structures into a systematic framework
2. It enables us to guess at orientations of (former or current) geologic stress which caused those structures to form
3. Stress orientation is related to tectonic events and plate motion.

Let's take the example of Kodiak Island, using this very brightly coloured map my colleague Eric Thompson put together for presentation use:
modified from Byrne and Fisher, 1982.

Faults are roughly planar or curvi-planar features in 3D* and so appear as lines or arcs on a geologic map. A first order observation one can make from this map is that the major faults on Kodiak Island are just about parallel to one another. Some of these faults are cross-cut by intrusive igneous rocks (red blobs) which have been dated to about 57-63Ma (just after the massive impact event at the end of the Cretaceous). That means some of these faults have not been active since before 63Ma. A second observation one can make, using the inset location map, is that they are parallel to the active plate boundary fault (toothed line) and if you are familiar with the area you might also notice that both modern and ancient faults are parallel to the volcanic arc.

So a hypothesis one could draw from the map, is that since old faults and modern faults are parallel, that the stress orientations have been consistent for a long time. Since today's geologic stresses are caused by the subduction of the Pacific Plate beneath Kodiak, one might hypothesize that an oceanic plate has been subducting under North America for a long time.

To get more information, we did a close-up study of one of these old faults: the Uganik Thrust where it cuts through Afognak Island. The location is shown by a little star "Big Waterfall Bay" on the geologic map.
Fig. 2, Rowe, Meneghini and Moore (in review)

In the map view (A) you can see little symbols of a line with a triangle on it and a number - these are recordings of compass measurements of textures in the rocks. These measurements are used in (C) to draw a cross section which shows how the rock textures are oriented in the third dimension.

From the data presented in this figure, we can make a few more observations. First, the rocks to the SE were thrusted underneath the rocks to the NW along the Uganik Thrust. This confirms that the Uganik Thrust has the same sense of offset as the modern subduction thrust active under Kodiak. Second, the rock textures in detail are not all parallel to the thrust fault, this suggests that the story has more complications to it. The fault cross-cuts some of the textures in the rock. The igneous rocks can be seen cross-cutting the fault (B). In fact, the rock fabrics in the fault, which cross-cut the older rock fabrics, can also be used to learn about water travelling through the fault. This is of interest because water can change the nature of the rocks, or cause fluid pressure to change the stress on a fault - affecting the earthquake behaviour of a fault.

I'll skip a few of the details here - even the reviewers on this paper might find the presentation of 12 individual stereonets to be a little much data. But the basic observations presented here are enough to hypothesize this comic novel history for the fault - this is Fig. 9 of Rowe et al., submitted which I hope to be published soon.

The cartoon doesn't just draw on my own data from this study, it's also consistent with previously reported general models for the structure and assembly of Kodiak Island. The first two panels are pretty much derived from previous theories from other geologists.

Our work at the Uganik Thrust adds panels C & D to the story - showing how the fault was a conduit for fluids and then was cross-cut and effectively killed when igneous intrusions pinned it shut. Kodiakites (Kodiakers?) may not be aware that prior to the development of today's subduction zone where the Pacific Plate goes under North America, displacing fishing boats up to Mac's Sporting Goods store at a whim, there was another plate in between NA & Pac. The long time subduction of that oceanic plate caused the creation of most of the rocks of Kodiak Island during the Permian, Triassic, Jurassic and Cretaceous periods. Eventually the entire Kula-Farallon plate was consumed in the subduction zone, and the boundary between the Pacific and Kula-Farallon plates was also swallowed. This brief event caused a hiccup in the long-term stable history of the margin - causing a misorientation of rock fabrics and the introduction of the igneous intrusions. Thereafter, the Pacific Plate continued to subduct and events returned to "normal" in south-central Alaska, as they continue to this day. In Panel D, the cross sectional view across the rocks of Kodiak is pretty similar to what you see today. In this panel, the "Ghost Rocks Fm." is at Pasagshak Point - so clearly there has been a lot more uplift in the ensuing 50+ million years. This uplift is also recorded in the orientation of structures - as it has occurred through landward tilt, the old faults in the rocks are "dipping" more steeply landward whereas they were originally gently sloping.

THE TOOLS
The geologic compass is pretty much indispensable. It differs from an ordinary compass in that it has a clinometer as well as the usual magnetic needle. Also, the dial is numbered "backwards" of a what you would see on a compass rose, so that you point the compass in a direction and it reads the bearing at which you are pointing. It also has an adjustable dial so that one can set the compass to measure to true north rather than magnetic north. This is done to avoid the introduced error due to temporal and spatial variation of magnetic north.

I am an adherent to the church of Brunton; we believe the Professional Pocket Transit can do no wrong. I have two - one balanced for the northern hemisphere and one balanced for the southern hemisphere.

* Except when they are not.

Succulent of the Week - Stapelia

2008-04-10T13:21:00.004+02:00

Stapelia - a group of stem succulents, mostly small, mostly South African. They consist of a clump of 4-sided stems, with or without little teeth along the edges. I have a little one in my window box in the office (you may remember that it smelled up the place when the flowers opened). Stapeliads are famous for their carrion flowers - big, star-shaped blooms that are pollinated by flies and therefore emit the odors which attract flies - I'll pause here to let you imagine some odors that attract flies...

This Stapelia does not have green stems! I bought this beauty at the Kirstenbosch garden store. It is quite a bit bigger than my other one and the stems are fuzzy like a peach. The colours are amazing, especially in my blue kitchen under the skylight on this sunny day:

After some googling I think it is probably Stapelia variegata v. rogosa but it will be easier to tell when it flowers. It's always possible too that the plant is drought stressed, although the stems are firm and it seems fine other than the colour. I have to say though - the Kbosch garden store does not seem to take very good care of their succulents. I made a couple of pity purchases that day as well.

In other Stapelia news, I had previously identified the little one in my office as Stapelia grandiflora because that's what the tag from the nursery said. Sucker! Now that I have seen S. grandiflora blooming in captivity I can assure you, that is a much bigger flower than the ones that keep on blooming and stinking up my office. The flowers are pretty hairy and purple with subtle tigery stripes perpendicular to the petals - I think it is S. hirsuta? It just keeps flowering. It seems to grow a new bud overnight the same day that the previous flower closes. Trying to photograph it with the macro setting on my new camera, I found this:

Fly maggots. In my office. The little Stapelia that just keeps on giving. Its frenzied flowering is the first sure sign of fall.

Rock of the Week #2

2008-04-09T09:40:00.001+02:00

1. Minerals
2. Rock Name
3. Tectonic environment

... this one doesn't fizz!

edited to add, by request from the lost geologist:

Scale bar is ~ 1cm.

Here's the solution to the last Rock of the Week #1:
Rock of the week #1:
the answer!

This rock is an ooid dune sediment from San Salvador
Island, The Bahamas. The grains are “ooids”: layered,
spherical carbonate grains which precipitate in the surf
zone on a high-energy beach. The grains were blown by
the wind into an aeolian dune. The wind sorted the ooids
into ripples with coarse grains on the crests and fine
grains in the troughs. Ripples migrating along the dune
face left laminated layers of coarse/fine ooids. The
current pyramidal shape of the hand sample is a
coincidence of erosion.

1. (1 pt) What is the dominant mineral?

: Calcite (carbonate also accepted)

Hons students who wrote “quartz” will write “I will not
forget the Mohs Hardness Scale” 100 times using a
stick of a mineral of hardness 7.

2. (2 pt) How did this rock form?
: “shallow marine precipitation” got a point
: “ooid” or “oolite” got a point

AWARDS OF THE WEEK:
FIRST PLACE: Shirley Whitmore for
“My dog puked that up in the back yard after eating some
bones”
RUNNERS UP: Ian & Tim for
“ Plaster of paris. Christie made it. You can’t fool a bunch
of fools”

Well, little grasshoppers, at least you got the cation right.

On Field Geology

2008-04-08T20:54:00.004+02:00

I hate to blog about blogs, and have made a point of not doing so here - but involvement in this very interdisciplinary project has brought the diversity within the concepts of data and evidence, and how that diversity translates into field practice, to the front of my thinking lately.

Rapidly becoming one of my twice-daily-checks-for-new-posts is Kim Hannula's blog All of My Faults Are Stress-Related. Kim is a structure professor at Fort Lewis College in Durango. Already that sounds like a lot of fun.

Anyway, Kim just posted this excellent discussion about the practice of collecting field data - especially structural data - where so much of the information we have comes directly in the field, without any instruments fancier than a compass to rely on. Although we collect a lot of rocks (and probably some of the biggest rocks, with exception of the zircon pickers), there is usually absolutely nothing we can do to those rocks back in the lab which will make up for missing, or incorrectly interpreted, one little piece of the key field data.

In the process, we keep all the data in our heads as we collect it... rolling it around until it fits one or two or ten hypotheses, differentiating these hypotheses by using them to make predictions, then testing them, rejecting some, developing others. Sometimes I come to a set of hypotheses that require a detailed look at the microstructure, or some specific information on a rock's chemistry, to sort them out. Only then can we fall back on the lab. And even then, the field relations form the basis of the interpreted history of the rocks. That's how I see it. And that's why I need a lot more time in the field than some of my colleagues who can bring a lot of their data collection home with them.

Structural geology is the lens through which I view the rocks; but I need to know a lot more than my specialty in order to practice it. Being a structural geologist is like being a specialist in remodeling. I better know all about demolition, but I better know plumbing, framing, brick & mortar, etc. to get the job done. Since "structures" are the result of deformation and/or fluid flow through any existing rock, I have to know everything I can about all kinds of rocks, what they should look like when pristine or partially or fully damaged and altered. I have to know enough about chemistry to know what minerals will react with fluids or with each other, and I have to know enough about physics to interpret the relationships between the structures we see in the field and the stress which could have caused them. Then I have to put it all together in 4D. If I do my job well.

I complain a lot about the geochemists who have crawled over ~~South~~ southern Africa, collected miscellany and analysed the major, minor, trace, elements, REE and LREE and PGE and isotope ratios, of every rock on the side of the road - excuse the hyperbole - without a map to pin the data on. To me this is backwards geology, but as it's been driven by exploration, and as two of the three world record mineral resources on which empires have been built are primary and igneous (diamond-bearing kimberlites and the platinum-bearing Bushveld Complex) it was probably the best way forward for some time. In addition, this focus has built a cadre of world-class expertise in high concentration in a country with a relatively small academic community, in geographic isolation from larger academia. Our students all get jobs as geologists. Imagine for a moment the impact of that simple fact.

However, a holistic approach is needed to tell the African geologic story and recent moves in South African domestic and international collaborative work streams show that the community is moving toward interdisciplinary teams. Let's hope it will lead to a move toward more recognition of interdisciplinary people. I think that is the way things are going - generally - but just like at home, we are watching intently as the era of the sitting government winds to a close, wondering what the next administration will bring to all of us.

A Range Front Fault... not so old, maybe?

2008-04-08T11:26:00.000+02:00

There are some really beautiful rocks in the Damara Sequence here - hanging wall of the Sole Thrust. Here's a lovely marble. So elegantly foliated. So flat-lying and unsheared. It's part of a strange and complex assemblage - just below it are the strangest diamictites I have ever seen. Could it be part of a Snowball Earth Assemblage? A "cap carbonate"?Just downsection from that, we have this ridiculously gorgeous volcaniclastic fluvial shale... Those are green mudclasts in a purple matrix. But what's this? It appears to be sheared downward to the north. (this sample did not survive transport home, by the way. One must always pack one's own rocks to avert tragedy!! I have a million small chips of purple shale in the bottom of a bucket now.)

Even better/weirder - here's a strange diamictite (further down-section still). The clasts are featureless or ooid-bearing dark blue limestone, generally well-rounded and aligned (e.g. this is not a tillite). The matrix is brownish carbonate and a bit of siliciclastic material (formerly clay). Here you can see the undeformed diamictite in outcrop (below) with a boulder (my boulder) of ductily strained diamictite above. So. Good.
Here's Ben and Jodie on the edge between the horizontal undeformed rocks (e.g. marble, top photo) and the steeply north-dipping, deformed rocks. Much discussion and waving of the arms. Ben is hunting for the perfect sample. Ben has quite a talent for this and will quietly chip at a rock for a long time until it is just right. Jodie: what do you mean, "recent fault"?

Along strike from where we are standing - this. You can see the steeply dipping rocks to the north (downhill) and the flat-lying rocks to the south (uphill). In between? chaos. Ben and I spent quite a while looking up there and trying to figure it all out- but no time to climb that hill!! I will return, I assure you.

Same hill, different vantage point; this time looking about ENE directly along the fault strike:

Retreating to the car, in advance of another rain storm. Ben carried his large sample on his head as he had learned as a child in Zambia. All the way, he kept up a monologue on the fact that African women are the most beautiful and hard-working in the world.
But wait, what's that behind Ben, in the range front? It's the Klein Blasskopf Tufa Cascade. Although I now know the proper terminology, I still prefer "death star of tufa". The interpreted photo below shows the bedding orientation uphill and downhill in the range front, the dashed line shows the approximate surface trace of the fault.

Now I will tell you some "geologic evidences" (as my Italian colleague likes to say):

this range-front is linear
2 additional tufa cascades occur along this range front
a pool fed by a spring coming up from below is on top of the tufa cascade
Drag of the folded strata in the range front suggests north-northwest-dipping normal faulting
this normal fault crosscuts low-angle thrusts which characterize the hangingwall - crosscuts Damara bedding and structures.

Now for a geochemical argument from a non-geochemist -
All things being equal, ground water flowing upward toward the surface will depressurize. This leads to precipitation of carbonates, for example, in local boreholes. Assuming the ground water reservoirs in the Naukluft are not significantly deep to be geothermal (supported by temperature data at sampling points), depressurization is the most significant effect on solubility. Therefore, a vertical conduit of increased permeability (e.g. a normal fault) may be expected to transmit fluids upwards and thereby cause cementation of its own conduit. This is a one-way process and permeability of the fault will therefore approach ambient permeability with time. Given the propensity of the regional system for A LOT OF CARBONATE MOVING AROUND and the observations that some tufa deposition is active today at the surface (Stone, pers. comm. 2008), I will hazard a guess that a fault conduit would close rapidly rather than slowly. Given that the Blasskrans Normal Fault (yes I am naming this speculative feature now) is an open conduit after a long period of tufa deposition, I suggest a mechanism is necessary for re-opening fluid conduits against the effects of cementation. Possibilities:

wild variations in fluid flux
wild variations in fluid source, carbonate under-saturated fluids dissolve cements
fault moves and breaks rocks/cements in recent past
fault is actually a barrier to fluid flow, causing venting at the surface when ground water flowing down hill cannot cross it and gets backed up
most of cascade are built of surface water and there isnt really that much spring water involved (isotopically testable; preliminary results show significant differences in deuterium ratios between spring and surface waters and rain, Naude, pers. comm. 2008)
i'm sure there are others....

Note that 1, 2, and 3 can all be explained by motion on the fault. Only problem? No documented evidence for tectonic activity in this region (like, all of W Africa) in the last... I don't know... 500Ma give or take a few? Yah. Well, that's not recent enough to explain 1, 2, and 3. So.

My geographer friend and GIS geomorphologist has seen subtle features in the Kalahari which suggest some recent very slow tectonic strain (Eckhart, pers comm 2008). My predecessor in this job, Giulio, has calculated the torque on western southern Africa generated by the zipper-like opening of the East African Rift and predicted north-northwest principle stress across southern Namibia (Viola et al 2005 in EPSL), supported by offshore mud volcanoes along strike-slip faults.

So -no way to link my new fault into this framework yet, but hopefully this demonstrates to the skeptical reader that neotectonics are alive, well, painfully slow and sadly unrecognized in this part of Africa.

Still exploring ideas of post-orogenic relaxation and/or gravity for the Blasskrans fault. Further work is necessary....

Rock of the Week #1

2008-04-05T10:39:00.009+02:00

When we were out in the field, the third years told me they felt they needed more practice identifying rocks in hand sample. Of course I asked myself, "What would Hilde do? She would find a way to give a prize." Thus was born:
Each week I will put a new and different rock out in the office with 3-pts worth of questions and all the students will try to identify the rock and submit their answers. Winners for each class level are named at the end of the semester. Just for fun, I'll post the RoW here on my blog as well and you kids can play along at home. This is the e-RoW. No handlens, knife, or acid on the monitor.

RoW#1:
1. What is the dominant mineral in this rock (1 pt)
2. How was this rock formed? (2 pt)
Some third years examining RoW#1 in Shirley's office:

Lemon Tree Protection

2008-04-03T21:00:00.003+02:00

My lemon tree has a guardian angel

Or a fierce hidden predator

...depending on your trophic level.