Rock of the Week #4

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.


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

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

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.


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

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

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

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!

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

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

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

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.

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 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

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

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

FIRST PLACE: Shirley Whitmore for
“My dog puked that up in the back yard after eating some
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

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?

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:
  1. wild variations in fluid flux
  2. wild variations in fluid source, carbonate under-saturated fluids dissolve cements
  3. fault moves and breaks rocks/cements in recent past
  4. 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
  5. 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)
  6. 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

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.

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

My lemon tree has a guardian angel

Or a fierce hidden predator

...depending on your trophic level.

Succulent of the Week - Lithops

Maybe we need to break up the geology posts a bit... although I finally discovered the world of geology bloggers... how did I miss that until now? So cool. Anyway.

I found a new source for my newest ... um... hobby: covering any sun-touched surface with a strange and wonderful menagerie of South African succulents. I'm getting better at recognizing members of the more common genuses, but species recognition is still beyond my grasp. As with lots of South African flora, these tiny plants are highly evolved for specific niches, many endemic to areas only meters or kilometers in size!

I'll start off our new "Succulent of the Week" program with the quintessential South African succulent - a tiny "stone plant", Lithops karasmontana. (I'm not 100% sure about the species ID but I'm sure some real succulent enthusiast will pick this up on their blogwatch and correct me if necessary!)

Tiny Lithops are only about 3cm across, with just two very fat leaves (Afrikaans for succulent is vetplant, literally "fat plant". Afrikaans just tells it like it is sometimes.) Once a year, a new pair of leaves will grow from the center and eventually overtake the old leaves which will die/be resorbed by the plant. Then a bright daisy-like flower will emerge from the crack between the two leaves and cover the plant like a little umbrella. After that - no water! During the dormant season.

I bought these beauties from a couple in Plumsted who grow succulents in their back yard - and sell them in their own handmade pots. Even I can see that the composition here is amazing. Thank you Chris & Annelise, I'll be back for more, for sure.

A while ago, I ordered some seeds online... things I wanted for the garden mostly (including some multi-coloured carrots which have sprouted!). On a whim, I tacked on a packet of mixed lithops seeds, no idea what species they are. The seeds are so tiny I could barely see them! Maybe a quarter of the size of a typical sand grain? Smaller than a foram? Smaller than a Cretaceous radiolarian. I gently sprinkled a few onto a surface of wetted cactus soil, covered it with a plastic bag, and waited. Here are the sprouts 15 days after "planting".

They will take 3-5 years to achieve the adult size you see above.