A paradigm switch on the simple seds

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

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

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.)