Neoichnology II: Revenge of the Scorpion

While organizing my geo-picture collection, I ran across a Death Valley picture I hadn’t shared that ALSO tied in with the whole neoichnology trend from yesterday. The picture below is from the dune field in Death Valley, and shows a scorpion track left in a fine-grained sand substrate:


You can see the somewhat confusing scratch marks along either side of the trail; I guess having several pairs of legs skittering away all at once makes for some convoluted footprints. The central furrow in the trackway is from the tail. I’ve been told, though I’d have to look up a cite to be sure, that scorpions commonly only produce tail-dragging marks at night (or when it’s cool and shady), and will hold their tails up off the ground during the day. Thus, in SOME cases, you might be able to tell whether it’s night/day in the rock record depending on the scorpion trace fossil.

Seeing this picture again reminded me of a paper I had read a while back. Davis et al. (2007) wrote up a pretty nice summary paper of some experimental work on the neoichnology of some modern terrestrial arthropods. The point of their work was to investigate the effect of substrate conditions on both the morphology and taphonomy of the resultant traces. They used a variety of trace-making bugs (including Giant African Millipedes, Cockroaches, Tarantulas, Woodlice, and some Emperor Scorpions) to investigate the generalized range of bug bauplans, and they used a range of grain-sizes and moisture content to simulate varying substrate conditions, producing two taphoseries: A dry- to dampground series, meant to mimic fully subaerial conditions, and a soft- to firmground, meant to mimic a transitional state similar to a recently flooded overbank setting.

The approach used to produce the substrates was one I had never encountered in the literature before, and seemed fairly rigorous. For the subaerial setting, they simply sprayed an amount of water onto the substrate, and then the critter walked across it. For the transitional setting, though, they put 2 cm of sediment into the tray, removed it, filled the tray with 2.5 cm of water, and then sprinkled the sediment back into the tray. After allowing it to stand overnight, the siphoned off the water, and then proceeded to dump the animals into the experimental setup at regular intervals after the siphoning (0 mins, 60-75 min, 120-150 min).

The picture below is taken from Davis et al (2007; p. 292), and shows the dry to damp series for the Scorpion:


This picture is from Davis et al (2007; p. 293) and shows the soft- to firmground series:


The authors conclude that the increasing firmness of the substrate, related mostly to moisture content, exerted the largest control on the resultant morphologies. Overall, the authors saw a decrease in track width (or track row width) with increasing moisture. They also found, unsurprisingly, that big heavy animals make the best, most preservable trackways in these conditions.

The potential utility of the work is pretty interesting: maybe we could make interpretations of substrate moisture content, qualitatively at least, in some very special trackway settings, letting us get into some nitty gritty paleoenvironmental interpretations. Of course, all the old caveats would apply, least of which not being the fact that we don’t really KNOW how big the animal was or its specific physiology. Still, Davis et al. (2007) suggest a good starting point for this sort of work, and I think make a good case for the importance of careful neoichnological research and its potential impact to sedimentary geology.

WORKS CITED:

Davis, R.B., Minter, N.J., Braddy, S.J., 2007, The neoichnology of terrestrial arthropods: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 255, p. 284-307.

Neoichnology

Wandering around the autumnal woods here, I ran across a muddy little puddle that had been visited by at least a couple of different kinds of critters. You can clearly see the weird, hand-like footprints of a raccoon, as well as a the huge footprint of an extant therapod known for it's deliciousness (a turkey). Beercap I had in my pocket for scale.



This little puddle must have been a busy place; lots of animals had stopped by for a visit. Of course, if I was feeling snarky, I might make a joke at the expense of some dinosaur track people (about the Raccoon actively stalking the turkey, who had fled in terror from its masked foe). But, I'm not felling snarky, so I won't.

On an unrelated note, is it just me, or does everyone else out there ALWAYS want to somehow ensure animal tracks get preserved? Like dump a bunch of sand on em or something, so they enter the record. Whence comes this weird compulsion, I wonder?

OzCoasts

For a bunch of debtors and criminals, those Australians can put together some slick online Sciencey type resources, man. I just found this online: OzCoasts, which is a huge database of coastal environments, including much of the geomorphic, meteorological, biological, and geological data from something like 780 coastal waterways in Australia. These data are all searchable, so it seems to be a pretty powerful set of tools for looking at a variety of environments.

They also have a pretty impressive library of general block diagrams and coastal system models, tailored for specific settings, and detailing any number of attributes, including hydrodynamics, depositional environments, and critters living in the setting. Furthermore, you can make your own block diagram, which is actually a pretty handy little tool for quickly whipping up a diagram for class. There are also whole lot of "Coastal Indicator Factsheets", including sections on sea-level rise, sediment quality, and habitat issues (among other things).

Also, they have some very nice interactive 3-D models of several localities, including Cockburn Sound and Sydney Harbor, which are both areas where a lot of work has been done. These maps include CHIRP derived bathymetry and sub-surface data, as well as details on grab-cores and samples from these localities.

All in all, there is a lot of stuff to look at on this site, and it would serve as a nice model for other databases for other geographic (or geomorphic) settings. Someone should really get on that.

Anyway, just so this isn't only text, here's a picture (from NASA WorldWind) of the Gascoyne River Delta:


And here's an unknown river a little south of the Gascoyne, winding its way through some dunes.

Apparent Dip: Blog of Note

Congratulations to Apparent Dip, who is the "Blog of Note" as awarded by Blogger for October 14, 2008. Now that you're famous, I hope you can still find the time to blog...

I wonder what you win?

Fish Five Miles Down

The "deepest ever fish on film" was mentioned on the NPR website recently, and I thought I'd pass it along so that everyone could start celebrating early. The fish, a Liparid (or Snailfish) lives at around 7,700+ meters (that's nearly 5 miles) down in the Japan Trench.



The footage was taken by a "free-form lander", which is described in the news story as being some sort of a lunar lander type of device that they just hork off the side of the ship and come back for later. It's a weird looking fish, and some of the footage is available for viewing.

Wyoming Vista

Just a little picture to cleanse the Thursday-afternoon palate, straight from Wyoming to the interblogospherenet.

Earth Science Literacy

So the first Draft of the Earth Science Literacy Document is up and available for comments (right...HERE). This is an NSF-supported effort meant to explicitly spell-out the state of our knowledge of the Earth in a way that everyday, non-specialist citizens can understand. Effectively, it's a list of the Things Folks Should Know About the Earth, and is meant to go along with all the Ocean, Climate, and Atmosphere Literacy work that was recently undertaken.

Anyway, the document identifies 8 Big Ideas in the Earth Sciences, which I've summarized below. These ideas are supplemented by a series of Supporting Concepts that flesh out the overarching concept. The 8 Big Ideas (paraphrased) are:

1) Earth is 4.6 Ga, and the rock record contains its history.

2) Earth is a complexly interacting system

3) Earth is a continuously changing planet

4) Earth is the Water Planet

5) Life evolves in concert with the evolving Earth, and similarly modifies and effects the Earth in turn.

6) Humans depend on Earth for Resources

7) Earth Science helps us understand and mitigate natural disasters

8) Humans are a significant agent of change on the Earth

It's a pretty nice list, in my opinion, and would make a great hand-out in an undergrad intro class. I also like how the foundational concepts of Plate Tectonics and Evolution are distributed throughout the supporting points, driving home the unifying power of both of these fundamental concepts.

The only (vague) comment that I have would be that I'd like to see maybe a little more about radioactive decay and radiometric dating. Maybe not as a BIG IDEA, but as another supporting point (somewhere, maybe under #1?).

Importantly, this is only a draft, and if you've got any concerns or issues or burning bits of illumination to add, we have until Oct 31 to make comments, so get to it!

I'd also be more than happy to hear what you guys think about it too, of course.

EDIT: Here are some links to chew on! The Ocean Literacy Network, and their Ocean Literacy Statement; The Atmospheric Science Literacy Framework and their Statement; and the Climate Program Network, and their statement! Whew! That's a lot of statements!

Community Sedimentary Model for Carbonate Systems

I'm sure everyone has already read up on the CSDMS from the most recent "Sedimentary Record", but I thought I'd post a link to their website right here. It has some fairly slick pdfs of the talks, posters, and Working Group Summaries, which make for some pretty nice bleeding-edge "State of the Strata" resources for Carbonate naifs (like myself). Though it's not up yet, the Group says they hope to have a PDF copy of the resultant white paper up soon, so stay tuned!

Sarah Palin - Dinosaur Rider

Ron Numbers, a scholar who studies the History of Science and Religion, and author of The Creationists, has a pretty nifty little assessment of Palin's creationist bullshit.


Enjoy!

Kinematic Theory of Unsteady Seperation

One of the problems with so much of our understanding of hydrodynamics (and, more broadly, all Earth Processes) is that we have to make so many damn generalizations and simplifications. Of course these are important first steps in developing greater insight into the world, but sometimes, you just want to have a firm grasp on what the hell is going on, you know?

Two recent papers, Weldon et al. 2008 and Lekien and Haller 2008, have made some impressive advances in our ability to describe and predict flow separation under unsteady conditions; the ramifications of this are pretty big, and if you've got a secret love of hydrodynamics (like me), it's pretty exciting stuff!

Fundamentally, flow separation occurs where a fluid is moving away from a solid boundary of some sort. In sedimentology, this is commonly illustrated by the behavior of a fluid flowing over a bedform, such as a dune in a river. While we have always had a general, qualitative appreciation of the effects of flow separation on bedform dynamics (i.e., back-flow eddies in the lee-sides of dunes, Kelvin-Helmholz instabilities in turbidity currents, etc), a quantitative description of the behavior has been lacking; as such, modeling these systems is difficult, and requires some arm-waving.

In fact, the nearest thing we've had to a kinematic solution for flow separation was Prandtl 1904. Using some mind-bogglingly complex math, ol' Prandtl was able to come up with a solution for laminar boundary separation in steady 2-D flows. Sentences like the previous one make sedimentologists involuntarily twitch: "laminar" and "steady" are both exceedingly rare in the natural world, making Prandtl's work useful for gross generalizations, but frustratingly weak in unsteady and turbulent flows.

Now, however, Weldon et al. and Lekien and Haller have both shown numerical and -most importantly- EXPERIMENTAL data that advances a kinematic theory of unsteady separation, allowing us to accurately predict separation points in unsteady flows. Furthermore, part of Weldon et al. (2008)'s work has shown that their kinematic theory accurately predicts flow separation in flows that are kinematically equivalent to turbulent flows.

Lekien and Haller (2008) also apply this particular kinematic theory to boundary separation models of the North Atlantic geostrophic current AND to boundary current separation and reattachment in Monteray Bay, based on field data collected from real live currents.

The public take on this (see here for MIT's own press release on the research) is focused on larger, non-geologic issues, such as increasing fuel efficiency by decreasing shear drag on cars. However, for selfish reasons, it will be particularly exciting to see where this sort of research leads to in the sed realm. We might finally start to home in on some robust models of mixing layer dynamics in sediment laden flows, or even (bestill my heart!) start being able to really interrogate bedform morphodynamics and evolution under realistically complex flow conditions!

WORKS CITED:

Weldon, M., Peacock, T., Jacobs, G.B., Helu, M., and Haller, G., 2008, Experimental and numerical investigation of the kinematic theory of unsteady separation: Journal of Fluid Mechanics, v. 611, p. 1 - 11.

Lekien, F., and Haller, G., 2008, Unsteady flow separation on slip boundaries: Physics of Fluids, v. 20