Inspired by a recent search string

I was looking through my visitor log, and while I don't have as many weird and wonderful search engine hits as other blogs, I did see a phrase that fits with some of the sedimentology topics I've been thinking about for a blog post. This particular phrase:

Why does wet beach sand look dry in front of your footprint?

Is one of those fun, yet hard-to-conceptualize questions that requires a little understanding of how granular materials behave. In particular, the behavior of saturated sand. The process that makes the wet beach sand look "dry" when you step on it is called dilatency. You step on the saturated sand and some of the sand gets "squished" beneath your feet. Some of the sand is compressed downwards - but, due to the granular behavior of sand, some of it is forced sideways (in a process called "lateral yielding") and this sand forces some additional grains to get shoved upwards. The spot away from your foot is not being forced down, so it's easier for the sand to be pushed upwards to make room for all this sand forced out sideways.

The small spaces (interstices) between sand grains that are forced out and up become larger (dilatency) - more space between grains means that the water can't fill those other spaces and the sand appears dry. See the illustration below:


Since water fills all the open space between the grains, the sand appears dark and wet. You push down on the sand with your foot, and force the sand outwards:


The grains forced out and up now appear dry - there isn't water between those grains (thanks in part to gravity and the lack of sufficient surface tension in water to pull it up into those spaces). If you stop moving, or take your foot away, you may notice that some of the sand "sinks" back downwards as the grains re-arrange themselves again, allowing the grains to settle together and the water re-fills those empty spaces.

If you try this on mud - it doesn't have the same effect. Clay particles behave quite differently compared to sand-sized particles. But that's a post for another time. For now, it's important to note that the behavior of granular materials like sand depend largely on the contacts between individual grains. This "internal friction" helps sand stay in a pile (it's angle of repose), but when they are saturated (when all the voids are filled with water), this friction essentially disappears. The sand is now very susceptible to external stresses (like your feet) and move easily. Thus, when anyone claims that the Coconino (and other large sandstone formations) was deposited in sea water, then eroded prior to lithification has either not walked on the beach, or does not fully understand the behavior of saturated sands.

Which reminds me - I need to spend some time talking about things like "lithification" and "consolidation" since these terms are often mis-used or conflated. They are two different processes - sometimes related, but they imply rather different behaviors.

Origin's Sesquicentennial

150 years ago today, Darwin published "The Origin of Species." It was one of those seminal moments in science where an individual managed to put into words how we might understand the way the world works. I don't think Darwin got everything "right," nor was he working in a vacuum. His insights were built on observations both of his own and others. But he did eloquently illustrate the concepts of natural selection and how it might work and explain the diversity of life we see today.

It's too bad we have so many people (some of them well-intentioned, some of them much less so) opposed to the concepts that have been borne of this work.

Ornaments

Another bonus of using strong, tiny magnets? Putzing around with 'em to make geometric shapes.



Happy holidaze. Bonus: they spin quite freely.

Chaos and Sedimentology

I'm rereading the book "Chaos." Last time I read it I was in 10th grade, but now I've got a little more math background, so the underlying mechanics are easier for me to describe.

A few things have leaped out at me:

1. The concepts related to chaotic systems, such as the "Butterfly Effect" didn't take long to enter and become part of a "public consciousness" regarding the world around us


2. I'm not sure if this is because I've not finished rereading the book, or its place as an early summary of the work, but I think they're overselling the concept of "dependence on initial conditions."


3. One of the more powerful ideas here is in scale independent behavior - especially from a geologic standpoint (see the post in Clastic Detritus regarding sediment plumes in the GoM for an example).


4. For my own scientific work, I think I may need to change my thinking about chaotic systems and fractals.

I think more attention needs to be paid to the "boundary conditions" controlling chaotic systems. Especially with regards to sediment deposition and transport. While a turbidite displays chaotic behavior, there are often predictable results from these systems - Bouma spent a great deal of time describing the general pattern often seen in turbidite deposits. This holds for other sedimentary systems: you may see all sorts of variation within an eolian deposit, but you're also not likely to see certain things. So while any particular eolianite may display a wide variety of textures and internal structures, there are specific patterns that will usually show up (not every single time, perhaps). The system may be chaotic and display variety of internal features, but you're not likely to produce a diamict, or massive clays as a result of wind-deposition. The mechanics and source of materials form some of these boundary conditions.

Chaos and fractals are fun stuff. But, the concepts are abstract enough that it's easy to misunderstand and apply them. I'll be exploring some of these features in future posts.

Magnetic Sediments

I've been poking around with magnetic sediments recently. There's a bit "to-do" going around Quaternary geology circles regarding a potential bolide impact during the Younger Dryas -YD - (ca. 13,000 years before present - YBP). Whether or not this actually happened, and whether this has any lasting climate and ecological impacts have yet to be sorted out. However, the presence of magnetic materials in high concentrations in sediments from the YD is intriguing purely from an academic standpoint. So I've been poking around the late Pleistocene (ca. 20,000 to 10,000 YBP) sediments in the UMV, looking at what's in the magnetic fraction.

So far things look interesting - no confirmation of micrometeorites or other impact debris, but definitely lots of magnetic materials in certain layers. The difficult part is going to be analyzing these grains under an electron microscope or some big machine to see what they're made of.

Here are a few pictures of the extraction process (these are slightly modified from A. West's methods link to PDF)

The bulk sample - the small bucket contains another sample that I dried at about 100°C to determine moisture content of the portion soaking in water.

The basic method involves sticking some strong magnets in a bag...


...then placing the covered magnets into the wet sediment slurry to pick up magnetic grains.

Withdrawing the magnet reveals a big batch of magnetic grains stuck to the outside of the bag. These are placed in another container of clean water. Pulling the magnet away allows the grains to fall into the clean water.

Some of the extracted grains. Once the water evaporates, I can pick out individual grains (with a small, moistened brush or needle).

I haven't started extracting individual grains yet - I'm in the process of refining my extraction and separation methods - doing this all by hand is both slow and not as systematic as would be preferred.

Rainbow

Nothing much to say right now - I have a lecture about soil shear strength I need to prepare. I plan to put some of the points about the strength of unlithified materials into another discussion about sediments, but for now here's a lovely rainbow I saw from my front steps this summer:

Logical Fallacies

Here's a quick description of some commonly employed logical fallacies. I've observed similar arguments made by scientists on occasion, so it's useful for more than just E/C issues.

Syntectonic Deposition

One of the major aspects of the "flood-geology model" is that the Paleozoic and Mesozoic sediments were laid down by this giant flood. The major structural features like the faults of the Rocky Mountains, Great Basin, and recent Orogenic (mountain building) events occurred immediately after the deposition of all this material. Some young-Earthers lump the Cenozoic (all the way to the Pleistocene) units into these flood deposits. However, Whitmore and some others recognize that many of these Cenozoic sediments lie atop these major structural features - thus they have to be younger. While I think their base assumptions about the amount of time is ridiculous, I can't disagree that many Cenozoic sediments post-date most of the major structural features in the Rocky Mountains.

If their numeric time frame is correct, then we have large piles of unlithified sediment being tossed about by these large structural features. How you achieve brittle deformation (faults) in unlithified sediment is a subject for later. But, for the sake of argument, let's assume we have major structural features forming in this stuff. One of the great places to see examples of Syntectonic sedimentation (deposits of sediments occurring at the same time as structural deformation) is in Echo Canyon, Utah.



Notice how the beds in the left-most bluff are nearly horizontal, and increase in the magnitude in dip as you go towards the bluffs on the right. Here we see deposition off of an uplifting block of crust - as the crust is thrust upward, the angle changes (this is somewhat oversimplified, but the facts are illustrated here: the angle changes, and can be traced back to tectonic uplift). The material being uplifted are some of these younger blocks of sediment. The materials making up these rock cliffs are sands, silts, and even large, rounded cobbles:



How do you form big, round cobbles from unlithified material? It's not a solid, coherent material: therefore forming well-rounded pieces is virtually impossible (I say "virtually" since there are rare examples). There is no evidence that these thousands of feet of rock were unlithified during faulting. None. And yet the YEFPs try to force their limited observations into a rather dogmatic model. All of the evidence points to a rather straightforward explanation, yet they demand an alternative, non-functional model. This is not, nor will it ever be, science.

Physical Constants

If I were to try and revolutionize science, I wouldn't bother with the higher order observations such as stratigraphy, landscape evolution, or even biological evolution. Because these are all tightly-bound, and widely agreeing observations. They all point to an old earth, and changes in organisms over long spans of time. Nor would I try and sow doubt by pointing out minor and insignificant anomalies. By pecking at the surface of science, YECP's are doing little more than rearranging the deck chairs on the Titanic. Sure, it may look different, but the icebergs are still in the water, and the boat is still moving forward.

Instead, if I were to try and disprove all of these observations, I would attack the physical constants. If I could demonstrate that universal "constants" such as gravitation, nuclear strong and weak, even electrostatic forces varied over time, only then would it be possible to cast sufficient doubt over the concept of Unformity, providing an empirical and non-religious basis to support a young-Earth flood model.

If nuclear decay was faster, that means more heat - if we could show heat-flow through rock was reduced, then perhaps all this radioactive decay wouldn't have cooked all of Noah's family and the animals headed to the Ark. Unfortunately, we are faced with the problem of large bodies of intrusive, igneous rocks. To quickly cool (within a thousand years or less), heat dissipation would have had to be higher. Thus not only would we have to demonstrate heat flow was less, we then have to demonstrate how it also (either concurrently, or immediately following this flood) sped up. We could, perhaps, avoid some problems by focusing on the elements in rock forming minerals, such as silicon, iron, and magnesium - this way we can concentrate these variations within the crust. Or, perhaps there is some multiplier attached to these constants that can change - thereby altering the magnitude and direction of these constants.

So what is the value of this "constant" modifier? Well, the only source of information that suggests this is possible comes from some interpretations of biblical Genesis. We don't see consistent (let alone any) and, importantly, independent evidence of this modifier in action. The only record is a religious text (and, depending on which chapter you read, a widely varying one). Thus, it fails the basic requirement of science.

But, if YECP's could effectively demonstrate that physical constants could change - then things would at least become more interesting. Instead, nearly 60 years after Morris' "Flood Geology" book, we are still faced with the same inane arguments about the same rocks, the same claims, and the same lack of basic science (albeit dressed up with fancy new words and some vaguely scientific techniques).

Ecophenotypy and Phenology?

So, are organisms that display a variety of ecophenotypic variation well-adapted to climatic shifts towards more seasonality?

Stokes Law

I like Stoke's Law. It's one of those fundamental relationships that is very powerfull:

A particle, falling through a fluid under its own weight. There are two fundamental forces at work: gravity, which tends to accelerate the particle downward, and an opposing drag force, which is a result of the density of the fluid through which the particle falls. As the particle falls downwards, it will accelerate due to gravity until the drag force (which is velocity dependent) equals the gravitational force. At the point the two forces are equal, there is no more acceleration, and the particle continues downward at a constant speed (uniform motion). This is the object's terminal velocity. It's the basic principle upon which parachutes are based. It also explains why a penny dropped from the top of the Empire State Building won't bury itself into the concrete below. The drag of the fluid (air in this case) balances out gravity, and the object falls at a constant speed.

This same principle applies to sediments deposited in air or water - they fall through a column of water at a constant velocity. The equation that describes the drag force (F_D) on a sphere is:

F_D = C_DAρv_s²/2

Where C_D is the drag coefficient, A is the cross-sectional area of the sphere (A=πr²), ρ is the density of the fluid, and v_s is its velocity. The gravitational force (F_W) acting on the sphere - its submerged weight - is described by:

F_W = VΔρg

Where V is the volume of the sphere (4πr³)/3, Δρ is the difference in density between the sphere and the fluid, and g is the acceleration due to gravity (9.8 m/s². For uniform motion, then, F_W = F_D. And if we know the density and size of the sphere, the density of water, gravitational acceleration, and drag, we could estimate how long it would take this particle to fall through a column of water.

Now it would be tempting to calculate the settling velocity for a tiny sand grain, or clay particle and then infer a time required to deposit a given thickness of sedimentary rock from this. The real world is not quite as simple as this. However, a nearly spherical grain 0.01 mm in diameter (a silt-sized particle) falling through non-turbulent water would reach a terminal velocity of about 0.01 cm per second. Thus, to fall 200 m (the average depth of the continental shelf), the grain would take about 2,000,000 seconds (20,000 cm/0.01 cm s^-1). That's more than 23 days.

Now it's also tempting to calculate the settling velocity for a clay-sized particle (it would take about two orders of magnitude longer to fall 200 m (~230 days), but - as I've said before - the real world is a little more complicated. But, a flood model would do well to account for Stoke's Law: for a global flood would create a great deal of turbulence, and while some super-concentrated muds may settle quickly, some mud would remain suspended for much longer. As Noah supposedly waited for the Dove to return - both times - this mud would remain suspended far longer than the sands and gravels and everything else that supposedly was deposited in this world-wide event. Thus, at the very end of this "flood," a thin drape of mud should cover much of the world (those of you who have seen the effects of flooded rivers (or flooded basements) know this well. And yet, we do not see any evidence for a world-wide mud drape anywhere! While I can understand the desire of YEFPs to reconcile the natural world with their biblical beliefs, it just ain't gonna happen. Ever.

Those that attempt to explain the world's geology as a supernaturally-caused event MUST violate the physical constants that control our world. Simple things like gravity. And heat. Once you claim that physical constants are not constant, the laws of physics cannot be applied to anything. So those that use the laws of physics to justify violating those same laws are caught in a self-nullifying situation. Catch-22. Uniformitarianism works because it cannot violate the laws of physics. Ever.

A brief review of "For the Rock Record: Geologists on Intelligent Design"

At GSA, I picked up a copy of a new book edited by Jill S. Schneiderman and Warren Allmon, "For the Rock Record: Geologists on Intelligent Design" (Amazon link)

I read it in about a day and a half (I did have a four hour flight, after all). It's a collection of essays on how geology is in full support of evolution. There are some very good descriptions of the nature of science, and how concepts such as ID and flood geology are not science. It's not technical, and likely approachable by the general public. While I wasn't sold on all of the suggestions about how to counter the ID movement, I do think it provides an invaluable service to the geosciences. Any middle school, high school and college earth science professor would do well to at least read this book and ponder some of the topics discussed. We need more books like this - especially in a time where the growth in the number of active young-Earth flood models and "flood geologists" is unprecedented.

One of the more salient points was that, given the deep roots of religion in this country (the vast majority of Americans claim a belief in some supernatural deity), is it any wonder that the "Wedge" strategy has been so successful? If the public believes that they can either 1) believe in God or 2) accept science, is it any wonder that they choose #1? It's a false dichotomy, but one that has been effectively used by ID and others to gain support for their ideas.

Footprints in the Sand

Fossil footprints are among the most interesting traces of ancient life. They can tell us about how an animal walked and, based on the distance between the footprints, we can estimate how quickly the animal may have been running. To be formed, the ground has to be soft enough for the animal to deform the soil, but not so soft as to collapse after the animal's foot is removed. To be preserved, the footprints need to be covered relatively quickly, or erosion can quickly remove them.

One interesting argument made by the YECFP's is that these footprints could have been made underwater. By studying a salamander in a tank, on a sandy substrate, they made dozens of measurements of footprints, looking at how the tracks formed. It was interesting enough from an empirical standpoint that it was published in Geology (Brand and Tang, 1991). The basic findings were indeed intriguing. Some footprints may form subaqueously (underwater). But Brand made a big leap - he compared the lab experiments to the Coconino, and suggested the tetrapod footprints in the Coconino were also made subaqueously. This was thoroughly refuted by comments by Lockley and others (Geology, 1992). But this hasn't stopped the YECFPs from insisting the Coconino was subaqueous (therefore NOT eolian at all...). Unfortunately, their arguments about footprints do not "stand up" very well, when actually LOOKING at the Coconino footprints.

Footprints in the Coconino Sandstone are generally viewed as being formed on moist sand in an eolian environment. Here's an example from Wikipedia (http://upload.wikimedia.org/wikipedia/commons/c/c5/Coconino_Sandstone_with_footprints.jpg)



The footprints are all lined up with the toes pointing to the right. Note that the entire footprint is well-preserved, front to back. You can see little "chips" of the sandy surface pushed backwards behind the animal's heel as the animal propelled itself forward. Also, note the low relief "ripples" running left to right in the image. These sedimentary structures are the result of fluid transport of a granular medium (in this case, wind ripples in sand). They can form underwater too. But they form perpendicular to the direction of fluid flow. Thus, the wind was blowing top to bottom (or bottom to top) in relationship to the animal's movement.

What does a footprint, formed underwater, with a flowing current look like?

My feet are being covered by the gentle waves on a beach - the sand along this spot on Lake Superior is not unlike the sand that makes up some of the Coconino (in terms of grain size and mineralogy). Note how the water is more turbulent around my footprints. As the waves recede, they leave behind tell-tale signs of the turbulent water:


Unfortunately, I didn't get a picture of my footprints in this example, but the scours left by the pebbles demonstrate the structures you would find if flowing water were present when an animal places its foot on the sandy bottom: prominent scours form as a result of the turbulence and redirected current. You can try this yourself on any sandy beach - what do your footprints look like? If you're out walking your dog, or other pet basal tetrapod, look at their footprints on dry land compared to those made underwater. The water has a tangible effect. Especially if made in sand, not clay-rich mud.

Compare that to the footprints in the Coconino at the top: no scours, no evidence of water being redirected around the animals feet. Even a very gentle current (the waves were moving no faster than a person could walk) should affect the substrate. But we se NO evidence of this in the Coconino Sandstone. While this little analogy doesn't completely falsify the subaqueous footprint argument, it does point to some serious flaws and demonstrate a more rigorous analysis of the Coconino footprints is required before any underwater formation can be seriously postulated.

A modest defense of Eolianites

One of the most prominent targets of YEC flood-pseudoscience (henceforth YECFP) is the Coconino Sandstone - a prominent wall-forming rock formation in the Grand Canyon. This thick sandstone unit is widely interpreted by geologists to be the result of eolian (wind-blown) deposition. If one were to attempt a flood-origin for all the major sedimentary rocks in the world, eolian deposits pose a difficult hurdle in their water-logged models. Not surprisingly, the Coconino has been a target for years in flood-research circles (really, just a handful of prominent researchers - maybe six trained geologists and a band of amatuer enthusiasts). Their goal is to demonstrate the Coconino was, in fact, formed in a marine environment.

Most of their arguments are classic anti-science canards: creating false dichotomies: (if it wasn't purely eolian, it MUST have been marine), arguments from authority: (if this "trained geologist with a PhD" says it might not be eolian, then it MUST have been marine), and misrepresentation or selective use of "data:" (most eolian cross-beds form at the angle of repose, since the cross-beds in the Coconino are not at the angle of repose - as seen in modern sand piles - then it MUST have been marine [or, more recently] the presence of ooids, euhedral dolomite, and mica in small sections of the Coconino [I note, with great interest, that they have never, as of yet, stated exactly WHERE stratigraphically they have been looking] can't form in eolian environments, then it MUST have been marine).

In general, the work to date has been of dubious quality. Some of the thin section work and mineralogy is not bad, in terms of technical skill. The sections are well-made, the photographs are clear and relatively sharp. But the application of sedimentary and stratigraphic principles is poor at best. Most of it is wrong.

This will be the first post in a series devoted to sedimentary analysis and interpretation of eolian deposits. In particular, I'll spend some time talking about how a geologist should study rocks in outcrop and compare these methods to those employed by YECFP's to highlight the flaws in their claims/interpretations.

For now, I'll leave you with a photograph of the Wingate Sandstone - another eolian deposit from the Early Jurassic (about 200 million years old):



In the photo above, you'll see some classic eolianite features: huge multi-meter high cross beds. You also may notice a few reddish bands: one at the base of the pinnacle near the feet of the students, and another about halfway up. These reddish layers are "interdune" deposits. Laid down during a period of wetter conditions - perhaps as a groundwater-fed "oasis" surrounded by large fields of sand, or perhaps during episodes of greater precipitation. These interdune deposits contain a great deal of other minerals including ooids, carbonate minerals, and mica grains. This is not surprising, nor should it be. I'll explain why later. However, it illustrates one common mis-application of science. By looking exclusively at these thin interdune layers, one might be tempted to make a particular interpretation at odds with the rest of the formation. You CANNOT take one small part and make sweeping generalizations about the whole. That is not science. Generously, I'll call it pseudoscience (often lazy pseudoscience at that). When used to further a particular agenda, it's dishonest and deceitful. On occasion, this has been done by people doing real science. Most of the time, however, when faced with overwhelming evidence to the contrary, real scientists relent - or at least stop publishing their falsified claims.

It appears that the YECFP's have not changed their tune despite being consistently rebuffed by additional facts for the past 50 years. That is not science, yet these YECFP's claim to be doing "science." This is a cargo-cult of pseudoscience. They may use methods that appear scientific at times, but the process is not actual science. It is risky thinking that can lead to a total abandonment of what we know about the physical mechanisms that govern the formation of rocks, fossils, even precious resources like gold, oil, and uranium. To hold to a flood-model of geology is to abandon logic and empirical evidence in favor of a particular aspect of the Christian faith. And by so doing, place the entire world at risk of never finding needed resources, or identifying the potential risks that society faces.

Phizix is phun

One of my roles at the University I'm currently teaching at is that of lab/discussion instructor for a Calculus-based 2nd semester Physics class. It's a small department (without a separate earth sci/geo dept), but the people are great to work with. Plus, I get to learn and review a whole bunch of physics that I've spent the last few years forgetting as I worked on my dissertation.

Science is fun for the mind. Geology draws on biology, chemistry, physics, math - it is the ultimate applied science. So how does a sedimentologist/paleontologist teach physics? The first part is easy - I have the answers and solutions beforehand. The second part is harder, but much more important. I can't just hand out a problem set or lab activity and then disappear, waiting for them to hand in their work. I have to answer their questions about the activity. Which means I have to understand the problem set at a level beyond just the answer. I have to be able to identify whether the students' thought process will lead them to a proper solution - and help extract them from an untenable solution attempt, no matter what mess they may have gotten themselves into. Ultimately, I have to understand how to solve the problem, but I also have to understand how an undergraduate views and may attempt to solve the problem.

Plus, when we (as geologists) draw a geologic cross section, or a sedimentary particle falling through a column of water, we are constructing a physical model of how the world works. The skills required for successful analysis and problem-solving in physics are similar to those of all branches of science: identify the desired outcome, lay out the steps required to reach a solution (including formulae, quantitative estimations, etc.), solve the problem, check the calculated/estimated answer to what may be reasonably expected (and revise/retry if necessary). It's good exercise for the scientific mindset.