December 14, 2007 | David F. Coppedge

Geology Sinks in the Mud

Question: what is the most abundant sedimentary rock in the world?  Follow-up question: what would happen to the science of geology if the consensus theory of how this most abundant sedimentary rock was deposited turns out to be wrong?  Prepare for a paradigm shift: experiments have shown mistakes in long-held assumptions about mudstone formation.

Here’s what Macquaker and Bohacs said in Science1 about a paper in the same issue by Schieber, Southand and Thaisen:2 On page 1760 of this issue, Schieber et al. document a mechanism for depositing mud that is at odds with perceived wisdom.”  Later, “These results come at a time when mudstone science is poised for a paradigm shift.”  What they found is that “Mudstones can be deposited under more energetic conditions than widely assumed, requiring a reappraisal of many geologic records.”

Mudstone is made up of very fine particles, typically just microns in diameter.  Think tiny clay particles in muddy water in the ocean or a lake, slowly settling down in calm water to the bottom.  Over long periods of time, the mud gradually builds up, micron by micron, millimeter by millimeter, leaving very fine strata (laminae).  It compacts and compresses and sometimes dries out.  That’s where mudstone and shale came from.  That’s what they thought.  Schieber and team decided to test these ideas with flume experiments in the laboratory.  Earlier experiments used centrifugal pumps, but these have a tendency to break up the clumps of clay particles, called floccules.  It’s these floccules, however, that turn out to be essential to understanding mud transport and deposition.

This time, the team used a “racetrack flume” at Indiana University specially devised to eliminate the breakup of floccules.  They discovered that rapidly-moving currents can stratify mud deposits in ways that mimic slow, calm-water settling.  Here is the abstract:

Mudstones make up the majority of the geological record.  However, it is difficult to reconstruct the complex processes of mud deposition in the laboratory, such as the clumping of particles into floccules.  Using flume experiments, we have investigated the bedload transport and deposition of clay floccules and find that this occurs at flow velocities that transport and deposit sand.  Deposition-prone floccules form over a wide range of experimental conditions, which suggests an underlying universal process.  Floccule ripples develop into low-angle foresets and mud beds that appear laminated after postdepositional compaction, but the layers retain signs of floccule ripple bedding that would be detectable in the rock record.  Because mudstones were long thought to record low-energy conditions of offshore and deeper water environments, our results call for reevaluation of published interpretations of ancient mudstone successions and derived paleoceanographic conditions.

One reason the theory has been muddy is that there are 32 variables to take into account.  It’s a fundamentally complex system.  Floccule formation, for instance, relies on variables such as “settling velocity, floccule size, grain-size distribution, ion exchange behavior, and organic content” as well as particle concentration and the intensity of turbulence.  Other variables affecting the outcome include electromagnetic properties, biological material present, chemical composition, and more.  The scientists did the best they could controlling variables.  They tried distilled water, lake water, and salt water, with various types of mud particles.  They watched what happened on all sides of the flume, including looking up from the bottom, and examined the floccules with electron microscopes.

Previously, geologists thought that mudstone had to be deposited in calm water because currents would disrupt the previously-deposited mud on the seabed or lakebed.  Not so.  These experiments showed that laminated mud can be deposited under currents strong enough to transport sand particles – orders of magnitude larger than mud particles.  Floccules can actually grow up to the size of sand particles.

Mudstones can be deposited under more energetic conditions than widely assumed, requiring a reappraisal of many geologic records.

A glimpse at the implications of this paradigm shift can be gleaned from these quotes:

  • A century ago, Henry Clifton Sorby, one of the pioneers of geology, pointed to the study of muds as one of the most challenging topics in sedimentary geology.  Today, with our knowledge clearly expanded, muddy sediments are still considered highly complex systems that may require as many as 32 variables and parameters for a satisfactory physicochemical characterization.  More research may clarify interdependencies between a number of these parameters and may allow us to consider a smaller number of variables, but the fundamental complexity of muddy sediments is likely to remain.
  • Mudstones constitute up to two-thirds of the sedimentary record and are arguably the most poorly understood type of sedimentary rocks.  Mudstone successions contain a wealth of sedimentary features that provide information about depositional conditions and sedimentary history, but presently we lack the information that would allow us to link features observed in the rock record to measurable sets of physical variables in modern environments.
  • It appears that irrespective of what drives flocculation in a given experiment, flocculation provides deposition-prone particles without fail over a wide range of experimental conditions.
  • Our observations do not support the notion that muds can only be deposited in quiet environments with only intermittent weak currents.  Instead, bedload transport of flocculated mud and deposition occurs at current velocities that would also transport and deposit sand.  Clay beds can accrete from migrating floccule ripples under swiftly moving currents in the 10 cm/s to 26 cm/s velocity range, a range likely to expand as flows with larger sediment concentrations are explored.
  • Whereas the clay beds formed in our experiments consist of downcurrent-inclined laminae, they appear to be parallel-laminated once fully compacted (Fig. 4A).  Because floccule ripples are spaced 30 to 40 cm apart, ancient sediments of this origin are likely to appear parallel-laminated (Fig. 4C) as well.
  • Detection of ripple-accreted muds in the rock record will require carefully defined, and yet to be developed, criteria.
  • In the course of two decades of detailed studies of shales and mudstones, one of us has seen comparable low-amplitude bedforms (Fig. 4D) in shale units that were deposited in a wide variety of environments…. This suggests that mud accretion from migrating floccule ripples probably occurred throughout geologic history.
  • Many ancient shale units, once examined carefully, may thus reveal that they accumulated in the manner illustrated here, rather than having largely settled from slow-moving or still suspensions.  This, in turn, will most likely necessitate the reevaluation of the sedimentary history of large portions of the geologic record.

As if these issues are not daunting enough, Macquaker and Bohacs added this thought:

The results call for critical reappraisal of all mudstones previously interpreted as having been continuously deposited under still waters.  Such rocks are widely used to infer past climates, ocean conditions, and orbital variations.

In short, a huge tower of interpretation, touching on fields as diverse as climate change, earth history and even solar system dynamics, has been built on a flawed assumption: that mudstones always settled out slowly in calm water.  Now that the assumption is shown to be unfounded, it is not just the geologists who will have to consider a paradigm shift.

Speaking of mud, Live Science reported the discovery of undersea mud waves in the Arctic, an “unexpected surprise.”  In a quizzical inversion of the above story, scientists thought strong currents were required for such things; “researchers had thought the Arctic was too calm to produce the mud waves,” the article stated.  “Scientists aren’t sure what formed them.”  With apologies to Thomas Kuhn, maybe it was another paradigm shift.

1.  Macquaker and Bohacs, “Geology: On the Accumulation of Mud,” Science, 14 December 2007: Vol. 318. no. 5857, pp. 1734-1735, DOI: 10.1126/science.1151980.
2.  Schieber, Southard and Thaisen, “Accretion of Mudstone Beds from Migrating Floccule Ripples,” Science, 14 December 2007: Vol. 318. no. 5857, pp. 1760-1763, DOI: 10.1126/science.1147001.

A quick conversion shows 25 cm/sec to be a little shy of a foot per second, or about half a mile per hour – a slow current.  But like they said, the speed could be revised upward when fluids with higher concentrations are tested.  Also, currents could be stronger on the surface than the ocean bottom.  Of more consequence is the fact that nearly a century of assumption has undergirded a geological foundation that is more like quivering mud than rock-solid support.

A quick look at Grand Canyon layers shows that the following (bottom to top) contain shales and mudstones: the Unkar group, the Bass formation, Hakatai Shale, Dox (the thickest formation of all), the Chuar Group, Bright Angel Shale, Supai Group, and Hermit Formation.  These represent thousands of feet of sediments.  Previously thought to have formed in calm, placid seas, it is now possible to look at these anew as having been deposited under currents of water.  Will Flood geologists now be able to say “I told you so” to their uniformitarian rivals?

The implications of this announcement should send seismic waves throughout geology and earth science.  Geologists have looked to mudstones for clues about depositional history.  Chemists have looked to mudstones for clues about the chemical history of the earth and its oceans.  Oceanographers have looked to mudstones for clues about plankton cycles and patterns.  Atmospheric scientists have looked to mudstones for clues about climate history.  Biologists have looked to fossils in mudstones for clues to evolutionary history.  Physicists have looked to mudstones for clues about geomagnetic history.  Even planetary scientists have looked to mudstones for clues about the orbital history of the Earth.  All of these have assumed that mudstone left a reliable record of slow, quiet deposition under calm water conditions.  Now what?  If their chosen methodology shepherds them not beside the still waters, it cannot restore their soul.

It may turn out that geologists can save face with further experimentation, or that they could argue that there are narrow limits under which mudstones can form that are not too far removed from the calm-water paradigm.  Remember, however, that mudstones are very complex, with at least 32 parameters to consider.  That’s the known parameters; what about the unknown ones?  To what extent can geologists infer past conditions by “reading” rocks when they don’t know the language?  And how sure can we be now that future experiments won’t upset the current paradigm again, even more radically?

There are important lessons here about the philosophy of science: particularly, the fundamental difference between the observational sciences and the historical sciences.  Even experiments as carefully controlled as these cannot prove that the Dox Formation or the Bright Angel Shale were laid down under comparable conditions.  Lab experiments are only simulations.  Many parameters cannot be controlled; others are not even known.  Science can say with some confidence that such-and-such a rock is composed of quartz or montmorillite or limestone in the present.  Describing where it came from and how it got there is a completely different kind of investigation.  Why should geology limit itself to observation of present resources and processes?

In 1825, Granville Penn, a Bible-believing British geologist, wrote that trying to understand the rock record from field observations alone is like trying to understand the history of Rome by studying scattered ruins of the empire without access to Roman historians like Tacitus.  Geology is a compound work, he argued: “it is both physical and historical, for it seeks the historical truth of a physical fact.”  He explained,

“It is evident to reason, that certainty concerning a past fact – such as is, the mode by which all material existences were really first formed, or were really afterwards altered – must be historical certainty: the subject, therefore, is no longer a subject for philosophical or scientific induction, but for historical evidence, it demands a voucher competent to establish its truth.  Now, the voucher that could establish the fact respecting the true mode of first formations, must have been a witness of that mode; but, the only witness of the mode of first formations or creations, was the Creator himself.”

(cited in Terry Mortenson, The Great Turning Point [Master Books, 2004], p. 64.)  His point is, that rather than restricting themselves to insufficient evidential resources, geologists should be willing to use the same methods of historical evaluation from the available sources that a historian would use in reconstructing the history of a past civilization.  It would be folly for a historian of Rome to ignore Tacitus, Julius Caesar, Livy or Cicero, even if the sources were dubbed biased or incomplete.  The eyewitness accounts of Rome cannot provide exhaustive information, but they provide anchor points for a basic framework of investigation.  Is it not a superior methodology for a historian to avail himself of both the extant written documents and the monuments?

Similarly, Penn argued, the works of Moses, though not a geological textbook, provide enough intersection points of geological events with human history with which to begin building a geological system.  Geologists in the 1830s abandoned that methodology – not because the data forced them to, but because they made it their choice to study only the monuments.  Well, you see where it has led.  This is just one example (try some others: 11/30/2007, 11/26/2007, 10/03/2007, 09/19/2007, 03/27/2007, 02/19/2007, 01/12/2007 – and that’s just from this year.  The story about volcanoes in 11/13/2006 was instructive, and remember the puzzle of the ultra-pure sandstones of world-wide distribution from 06/27/2003?).  Reading Geology papers is like reading Darwinian evolution papers: a little bit of data, a lot of storytelling, and frequent announcements that everything you know is wrong.

Try a change of perspective.  In a parallel world outside the mainstream geological institutions, which followed Lyell, Darwin and Huxley wholesale into materialism in the 19th century, there remains today an active body of creation geologists who still work within the framework of the written historical record.  You would be hard-pressed to notice any difference in scientific rigor in their papers.  Often there is active debate about how certain formations are to be interpreted.  Frequently they find the interpretations of the secular geologists to be untenable in light of the observational evidence.  Many of the creation geologists have PhDs, and some are more experienced in field work than their secular counterparts.  They go out to interesting sites all over America, Australia and the world, investigate them carefully, and interpret the same data – only through the lenses of a different worldview (example: 03/05/2006 commentary).  Sound interesting?  Tired of the often-contradictory secular approach?  Here are two journals where you can test the alternative: the Creation Research Society Quarterly and the Journal of Creation.  Both of these general-science technical journals frequently contain interesting and informative articles on geology and earth history.

Leave a Reply