Home Ec. 101 Revisted ~ Trumping A Lousy Report Card

My previous post on this blog described steps I took to prepare some sediment from a middle Miocene site for exploration under the microscope.  I am pursuing microfossils, particularly the shells from ostracodes (tiny crustaceans with a hoary fossil record and the temerity to still be around today).  Ostracodes are complex animals on an incredibly small scale, which explains part of my interest.  I'd also like to have some concrete evidence to back up the assertion I'm prone to make about them - "They're likely to be found in almost any sedimentary rock."  But, as of that previous post, I’d failed to turn up an ostracode in this Miocene material though, as recounted previously, I did stumble upon several fossils shells from foraminifera (single celled organisms that either secrete or build their shells, appear to have an even longer history than ostracodes, and remain in today’s fauna).  The process I went through to wash, screen, and dry the sedimentary material for analysis had all the elements of a high school Home Economics class.

When I considered how I performed in that ersatz Home Ec. class, I decided a report card was in order.

THE REPORT CARD

Grade:

C+

Teacher’s Comments:

Tony has been an enthusiastic student in this class, but, unfortunately, he seems unwilling or, perhaps, unable to take direction.  Though I have advised him to slow down, to think before acting, and to study the recipes and follow them closely, he has failed to heed my advice.  His recent work on the sedimentary material cooking project is a case in point.  He read descriptions of several different methods for preparing the material and then proceeded to pick and choose from among them, almost at random. It was particularly disheartening that he initially reported having followed one set of steps when, in retrospect, that turned out not to be the case.  When I asked him why he did that, he mumbled, “I don’t know.  Too much going on, maybe?”

Though many of the sources he consulted mentioned the use of a mixture of water and Calgon water softener (I would note that he was singularly intrigued by the Calgon), none specified what concentration would be appropriate.  Out of thin air he used a solution with a concentration of approximately 0.5% Calgon.  Though several of the sources he consulted gave times for soaking the material (typically “over night”), he bathed his material in this solution for a full 48 hours.  Of all aspects of this project, the one he seemed to grasp the best, and the one with probably the least consequence, was the time needed to dry the material.

In light of the shortcomings of his work on the recent project, I have given Tony an additional assignment:  read the article titled Microfossil Processing:  A Damage Report, by R. Hodgkinson (Micropaleontology, 1991) and prepare an essay reflecting on the implications of this article for preparing material for microfossil exploration.

MY ESSAY RESPONSE

The most damning thing about Hodgkinson’s article is that I had actually read it at some point in the process of preparing my material.  Why didn’t the post reflect that?  “I don’t know.  Too much going on, maybe?”

Hodgkinson's piece is for micropaleontology students, drawing from a manual used in the Micropalaeontology Section of the Natural History Museum, London.  His focus is on the negative outcomes possible from the various methods in use to separate microfossils from their matrix and clean them.  He notes that many of these techniques arise from two sets of competing interests involved in collecting microfossils – those of commercial enterprises, such as oil companies, that want to extract microfossils quickly, and those of academic institutions seeking complete and undamaged specimens.

Frankly, after reading the article, I’ve reached the conclusion there’s very little in these various techniques that does not pose a risk to the integrity of the fossils, regardless of whether commercial or academic objectives are being served.  Granted, Hodgkinson is focused on the damage done, so he’s clearly striking a very strong cautionary note.

First lesson learned from the review – BE CAREFUL.

Hodgkinson reviews a number of mechanical methods which, upon reflection, may in some indirect ways challenge my blithe statement in the previous post that there are no hand tools for extracting individual microfossils from matrix.  Anyway, among the methods he considered are abrasion, centrifuging, crushing, and applying ultrasound.  Of these, two actually have some relevance to my sedimentary material.  This material was collected in the so-called reject pile outside of the Aurora Fossil Museum, in Aurora, North Carolina.  This material, from the Pungo River Formation, is dumped outside the museum by the corporation running the Lee Creek Mine and it has, in fact, gone through processing at the phosphate mine.  So, without a doubt, abrasion and crushing have been in the cards for any microfossils I turn up.

Hodgkinson’s review of the chemical methods should clearly have informed my work with my Miocene material.  The chemicals considered here are intended to do one of two things – either dissolve the matrix, thereby releasing the fossils, or disaggregate particles in the sediment, allowing collection of the fossils.  Frankly, it’s amazing that any paleontologist, professional or amateur, ever successfully prepared microfossils with these chemicals given how brutally most of them can treat the fossils.

The damage that these chemicals can do to the microfossils includes cracking, coating (covering up details), etching (eating into the fossils), thinning (making the fossils more fragile), dissolving, changing color, and exploding (yes, indeed).

The last of these evils is laid at the doorstep of sodium hypochlorite (i.e., bleach) along with other sins.  Hodgkinson writes that one report on the use of this chemical to prepare scolecodonts (the jaws of a segmented worm), noted that “it rendered the specimens translucent, and also digested denticles, fangs, tips and other un-named parts.”  Further, the sodium hypochlorite made the specimens “very fragile and light-sensitive and that, any evaporation of the solution allowed crystal growth, which exerted a bursting pressure from within.”  Pretty nasty stuff.

The range of chemicals reviewed here is broad, including acetic acid, carbonic acid, formaldehyde, formic acid, hydrochloric acid, hydrogen peroxide, and sodium hexametaphosphate.  Certain brand names are mentioned, including Clorox, Decon (a cleaning product used in labs), Extran (commercial name for another cleaning agent), and Calgon (my favorite and what I have used).

So, on to Calgon.  Hodgkinson’s review, dated 1991, identifies Calgon as containing the chemical compound sodium hexametaphosphate.  The risks to microfossils included “dissolution” (clearly “end times” for the micros), etching, and coating.  Critical to the well-being of fossils soaked in a Calgon solution is the concentration of the chemical and the length of time they are exposed.  Apparently, 0.01% is considered a safe concentration, though etching reportedly has occurred even at that level.  The review actually says very little about the most appropriate length of time.

But perhaps there isn’t much specific to learn about Calgon from Hodgkinson after all.  According to the manufacturer, sodium hexametaphosphate is no longer an ingredient.  Today’s Calgon is made up of carbonic acid, sodium salt, sodium citrate, and sodium sulfate.  One of the sodium compounds, sodium citrate, is described as an organic deflocculant which serves to break up sedimentary particles in a solution, presumably releasing the microfossils and cleaning them of any matrix.  So, Calgon in its current configuration may be useful, but I don't have any specific guidance as to concentration or soaking time.

In fact, the review overall is often short on specifics, regardless of method or chemical used, but rich in examples of getting it wrong.  There’s method to that madness I think, which leads to another conclusion.

Second lesson learned from the review:  Experiment, experiment, experiment, until you stumble on a method that works.

NOT COMPLETELY OUT TO LUNCH

The method I described in my previous posting was the one I used to prepare the sample that yielded some foraminifera shells.  Did my heavy concentration of Calgon and my 48 hours of soaking destroy much of the microfossil fauna I might have discovered in this material?  I don’t know.  But while preparing that particular sample, I was actually following the second lesson learned from Hodgkinson’s review – experiment, experiment, experiment.  I applied parallel cleaning processes to the Miocene material.  In one, I followed the advice on the Hull Geological Society’s website and boiled (yikes) a mixture of Calgon/water/matrix, trying to achieve the custardy consistency described in this piece . . . I failed, but still washed, screened, and dried the material.  I have not yet explored it under the microscope, but I have to wonder about the impact of boiling on fragile fossil shells.

In another, more sane process, I simply soaked the material for 48 hours in plain water, no chemicals added, then washed and screened it (the stocking method – see previous post), and finally dried it in the oven at 170º F for 2 hours.  It was to this latter sample that I turned when I began to think there was more madness than method to my Calgon processing.

A mere 15 minutes after I began my search, there it was, sitting in my field of view, a glorious ostracode.  (As for the size of this fossil, I think it may be as much as one millimeter in length.  Given how hesitant I am to play around with a microfossil, I've yet to figure out a way to measure one with any precision.)

To me, this is a dramatic first find because this ostracode fossil consists of two articulated shells.  That is, the two shells the animal was sporting in life have remained together as a fossil.

A bit of background on the shell structure of ostracodes may be appropriate.  The animals live inside two shells or tests, a right one and a left one hinged at the top.  In the Podocopida, the class of ostracode most common in the Mesozoic and Cenozoic (from 250 million years ago to the present), one shell is generally slightly larger than the other, creating a lip that runs along the outside edge of the larger shell when the two are closed.  That lip is strikingly evident in the first photo below.  The dorsal (top) side of this specimen, where the tests are hinged, is straight, while the ventral side is convex.  The articulation of the two shells shows clearly in the second photo.

Without much doubt, the beastie inside has long since decayed away, but, for some 15 million years or so, its two shells have stayed closed, one nestled inside the other.  An amazing feat given the rigors of the fossilization process and the terrors of phosphate strip mining, not to say the extreme hazards of my treatment of the material (Calgon or not).

Now, I have only vague clues as to the identity of this particular fossil.  Unfortunately, my summer vacation has intruded, so I am stranded some 300 miles away from a couple of my sources that might provide guidance.  Further, the web is actually largely destitute when it comes to ostracode identification.  Though the Microfossil Image Recovery and Circulation for Learning and Education (MIRACLE) of the University College London gives a good introduction to ostracodes (or ostracods, the British spelling), its images of different genera and species are too few to be of much use with the one at hand.  The closest I can come in the several volumes produced on the Lee Creek fauna under the auspices of the Smithsonian is an article on the stratigraphy of younger formations at Lee Creek which does focus on ostracodes.  These formations are younger than that which yielded my find (Pungo River Formation).  (Joseph E. Hazel, Age and Correlation of the Yorktown (Pliocene) and Croatan (Pliocene and Pleistocene) Formations at the Lee Creek Mine, in Geology and Paleontology of the Lee Creek Mine, North Carolina, Volume I, edited by Clayton E. Ray (1983).)  But it’s only suggestive.

Heeding the advice of my Home Ec. teacher, I think I will take my time and ponder, withholding an identification for the time being . . . though . . . if pressed . . . I’d put Cytheridea as a genus into the mix.

So, is that it for the ostracodes in this sample?  Does that render a verdict on the presence or absence of these microfossils in this Lee Creek material of mine?  On the methods of preparing the material?  At this stage, none of the above is the correct answer.  Even as the car was being packed up for the trip north to the fossil-barren landscape of Long Island, I took a few minutes to scan some more of this material (the sample soaked in plain water).  A single ostracode shell showed itself (same genus as the first, I have to assume).  Disappointing?  Hardly.  Just whetted my appetite.

Source
For a fine overview of ostracode fossils, I recommend the relevant chapter in Microfossils, by Howard A. Armstrong and Martin D. Brasier (2005, Second Edition).  Being British, they do insist on ostracod.  I discovered that they also have an appendix on methods for preparing material - they title it "Extraction Methods."  No need to get into that, though they do feature some fairly dramatic methods.