Disaggregating Shales, etc.

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Hola!

I'm a Ph.D. student at USC whose current interests include (among
other things), colonization of early deepsea environments and
paleoecologic and paleobiologic changes which were occuring during the
Late Proterozoic and Early Paleozoic. 

However, I recently completed a M.S. thesis project in which I
encountered problems similar to Don Chesnut.  Although I was working
with Cenozoic 'sediments' from the Gulf Coast of the U.S., I
encountered similar problems with: a) disaggregating fragile
aragonitic shells from lithified to semi-lithified sediments; and b)
finding Quaternary-O. To make a long (trial-and-error-filled) story
short, you might try one of the following strategies to disaggregate
shales or any other non-metamorphosed sedimentary rocks you might
have:
	i) If your rock samples are relatively "dry", you can soak
		them in buckets of household bleach (preferably under
		a fume hood). Once the samples have disaggregated,
		decant the bleach and carefully sieve or pick out your
		fossils.
	ii) If this does not work, then try baking your rocks for 24
		hours in a very low temperature oven (I have had good	
		luck at 50 degrees). You may need to dry out your
		samples for a longer period of time. Go to step i).
		Occasionally you will notice (depending on your sample
		size) that only the exterior of your samples
		exfoliates or disaggregates when placed in bleach.  If
		this happens, you may need to bake your rock samples
		for a longer period of time and/or repeat this process
		multiple times.
	iii) If these do not work, you can try immersing your samples
		(after 'drying' them out) in a bleach (or hydrogen	
		peroxide) solution within an ultrasonic-style basin to
		speed along particle disaggregation.

Success using bleach will obviously vary depending on how much
organic material is preserved in your samples. Different lithologies
will even disaggregate with diluted concentrations of bleach. I have
also tried using various concentrations of hydrogen peroxide to
disaggregate samples -- this will also work, but is much more expensive.

I don't know what type of fossils you are trying to remove from your
rock samples, but you can always try using nastier solutions such as
hydroflouric acid, paint or laquer thinner, hydrochloric acid (if f.g.
carbonates & phosphatic skeletal elements), etc. etc.  I had
relatively painless success using bleach -- and at ~$1/gal.-it is a
bargain!

Am at home right now and thus don't have the exact reference, but if
these don't work, you might check out a volume called
"Paleotechniques" which I believe was put out as a PS (or possibly
SEPM?) special publication sometime in the '80's. 

Best of luck in your rock-disaggregating adventures...

Plan to use up/destroy plenty of trial samples first! :) 

Regards,

Whitey Hagadorn


************************************************************************
James W. Hagadorn
hagadorn@usc.edu
Dept. of Earth Sciences
University of Southern California
Los Angeles, CA 90089-0740
				...surfing waves and the internet...
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