Did you try sonication? I would try to put the partially disaggregated rock into distilled water then use a probe sonicator for at least half an hour.

Thank you for your answer Debora!

Is there a risk of fossils fracturing in the process?

No, it will not affect the fossils but it will generate heat so I'd monitor temperature and pause sonication if necessary.

Direct answer to your question:

"Is there a risk of fossils fracturing in the process?"

Ultrasonic treatment is the most effective by far, while most gentle cleaning method for sensitive materials.

If even this cleaning method is not sufficient, you should embed the microfossils in resin and either make a polished thick section or on both sides polished thin section. Then you can determine the microfossils in oriented sections, although there are still leftover rock fragments adhered.

I suggest ultrasonic treatment. Be carefull with the time in the equipment  and check if the carapaces are fractured before putting the equipment. Sometimes a few seconds are needed for cleaning the surfaces.

I suggest placing the sample in a large steel beaker and and Glauber's salt then add boiling water and let sit til it reaches room tempetarute.  Put the beaker in the freezer for 24 hours, remove it and let it thaw for 24 hours.  Repeat the cycle if necessary.

I suggest that it is better to heat and freez samples repeatedly.I got good result of same samples.

You can also try with diluted acetic acid (normal vinegar diluted in water, you can try with 1/10 of vinegar) but be careful because this acid may dissolve the forams.

Good luck

Yes, Calgon or Alconox are two options to breakdown clay sediments combined with freeze and thaw intervals.  This is the technique I usually work with.  However, because of the rock matrix you mentioned for your samples, I assumed Glauber's Salt would be a stronger and more efficient option.  It is more expensive, though.

As per my own experience, the best way to isolate fossil from sediments as you described is:

1- Sock them in diluted acidic acid for overnight followed by gently washing them with distilled water(while pouring out the water maximum care must be taken and if possible use sieve to keep sediments containing fossils).

2- Treat them with diluted H2O2 (10-15%) for 6-8 hours followed by gently washing them with distilled water(while pouring out the water maximum care must be taken and if possible use sieve to keep sediments containing fossils).

by this method you will get maximum fossils. if still there is sediments attached to fossils, then use ultrasonic method, but you should be very careful to to break the shells. 

LN2 [liquid nitrogen] method.

It is very simple, very fast and very cheep. The microfossils are beautifully preserved [compare the paper below] - usually you dont need to clean them in ultrasonic cleaner. This method has one fundamental advantage over Glaubert's Salt method. The already extracted microfossils are not exposed to multiply crystallization of the salt what led to disintegration of fossil itself and affect the microfossil composition.

The use of GS method markedly underestimate planctic forams [both in quantity and quality] what affect P/B ratio and in consequence your final interpretations.

I don’t know how you rock samples are indurated although you are able to disintegrate the rock and simultaneously extract your micro in less then 1-2 hours [this can be translated in several days of Salt treatment].

Please try…

Best Zbyszek

Article A new method of rock disintegration and foraminiferal extrac...

The procedure should follow the purpose of the research.For simple biostratigraphy and For hard sediments I usually put them in hydrogen peroxide (60 volumes) in a glass becker, for a while (10 minutes are enough, or until it starts bubbling), then I put them on a hot plate until boiling. From the hot plate I put sediments  in the sieve where I want to wash them and pass them in very cold water. If necessary repeat the procedure 2 or 3 times. You will see that the sediments become very soft and you can disaggregate the microfossils. They do not break, do not worry. If they are in hard chalk they are recrystallized and are very hard.

One of the answer suggest acidic acid, probably he meant ACETIC acid, not acidic, which is not the same. ACETIC acid is also a good way to proceed but it is not the safest product to use.

I never tried the liquid nitrogen, but it has the same concept of my method, exposure to warm and cold. But hydrogen peroxide at 60 volumes  is a lot cheaper than liquid nitrogen and a bit less dangerous.

liquid nitrogen is cheaper then sparkling water.....

I'm paying for it about 5 euro per 30 litre container... every physical and chemical lab has it almost for free

best

zbyszek

Silvia was right. It was writing mistake. Acetic acid is correct, but as I mentioned, you should use diluted acetic acid (20-30%) to prevent any harmful effect of it.

I am working on charophytes and experimented several methods (but not liquid nitrogen), depending on the sediment,, to extract and clean them safely. It would be too long to present them here.You find these methods explained in the charophyte Treatise (2005), reference on my Research Gate site.

Monique is right.

But you can also have a look on the "Handbook of paleontological techniques" or else to Lethiers & Soleau-Crasquin in the "Revue de Micriopaléontologie" using hot acetolysis (very efficient if you dry your carbonated sediments for 24/48h).

Good luck for your future process.

Try the 80% diluted Acetic acid method. this is the way I treat my samples: Indurated marlstone and limestone samples are crushed manually into mainly three classes ranging from powder to pea-size fractions with the importance of having at least 25% of the sample of powder size. Put about 50 ml of sample in 500 ml beaker and immerse in 100 ml of diluted 80% acetic acid following the method proposed by Kariminia (2004) . Duration of sample immersion varies from sample to sample and depends on the degree of induration and %CaCO3 content, ranging from 4 to 8 hours, at which time the chemical reaction changes from gentle bubbling to vigorous bubbling and begins forming foam. Once the samples began to vigorously bubble and create a foam, they should then continuously rinsed with water for at least 15 min over a 63 μm sieve to prevent reactivation of the chemical reaction.

I fully agree with the method mentioned by Silvia, then you can pick the fossils one by one using very fine and sharp ended brash

Acetic is good for phosphatic and occasionally silicified microfossils but it will dissolve calcium carbonate. Ostracods and forams are calcium carbonate so be careful not to dissolve them!

Very good point, Marissa, which no one else addressed.  Without knowing the chemistry of the matrix and specimens, blanket recipes are dangerous for the fossils!

Could you let me know the details on degree of induration (interlocking or loose textures), the specimens have gone through, the precise composition of main constituents, cementing materials, and grain sizes of fossils as well as clasts.

Try to use kerosen procedure

Try to soak in kerosine for about 24 hours...

Try to use kerosine and add few drops of engine oil.

Good luck

try a sonic water bath for a few seconds. But....in all techniques remember the health and safety aspects of the procedures you try.

Hydrogen Peroxide will not work well for marly samples, it is only good for shale.

Dear Šoster,

If the limestone is not hard and compacted (later case need thin sectioning), you can try to use boiling water and adding hydrogen pyroxide with a continuous stirrer for at least 72 hours (best for chalky and marly limestone). This method leads to getting better and clean tests usually. If they still coagulate, you can add, but be careful, very very little amount (one drop or two) of diluted sodium hydroxide (the later dissolved calcareous tests and etching siliceous tests).

Dear Toyin, use boiling water and hydrogen pyroxide for at least 72 hours with stirring give much better, clean residue chalky limestone, marly limestone, and shale.

Good Luck

Use Hydrogen Peroxide and Ammonia solutions for soaking the samples and may also try very limited stirring in an ultra-sonic vibrator

Try to use liquid nitrogen method. It works for foraminifers and ostracods. Best, Zbyszek

I suggest the use of Rewoquat. See https://palaeo-electronica.org/content/component/content/category/188-382

I second Luca`s suggestion for Rewoquat in case the problem is about flakes of clay, marl or marly limestone clogging fine depressions (pores, aperture, etc.). Without a clay component (e.g. limestone) it does not work.

The glacial acetic acid method is really good and simple for limestone disintegration I guess.

There are different techniques that can liberate microfossils, Here the most used five techniques acetic acid, H2O2 at 10% and 25% concentration, neosteramina, and liquid N2. The attached paper summarizes these techniques and their impact on Foraminiferal asssemblage particularly the delicate planktonic one