Paleonet: Disintegrating Microfossils in organic-rich mudstones

[Michael Hesemann]

Dear Dr. Etter

after having tried several methods in disintegrating mudstones and 
rather stiff sedimentary glacial erratics for picking of foraminifera > 
63µm we apply only these gentle methods:

we keep some of the material untouched

1.) If the material is stiff we cook it a bit in water and put into 
deep-freeze and repeat this for up to 50 times. We check in between, 
whether there is a high amount of broken shells, which in 95% is not.

2.) We cook it then in a 10-15% solution of sodium carbonate for 30 
minutes, stir it a bit and let it stay for 12-24h with occasional stirring

3.) We wash it over 63µm mesh and let it dry (oven or for 48h covered)

4.) We look into the fraction <2000µm and decide, whether to apply the 
preceding methods again.

5.) We split, pick and count.

6.) For finding nice specimens for illustration we put parts of the 
residue in a glas vial with a tensid, stir it heavily, stop and after 
10-15 seconds when the heavy particles have settled we decant the foam 
and upper layer.

The procedure is described and the results are illustrated in: Hesemann, 
M. 2020: Foraminifera in the glacial erratic rock Heiligenhafener 
Kieselgestein of northern Germany in Micropaleontology 66(5):397-418

You may also see some results on www.foraminifera.eu linking to 
Oligocene, Paleocene and Jurassic foraminifera extracted from glacial 
erratics.

best wishes

Michael

-- 
Michael Hesemann
The Foraminifera.eu Project
Hamburg, Germany
www.foraminifera.eu


Am 10.01.22 um 08:28 schrieb Walter.Etter at bs.ch:
>
> Dear paleonetters,
>
> does anybody of you have experience using surfactants for microfossil 
> processing?
>
> The disintegration of mudstones rich in organic material is difficult. 
> Standard procedure with 5-8% peroxide and subsequent washing over a 
> sieve-stack (I use 250mm, 125mm, 63mm) sometimes reduces the amount of 
> sediment to only one quarter (from 200g to 50g) which makes it an 
> almost impossible task to pick the microfossils. For a further 
> reduction of the clayey material various methods were suggested such 
> as cooking in sodium carbonate which leads to a modest but still 
> unsatisfactory reduction.
>
> In the past we used the slightly acidic surfactant «Bradophen» 
> (Benzozoniumchloride) and obtained very good results. Alkaline 
> surfactants, however, were not effective. Since «Bradophen» is no 
> longer available, I tried using «Rewoquat» (Imidazoliniumquat) which 
> is also a slightly acidic surfactant and reduces the residue to less 
> than 10%. But of course we do not know what mechanism is behind that, 
> and if certain microfossils are (at least partially) dissolved. 
> Therefore I highly appreciate any suggestions/recommendations 
> regarding the use of surfactants or other methods for the reduction of 
> the clayey material.
>
> With best wishes for the New Year, Walter
>
> Dr. Walter Etter
> Naturhistorisches Museum
> Kurator Geowissenschaften
> Augustinergasse 2
> CH 4001 Basel
>
> Telefon +41 61 266 55 63
> Fax +41 61 266 55 46
> walter.etter at bs.ch
> www.nmbs.ch <http://www.nmbs.ch/>
>
>
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