Paleonet: Microfossils in organic-rich mudstones

[Øyvind Hammer]

... the technology is perhaps not yet quite there, but will be very soon: In our microfocus CT we can usually see both calcareous, agglutinated (siliceous) and pyritized forams inside shales and mud rocks. We are already using this to screen samples before disaggregating, but the resolution on cm-scale samples is not good enough for species identification.

With the new generation of "zoom" CT, we will soon be able to count and id forams in mud rocks efficiently and completely, with no damage to the specimens, and with precise information on their 3d distribution.

Øyvind Hammer
Natural History Museum
University of Oslo

11. jan. 2022 03:34 skrev "Thomas, Ellen" <ellen.thomas at yale.edu>:
Dear all,

In my experience all processing methods have (at least some) negative effects on the foraminifera in the processed sediments, with more fragile species breaking and/or partially dissolving.  I have recently had reasonable success with the liquid nitrogen method (Remin et al., 2012, A new method of rock disintegration and foraminiferal extraction with the use of liquid nitrogen [LN2]. Do conventional methods lead to biased paleoecological and

paleoenviromental interpretations? Marine Micropal 86-87, 11-14). For very indurated sediment I have used the oil-method, which leads to considerable breakage, but at least gets a reasonable number of specimens out: break sediment in pieces, dry, soak in some sort of mineral oil for a few days, decant, heat in soapy water, decant.

 Best

Ellen Thomas


From: Paleonet <paleonet-bounces+ellen.thomas=yale.edu at paleonet.org> on behalf of "Walter.Etter at bs.ch" <Walter.Etter at bs.ch>
Reply-To: PaleoNet <paleonet at paleonet.org>
Date: Monday, January 10, 2022 at 02:33
To: "paleonet at paleonet.org" <paleonet at paleonet.org>
Subject: Paleonet: Microfossils in organic-rich mudstones

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 250*m, 125*m, 63*m) 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<mailto:walter.etter at bs.ch>
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