Paleonet: Microfossils in organic-rich mudstones

[Robert Speijer]

Dear Walter


I never noticed that the use of Rewoquat affected the foraminifera in a negative way through dissolution, but of course this does not mean that it has no effect at all. We mostly used it for indurated marls (if a soda solution was not sufficient) and perhaps the dissolution of fine-grained components like calcareous nannofossils may have buffered the solution.


For sure using a H2O2 solution with clays or marls containing pyrite is much more destructive: upon oxidation the pyrite produces sulfuric acid and this obviously will affect the calcareous microfossils, especially when they are infilled by pyrite, as often is the case for foraminifera in mudstones. Despite these adverse effects, still quite a few micropaleontologists stil use this.

A must read for anyone processing samples for calcareous microfossils and especially to those who are using H2O2: Kennedy, A.E. & Coe, A.L. (2014) : Development of the freeze-thaw processing technique for disaggregation of indurated mudrocks and enhanced recovery of calcareous microfossils. Journal of Micropalaeontology. http://dx.doi.org/10.1144/jmpaleo2013-020
"Samples processed with hydrogen peroxide contained damaged microfossils and an under representation of delicate calcareous foraminifera. Many other studies of indurated mudrocks have used hydrogen peroxide to extract foraminifera, and this might have resulted in apparently barren intervals" (from the abstract).

Note that Kennedy and Coe also pointed out that that Rewoquat contains components that are a threat to the aquatic environment. Clearly, the authors obtained very good results with freeze-thaw processing.


Best regards / Met vriendelijke groeten

Robert P. Speijer

Professor of Paleontology - <https://bwk.kuleuven.be/hydr/marine@kuleuven/BIOGeology_KuLeuven> Biogeology research group<https://ees.kuleuven.be/geology/biogeology/>
Department of Earth and Environmental Sciences, KU Leuven
Celestijnenlaan 200E, B-3001 Leuven, Belgium
Tel: +32 16 326404; Fax: +32 16 322980
Papers at ResearchGate<https://www.researchgate.net/profile/Robert_Speijer/?ev=hdr_xprf>
________________________________
Van: Paleonet <paleonet-bounces+robert.speijer=kuleuven.be at paleonet.org> namens Walter.Etter at bs.ch <Walter.Etter at bs.ch>
Verzonden: maandag 10 januari 2022 08:28
Aan: paleonet at paleonet.org
Onderwerp: 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>
www.nmbs.ch<http://www.nmbs.ch/>

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