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An acid-free method of microfossil extraction from clay-rich lithologies using the surfactant Rewoquat

Emilia Jarochowska, Petra Tonarová, Axel Munnecke, Lenka Ferrová, Jan Sklenář, and Stanislava Vodrážková

Plain Language Abstract

Microfossils, i.e., small fossils in the size range of ca. 0.005 to 100 mm, are commonly used to establish the geological age of sedimentary rocks. To release phosphatic or organic-walled microfossils from calcareous rocks (limestones, dolostones, marls), the most common approach is to digest the rock in an acid solution. The acid dissolves the calcareous matrix, but not fossils built of acid-resistant substances, e.g., with organic walls. Acid digestion is nevertheless very slow and inefficient in treating rocks with high clay content, as the clay clogs the rock pores and forms aggregates which put an end to the dissolution. We describe the use of Rewoquat, an organic substance, to disintegrate clayey rocks and release microfossils faster (days) than through acid digestion (weeks to months). In addition to be less time-consuming, this method preserves calcareous microfossils, which are otherwise dissolved.

Polish

Morskie skały cechujące się wysoką zawartością iłu stwarzają doskonałe warunki zachowania skamieniałości, szczególnie w przypadku skamieniałości o ścianach z substancji organicznych, takich jak retiolitowe graptolity lub chitinozoa. Niemniej krzemiany warstwowe tworzące składniki ilaste utrudniają ekstrakcję mikroskamieniałości. Problem wynika z tendencji krzemianów warstwowych do tworzenia agregatów w niskim pH, gdyż standardowe metody ekstrakcji mikroskamieniałości wykorzystują trawienie skał kwasami. W rezultacie zastosowanie kwasów do skał bogatych w ił często jest nieefektywne i czasochłonne. Proponujemy tutaj metodę dezintegracji skał z użyciem środka powierzchniowo czynnego o nazwie Rewoquat oraz porównujemy ją z dwoma powszechnie stosowanymi podejściami: trawieniem w buforowanym kwasie octowym oraz w HCl-HF. Wykorzystując ogniwo Mulde Brick-clay z syluru Gotlandii oraz łupki Daleje z dewonu Basenu Praskiego jako przykłady, zaobserwowaliśmy, że dezintegracja w Rewoquacie była szybsza (dni) niż trawienie w kwasie (miesiące), i pozwoliła uzyskać nie tylko skamieniałości o ścianach organicznych, ale także skamieniałości węglanowe. Uzysk i zachowanie palinomorf były porównywalne, z wyjątkiem konodontów otrzymanych z użyciem HCl-HF, które były mocno nadtrawione. Retiolity uzyskane z użyciem Rewoquatu były zachowane w 3D i wykazywały niższy stopień fragmentacji. Zawartość skamieniałości w nierozpuszczalnym osadzie otrzymanym z użyciem Rewoquatu była wyższa dzięki rozproszeniu agregatów ilastych. Jednak do obserwacji delikatnych skamieniałości zalecamy jedynie powlekanie próbki Rewoquatem. Zastosowanie Rewoquatu może uwidocznić delikatne formy i stadia wzrostu, a tym samym dostarczyć nowych danych dotyczących ontogenezy, autekologii i rozkładów rozmiaru ciała dla wielu grup skamieniałości.

Translation by authors

Resumen en Español

Un método sin ácidos para la extracción de microfósiles de litologías ricas en arcilla mediante el uso del tensoactivo Rewoquat

Las rocas marinas con un alto contenido en arcillas presentan excelentes condiciones para la preservación de los fósiles, particularmente la de los microfósiles de pared orgánica como los graptolites retiolítidos y los quitinozoos. Sin embargo, los filosilicatos que constituyen la arcilla dificultan la extracción de los microfósiles. Ello es debido a la tendencia de los filosilicatos a formar agregados en medios con valores de pH bajos, como los que se dan en los métodos habituales de extracción de microfósiles en los que se emplean ácidos para la disgregación de la roca. En consecuencia, el uso de ácidos para rocas ricas en arcilla resulta ser a menudo un proceso largo e ineficaz. En este trabajo proponemos un método para desintegrar la roca basado en el uso del tensoactivo Rewoquat y lo comparamos con dos técnicas frecuentemente aplicadas: disolución en un tampón de ácido acético y en una mezcla de HCl y HF. Utilizando muestras de arcillas del Miembro Mulde, del Silúrico de Gotland, y de pizarras del Miembro Daleje, del Devónico de la cuenca de Praga, hemos observado que la desintegración en Rewoquat fue más rápida (días) que la digestión en ácido (meses), permitiendo además la recuperación de microfósiles calcáreos junto a los de pared orgánica. El rendimiento y la preservación de palinomorfos son análogos en todos los casos, pero los conodontos sufren una intensa corrosión con la mezcla de HCl y HF. Los graptolites retiolítidos recuperados con Rewoquat se preservan en tres dimensiones y muestran un menor grado de fragmentación. El contenido fósil del residuo obtenido mediante el uso de Rewoquat es mayor debido a la dispersión de los agregados de minerales de la arcilla. Para la observación de fósiles delicados recomendamos recubrir la muestra con el tensoactivo. La aplicación de Rewoquat puede poner al descubierto las formas y estados de crecimiento más sutiles, proporcionando así una mejor percepción de la ontogenia, autoecología y distribución de tamaños de varios grupos fósiles.

Palabras clave: fósiles calcáreos; microfósiles de pared orgánica; microfósiles fosfáticos; disgregación de la arcilla; digestión en ácido; preservación en tres dimensiones

Traducción: Miguel Company

Résumé en Français

Une méthode d'extraction sans acide, utilisant du surfactant Rewoquat, pour les microfossiles provenant de lithologies riches en argile.

Les roches marines sont caractérisées par une composition forte en argile permettant d'excellentes conditions de préservation pour les fossiles, particulièrement pour les fossiles à tests organiques tels que les graptolites retiolitidés et les chitinozoaires. Toutefois, les minéraux phyllosilicatés, qui constituent la composante argileuse, rendent l'extraction des microfossiles difficile. Le problème vient de la tendance des phyllosilicates à former des agrégats dans des conditions de pH faibles, alors que les méthodes standards d'extraction des microfossiles utilisent des acides pour la dégradation des roches. En conséquence, l'utilisation d'acide pour les roches riches en argile est souvent inefficace et longue. Nous proposons une méthode de dégradation des roches utilisant du surfactant Rewoquat et nous la comparons avec deux autres approches souvent utilisées : dégradation dans l'acide acétique tamponné et HCI-HF. Sur la base d'exemples provenant du Membre d'argiles à briques de Mulde dans la Silurien de Gotland et des argiles schisteuses de Daleja dans le Dévonien du bassin de Prague, nous avons observé que la désintégration dans le Rewoquat a été plus rapides (jours) que la dégradation dans l'acide (mois), et a permis de récupérer les fossiles calcaires en plus des fossiles à tests organiques. L'extraction et la préservation des palynomorphes ont été bonnes avec toutes les méthodes, mais les conodontes ont été fortement marqués âpres l'utilisation de HCI-HF. Les graptolites retiolitidés extraits avec le Rewoquat ont été préservés en 3D et ont montré une moindre fragmentation. Le contenu en fossiles des résidus obtenu par l'utilisation du Rewoquat a été supérieure du à la dispersion des agrégats d'argiles. Pour l'observation de fossiles fragiles nous recommandons de couvrir des échantillons de surfactant. L'application de Rewoquat peut révéler les formes et les étapes de croissance les plus délicates, et fourni donc une meilleurs vue de l'ontogénie, l'autécologie, et des distributions de tailles pour de nombreux groupes fossiles.

Mots clés : fossiles ; calcaire ; microfossiles ; tests organiques ; phosphatique ; dispersion de l'argile ; dégradation par l'acide ; préservation en trois dimensions

Translator: Olivier Maridet

Deutsche Zusammenfassung

In progress

Translator: Eva Gebauer

Arabic

382 arab

Translator: Ashraf M.T. Elewa

 

 

FIGURE 1. Retiolitid graptolite Gothograptus nassa (Holm, 1890) from the Mulde Brick-clay Member (Blåhäll 1, middle Silurian, Gotland), extracted using Rewoquat. 1-2 – ventral view of a rhabdosome with partly preserved proximal part, scale bar = 1 mm; 3-4 – ancora umbrella with preserved sicula, scale bar = 200 μm; 5-8 – membranes preserved between cortical lists, 5-6 scale bar = 15 μm, 7-8 – scale bar = 50 μm. 2, 4, 6, 8 – 3D anaglyphs.

figure 1

FIGURE 2. Example fossils recovered with Rewoquat from the Mulde Brick-clay Member (Blåhäll 1, middle Silurian, Gotland): 1-5. Scale bar = 100 μm; 1. Conochitina? sp.; 2. Conochitina tuba Eisenack, 1932; 3. Conochitina claviformis Eisenack, 1931; 4. Conochitina pachycephala? Eisenack, 1964; 5. C. pachycephala Eisenack, 1964; 6. Kettnerites martinssonii Bergman, 1987, right first maxilla (MI); 7. paulinitid right MI; 8. deformed first paulinitid maxilla; 9. Kettnerites sp., left second maxilla (MII); 10. Leptoprion? sp., right MI; 11, 15-16. Echinoderm ossicles, 11 – scale bar = 200 μm; 16 – scale bar = 500 μm; 12 – Aechmina cf. cuspidata Jones and Holl, 1869; 13-15 – scale bar = 100 μm; 13 – Hexophtalmoides sp. Martinsson, 1963; 14. Bollia sp. Jones and Holl, 1886; 17-18 – scale bar = 200 μm; 17. Panderodus unicostatus (Branson and Mehl, 1933), simplexiform element, lateral view; 18. P. serratus Rexroad, 1967, costate element, lateral view.

figure 2

FIGURE 3. Example fossils recovered with Rewoquat from the Mulde Brick-clay Member (Blåhäll 1, middle Silurian, Gotland): 1. Volynites muldiensis? Larsson, 1979, scale bar = 500 μm; 2-3. juvenile parts of unidentified tentaculitoids, scale bar = 500 μm; 4. tabulate coral resembling Planalveolites sp.; 5. probable tabulate coral encrusted with Allonema sp., scale bar = 500 μm; 6. Conchicolites sp. encrusting a probable tabulate coral, scale bar = 1 mm; 7. fragment of a bryozoan colony encrusted by Conchicolites sp., scale bar = 2 mm; 8. trilobite genal? fragment encrusted with Allonema sp. and some unidentified encrusting organisms, scale bar = 1 mm; 9. trilobite pygidium, scale bar = 1 mm; 10, 13-14. unidentified juvenile brachiopods, scale bar = 200 μm; 11. Stegerhynchus borealis? encrusted with a microconchid or a juvenile Anticalyptraea sp., scale bar = 1 mm; 12. Resserella sp.? with encrustations, scale bar = 500 μm.

figure 3

FIGURE 4. Example fossils recovered with buffered acetic acid from the Mulde Brick-clay Member (Blåhäll 1, middle Silurian, Gotland): 1-5. Scale bar = 50 μm for chitinozoans, 100 μm for scolecodonts; 1. Conochitina claviformis? Eisenack, 1931; 2. Conochitina tuba? Eisenack, 1932; 3. Conochitina tuba? Eisenack, 1932; 4. Conochitina sp.; 5. Kettnerites sp., right MII; 6. Kettnerites martinssonii Bergman, 1987, left MII; 7. Conochitina pachycephala Eisenack, 1964; 8. K. martinssonii, left MI; 9. K. martinssonii, right MI; 10. K. martinssonii, right MII.

figure 4

FIGURE 5. Example calcareous fossils recovered with Rewoquat from the Daleje Shale (layer CH15b, Pekárek Mill, Lower Devonian, Prague Basin): 1-2. Nowakia barrandei Bou?ek and Prantl, 1959, scale bar = 500 μm; 3. Cribroconcha sp. Cooper, 1941, scale bar = 200 μm; 4. healdiid ostracod, scale bar = 500 μm.

figure 5

FIGURE 6. Example microfossils from the Daleje Shale (Pekárek Mill, Lower Devonian, Prague Basin). Scale bar = 100 μm, except for Figure 5.24, where the scale bar = 200 μm. Fossils in figures 1-13 were obtained using the HCl-HF-HCl technique and in figures 14-26 through disintegration with Rewoquat. 1. Calpichitina? sp., sample CH16b; 2-4. Ramochitina sp., 2. s. CH18b, 3. s. CH16b, 4. s. CH14b; 5. Calpichitina sp., s. CH16b; 6. Lunoprionella sp., s. CH18b; 7. polychaetaspid basal plate, s. CH16b; 8. Kettnerites sp., right second maxilla (MII), s. CH16b; 9. Kettnerites sp., left first maxilla (MI), s. CH16b; 10. Kettnerites sp., right MII, s. CH16b; 11. Pseudoonetodus beckmanni (Bischoff and Sannemann, 1958), s. CH15b; 12. P. beckmanni, s. CH14b; 13. unidentified prasinophyte, s. CH14b; 14. Bulbochitina sp., s. CH18b; 15. Angochitina sp., s. CH18b; 16. Calpichitina sp., s. CH16b; 17. Angochitina? sp., s. CH18b; 18. fragment of paulinitid MI, s. CH15b; 19. lateral tooth of Placognatha indet., s. CH15b; 20. Placognatha indet., s. CH17b; 21. Oenonites sp., s. CH17b; 22. Calpichitina sp., s. CH17b; 23. lateral tooth of Placognatha indet., s. CH16b; 24. prasinophytes, s. CH14b; 25. P. beckmanni, s. CH16b; 26. P. beckmanni, s. CH16b.

 figure 6

 

author1Emilia Jarochowska
GeoZentrum Nordbayern
Fachgruppe Paläoumwelt
Universität Erlangen-Nürnberg
Loewenichstrasse 28
|91054 Erlangen
Germany
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Emilia Jarochowska has graduated in biology (2010) and geology (2012) at the University of Warsaw, Poland. She is now doing a PhD project at the University of Erlangen-Nuremberg, Germany, under the supervision of Axel Munnecke. She works on a model for the sea-level development and the biotic turnover during the middle Silurian Mulde Event, employing conodonts, graptolites and stable carbon isotopes in sections located in Poland and Ukraine.

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author2Petra Tonarová
Institute of Geology at Tallinn University of Technology
Ehitajate tee 5
19086 Tallinn
Estonia
and Czech Geological Survey
Geologická 6
152 00 Prague 5
Czech Republic
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Petra Tonarová is a postdoctoral researcher in the Institute of Geology at Tallinn University of Technology. Since 2007 she has been a part-time researcher at the Czech Geological Survey in Prague. In 2012, she received a PhD degree from the Charles University in Prague, Czech Republic, based on the study on the Silurian scolecodonts of the Prague Basin. Her research is focusing on the lower Palaeozoic micropalaeontology, mainly scolecodonts (jaws of polychaete worms).

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author3Axel Munnecke
GeoZentrum Nordbayern
Fachgruppe Paläoumwelt
Universität Erlangen-Nürnberg
Loewenichstrasse 28
91054 Erlangen
Germany
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Axel Munnecke is a carbonate sedimentologist and palaeontologist at the University Erlangen-Nuremberg, Germany. He graduated in 1993 and completed his PhD at the university in Kiel (Germany) in 1996. From 1996 to 2002 he worked at the universities of Bremen (Germany), Lille (France), and Tübingen (Germany). Since then he works as assistant professor in Erlangen. His research interests are (a) palaeoclimate reconstructions based on facies analysis and stable C- and O-isotopes, (b) reconstruction of palaeoenvironmental changes during times of strong isotopic shifts in the Ordovician and Silurian, (c) correlation of bio- and chemostratigraphy, (d) origin and diagenesis of calcareous rhythmites (especially limestone-marl alternations), and (e) calcareous Palaeozoic micro- and nannofossils as fossil counterparts to modern calcareous plankton. Since 2003 he is organising the renowned annual “International Course on Carbonate Microfacies (Flügel Course)” in Erlangen, Germany.

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author4Lenka Ferrová
Czech Geological Survey
Geologická 6
152 00 Prague 5
Czech Republic
and Faculty of Science
Charles University in Prague
Albertov 6
128 43 Prague 2
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Lenka Ferrová is a PhD student at the Charles University in Prague and the research worker of the Czech Geological Survey. Her Bsc. and Master thesis dealt with Devonian Daleje Bioevent (Emsian, Lower Devonian). She studied the dacryoconarid tentaculites biostratigraphy, carbonate sedimentology and paleoecology with application of paleontological numerical methods on sections in the Barrandian area (Czech Republic). Her work brought new important data for long-running discussion on the subdivision of the Emsian Stage. She has worked on several sections from the same stratigraphical level in Nevada and New South Wales. Obtained material from Australia and North America together with ongoing research in the Barrandian area form the basis of her Ph.D.

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author5Jan Sklenář
Palaeontological Department
Natural History Museum
National Museum
Václavské náměstí 68
115 79 Praha 1
Czech Republic
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Jan Sklenář has worked as a curator of the Mesozoic Invertebrates collection at the National Museum in Prague since 2004. His primary interests are Late Cretaceous brachiopods, but he also studies other members of marine benthic communities, like polychaete worms. The Late Cretaceous brachiopods and polychaetes of the Bohemian Cretaceous Basin are also the topic of his Ph.D. thesis, completed in 2013. As a collection manager, he also deals with preventive and remedial conservation of fossils with iron-sulphide content. He is the leader of a group of palaeontologists, mineralogists and research chemists currently addressing this issue. Furthermore, he is interested in graphic and illustration techniques that have been employed in palaeontology throughout the history of the discipline.

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author6Stanislava Vodráková
GeoZentrum Nordbayern
Fachgruppe Paläoumwelt
Universität Erlangen-Nürnberg
Loewenichstrasse 28
91054 Erlangen
Germany
and Czech Geological Survey
P.O.B. 85
118 21 Prague 1
Czech Republic
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Stanislava Vodrážková finished her PhD in 2010 on environmental changes close to the Lower-Middle Devonian boundary in the Prague Basin (Basal Choteč Event), Czech Republic. She is currently a postdoctoral researcher at GeoZentrum Nordbayern, Friedrich-Alexander University of Erlangen-Nürnberg, studying the Middle Devonian Kačák Event. Her main research topics are conodont and tentaculite biostratigraphy, carbonate sedimentology and stable isotope geochemistry.

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TABLE 1. Number of chitinozoans and scolecodonts recovered from 10 g subsamples of the Mulde Brick-clay Member sample disintegrated using buffered acetic acid and Rewoquat (average of 3 replicates).

 
 

Chitinozoans

Scolecodonts

Buffered acetic acid (7%)

319.4

97.7

Rewoquat

833.7

311

 

TABLE 2. Mineral composition of studied samples, determined using XRD analysis.

 
 

Mulde Brick-clay Member

Daleje Shale

Illite

35.63%

24.76%

Clinochlore

4.47%

4.43%

Calcite

24.17%

41.82%

Dolomite

4.29%

-

Quartz

20.48%

22.25%

Albite

5.04%

5.91%

Illite/Smectite

1.29%

0.83%

Ankerite

4.09%

-

Pyrite

0.53%

-