The Studying of Foraminifera in Thin Sections

B y R É K A M . NYÍRŐ, Budapest

There was no systematic investigation regarding thin section studies of Foraminifera in Hungary up to now, though to study specimens in thin sections is important for several causes. The main points of view are :

1. The knowledge of the internal structure of Foraminifera ; 2. The comparison of external features and internal structure ; 3. The comparative studies of the internal structures of the species ; 4. The comparison of Foraminifera of a known internal structure with the micro-fauna

of unsluiceable rocks. At first, the study of thin sections of Foraminifera characteristical of the several strati-

graphic units seemed to be suitable. Later, however, i t was found to be more expedient and fruitful to switch investigations over on a systematical base, that is, the comparison of species and genera within the frames of a family. This paper was yet prepared on the base of the first conception. The history of research methods and directions is as follows.

With the exception of Nummulines, we meet but rarely in literature with thin section studies of the minute Foraminifera. Contrarily with Nummulines namely, to study sections of the small sized Foraminifera one has to have a suitable method of microtechnique. H o h e r experiments with Canada balsam in 1933. D u m b a r t and H e m b e r t use a bakélite impregnation for the cutting of thin-shelled specimens.

G l a e s s n e r (10) continues to use Canada balsam, yet, at the same time, mentions the successful application for the sectioning of harder samples the cement" prepared by R o s e n b u s c h (ingredients : 50% shellac 50% paraffine).

S t a c h (28) uses the so-called „Schneide höhn" resin for the calcareous Foraminifera. His method, however, is not suitable for the arenaceous forms, since this resin wears out speedily and the harder shell cracks away.

E m i l i a n i (9) recommends an imbedding material called thermoplast, worked out by M e y e r and L e v i n s o n . Its drawback is that this material is applicable only about 80° C, and so the imbedding is very complicated.

B e c k m a n n (4) advises shellac as an imbedding material, and Z e i d 1 e r (4) tooth cement instead of the obsolete Canada balsam and paraffine imbedding methods.

K r e m p and J o h s t (20) are also against the use of the Canada balsam and paraf­fine method expounded by G l a e s s n e r (10), since they found i t unsuitable for the imbed­ding of fossils with a harder shell. The same as Beckmann, they too apply the shellac imbedding.

K r e m p (19), when treating the thin sectioning studies of microfaunas from the Carboniferous, calls attention to learn the internal structure of arenaceous forms.

H a g n (11, 12, 13, 14) recommends the use of a honey-like polyester resin, applicable without heating also on room terqperature. As a preparation, he steeps the thin and fragile -pecimens in shellac or Canada balsam unti l they reach the necessary hardening.

H a g n considers the sectioning school especially important for the study of Globotruncanas and arenaceous forms. He emphasizes the necessity of collaboration and close connection of the workers in this field for the sake of development of microtechnique methods and research directions.

C u m m i n g uses the so-called ,,Marco Resin" material for the imbedding of the micro-fauna. His methods roughly corresponds with the one described by H a g n.

Of the methods discussed above, the ,,polyester"-resin method of H a g n and C u ni­ni i n g's treatment seem to be the most appropriate. Their advantage against the other ones is that there is no need for a heat treatment.

I n Hungary, E. V a d á s z , Gy. R a k u s z and L . M a j z o n worked on thin sectioning studies of Foraminifera.

The microtechnique used by me is the following.

For my studies, I used a synthetic imbedding material. The Czechoslovakian product „Spofacryl" proved to be the most suitable. The course of preparation is taxatively set out below :

1. The preparation of the imbedding material: we placed an amount (of two or three knife-points) of the powder on a sheet of glass, and added a polymerisator unt i l i t reached the suitable hardness, that is, plasticity.

2. The imbedding of the Foraminifera in the basic material : the specimens were placed orientated into the tooth cement paste under magnification ; even more than one specimen at a time, for the sake of obtaining as many cuts as possible. After the imbedding of the Fora­minifera, we covered the synthetic mass with a cellophane sheet, placing a sheet of glass on i t afterwards. Then, applyng a pression on the sheet of glass, we waited for one and a half or two hours for the hardening of the material.

3. Cutting : the hardened synthetic preparation was first cut on the imbedding side. Namely, the Foraminifera specimens are in the vicinity of the surface on the imbedding side. The covering layer is the thinnest in this place. We worked with the finestly grained cutting powder, on a glass sheet, controlling the cut surface at all times. Having reached the surface appropriate for study, we glued the preparation by Canada balsam onto an object slide, but carefully, since the synthetic imbedding material contracts on the action of heat. After gluing, we cut the other side of the- preparation. Cutting was first done on an iron sheet, then, having reached the suitable thinness, we continued i t on a sheet of glass. The appropriately thin cut was covered by an object slide.

In the course of cutting, we have established the following advantages of the use of this synthetic material :

1. For the preparation of the mass, room temperature is enough ; 2. The Foraminifere specimens can easily be imbedded into the paste under magnifi"

cation ; 3. Due to the elasticity of the synthetic material, the danger of the cracking of the tests

is considerably diminished ; 4. I t is suitable also for making preparation series.

Its disadvantage is that the polymerisator of Spofacryl binds rather quickly. This makes rather difficult the orientation of the specimens. For this cause, we used butylacetate instead of the original solvent. I n this way, the binding effect of the paste slowed down, and orien­tation could be made conveniently.

I t appeared during sectioning that for the purposes of our studies especially the Fora -minifera filled with minerals are the most suitable, since the walls of specimens of empty cham­bers cracked during cutting, impeding to obtain the necessary thinness. On the other band, the forms filled with pyrite are especially conforming for photographs, since, aside of the ex­ternal, also the internal contours are well delineated.

As mentioned above, the forms of thin calcareous tests or of empty chambers cause many difficulties. One has to be specially careful to cut these specimens, since the fine, thin separating walls wi l l soon crack, but this also can be obviated by a careful cutting. Forms with such fine walls were not imbedded in Spofacryl but in ,,Superacryl", (also a Czechoslovakian product), the more so as the color of the wall did not contrast with the color of the first mate­rial. This method does not essentially differ from the first one, but the latter material has a strong rosy hue, thereby differing from the color of the imbedded specimen, so its study and photographing are also easier.

I w i l l introduce some thin section pictures in the followings. Photographing the cuts meant some serious difficulties, since we could not obtain a cutting

thinness adequate for taking pictures. So the microphotographs are not always satisfactory. Recently, we make only surface cuts, since falling-on light is more appropriate.

Textularia carinata d 'Orb. Plate figs. la-b.

A form in the shape of a braid of hair, characteristical also in a th in section. The ini t ia l chamber is circular. The older chambers first appear i n an involuted form and only from the f i f th chamber on does the characteristical braid-like or biserial structure appear. The single chambers are elongated. The old apertures are well visible between the chamber walls i n the median line. The material of the test consists mainly of minute calcite grains, cemented also by CaCo3. This is proven by solving in hydrochlorid acid, as also by an examination w i t h a polarizing microscope. The inner separating walls of the chambers are thick, especially well observable i n younger chambers. The characteristical r im w i l l about disappear during cutting. Number of cham­bers : 22—24.

Textularia deperdita d'Orb. Plate figs. 2a-b.

Even the younger chambers develop immediately into the braid-like structure. Number of chambers : 10—12. Its material is agglutinated from calcite grains, the same as that of Textularia carinata.

Vulvulina pectinata Hantk . Plate figs. 5a-b.

A n arenaceous form of fine, minute calcite grains ; the older chambers take the shape of a narrow, elongated test. The younger chambers take a broader form, due to their shape. The separating walls of the younger chambers are thinner. The apertures of the chambers can be seen on the th in sections i n the younger ones only, and those too along the median line. Number of chambers : 25—26, joining each other i n the shape of a roof.

Vulvulina capreolus d'Orb. Plate figs. 4a-b

I t makes a big, broad test of fine mineral materials w i t h a chalk cement. The shape of the chambers is elongated, bending downwards. The line of the walls of its chambers presents an S-shape in the older chambers, that of the younger ones flows gradually into the external wall . The aperture is big between the younger chambers. The last chamber embraces, that is, covers, the two older ones. This is a very characteristical feature of the species, differring thereby from sublabelliformis. Number of chambers : 16—18. j

Gaudryina siphonella Rss. Plate figs. 6a-b

A n elongated form. Agglutinated from fine mineral grains. Tapering toward the older chambers. The torsional structure is observable also i n th in sections.

3 T e r m é s z e t t u d o m á n y i Múzeum É v k ö n y v e

Its chambers are oval, the apertures between the chambers are well visible. The ini t ia l chamber is circular also in this genus. Number of chambers visible in cuts : 20—21.

Clavulinoides szabói (Hantk.) Plate figs. 3a-b-c

Its section shows a cone-like shape. The triserial structure of the older chambers are well discernible. Upon these the younger, uniserial chambers are budt. The characteristical, tubuliform aperture can be seen only on the youngest chamber. The younger chambers are bui l t lobately onto the smaller, older chambers. The material of the test is agglutinated from relatively finer mineral grains. Number of chambers : 18—19.

I present the th in section picture of Clavulinoides szabói (Hantk.) shown by H a g n in figure 3 c. There is a rather big difference between the specimens shown by the above author and mine. As is to be seen on the figure (3 c), the shape is less like a cone, its chambers are not even, and i t is more roughly are­naceous. Number of chambers : 16. One may assume that the specimens intro­duced by H a g n is, at the best, a variation of szabói, but not a typical szabói.

I have made the t h in sectioning of the above enumerated arenaceous tests. Though there are many similarities among the several species, indeed, genera, we st i l l dispose of features which should demand the separation of species and genera, even on the base of th in sections.

I n the followings, I introduce some calcareous forms.

Robulus inornatus (d'Orb.) Plate figs, l la -b-c

I present, in th in sections, a megalospheric ( l i b ) and a microspheric (11c) form. The ini t ia l chamber of the megalospheric form is big, circular. The younger chambers are triangular. The separating walls are thick, similarly to the external wall . Number of whorls : 3. Number of chambers : 10—12.

I n the microspheric form, the ini t ia l chamber is also a sphere, yet very small. The younger chambers are bigger than the older ones. I t has more whorls than the megalospheric form, namely 5. The number of chambers is also higher : 19—20. The walls are also thick. The aperture characteristical of Rubulus is well visible on the external wall, at every chamber. I t shows no relationship w i t h any of the involuted forms described up to now. Its th in section picture resembles the best the section of Epislommina pacrtshiana (d'Orb.).

Marginulina fragaria Gümb. Plate figs. 8a-b

The younger chambers are broadening, uniserial, whilst the older ones are involuted. I t is a smaller and broader form than gladius. The characteristical ornamentation of the test disappears in the section. The in i t ia l chamber is circular.

The apertures are to be traced along the separating walls, situated near the wall of the test too. The more elongated aperture of the last chamber is also well discernible. Number of chambers : 12—13.

Nodogenerina badensis (d'Orb.) Plate figs. 7a-b

Of a gu t t ä t e form ; the number of chambers few : 3—4. The chambers are regularly increasing, of a semicircular shape. The ini t ia l chamber shows a well-formed circular shape. The elongated, tubuliform aperture is recognizable in the inside of the test, at the separating walls of the chambers. The test is relatively th in . The elongated, tubuliform apertures of the chambers are well visible on the figures.

Uvigerina pygmaea d'Orb. Plate figs. 9a-b-c-d

Racemose, of a torsional structure, w i th a tubuliform aperture. The material of the test is calcite. I present two forms, one of them is the microspheric big form w i t h a small in i t ia l chamber, w i t h the ribbing absent on the last chamber. This ribbing is naturally invisible on the th in section picture ; the older chambers are very small, whilst the younger ones are suddenly inflated ; this feature gives the tapering to the uinmpaired specimen.

The in i t ia l chamber of the macrospheric form is big, the form itself is small. The ribbing is absent also here on the young chamber. The number of chambers is much less i n than that of the megalospheric form.

Planulinella osnabrugensis (Miinst.) Plate figs. 13a-b

Its in i t ia l chamber is circular. The younger chambers have a trapezoid form. The last two chambers are larger than the others. The test is th in , there is no perforation visible. There is a pearl-like ornamentiation on the external shell, visible also in a th in section. The separating walls describe an undulating line. The number of whorls is very small : 3—4. The number of chambers is, based on the section : 14—16.

Well separable from the involuted forms discussed above. I n th in sections, its chief characteristics is the wavy separating line of the walls.

Cibicides ungerianus (d'Orb.) Plate figs. lOa-b

The ini t ia l chamber is circular. The chambers are relatively small. The separating walls of the chambers thicken towards the external wall so that the chambers seem to be lobate. The last whorl is visible on the umbilical side.

The walls of the chambers radiate towards the umbilicus. The perforation of the walls are but slightly visible. There are no apertures visible on the chamber walls. Number of whorls : 4. Number of chambers : 27—28.

Cibicides lobatulus (Walk.-Jon.) Plate figs. 12a-b

The ini t ia l chamber is circular. The younger chambers are narrow, elongat­ed, the separating walls tend radially towards the umbilicus. The last chamber, related to the others, is inflated, bigger. This influences the shape of the whole specimen. I t is slightly perforated. The apertures of the chambers are not dis­cernible. There are but 5 chambers visible in a cross section. Number of chambers: 18—20.

Summary

Of the fewr Foraminifera species examined up to now, dimorphism could be shown for Textularia depertita d'Orb., Marginulina gladius, and Robulus inornatus. There is a trimorphism in the case of Uvigerina pygmaea d'Orb.

Explanation of the Plate

1 a. Textularia carinata d'Orb.; a whole specimen 1 b. Textularia carinata d'Orb.; a thin section 2 a. Textularia deperdita d'Orb.; a whole specimen 2 b. Textularia deperdita d'Orb.; a thin section 3 a. Clavulinoides szabói (Hantk.); a whole specimen 3 b. Clavulinoides szabói (Hantk.); a thin section 3 c. Clavulinoides szabói (Hantk.); a thin section published by Hagn 4 a. Vulvulina capreolus d'Orb.; a whole specimen 4 b. Vulvulina capreolus d'Orb; a thin section 5 a. Vulvulina pectinata Hantk.; a whole specimen 5 b. Vulvulina pectinata Hantk.; a thin section 6 a. Gaudryina siphonella Reuss.; a whole specimen 6 b. Gaudryina siphonella Reuss.; a thin section 7 a. Nodogenerina badensis (d'Orb.); a whole specimen 7 b. Nodogenerina badensis (d'Orb;.); a thin section 8 a. Marginulina fragaria Gümb.; a whole specimen 8 b. Marginulina fragaria Gümb.; a thin section 9 a. Uvigerina pygmaea d'Orb.; a whole specimen of the megalospheric form 9 b. Uvigerina pygmaea d'Orb.; a thin section of the megalospheric form 9 c. Uvigerina pygmaea d'Orb.; a whole specimen of the microspheric form 9 d. Uvigerina pygmaea d'Orb.; a thin section of the microspheric form

10 a. Cibicides ungerianus (d'Orb.); a whole specimen 10 b. Cibicides ungerianus (d'Orb.); a thin section 11 a. Robulus inornatus (d'Orb.); a whole specimen 11 b. Robulus inornatus (d'Orb.); a thin section of the megalospheric form l i e . Robulus inornatus (d'Orb.); a thin section of the microspheric form 12 a. Cibicides lobatulus (W.—J.); a whole specimen 12 b, c. Cibicides lobatulus (W.—J.); thin sections 13 a. Planulinella osnabrugensis (Münst.) a whole specimen 13 b. Planulinella osnabrugensis (Münst.) a thin section

On the basis of our studies, i t was shown that the in i t ia l chamber of every Foraminifera examined is circular in the cases of both the arenaceous and the calcareous forms, that is, independently of shape and material of test.

Generally, th in section studies may answer also taxonomical problems and systematical connexions. B y their use, also relationships and transitional forms have been possible to observe.

As I have mentioned also in my introduction, i t appeared during my work that i t is more advisable and assures a better and more systematical treatise to examine the specimens by genera and, wi th in them, by formations. I deem i t especially important to work out systematically the th in section pictures of the genera of arenaceous forms. By the use of an adequate microtechnical equipment, we shall obtain valuable data also for the structure of the test walls of Foraminifera.

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