Assoc. Prof. I. I. Ammosov

FOSSIL MICROFLORA FROM THE COALS OF THE BUKACHACHA DEPOSIT IN TRANSBAIKALIA

GENERAL REMARKS

Twenty-three samples of Bukachacha coals were subjected to study, characterizing seams 0, I, II, IIbis, and III. The work was carried out at the request of the East Siberian Geological Trust. The samples were given to me by Engineer Yu. P. Deev.

All the samples studied are readily macerated by Schulze’s mixture, i.e., a mixture of concentrated nitric acid and potassium chlorate. The study of the maceration products was carried out in permanent preparations and was accompanied by drawings, photographs, and measurements. Fairly high magnifications (up to 1000) were used for the drawings. In studying maceration products in permanent preparations, oil immersion should be recommended.

The best results are obtained by maceration of semidull coal, as well as of semibright coal with lenticular parting. The maceration products of these coals have a brown or brownish-brown color and contain an abundant microflora, often well preserved, as well as a varied cuticle and rare algae. In the maceration of dull coal, poorer results are obtained. Thus, in a fairly abundant solid residue, black in color, there is usually a considerable quantity of dark fragments of the cellular tissues of coal-forming plants, in which the cellular structure is clearly visible; there are also rather many mineral impurities here, but considerably less pollen and cuticle.

In the maceration of vitrain, of bright striated coal, and also of semibright coal lacking lenticular parting, in most cases less favorable results are obtained than in the maceration of semidull coal or semibright coal with lenticular parting. For example, vitrain contains no pollen and, after maceration, yields a very small residue, in which inorganic formations predominate, since the entire organic mass dissolves during maceration of this ingredient. In the maceration of bright striated coal, a rather considerable brown residue remains, but cuticle predominates in it, while comparatively little pollen is present. From semibright coal lacking lenticular parting, a dark residue is obtained that likewise contains little microflora.

Pollen and macrospores of plants have been studied very little. This applies not only to fossil plants, but also to modern ones.

In modern botanical literature one can only rarely find schematic drawings of the pollen of certain modern plants. From these drawings it is impossible to form an idea either of the variations in the character of the pollen of a single species, or of the features that distinguish the pollen of a given species or genus from other species and genera. In comparing the pollen found in the maceration products of the Bukachacha coals with the pollen of modern plants, I prepared slides containing the pollen of modern conifers, since the organs of plants of this class are most frequently encountered in the coals studied. These slides contain the pollen of the following modern conifers (8).

All these slides were prepared from plants preserved in the herbarium of Tomsk State University, which were kindly placed at my disposal by Associate Professor L. P. Sergievskaya, curator of the herbarium; I take this opportunity to express my gratitude to her.

The pollen of modern conifers examined in the above-mentioned slides differs rather markedly among the various subfamilies. Especially sharply distinguished is the pollen of the subfamily Abietineae. This pollen consists of a central body (the living cell) and two paired air sacs attached to the central body¹. The sacs are filled with air and are intended for the aeration of the pollen.

The envelopes of the central body and of the air sacs are composed of a very resistant organic substance—pollenin (sporonin), which, according to Zetzsche’s data,^1 has the formula \(C_{90}H_{131}O_{16}(OH)_{13}\). This formula was determined by Zetzsche for the envelope of the pollen of Pinus silvestris. Pollenin contains 67.11% carbon and 9.02% hydrogen. In the process of humification and coalification it changes very slowly, which accounts for the preservation of the form and structure of pollen-grain envelopes in fossil coals.

In the description we shall distinguish the dorsal and ventral sides of the pollen grain (Appendix I, Fig. 1), as well as the central body and the air sacs. In addition, in describing pollen it is often necessary to indicate the dimensions of the central body and of the air sacs. By the letter \(L\) we shall denote the greatest total length of the pollen grain; the length, height, and width of the central body will be denoted respectively by the letters \(l_1\), \(h_1\), and \(b_1\), and the length, height, and width of the air sacs by the letters \(l_2\), \(h_2\), and \(b_2\) (Appendix I, Fig. 1, and Appendix II, Fig. 2).

Most often in the maceration products of the Bukachacha coals there occur pollen grains with paired air sacs (Appendices I, II, and III), intended for aeration of the pollen. The anatomical structure of these pollen grains is analogous to the structure of modern conifers of the subfamily Abietineae.

In studying pollen grains possessing paired air sacs, a very great diversity is observed in permanent preparations, caused both by different positions of the grains (Appendix II, Figs. 1, 2, 6, and Appendix III, Figs. 1 and 2) and by their features characteristic of different genera and species. Among the latter features of pollen grains, it seems to me, should be included the size and shape of the central body, as well as the absolute size of the air sacs, their shape, and the manner in which they are attached to the central body. In addition, the relative dimensions of the air sacs and of the central body may serve as a taxonomic character.

It should be noted that, when examining pollen belonging even to a single species of the subfamily Abietineae, one may observe a fairly great apparent diversity in the outlines and structure of the pollen grains. Thus, they are observed now from the ventral side, now from the dorsal side, now from the side, and are not infrequently turned half over. In addition, the air sacs are sometimes strongly deformed or completely torn away from the central body. The latter is especially often observed in fossil pollen. All this greatly complicates the study of pollen of the subfamily Abietineae.

^1 I quote according to G. L. Stadnikov.

DESCRIPTION OF THE MICROFLORA

A. POLLEN OF CONIFERS OF THE SUBFAMILY Abietineae

1. Picea kryishtofovichi n. sp. (Plate I, figs. 2 and 4).
Dimensions of the pollen:

\[ \begin{aligned} L &= 83\text{—}120\ \mu \\ l_1 &= 59\text{—}62\ \text{»} \\ b_1 &= 85\text{—}94\ \text{»} \\ l_2 &= 35\text{—}53\ \text{»} \\ b_2 &= h_1 = 85\text{—}94\ \mu \end{aligned} \]

The line of attachment of the air sacs to the central body is oriented with its convex side from the center toward the periphery (Plate I, figs. 3 and 5). When viewed from the ventral side, the central body has a biconstricted form and relatively thin walls, 2–3 μ thick, the thickness of which can be observed in optical sections.

From the ventral side the air sacs almost cover the central body. As a result, only a narrow lens-shaped “slit” of the uncovered part of the central body remains, outlined by the lines of attachment of the air sacs.

No polygonal network, usual for the pollen of modern conifers, was observed on the air sacs (Plate I, figs. 3 and 5). In the pollen described here, the surface of the air sacs is weakly granulated. However, the absence of the polygonal network usually observed on the sacs of pollen of modern conifers may be attributed to deformations during the process of coalification, as well as to optical distortions.

In size, form, and the character of the line of attachment of the pollen sacs, convex toward the periphery, the pollen described very strongly resembles the pollen of the modern P. vulgaris, drawings of which are given for comparison (Plate I, figs. 3, 5, and 6).

It seemed that the pollen shown in figs. 2 and 4 (Plate I) could be assigned to different species of conifers; however, study of the pollen of P. vulgaris made it possible to establish, in one preparation, homologous forms shown in figures 3, 5, and 6 (Plate I). Thus, it is more correct to assign this pollen to a single species.

2. Pinus ussovi n. sp. (Plate II, figs. 1, 2, 4).
The characteristic dimensions of the pollen vary within the following limits:

\[ \begin{aligned} L &= 70\text{—}84\ \mu \\ l_1 &= 43\text{—}50\ \text{»} \\ h_1 &= 38\text{—}49\ \text{»} \\ l_2 &= 36\text{—}41\ \text{»} \\ h_2 &= 37\text{—}39\ \text{»} \end{aligned} \]

From the ventral side of the pollen it is evident that the line of attachment of the air sacs is oriented with its convexity from the periphery toward the center (Plate II, fig. 2). By this feature the pollen described is strong-

but differs from the preceding genus. The thickness of the walls of the envelope of the central body is greater (3–5 μ) than in the preceding genus (2–3 μ).

The central body, from the ventral side (Plate II, figs. 2 and 4), has an oval or rounded form. When the pollen grain is viewed from the side, the form of the central body is rounded-triangular (Plate II, fig. 1).

The air sacs are shifted toward the ventral side, where they almost touch (Plate II, figs. 1 and 2). On the surface of the sacs of some specimens a polygonal network is clearly visible (Plate II, fig. 1). On the air sacs of other specimens, however, this network is less well preserved (Plate II, figs. 2 and 4). In the latter case, on the surface of the air sacs we see only small dots, which may be explained by the causes mentioned above.

The specimens shown in the drawings most closely resemble the pollen of the modern genus Pinus. For comparison I give several drawings of two species of modern pine, namely: P. pinaster (Plate II, fig. 3) and P. silvestris (Plate II, fig. 5). The drawing of the pollen of P. pinaster was made with the microscope objective in such a position that the outline of the central body is in focus, while the swollen air sacs, facing their convex side toward the observer (before us is the ventral side), are in optical section; as a result, the polygonal network is not visible on them.

Two drawings of the pollen of P. silvestris (Plate II, figs. 5a and 5b) were made from a single specimen, but at different positions of the objective. The drawing designated by the letter a, in which the air sacs turned toward the observer are clearly visible, was made at a greater distance from the pollen to the frontal lens of the objective, while drawing b was made after the objective had been brought somewhat closer. Thus, in the second case we obtain an optical section of the pollen shown above from the ventral side. In drawing b the thick walls of the central body can be seen.

Comparing the fossil pollen with the modern pollen (Plate II), we see that fig. 2 has a great resemblance to the pollen of P. pinaster (fig. 3), while fig. 4 is rather close to fig. 5. This resemblance will be still greater if one takes into account that the pollen shown in fig. 4 is somewhat turned. This confirms the correctness of assigning the fossil pollen to the genus Pinus.

1. Pinus parva n. sp. (Plate II, fig. 6). This pollen differs from the preceding forms by its small dimensions:

\[ \begin{aligned} L &= 44\ \mu \\ l_1 &= 40\ » \\ h_1 &= 32\ » \\ l_2 &= 20\ » \\ h_2 &= 23\ » \end{aligned} \]

The relative dimensions of the central body and the air sacs also sharply distinguish this pollen from the two preceding genera. Thus, its central body is large, while the air sacs are relatively small, as is evident from a comparison of the dimensions \(l_1\) and \(l_2\).

It should be noted that the pollen described occurs rather rarely.

1. Pityophyllum (?) disertum n. sp. (Plate III, figs. 1 and 3).

This pollen differs from all the preceding genera and species in that its air sacs are considerably larger than the central body. The width of the air sacs \((b_2)\) is especially sharply distinct, being considerably greater than the width of the central body \((b_1)\).

\[ \begin{aligned} L &= 88\text{—}96\ \mu \\ l_1 &= 35\text{—}47\ » \\ b_1 &= 40\text{—}54\ » \\ l_2 &= 46\text{—}47\ » \\ b_2 &= 55\text{—}75\ » \end{aligned} \]

The line of attachment of the air sacs is convex from the center toward the periphery. The central body is often divided down the middle by a dark line. When viewed from the dorsal side, the central body has a pear-shaped or quadrangular outline (Plate III, figs. 1 and 2). The thickness of the walls of the central body is slight along the margins, but toward the ventral and dorsal sides of the pollen it usually increases (Plate III, fig. 1). No polygonal mesh was observed on the air sacs. Usually the surface of the sacs is covered with small, grain-like dots.

Among all the preparations of pollen of modern conifers examined by us, no pollen grains were found resembling the pollen described. On the basis of the presence of paired air sacs, their original form and attachment, it may be suggested that the pollen described belongs to an extinct conifer of the subfamily Abietineae (see below).

B. MICROSPORES OF OTHER PLANTS

In addition to conifer pollen, which is the most numerous, the maceration products of the Bukachacha coals also contain pollen (microspores) of cycads, ferns (?) and horsetails (?).

The pollen of cycads has a wedge-shaped, elongated form. Its ends are sometimes sharp, sometimes somewhat blunted (Plate III, figs. 3 and 4). The surface of the pollen envelope is often covered with small and sparse grain-like thickenings—granules. In addition, on some specimens two lens-shaped films can be observed, slightly overlapping one another (Plate III, fig. 3). Such pollen is present in all the seams, but in a small number of specimens.

Fern microspores also occur in many samples, but their number is small. The form and size of the fern microspores, as well as the sculpture of the wall, are varied. Thus, triangular, oval, and round fern microspores are encountered. Among them, forms with a smooth surface predominate. Only occasionally is pollen observed with a granular, granulated sculpture (Plate III, fig. 6), and pollen with a coarsely tuberculate sculpture is entirely absent. The latter is often observed in the maceration products of Kuznetsk and Tunguska coals.

In addition, pollen resembling horsetail pollen is encountered rarely. However, I am not confident of the correctness of this determination. Such pollen is shown in fig. 5 (Plate III). It is possible that the darker band, capriciously curving within the outline of the spore, is the remnant of one of the elater ribbons characteristic of horsetail spores.

AN ATTEMPT TO CORRELATE POLLEN WITH PLANT IMPRESSIONS

The maceration products of the Bukachacha coals contain various microspores, cuticle, fragments of tracheid tissue of conifers, and also rare algae.

The microspores correspond to the taxonomic groups of fossil plants established in the Baikalian division of the Angara series of Transbaikalia (3) by various paleobotanists. Thus, in the maceration products we have horsetail pollen (Plate III, fig. 5), cycad pollen (Plate III, figs. 3 and 4), fern microspores (Plate III, fig. 6), but conifer pollen is especially abundant here. In the present work, the conifer pollen has been studied in more detail than the rest of the microflora. It proved that this pollen belongs to the subfamily Abietineae, in which it was possible to establish three genera and four species.

In the Jurassic continental deposits of Transbaikalia, in the broad sense, the following impressions of conifers or plants close to them have been established:

1. Pinus witimi Reis
2. Pinites kobucensis Sew.
3. Brachyphyllum boreale Heer.
4. Pagiophyllum sp.
5. Schizolepis möleri Sew.
6. Pityophyllum lindstromi Nath.

Of all these conifers, only Pinus witimi Reis is more definitely assigned to the subfamily Abietineae. However, impressions of seeds of this conifer, named by O. Reis P. witimi (6), were found considerably northwest of the area of development of Jurassic coal-bearing deposits of Transbaikalia proper, on the Vitim River, and relative to the deposits of the productive sequence of the Bukachacha deposit

…they have no direct relation. For us this find is of interest in that it definitely establishes the presence of conifers of the subfamily Abietineae in the Jurassic continental deposits of Siberia.

With regard to the genus Pinites, A. N. Krishtofovich (4) indicates that “the designation by this genus of impressions from Jurassic deposits must be regarded as purely provisional, since neither by the structure of the wood nor by the cones has it yet been possible to confirm their definite taxonomic position.” The four species of conifer pollen from the subfamily Abietineae that I have discovered indirectly point to the probable belonging of the genus Pinites to the subfamily mentioned.

In describing impressions of P. kobucensis from the Jurassic continental deposits of Transbaikalia, A. N. Krishtofovich (2) notes in them a narrow, not more than 1 mm wide, but rather long, not less than 3 cm, needle, characteristic of this species.

With regard to the genus Schizolepis it should also be noted that its taxonomic position has not been firmly established. For example, A. N. Krishtofovich remarks: “the assignment of the genus mentioned to the subfamily Abietineae is somewhat questionable. This genus is characterized by long loose cones, by a scale split into two lobes, and by leaves of the pine-needle type” (4, p. 240).

S. mölleri was described by A. N. Krishtofovich from the Jurassic continental deposits of Transbaikalia (2, p. 86). Here the cones and scales were found isolated from the vegetative parts, but in the same place with them, as A. N. Krishtofovich indicates, there are impressions of needles of Pinites kobucensis, which makes possible the supposition that they belonged to one and the same plant (2, p. 92). Let us note, however, that the peculiar long, loose cones may indicate their belonging to the genus Picea, the pollen of which I have found in the Bukachacha coals.

The genera Pagiophyllum and Brachyphyllum are considered by Potonié (7, p. 334) in the group of conifers occupying an indeterminate systematic position, which also includes the leafless parts of these plants. A. N. Krishtofovich recommends considering these genera outside systematic limits (4, p. 241). Will not our finds serve as material for deciphering the systematic position of these genera as well? Thus, it is possible that the impressions assigned to the genera mentioned in the Jurassic deposits of Transbaikalia are leafless parts of conifers of the subfamily Abietineae; as mentioned above, the characteristic pollen of these conifers is very abundant in the maceration products of the Bukachacha coals.

The genus Pityophyllum was formerly assigned to the conifers. For example, Nathorst even considers it possible provisionally to place it in the subfamily Abietineae (7, p. 326). In A. N. Krishtofovich’s course of paleobotany (4), this genus is not mentioned in the characterization…

systematic groups of fossil plants. However, in the description of the Jurassic flora of extratropical Asia, we find the following indication: “it should be noted that what was previously described as the conifer Pityophyllum nordenskiöldii more likely belongs to some horsetail plant, probably close to Neocalamites” (4, p. 329). In another work, A. N. Krishtofovich and V. D. Prinada (5, p. 23) divide the genus Pityophyllum into two independent genera—P. moor, assigned to the class Bennettitales, and P. nath, left in the class of conifers.

In the Jurassic continental deposits of Transbaikalia, impressions of P. nordenkisoldi and P. lindstromi Nath. have been found. If doubts arise concerning the assignment of the first form to the conifers, the second occupies a firmer position. Taking into account the possibility, indicated by Nathorst, of assigning this genus to the subfamily Abietineae, and making use of the data from the study of the pollen, it is possible to suppose that the Transbaikalian impressions of P. lindstromi Nath. also belong to this subfamily. Probably the original pollen, described above as P. disertum, belongs to this extinct conifer.

An approximate parallelization of the conifer impressions with our names for the pollen, not claiming precision, may be made as follows:

Since there is no complete certainty as to the correctness of such a parallelization, which must be clarified by further work, it should be considered appropriate to use the new names designating the pollen of various representatives of the subfamily Abietineae from the Bukachacha deposit of Transbaikalia.

CONCLUSION

Some impressions of fossil plants from the Jurassic continental deposits of Transbaikalia, mentioned above, were provisionally assigned by previous investigations to the conifers. The study of the microflora, represented chiefly by pollen of conifers with paired air sacs, confirms the correctness of such determinations and permits the suggestion that some of the impressions belong to the subfamily Abietineae. This is of particular interest for the genera Schizolepis

and Prtyophyllum. Thus, in my opinion, based on a comparison of the fossil pollen and plant impressions, they may be assigned to two different genera of the subfamily Abietineae. At the same time, Schizolepis, described by A. N. Krishtofovich from impressions of long and loose cones, can perhaps be paralleled with the modern genus Picea, since abundant spruce pollen was established by me in the maceration products of the Bukachacha coals. Spruce has been discovered in the Jurassic deposits of Siberia for the first time. Until now it had been believed that it occurs no lower than the Cretaceous deposits.

The abundance of conifer pollen in the coal-bearing deposits of the Bukachacha deposit indicates the strong development of plants of this class as early as the Jurassic period. On the other hand, the abundance of conifers and the presence among them of the genus Picea indicate that the age of the Bukachacha deposits is certainly no older than the very uppermost Jurassic.

In addition, the abundance of conifer pollen, as well as the presence in the maceration products of tracheid tissue of conifers, makes it possible to make some observations on the original material of the Bukachacha coals. Conifers were probably the principal source material in the formation of these coals. The accumulation of dead plant material apparently took place in distinctive forest peat bogs.

The usual poor preservation of conifer impressions, on the one hand, and, conversely, the excellent preservation of their pollen, on the other, make the study of fossil conifers by means of pollen highly desirable; this should yield much that is new. The powerful method of studying microflora, based on the maceration of coals and carbonaceous rocks, places in the hands of the modern investigator the richest material, which was not available to our predecessors.

LIST OF REFERENCES USED

1. Krishtofovich, A. N., Jurassic plants from the Tyrma River, collected by V. S. Dokturovskii. Transactions of the Geological Museum of the Academy of Sciences, 1914, vol. VIII, issue II.

2. Krishtofovich, A. N., Plant remains from the lacustrine Jurassic deposits of Transbaikalia. Proceedings of the Mineralogical Society, 1918, series II, part 51.

3. Krishtofovich, A. N., The Baikal division of the Angara series, Transactions of the All-Union Geological Prospecting Association, 1933, issue 326.

4. Krishtofovich, A. N., Course in Paleobotany, 1934.

5. Krishtofovich, A. N. and V. S. Prinada, Guide to the Mesozoic Flora of the USSR, 1934.

6. Reis, O., Fauna of the fish shales of the Transbaikal region. Geological investigations and prospecting work along the Siberian Railway, 1910, issue XXIX.

7. Potonie, H., Lehrbuch der Palaeobotanik, 1921.

8. Reisner, L., Handbuch der Nadelholzkunde, 2nd edition, 1909.

APPENDIX I

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 1. Schematic representation of conifer pollen from the subfamily Abietineae, indicating the elements mentioned in the descriptions.

Fig. 2. Picea kryshtofovichi n. sp. Microphotograph of pollen of fossil Jurassic spruce from the ventral side. Seam II from the Ibis mine (×220).

Fig. 3. P. vulgaris Link. The same, of a modern spruce (×420).

Fig. 4. P. kryshtofovichi n. sp. The same, of fossil Jurassic spruce. Seam II from mine I (×420).

Fig. 5 and 6. P. vulgaris Link. The same, of a modern spruce. Seam II from borehole 11 (×420).

APPENDIX II

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5a.

Fig. 5b.

Fig. 6.

Fig. 1. Pinus ussovi n. sp. Pollen of a Jurassic pine, lateral view. Seam II from the Ibis mine (×420).

Fig. 2. P. ussovi n. sp. The same, view of the abdominal side. Seam II from the Ibis mine (×420).

Fig. 3. P. pinaster Sol. View of the abdominal side of pollen of a modern pine (×420).

Fig. 4. P. ussovi n. sp. Pollen of a fossil Jurassic pine. Seam I from borehole 11 (×420).

Fig. 5. P. silvestris L. Pollen of a modern pine: a) abdominal side, b) optical section. Both drawings were made from a single specimen (×420).

Fig. 6. P. parva n. sp. Pollen of a fossil pine in two projections. Seam II from the Ibis mine (×420).

APPENDIX III

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 1. Pityophyllum disertum n. sp. View of the pollen grain from the dorsal side.
Bed III from borehole 11 (×420).
Fig. 2. P. disertum n. sp. The same (×420).
Fig. 3, 4. Cycad pollen (?). Bed II from borehole 11 (×420).
Fig. 5. Horsetail pollen (?). Bed II from borehole 11 (×420).
Fig. 6. Fern microspore (?). Bed I from borehole 6 (×420).

1. An exception is the pollen of the genus Larix. ↩