Libmonster ID: BY-1548
Author(s) of the publication: Sergei NAUGOLNYKH

by Sergei NAUGOLNYKH, Dr. Sc. (Geol. & Mineral.), RAS Geological Institute

The Mazuevka locality, where different plant fossils can be found, of the early-Permian age (more precisely-of Kungurian, 273-269 mln years ago), was discovered several years ago, in 180 km to the south-east of the city of Perm, thanks to the studies of the large outcrop of sandstones and clayey shales on the left bank of the Sylva river between the village of Mazuevka and the Cherny Yar.

Although specimens of ancient fossil plants from this outcrop appeared in paleobotanical collections even before, they originated from small localities and their number was insignificant.

The recent, much more plentiful findings of fossil plants permitted to look at the origin of this locality under new viewpoint.

FROM BIOSPHERE TO LITHOSPHERE

At first we should talk about taphonomy, as it and its conceptual apparatus are especially valuable for paleobotanical studies* of the Permian plants.

The fundamentals of this science as an independent discipline about regularities in the origin of localities of fossil organic remains were suggested in the 1940s by Ivan Efremov, Dr. Sc. (Biol.), famous Russian paleontologist and science-fiction writer. In his fundamental work Taphonomy and Geological Chronicle (1950), he analyzed in detail prerequisites for setting apart the taphonomy

See: S. Naugolnykh, "Seven Steps Into Paleozoic", Science in Russia, No. 5, 2005.--Ed.

among geological and biological sciences, drew up a generalized typological scheme of land vertebrates' localities (and that is not surprising, as he was mostly dealing with studies of the Late Paleozoic and Mesozoic terrestrial tetrapods), introduced methodological principles for the reconstruction of their way of life and of the landscapes they inhabited.

One of the key illustrations in the above-mentioned book is a diagram, expressively demonstrating the optionality of burials of organic remains, which is directly reflected in the remoteness of their transfer. Dr. Efremov clearly showed that the biggest and the most massive remains are usually preserved not far from the place of the

стр. 25

animal's death, and more lightweight ones are transferred further by water flow By the way, this rule does not prove to be true for plants, as big stems are spread with flows and torrents very far from the place they initially grew.

The paleontological society, which is as a rule very conservative, took the publication of the Taphonomy with enthusiasm. Moreover, the new science was hailed even abroad.

It should be noted that taphonomic methods are important not only for studies of vertebrates, but also for determining the conditions of fossil plants' burials, which Dr. Efremov repeatedly mentioned in his monograph. And this is just the time to turn to the subject of this article.

OVER THE SYLVA FLOODLANDS

The first extensive collections of ancient plant residues near the Mazuevka were made in 2008-2009 by the employees of Kungur Historical, Architectural and Arts Museum (Perm region). During my trip to Kungur, Director of the Museum Sergei Mushkalov and head of the nature department Ludmila Dolgikh gave me an opportunity to get acquainted with the collection. Even the preliminary examination of the specimens showed that it was necessary to continue the studies. And in 2009-2010 we and the colleagues from this museum organized joint field works at the Mazuevka locality. In previous expeditions, I repeatedly came across the Permian sections not only in the Urals, but also in other regions of the Northern Hemisphere. However, the Mazuevka section not only made me happy by new finds, but also surprised me.

The total thickness of the rocks exposed here is about 80 m. The lower part of it consisted of intercalating finegrained siltstones and argillites*. The observed thickness of this packet (or sedimentary unit labeled as A) is 3 m. Higher there is a considerable--from 40 m to 50 m--packet of polymictic (i.e. assembled grains of different minerals) sandstones (B). Above it there are black and dark-gray thin-layer mudstones (C) with the thickness of approximately 20 m.

Judging by the lithological particularities, the sediments, which had formed all three packets, were deposited in conditions of relatively shallow water. One can sup-

* Siltstone is a sedimentary rock, consisting of consolidated fragments of mineral grains of a size of 0.1-0.01 mm; argillite is a clayey rock, which does not soak in water.--Ed.

стр. 26

pose more considerable depth only for the accumulation (but hardly more than 100-200 m) of last packet C.

The overwhelming majority of plant remains in the Mazuevka locality is concentrated in the lower part of packet B. Taxonomic composition of this flora includes equiseto-phytes Annulina neuburgiana (Radczenko) Neuburg, Phyllo-theca sp., Paracalamites sp., ferns Pecopteris uralica Zalessky, P. anthriscifolia (Goeppert) Zalessky, lycopodiophytes (which belong to a previously unknown species and genus and require further studies), peltasperms (they belong to gymnosperms) Rhachiphyllum (al. Callipterisretensorium (Zalessky) Naug., Gracilopteris lonchophylloides Naug. Here are preserved pre-ginkgophytes* Psygmophyllum expansum (Brongn.) Schimper, P. cuneifolium (Kutorga) Schimper, ginkgophytes Kerpia sp., Karkenia sp., vojnovskyans**. In

* Pre-ginkgophytes are predecessors of ginkgophytes, an almost extinct class of gymnospermous plants, with a single present day representative--Ginkgo biloba.--Ed.

** Voinovskyales, vojnovskyans, is an order of gymnospermous deciduous plants, growing in temperate and mountainous zones of the Northern Hemisphere during the Permian.--Ed.

the sandstones of packet B one can find fossil remains of shoots of conifers Tylodendron sp., Walchia sp.

The fossil remains of pre-ginkgophytes--psygmofylloids, a very interesting and uncommon group of plants, the ancestor of the Ginkgoales, which were widespread in the Mesozoic (it started about 235 mln years ago and lasted for 170 mln years), are prevailing in the Mazuevka deposits. Ecologically, they and primitive ginkgophytes (they can also be occasionally found in the Mazuevka locality) were mesophiles*, which preferred middle, neither the highest nor the lowest parts of drainable slopes of the Paleo-Urals, along to the vast, but relatively shallow warm bay.

TAPHONOMIC PARADOX

Mazuevka section differs from other sections of the Kungurian deposits in this region taphonomically. We can see that the sediments of the Mazuevka section were

* Mesophiles are organisms, which normally prefer average temperatures (20-40°C), and are dominant in temperate zones.--Ed.

стр. 27

formed in relatively shallow conditions. But there are practically no fossils of water - or near-water plants, though seemingly they must be there first of all.

Alas, "Taphonomy of land plants", comparable with Efremov's work, has not been written yet. However, almost all paleobotanists, who regularly take part in expeditions, work on the field taphonomic observations. I generalized results of my own observations on taphonomy, accumulated for many years of field work, in a paleoecological chapter of the monograph Permian Floras of the Urals (M.: Geos, 2007). I compared data of taxonomic composition of the fossil plants in different deposits and localities, their coincidence with sediments of definite types. Also, on the basis of ecologically significant morphological and microstructural characters-markers, pointing to conditions, in which the parent plant was growing, I came to the following conclusions.

Vegetation of the Early Permian* (Kungurian age of the Early Permian) formed two distinct basic plant associations (communities) in the Urals area. Each of these plant associations was structured, but with less clearness. One of them, represented the near-water community, consisting mostly of representatives of different groups of equisetophytes, was situated mainly on flat and frequently waterlogged sea shores, lagoons, or lakes. Another plant association was situated on upliftings, and was formed by mesophilic and xerophilic** plants, presented by different gymnosperms and some groups of ferns.

Obviously, the near-water plant association of the Mazuevka flora was poorly developed, while mesophilic plants were flourishing, inhabiting the middle part of

* The Permian-is the last period in the Paleozoic. It extends from

280± 10 to 235+10 mln years before the present.--Ed.

** Xerophytes are plants, able to survive in dry habitats.--Ed.

стр. 28

catena*. Their fossil remains are dominating in the Mazuevka locality. There are not many plants from higher parts of the catena (evidently, due to relative remoteness of transfer of their fragments to the formed locality). Fossils of the equisetophytes, e.g. paracalamites, are very rare there. It is forming the main component of Permian near-water plant associations of Angarida**, are very rare there. So, why there are no abundant near-water plants in the Mazuevka locality? Solution of this paradox consists in reconstruction of general paleogeographical and paleolandscape situation, which took place in the Urals in the Early Permian.

* Catena is a sequence of plant associations (communities) consisting of ecologically different plant groups, which replace each other in correspondence with the distance between association and a water reservoir or a stream, according to the altitude gradient changing.--Ed.

** Angarida is a continent, which existed at the place, where Northern Asia is located, in the second half of the Paleozoic and the first part of the Mesozoic, was separated from Gondwana by the Tethys Sea.--Ed.

Some segments of the Paleo-Urals, more exactly its coastal ranges facing the sea gulf to the west, felt rapid, but low amplitude elevations in the conditions of last phases of mountain-forming movements in Late Paleozoic. Therefore, conditions for growing of near-water plants disappeared in such raised segment or tectonic miniblock, and all near-water plants died out there. Associations of moisture-loving plants, existing in near-water habitats, had disappeared there. In contrast, mesophilic and xerophilic plants received competitive advantages in such conditions.

The basis of erosion had changed, which affected the character of sedimentation: mighty mass of coarsegrained polymictic sandstones with interlayers of conglomerates, consisting of Ural rock fragments (clasts) started to form instead of thin-layered and fine-grained Kungur argillites, siltstones, and marls, accumulating in shallow lagoons.

стр. 29

Thus, the Mazuevka locality was formed in conditions of high hydrodynamics and active drift of clastic (granulated) material from the foothills of Paleo-Urals. The Mazuevka locality characterizes the time of development of the vegetation of drained mountain slopes, but not vegetation of near-water plant community. Probably, this is a clue to the solution of the phenomenon under consideration. Such taphonomic situation could arise only in case, when the first segment of the catena, consisting of the near-water plant association, was absent due to an unfavorable landscape for its development. Fossil remains of mesophilic plants predominated in a relatively coarse-grained sediments.

VOJNOVSKYOPSIDA IS A NEW CLASSIS OF GYMNOSPERMS

It is paradoxical, but a rather low taxonomical variety of the Mazuevka locality (for example, in comparison with the world famous locality of Chekarda-1 also disposed on the left bank of the Sylva River, in 60 km upstream from the Mazuevka locality) allows to answer some important questions, concerning understanding of biological features of the ancient plants belonging to the extinct groups, which are absolutely absent in the present-day vegetation.

One of such groups is the Vojnovskyales order. Gymnosperms belonging to this order often informally are called vojnovskyans. The reproductive organs of vojnovskyans are very uncommon, and hence the interpretation of the reproductive organ morphology was intricate and unclear for a long time. Relationship of different organs of the vojnovskyans also was not clear.

The author of the present article has suggested to consider vojnovskyans as a new Vojnovskyopsida classis, which is forming a sister group with other closely related Pinopsida classis.

Gymnosperms of Vojnovskyopsida classis are characterized by cone-like female reproductive organs belonging to

стр. 30

the genera Bardocarpus, Suchoviella and a number of already known, but still undescribed, forms from the Permian deposits of Angaraland, the flattened and shortened female reproductive organs of the genera Gaussia, Taibia, Niazonaria, and Scirostrobus, bearing seeds of Samaropsis and Sylvella types. Male reproductive organs of vojnovskyans assigned to the genera Vojnovskya and Pechorostrobus, which consisted of the axes sometimes expanding to their apices. The microsporangia ("andro-phores") were attached to the axes in a spiral order. The lower parts of the male reproductive organs possessed the sterile appendages.

The Mazuevka locality represents a rare possibility for making quite definitive conclusions on a possible combination of various organs of vojnovskyans. There are the lanceolate leaves assigned to the Rufloria genus, which most likely belong to one or maybe two species of parent plants. Insignificant differences of these leaves can be explained in terms of intraspecific variability. The scale-like leaves Nephropsis sp. of characteristic subtriangular shape were found together with the lanceolate leaves of Rufloria recta (Neub.) S.Meyen. The Nephropsis scales were attached to the reproductive shoots with the male lateral cones disposed on the same shoot.

The female (seed-bearing) reproductive organs Gaussia sp. were characteristic of the vojnovskyans with the Rufloria recta leaves. Only isolated seed scales of Gaussia were found in the Mazuevka locality, but completely preserved cones of Gaussia, often together with the Rufloria recta leaves, were collected from Chekarda-1 locality.

Similar repeating associative combinations of different organs of vojnovskyans are known from the other Permian floras of the Cis-Urals, Siberia, and Mongolia, i.e. practically on the whole territory of Angaraland in the Late Paleozoic.


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Sergei NAUGOLNYKH, PERMIAN FLORA: MYSTERIES AND PARADOXES // Minsk: Belarusian Electronic Library (BIBLIOTEKA.BY). Updated: 20.09.2021. URL: https://biblioteka.by/m/articles/view/PERMIAN-FLORA-MYSTERIES-AND-PARADOXES (date of access: 27.10.2021).

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