Taphonomy and paleoecology of fauna and flora from deltaic sandstones of Mospinka Formation (Middle Carboniferous) of Donets Basin

In addition to the body remains of Arthropleura, traces of their locomotion are also well studied, which were called Diplichnites cuithensis Briggs, Rolfe et Brannan, 1979 (tracks up to 38 cm wide, belonging to adult animals) and Diplichnites minimus Walter et Gaitzsch, 1988 (tracks left by juvenile individuals) (Briggs et al., 1979; Schneider et al., 2010). Nevertheless, the second ichnospecies is apparently a subjective synonym for the first (Getty et al., 2017). These trace fossil are known from the Upper Visйan - Asselian deposits of the USA, Canada, Scotland, Germany, and France (Schneider et al., 2010; Whyte, 2018).

There is evidence for the presence of traces of Arthropleura locomotion in the Pennsylvanian sediments of the Zhezkazgan depression (Kazakhstan) (Nelikhov, 2010). Here, P. K. Chudinov in 1958, among the deposits of the Zhezkazgan Series, studied numerous traces of the locomotion of "labyrinthodonts and pelicosaurs" (Esenov, Shlygin, 1972). These tracks are confined to the lower surface of the layer of hard, apparently deltaic sandstones. In Gubin et al., 2003, it is assumed that some of the tracks from Zhezkazgan belong to Parabaropus isp. Together with the tetrapod tracks, one track of Arthropleura (2.5 m long with a width of 12-13 cm) was discovered (Nelikhov, 2010).

Fig. 6. Remains of arthropods from sandstones (outcrop 1-3): 1-5 - remains of arthropod Arthropleura sp. (layer no. 9, outcrop 1; 1, 3-5 - field photo, 2 - fragment of phototable XXV from the monograph by Pruvost, 1919; 6, 7 - remains of the dorsal plate of arthropod Arthropleura sp.: 6 - from layer no. 9 (outcrop 1; sample no. 3778), 7 - photo from Schneider, Werneburg, 2010, fossil from the Cisuralian of Thuringia; 8 - remains of the K-plate of the arthropod Arthropleura sp. (layer no. 9, outcrop 1; no. 3736); 9 - undetermined remains of arthropods from layer no. 9 (outcrop 1; field photo); 10 - presumed remains of sintergite of the arthropod Arthropleura sp. (layer no. 9, outcrop 1; no. 4928); 11 - remains of integument of arthropod Arthropleura sp. (outcrop 3, scree; sample no. 6732); 12 - ?Arthropleura sp. (layer no. 2, outcrop 2; sample no. 7854). The scale bar is 10 mm (1, 4, 5, 8, 10, 12), 5 mm (3), 20 mm (9).

Рис. 6. Рештки членистоногих з пісковиків (відслонення 1-3): 1-5 - рештки членистоногих Arthropleura sp. (шар № 9, відслонення 1; 1, 3-5 - польове фото, 2 - фрагмент фототаблиці XXV з роботи (Pruvost, 1919); 6, 7 - рештки дорсальної пластинки членистоного Arthropleura sp.: 6 - з шару № 9 (відслонення 1; зразок № 3778), 7 - фото з роботи (Schneider, Werneburg, 2010), фосилія з нижньої пермі Тюрингії; 8 - рештки К-пластинки артроподи Arthropleura sp. (шар № 9, відслонення 1; зразок № 3736); 9 - невизначені рештки артропод з шару № 9 (відслонення 1; польове фото); 10 - здогадно рештки синтергіту артроподи Arthropleura sp. (шар № 9, відслонення 1; зразок 4928); 11 - рештки покривів членистоногого Arthropleura sp. (відслонення 3, осип; зразок № 6732); 12 - ?Arthropleura sp. (шар № 2, відслонення 2; зразок № 7854). Масштабний відрізок для фіг. 1, 4 5, 8, 10, 12 - 10 мм, для фіг. 3 - 5 мм і для фіг. 9 - 20 мм.

Based on the information on their morphology, this trace fossil should be attributed to Diplichnites cuithensis. The red-bed sediments of the Zhezkazgan Group represented by sandstones, siltstones, mudstones and pelitomorphic limestones were formed mainly in deltaic, lakustrine and floodplain conditions, as well as in conditions of coastal plain and epicontinental sea (Esenov, Shlygin, 1972). Currently, Zhezkazganian traces are the most northern (in relation to the ancient coordinate grid) finds to evidence the presence of Arthropleura. According to Schneider, Werneburg, 2010, the modern Zhezkazgan depression in the Carboniferous and Permian was located in the arid zone.

We focused on the Zhezkazganian finds in detail, since this trace fossil is unknown to the scientific community, because scanty information about this unique find was presented only in a brief historical sketch by A. Nelikhov (2010). Note that the "Fundamentals of Paleontology" (Novozhylov, 1962) mentions the presence of Arthropleura in Carboniferous deposits of the Karaganda Basin. In the message, it is emphasized that the remains have not yet been described.

On the scree of outcrop 3 trace fossils were also revealed, which can be defined as Diplichnites cuithensis Briggs, Rolfe et Brannan (fig. 8, 9).The remains and traces of locomotion of the giant arthropod Arhropleura are known mainly from limnic basins. Apparently, the conditions of the paralic Donets Basin contributed little to the widespread development of terrestrial fauna here, including Arthropleura.

In megaconcretion of carbonate sandstone from layer no. 2 outcrop 3, the imprint of a wing fragment of an undefined Paleodictyoptera was found (fig. 5, 4). This fossil was found in an accumulation of plant detritus, which were oriented by surf. Sandstones are extremely unfavorable for preserving insect remains. However, due to the mechanical strength of the wing and more intensive cementation of nodule sandstone compared to the lateral rock, the fossil has sufficient preservation for approximate determination. Paleodictyoptera are large and very large flying insects, the remains of which are known from Namurian B (= Lower Bashkirian) and ending with deposits of the Cisuralian. According to A. G. Sharov (1973), these insects lived in the crowns of tree-like pteridosperms and cordaitanth. They were feeding on the reproductive organs of these plants, in particular juices of immature seeds of Cordaitales. Apparently, many Carboniferous ovipositions confined to plant organs belong to Paleodictyoptera. These ovipositions were also discovered in Pennsylvanian sediments of the Donets Basin (unpublished data of the author).

In the nodule from siltstones of layer no. 6b (outcrop 1), an imprint of an insect wing fragment was found. This fossil could not be determined due to the strong weathering of the nodule, which is why only a part of the venation is visible on the imprint.

<- Fig. 7. Trace fossils and body remains of animals from the studied sandstones: 1 - Lockeia siliquaria James, 1879 (layer no. 8, outcrop 1; field photo); 2 - ?trace of swimming of Tetrapoda (layer no. 7, outcrop 1; sample no. 6938); 3 - Selenichnites isp. 4 (outcrop 3, scree; field photo); 4 - plant remains with traces of exposure to arthropods (outcrop 3, scree; sample no. 6774); 5 - remains of prosoma of the large horseshoe crab (layer no. 9, outcrop 1; sample no. D-10d); 6 - the foliage of Paripteris gigantea (Sternb.) with traces of marginal feedings of arthropods (siltstones above a sandstones under G₁², quarry 3 km west of outcrop 4; field photo); 7 - remains of the B-element of the Arthropleura sp. (layer no. 9, outcrop 1; no. 5476); 8 - indefinite arthropod remains from layer no. 7 (outcrop 1; field photo); 9 - indefinite arthropod remains (layer no. 9, outcrop 1; no. 5655); 10, 11 - indefinite arthropod remains (layer no. 9, outcrop 1). The scale bar is 70 mm (1), 15 mm (2-4, 7-10), 20 mm (5), 5 mm (6 and 12).

Рис. 7. Іхнофосилії та тілесні рештки тварин із вивчених пісковиків: 1 - Lockeia siliquaria James, 1879 (шар № 8, відслонення 1; польове фото); 2 - здогадно сліди плавання тетраподи (шар № 7, відслонення 1; зразок № 6938); 3 - Selenichnites isp. 4 (відслонення 3, осип; польове фото); 4 - рештки рослини зі слідами впливу членистоногих (відслонення 3, осип; зразок № 6774); 5 - рештки просоми крупного мечохвоста (шар № 9, відслонення 1; зразок № D-10d); 6 - пір'ячко Paripteris gigantea (Sternb.) зі слідами крайових об'їдань членистоногими (алевроліти вище пісковиків, що залягають під вапняком G₁², кар'єр в 3 км західніше відслонення 4; польове фото); 7 - рештки Б-елементу членистоногого Arthropleura sp. (шар № 9, відслонення 1; зразок № 5655); 10, 11 - невизначені рештки артропод (шар № 9, відслонення 1). Масштабна лінійка - 70 мм (фіг. і), 15 мм (фіг. 2-4, 7-10), 20 мм (фіг. 5) і 5 мм (фіг. 6 та 12).

Insect remains are studied from Carboniferous deposits of the Donets Basin and the Dnieper- Donets depression rather poorly. Many paleontologists, mainly paleobotanists (for example, O. P. Fisunenko and A. K. Shchegolev (Fisunenko, 1987), indicated the presence of remains of "dragonflies" in Pennsylvanian deposits of the Donets Basin. E. O. Novik (1941) reported the find of an imprint of the cockroach wing in Pennsylvanian sediments exposed by one of the boreholes in the territory of Romny Raion (Sumy Oblast, Ukraine). The deposits in which the remains were found were compared with the upper part of the Gorlovka Formation and lower part of the Isaevka Formation (upper part of Moscovian Stage) of the Donets Basin. Complete imprint of the body of a dragonfly is known from marine dark gray mudstones of the upper part of the Dyakovska Series from vicinities of Dovzhans'k (south of Lugansk Oblast, Ukraine) (Dernov, 2016).

The only species of Carboniferous insects described at the moment from the territory of the Donets Basin is the Paleodictyoptera Spilaptera tanaica Sharov et Sinitshenkova, 1977 found in deposits of the Isaevka Formation (Lower Kasimovian) of the Lomovatka site (Sharov, Sinichenkova, 1977). Insect finds are not abundant, although the Donets Basin is quite promising for new finds of insect remains.

Other invertebrates. In the upper part of layer no. 9 (outcrop 1), a body imprint supposedly of a freshwater jellyfish Medusina was found (fig. 5, 5). The remains of these animals are known from Cisuralian lakustrine sediments of limnic basins of the Czech Republic, Germany, France, and Italy (Gand et al., 1996; Santi, 2010). The fact of the presence of well-preserved remains of freshwater jellyfish indicates a greatly reduced salinity of the waters of the basin, in which sediments of layer no. 9 were deposited. The good preservation of the body indicates, apparently, its rapid burial.

Vertebrates. In the nodule from siltstones of layer no. 6c (outcrop 1), an indefinite scale of Actinopterigia was found (fig. 5, 9).

Trace fossils of animals are often found in different layers of the studied outcrops and are relatively numerous there (fig. 7, 1-3; fig. 8, 2, 4, 5-7, 10-11). For example, the average density of burrows of Scolithos linearis (Haldeman) from the sandstone interlayer in layer no. 3 (outcrop 1) is 17 specimens/25 cm² of the layering surface. The density of pelecypods resting traces Lockeia siliquaria James from layer no. 4 is 7-20 specimens/1800 cm²; from layer no. 6d is 8 specimens/25 cm² and from layer no. 8 is 10 specimens/225 cm². The total length of trace fossil Aulichnites isp. on the layering surfaces of layer no. 7 is 7-8 cm/25 cm². However, the bioturbation of the rocks is rather weak. For example, for the most part of the deposits of the outcrop 1 ichnofabric index is 1/5 and only in some layers reaches 2/5 and 3/5. The composition of ichnocenoses is shown in Table 2.

Table 2. The composition of ichnocenoses from the studied sandstones Таблиця 2. Склад іхноценозів вивчених пісковиків

In siltstones that directly overlap sandstones under G_x² in a quarry 3 km west of outcrop 4, remains of pteridosperm Paripteris gigantea (Sternb.) with traces of marginal feedings of the millipedes or other arthropods were found (fig. 7, 6). In nodules from layer no. 6b of outcrop 1, the phyloid remains Cyperites bicarinatus Lindley et Hutton with galls on the surface are often found (fig. 5, 10). On outcrop 3, the imprint of a leaf with a clearly visible groove, divided by a longitudinal medial elevation (fig. 7, 4) was found. The origin of this groove is unknown.

When studying outcrops 1 and 3, we repeatedly noted resting traces of horseshoe crabs Selenichnites Romano et Whyte, 1990 (fig. 7, 3; fig. 8, 1, 3, 8). Romano and White (2015) propose to separate similar trace fossils from the ichnogenus Selenichnites into ichnotaxon Crescentichnus Romano et Whyte, 2015 and some others. It is hard to agree with this point of view. We determined 6 forms of Selenichnites (see Table 2), which differ in size and morphology. It is difficult to establish the ichno- species affiliation of most of these ichnofossils due to the complexity of their parataxonomy. A recent revision of this ichnogenus (Romano, Whyte, 2015), in our opinion, only exacerbated the situation. It is likely that some of the traces we have identified are new ichnospecies. We focused on trace fossils of Selenichnites isp. 1 (fig. 8, 1) and Selenichnites cf. tesiltus Gibb, Chatterton et Pemberton. Four trace fossils were studied: one isolated (S. isp. 1) and three concentrated in a group on an area of about 700 cm² (S. cf. tesiltus). Apparently, the width of the prosoma of the horseshoe crabs that left these traces was not less than 15 cm. For the Paleozoic horseshoe crabs, these are more than significant sizes (for example, the species Xaniopyramis linseyi Siveter et Selden described from Namurian deposits of Britain, with the prosoma width of about 15.5 cm was called "giant" by the authors (Siveter and Selden, 1987). Morphologically, the traces of Selenichnites cf. tesiltus are similar to Selenichnites isp., known from the Middle Jurassic of Morocco (Oukassou et al., 2015). The sizes of Moroccan ichnofossils are approximately the same as trace fossils from the Donets Basin. Selenichnites isp. 4 (fig. 8, 3), very similar to Selenichnites tesiltus, but having a triangular area was located behind the arched indentation left by the front edge of the horseshoe crab prosoma. Such morphological diversity of Selenichnites among rocks of a limited stratigraphic interval can be explained by the presence of individuals of different degrees of maturity in the same biotope and, obviously, of different species, which left traces of different size and morphology.

Noteworthy is the finding of a trace fossil in sandstones of layer no. 7 (outcrop 1), very similar to the swimming traces of tetrapods (fig. 7, 2). In Fillmore et al., 2012, such traces are identified as Characichnos isp.

Traces of Aulichnites are often observed on surfaces on which microbial sedimentation textures were also discovered. This fact, perhaps, testifies to the trophic attachment of gastropods represented by traces of Aulichnites to microbial mats. In Buatois, Mangano, 2016, four categories of interaction of organisms and microbial mats are identified. They, with slight changes, can be taken as a model for the deposits we studied. For layer no. 2 (outcrop 1), the category "mat grazers" can be distinguished. It includes Aulichnites isp. and Helminthopsis hieroglyphica. According to Buatois, Mangano, 2016, this category includes the ichnocommunity Helminthopsis (this includes trace fossils Helminthopsis, Helminthoidichnites, Archaeonassa, Gordia). Trace fossils that make up this community are abandoned by animals that feed on organic matter concentrated on the surface of microbial mats or under a thin layer of sediment.

In layer no. 7 of the same outcrop, one can distinguish the already mentioned category of "mat grazers" (Aulichnites isp., Helminthopsis isp.), as well as the category of "undermat miners": Treptichnus pollardi. It includes the ichnocommunity Treptichnus-Saerichnites (Treptichnus) represented by traces in the sediment just below the microbial mats. The same community is also characteristic for layer no. 8, in which Saerichnites bioturbations are found.

In addition to traces of animal activity, phytoturbations caused by the influence of plant root systems on sediment and confined to paleosol profiles were also noted in the studied sections.

<- Fig. 8. Some trace fossils from the studied sandstones: 1 - Selenichnites isp.1 (layer no. 9, outcrop 1; field photo); 2 - Diplopodichnus biformis Braddy, 1947 (outcrop 3, scree; field photo); 3 - Selenichnites isp. 4 (layer no. 8, outcrop 6b; field photo); 4 - Rhizocorallium isp. (outcrop 3, scree; field photo); 5 - Bergaueria isp. (outcrop 3, scree; no. 6446); 6 - Circulichnis montanus Vyalov, 1971 (outcrop 3, scree; field photo); 7 - Avetoichnus luisae Uchman et Rattazzi, 2011 (layer no. 6, outcrop 8, field photo); 8 - Selenichnites isp. 3 (outcrop 3, scree; no. 6416); 9 - Diplichnites cuithensis Briggs, Rolfe et Brannan, 1979 (outcrop 3, scree; field photo); 10 - Treptichnus pol- lardi Buatois et Mangano, 1993 (layer no. 7, outcrop 1; field photo); 11 - Aulichnites isp. (layer no. 7, outcrop 1; sample no. 6545). The scale bar is 35 mm (1, 4, 9), 10 mm (2, 3, 5, 10, 11), 5 mm (6), 15 mm (8).

Рис. 8. Деякі іхнофосилії з вивчених пісковиків: 1 - Selenichnites isp.1 (шар № 9, відслонення 1; польове фото); 2 - Diplopodichnus biformis Braddy, 1947 (відслонення 3, осип; польове фото); 3 - Selenichnites isp. 4 (шар № 8, відслонення 6b, польове фото); 4 - Rhizocorallium isp. (відслонення 3, осип; польове фото); 5 - Bergaueria isp. (відслонення 3, осип; зразок № 6464); 6 - Circulichnis montanus Vyalov, 1971 (відслонення 3, осип; польове фото); 7 - Avetoichnus luisae Uchman et Rattazzi, 2011 (шар № 6, відслонення 8; польове фото); 8 - Selenichnites isp. 3 (відслонення 3, осип; зразок № 6416); 9 - Diplichnites cuithensis Briggs, Rolfe et Brannan, 1979 (відслонення 3, осип; польове фото); 10 - Treptichnuspollardi Buatois et Mangano, 1993 (шар № 7, відслонення 1; польове фото); 11 - Aulichnites isp. (шар № 7, відслонення 1; зразок № 6545). Масштабний відрізок 5 мм (фіг. 6), 10 мм (фіг. 2, 3, 5, 10, 11), 15 мм (фіг. 8), 35 мм (фіг. 1, 4, 9).

The results of the study of trace fossils show that the sandstones were accumulated under conditions of at least three ichnofacies: Psilonichnus, Scolithos, and Cruziana. Psilonichnus Ichnofacies is common in the tidal zone at the border of marine and fresh waters (Mikulas, Dronov, 2006). Scolithos ichnofacies is inherent in coastal environments with high hydrodynamic activity (Mikulas, Dronov, 2006). The Cruziana ichnofacies is characterized by calmer sedimentation conditions compared to the Scolithos ichnofacies (Mikulas, Dronov, 2006). Noteworthy the presence in the outcrop of stratigraphic intervals composed of sediments accumulated in extremely shallow, apparently periodically drained conditions. This is indicated by the presence of traces of terrestrial organisms (for example, ichnofossils of terrestrial arthropods Diplichnites and Diplopodichnus).Sedimentation conditions

From all of the above information, it becomes clear that the two studied sandstone beds have significant litho-facial similarity, which is expressed by the similarity of lithotypes of rocks, the presence of carbonate megaconcretions and pebbles of metamorphic slates, paleosols, as well as almost identical paleontological filling of sediments. Of course, this similarity is caused by the similar conditions of sedimentation.

Outcrop 1. Layers no. 1 and 2 were formed under avandeltaic conditions. Since gray siltstones (layer no. 3) are often absent or their thikness is reduced, it follows that sedimentation was very uneven. Accumulation of sediments of layer no. 3 was of the intra-deltaic gulf with silt bottom, which was characterized by slow sedimentation, content of hydrogen sulphide in water and silt and complicated aeration of the water column that arose due to a rather calm hydrodynamic regime. The salinity of the bay was reduced due to the penetration of significant volumes of fresh water, enriched, moreover, with dissolved iron. An interlayer of sandstones in the siltstones of layer 3 was formed during a short-term decrease in the depth of the bay and, accordingly, an increase in water activity and an improvement in its aeration. The overlying sandstones of layer no. 4, apparently, were also formed under avandeltaic conditions.

The sandstones of layer no. 5, which form the PS-1/1 paleosol profile, are sediments of subaerial deltaic plain. The prevailing landscape of this situation, apparently - marshes, which were characterized by monotaxic groupings of tree-like lycopsids. Deposits of layer no. 6 were formed under conditions of an extensive desalinated lagoon with soft bottom silts, good aeration, and moderate sedimentation rates. The coastal zone of the lagoon (or lagoons) was inhabited by small horseshoe crabs. Bivalves lived in parts of the water area further from the coast. In the western part of the quarries, the PS-1/1a paleosol is observed, apparently lying within the subaerial bar, wich separate the lagoon from the shallow water marine basin. The overlying part of the section (layers no. 7 and 8) refers to the sediments of the avandelta.

Fig. 9. Landscape of the accumulation time of sandstones of layers no. 9 (outcrop 1) and no. 2 (outcrop 2): 1 - large horseshoe crab, 2 - arthropod Arthropleura, 3 - Diplichnites cuithensis - traces of locomotion of Arthropleura, 4 - Selenichnites - traces of rest of horseshoe crabs, 5 - tree-like lycopsids, 6 - tree-like horsetails, 7 --windbreak (trunks of tree-like lycopsids and horsetails), 8 - insect of the order Paleodictyoptera; gray filling - water; white filling - land.

Рис. 9. Ландшафт часу накопичення пісковиків шару № 9 (відслонення 1) та № 2 (відслонення 2): 1 - крупний мечохвіст, 2 - артропода Arthropleura, 3 - Diplichnites cuithensis - сліди локомоції артропод Arthropleura, 4 - Selenichnites - сліди лежання мечохвостів, 5 - деревовидні лепідофіти, 6 - деревовидні хвощеподібні, 7 - бурелом (стовбури деревовидних лепідофітів та хвощеподібних), 8 - комаха ряду Paleodictyoptera; сірим кольором позначено воду, а білим - суходіл.

Apparently, for layer no. 9 (fig. 9), formation about conditions of a subaerial delta plain can be assumed. For rocks of the upper part of the layer, the accumulation environment can be detailed. Apparently, these sandstones were accumulated under conditions of an extensive gently sloping beach covered with thickets of semi-aquatic horsetails of the genus Calamites and located within the supra- littoral. On land, they were replaced by tree-like lycopsids and pteridosperms, and by cordaitant and pteridosperms in more elevated sections of the coastal lowland. The described coast and coastal waters were the habitat of adult large horseshoe crabs, which were buried along with the remains of severely damaged flora and fragments of Arthropleura bodies. Remains of Arthropleura were delivered by streams from the surrounding flooded thickets of lycopsids. Significant desalination of the waters may be indicated by the find of remains of presumably fresh-water jellyfish in the upper part of layer no. 9. Siltstones of layer no. 10 can be attributed to prodeltaic deposits.

An analysis of trace fossils from the sandstones below the G_x² limestone suggests a richer composition of organisms living near and at the deposition site of the studied sediments, but whose body remains were not found. Among them, worms, anemones, crustaceans, and amphibians should probably be noted.

Outcrop 2. Summarizing the obtained data, we can assume about the formation of sediments of layers no. 1 and 2 under avandeltaic conditions. Sandstones of layer no. 3 were formed on the subaerial deltaic plain. Layer no. 4 is represented by shelf sediments.

Outcrops 3 and 11. Siltstones of layer no. 1 are, apparently, sediments of prodelta. The sandstones of layers no. 2-4, 6, 7, 9, 11, 13, 14, and 16 are, apparently, avandeltaic formations. Siltstones of layer no. 5 are, apparently, lagoonal sediments. Phytoturbated sandstones of layers no. 8 and 8a are deposits of the subaerial deltaic plain. Siltstones (layer no. 8b) are obviously deposits of the intra deltaic lagoon. Sandstones of layer no. 10 are deposits of the inclined part of the delta. Presumably, the lower part of layer no. 10 on the outcrop 6b corresponds to the interbedded interlayer of prodeltaic siltstone. Coarse-grained sandstones of layer no. 12, which, despite varying thicknesses (from 1,5 to 3 m), some variations in lithology and local presence at the base of a layer of coarse siltstone-fine-grained sandstone, are quite consistent in area and established by us as in the most western one, and the most eastern outcrops. Regarding the conditions of accumulation of these coarse-grained sandstones, we can only assume that these are sediments of the bar. Siltstones of layer no. 15 are apparently lagoonal deposits. Siltstones of layer no. 17 are sediments of the coastal swampy plain. Layer no. 18 is deposits of peat swamps.

Conclusions

1) Deltaic sandstone beds of different age of the Pennsylvanian of the Donets Basin sometimes demonstrate a significant degree of lithological and facies similarity, down to the smallest detail.

2) Significant variations of lithological sets of sediments and conditions of their accumulation in the section and in the space are observed within a single thickness of deltaic sandstones.

3) For the first time, paleosol are studied that occur among the deposits of the Bashkirian Stage of the Donets Basin.

4) Deltaic deposits are distinguished by the richness of oryctocenoses, which is associated with a variety of living conditions of organisms and the burial of their remains.

5) The presence of remains of the giant arthropod Arthropleura and supposedly jellyfish in Carboniferous deposits of the Donets Basin were revealed for the first time. The most diverse ichnoce- nosis from the Carboniferous of the Donets Basin was also studied. For some taxa of fossil plants, their stratigraphic distribution was detailed.

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