Investigation of mixed carbonate-siliciclastic Lower Devonian deposits have been carried out in the Ivanye Zolote and Ustechko sections in Podolia, Ukraine. Based on palynomorph evidence, the age of the samples studied is late Lochkovian, not older than the NM Oppel Miospore Zone, specifically the Si Lineage Zone. The presence of acritarchs and chitinozoans points to dominantly marine depositional conditions. However, a regressive environmental change to-ward more brackish conditions is indicated by a decrease in the taxonomic diversity of acritarchs in the topmost samples, the simultaneous disappearance of chitinozoans, and an increase in leiosphaerid frequency. Furthermore, evolution of limestone microfacies demonstrates a progressive transition from a shrinking marine basin toward a brackish, storm-af-fected muddy lagoon, manifested by recurrent profusion of impoverished, mostly opportunistic and euryhaline shelly benthos (nuculanid bivalves, leperditicopids and other ostracods, terebratulid brachiopods), chaetetid demosponges and diverse ichthyofauna. The association of plant (mainly nematophytes and some tracheids) and animal (eurypterid, ?scor-pion, and possibly other arthropod) remains points to the presence of nearby Early Devonian wetland vegetation, provid-ing food and shelter for various semi-aquatic and other terrestrial arthropods.
Upper Silurian and Lower Devonian deposits occur as many natural exposures in the Podolia region of Ukraine (Fig. 1). However, biostratigraphic subdivision of the sedimentary successions remains unsatisfactory, especially of those strata deposited during the late Lochkovian, when conditions changed from marginal marine to alluvial (Uchman et al. 2004; Małkowski et al. 2009; Drygant 2010; Voichyshyn 2011). Palynological studies have proven useful for subdi-viding and correlating various sedimentary facies, as well as can also assist in interpreting changes in sedimentary envi-ronments (e.g., Tyson 1993; Batten 1996; Wicander and Wood 1997; Filipiak 2002; Filipiak and Zatoń 2011). In Podolia, such integrative palynological analyses are espe-cially needed (Le Herisse et al. 1997) to decipher the evolu-tion of sedimentary conditions during this regressive Early Devonian interval, supplementing the sedimentological-eco-logical data provided by Uchman et al. (2004).
Kirjanov (1978) presented comprehensive data concerning phytoplankton (mainly acritarch) distribution in the Silurian of the Volyno-Podolia region. He described over 70 species, some of which were recognized during the current study. Arkhangelskaya (1980) identified such miospores as Em-phanisporites cf. micrornatus and Streelispora sp. from the Ivanye Horizon, indicative of the middle and upper parts of the Emphanisporites micrornatus—Streelispora newportensis Spore Zone of Richardson and McGregor (1986). Based on the presence of Emphanisporites micrornatus, Richardson et al. (1981) and Richardson and McGregor (1986) assigned the Ivanye Horizon to the NM Miospore Zone. Paris and Grahn (1996) studied chitinozoans of Přidoli and Lochkovian beds of Podolia and tentatively dated their youngest low-diversity Ancyrochitina-dominated assemblage, from the Ivanye Hori-zon, as Lochkovian. Palynostratigraphic data from two sam-ples from the Ustechko section were presented by Turnau in Uchman et al. (2004). Based on the presence ofmiospore taxa, Turnau recognized the Lochkovian Emphanisporites micrornatus—Streelispora newportensis Miospore Zone. In the phy-toplankton assemblage she only noticed the occurrence of Leiosphaeridia and Lophosphaeridium. The presence of amorphous organic matter and plant tissues was mentioned by Uchman et al. (2004).
The aim of the present paper is to establish a palyno-stratigraphic framework and to characterize, in the paleo-environmental context, the palynofacies and carbonate micro-facies in the upper part of the Lochkovian deposits of Podolia. In particular, analysis of associations of marine and land-de-rived palynoflora, as well as plant and animal cuticle remains, refines interpretation of the development of marginal-marine facies in the section under study.
Institutional abbreviations.—GIUS, Faculty of Earth Sci-ences, University of Silesia, Sosnowiec, Poland.
Other abbreviations.—AOM, amorphic organic matter; CH., chitinozoa; IZ, Ivanye Zolote; LEIO., leiospheres.
Lower Devonian deposits of the Dniester Basin are located on the southwestern margin of the East European Platform(Fig. 1; Nikiforova et al. 1972; Małkowski et al. 2009; Drygant 2010). Their lower part, about 530 mthick, comprises an open marine sedimentary sequence, the Tyver Series (Fig. 2A). This unit is composed mainly of shale and siltstone beds with irregular limestone interbeds and passes upwards into terrigenous, mar-ginal-marine and fluvial facies of the Old Red Sandstone-type referred to as the Dniester Series (Nikiforova et al. 1972; Abushik et al. 1985; Małkowski et al. 2009; Drygant 2010; Voichyshyn 2011). All the deposits are well exposed at many localities along the Dniester River valley and its tributaries. Their stratigraphy has been based on abundant and diverse in-vertebrate fossils, abundant fish remains and microfossils, which have been extensively studied since the 19th century (see Kozłowski 1929; Nikiforova et al. 1972; Drygant 2010; Voychyshyn 2011; Olempska 2012; Olempska et al. 2012). The open marine sediments are most probably of Lochkovian age. However, the precise stratigraphic position of their bound-arywith the overlying red beds of theDniester Series is still un-der discussion (Drygant and Szaniawski 2012). The problem is complicated by diachronism caused by gradual shrinking of the marine basin and its shifting toward the west. The Tyver Series is biostratigraphically and lithostratigraphically subdi-vided into three units: in ascending order, the Borshchiv, Chortkiv and Ivanye horizons and beds (Fig. 2A). Only the up-permost part of the Ivanye Horizon/Beds (ca. 30 m thick) has been sampled for the palynofacies analysis. The youngest ma-rine deposits, passing gradually into the Old Red facies, are well exposed near the village of Ivanye Zolote, and in part also near Ustechko (Fig. 1), at the locality studied by Uchman et al. (2004). The Ivanye Zolote section is ca. 25 m thick, whereas near Ustechko only the uppermost 5 m were available for sam-pling (Fig. 3). The argillaceous content gradually increases up-wards in both of the outcrops. The “calcareous interbeddings” within the uppermost part in fact contain only a small admix-ture of calcium carbonate. As shown by geochemical analyses (7 samples) of the coeval facies transition at nearby Zalishchyky locality (Fig. 1B; section 58 in Małkowski et al. 2009; Voichyshyn 2011), the CaCO3 content drops upwards from ca. 80% to less than 2%, whilst quartz (SiO2) and alumi-nosilicate (Al2O3) levels increase simultaneously from ca. 10% and 2% to above 50% and 15%, respectively; total organic car-bon (TOC) content for 3 samples is between 0.17 and 0.22% (see details in Racki et al. 2012: SOM 3 and 4).
The diversity and number of macrofossils mostly bi-valves, brachiopods, and nautiloids, gradually decrease up the section (Nikiforova et al. 1972; see below). However, most of the microfossils (ostracods, conodonts, scoleco-donts, chitinozoans, nematophytes, and prasinophytes) are still abundant, even in the uppermost “calcareous layers” (Fig. 3). Phosphatic fish scales and spines are very abundant, and in some layers fragments of acanthodian jaws are com-paratively well preserved (Voichyshyn 2011; Voichyshyn and Szaniawski 2012). The uppermost gray-coloured and marine in origin beds of the Tyver Series can easily be distin-guished from the overlying pink or red “Old Red” rocks.
Material and methods
In total, twenty three samples were collected from the two lo-calities. Ten of them were taken mainly from marly limestone layers for the palynological investigation—eight from the ∼25 m thick interval of the Ivanye Zolote (IZ) section and two from the ∼5 m thick Ustechko section (Fig. 3). An additional ten samples from the Ivanye Zolote section were studied in large-sized (4.5 ~ 6.5 cm) thin sections. Eight of them repre-sent calcareous layers and two of them represent the Old Red facies (Fig 3). Three additional samples (IZ10–IZ12) have been studied with respect to chitinozoans exclusively.
Standard laboratory procedures for palynological samples containing mineral matter were employed (Wood et al. 1996). Samples were treated using palynological HCl-HF-HCl acid maceration techniques. The organic residue obtained was fi-nally sieved using an 18 ìm mesh nylon sieve. At least four slides were prepared from each residue. The preservation of palynomorphs from Ivanye Zolote varies in quality. Some samples are completely weathered (IZ-3), some are partly weathered (IZ-6) but generally the state of preservation of organics in the rest of the samples analysed is good, especially those from the lower part of the section. Generally, microflora derived from the Ivanye Zolote is moderately rich in taxonom-ically differentiated assemblages of miospores and phyto-plankton taxa. Some plant tracheids, scolecodonts, chitino-zoans, and arthropod remains were noticed, as well. The worst preserved and less taxonomically differentiated material have been derived from the Ustechko outcrop. Phytoplankton is better represented here but miospores are rare and possess less stratigraphic value. Therefore, those two samples were ex-cluded from further quantitative analyses.
For quantitative palynofacies analyses, each countable kerogen component from the samples from the IZ section was counted for up to 100 specimens. The relative frequency of cryptospores, miospores, acritarchs, chitinozoans, and leiospheres was noted. The remaining slides were examined for the presence of other components that had not been iden-tified in the previously examined portions. Furthermore, oc-currences of amorphous organic matter (AOM), miospore tetrads and arthropod remains were noted, as well.
The palynological slides and residues are housed at GIUS. Examination and documentation was done using the Nikon Eclipse 50i transmitted light microscope. The stratigraphically important miospores and phytoplankton taxa are illustrated on Figs. 4, 7; other plant, animal remains, and some chitinozoans are showed on Figs. 5, 8, 9.
The presence of several characteristic and eponymous spe-cies for the Lower Devonian (Table 1) permits to assign the miospore assemblages to the assemblage zones of Richard-son and McGregor (1986), and the Oppel and interval/lin-eage zones of Steemans (1989; Streel et al. 1987; Fig. 2B). The latter division is more detailed and useful for the finer biostratigraphy and therefore will be employed in this paper.
Ivanye Zolote.—Based on the presence of eponymous and characteristic miospore species, the Lochkovian MN Oppel Zone that corresponds to the Emphanisporites micrornatus— Streelispora newportensis Assemblage Zone has been recog-nized (Fig. 2B). Emphanisporites micrornatus var. micro-rnatus the index species of the NM Oppel Zone is present in the lowermost analysed sample but Streelispora newpor-tensis has not been detected in the material analysed. The presence of Amicosporites jonkeri in the lowermost sample is also important. According to Steemans (1989), its first ap-pearance marks the base of the Si Lineage Zone (Fig. 2B), at-tributed to upper Lochkovian, which tentatively corresponds to the Latericriodus woschmidti/postwoschmidti—Ancyrodel-loides delta conodont zones (House and Gradstein 2004); however, Drygant and Szaniawski (2012) dated the upper part of IZ Horizon, according to present zonation, as the Pedavis gilberti—Caudicrodus steinachensis Conodont Zone (guided by uncommon species Pandorinellina praeoptima, Zieglerodina serrula, and Caudicriodus serus). Microspore species defining the base of the next succeeding palyno-logical zone (BZ Oppel Zone) were not encountered.
The assemblage is moderately taxonomically diverse. Cryptospores are not diverse and represented by ca. 20—40% of all kerogen components. Among miospores the most commonly occurring taxa are Archaeozonotriletes chulus, Cym-bosporites sp., Retusotriletes dubiosus, and R. triangulatus. Less common are Apiculiretusispora plicata, Chelinospora retorrida, Cymbohilates pusillius, Emphanisporites neglec-tus, and Leonispora argovejae (Fig. 4; Table 1). According to Richardson and McGregor (1986), Apiculiretusispora pli-cata is an important miospore for the E. micrornatus—S. newportensis, the stratigraphical equivalent for theNMZone (Fig. 2); moreover, according to Turnau (1986) also impor-tant is the presence of Chelinospora retorrida which does not extend above the Lochkovian. The stratigraphical range of these taxa is well known from SE Poland (Turnau 1986). Among cryptospores, frequent were: Artemopyra recticosta, Chelinohilates glabrimarginatus, Gneudnaspora divello-media, and Gneudnaspora plicata (Fig. 4). Quadrisporites, previously treated as miospore but recently classified as nonmarine or brackish acritarch or algal fossils by Le Herisse et al. (2009), were noticed as well.
Distribution of some frequent and important spore and phyto-plankton taxa in the sections investigated.
Four of seven samples prepared from the Ivanye section contain a moderately well preserved chitinozoan assemblage comprising Calpichitina sp. cf. C. velata; Angochitina filosa; Sphaerochitina sp. aff. S. densibaculata (Fig. 5). This poorly diversified assemblage, however, represents species occurring in the upper Lochkovian up to the lowermost Pragian (Paris et al. 2000). Chitinozoan vesicles are compressed, deformed, of-ten with partly destroyed ornamentation and broken spines. The abundance in the studied samples ranges from a several dozens of specimens in the lowermost sample (IZ-1) and de-creases up to a few specimens in the upper-lying sample (IZ-5) in the section. Three uppermost samples (IZ-6, IZ-7, IZ-8) were barren of Chitinozoa. The observed pattern of the chitinozoan distribution is also consistent with a frequency pattern in adjacent contemporaneous Early Devonian se-quences in Poland (Wrona 1980), Barrandian region (Paris et al. 1981; Chlupač et al. 1985; Chlupač and Hladil 2000), and many other different areas (Paris et al. 2000).
Ustechko.—The land-derived microflora is poorly represen-ted only in the two uppermost samples analysed (Uo-2 and Uo-4; Fig. 3, Table 1). Any important miospores for strict microfloristic horizons were not recognized. The assemblage consists of miospores and cryptospores with broad strati-graphical ranges. Among them such species were recognized as: Ambitisporites sp., Archaeozonotriletes chulus, Emphani-sporites sp., Gneudnaspora divellomedia, and Retusotriletes dubiosus (Fig. 4, Table 1). The lack of eponymous and charac-teristic taxa precludes assignment to a biozone; the presence of the species mentioned above is rather characteristic for the broad Upper Silurian—Lower Devonian interval (Richardson and McGregor 1986; Rubinstein and Steemans 2002).
Palynofacies from the Ivanye Zolote section
Organic matter preserved in the samples comprises two com-ponents: (i) autochthonous, represented by acritarchs, leio-spheres, chitinozoans, and scolecodonts, and (ii) allochtho-nous, represented by miospores and land plant cuticles and tra-cheids. Animal remains probably belonging to semi-aquatic creatures like eurypterids form the third category. All those particles are mixed and appear in different relative frequency. The proportions of miospores, acritarchs, leiospheres, and chitinozoans are shown in Fig. 6.
Miospores are represented by spores and cryptospores. Their relative proportion ranges from ca. 40% to 80% of all countable components. Cryptospores appear slightly more than spores. The most frequently appearing and im-portant taxa arementioned in the palynostratigraphic chapter.
Taxonomically differentiated acritarchs are represented by ca. 5% in the IZ-4 sample to over 50% of all countable components in the IZ-2 sample. The assemblage is more dif-ferentiated in bottom samples (IZ-1–5; Table 1). Frequently appear acritarchs like: Baltisphaeridium scabrosum, Dictyo-tidium eurydictyotum, Elektoriskos sp., Geron gracilis, G. guerillerus, Helosphaeridium guttatum, H. microclavatum, Multiplicisphaeridium cf. raspa, Oppilatala cf. Oppilatala vulgaris, Riculasphaera fissa, Tyligmasoma alargadum, and Veryhachium trispinosum “complex” (see Fig. 7; Table 1). Small acritarchs with short spines (Helosphaeridium type) are more frequent in samples from the top of the section (IZ-8).
Prasinophyta are represented by Leiosphaeridia spp. Their relative frequency constantly increases, reaching ca. 8% in the upper part of the section. They are more frequently represented in the upper part of the section as compared to its lower part. Chitinozoans, on the other hand, are more fre-quent in the lower part and nearly absent in the upper part of the section investigated. Their maximum frequency was noticed in the IZ-1 sample, reaching ca. 8%. Also scolecodonts, and other animal cuticles, including the parts of eurypterid respiratory organs, accompanied by land-derived plant de-bris were noticed in the kerogen. The presence of AOM was noticed only in the topmost IZ-8 sample (Fig. 6).
Among plant particles, sheets of enigmatic Nematothallus sp. were more frequently noticed than those of Cosmochlaina sp. (Fig. 8A–C). Plant tubes and filaments were mainly repre-sented by Laevitubulus spp., Porcatitubulus spiralis, and P. annulatus tissue (Fig. 8H, I, K). Paris and Grahn (1996: pl. 2: 7–9) also documented the presence of Porcatitubulus taxa from the Ivanye Beds. Some cuticles were encountered, but none had stomata like those of higher plants. Similar cuticles of enigmatic taxa were recently noticed in the marginal-ma-rine/alluvial clastic Pragian—Emsian deposits from southern Poland (Filipiak 2011; Filipiak and Zatoń 2011).
Animal cuticle remains
The most numerous animal cuticle remains are of arthropod origin well known from the Podolian Upper Silurian to Lower Devonian localities (e.g,. Krzemiński et al. 2010). They are often characteristically folded, possess irregularly distributed pores, setae, and spines, or may be stiffened. In that manner they differ from the associated plant cuticles (e.g., Gensel et al. 1990; see also Filipiak and Zatoń 2011). None of the animal cuticles are found to be associated with any larger diagnostic part of arthropod exoskeleton, so many of them are difficult to be unequivocally assigned to a particular group of arthropod animal. Only some character-istic respiratory organs allow identification as belonging to eurypterids that are known to occur in the strata studied (see Voichyshyn 2011). In transmitted light, the cuticles are translucent yellowish-brown in appearance.
Eurypterid respiratory organs.—These are the most char-acteristic animal structures present in the material investi-gated (Fig. 9B–D). They are represented by conical struc-tures (spinules) that usually occur as single individuals (Fig. 9B, C) and very rarely as grouped structures (Fig. 9D). Usually, they are preserved as fragments. The best preserved (?complete) spinule is ca. 175 ìm in length and ca. 100 ìm in width. Two morphological varieties of spinules are present: (i) conical, with a wide base and narrow top ended with a distinct spine (Fig. 9B), and (ii) oval in outline, with well-rounded top devoid of a spine, slowly widening toward its base (Fig. 9C). The entire surface of spinules is covered by thin microscopic cuticular projections, ca. 10 ìm in length and ca. 10 ìm in width (Fig. 9B, C). The projections are dis-tinctly arranged in groups of six, forming a hexagon that is internally empty (Fig. 9B) (see also Manning and Dunlop 1995; Filipiak and Zatoń 2011).
Our spinules are very similar to those described from Up-per Silurian and Lower Devonian by Manning and Dunlop (1995) and Filipiak and Zatoń (2011), and interpreted as eurypterid accessory air-breathing respiratory organs (Kie-menplatten or “gill tracts”, see Manning and Dunlop 1995 and references cited therein). Those spinules possessing a spine at their top are especially similar to those from the Up-per Silurian (Manning and Dunlop 1995). The latter may only differ in having somewhat more robust spines. Those that are spine-less and have rounded top, on the other hand, are most similar to those described recently by Filipiak and Zatoń (2011) from the Lower Devonian of Poland. Although morphologically different, it is not excluded that the both forms of spinules described here may have belonged to the same eurypterid species, as such grouped spinules consisting of both spiny and spine-less forms are known from the Emsian—Eifelian of Saudi Arabia (Breuer 2007).
Eurypterid and ?scorpion cuticles.—The dispersed arthro-pod cuticle fragments studied have more or less folded sur-face showing pores, spines and tooth-like projections. How-ever, as all of them are dissociated from the larger diagnostic parts of the exoskeleton and as their ornamentation may dif-fer between different exoskeletal parts (e.g., Wills 1959; Tollerton 1989; Jeram 1994), their unequivocal determina-tion to a specific arthropod group is difficult.
Some of the cuticle remains, however, possess features identical or very similar to other cuticle remains previously illustrated in the literature. Thus, at least some of them may be classified with a greater confidence.
The cuticles having characteristic crescent-shaped foldings (lunules) on the surface (Fig. 9J) can be found in eurypterid (e.g., Eurypterus, Pterygotus) cuticles illustrated by Clarke and Ruedemann (1912) from the Silurian of the New York State. They were also described and illustrated by Taugourdeau (1967) from Silurian—Devonian of Africa, as belonging to eurypterids. The same concerns the cuticle fragments with dis-tinct raised, elliptical openings (Fig. 9K) presented by Tau-gourdeau (1967) as true eurypterid cuticles. Structures similar to the latter were also found in the Lower Devonian of Scot-land. They were figured, but not discussed further (Wellman 1995). Such structures were also recently described and illus-trated by Filipiak and Zatoń (2011) from the Lower Devonian of Poland. The cuticles showing characteristic meandering structures on the surface (Fig. 9F, H) somewhat resemble the cuticle ornamentation present in the eurypterid Tylopterus (see Clarke and Ruedemann 1912: 217, fig. 42).
The rest of the cuticles and cuticular structures associated with the eurypterid remains, are equivocal and difficult for confident assignment. They may well belong either to eury-pterids, scorpions or even other arthropod groups. They con-sist of different, more or less folded cuticle remains with or without openings and characteristic wrinkles (Fig. 9G), and setae detached from the cuticle surface (Fig. 9E), as well as long, stiff conical structures pointed distally (Fig. 9A). Such setae and conical structures have already been described and illustrated by Taugourdeau (1967) and recently by Filipiak and Zatoń (2011). These structures could well be either of eurypterid, scorpion or even different arthropod origin. The stiff spiny structure with sharply pointed tip and wide base (Fig. 9I), for example, is somewhat similar to some scorpion claws (e.g., Bartram et al. 1987), but again, a larger diagnos-tic cuticle fragment attached would be better for more certain assignment.
Cuticles of uncertain affinity
Some of our cuticles are characterised by reticulate, polygo-nal-like pattern and smooth surface lacking stomata (Fig. 8D–G). In this respect, they are very similar to the plant cu-ticles classified as Nematothallus (Pratt et al. 1978; Edwards 1982; see also Filipiak and Zatoń 2011). It is possi-ble, that the Nematothallus cuticles could represent the re-mains of early liverworts (Graham et al. 2004). However, the similarity of the cuticles investigated here to Nemato-thallus seems to be superficial. The cuticles discussed are stiffer, and have much smaller polygonal, cell-like fields and tiny flanges, well-visible on the cuticle margins (Fig. 8F, G). In most cases, they are delicate, from 2 to 2.5 µm high but sometimes they are completely reduced forming only the flat pattern on the surface. However, the thickness and projection of flanges are uniform in each individual sheet. A regular reticulum with more or less isodiametric, angular units are 3 × 4.5 ìm in size, so they are twice as small as in typical Nematothallus taxa sensu Edwards (1982; see Fig. 8B, C). Therefore, the systematic position of these cuticle remains is uncertain.
Microfacies of calcareous layers
In the Ivanye Horizon to Ustechko Member transition at Ivanye Zolote, calcareous interbeddings within the mixed carbonate-siliciclastic succession embrace two distinct micro-facies types, extremely differing in fossil frequency. The most characteristic are thin (mostly less than 10 cm) coqui-nas, corresponding to bivalve-ostracod packstone to grain-stone (Fig. 10). The frequently sorted shell accumulations show typically a densely-packed biofabric, in places clus-tered (nesting to stacking sensu Kidwell et al. 1986) or cha-otic. These skeletal concentrations rarely display an ero-sional contact with underlying mudrocks and graded bed-dingin, and comprise mostly concordantly oriented, con-vex-upward millimetre-sized disarticulated shells and frag-mented, non-micritized valves; larger fossils (above 1 cm) occur only in some debris layers. Silty/sandy and/or peloidal partings are common, paired with plane parallel (rarely, oblique and/or graded) laminations in some layers. Among other skeletal constituents, diverse ichthyolites are most nu-merous, accompanied by orthocone nautiloids and brachio pods (articulates and lingulids), as well as subordinate gas-tropods, tentaculitids (including putative “vermiform” micro-conchids), chaetetid sponges and fragmented probable grapto-lites. In addition, nautiloids and in situ lingulids are abundant e.g., in time-equivalent beds at Zalishchyky.
Calcareous-sandy layers, characterized by variable thicknesses (up to 15 cm), occur in the topmost Ivanye Horizon, and a discontinuous level is found also in the bottom part of red clayey Ustechko Member. Mostly extremely impover-ished fossil remains, limited to ichthyolites and poorly-pre-served shelly, largely ostracod faunas, occur in the micrite-or sparry-sandy, frequently laminated matrix (Fig. 11).
Palaeoenvironment and paleoecology
Investigated samples from Ivanye Zolote and Ustechko were taken from the Early Devonian marginal marine sequences consisting of carbonates intercalated with siliciclastics. Inor-ganic geochemical proxies from the correlative uppermost Ivanye Beds at adjacent Zalishchyky section (see above) re-veal an overall environmental characteristics close to the re-gional background (Racki et al. 2012: fig. 8), and suggest mostly progressively clay-dominated, lower-productivity, and well-oxygenated sedimentary conditions up the succession. In addition, a distinctive enrichment trend in light carbon and ox-ygen isotopes in this locality is explained by a hydrochemical peculiarity and/or early meteoritic diagenetic overprint in an episodically restricted epeiric sea (Małkowski et al. 2009).
The highest calcareous layers in the Podolian succession well illustrate a consequent paleoenvironmental shallowing-upward evolution of the shrinking marine basin, forced by an eustatic sea-level fall (e.g., Walliser 1996: fig. 3), manifested in a recurrent blooming of low-diversity opportunistic shelly benthos only. Progressive fluctuating brackish or even fresh-water conditions, suitable for the fish fauna thriving (all major agnathan and gnathostome groups; Voichyshyn 2011: table 1; Voichyshyn and Szaniawski 2012)may be assumed (see sum-mary in Flugel 2004: 618–619), as well as their link with grad-ual development of the Old Red-type, coastal lagoon to flu-vial-estuarine habitats (Uchman et al. 2004). The rock-form-ing assemblage includes the nuculanid bivalve Palaeoneilo tschortkovensis and more diverse ostracods (Leperditia tyraica and several species of Welleriella, among others; see full faunal lists in Nikiforova et al. 1972: 247–250). In fact, re-markable leperditicopid microcoquinas probably record large populations of detritus-feeding euryhaline arthropods on mi-crobial and/or algal mats developed in tidal mudflats and supratidal marshes, within semi-restricted lagoons, bays or estuarian complexes (Vannier et al. 2001).
Such noteworthy sessile benthic species as the terebratulid brachiopod Mutationella podolica (also athyridid Protathyris) and chaetetid demosponge Tiverina vermiculata, as well actinocerid nautiloid Ormoceras dobrovljanensis, and Tenta-culites ornatus were listed by Nikiforova et al. (1972) and Gritsenko et al. (1999; their M. podolica and T. vermiculata communities, as updated by Mike Foote in the Paleobiology Database). The most common bivalve Palaeoneilo represents mobile infaunal deposit feeders (see Gritsenko et al. 1999), whilst M. podolica is well known in the low-diversity, high-dominance suspension-feeder biotas in extremely shallow-shelf habitats (“intertidal” Benthic Assemblages, BA 1–2 of Boucot 1975; compare Kozłowski 1929: 11–14). This en-demic species was probably also successful in unstable salin-ity conditions (as several other Middle Paleozoic “schizo-haline” terebratulids; Racki 1988) because it is reported even from the highest calcareous layers in the succession as the only macrofaunal element (Nikiforowa et al. 1972; see the Rhenish biofacies pattern in Boucot 1975: 215–216). In addition, also Tiverina vermiculata is seen as a unique colonizer of Siberian hypersaline basins (Dubatolov and Krasnov 1997), and simi-lar euryhaline preferences are postulated for tentaculitoid microconchids (= “vermiform gastropods” of Uchman et al. 2004; see Zatoń and Vinn 2011). Gritsenko et al. (1999: 481) suggest “transition from BA 2, for medium diversity community, through BA 1 for themonospecific unit, to the nonmarine or estuarine vertebrate community”.
Nautiloids exemplified the most frequent open marine mobile macrofaunal dwellers, but probably redeposited into the nearshore muddy lagoon due to episodic, both simple and complex storm actions. The recurrent well-agitated condi-tions are mostly extensively recorded in the bioclast rework-ing of bivalve shelly banks near carbonate/siliciclastic shoals and barriers, whereas bioturbation was generally minor. Sim-ilar upward shift from marginal-marine to fluvial facies was described from the Ustechko succession by Uchman et al. (2004).
Generally, amongst the palynofloral remains, those of land-origin predominate. Spore assemblages are taxonomi-cally moderately diverse comprising ca. 40%–80% of the rel-ative abundance. The other component, phytoplankton, com-prises the remaining ca. 20% but sometimes reaches 60% (Fig. 6). Besides palynomorphs, large-sized cuticles and plant tracheids together with organic sheets of Nematothallus and Cosmochlaina are present, as well. Moreover, some ar-thropod remains are also present in the material investigated.
The constant presence of acritarchs in the all samples in-vestigated points to marine conditions during sedimentation (e.g., Batten 1996). It is worth to notice the decreasing ten-dency in taxonomic diversity of acritarchs in the topmost samples what is characteristic for nearshore environments (Dorning 1981). Also interesting is the proportion between the microflora of land-origin (spores and cryptospores) ver-sus phytoplankton (represented mainly by acritarchs), which shows distinct fluctuations (Fig. 6). It can be explained as a result of the sea level changes and/or the presence of some factors influencing macroflora development on a nearby land. Three periods of domination of the land-derived parti-cles (IZ-1, IZ-4, and IZ-7), separated by three periods with phytoplankton increase (IZ-2, IZ-5, and IZ-8) can be distin-guished. Interesting is also the constant chitinozoan decrease with simultaneous leiosphaeres increase (Fig. 6). The pres-ence of leiosphaeres is explained as a result of brackish sur-face water conditions (Tyson 1993). Thus, changes of marine chemistry to more brackish, as noted above, could also be re-sponsible for the decrease of a relative abundance of chitino-zoans (Wrona 2009) and an impoverishment of acritarch as-semblage at the same time. Symptomatic is also a small dom-inance of cryptospores over trilete spore taxa (Fig. 6). Ac-cording to Steemans et al. (2007) crytospores were environ-mentally more restricted to damp land habitats comparing to trilete spores (see also Wellman et al. 2000).
Generally, the palynofacies described above is character-istic of nearshore environments. In such sedimentary condi-tions the land-derived organic particles are deposited fre-quently (e.g., Batten 1996). The presence of large-sized plant tracheids (Laevitubulus and Porcatitubulus), cuticles of enigmatic Nematothallus and Cosmochlaina, and abundant miospores and arthropod remains confirm such an interpreta-tion (e.g., Tyson 1993; Batten 1996).
Moreover, large number of phytoclasts (e.g., Nemato-thallus, Cosmochlaina, and banded tubes) may suggest the presence of sufficient vegetation on the Early Devonian Ukrainian land, which was a source of perspective food and a temporary shelter for the semi-aquatic eurypterids and maybe even other terrestrial arthropods (see also discussion in Filipiak and Zatoń 2011). It is also obvious, that the Early Devonian macroflora were, to a great extent, spore-produc-ing plants, strongly restricted to moist environments.
Palynological results from the Podolian sections are also consistent with sedimentological factors and comparable with those observed in the neighbouring Silurian–Devonian boundary section in the Barrandian area, Czech Republic (Fatka et al. 2003; Brocke et al. 2006). Moreover, Podolian occurrence of the eurypterid fauna is in accordance with sim-ilar purely marine eurypterid faunas known from Scotland, America, Africa, and Europe, where they occur together with other marine biota and well document their marine environ-mental conditions (e.g., Kjellesvig-Waering 1961; Caster and Kjellesvig-Waering 1964; Křiž et al. 1986).
Palynological investigation indicates the existence of abun-dant, well-preservedmicroflora assemblages in the mixed car-bonate-siliciclastic Lower Devonian deposits from Podolia, consisting mainly of miospore and phytoplankton taxa. Based on the appearance of characteristic miospores, this assemblage is not older than the NM Oppel Miospore Zone, strictly the Si Lineage Zone (upper Lochkovian) and tentatively corre-sponds to the Latericriodus woschmidti/L. postwoschmidti— Ancyrodelloides delta conodont zones.
The constant presence of acritarch taxa in all samples in-vestigated indicates marine conditions during sedimentation. However, the decreasing tendency in taxonomic diversity of acritarchs in the topmost samples, together with simulta-neous disappearance of chitinozoans and increase in leio-sphere frequency may indicate a change of environmental conditions from marine toward more brackish ones at the top of IZ section.
Microfacies evolution of stratigraphically highest calcare-ous layers also well demonstrates progressive shallowing-up-ward transition from the marginal marine basin to brackish habitats, manifested in recurrent thriving of impoverished, mostly opportunistic and euryhaline benthos and diverse ich-thyofauna only. Effective storm and current reworking of bi-valve-dominated shelly banks is well recorded in the bioclastic accumulations, widely distributed in the shallowing mud-rich lagoonal environments (compare Uchman et al. 2004).
The association of plant and arthropod cuticles point to the presence of sufficient vegetation on the nearby land, where semi-aquatic eurypterids and other terrestrial arthro-pods could have found food and temporary shelter in that moist environment.
Geoffrey Playford (University of Queensland, Brisbane, Australia), Reed Wicander (Central Michigan University, Mount Pleasant, USA), and Philippe Steemans (University of Liège, Belgium) are thanked for the taxonomic consultation concerning microflora taxa. We are deeply grateful to El¿bieta Turnau (Polish Academy of Science, Cracow, Po-land) for her valuable insight into the first version of this manuscript. We warmly thank Daniel Drygant (State Museum of Natural History, L'viv, Ukraine) for introducing us into the field at Podolia. Geoffrey Playford, Claudia Rubinstein (Unidad de Paleopalinologia, CONICET IANIGLA, Mendoza, Argentina) and an anonymous referee are ac-knowledged for valuable remarks and constructive comments. Kyle Freeman (Institute of Paleobiology, Warsaw, Poland) is acknowledged for linguistic improvement of the final version of the text. The research was supported by a grant (No. N N307 057834) from the Ministry of Science and Higher Education to Hubert Szaniawski (Institute of Paleo-biology, Warsaw, Poland). This is a contribution related with the UNESCO/IGCP projects no 596 on “Climate change and biodiversity patterns inMid Paleozoic (Early Devonian to Early Carboniferous)” and no 591 on “The Early to Middle Paleozoic Revolution”.