Gigantocharinus szatmaryi, a new trigonotarbid arachnid from the Late Devonian of North America (Chelicerata, Arachnida, Trigonotarbida)

A new trigonotarbid arachnid, Gigantocharinus szatmaryi new genus and species, is described from Upper Devonian (Late Famennian) sediments in Pennsylvania. Devonian trigonotarbids were known before from only a single North American locality and several European ones. The new trigonotarbid occurs in what had previously been a significant time gap between the faunas of the Middle Devonian and the late Carboniferous. Gigantocharinus szatmaryi is assigned with some hesitation to the family Palaeocharinidae.

Since the 1960s, two gas fields (Lokachi and Velyki Mosty) have been discovered in the Devonian sequence of the Volyn-Podillya Plate, and numerous gas shows have been observed in the Lokachi, Olesko, Horokhiv, and Oglyadiv areas. Organic-rich rocks within the Volyn-Podillya Plate are widespread in the Lower, Middle and Upper Devonian strata. They are represented by terrigenous, clayey and carbonate layers. The objective of this study is to investigate the generation potential of the Devonian rocks of the Volyn-Podillya Plate and the possibility of their participation in the petroleum system of the region. Geochemical studies covered the entire territory of the Volyn-Podillya Plate as well as the entire chronological interval of the Devonian strata. Rock-Eval pyrolysis studies showed that the content of total organic carbon in the Lower Devonian organic-rich rocks ranges from 0.01 to 0.45 % (average values 0.12 %). The organic matter in these rocks contains mainly kerogen of marine origin type II, and has undergone primary and/or secondary oxidation processes. The content of total organic carbon in Middle Devonian sediments varies: in rocks of the Eifelian Stage from 0.02 to 0.64 % (average values 0.08 %), in Givetian from 0.01 to 2.35 % (average values 0.19 %), in Frasnian from 0.04 to 1.43 % (average values 0.08 %), in Famennian from 0.07 to 0.10 % (average values 0.09 %). The thermal maturity level of the Lower (Lochkovian Stage), Middle (Eifelian, Givetian Stages) and Upper (Frasnian, Famennian Stages) Devonian ranges from immature to overmature rocks. The Middle and Upper Devonian rocks are dominated by type II marine kerogen, which underwent primary oxidation during sedimentation and/or secondary hydrothermal oxidation of dispersed organic matter during dolomitization. The pyrolysis temperature Tmax varies from 422 to 527 °C, demonstrating that the degree of thermal transformation of kerogen ranges from immature to overmature, with a significant part of the sediments being within the zones of generation of liquid and gaseous hydrocarbons, which indicates the significant role of Devonian sediments in the formation of the petroleum system of the region. Geochemical studies of the generation properties of the Middle and Upper Devonian sediments within the Volyn-Podillya Plate showed that they can be considered as oil and gas source rocks in the Upper Paleozoic sequence.

SINCE 1932, the earliest known undisputed tetrapods have been of uppermost Famennian (late Upper Devonian) age1–3. Although a probable tetrapod jaw has been described from the Lower Famennian4, and tetrapod tracks of supposedly Frasnian5 (and possibly earlier6) age are known, no fossil limb material older than the latest Famennian has been discovered. The 'panderichthyids'Panderichthys7 and Elpistostege8 from the Lower Frasnian (early Upper Devonian) are regarded by some8–10 as the closest known sister group of tetrapods, but Panderichthyshas paired fins rather than limbs11. Here, I describe a hitherto unrecognized tibia from the Upper Frasnian (middle Upper Devonian) site of Scat Craig, near Elgin, Scotland12–14, collected during the nineteenth century, which extends the fossil record of the tetrapod-type hind limb by roughly seven million years15. Other isolated bones from the same locality also show tetrapod characteristics. The tibia, a humerus and some incomplete jaws are discussed below, but a complete description of the material is in preparation.

Evidence for long-term climate change in Upper Devonian strata of the central Appalachians

Upper Devonian rocks of the Iberian Pyrite Belt (IPB) in southwest Spain, comprising the Phyllite-Quartzite Group (PQ) and the lower part of the overlying Volcano-Sedimentary Complex (VSC), contain a diversity of terrestrial and marine palynomorphs (miospores and organic-walled microphytoplankton, respectively), which constitute the basis of this biostratigraphically oriented research project. Part One of the report has previously detailed the miospore content of the constituent 117 palyniferous samples. In the present paper (i.e., the concluding Part Two), the organic-walled microphytoplankton (acritarchs and prasinophyte phycomata) are systematically described and illustrated, and their occurrence in the study material is fully documented. The acritarchs are represented by 23 species (including one species complex) allocated among 14 genera (one of which, Dupliciradiatum, is newly established), together with a very rare and novel category (informally termed Gen. nov. A). The following new acritarch species are formally instituted: Dupliciradiatum crassum (type species), D. tenue, Histopalla languida, and Winwaloeusia repagulata. Five genera allied with the prasinophycean algae are identified; these accommodate a total of 15 species of which two - Cymatiosphaera tenuimembrana and Maranhites multioculus - are formally proposed as new. In addition, representatives of the prasinophyte genera Leiosphaeridia and Tasmanites are recorded but are not discriminated at species level. The microphytoplankton suite is clearly consonant, from previously published occurrences in other regions, with a Late Devonian dating. However, most of the species are known to be relatively long ranging through (and in some cases beyond) that epoch and hence are not amenable to detailed biozonal subdivision of the IPB succession. Moreover, the distribution of the species therein tends to be erratic in comparison with the more consistently occurring miospores, possibly due to stress factors induced by fluctuating conditions in the IPBs Upper Devonian marine environment. By contrast, the land-derived (miospore) assemblages are readily applicable in a blostratigraphic context: they can be correlated precisely with the Devonian miospore biozonation scheme for Western Europe. In those terms, the sampled PQ strata are assignable to the Diducites versabilis-Grandispora cornuta (VCo) Biozone of late Famennian age; while the samples from the anoxic sequence at the base of the VSC belong to the Retispora lepidophyta-Verrucosisporites nitidus (LN) Biozone (latest Famennian = latest Devonian). The biochronostratigraphic data, in conjunction with the findings from earlier IPB studies, imply two appreciable palynostratigraphic breaks within the PQ. These are representative, respectively, of the lower Frasnian-middle Famennian interval and of part of the Strunian/upper Famennian. Speculation currently remains as to whether the inferred gaps are more apparent than real; i.e., whether one or both represent actual hiatuses in IPB sedimentation or are simply a manifestation of hitherto unsampled and/or non-palyniferous PQ strata.

Major and trace element analyses were made on twenty nine Middle-Upper Devonian and Lower Carboniferous sedimentary rocks from the Sudut area. Negative linear correlation trend on a SiO2-Al2O3 plot and positive correlations of other major oxides with Al2O3 indicates that the proportions of quartz, feldspar and lithics relative to clays is the dominant control on the chemistry of the basement sedimentary rocks. Positive correlations among Al2O3, Zr, Y, Nb, P2O5 and Th suggest that both heavy minerals and clay phases control the abundances of these elements. Major and trace element concentrations in the basement sedimentary rocks suggest a relatively homogeneous source, with felsic composition similar to Upper Continental Crust (UCC). Average Chemical Index of Alteration (CIA) values of the Middle Devonian (58.9), Upper Devonian (53.3), and Lower Carboniferous (54.9) sediments are very low, suggesting weak to moderate weathering of their original source. Middle Devonian sediments were suffered more intense post-depositional K-metasomatism than the Upper Devonian and Lower Carboniferous sediments.

The Middle to lower Upper Devonian succession of the Rügen Depression in NE Germany consists of largely clastic sediments, whereas the Upper Devonian deposits are mixed carbonate and clastic. Petrographic and geochemical data suggest that the sediments were deposited in a cratonic or recycled setting. Deposition was largely confined to a fault-bounded basin, located between two structural highs. During the Devonian, the Rügen area underwent evolution from a continental and marginal marine area during the Eifelian-early Frasnian to a deeper marine environment during the late Frasnian-early Famennian. By the latest Famennian, an open-shelf carbonate-facies environment was established.

Conodont investigations in the German standard Upper Devonian sections resulted in establishing a conodont zonation. Altogether 26 conodont zones and subzones have been recognized. The conodont succession was obtained mainly from known ammonoid zones beginning with the uppermost Middle Devonian cephalopod zone of Maenioceras terebratum and extending through the entire Upper Devonian into the Wocklumeria Stage. To determine the regional constancy of conodont succession, more than 100 Upper Devonian sections from Germany were studied. The same Upper Devonian conodont succession, recognized in much of Europe, as detailed investigations have subsequently proved. These zones have been found in eastern Germany, Carnic Alps in Austria, Montagne Noire and northern Massif Central in France, Pyrenees and Cantabria in Spain, and Moravia and Bulgaria in southeastern Europe. In addition, in the Belgian Upper Devonian, where the sediments were laid down in a different environment, similar zonal associations and successions coincide with others. Results of studies in the Upper Devonian outside of Europe (mid-western and northern Africa) support the opinion that conodont succession in the Upper Devonian is the same as that in Europe. Presently known deviations are caused by peculiarities within the local geological sequences (breaks in sedimentation, slow deposition, reworking, redeposition, etc.). A recent study of the ammonoid-bearing Upper Devonian sequence of northwestern Australia carried out by Glenister and Klapper indicates that the European conodont zonation also can be applied effectively in this region. Conodonts can be used to zone the Upper Devonian in greater detail than the standard cephalopod succession. Recent studies reveal that boundaries between some ammonoid stages are inexactly defined or that there are gaps in the ammonoid succession. By means of conodonts such gaps may be bridged with the result that the best and most complete biostratigraphic subdivision of the Upper Devonian at present is based on conodonts.

The analysis of the potential of natural gas resources of gas prospective shale formations in the main oil and gas basins of Ukraine, that is of Eastern, Western, Southern ones. On the basis of economic and mathematical modeling of geological and economic characteristics of shale formations, from which successful shale gas mining is currently being carried out in the world, correlation-regressive dependencies have been established. They allow to carry out a predicted estimation of the gas content, the initial rate of gas extraction wells, the marginal cost limit, at which a break-even production of natural gas from shale formations is possible. Using these dependencies, an analysis of the resource potential of slate formations has been carried out and it has been established that in the Eastern region stratigraphic complexes with promising shale formations are included: Devonian deposits - Upper Devonian (Famensian tier); coal deposits - Lower Carboniferous Complex (Tourney, Viseu, Serpukhov Tiers); middle-complex complex (Bashkir and Moscow tiers); Carboniferous complex (Kasimovsky and Gzhel tiers). Yevgenivsko-Druzhelyubivsk, Mirgorod-Livensk, Borkivsk-Velikzagorivsk and Zachipelsk-Livensk areas are the most investments-attractive in the prospects for shale gas extraction in the Eastern region. In the Western region, prospective stratigraphic complexes include deposits of the Cambrian, Silurian and Oligocene-Miocene age. The most investment attractive for shale gas extraction in the Western region is Davydivsky, Rava-Russkaya, East-Lishinskaya and Oleska districts. In the Southern region, perspective shale gas extraction is the deposits of the Middle Jurassic, the upper part of the Visean tier and the lower part of the Serpukhov tier of the carbon fiber of the Pre-Dobrug Trough. The results obtained can serve as a basis for investors to select priority objects for the development of natural gas resources from shale formations in Ukraine.

The lithostratigraphic scale of Belgium, which is the cradle of several global Devonian stages, has been revised after completion of the update of the Geological Map of Wallonia (Carte géologique de Wallonie) at a scale of 1/25,000 and recent stratigraphic and sedimentological research. As a result, 100 lithostratigraphic units (groups, formations, members, facies, horizons) for the Upper Devonian Series have been re-defined. Whereas most of the units discussed in this overview are traditional divisions of the Belgian lithostratigraphic scale, this update includes revisions to their definitions, boundaries, and ages. New terms have been introduced essentially for notable horizons and facies. Additionally, some previously described formations have been reclassified as members as they are difficult to distinguish and separate on geological maps. The Frasnian lithostratigraphic units reflect the development of mixed argillaceous-carbonate deposits during the major transgressions that culminated at the end of the stage. This was followed by the gradual emergence of littoral siliciclastic facies that took place during the Famennian regression. Re-installation of carbonate deposits was recorded during the latest Famennian (Strunian transgression), heralding the lower Carboniferous carbonate succession to come. Reefs occur in the Frasnian (buildups, mud mounds, biostromes) and their presence in the middle Famennian is remarkable.

Devonian charcoal

Lectotypification of the Famennian pre-ovule Condrusia rumex Stockmans, 1948

The radiation of early Carboniferous foraminifers and rugose corals following the Devonian–Carboniferous crisis offers the best tool for high-resolution correlations in the Mississippian, together with the conodonts in the Tournaisian, notably in the Namur–Dinant Basin. However, some of the guides are facies-controlled and an integrated approach combining biostratigraphy, sedimentology and sequence stratigraphy is critical to identify delayed entries, potential stratigraphic gaps and to avoid diachronous correlations. The main difficulty is in correlating shallow and deeper water facies at any given time. In existing zonations, the Viséan part of the scheme is always more detailed, reflecting the widespread development of shallow-water platforms in the early Viséan which created conditions more suitable for foraminifers and rugose corals over large areas. In contrast, the Tournaisian zones, less well documented, reflect unfavourable environmental conditions in the lower ramp (Dinant Sedimentation Area) and pervasive dolomitization of the inner ramp (Condroz and Namur Sedimentation Areas). Recent progress in understanding the Belgian early Carboniferous sequence stratigraphy and lithostratigraphy, and revision of the biostratigraphy of the key sections, strongly modify former biostratigraphic interpretations. Improvements mainly concern the latest Devonian, the late Tournaisian and the early Viséan. The late Devonian and the Tournaisian are equated with foraminifer zones DFZ1 to DFZ8 and MFZ1 to MFZ8 respectively. The Viséan correlates with zones MFZ9 to MFZ14. Zone MFZ15 straddles the Viséan–Namurian boundary and Zone MFZ16 is the youngest Mississippian zone. The rugose corals allow the recognition of ten zones, RC0 to RC9, covering the Strunian (late Famennian) to Serpukhovian interval. Discrepancies with former zonations are discussed. The Moliniacian Stage is emended to restore the coincidence between its base and that of the Viséan.

The Famennian (Upper Devonian,c. 372 to 359 Ma) strata of Belgium have recently received much attention after the discoveries of early tetrapod remains and outstandingly preserved continental arthropods. The Strud locality has yielded a diverse flora and fauna including seed-plants, tetrapods, various placoderm, actinopterygian, acanthodian and sarcopterygian fishes, crustaceans (anostracans, notostracans, conchostracans and decapods) and a putative complete insect. This fossil assemblage is one of the oldest continental – probably fresh-water – ecosystems with a considerable vertebrate and invertebrate diversity. The study of the palaeoenvironment of the Strud locality is crucial because it records one of the earliest and most important phases of tetrapod evolution that took place after their emergence but before their terrestrialization. It raises the question of environmental and ecological conditions for the Devonian aquatic ecosystem and the selection pressures occurring at the onset of tetrapod terrestrialization. The present study characterized the fluvial facies of the Upper Famennian sedimentary rocks of Strud and the surrounding areas. The exceptional preservation of arthropods and plants in the main fossiliferous layers is explained by rapid burial in the fine-grained sediment of the quiet and confined flood plain environment. Newly investigated fossiliferous sections in the Meuse–Samson area led to the description and correlation of key sections (Strud, Wierde and Jausse sections, complemented by the less continuous Haltinne, Huy and Coutisse sections). Moreover, the investigated sections allowed a review of the age of the fossiliferous horizon, which is now definitely considered to be Late Famennian in age.

Late Devonian aquatic environments hosted the fin-to-limb transition in vertebrates. Upper Devonian (ca. 365–360 Ma) strata in Pennsylvania, USA, preserve a diversity of fishes and tetrapods in coastal marine to fluvial depositional environments, making this region ideal for investigating the ecology and evolution of Late Devonian vertebrates. A key unresolved issue has been reconstructing the specific aquatic habitats that hosted various vertebrates during this period. Specifically, the salinity of environments spanning fresh to shallow marine water is difficult to discern from sedimentological and paleontological analyses alone. Here, we analyze rare earth elements and yttrium (REY) as well as stable oxygen and sulfur isotope compositions (δ18O, δ34S) in fossil vertebrate bioapatite from late Famennian (ca. 362–360 Ma) strata of the Catskill and Lock Haven formations in the Appalachian Basin, USA, to determine the relative salinity of their aquatic environments. These results confirm the ecological euryhalinity of several taxa (Bothriolepis sp., tristichopterids, and Holoptychius sp.). Our results are the first demonstrating that some early tetrapod species occupied unequivocally freshwater habitats by late Famennian time (ca. 362–360 Ma). Our study shows that integrating sedimentological and paleontological data with combined oxygen and sulfur isotope analysis allows precise tracing of the relative salinity of vertebrate habitats deep in the past.