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Highlights • First described Laotian graptolites are from Llandovery of Truong Son Terrane. • Graptolites have higher latitude, Gondwanan not tropical South China affinities. • Fauna implies Truong Son was closer to Southern Europe-Arabia than to South China. Abstract Graptolites are described from the Llandovery of the Sepon mine area, central Laos, part of the Truong Son Terrane. The palaeobiogeographical affinities of the Rhuddanian graptolites are with peri-Gondwanan Europe and Arabia rather than equatorial regions such as South China and Laurentia (Arctic Canada). A review of previous palaeontological research on the middle Palaeozoic of the Indochina terranes reveals an often contradictory picture with vertebrates suggesting close proximity of South China to the Truong Son Terrane in the Devonian and invertebrates and radiolarians providing evidence for a palaeogeographical barrier between the two. Graptolites from the Mojiang area, Yunnan are typical of low latitude Silurian faunas and suggest that this area (Simao or Loei Terrane) was separate from the Truong Son Terrane. [ABSTRACT FROM AUTHOR]

Warm-water Dasycladaceae algae Mastopora and Cyclocrinites were for the first time recorded from the Takche Formation (Upper Ordovician-lower Silurian), Parahio Valley, Spiti, India. They are preserved as external and internal moulds of the non-globular or possibly bulb-like cortical skeleton showing flattened thalli with a high degree of compaction. The occurrence of abundant cyclocrinitid remains in the Takche Formation indicates that the Spiti region of the northwestern Himalaya must have been located at about 30° palaeolatitude during the Late Ordovician and early Silurian. The cyclocrinitids were warm-water algae and their extinction at the end of the Ordovician is related to cooling and glaciations. The cyclocrinitids in the Ordovician are known from several localities in central and southern Asia, including Kazakhstan and western China. [ABSTRACT FROM AUTHOR]

Abstract The Diancangshan-Ailaoshan fold belt (Yunnan, SW China) represents the remnants of the once vast Ailaoshan Ocean, a branch or back-arc basin of the Eastern Paleotethys. However, when and how this ocean/back-arc basin opened, and rifted South China away from Gondwana are still unresolved. In this study, Ordovician-Silurian high-Nb basalts (HNBs; 420 Ma), Mg-rich andesite (435 Ma), high-Mg basalt (446 Ma) and I-type granite (423 Ma) were newly identified in the Diancangshan-Ailaoshan fold belt. The HNBs are alkaline with high TiO 2 (1.8–1.9 wt%) and Nb (16.9–23.1 ppm) contents, high Nb/U (36.8–39.1) and (Nb/Th) PM (1.17–1.21) ratios, positive Nb-Ta anomalies (primitive mantle-normalized) and positive ε Nd (t) values (+3.2). The HNBs were likely derived from an OIB/arc-mixed mantle source in the garnet stability field. The Mg-rich andesites are medium-K calc-alkaline andesite with negative ε Nd (t) values (−10.1) and negative Nb-Ta anomalies. The magma was likely derived from a mixture of depleted mantle peridotites and subducted sediments under low pressure and high H 2 O conditions. The high-Mg basalts are high-K calc-alkaline and characterized by high MgO contents (9.3–9.4 wt%; Mg# = ~70), high Cr (369–379 ppm) and low Al 2 O 3 (13.6–13.9 wt%) contents. They were likely derived from an enriched mantle source metasomatized by marine sediment-derived fluids. The I-type granites show medium SiO 2 content (63.6 wt%), low A/CNK ratio (0.9) and negative ε Nd (t) value (−9.8), and may have formed by the partial melting of meta-basalts. These HNB, Mg-rich andesite, high-Mg basalt and I-type granite were likely formed in an intracontinental back-arc rift setting. Integrated with our published detrital zircon U Pb age and Lu Hf isotope evidence, we propose that South China may have commenced its break-up from Gondwana in response to the Late Ordovician-Silurian (446–420 Ma) Proto-Tethyan subduction, which opened a back-arc basin along the Ailaoshan fold belt. Graphical abstract Unlabelled Image Highlights • Silurian HNBs and associated igneous rocks were found in the Ailaoshan belt. • These rift-related rocks are zircon U Pb dated to be ca. 446–420 Ma. • HNBs were sourced from an OIB/arc-mixed mantle in the garnet stability field. • These Silurian rocks generated in a back-arc intracontinental rift setting. • Break-up of the South China from Gondwana may initiate from 446 to 420 Ma. [ABSTRACT FROM AUTHOR]

The Silurian fishes from north-western Hunan, China are characterised by the earliest known galeaspids Dayongaspis Pan and Zeng, 1985 and Konoceraspis Pan, 1992, and the earliest known antiarch Shimenolepis Wang J.-Q., 1991, as well as rich sinacanth fin spines. Shimenolepis from Lixian County in north-western Hunan, which was dated as the Telychian (late Llandovery), has long been regarded as the oldest representative of the placoderms in the world. As such, in addition to eastern Yunnan and the Lower Yangtze Region, north-western Hunan represents another important area in South China that yields important fossil material for the research of early vertebrates and related stratigraphy. Here we summarise the Silurian fishes known in north-western Hunan so far, and classify them into three vertebrate assemblages (i.e., the Wentang, Maoshan, and Yangtze assemblages). Based on the updated Silurian vertebrate and stratigraphic databases, the Silurian fish-bearing strata in north-western Hunan can be subdivided into the Rongxi, Huixingshao, and Xiaoxi formations in ascending chronological order, which can be correlated with the Lower Red Beds, the Upper Red Beds, and the Ludlow Red Beds in South China, respectively. A new look at the Silurian strata in Lixian suggests that the age of Shimenolepis is late Ludlow rather than late Llandovery as previously suggested. The research on Silurian fishes and biostratigraphy in north-western Hunan not only provides morphological data of early vertebrates, but also offers new palaeoichthyological evidence for the subdivision, correlation, and age assignment of the Silurian marine red beds in South China. The establishment of a related high-precision Silurian stratigraphic framework in north-western Hunan will help to elucidate the temporal and spatial distribution of Silurian fossil fishes, deepen the understanding of the evolution of early vertebrates, and unravel the coevolution between Silurian vertebrates and the palaeoenvironment. [ABSTRACT FROM AUTHOR]

A significant proportion of shale gas resources occurs in Lower Silurian Longmaxi Formation in southeast Sichuan Basin, South China, where commercial gas production has been achieved at Fuling Shale Gas Field. This study area is located adjacent to Fuling Jiaoshiba shale play. Elemental geochemistry regarding paleoenvironment aspects of lower Silurian Longmaxi shale gas is poorly understood. However, the samples in this study are representative, revealing the complete elemental geochemical characteristics of Longmaxi Shale. This research has analysed trace and rare earth elements of lower Silurian Longmaxi Shale and investigated the depositional environment, provenance, and tectonic settings when this type of shale formed. Sedimentary structures include horizontal lamination, massive lamination, and deformation structures that are well developed in black shale and grey silty shale of lower Silurian Longmaxi Formation. Gamma ray, total organic carbon, and pyrite contents are relatively higher in the lower part of the shale. The enrichment of sulfophile heavy metal elements (Cu, Zn, Pb, Mo, Ni) indicates that a reducing environment is common during the deposition of Longmaxi Formation. The concentration of rare earth elements is generally constant with relatively high concentration of light rare earth elements, stable concentration of heavy rare earth elements, and negative Eu anomalies. The sediments of Longmaxi Formation are derived primarily from the sedimentary rocks and granites in continental crust. The combination of trace and rare earth elements indicates that the tectonic settings of the provenance are continental island arc and active continental margin. [ABSTRACT FROM AUTHOR]

The Silurian period, and the Wenlock epoch in particular, experienced a series of powerful bioevents, among which was the Mulde event (upper Homerian). Here, the results of a study of the mid- to late Wenlock conodont paleocommunities in the shallow platform environments of the Lithuanian part of the Silurian Baltic Basin are presented. The analyses are based on a detailed quantitative description of the abundance and diversity patterns of the conodonts, as well as the geochemical and geophysical environmental proxies in the Ledai-179 core (central Lithuania). A model selection analysis of the conodont rank abundance distributions revealed episodic and progressive change from the complex communities of the early Jaagarahu time (lower Homerian), to the simple and much more even communities of the early Gėluva time (lower part of the upper Homerian). Spectral and cross-spectral analyses of the conodont species' apparent richness, evenness and abundance, as well as the δ 13 C and natural gamma ray trends, revealed transient episodes of 5th order periodic fluctuations. It is shown that the transitions in the community states and the transient episodes of the oscillations approximately coincided with the onset of the Mulde event (latest Jaagarahu and early Gėluva time). [ABSTRACT FROM AUTHOR]

The geological record of the mid-Homerian Mulde event in the deep-water settings of the East European Platform is characterized by a profound graptolite extinction event and a low amplitude positive δ13C excursion. It is also associated with a negative natural gamma excursion occurring in a monotonous shaly succession, visible on well logs and traceable across the entire basin. Nevertheless, its origin has not been clarified yet. We present new data on the geophysical and microfacies record across the stratigraphic interval of this event in northern Poland. The present paper tests a hypothesis that the anomalies are related to the appearance of syngenetic and/or detrital carbonates at the onset of this Silurian event. New data reveal that both: (1) natural gamma radiation and magnetic susceptibility negative anomalies and (2) facies changes manifested in the increased carbonate content and ingression of ‘varve-like’ laminated calcisiltite containing large amounts of ‘sparoids’ (interpreted as carbonate suspensoids) occur simultaneously in the middle Homerian. Despite different palaeogeographic situations of the basin in the Wenlock and Ludlow due to the progressive collision of Baltica with Avalonia and the evolution of Caledonian foredeep, the geophysical and facies record of the Mulde Event is strikingly similar to that of the Ludfordian Lau Event record from the same basin. This leads to the conclusion that carbonate hypersaturation, resulting in the mass appearance of water-column carbonate precipitates (whitings) played a significant role during both Mulde and Lau events and represents palaeoceanographic phenomena rather than single case local anomalies. [ABSTRACT FROM AUTHOR]

Horizon annealing ( HA) provides a method to order all horizons in a chronostratigraphic data set, including marker beds and isotopic excursions, as well as horizons that lack exact local markers (such as taxon first appearances) and are, thus, constrained only by local stratigraphical order. Global stratotype section and point ( GSSP) levels placed within an HA composite succession can be precisely correlated with levels in all other sections in the composite that span the same interval. We present two approaches to the quantitative assessment of the uncertainty or error in the placement of horizons within the composite section: a permutation method (jackknife analysis) and a sensitivity analysis (the relaxed fit curve). From jackknife analysis, we calculate a standard deviation ( σ) of the variation in horizon placements and estimate the 95% confidence interval of the variation in horizon placement within the composite. We also directly assess the relative stability of event positions using the results of the jackknife. These approaches provide an objective method for assessing the relative strengths of GSSP candidates, in which we prefer those sections and horizons that are the most precisely controlled in the HA composite. Integration of biostratigraphical, chemostratigraphical and lithostratigraphical marker horizons into the HA process markedly improves levels of constraint within the composite compared to biostratigraphical data alone. In a temporally scaled composite, the 95% confidence intervals on horizon placements could be used to estimate temporal resolution. In our study, we estimate that the average temporal resolution is approximately 319 kyr, which approaches the range of that needed to test hypotheses of orbitally driven cyclicity. [ABSTRACT FROM AUTHOR]

A new data set of ca. 500 LA–ICP-MS U–Pb detrital zircon ages for six metasedimentary units from the Tuscan basement (Apuan Alps, Monti Pisani, Monticiano-Roccastrada), along with a precise SHRIMP U–Pb crystallization age of a metavolcanic unit (Apuan Alps) have been collected to determine their depositional ages and provenance. These results have been integrated with the recently published ca. 900 U–Pb detrital zircon ages from Elba Island to draw a complete picture of the Paleozoic journey of the Tuscan basement. A major change in the sources supplying sediments to the Tuscan basins is shown to occur during this journey. Detrital zircon ages of early Cambrian to middle Ordovician metasediments mirror those of coeval northern Africa sediments: most samples were sourced in western Africa, while one sample is derived material from central northern Africa. The Tuscan block was therefore located at the peri-Gondwana margin, close to central northern Africa. The prominent mid-Ordovician magmatic arc activity (ca. 460 Ma) at the northern Gondwana margin and its detritus, characterise the zircon age distribution of Ordovician and Silurian volcano-sedimentary rocks, that were therefore generated at the northernmost Gondwana margin during subduction and subsequent initial Paleotethys rifting. The Carboniferous–Permian metasediments are dominated by populations of Ordovician and Variscan-age zircons, with a minor occurrence of Neoarchean and Paleoproterozoic zircons that is best explained by recycling of European Neoproterozoic–Cambrian metasediments. In summary, the main sources supplying the Tuscan basins were located in northern Africa throughout Cambrian–Ordovician times, shifting to the volcanic arc active at the northern Gondwana margin during the middle Ordovician. During Variscan and post-Variscan times, detrital zircon sources were mostly located in European terrains, witnessing the shift of Tuscany from Africa to Europe. [ABSTRACT FROM AUTHOR]

The Pridoli epoch is one of the most geobiologically unstable intervals in the Silurian period. However, the ecological and evolutionary dynamics of the biota from this time are still poorly understood. Here we present a comprehensive quantitative time-series analyses of conodont abundances during the middle and the upper parts of the Pridoli epoch. The study reveals that the stratigraphic series of conodont abundances has a multifractal structure. This feature implies the presence of multiple serially correlated processes hierarchically operating on different time scales and interacting in a multiplicative fashion. Estimation of a maximal Lyapunov exponent and a test for presence of determinism also revealed a chaotic and non-linear low-dimensional nature of long-term conodont abundance dynamics. The most probable (but not exclusive) mechanism for the origin of chaos in the time series of conodont abundance is that conodont abundances tracked changes in crucial environmental parameters, most probably related to the climate that exhibits long term chaos. The complex and non-linear nature of the conodont dynamics is also revealed by a moving-window correlation analyses of conodont abundances and by an environmental proxy time series. We found three alternating episodes of different correlation patterns between conodont abundances and the o13C record. In the middle and upper most Pridoli interval there are positive but statistically non-significant correlations between these two variables. In contrast the lower part of the upper Pridoli (middle of the Jura formation) exhibits negative and statistically significant correlation between the variables. In addition moving-window standard deviation analyses reveals that during the transitions between these episodes, there were abrupt changes in the variance in both the carbon isotopes and the conodont abundances, which implies that these episodes represent alternative states in the way the earth system functioned that were punctuated by the critical transitions between them. The interval with negative correlations between abundances and isotopes was also marked by a profound evolutionary turnover of acanthodians and to lesser extent conodonts. This interval most probably represented an anomalous time, with differing ecological rules and increased macroevolutionary rates, which can be interpreted as a turnover pulse. The spectral cyclostratigraphic analyses of the abundance data reveals that conodont abundances also exhibited periodic oscillations at several frequencies. The cycles determined for the analysis have the period lengths of 56, 99, 127 and 950 Ka, which probably were caused by the periodic changes in the obliquity and eccentricity of Earth's orbit. The proposed proximate mechanism that controlled cyclic changes in the abundances of conodonts, based on the climatological deductions, was a variation in nutrients supplies that was due to changes in the degree of seasonality in the tropics, driven by Milankovitch cycles. It is probable that the described state shifts in the way that the ecosystem functioned were also forced by long-term Milankovitch cycles. [ABSTRACT FROM AUTHOR]

The polychaete annelid Kingnites diamondi, a new paulinitid genus and species, is described from the Silurian of Baltoscandia. Its large maxillae differ morphologically from those of all other known paulinitids, particularly in being very elongate and having conspicuous myocoele openings and posterior portions of the first maxillae (MI). Albeit rare, this polychaete taxon is highly characteristic and appears to be confined to the Wenlock–Ludlow transitional interval on Gotland, Sweden, and ranges into the upper Ludlow on Saaremaa, Estonia. All samples yielding this species derive from strata formed in proximal carbonate platform environments. The temporal and geographical distribution indicates that it first appeared in Gotland and subsequently spread north-eastwards to the present-day Saaremaa. Kingnites diamondi adds to the list of known members of the Paulinitidae and reinforces the importance of this family, in terms of abundance and diversity, in Silurian polychaete faunas of Baltica. This is the biggest paulinitid recorded from the Silurian with an inferred body length of approximately half a metre and its diagnostic jaws may serve as a proxy for shallow water, backreef (marginal marine to lagoonal) environments. [ABSTRACT FROM AUTHOR]

The steep biogeochemical gradients near deep sea hydrothermal vents provide various niches for microbial life. Here we present biosignatures of such organisms enclosed in a modern and an ancient hydrothermal sulfide deposit (Turtle Pits, Mid-Atlantic Ridge, Recent; Yaman Kasy, Russia, Silurian). In the modern sulfide we found high amounts of specific bacterial and archaeal biomarkers with δ13C values between −8 and −37‰ VPDB. Our data indicate the presence of thermophilic members of the autotrophic Aquificales using the reductive tricarboxylic acid (rTCA) cycle as well as of methanogenic and chemolithoheterotrophic Archaea. In the ancient sample, most potential biomarkers of thermophiles were obscured by compounds derived from allochthonous organic matter (OM), except for an acyclic C40 biphytane and its C39 breakdown product. Both samples contained high amounts of unresolved complex mixtures (UCM) of hydrocarbons. Apparently, OM in the sulfides had to withstand high thermal stress, indicated by highly mature hopanes, steranes, and cheilanthanes with up to 41 carbon atoms. [ABSTRACT FROM AUTHOR]

Abstract: The Late Ordovician culminated in a major glacial period that has been related to one of the strongest mass extinctions recorded during the Phanerozoic. During this interval, Anticosti Island (Québec, eastern Canada) was located at low to intermediate palaeolatitudes (15–30° S) on the eastern margin of Laurentia. It displays a relatively complete section across the Ordovician–Silurian (O/S) boundary. Upper Ordovician to Lower Silurian strata of Anticosti studied here comprise the Vauréal (Katian), Ellis Bay (Hirnantian) and Becscie (latest Hirnantian–Rhuddanian) formations. Phytoplankton dynamics inferred from the acritarch content of these strata are locally compared with new geochemical environmental proxies (δ13C), with recent palynological data from Baltica and also with phytoplankton dynamics as described from near-polar, high latitude localities of the Gondwana region. Two positive excursions of the carbon isotope record have been identified in the lower and upper Ellis Bay Formation. Overall, phytoplankton trends are as follows: (1) as with chitinozoans, conodonts, brachiopods and corals, acritarchs from Anticosti display a major turn-over during the early Hirnantian (uppermost Vauréal Formation–lower Ellis Bay Formation), with the appearance of taxa that exhibit Silurian affinities (e.g., Tylotopalla sp., Ammonidium sp., Oppilatala sp., Evittia sp., Dilatisphaera spp.). High polymorphism for some common taxa is observed in the interval corresponding to the first δ13C positive excursion. Using sequence stratigraphy, this period may be related to a first glacially driven sea-level drawdown corresponding to terrestrial ice-sheet growth on Gondwana, such as recorded in Morocco. (2) Subsequently, during the late Hirnantian of Anticosti (uppermost Ellis Bay Formation), phytoplanktic communities suffered a crisis, exemplified by the disappearance of several typical, large Late Ordovician taxa (i.e., Orthosphaeridium spp., Peteinosphaeridium spp., large Baltisphaeridum spp., Sacculidium sp.). The lower Becscie strata, corresponding to the time of deglaciation at the O/S boundary interval, only contain a low diversity assemblage dominated by large acritarchs of the genus Hoegklintia and other morphologically related forms, and a few tolerant and long-ranging taxa (e.g., Evittia remota, Micrhystridium spp., leiospheres). Despite a possible taphonomic bias in the uppermost Ellis Bay Formation, the major crisis in the late Hirnantian coincides with the second δ13C excursion and a second, stronger glacially-driven sea-level fall corresponding to the time of the maximum extend of the ice sheets on Gondwana. (3) Such phytoplankton events have also been detected in Gondwanan ice-center area, but with “typical Ordovician taxa crises” occurring apparently later when plotted against positive carbon isotope excursions, as also observed in Baltica. This time-lag may be linked to a basin configuration of the studied areas, where environmental stress consequently differed or linked to the presence of omission surfaces coupled with preservation bias of acritarch assemblages in the uppermost Ordovician strata of Anticosti. In addition to their biostratigraphic and palaeobiogeographic utility, acritarchs turn out to be more specific in highlighting palaeoenvironmental conditions. [Copyright &y& Elsevier]

More than 99 per cent of the roughly 58,000 living vertebrate species have jaws. This major clade, whose members are collectively known as gnathostomes ('jawed mouths'), made its earliest definitive appearance in the Silurian period, 444-416 million years (Myr) ago, with both the origin of the modern (crown-group) radiation and the presumptive invasion of land occurring by the end of the Devonian period (359?Myr ago). These events coincided with a major faunal shift that remains apparent today: the transition from Silurian ecosystems dominated by jawless fishes (agnathans) to younger assemblages composed almost exclusively of gnathostomes. This pattern has inspired several qualitative descriptions of the trophic radiation and ecological ascendance of the earliest jawed vertebrates. Here we present a quantitative analysis of functional variation in early gnathostome mandibular elements, placing constraints on our understanding of evolutionary patterns during this critical interval. We document an initial increase in functional disparity in the Silurian that stabilized by the first stage of the Devonian, before the occurrence of an Emsian (?400?Myr ago) oxygenation event implicated in the trophic radiation of vertebrates. Subsequent taxonomic diversification during the Devonian did not result in increased functional variation; instead, new taxa revisited and elaborated on established mandibular designs. Devonian functional space is dominated by lobe-finned fishes and 'placoderms'; high disparity within the latter implies considerable trophic innovation among jaw-bearing stem gnathostomes. By contrast, the major groups of living vertebrates-ray-finned fishes and tetrapods-show surprisingly conservative mandibular morphologies with little indication of functional diversification or innovation. Devonian gnathostomes reached a point where they ceased to accrue further mandibular functional disparity before becoming taxonomic dominants relative to 'ostracoderm'-grade jawless fishes, providing a new perspective on classic adaptive hypotheses concerning this fundamental shift in vertebrate biodiversity. [ABSTRACT FROM AUTHOR]

Data obtained using different methods: paleontological, sedimentological, event stratigraphy and C-isotope chemostratigraphy of a unique succession of the Upper Ordovician and lower Silurian, located on the western slope of the Subpolar Urals, are presented in this work. The data obtained made it possible to revise some existing ideas about the texture of the Upper Ordovician succession and clarify the position of the Ordovician-Silurian boundary in the region. In addition, the Upper Ordovician Yaptiknyrd Formation was correlated with the synchronous formations in Scotland and Estonia. [ABSTRACT FROM AUTHOR]

Abstract: Taxonomic diversity structure of crinoids is measured as a number of genera in orders for each epoch of the Silurian. Changes in this structure are evaluated with two similarity indices, namely the Czekanowski''s Quantified Coefficient and the Gower Index. Dynamics of the taxonomic diversity structure of crinoids was slow in the Silurian. The relatively strong turnovers occurred at the Ordovician – Silurian and Silurian – Devonian transitions. In contrast, the Wenlock – Ludlow transition was marked by an outstanding stability. When assemblages of non-successive epochs are considered, a persistence of similarity in this structure and a possibility of its re-appearance also indicate a certain stability. Nonetheless, some patterns of dynamism are also reported. The noted stability persisted despite palaeoenvironmental changes and biotic crises (like the end-Ordovician mass extinction and the Ireviken event). This highlights the role of intrinsic (biological) factors in the Silurian evolution of crinoids. [Copyright &y& Elsevier]

Fourteen samples of the Valga-10 drill core, south Estonia, from the lower Jelgava Formation (middle Pirgu Regional Stage, Upper Katian) to the lowermost Ohne Formation (lowermost Juuru Regional Stage, Lower Rhuddanian) were investigated for acritarchs. The section is biostratigraphically and chemostratigraphically well constrained; it comprises the rugata, taugourdeaui and scabra chitinozoan zones, the ordovicicus and giradeauensis conodont zones and the Hirnantian Isotopic Carbon Excursion (HICE). The good preservation allowed the identification of three prasinophyte phycomata and 52 acritarch species including the four new species Evittia porkuniensis, Helosphaeridium tongiorgii, Nexosarium leherissei and ? Veryhachium bulliferum. One new combination is proposed: Poikilofusa obliquipunctata (Uutela & Tynni 1991) comb. nov. Comparison with contemporaneaous palynofloras shows that eastern Laurentia and Baltica share a high number of species during the latest Katian-Hirnantian. Some of these species show a potential for future improvement of biostratigraphical correlation between the uppermost Katian-Hirnantian strata of low to mid-latitude carbonate platforms in eastern Laurentia and Baltica. Conversely, significant taxonomic differences exist between the assemblage studied and typical Gondwanan palynofloras. These results suggest that the Laurentian/Baltic and Gonwanan phytoplanktonic palaeoprovinces existed during latest Ordovician times. Published data reveal similar distribution pattern for chitinozoans and graptolites during the Hirnantian. A bathymetric ridge rise associated with the opening of the Rheic Ocean, coupled with the Hirnantian glacially-driven sea-level fall might have prevented water mass exchange and mixing/migration of phytoplankton between Gondwana and Laurentia/Baltica, thus being at the origin of the observed acritarch bioprovincialism. Additionally, distribution and diversity patterns of acritarchs are compared to those of other microfossils in the Valga-10 section. Near the base of the Hirnantian (Porkuni Regional Stage), benthic organisms (ostracods and scolecodonts) and phytoplankton (acritarchs) show increasing diversity with appearances of new taxa and new morphologies. Planktonic (chitinozoans) and nektonic (conodonts) organisms show a different pattern, with a decline in diversity during the earliest Hirnantian and a marked increase in the later part of the stage. Two alternative hyptotheses are proposed to explain these differences in diversification patterns: (1) the development of a shallower, proximal environment in the locality studied during the Hirnantian glaciation may have been more favourable to the diversification of benthonic organisms; (2) the planktonic and nektonic organisms suffered the effects of glaciation more than benthonic ones. [ABSTRACT FROM AUTHOR]

Abstract: Surface samples from the Ghelli and Soltan Maidan Formations in the Khoshyeilagh area of the eastern Alborz Range, northern Iran, were analyzed to determine the age and the stratigraphic relationship of these two units. The samples contained rich palynomorph assemblages, dominated by acritarchs (36 species recognized, distributed among 28 genera) and chitinozoans (nine species identified, distributed among seven genera). Cryptospores and scolecodonts as well as a few graptolite remains were also observed, although not studied in detail. Based on the restricted stratigraphic range of chitinozoan and acritarch species, a Late Ordovician (late Katian–Hirnantian) age is assigned to the Ghelli Formation. Palynological samples from the Soltan Maidan Formation yielded acritarch assemblages characterized by species commonly found in Upper Ordovician sediments together with typical middle Silurian forms. Considering reworking of the Upper Ordovician species, the age of the investigated part of the Soltan Maidan Formation is not younger than Gorstian (early Ludlow, early late Silurian). U–Pb zircon ages of 434.4±6.4Ma (Telychian, late Llandovery, late early Silurian) obtained for granitic clasts collected at the base of the Soltan Maidan Formation, are consistent with the inferred palynological age and indicate that granite emplacement, cooling, exhumation, erosion, transportation and deposition of its clasts took place in a time interval estimated to be 5 to 10 million year long. Based on the presence of diagnostic chitinozoan taxa, the Ghelli Formation can be assigned to the Armoricochitina nigerica, Ancyrochitina merga, and Spinachitina oulebsiri chitinozoan biozones. Chitinozoan assemblages reflect a clear palaeobiogeographic affinity with the previously defined ‘North Gondwana Domain’. The composition of acritarch assemblages also appears to be consistent with newly proposed hypotheses of a Late Ordovician phytoplanktonic biogeographical differentiation between a Laurentian/Baltica realm, and a Gondwanan realm to which the present assemblages belong. The presence of cryptospores together with taxonomically diverse chitinozoan, acritarch, and scolecodont assemblages, suggest a relatively shallow marine, platformal depositional environment for the Ghelli Formation. [Copyright &y& Elsevier]

Abstract: The Wenlock–Přidoli sequence has been subdivided and mapped offshore Saaremaa in the Baltic Sea by means of high resolution seismic reflection profiling. The most striking and consistent seismic reflectors correlate with contrasting lithological boundaries of the Silurian regional stages, the Jaani/Jaagarahu (S8), the Jaagarahu/Rootsiküla (S10), the Rootsiküla/Paadla (S11), the Paadla/Kuressaare (S12), the Kuressaare/Kaugatuma (S13) and the Kaugatuma/Ohesaare (S14) stages, which often coincide with erosional disconformities on Saaremaa. The shallow-shelf Silurian sequence that crops out on Saaremaa is also exposed in the closest offshore area of the island. Due to the westerly to south-westerly increasing erosional cut below the Baltic, the deeper facies varieties that are concealed in southern Saaremaa, are revealed and exposed at the seafloor towards Gotland. This is particularly well expressed in the Jaagarahu Stage, which undergoes a facies change with significant increase in thickness on the basinal slope of the Baltic Silurian Basin, both onshore and offshore Saaremaa. The Silurian sequence overlying the Jaagarahu Stage does not show any considerable thickness or facies changes neither below nor offshore Saaremaa. Offshore Saaremaa, seismic reflectors limiting new deeper facies subunits in the Jaagarahu Stage become either successively or simultaneously exposed inside the Vilsandi (S8–S9) respectively the Maasi–Tagavere (S9–S10) seismic units towards Gotland. These outcrop patterns were largely formed by two different erosional agents that during different time periods have played a considerable role in the formation of the present day Baltic Sea depression. Hence, the gradually south-westerly deepening cuesta landscape formed by the Cenozoic erosion, namely the Silurian Klint and the plateaus north and south of it, discloses progressively deeper part of the Baltic Silurian Basin. The deeper facies subunits are exposed rapidly by the submeridional erosional incisions of the Pleistocene glaciers. Except for the erosional component, there appears also a distinct tectonic factor in the genesis of the present Baltic Sea depression. Today, the coeval Silurian rocks that once were formed in separate facies belts, i.e. in different depth intervals of the same sedimentary basin on Saaremaa and on Gotland, are presently located at about equal altitude. [Copyright &y& Elsevier]

The article examines the characteristics of soft-bodied lophophorate with the use of an unmineralized fossil from Silurian, England. The researchers assessed the holotype of the tube-like structure of the ventral and dorsal valves comprising brachiopods. They described the fossil's dorsal side as enclosed by a hood that has a length of 2.2 millimeters and a maximum width of 1.7 millimeters. They mentioned that the animal possesses a subcircular disc with an approximate thickness of 0.15 millimeters.

Understanding ancient climate changes is hampered by the inability to disentangle trends in ocean temperature from trends in continental ice volume. We used carbonate "clumped" isotope paleothermometry to constrain ocean temperatures, and thereby estimate ice volumes, through the Late Ordovician-Early Silurian glaciation. We find tropical ocean temperatures of 32° to 37°C except for short-lived cooling by ∼5°C during the final Ordovician stage. Evidence for ice sheets spans much of the study interval, but the cooling pulse coincided with a glacial maximum during which ice volumes likely equaled or exceeded those of the last (Pleistocene) glacial maximum. This cooling also coincided with a large perturbation of the carbon cycle and the Late Ordovician mass extinction. [ABSTRACT FROM AUTHOR]

A new genus and species of synziphosurine (Chelicerata) is described from the Silurian (Wenlock) Scotch Grove Formation Konservat-Lagerstätte in Clinton County, Iowa. Camanchia grovensis n. gen. n. sp. is characterized by a sub-triangular carapace, ten opisthosomal segments divided into a preabdomen of seven and a postabdomen of three, and a tuberculate ornament on the carapace and pleural margins. A single new specimen from the same location is assigned to Venustulus waukeshaensis, originally described from the Late Llandovery Waukesha Konservat-Lagerstätte of Wisconsin. A comparison of the musculature of C. grovensis with that of living Limulus polyphemus and the Jurassic Mesolimulus walchi from Nusplingen, Germany shows that it is much simpler, consistent with the status of synziphosurines as stem xiphosurids. [ABSTRACT FROM AUTHOR]

Cascales-Miñana, B., Muñoz-Bertomeu, J., Ros, R., Segura, J. 2010: Trends and patterns in the evolution of vascular plants: macroevolutionary implications of a multilevel taxonomic analysis. Lethaia, 10.1111/j.1502-3931.2009.00212.x Studying the macroevolutionary patterns of vascular plants from the Silurian to the present-day provides a global record of plant life history. Evolutionary rates (origination, extinction and diversification) for families, orders, classes and divisions were analysed, as was abundance and richness for 21 time intervals. An accumulative analysis, based on the total plant fossil record, the accumulated extinctions and relative diversity, was also carried out. The diversification rate shows a uniquely constant and progressive reduction from the end of the Carboniferous to the Permian when the lowest values are registered. Very small peaks seem to reflect Cretaceous extinction for families. At family level, only two time intervals present higher extinctions, than originations. Richness and accumulative analyses reveal that only 32% of the families analysed became extinct, and that approximately 90% of them disappeared at the end of the Palaeozoic. Our results indicate that plants did not undergo mass extinction events in the 'big five' sense, but rather, mass ecological reorganization the absence of important extinction events or evolutionary innovations producing diversification patterns without abrupt changes. □ Diversification, evolutionary, extinction, fossil record, innovations, radiation, vascular plants. [ABSTRACT FROM AUTHOR]

Abstract: Six distinct bryozoan paleobiogeographical provinces existed during the Silurian of North America, Baltica and Siberia. These provinces are based on parsimony analysis of endemicity (PAE), each supported by a number of endemic genera only present in that assemblage. The area cladogram displays a nested pattern, permitting the clustering of assemblages into larger units that might be indicative of their areas of origin. Paired-group cluster analysis supports the existence of provincial assemblages. Relationships indicate the action of both vicariance and geodispersal. Geographic boundaries between the provinces include land, deep sea, and climate zone boundaries, including barriers created by the Iapetus Ocean and the Tornquist Sea. [ABSTRACT FROM AUTHOR]

Five new species of Maurotarion Alberti, 1969 from the Silurian Lipeón Formation and Lower Devonian Talacasto Formation of Argentina are recognized. The comparisons with Bolivian and South African species support a Malvinokaffric dade based on librigenal synapomorphies, here erected as Maurotarion (Malvinotarion) new subgenus. The Malvinokaffric origin of the family would not be a migration from lower paleolatitudes but an Early Silurian stock of rare cosmopolitan ancestors which underwent a great Devonian radiation. Two lineages can be recognized within Malvinokaffric Maurotarion. The Silurian-Pragian dereimsi lineage is a plesiomorphic one resembling Silurian representatives and involves M. (Malvinotarion) dereimsi, M (Malvinotarion) talacastoense new species, M. (Malvinotarion?) new species A, M. (Malvinotarion?) new species B, M. (Malvinotarion) sp., and eventually M. (Malvinotarion?) cf. dereimsi. The isaacsoni lineage ranges from the Lower Pragian to Eifelian exhibiting a defined morphologic trend in the librigena. This lineage comprises M. (Malvinotarion) isaacsoni, M (Malvinotarion) sp. A from South Africa, M (Malvinotarion) gaucho new species, M. (Malvinotarion) haudei new species and M. (Malvinotarion) legrandi. A Lochkovian diversification probably took place yet an adequate assessment remains difficult. In contrast, a great evolutionary burst is recognized during the Emsian and is related to Pragian-Emsian global relative sea level curves which are coincident with those proposed from Bolivian and Argentinian basins. [ABSTRACT FROM AUTHOR]

Sanidine composition and bulk geochemistry of volcanic ash beds from the East Baltic indicate the subalkaline nature of the volcanism near themargins of theBaltica plate during the Silurian. Several bentonites in the Wenlock include a previously unknown sanidine with 48 to 58 mol % of the Na+Ca component. In contrast to the earlier Telychian volcanism, sodium-rich sanidine occurs in ash beds which originate from relatively moderately evolved dacitic magma. The studied material from two drill cores integrated with previous research enables production of a more complete list of 49 volcanic eruption layers for the lower to middle Wenlock in the East Baltic. This updated list of bentonites characterized by their sanidine compositions forms a good basis for future integrated bioand chemostratigraphic correlations in northern Europe. [ABSTRACT FROM AUTHOR]

The anatomy and affinities of Jamoytius kerwoodi White have long been controversial, because its complex taphonomy makes unequivocal interpretation impossible with the methodology used in previous studies. Topological analysis, model reconstruction and elemental analysis, followed by anatomical interpretation, allow features to be identified more rigorously and support the hypothesis that Jamoytius is a jawless vertebrate. The preserved features of Jamoytius include W-shaped phosphatic scales, 10 or more pairs of branchial openings, optic capsules, a circular, subterminal mouth and a single terminal nasal opening. Interpretations of paired 'appendages' remain equivocal. Phylogenetic analysis places Jamoytius and Euphanerops together (Jamoytiiformes), as stem-gnathostomes rather than lamprey related or sister taxon to Anaspida. [ABSTRACT FROM AUTHOR]

The retiolitid graptolite Reticuloplectograptus serpaglii gen. et sp. nov. from the Gorstian, lower Ludlow, has been found in two localities: the Bartoszyce borehole of Poland (Baltica), and the Bykoš section, Barrandian, Czech Republic (PeriGondwanan Europe). The Polish material is isolated and was studied under the SEM. The main characters of Reticuloplectograptus are similar to those of Plectograptus: an asymmetrical ancora, simple ancora umbrella with an incompletely developed rim and parallel ventral walls with mid-ventral lists. The paired genicular processes of the new species are similar to but much wider than those of Plectograptus trijunctus and Plectograptus robustus. The main differences between the new genus and Plectograptus are the dense ancora sleeve wall and small proximal lateral orifices of the former. These primitive characters suggest that Reticuloplectograptus might be ancestral to genera with strong reduction in the proximal end, such as Plectograptus, Valentinagraptus and Kirkigraptus. However, Reticuloplectograptus appeared stratigraphically later than Plectograptus, indicating that this aspect of retiolitid evolution is more complicated, needing further study. [ABSTRACT FROM AUTHOR]

Abstract: suggested that the high mountains of southern Scandinavia are the result of protracted exhumation since the Silurian. The evidence cited by in support of this hypothesis is, however, very selective and other published evidence shows that their hypothesis is untenable. We suggest that an objective review of available evidence shows that the mountains of Norway are the result of uplift resulting from Cenozoic tectonism amplified by the isostatic response to resulting erosion, similar to many other continental margins around the world. [Copyright &y& Elsevier]

The shell microstructure of Ordovician Cornulites species is in general similar to Silurian species. The earliest cornulitid from Baltica, C. semiapertus Opik, 1930 (Darriwilian), has vesicles, lamellar shell structure, but no pseudopunctae. The earliest Cornulites with pseudopunctae appears in the Katian. The initial shell structure of cornulitids may have been microlamellar, but without pseudopunctae. [ABSTRACT FROM AUTHOR]

Silurian dolostones representing the Jaani (Verknė and Jočionys formations (Fms)) and Minija (Pabradė Formation (Fm.)) regional stages were studied in the Jočionys 299 borehole located in eastern Lithuania. In addition to petrological studies, dolostones were subjected to XRD, XRF and ICP-MS analyses. X-ray diffraction analysis revealed that dolomite crystals in dolostones were very close to stoichiometric and well ordered and could be interpreted as early diagenetic. Strontium in dolostone of the Pabradė Fm. is comparable to that of other ancient dolomites, and is much lower than Sr concentrations in typical modern marine dolomites. Slight enrichment in Sr and S in the Verknė and Jočionys Fms is due to the presence of celestine (SrSO4) and gypsum. Evaporative (sabkha), seepage-reflux, mixing-zone, burial and seawater dolomitization models of modern and ancient examples from literature were considered. For the Jočionys Fm. we suggest seepage-reflux and burial(?) models. Evaporative (sabkha) and mixing-zone dolomitization models may be applied to the Verknė Fm. and the Pabradė Fm., respectively. [ABSTRACT FROM AUTHOR]

Abstract: The paper discusses the evolution of Stromatoporoidea in the epicontinental sedimentary basin of the Siberian Platform and Taimyr during the Ordovician and Silurian. Specimens of the oldest genus, Priscastroma, were found in the middle of Middle Ordovician sediments. This genus is represented by the species P. gemina Khrom., which has two forms, A and B. Tracing the emergence of new genera over time, we identified two distinct branches in stromatoporoid evolution. The ancestor of the first branch is P. gemina f. A, which gave rise to the genus Cystostroma. The latter is the ancestor of two subbranches with predominant horizontal skeletal elements. The subbranches differ only in tissue microstructure. The genera Stromatocerium, Dermatostroma, and Aulacera display dense fibrous microstructure, whereas the genus Rosenella and its descendants display dense microstructure. The genus Lophiostroma, with a lamellar–fibrous tissue, may be a dead branch of evolution. The ancestor of the second branch is P. gemina f. B, which gave rise to the genus Labechia and its descendants. This branch has a dense tissue, with predominant vertical skeletal elements. Ordovician stromatoporoids from Siberia were compared with those from other basins of the world. Comparison shows that all the Ordovician genera from the epicontinental basin of the Siberian Platform and Taimyr originated here. Thus, this basin was one of the centers of stromatoporoid origin. [Copyright &y& Elsevier]

An enigmatic microproblematicum, Tuxekane/la Riding and Soja (1993), has been identified in the shallow water carbonate succession of the Late Silurian Skala formation (Podolia, Ukraine). The newly found specimens suggest most probably the algal nature of this enigmatic microfossil. Tuxekanella is known only from two extremely distant regions at the moment: the Alexander terrane in Alaska and Podolia. The possibility of their paleobiogeographical link is discussed in the context of paleotectonic models, assuming the peri-Gondwanan origin of the Alexander Terrane. [ABSTRACT FROM AUTHOR]

Abstract: Samples of uppermost Ordovician and Silurian strata from two cores from north-eastern and western Illinois were processed for chitinozoans. Due to apparent sea-floor oxidation or palaeoenvironmental constraints, very few samples yielded specimens, but those that did allow tentative correlation with established biostratigraphical zonations for the Chitinozoa. Samples from the Wilhelmi Formation of core DH76-21 in north-eastern Illinois yielded Spinachitina fragilis, a typically earliest Silurian taxon. A sample from the Maquoketa Group strata of core Principia #4, western Illinois, yielded a monospecific assemblage of Conochitina elegans, which is suggestive of a late Ordovician age. Higher in this core, a sample from the upper strata of the Bowling Green Dolomite yielded an assemblage indicating a late Rhuddanian to Aeronian age, including Angochitina hansonica, previously only described from strata in Nevada, and one new species, Fungochitina illinoisensis. [Copyright &y& Elsevier]

The article offers information on trigonotarbids, a species of the class arachnida of the phylum arthropods. As stated, trigonotarbids were amongst the earliest and most important predators in the nascent terrestrial communities of the Silurian period. Their body is split into two halves in which the anterior half is covered by the carapace. Fossil evidence has proved that trigonotarbids were present in some of the earliest terrestrial ecosystems and lived on land.

Data on the diversity of the East Baltic Silurian chitinozoans have been compared to global chitinozoan biozones that are approximately correlated with the graptolite scale. The total diversity and balanced total diversity curves have three main positive peaks in the Wenlock and Ludlow and diversity lowstands in most of the Llandovery and Pridoli. The turnover ratio and species origination curves are lowest and species extinction is highest in the lower Wenlock, correlating partly with the Ireviken Event. Chitinozoan diversity is related to the transgression—regression phases of the Silurian Baltic basin, water chemistry and temperature, and evolutionary processes of the faunal group. At the level of the Silurian standard stages the trends in the East Baltic and Swedish chitinozoan diversity curves are in general outline similar to the global diversity curve. [ABSTRACT FROM AUTHOR]

Armoured stem-gnathostomes (jawless vertebrates previously termed ‘ostracoderms’) have long been assumed to exhibit strong endemicity. This assumption has underpinned their utility in many palaeobiogeographic studies as well as scenarios regarding the evolution and dominance of jawed vertebrates over their jawless relatives. The hypothesis of endemicity in stem-gnathostomes is investigated for the first time in the light of the phylogeny of the closest relatives of jawed vertebrates – Osteostraci and Galeaspida. Palaeobiogeography of each is reconstructed using Fitch optimization and modified Brooks Parsimony Analysis. Palaeobiogeographic distributions corroborate phylogeny. Results, along with consideration of the Heterostraci, enable identification of similar patterns across groups (broad ancestral range, Early Devonian expansion, endemic and pandemic clades within each, and Middle Devonian radiation events) and inferences to the palaeogeographic relationship between major terranes (i.e. Laurentia, Baltica, Avalonia, Kara, Altaids, South China, Tarim). Comparison of basin and terrane level analyses identifies the different palaeogeographic processes responsible for the distributions of each group: sea-level changes in the case of the Osteostraci and rifting in the case of the Galeaspida. The general endemic nature of the Osteostraci and Galeaspida is confirmed, and thus the hypothesis that the demise and extinction of stem-gnathostomes was because of their limited dispersal capacity is supported. [ABSTRACT FROM AUTHOR]

New internal and external structures are described from unusually well-preserved specimens of the acritarch genus Hoegklintia Doming 1981, recovered from the Lower Silurian Osgood and Estill shales of Kentucky and Estill Shale of Ohio (U.S.A.). The morphological variability of internal features ranges from irregularly dispersed organic remains and clusters of circular bodies within the vesicle, to structures congruent with the contours of the vesicle and processes. External bodies are primarily ovoid, and may have a 'tube-like' extension penetrating the vesicle interior. Published studies mention and/or depict Hoegklintia with dispersed internal organic matter, but the specimens illustrated here are the first to exhibit morphologically discernible contents. Evidence suggests that these various entities represent coagulated cell contents, life-cycle stages, or manifestations of parasitism/mutualism. [ABSTRACT FROM AUTHOR]

Documenting the morphology and ultrastructure of spores from known Silurian-Devonian plants clarifies organization and probable affinities of dispersed spores and contributes to analyses of evolutionary changes and phylogenetic relationships in early plants. In this study of fossil in situ spores from the early protolepidodendralean lycopsid Leclereqia, we identified new characters including an additional synapomorphy of the ligulate lycopsid dade. A detailed light (LM), scanning electron (SEM), and transmission electron microscope (TEM) analysis of spores from two species of Leclercqia from the Lower Dcvonian (Emsian)of New Brunswick, eastern Canada, L. andrewsii and L. complexa, shows both are homosporous, yielding spores belonging to the dispersed spore form taxon Acinosporites Iindlarensis. Important features of wall ultrastructure include the presence of a paraexospore, peculiar exospore-derived, peg-like structures located in the gap between the outer exospore/inner paraexospore, and multilamellate regions in the interradial areas of the proximal surface. Similar interradial multilamellate regions occur in other ligulate lycopsids (fossil and extant). This character is probably a further synapomorphy for the ligulate lycopsid dade, within which heterosporous lycopods form a monophyletic group. These data suggest the ligule and interradial multilamellate region appeared prior to heterospory. [ABSTRACT FROM AUTHOR]

A new agelacrinitid edrioasteroid, Multiplexidiscus mckenziensis n. gen., n. sp. is described froni the middle Silurian upper McKenzie Shale Member of the Mifflintown Formation of Pennsylvania. These edrioasteroids were attached to a large hardground clast that was reworked and flipped during a storm event. The occurrence of edrioasteroids in a near shore, perhaps in sub-normal salinity, is unusual for echinoderms. The edrioasteroids show a dispersed spatial distribution and weak thecal orientation. Multiplexidiscus differs from other agelacrinid edrioasteroids in the presence of a complex pattern of ambulacral cover plates combined with nearly straight paedomorphic ambulacra. [ABSTRACT FROM AUTHOR]

Thirty samples from 22 sections collected by the SWEDARCTIC international expedition to Severnaya Zemlya in 1999 contained Ordovician and Silurian conodont faunas. Several taxa, including Apsidognathus cf. milleri, Aulacognathus cf. kuehni, Nudibelodina sensitiva, Ozarkodina broenlundi and Pterospathodus eopennatus, allow precise dating of the strata in this region for the first time. The occurrence of Aphelognathus pyramidalis and Rhipidognathus aff. R. symmetricus in samples from the Strojnaya Formation fits well with the earlier dating of these strata as latest Ordovician. However, Aphelognathus sp. in sample BG-99/14-a, collected from the upper Ushakov Formation, indicates that at least in the lower reaches of the Ushakov River the top of this formation is considerably younger than considered earlier: the sampled strata are Late, not Early Ordovician in age. In the Ordovician and Silurian the present-day Severnaya Zemlya region was dominated by extensive shallow-water, mainly semi-restricted basin environments with habitat specific faunas. The occurrence of Riphidognathus aff. R. symmetricus at some levels in the Upper Ordovician suggests extreme shallowing episodes in the basin. On Severnaya Zemlya, 'normal-marine' faunas (including Pt. eopennatus) invaded the distal peripheral regions of the wide shallow-water platform at times of maximum sea-level rise only. The occurrence of Oz. broenlundi and N. sensitiva indicates that in the early Silurian the Severnaya Zemlya basin was quite well connected to the basins over modern North Greenland as well as to the Baltic Palaeobasin. The lower Silurian conodont assemblages in the Vodopad to Samojlovich formations are most similar to those described from the eastern Timan-northern Ural region. [ABSTRACT FROM AUTHOR]

Abstract: The large-scale global biogeochemical perturbation across the Silurian–Devonian (S–D) boundary, recorded in the major positive excursion of the δ13C time curve (Klonk Event) of an amplitude of 2.5 to 3.0‰ (max. 4.0‰) in Europe and up to 5.0‰ in North America, reflects a unique combination of palaeogeographic, biogeochemical and evolutionary processes in the late Caledonian geodynamic setting. The steady sulfur isotopic ratios show an overall stability of the S–D oceanic geochemical system as a whole and do not indicate any synchronous changes in anoxic deep oceanic and sediment processes. Therefore this led us to a hypothesis that the crucial changes that contributed to the recorded carbon cycling turnover are related to rapidly evolving ocean–continent–biosphere feedback. Coastal zones of the latest Silurian epicontinental seas accumulated considerable quantities of organic carbon from early vascular vegetation, which explosively expanded to inhabit vast near-coastal shallows and deltas. Large primary production of these early terrestrial plants and rapidly enhanced sedimentary burial of organic carbon were also responsible for CO2 drawdown, which have resulted in reversed-greenhouse effect and a global climatic cooling tendency. This feedback was blocked when the sea level gradually dropped and led to shrinking of the Silurian epicontinental seas and the growing climatic deterioration during the S–D transition limited primary production. Furthermore, continued processes of regressive abrasion and erosion limited the storage of organic carbon, as well as the efficiency of the carbonate factory. During the following Early Devonian greenhouse interval, marine regression and active latest Caledonian tectonism promoted progressive weathering of the sedimentary organic matter. The oxidation of C-rich deposits caused the subsequent growth of CO2 levels in the Early Devonian, culminating in the warming of global climate. [Copyright &y& Elsevier]

The evolutionary history of osteichthyans (bony fishes plus tetrapods) extends back to the Ludlow epoch of the Silurian period. However, these Silurian forms have been documented exclusively by fragmentary fossils. Here we report the discovery of an exceptionally preserved primitive fish from the Ludlow of Yunnan, China, that represents the oldest near-complete gnathostome (jawed vertebrate). The postcranial skeleton of this fish includes a primitive pectoral girdle and median fin spine as in non-osteichthyan gnathostomes, but a derived macromeric squamation as in crown osteichthyans, and substantiates the unexpected mix of postcranial features in basal sarcopterygians, previously restored from the disarticulated remains of Psarolepis. As the oldest articulated sarcopterygian, the new taxon offers insights into the origin and early divergence of osteichthyans, and indicates that the minimum date for the actinopterygian–sarcopterygian split was no later than 419 million years ago. [ABSTRACT FROM AUTHOR]

In the central part of the Mid-Ordovician-Early Silurian Baltic Basin, two different transport pathways of terrigenous material can be recognized. Kaolinite indicates the south-to-north sediment influx, and Cr the western and northern sources. A pathway from the Ukrainian Shield in the South was active in the Floian-Darriwilian (Ordovician) and in the Llandovery (Silurian). The influx from the western source was active in the Sandbyan, and influx from the northern side occurred in the Katyan. The sediment transport was carried out by water flows, which turned into rapid currents from time to time. These currents, coming from the ocean surface waters, were oxygenated facilitating red facies formation in the central Baltic Basin. Currents on the shelf were linked to the adjacent oceanic currents, which changed in course with the drift of Baltica from temperate to subtropical latitudes. [ABSTRACT FROM AUTHOR]

Algae have always been the most diverse and numerous eukaryotic autotrophs in marine ecosystems. Both fossil and molecular data point to an early Proterozoic origin for algae. Although known for their long evolutionary history, the fossil record of algae is sparse and mainly remains of taxa with heavily calcified thalli are preserved. However, fossils of noncalcareous algae, known as extremely sporadic and occasional finds from different parts of the world, provide important insights into the palaeobiology of algal flora in the Earth.s past. Here we describe highly diverse flora of noncalcareous thallophytic algae from a Silurian age deposit. [ABSTRACT FROM AUTHOR]

Pander (1856, Monographie der fossilen Fische der silurischen Systems der Russisch.Baltischen Gouvernements. Obersilurische Fische. Buchdruckerei Kaiserlichen Akademie des Wissenschaften, St. Petersburg, 91 pp.) first established four Oniscolepis and three Strosipherus species, which later, except O. magna, were referred to Oniscolepis dentata, the name fixed by Rohon (1893, Mémoires de l'Académie Impériale des Sciences de St.-Petersbourg, 41, 1.124) as the senior synonym. Using modern techniques, we redescribe and illustrate morphological and histological varieties of its platelets, tesserae, and scales. No articulated specimen of O. dentata has ever been found. Fragments of head platelets, two branchial plates, an orbital plate (or tessera), and body ridge elements are described for the first time. The microstructure of scales of O. dentata specimens from the East Baltic and North Timan differs only slightly from that of scales from the type locality, Saaremaa Island, Ohesaare Cliff, which has fewer and finer dentine tubules and Sharpey.s fibre tubules than the specimens from North Timan. Oniscolepis Pander and Kallostrakon Lankester are united into a new family Oniscolepididae fam. nov. with the type genus Oniscolepis Pander. [ABSTRACT FROM AUTHOR]

The article discusses the research study on the machaeridian marine Palaeozoic fossils in the lower Silurian of Shropshire, England. Considerations on the characteristics and classification of the said fossil is given, along with the description of the localities where the fossil is situated and the geology of it. The results showed that, among others, the varieties of machaeridians in the Purple Shales implies the importance of small invertebrates in the Telychian marine ecology.

The continuous Upper Ashgill–Sheinwoodian carbonate succession in the most eastern Kozhym River area in the Subpolar Urals comprises the Yaptikshor (Rawtheyan), Kamennaya baba (Hirnantian), Ruchej and Manyuku (Llandovery–?Sheinwoodian) formations. The facies of the deep subtidal Yaptikshor Fm. mark an abrupt sea-level rise following emergence of the Bad’ya reef (Rawtheyan). Carbonate breccias at the base of the Kamennaya baba Fm. correlate with the beginning of the Hirnantian glaciation and change upwards towards the Ordovician–Silurian boundary with the development of light-grey massive boundstone/packstone shoal deposits. An abrupt change in facies to the Rhuddanian–Aeronian Ruchej Fm. continental slope environment marked the start of a long-term sea-level rise. The uppermost Aeronian–?Sheinwoodian is represented by submarine canyon carbonate conglobreccias of the Manyuku Fm. unconformably underlying the Balban’yu reef. The rapid facies changes at the base of the Hirnantian and at the Ordovician–Silurian boundary were of global eustatic origin. In contrast, the abrupt changes in the Rawtheyan and the formation of the Manyuku Fm. conglobreccias were of local or regional origin associated with tectonics. They were followed by the start of a regional transgression (Yaptikshor Fm.) and a global transgression marked by the initiation of the Balban’yu Reef in the Sheinwoodian. [ABSTRACT FROM AUTHOR]

The morphology of the Late Silurian (Přídolí) scorpion Proscorpius osborni ( Whitfield, 1885 a ) (Arachnida: Scorpiones), from the Phelps Member of the Fiddlers Green Formation of New York, the ‘Bertie Waterlime’ of earlier stratigraphic schemes, is revised based on studies of new and existing material (a total of 32 specimens). Previous reports of four cheliceral articles, gnathobasic coxae, a labium and gill slits in P. osborni can be dismissed. However, we confirm the presence of both median and compound lateral eyes, a pair of tarsal claws, albeit on a more digitigrade foot compared to that of modern scorpions, more than five ventral mesosomal sclerites and a fairly modern pattern of metasomal (i.e. tail) carinae. The co-occurring Archaeophonus eurypteroides Kjellesvig-Waering, 1966 and Stoermeroscorpio delicatus Kjellesvig-Waering, 1986 are regarded as junior synonyms of P. osborni. Fossil scorpion higher systematics is plagued by a plethora of unnecessary and largely monotypic higher taxa and we draw on the results of Jeram’s cladistic analysis from 1998 to synonymize formally a series of families and superfamilies with Proscorpiidae Scudder, 1885 . [ABSTRACT FROM AUTHOR]

The results presented in this paper indicated that the carbazole-type compounds have high thermal stability and also show stability in oxidation and bio-degradation. This kind of compounds still has high concentrations and a complete distribution in the analyzed dry asphalt samples, showing that they are particularly useful in the study of hydrocarbon migration of the paleo-pools. The difference in the contents of nitrogen compounds in the Silurian dry asphalts from the Awati, Tabei and Tazhong areas is attributed to the difference in the extent of oxidation and (or) bio-degradation for the areas; the Awati and Tabei areas underwent relatively strong oxidation and bio-degradation. During the first stage of hydrocarbon pool formation in the Silurian system in the Tazhong and Tabei areas of the Tarim Basin (at the end of the Silurian period) and at the second stage in the Awati area (in Permian), the hydrocarbons experienced a long-distance migration. [ABSTRACT FROM AUTHOR]