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Over the last two decades, there has been an intensive research effort focused on studying the climate fluctuations during the Ordovician period. In this study, we provide brachiopod and bulk carbonate rock stable isotopic data for oxygen (O) and carbon (C) from the Middle Ordovician succession from northern Estonia for evaluating the Middle Ordovician palaeotemperature and palaeoenvironmental history. We present δ18O curves from eight northern Estonian outcrops. This new data, together with the published results, enable compiling the first complete stable oxygen isotopic curve for Middle Ordovician to early Silurian for the eastern Baltoscandian Palaeobasin. Combining the published and new δ13Cbrac and δ18Obrac data allows us to address chemostratigraphic correlation in the Middle Ordovician. The Baltoscandian δ18O data generally confirm a cooling trend from Early to Middle Ordovician documented by previous studies in different palaeobasins. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cause of marine biodiversity decline following the GOBE investigated. • Hg isotopes indicate dynamic PZE fluctuations in slope and basinal facies. • Due to environmental instability tied to global cooling & stronger ocean circulation. • ∼23 % of atmospheric Hg sequestered by marine sediments during PZE events. The Darriwilian (Middle Ordovician) is marked by a striking peak of the Great Ordovician Biodiversification Event (GOBE) followed by an abrupt ∼50 % decline in invertebrate species. Understanding the ultimate driving mechanism behind this biotic turnover and its correlation with those proximate climatic-oceanic changes that directly result in elevated biotic mortality have garnered considerable attention. One hypothesis posits that oceanic redox evolution actively influenced biodiversification, and progressive expansion of marine anoxia caused the termination of this biotic event. In this study, we present sedimentological and geochemical profiles for three outcrops of different lithofacies across the Middle-Upper Ordovician transition, ranging from carbonate platform to deep-water slope-basinal facies of the Tarim and South China cratons. Mercury isotopes reveal that recurrent and spatially dynamic photic-zone euxinia (PZE) occurred in the slope-basinal facies while being absent in platform facies. Mass balance model results suggest that ∼23 % of local atmospheric Hg was sequestered in marine sediments due to elevated dissolved H 2 S in surface waters. This finding suggests that destabilized oceanic redox conditions developed during climatic cooling, particularly shoaling and upwelling of deep-marine euxinic waters into the photic zone, coupled with global carbon-cycle disturbances, resulted in biodiversity decline following the peak of the GOBE. [ABSTRACT FROM AUTHOR]

[Display omitted] • South Tibetan Detachment System, NW Himalaya as a Cambro–Ordovician terrane boundary. • C–O granites during Kurgiakh Orogeny between Sutlej and Dhauliganga valleys. • U-Pb zircon ages of granites between ∼ 499 and 487 Ma, remobilized from ∼ 34 to 13 Ma. • Extensional STDS controlled sediment supply into Tethyan Basin since early Cambrian. The South Tibetan Detachment System is an important extensional fault zone, separating the Greater Himalayan Sequence from the overlying Tethyan Himalayan Sequence, and is well exposed in the upper reaches of the Dhauliganga valley, NW Himalaya. This fault system is characterized by the occurrence of an extensive Cambro–Ordovician granite belt between Sutlej and Dhauliganga valleys, although only a few small granitoids intrude the high-grade mylonite gneiss of the Greater Himalayan Sequence in its immediate footwall. These bodies yielded U-Pb zircon crystallization ages between 498.92 ± 5.5 Ma and 486.54 ± 2.3 Ma. This work postulates that the South Tibetan Detachment System evolved as a major proto-tectonic marginal extensional terrane boundary during the Cambro–Ordovician Kurgiakh/Bhimphedian Orogeny, when it was the conduit for emplacement of the Cambro–Ordovician granite belt. Denudation of the Neoproterozoic Greater Himalayan Sequence and the Paleozoic granites on its footwall provided approximately ∼ 10 km thick sediments into the Tethyan Basin due to this fault system as a master growth fault. Reactivation of this fault system controlled further melting and emplacement of the Higher Himalayan Leucogranite belt during the Cenozoic. Zircon growth is observed in two distinct modes: pulsative from the Late Eocene to Early Oligocene, with peaks at 33.99 ± 1.07 Ma, 30.53 ± 0.32 Ma and 25.03 ± 0.54 Ma; and in the continuous mode from 23.68 ± 0.94 Ma to 13.30 ± 0.30 Ma, in the Miocene, for nearly 10.0 myr. These datasets reveal some of the oldest pulsative movements in the Late Eocene–Early Oligocene during crustal thickening, thrusting and associated metamorphism, followed by continuous extension during the Miocene. Data from the South Tibetan Detachment System are distinct in character, and do not support either its eastwards younging or diachronous movements along the Dhauliganga valley. [ABSTRACT FROM AUTHOR]

Based on logging, core, thin section and geochemical analysis, the tectonic-lithofacies paleogeographic pattern of first member to third member of Ordovician Majiagou Formation (O1m1-O1m3 for short) in Ordos Basin is reconstructed, and the tectono-sedimentary evolution characteristics and oil-gas geological significance are discussed. The results are obtained in four aspects. First, a set of marginal argillaceous dolomites with high gamma ray value developed steadily and diachronously at the bottom of Majiagou Formation, which distributed over the Huaiyuan Movement unconformity, with d13C values positive drift characteristics comparable to global transgression of the Early Ordovician Floplian. Second, the global sea level rose and the ancient land was submerged into the underwater uplift in O1m1 to O1m2, and the central uplift was deposited for the first time in the Ordovician, forming a tectonic pattern of "one uplift and two depressions". Subsequently, the subduction and extrusion outside the basin and the differentiation of uplift and depression in the basin of O1m3 resulted in the activation of the Wushenqi-Jingbian bulge. Third, the evolution of the tectonic pattern had a significant impact on the sedimentary paleoenvironment. The O1m1 overlaps westward, and saline lagoon is formed in eastern depression and influenced by the transgression. The transgression continued in O1m2 and resulted in communication with the wide sea, and the large-scale grain shoal developed around eastern depression, and the late dry shrinkage formed a small scale evaporite lagoon in upper part. Under the influence of highland sealing in O1m3, the water body gradually differentiated into dolomitic gypsum and saline lagoons to the east, and the grain shoal spread along the highs around sag. Fourth, the source rocks developed diachronously at the bottom of Majiagou Formation form a favorable source-reservoir assemblage with the shoal facies reservoir distributed around the slope of O1m2-O1m3, and they have certain exploration potential for natural gas. [ABSTRACT FROM AUTHOR]

[Display omitted] • The detrital zircons with an anomalous peak age of ca. 976 Ma in NTB were derived from YCTB. • The provenance of early Paleozoic detrital zircons in the northwestern platform was Southwest Tarim. • The northeastern margin had transformed into an active continental margin in the late Ordovician. The northern margin of the Tarim Block (NTB) is an essential tectonic unit for understanding the tectonic-sedimentary system and geodynamic mechanisms of the Tarim Block and the surrounding region. Five Ordovician limestone samples and six Silurian sandstone samples were collected from the Keping-Bachu area, an early Paleozoic platform basin. Detrital zircon U-Pb chronology analysis shows that most of the early Paleozoic samples yield evident detrital zircon U-Pb age peaks of 454 Ma, 768/804 Ma, 976 Ma, 1818 Ma, and 2372 Ma. However, there was a 1000–940 Ma gap in the igneous rock records of the NTB, which means no magmatic provenance corresponding to the early Neoproterozoic detrital zircons with a peak age of ca. 976 Ma. Based on comparisons with potential provenance areas, the Yili-Central Tianshan Block (YCTB) may be the missing source, which was migrated to the NTB after the mid-Neoproterozoic orogenic event. The detrital zircon U-Pb age spectra of different regions in the NTB are significantly different. The early Paleozoic detrital zircons were abundant in the Ordovician strata in Keping-Bachu, but rare in Tabei and Quruqtagh. With the Hf isotopic compositions, the early Paleozoic detrital zircons came from the Southwest Tarim during the late Ordovician. Here, we present a bidirectional model for the provenance supply of the northwestern platform controlled by Tabei Uplift and Southwest Uplift. Moreover, the proportion of 480–420 Ma detrital zircons in Silurian strata gradually decreased from east to west, implying that the magmatic activity in the northern margin gradually weakened along the margin. By comparing the peak ages of early Paleozoic detrital zircons in the northwestern platform (435–434 Ma), Tabei (436 Ma), and Quruqtagh (454–450 Ma), we propose that the northeastern margin had transformed into an active continental margin in the late Ordovician, while the northwestern margin was later than it. [ABSTRACT FROM AUTHOR]

[Display omitted] • C, N and Hg isotopes and trace element stratigraphies across the OST are investigated. • Synchronous Hg/TOC spike and Δ199Hg ∼ 0 ‰ recorded coeval volcanism in the LOME 2. • Odd-MIF Hg isotope pattern shaped by volcanism/glaciation /sea-level fall in LOME 2. Global geological processes that occurred during the Ordovician–Silurian transition (OST) were investigated exploring sections from the Argentine Precordillera (Cerro La Chilca, Baños de Talacasto and Villicum) which were deposited close to polar zones of Gondwana during the oldest Phanerozoic glaciation. C-N-Hg isotopes and redox-sensitive trace metal chemostratigraphy allowed to assess the relative importance of volcanism, glaciation, post-glacial sedimentation and extinction events during the OST. At Cerro La Chilca and Baños de Talacasto sections, Katian and early Hirnantian strata are missing. Hirnantian and Rhuddanian strata occur in the all three sections. At Cerro La Chilca, coeval positive δ13C org shift, Hg spike and Δ199Hg ∼ 0 ‰ were recorded in the Sandbian Los Azules Formation, suggesting volcanic Hg loading. Coeval Hg/TOC spikes at the Baños de Talacasto and Villicum sections and Δ199Hg ∼ 0 ‰ in the late Hirnantian (M. persculptus Zone) recorded the second pulse of the Late Ordovician mass extinction (LOME 2), for which volcanism was postulated as the cause of warming and anoxia. Another Hg/TOC spike in the early Rhuddanian at Baños de Talacasto and Villicum is coeval with slightly positive Δ199Hg values, an enrichment related, perhaps, to an enhanced continental runoff that followed the Late Ordovician glacial cycle (LOGC-3). At the Cerro La Chilca, positive δ15N values in the Sandbian suggest less intense water-column denitrification while negative nitrogen isotope values in the LOME 2 period indicate denitrifying conditions. At the Baños de Talacasto and Villicum sections, sea-level fluctuations and nitrogen upwelling helped shaping the δ15N pathway within the LOME 2 and early Rhuddanian intervals, with negative δ15N values attesting that conditions became less reducing closer to the OST. The odd-MIF Hg isotope pattern within the LOME 2 time interval was probably induced by coeval volcanism, glaciation and sea-level fall, and in the early Rhuddanian by deglaciation and sea-level rise. [ABSTRACT FROM AUTHOR]

Caryocaridids are a unique representative of pelagic arthropods from the Ordovician period. They are typically found as flattened carapaces in mudstones and shales. This study reports on a species of caryocaridids, Soomicaris cedarbergensis , discovered in the Lower Ordovician of northwestern Xinjiang, NW China. The species shows the rare enrolled carapaces with a preserved cuticular ultrastructure. These specimens of caryocaridids from Xinjiang are the first reported in the Yili Block, and provide the substantial evidence that the paleogeographic distribution of caryocaridid phyllocarids could extend to the Central Asian Orogenic Belt. This species existed from the late Tremadocian until the end of the Ordovician (Hirnantian), making it the longest-ranging known species of caryocaridids. The carapace cuticle of S. cedarbergensis is composed of carbonate-fluorapatite and can be divided into three mineralized lamellae: outer, middle, and inner. The outer and inner lamellae each consist of three layers that correspond to the epicuticle, exocuticle, and endocuticle of extant crustacean carapaces. Moreover, the polygonal reticulation structure of the carapace in archaeostracans appears to be similar in shape and size to the hemolymph sinuses of leptostracans. This unique ultrastructure of the carapace cuticle in caryocaridids is believed to be better suited for a pelagic lifestyle. [ABSTRACT FROM AUTHOR]

The relationship between fracture calcite veins and shale gas enrichment in the deep Ordovician Wufeng Formation–Silurian Longmaxi Formation (Wufeng–Longmaxi) shales in southern Sichuan Basin was investigated through core and thin section observations, cathodoluminescence analysis, isotopic geochemistry analysis, fluid inclusion testing, and basin simulation. Tectonic fracture calcite veins mainly in the undulating part of the structure and non-tectonic fracture calcite veins are mainly formed in the gentle part of the structure. The latter, mainly induced by hydrocarbon generation, occurred at the stage of peak oil and gas generation, while the former turned up with the formation of Luzhou paleouplift during the Indosinian. Under the influence of hydrocarbon generation pressurization process, fractures were opened and closed frequently, and oil and gas episodic activities are recorded by veins. The formation pressure coefficient at the maximum paleodepth exceeds 2.0. The formation uplift stage after the Late Yanshanian is the key period for shale gas migration. Shale gas migrates along the bedding to the high part of the structure. The greater the structural fluctuation is, the more intense the shale gas migration activity is, and the loss is more. The gentler the formation is, the weaker the shale gas migration activity is, and the loss is less. The shale gas enrichment in the core of gentle anticlines and gentle synclines is relatively higher. [ABSTRACT FROM AUTHOR]

The Fezouata Shale Formation has dramatically impacted our understanding of Early Ordovician marine ecosystems before the great Ordovician biodiversification event (GOBE), thanks to the abundance and quality of exceptionally preserved animals within it. Systematic work has noted that the shelly fossil subassemblages of the Fezouata Shale biota are typical of open-marine deposits from the Lower Ordovician, but no studies have tested the quantitative validity of this statement. We extracted 491 occurrences of recalcitrant fossil genera from the Paleobiology Database to reconstruct 31 subassemblages to explore the paleoecology of the Fezouata Shale and other contemporary, high-latitude (66°S–90°S) deposits from the Lower Ordovician (485.4–470 Ma) and test the interpretation that the Fezouata Shale biota is typical for an Ordovician open-marine environment. Sørensen's dissimilarity metrics and Wilcoxon tests indicate that the subassemblages of the Tremadocian-aged lower Fezouata Shale are approximately 20% more heterogenous than the Floian-aged upper Fezouata Shale. Dissimilarity metrics and visualization suggest that while the lower Fezouata and upper Fezouata share faunal components, the two sections have distinct faunas. We find that the faunal composition of the lower Fezouata Shale is comparable with other Tremadocian-aged subassemblages from high latitudes, suggesting that it is typical for an Early Ordovician open-marine environment. We also find differences in faunal composition between Tremadocian- and Floian-aged deposits. Our results corroborate previous field-based and qualitative systematic studies that concluded that the shelly assemblages of the Fezouata Shale are comparable with those of other Lower Ordovician deposits from high latitudes. This establishes the first quantitative baseline for examining the composition and variability within the assemblages of the Fezouata Shale and will be key to future studies attempting to discern the degree to which it can inform our understanding of marine ecosystems just before the start of the GOBE. [ABSTRACT FROM AUTHOR]

[Display omitted] • Discrimination between arc, slab failure, A-type magmatism in the Appalachian Belt. • Inferred chain failure of two closely spaced subducting slabs. • Reactivation of a failed subduction zone by a nearby continent-continent collision. Geochemical data from Katian to earliest Emsian (∼453–405 Ma) igneous rocks in northeastern North America and the British Isles were compiled to identify tectono-magmatic events related to ocean closure and the formation of the Appalachian–Caledonian Belt. These rocks all have geochemical affinities with plate-margin settings, but only a few can be attributed to arc magmatism, whereas the others have slab-failure signatures or affinities with anhydrous, extensional plate-margin (A2-type) settings. Based on these setting attributions as well as constraints from the palaeomagnetic, palaeontologic, structural, stratigraphic and sedimentologic records, a model for Iapetus and Rheic ocean closure is proposed, which also involves three subordinate ocean plate segments: the Tornquist Sea, Acadian Seaway and Tetagouche–Exploits oceanic back-arc basin. The model includes several new perspectives, such as (1) an early Silurian rather than late Silurian closure of the Tetagouche–Exploits back-arc basin; (2) Acadian Seaway slab failure at the Ludlow–Pridoli boundary due to its interaction at depth with the overlying and slowly-sinking Tetagouche–Exploits slab, which generated profuse, extensional, A2-type volcanism; and (3) an Early Devonian reactivation of Acadian Seaway slab subduction, possibly due to Rheic Ocean closure and the convergence of a Gondwanan promontory against Avalonia, which was attached to oceanic lithosphere of the Acadian Seaway. Furthermore, age constraints allowed to identify chronological trends in the geochemical signatures of the igneous rocks under study, which suggest that development of a new tectono-magmatic signature was gradual due to compositional inheritance from the previous setting. These trends also suggest that, although the transition from active subduction to slab failure generates an increase in Nb/Y and light over heavy rare earth elements, these ratios tend to decrease with time due to a fading contribution of the sinking slab at the source, whereas high-field-strength element contents tend to increase due to a lack of new water input from subduction. [ABSTRACT FROM AUTHOR]

Limestones of the Takche Formation (Spiti, Himalaya) are characterized by normal marine fauna and flora typical for the Late Ordovician. The flora is represented by algae, mostly by receptaculitids and dasyclad green algae. Various calcareous microorganisms such as calcitarchs, Rothpletzella and Girvanella are present. There are some differences in the microfossil content and abundance between different lithofacies of the Takche Formation. Two main biofacies types could be recognized on the basis of the abundance of algae and calcitarchs, namely algal rich and algal poor biofacies. The abundance of dasyclad green algae in limestones of the Takche Formation is characteristic of the warm climate. The Himalaya (Gondwana) has calcitarchs in common with Baltica. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ∼520 km-diameter Deniliquin multiple-ring buried impact structure (DMS), southeastern Australia, is identified by geophysical criteria. • The Hirnantian (445.2 and 443.8 Ma), likely represents the consequence of the Deniliquin impact. • A search for impact-deformation effects is required to further test this suggestion. The buried ∼520 km-diameter Deniliquin multiple-ring impact structure (DMS), southeastern Australia, is regarded as likely to have triggered the ∼ 1.4 million years-long Late Ordovician (Hirnantian) glaciation and mass extinction event (445.2 and 443.8 Ma), which eliminated about 85% of species. The Hirnantian, second in severity relative to the Permian-Triassic boundary extinction (251 Ma) and almost twice as severe as the K–T impact and extinction event (66 Ma), is considered likely to represent the consequence of the Deniliquin mega-impact event. The geophysical evidence for a deep-seated impact origin of the DMS includes its distinct symmetric multiple-ring pattern (Fig. 1), a central magnetically quiet TMI core, radial faults and an underlying mantle dome about 10 km shallower than the regional MOHO. The magnitude of the DMS is consistent with the scale of the Hirnantian glacial and extinction events and much larger than Cambrian extinction events, which occurred on a smaller scale, suggesting the DMS is likely to represent the trigger for Hirnantian glacial and extinction events. A search for impact-deformation effects in proximal and distal Ordovician strata around the Deniliquin mega-impact structure is required to further test this suggestion. [ABSTRACT FROM AUTHOR]

The frequency of biotic invasions in modern ecosystems is increasing due to global trade moving taxa outside their native ranges and climate change facilitating establishment of taxa in previously inhospitable regions. Thus, developing a holistic understanding of biotic invasions and how they impact ecosystems over different timescales—from annual to geologic timescales—is vital. Herein we examine a geologically brief invasion event, the Clarksville Phase of the Richmondian Invasion. Prior analyses have established general ecological and evolutionary patterns across the entire Richmondian Invasion, but recent sequence stratigraphic refinement makes analysis of individual invasion pulses possible for the first time. We examine biotic change across the Clarksville Phase and identify invasion impacts on diversity, paleocommunity composition, and niche stability. Invader arrival and success was strongly linked to increased propagule pressure facilitated by sea-level changes. Invaders initially colonized deep subtidal environments and then moved offshore facilitated by rapid niche evolution during the invasion interval. Invasive taxa that attained the largest population sizes belonged to previously underutilized ecological guilds. Overall, the introduction of the invasive taxa resulted in increased diversity that was maintained into the postinvasion interval accompanied by a change in community composition in which the invaders became dominant paleocommunity members. Combined, these analyses document a biotic invasion facilitated by climate change that increased local diversity through invaders occupying underutilized ecospace and competition-related niche contraction on millennial timescales. Developing a long-term perspective to accompany shorter-term studies facilitates predicting the long-term impacts of modern invasions and creating better-informed policies and practices. [ABSTRACT FROM AUTHOR]

Plutonic rocks in different ages are cropted out and form the basement rocks in the Istranca Massif. One of the plutons located at the basement is the Cambrian-Ordovician Vize pluton (Vize-Kırklareli) and is distinguished from other plutons by some of its characteristic features. This pluton intruded into the high-grade metamorphic sedimentary rocks, and is unconformably overlay by Triassic low-grade metamorphic rocks and Eocene aged coral reef limestones (Soğucak Formation). Based on new whole rock geochemical and zircon U Pb data concentrated in two different ages, it can be said that the Vize pluton was affected by protracted magmatic activity. The igneous minerals and texture of Vize pluton are partly preserved, It has a mylonitic texture, a distinct foliation consisting of light and dark zones. In addition, metagranites contain mafic magmatic enclaves (MMEs) in some places. The Vize pluton is an I-type pluton with predominantly peraluminous and slightly metaluminous character. It is also High-K, calc-alkaline, and reflecting volcanic arc and post-collisional tectonic settings. Mineral chemical analyses show that the mafic minerals in the Vize pluton consist of Fe-biotite and calcic amphibole (hornblende). Ti-in biotite thermometry shows that the temperature of the pluton in the final crystallization temperatures are between 834 and 850 °C (mean = 845 ± 4 °C), while the crystallization temperatures of amphiboles are between 876 and 910 °C (mean = 893 ± 22 °C). Crystallization depths are estimated to be a range of 6.5 to 7.9 km. It can be assumed that the oxygen fugacity of calcic amphiboles (logƒO 2) is stabilized between −10.7 and − 11.3 bar (mean = −11.05 ± 0.4 bar). ∆NNO values are between 0.72 and 1.11 (mean = 0.96 ± 0.12) and H 2 O melt content is between 4.63 % and 5.43 % (mean = 5.04 ± 0.4 %). Oxygen fugacity values are among the typical values of calc-alkaline magma crystallization. The Vize pluton was crystallized in Cambrian to Ordovician times according to zircon U Pb dating is concentrated in two different populations as 526.16 ± 3.26 Ma and 452.93 ± 2.76 Ma. All data obtained are consistent with the ages of the magmatism that produced the Vize Pluton in the Balkanides and Istranca Massif of 420–470 Ma (mean 447.17 ± 3.24 Ma) and indicate that it probably formed in the northern Gondwana. It was affected by the magma-mixing processes of coeval felsic and mafic magmas, and anatexis processes. Geochronological and geochemical data indicate the existence of a protracted magmatic activity related to convergent setting (long-lived magmatic arc) that forced the Vize-Pluton to undergo multi-stage melting-crystallization processes. • Precambrian-Cambrian metagranitic and metamorphic basement rocks of Istranca massif take place in eastern part of Balkanides • The new zircon U-Pb dating results of Vize pluton is Cambrian-Ordovician (526.16+3.26 and 452.93+2.76 Ma) aged • Vize pluton was effected such as FC -AFC and magma mixing solidification processes and metamorphic deformations • Amphibole and biotite mineral chemistry show that the Vize pluton was formed under relatively higher oxidation state • The wide range age of metagranitoids in Vize –Istranca Massif give evidences to subduction related protractive arc magmatism [ABSTRACT FROM AUTHOR]

A length–frequency sample (n = 295) from a fossil population of the Ordovician trilobite Triarthrus eatoni Hall, 1838, assembled and analyzed by J. L. Cisne in 1973 is here reexamined using methods of length–frequency analysis commonly used in fishery science and marine biology. Theoretical considerations and the empirical data at hand suggest that the growth of T. eatoni was not "linear," but asymptotic, as is the growth of most Recent marine invertebrates. The parameters of the von Bertalanffy growth function (L ∞ = 41 mm, K = 0.29 yr−1) suggest that T. eatoni , which apparently lived in a challenging environment, grew somewhat more slowly than the extant marine isopod Ceratoserolis trilobitoides (Eights, 1833), used here as Recent analogue to T. eatoni. This trilobite probably lived up to 10 years, rather than the suggested 4 years, and its mortality rate was 15%–20% per year rather than 30%–40% per year. These represent the first estimates of trilobite absolute growth characteristics using methods known to accurately model growth in extant water-breathing ectotherms. These provide a baseline for trilobite growth that can be used to make inferences about growth in other species. The approach used here may also be applied to other trilobites for which suitable length–frequency data exist. [ABSTRACT FROM AUTHOR]

New trilobite material and the first graptolites from outcrop are described from the Am5 member of the Amdeh Formation near Al Fleij in northeast Oman. The sediments in which these faunas occur are interpreted as distal-shelf deposits with storm beds packed with brachiopods and orthoconic nautiloids. The deposits and its faunas are considered of late Darriwilian age and younger than the shallower-water Am5 deposits known from other outcrops. No palynomorphs could be recovered to confirm this due to the increased burial temperature the Al Fleij area has experienced. The trilobites are of considerable palaeo-biogeographic interest as few faunas of this age are known from the Arabian Plate, though their preservation precludes the establishment of new species. They include Isabelinia aff. glabrata , Liomegalaspides sp., Neseuretus tristani , Neseuretinus sp. and the deeper-water forms, Cyclopyge cf. C. bohemica , Arthrorhachis sp. and Brachypleura sp. The graptolites are pendent Didymograptus spp. of later Darriwilian type. Rare elements of the conodonts Nordiora , Amorphognathus and Microzarkodina have been recovered from shell beds that occur interbedded with the faunas. They too indicate a late Darriwilian age and differ from richer, restricted, shallow-water faunas known from the Am5 at other locations, and the more cosmopolitan shelf fauna from the Ayim Member of the Rann Formation of the United Arab Emirates. A coarser, 80 m-thick, terrestrial sequence containing igneous pebbles, included in the Am5 in the 1980s, is shown from the occurrence of fossil plants to be of Permian age and probably equivalent to the Basal Saiq Clastics of Jabal al Akhdar. [ABSTRACT FROM AUTHOR]

[Display omitted] • A complete subduction initiation record exposed in the ophiolitic complex. • The ocean spreading reached a peak age during the Cambrian–Early Ordovician. • The SW Paleo-Asian Ocean started to subduct in the Early Ordovician. • Slab-derived sediments have a significant contribution to oceanic arc evolution. As a key step of the Wilson cycle, subduction initiation is regarded as a start hallmark of the ocean-continent transformation. However, the crust-mantle interaction and crustal growth processes related to subduction initiation remain enigmatic. Here we report a newly recognized complete magmatic sequence containing three rock assemblages in the Hongguleleng ophiolitic complex (HOC) in West Junggar, NW China. Group I contains typical Mid-Oceanic Ridge (MOR)-derived rocks including abyssal peridotite, gabbro, plagiogranite, and basalt. Group II consists of forearc basalt (FAB) and boninitic gabbro and has a high continentality index (CI > 130), similar to the rock assemblages in the Mariana proto-arc. Group III composed of calc-alkaline andesite and arc tholeiite basaltic andesite exhibits middle CI values (50 < CI < 100), suggesting that they form in a transitional oceanic arc. Zircon U-Pb ages show that the N-MORB gabbro and plagiogranite samples are emplaced at 483–481 Ma, and the boninitic rocks, calc-alkaline andesites, and arc tholeiite basaltic andesites have the crystalline ages of 472–467 Ma, 456 Ma, and 452 Ma, respectively. An increasing trend of Ba/Th and V/Ti ratios from Group I to Group II suggests the addition of aqueous fluid and elevated oxidation in the mantle source during subduction initiation. However, it exhibits an uptrend in Th/Nb and (La/Sm)cn ratios but a downtrend in Ba/Th ratios from Group II to Group III, indicating a significant contribution of slab-derived sediments to the mantle during oceanic arc evolution. Combined with regional data, we consider that there developed an E-W–trending sub-ocean basin of the Paleo-Asian Ocean spanning northern West Junggar and East Kazakhstan during the Middle Cambrian–Ordovician. The MOR-type and forearc ophiolites in northern West Junggar as well as our results suggest that the ocean happened mid-ocean ridge spreading at ca. 512–478 Ma and subduction initiation at ca. 476–467 Ma, and developed a transitional oceanic arc at ca. 456–452 Ma. [ABSTRACT FROM AUTHOR]

[Display omitted] • The first report of a Middle Ordovician-Silurian Large Igneous Province (LIP) from northern Gondwana. • Introducing the newly discovered LIP as a robust candidate as the cause of the end-Ordovician mass extinction. • Northern Iran is as a key region for understanding the cause of global environmental changes/events during the Middle Ordovician to Silurian. Proxies such as mercury and Hg/TOC anomalies document signatures for temporal correlations between major pulses of the Late Ordovician mass extinction (LOME) event and a postulated Large Igneous Province (LIP) as the main cause of extinction. Herein, for the first time, we report a series of voluminous intraplate volcanic events of the Middle Ordovician-Silurian from northern Iran, representing the erosional and deformed remnants of a LIP as well as a robust candidate as the cause of the LOME. These volcanic rocks, distributed over a length of ca. 1700 km and more than 1000 m thickness in some cases, were erupted during initial rifting of the Paleotethys Ocean in northern Gondwana. Based on fieldwork, relative ages, and high precision U-Pb ID-TIMS dating results we have identified one plutonic (granitic) and six volcanic (mainly basaltic) phases of mostly short duration for this chain of magmatism. The onset of volcanic events at 468.70 ± 0.30 Ma (2σ) coincided with the earliest Darriwilian, followed by a huge bimodal volcanic event between the Sandbian-Katian boundary and 450.61 ± 0.27 million years ago, and the climax of volcanism occurred during the late Katian-Hirnantian. An approximate coincidence between the onset of basaltic eruption and weathering in northern Iran and the beginning of significant global decline in seawater 87Sr/86Sr during the Darriwilian Stage may be a sign of the initial volcanic activities of our newly identified LIP. We suggest that the Middle Ordovician-Silurian volcanic rocks from northern Iran, and other related places, are remnants of this newly proposed LIP (herein labeled the Alborz LIP), with high potential to be the main cause of environmental and climatic changes that led to the LOME. [ABSTRACT FROM AUTHOR]

[Display omitted] • Data-analysis of the Ollo de Sapo Formation reveals an input of wet mafic magma. • A combined magmatic and metasedimentary source explains the Ollo de Sapo composition. • Felsic Igneous Province of NW Gondwana is derived from a fast melting event. Cambro–Ordovician silicic magmatism in the Central Iberian Zone of the Iberian Massif (Ollo de Sapo Formation, OSF) constitutes a voluminous and geochemically atypical magmatic event that formed preceding the breakup of the northern margin of Gondwana. To date, and due to uncommon geochemical signatures, such as a high Fe, Mg content compared to anatectic melts and the departing from the calc-alkaline trends, the origin of such magmatic event is not fully understood. Herein, we report a data-analysis of geochemistry linking magmas and source compositions. The analysis of the combined data from multiple studies ascribes the geochemistry of the OSF rocks to a combination of extensive melting of Ediacaran metasiliciclastic rocks and a Ca-rich component. It is hypothesized that fluids released by crystallization of mafic magmas contributed to partial melting of a thick metasedimentary pile represented by Ediacaran siliciclastic rocks. Such melting event gave rise to a mobile nebulite or migma , which was able to extrude and form the super-eruption or "flare-up" that characterizes Cambro-Ordovician silicic magmatism at the Gondwana margin. Fast, catastrophic crustal melting with large-scale restite entrainment, triggered by the influx of mafic magma-derived fluids, are considered the main cause of the unique features of this Cambro-Ordovician atypical silicic large igneous province of Gondwana. [ABSTRACT FROM AUTHOR]

This paper presents findings from the study into the relationships between the laboratory- and well log-derived data (including the comprehensive well-log interpretation data) on petrophysical properties of the Silurian and Ordovician shale gas formations in the Baltic Basin (North Poland). Approximately 70 samples of mudstone were examined in laboratory experiments to determine total and effective porosity; bulk, grain, and rock density; total organic carbon; physical pei-meability; total pore area. pore distribution: and mineral components. Some rock samples were further investigated using mercury injection porosimetry, helium porosimetry, dual liquid porosimetry, NMR, N, adsorption/desorption, rock-eval pyrolysis, and XRD to obtain the targeted petrophysical information from heterogeneous claystone/mudstone and their organic matter. Natural radioactivity, bulk density, total porosity, volume of kerogen, and other parameters were determined from the continuous curves plotted from the earlier depth matched well logging data, which were used to account for differences between vertical resolution of well logs and the point data obtained from the laboratory. The goal ofthis study was to provide a comprehensive characterization of the Silurian and Ordovician shale gas formalions in-Northern Poland to support the thesis about their heterogeneity. [ABSTRACT FROM AUTHOR]

New palaeogeographical reconstructions for the earlier Ordovician (480 Ma), and later Ordovician (450 Ma) integrate revised longitude-calibrated palaeomagnetic reconstructions and the inclusion of synthetic plate margins within the now-vanished oceanic areas. There are substantial published differences from the previous placing of some of the continents and terranes in Asia; for example, Siberia and Gondwana have previously been placed at varied distances and relative positions in relation to the Kazakh terranes, South and North China, and Tarim. But there are only minor changes for most of the world, particularly in the North American and European areas. The global distributions of benthic trilobites and brachiopods within faunal provinces and their changes through the Ordovician are plotted, including the new term Cathay-Tasman Province for some pan-equatorial brachiopod faunas from China and Australia, and key sites and provinces are shown on the revised maps. The 30 Myrs from 470 to 440 Ma (mid Ordovician to early Silurian) saw some of the most varied and changeable climates of the whole Phanerozoic culminating in the 'Hirnantian' ice age. Those changes in turn much affected the rates of evolution of many benthic and pelagic animal groups which were driven by both biological and environmental causes. Global cooling during the Ordovician was a prime factor by reducing sea surface temperatures which challenged life to evolve faster and more substantially than before. That cooling was driven by decreasing atmospheric CO 2 , for reasons that are not fully resolved, but probably included reduced sourcing (reduced continental arc activity) combined with increased silicate weathering due to the advent of land plants and perhaps the progressive exhumation of low-latitude collisional arcs. Since long-term CO 2 sinks are largely controlled by palaeogeography, the general increase in the concentration of continents in the tropics during the Ordovician increased the overall global weathering. [Display omitted] • New palaeogeographical reconstructions for the earlier Ordovician (480 Ma) and later Ordovician (450 Ma). • New maps show the global distributions of benthic trilobites and brachiopods within faunal provinces and include the new term Cathay-Tasman Province for some pan-equatorial brachiopod faunas from China and Australia. • Although the Great Ordovician Biodiversification Event was probably driven by a combination of biological and environmental factors, global cooling during the Ordovician must have been a prime factor, by reducing sea surface temperatures to temperatures that challenged life to evolve faster and more substantially than before. • Global cooling probably also caused the increase in modelled atmospheric O 2 that echo the diversity of global articulate brachiopods. • A 40 million years cooling trend during the Ordovician culminated in the 'Hirnantian' glaciations and the first Phanerozoic mass extinction at 444 Ma. [ABSTRACT FROM AUTHOR]

To analyze anomalies of a biomineralized exoskeleton of a trilobite. A specimen of Dalmanitina socialis from the Upper Ordovician Letná Formation at Veselá near Beroun, Czechoslovakia, curated at the Czech Geological Survey in Prague. The internal mold and external mold and latex casts were coated with ammonium chloride sublimate and photographed. A substantial reduction of the eye surface associated with changes in morphology and surface structure was noted. The anomaly is believed to be the result of a healed injury after an unsuccessful predatory attack. Based on the presumed mechanism of injury, a 'large arthropod' is proposed to be the potential attacker. The low incidence of sublethal attack to cephala in collections of Cambrian to Carboniferous trilobites implies that most such attacks were fatal, rendering this specimen unique and capable of providing insight into healing processes. Post-mortem damage rendered analysis difficult. Exploration of other cases of healed trauma in order to understand Ordovician ecosystems. [ABSTRACT FROM AUTHOR]