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The connection between the Ordovician bentonites on the southern margin of the Ordos Basin and the Early Palaeozoic volcanic rocks of the North Qinling Orogenic Belt is crucial for understanding the subduction and collisional closure of the Shangdan Ocean during the Early Palaeozoic. This paper investigates zircon U–Pb ages, geochemistry and Lu–Hf isotopic compositions of zircons in the Upper Ordovician Zhaolaoyu Formation bentonites located on the southern margin of the Ordos Basin. U–Pb dating of zircon indicates a coeval age of 453.3 ± 1.4 Ma (MSWD = 0.99), which represents the crystallisation age during the Late Ordovician Katian stage. The bentonites exhibit higher SiO2 (57.94–77.95 wt.%) and Al2O3 (9.21–14.33 wt.%), classifying them within the low‐potassium alkali basalt to medium‐potassium calc‐alkaline series. The parent rock of the bentonites is likely intermediate to felsic volcanic rocks. The rare earth element partitioning curves of the bentonites are right‐dipping, with a more pronounced negative Eu anomaly (δEu = 0.48–0.67). The zircons in the bentonites yield two‐stage model ages ranging from 546 to 956 Ma, along with εHf(t) values between 5.56 and 13.55. These results indicate that the bentonites are products of volcanic arc magma formed in a subduction–collision environment. The interbedded bentonites in the Upper Ordovician limestones of the southern margin of the Ordos Basin may be associated with the northward subduction of the Shangdan Oceanic crust, reflecting the subduction and consumption of the Proto‐Tethys Ocean along the southern margin of the North China Block. [ABSTRACT FROM AUTHOR]

ABSTRACT Knowledge of the early Palaeozoic tectonic evolution of the Indochina Block is critical for reconstructions of the Gondwana supercontinent in relation with other microcontinents. In the central Indochina Block, the Early Palaeozoic Tam Ky–Phuoc Son Suture Zone (TPSZ) and Po Ko Suture Zone (PKSZ) demarcate the boundary between the Truong Son Belt in the north and Kon Tum Massif in the south. In the southern parts of Truong Son Belt, we have identified meta‐mafic and meta‐intermediate rocks associated with plagiogranite, metapelitic and meta‐siliceous rocks. Here we present integrated field, geochemical and geochronological results of the meta‐gabbroic and amphibolitic samples in the southern Truong Son Belt to unravel the tectonic evolution of the Indochina Block during the Early Palaeozoic. The MC–LA–ICP–MS zircon U–Pb ages indicate magmatism at ca. 504–460 Ma. Based on geochemical composition, the samples range from gabbro to gabbro‐diorite. The gabbroic samples have slightly higher Mg# (58.9–62.8) than those of the gabbro‐dioritic samples (Mg# = 56.3–61.5), and both types of rock show low TiO2 contents (0.68–0.98 wt%), displaying enriched LREE ((La/Sm)N = 1.66–3.23) and LILE (e.g., Rb, Ba, Th and U), and pronounced negative HFSE (e.g., Nb, Ta and Ti anomalies) with low εHf(t) zircon values (from −6.34 to +0.71). These geochemical characteristics suggest that the metabasic rocks are of subduction‐related arc magmatic processes, and also indicate infiltration of sediment melt from subducting slab to mantle‐wedge prior to its partial melting. The new data suggests that northward subduction under the Truong Son Belt might have initiated during the Early Cambrian, and lasted until around the Middle Ordovician. On a regional scale, the ages of the Early Palaeozoic arc magmatism in the Truong Son Belt are comparable with the ages of tectonic events that occurred in Himalaya, West Qiangtang and East Tibet at the northern margin of the Gondwana supercontinent. [ABSTRACT FROM AUTHOR]

This contribution reports two graptolite assemblages from the Puna Turbidite Complex, outcropping in Sierra de Lina and Cauchari locality, western Puna, Jujuy and Salta provinces, Argentina. In Sierra de Lina, the graptolite assemblage comprises Didymograptus sp., Glossograptus fimbriatus, Cryptograptus schaeferi, Archiclimacograptus sp., Pseudamplexograptus distichus, Pseudamplexograptus latus, ?Urbanekograptus retioloides and Hustedograptus sp. The graptolite fauna collected from Cauchari locality includes Didymograptus spp., Archiclimacograptus caelatus, Archiclimacograptus sp. cf. A. micidus, scarce and incomplete specimens doubtfully referred to the genera Archiclimacograptus and Acrograptus and scarce siculae of Cryptograptus sp. The associations allow us to identify the Pseudamplexograptus distichus Zone in Sierra de Lina and possibly the Pterograptus elegans Zone at Cauchari locality. Graptolite assemblages recorded in both zones allow assigning a middle‐late Darriwilian (Middle Ordovician) age for the bearer levels. [ABSTRACT FROM AUTHOR]

A flare‐up of granitoids occurred at 465–445 Ma in the South Altyn Tagh, synchronously with the exhumation of subducted continental crust. Nevertheless, it remains enigmatic whether a petrogenetic connection exists between them. Here, we report a 454–451 Ma monzogranite pluton, which is characterized by abundant inherited zircons, located in the northern margin of the South Altyn Tagh high‐pressure (HP)—ultrahigh‐pressure (UHP) metamorphic terrane. U–Pb ages and Hf–O isotopic compositions of inherited and synmagmatic zircons are investigated to trace the source rocks and petrogenesis of this pluton. The inherited zircons (zircons that predate the magmatism) exhibit a wide range of ages from 2618 to 484 Ma, displaying three major peaks at 1800–1100 Ma, 1000–800 Ma and 500 Ma. By comparing these inheritance age patterns with zircon spectra of main (meta‐)sedimentary sequences and the widespread Early Neoproterozoic granites (presently as granitic gneisses) in South Altyn Tagh, along with zircon εHf(t) and whole‐rock Nd isotopic composition, we argue that the main source rocks of the studied monzogranite are Early Neoproterozoic granitic gneisses and Late Mesoproterozoic paragneisses from the South Altyn Tagh HP–UHP metamorphic terrane. The ca. 500 Ma inherited zircons have a metamorphic origin, which is simultaneous with the peak metamorphic ages of HP–UHP metamorphic rocks in the Altyn Tagh Complex. These observations indicate that the source rocks of the monzogranite pluton are the subducted continental crust, which underwent metamorphism at ca. 500 Ma and followed by partial melting at 454–451 Ma. In addition, synmagmatic zircons exhibit variable δ18O and εHf(t) values ranging from 5.4 to 11.7‰ and from −19 to +10.3, respectively, indicating a minor contribution of mantle‐derived melts in the formation of the monzogranite. Given the studied pluton and contemporaneous extensive granitoids (465–445 Ma), characterized by similar geochemistry and source rocks, are synchronous with the final exhumation of subducted South Altyn Tagh continental crust, we propose that the reworking of exhumed continental crust at middle to lower crustal depths is their main petrogenesis. [ABSTRACT FROM AUTHOR]

The Palaeozoic tectonic evolution of the Western Kunlun Orogen plays an important role in deciphering the Tethyan tectonic evolution. This study provides new geochronology, geochemistry and Lu–Hf isotopic data of igneous rocks from the Omixia Complex in the eastern section of the northern Western Kunlun, as well as detrital zircon ages from turbidites and meta‐sediments north of it. From the Omixia Complex, the determined ages of five ultramafic–mafic rock samples are approximately 470, 456, 429, 401 and 382 Ma. Two samples of acidic rocks from the same complex yielded ages of approximately 438 and 378 Ma. One pegmatitic plagiogranite sample exhibits feature of accretionary arc granites, while other samples show geochemical characteristics of island arc tholeiite and E‐MORB. Additionally, four turbidite matrix and two limestone samples, with a major peak around ca. 480–500 Ma, have the youngest zircon ages ranging from ca. 481 to 387 Ma, paralleling the age range of igneous rocks in the ophiolitic mélange. The εHf(t) values of these samples reveal a broad spectrum of crustal and mantle processes. The youngest zircon ages of five meta‐sedimentary rock samples north of the Omixia Complex range from ca. 581 to 535 Ma, with peak ages concentrated around ca. 0.9–1.0 Ga. Their provenance characteristics differ from the turbidite matrix in the southern Omixia Complex and from the meta‐sediments in the northern Tiklik terrane with peak ages of ca. 0.8 Ga. A younger limestone sample yielded youngest zircon age of ca. 294 Ma, which is unconformably overlain the Omixia Complex and surrounding older rocks. Based on these new results, combined with previous data, we propose a new tectonic model for the eastern section of the northern Western Kunlun Orogen, suggesting a continuous evolution process of multi‐terrane subduction–accretion collage from the Early Ordovician to the Middle Devonian in the Paleo‐Tethys Ocean, which evolved into an Andean‐type active margin in the Early Permian, contributing to the substantial continental growth of the southern Tarim Craton. [ABSTRACT FROM AUTHOR]

Ultra‐deep marine carbonate reservoirs is an important field for oil and gas exploration, and it is also a hot research topic in recent years. However, their hydrocarbon episodic charging model is still under debate up to now. A great breakthrough has been made in the newly discovered ultra‐deep fault‐karst oil reservoir in the Shunbei area of Tarim Basin. Based on quantitative gas chromatogram‐mass spectrometry, stable carbon isotopes of reservoir oils, microthermometry and confocal laser scanning analyses of fluid inclusions, the reservoir oil origin and hydrocarbon charging history in Shunbei No. 1, No. 5 and No. 7 strike‐slip fault zones are expounded. The results showed that the Ordovician reservoir oil derives from the source rocks within the Cambrian Yuertusi Formation deposited in a highly anoxic bottom water environment. There were four stages of hydrocarbon charging in the study area, in the late Caledonian, late Hercynian–Indosinian, middle Yanshanian and late Himalayan. During this period, the force‐field strength of the charged oil gradually decreased, and the early‐stage charged crude oil with low maturity and high force‐field strength preferentially accumulated in the Yijianfang Formation, while the late‐stage charged crude oil with high maturity and low force‐field strength preferentially accumulated in the Yingshan Formation. This study reveals the history and differences of petroleum accumulation in the Shunbei fault zones, which is significance for understanding the hydrocarbon distribution in ultra‐deep marine carbonate reservoirs. [ABSTRACT FROM AUTHOR]

The Indochina Block is considered as a part of the Indian and Australian margins of Gondwana, and the Tam Ky‐Phuoc Son Suture Zone (TPSZ) lies in its central region as the boundary between the Truong Son Belt and Kon Tum Massif (KTM). However, the early Palaeozoic tectonic nature and timing of magmatism within the TPSZ are still controversial. To tackle the issue, we present herein the zircon U–Pb ages with their trace‐element compositions of five dioritic–granitic granitoids in the TPSZ. U–Pb age dating of magmatic zircons from them suggests emplacement ages of ca. 447–450 Ma. Whole‐rock geochemistry of the samples shows low TiO2 contents (0.36–1.18 wt%) and Mg# (42.04–53.07). They display enrichment in light rare earth elements ([La/Yb]N = 4.10–15.19), pronounced negative Nb, Ta and Ti anomalies relative to the chondrite‐normalized rare earth element patterns and primitive mantle‐normalized trace‐element distribution diagrams. The whole‐rock geochemical characteristics together with zircon trace‐element compositions from the same samples revealed their petrogenesis of a continental arc tectonic setting. Combining the results from this study together with available data from the TPSZ and its neighbouring units, we suggest accretionary orogenesis was responsible for generation of the Ordovician magmatic arc in the KTM, which will provide better understanding of the Early Palaeozoic evolution of the eastern Indochina Block. [ABSTRACT FROM AUTHOR]

The Daniudi gas field in China's Ordos Basin is located in the transitional zone between palaeo‐topographic highs and slopes, whereby dissolution‐collapse breccias are widespread within the palaeokarstic reservoir. Abundant cores, well logs and thin sections were used to study palaeo‐topography, palaeokarstic breccia types, diagenesis and reservoir pore characteristics. The results indicated that reservoir quality is controlled by lithology, palaeo‐topography and diagenesis. The extent of palaeokarstic reservoir dissolution was shown to be determined by lithologic differences, whilst only gypsiferous dolostones and finely crystalline dolostones emerged in reservoir formation. Palaeo‐topography was also found to regulate reservoir development. The reservoirs are primarily located 20 m below the Ordovician unconformity in palaeo‐topographic hills and palaeo‐topographic slopes, whilst their depth is palaeo‐topography dependent. Lithology and palaeo‐topography also coordinate the distribution of palaeokarst breccia facies. Clast‐supported and matrix‐supported chaotic breccias were found in argillaceous dolostone strata. However, crackle–mosaic breccias occurred in gypsiferous dolostones and crystalline dolostones, located in palaeogeomorphic residual hills and slopes. Reservoirs generally develop in crackle–mosaic breccias of Ma51 and Ma52 sub‐Members, the quality of such reservoirs is dependent on the development and distribution of palaeokarst breccia facies and diagenesis. Dissolution of dolomite and anhydrite nodules was found to result in moldic pores and dissolution‐enlarged pores. Overall, the most damaging effect on reservoir quality resulted from calcite cement infilling moldic pores, enlarged pores and fractures. [ABSTRACT FROM AUTHOR]

A continuous record of abundant microspherules, pyrite framboids, and bacterial fossils is obtained from the Upper Ordovician in the Dawangou section of northern Tarim Basin, Northwest China. Chemical and physical characteristics of these microspherules were determined using a scanning electron microscope and an energy dispersive spectrometer. Microspherules were formed as a single spherule, spherule aggregates, and drop‐like particles. Physical morphology of the spherules has no relation to its formational process. Energy dispersive spectrometry results indicate that microspherules are mainly composed of Ca, C, O, Si, Al, S, Fe, and Ti. Thus, these microspherules are further categorized into 5 major types: iron, titaniferous‐iron, siliceous, calcareous, and organic microspherules. The first 3 types of microspherules are likely of volcanic origin rather than extraterrestrial origins (i.e., impact event or cosmic dusts) or modern industrial pollutions due to their morphologies and chemical compositions. Both calcimicrospherules and organic microspherules are biogenic, and they are distributed in the lower part of the studied section (Beds 4–6), in which cephalopods, brachiopods, and bacterial fossils are also commonly present and pyrite framboids are absent. These features generally point to an oxic condition. In contrast, other microspherules are abundant in the upper part of the section (Beds 9–13), in which tiny pyrite framboids (mean diameters 4.6–7.3 μm) are rather abundant and typical of euxinic to dysoxic conditions. Both microspherule and pyrite framboid evidences indicate that the northern Tarim region became oxygen‐poor conditions, which were coupled with intensive volcanic eruptions during the Late Ordovician. [ABSTRACT FROM AUTHOR]

The tectonic/stratigraphic interpretation of the Cambro–Ordovician rocks exposed in the south‐westernmost sectors of the Sardinia island (i.e., belonging to the Bithia Formation or Unit) is still a hot point of discussion. A debated question is also the age of the metavolcanics interbedded in these rocks. In order to provide a clear answer to this problem, in this paper, we provide new U–Pb zircon dating and a petrographic–geochemical comparison of metavolcanics interbedded within the Bithia Formation with similar Sardinian Ordovician calc‐alkaline rocks. The Bithia metavolcanics plot in the rhyodacite/rhyolite field. They show negative troughs for Nb and Ta, negative anomalies for Sr, P, and Ti, and positive peaks for Cs, Rb, K, Th, U, and Pb in the multielement diagram normalized to primitive mantle and significant LREE enrichment, marked negative Eu anomaly, and flat HREE patterns in the chondrite‐normalized REE diagram. Owing to these geochemical features, the Bithia metavolcanics plot in the volcanic arc and active continental margin fields closely resembling Middle‐Late Ordovician felsic metavolcanics from the Sarrabus, Gerrei, Goceano, and Mt. Grighini units. A new U–Pb zircon age of 462.1 ± 4.3 Ma yielded by a metavolcanic layer within the Bithia Formation at Capo Malfatano must be interpreted as the emplacement age. The CL and BSE images of zircon grains do not show any evidence of interaction with late hydrothermal fluids that could have caused Pb loss and rejuvenated ages, confirming the Middle‐Late Ordovician age of the metavolcanics. [ABSTRACT FROM AUTHOR]

The Upper Ordovician Xiazhen Formation, which crops out in Zhuzhai, near the Jiangshan–Changshan–Yushan region of southeast China, consists of a variety of carbonate–siliciclastic lithofacies representing a shallow‐water platform environment. A total of eleven stromatoporoid genera in two orders, comprising three clathrodictyid genera (Clathrodictyon, Ecclimadictyon, and Labyrinthodictyon) and eight labechiid genera (Cystostroma, Rosenella, Pseudostylodictyon, Aulacera, Stylostroma, Pachystylostroma, Labechia, and Labechiella), are recognized from 18 stratigraphic units representing a wide range of depositional environments in the formation. Clathrodictyon is the most abundant stromatoporoid genus, occupying a long stratigraphic range and a wide range of lithofacies. It also occurs as a major component of patch reefs throughout the formation. The labechiids, in contrast, are highly diverse but most genera have restricted stratigraphic distributions, occurring in a narrow range of depositional environments. The size and growth form of stromatoporoids in the formation are considered to be primarily intrinsic characteristics of each genus but in some cases also seem to be related to lithofacies: clathrodictyids exhibit a wide spectrum of growth forms and have broader ecological plasticity and more flexible growth strategies than do labechiids. The Late Ordovician stromatoporoids of the Xiazhen Formation exhibit close biogeographic affinities to those of central New South Wales and the Tasmanian shelf of Australia. The discovery herein of Labyrinthodictyon and Stylostroma from the Upper Ordovician of South China further supports this close relationship. The stromatoporoids from South China exhibited one of the highest diversities of all paleocontinents during the Late Ordovician, suggesting that South China, together with Australia, was a locus of Late Ordovician stromatoporoid diversification. [ABSTRACT FROM AUTHOR]

The distribution of conodonts and graptolites from the upper 13 m of the San Juan Formation and the first metre of the lower member of the Los Azules Formation, Los Gatos and Amarilla creeks, Cerro Viejo of Huaco, Central Precordillera from San Juan, Argentina, is studied. The conodonts from the top stratum of the San Juan Formation at the Los Gatos creek section correspond to the Lenodus variabilis Zone, whereas at the Amarilla creek section, they represent the Yangtzeplacognathus crassus Zone, verifying the diachronous top surface of the San Juan Formation. In the lower member of the Los Azules Formation, 81 conodont elements are recorded from bedding plane surfaces, where the presence of Paroistodus horridus horridus (Barnes & Poplawski) allows to recognize the Y. crassus Zone. On the basis of the graptolite and conodont association, we estimate that the top of the San Juan Formation at Los Gatos creek corresponds to the Levisograptus dentatus Zone, L. dentatus Subzone, whereas at the Amarilla creek, the Arienigraptus angulatus Subzone of the same zone is represented. The presence of the graptolite A. angulatus (Mu) in the lower member of the Los Azules Formation in both sections indicates the L. dentatus Zone (A. angulatus Subzone). The records of graptolites in limestones of the San Juan Formation and of abundant conodonts on bedding plane surfaces of the lower member of the Los Azules Formation are important, taking into account the type of facies where they occur. The conodont records in the referred type of preservation are scarce in the Ordovician, which allows for a more precise biostratigraphic correlation between conodont and graptolite biostratigraphy. [ABSTRACT FROM AUTHOR]

Graptolites and conodonts are frequent fossils in Sandbian (Late Ordovician) outcrops of the Argentine Precordillera, where they present continuous and abundant records that enable detailed biostratigraphic studies. This work deals with the integration of previously available information on early Sandbian graptolites and conodonts, together with new paleontological data from the Las Aguaditas Creek (middle and upper members of the Las Aguaditas Formation), Las Chacritas River (Las Aguaditas Formation), and Cerro La Chilca (Los Azules Formation) sections from the Central Precordillera of the San Juan Province. The presence of the key graptolite Nemagraptus gracilis and the associated graptolite taxa allow for the documentation of the N. gracilis Zone. Specimens of N. gracilis and key conodont species, such as Pygodus anserinus coexist, along with a rich conodont fauna including Baltoniodus variabilis, whose range straddles the boundary between the Pygodus anserinus and the Amorphognathus tvaerensis zones. Detailed biostratigraphic ranges of the rich graptolite and conodont associations documented in the three study areas are provided. These records and an accurate taxonomic review allow a thorough description of the recognized zones. The use of conodont and graptolite zones from different areas of the Precordillera enables the verification of a diachronous contact, representing a hiatus that spans the middle to upper Darriwilian. Moreover, a brief taxonomic description of the identified graptolite species is provided. [ABSTRACT FROM AUTHOR]

The Shuntuoguole region is situated at the center of the Tarim Basin, in NW China. It is bordered by the Tazhong Uplift to the west and the Manjiaer Depression to the east. Data obtained on samples collected from exploration wells highlight the large potential for gas discoveries in this region. Component and stable carbon isotopic analyses have been performed on gas samples from 5 wells in the Shuntuoguole region. The dryness coefficients of gas samples vary from 0.95 to 1.00, indicating that the gas samples belong to overmatured dry gas. The carbon isotopic values (δ13C) of all gas samples are heavier than −40‰, compared to the typical gas samples with different sources in the Tarim Basin, revealing that the gas in the Shuntuoguole region originated from source rocks in the Cambrian. The SN‐1 exploitation well was selected to undertake fluid inclusion studies revealing the mechanisms of natural gas charging and fluid evolution. Data from the SN‐1 well drill core indicate a 1,700‐ to 7,050‐m‐thick sedimentary sequence containing Ordovician to Tertiary strata. The Middle Ordovician Yijianfang Formation (Fm) constitutes one of the most important gas reservoirs. The Yijianfang Fm consists principally of limestone containing widely distributed sparry calcite. Numerous fluid inclusions are observed in calcite, and 4 types of fluid inclusions are recognized based on the observed phases and components. These are pure CH4 (P‐type), CH4‐bearing (C‐type), aqueous (W‐type), and solid‐bearing (S‐type) inclusions. The trapping temperatures and pressures, determined through the intersection of isochores from coeval fluid inclusions, reach 183 °C to 216 °C and 1,914 bars to 2,196 bars, respectively. When taking into account the regional burial history, we find the natural gas charged during the Neogene interval, from 20 Ma to 3 Ma. [ABSTRACT FROM AUTHOR]

Rapid expansion of shale gas development in China raises environmental and human health concerns. Several studies present related information on these concerns in the United States and Canada, yet they are few in China at present. This paper presents a series of original and published mineralogical and trace elements data from two gas shales (Niutitang shale and Longmaxi shale) considered as producing gas shale in China. Mineralogical and geochemical data surveyed can be applied to evaluate the potential environment pollutions during shale weathering and hydraulic fracturing. After compilations of the mineralogical and trace elements data, we can conclude that (a) there is generally more pyrite compared with carbonate for Niutitang shales, indicating that Niutitang shales are more prone to generate the hydrogen ions than Longmaxi shales; (b) many of the environmental hazardous trace elements considered here show an association with organic matter and/or pyrite, indicating that these trace elements are prone to mobilize and release during shale weathering and hydraulic fracturing; (c) some environmental hazardous elements like As, Ni, and Ba that have extremely high concentrations in some regions as compared with the screening limits for soil and drinking water should attract more attention; and (d) clay‐rich shale with abundant organic matter may be the most favourable shale gas reservoir for the Niutitang shale, especially for those shales in Lower Yangtze region. Moreover, more mineralogical and geochemical data will be required for a comprehensive environmental impacts assessment. [ABSTRACT FROM AUTHOR]

Binocalix dichotomus gen. et sp. nov. is the first British Ordovician aristocystitid diploporite to be named. It is known from a single holotype that is partly disarticulated and incomplete. Nevertheless, it differs from all previously described aristocystitids in having a pair of relatively large ambulacral facets developed above a smooth ambulacral platform and on a single circum‐oral plate. When densely developed, the diplopores become polygonal and have a central tubercle. They closely resemble those of the sphaeronitid subgenus Sphaeronites (Peritaphros), but all species of Sphaeronites s.l. have narrow ambulacral grooves ending in small facets. The similarities in the diplopores are thought to be convergent. Among aristocystitids, only "Calix" inornatus and Triamara are known to have paired ambulacral facets developed on single circum‐oral plates. The former differs from Binocalix in having a smooth thecal surface and flush ambulacral facets. Triamara has raised ambulacral facets but lacks the distinctive ambulacral platforms found in Binocalix. Its diplopores always lack central tubercles, and currently it is only known from the Silurian. [ABSTRACT FROM AUTHOR]

Abundant gas condensates have been proven in the Ordovician carbonate reservoirs in the Tazhong area, the centre of the Tarim Basin, where complicated geological evolution and multiple hydrocarbon accumulations have occurred. Property, geochemistry, and stable carbon isotopes of the Ordovician condensate are characterized to identify the oil and gas origins in the Tazhong area. Fluid inclusion data, combined with numerical modelling methods was used to determine petroleum accumulation processes. Our results suggest that oils are characterized by mixed sources, with 64% of contributions from the Middle‐Upper Ordovician (O2+3) source rocks and 36% of contributions from the Lower‐Middle Cambrian (Є1+2) source rocks. Gases are primarily generated from the thermal cracking of pre‐existing oils in the underlying strata, with a small amount derived from kerogen cracking accompanied with oil generation. Three petroleum filling stages are determined, including the filling of the Є1+2‐derived oils during the Late Hercynian period, filling of the O2+3‐derived oils during the Yanshan period and oil‐cracking‐gas charge during the Himalayan period. The accumulation processes and relative contribution ratios of the two source rocks vary among the reservoirs and are mainly related to the transport system. Due to the lack of faults in the regions away from the No. 1 Fault Belt, the Є1+2‐derived oils are difficult to fill into the Ordovician reservoirs through the gypsolyte, and thus the accumulated oils are mainly from the O2+3 source rocks. The percentage of the O2+3‐derived oils is high in the southeast and northwest segments of the No. 1 Fault Belt, but relatively low in the middle segment and the vicinity of the No. 10 Structure Belt. Likewise, the late gas charge intensity is controlled by regionally varying conduit systems. Gas condensate formed in reservoirs with high gas/oil ratios. Otherwise, light oil retains with respect to low gas/oil ratios. [ABSTRACT FROM AUTHOR]

The Lianglitage Formation (also named Lianglitag Formation) is an important hydrocarbon reservoir in the Tarim Basin; the reef and shoal facies of this formation have previously been extensively investigated. The paleokarst of the formation related to a tectonic unconformity at the top of the Ordovician (Tg5) has, however, not been widely investigated. In this paper, we undertake a comprehensive study of the paleokarst by an integrated analysis of seismic data, well‐logging data, and core data. Several geomorphologic units that formed at the end of the Ordovician period are identified, including a fault‐thrust uplift high, inter‐uplifts sag, uplift platform, and fault‐thrust anticline; these units are controlled by west–east and northwest–southeast striking faults. The thickness of erosion is estimated to be 200 to 700 meters. The paleokarst is characterized by large and small caves, dense vugs, and dissolution fractures. Large caves predominantly developed in exposed areas and on the slopes. Dense vugs and small caves, features that contribute to premium hydrocarbon reservoirs, are generally tens of meters away from the unconformity, whereas dissolution fractures, predominantly filled by mud and silts, are situated in close proximity to the unconformity and faults. Four karst zones can be identified from vertical profiles: weathered crust (1–2 m thick), vertical infiltration zone (tens of meters thick), phreatic zone (tens to hundreds of meters thick), and a bottom zone that is largely unaffected by karstification. The karst of the Lianglitage Formation at the end of the Ordovician was mainly controlled by tectonic movement, paleogeomorphology, lithofacies, faults, and fractures. The karstification process is summarized in a karst model. [ABSTRACT FROM AUTHOR]

The Shunnan area is a newly discovered hydrocarbon field in Shuntuoguole lower uplift, in which the host rocks are Lower–Middle Ordovician carbonates. The carbonate reservoirs are well affected by hydrothermal silicification with well‐preserved intercrystalline pore of replacement quartz and megaquartz cements. Based on the petrography, pore types, and diagenetic processes, this research evaluated the reservoir quality and re‐constructed the porosity evolution in different diagenetic stages. Samples are collected from 7‐cored wells distributed along NNE‐ or ENE‐trending sinistral strike‐slip faults. Nine types of lithofacies were identified in the study area, including mudstone, bioclast wackestone, peloidal bioclast packstone, boundstone, peloidal grainstone, ooid grainstone, slightly silicified limestone (silica less than 25%), strongly silicified limestone (silica around 50%), and chert. Chert has better porosity (average 21.3%) and permeability (average 44.7 mD) than other lithofacies. The main reservoir pores are mainly developed in forms of fractures, intercrystalline replacement quartz and dissolved vugs. The porosity evolution shows that the primary porosity was limited due to cementation and compaction, and the earlier secondary porosity was occlusive as a result of coarse calcite cementation. Therefore, the precursor limestones may be tight, and the reservoir quality of the Lower–Middle Ordovician carbonates was controlled by hydrothermal silicification. During the hydrothermal silicification event, the burial depth of the Lower–Middle Ordovician carbonates was more than 3,000 m and their stratum temperature was higher than 120°C, representing a deep burial condition. The statistical data of porosity‐depth/temperature trends for carbonates suggest that the early secondary pores would be significantly reduced when the burial temperature reaches 100°C (or depth of strata reaches 3,000 m). Therefore, the dissolved vugs in strongly silicified limestone or hydrothermal chert are caused by hydrothermal silicification and not inherited from precursor carbonate rocks. [ABSTRACT FROM AUTHOR]

The upper strata of the Santa Rosita and the Acoite formations (Lower Ordovician) exposed at Chulpíos Creek in the Santa Victoria study area of the Cordillera Oriental, NW Argentina, are analysed by means of conodont biostratigraphy. Four conodont zones are analysed for the referred formations, i.e. the Acodus apex, Acodus triangularis, Gothodus vetus and Gothodus andinus zones, on the basis of a collection with ca. 2800 conodont specimens that includes new conodont taxa. Acodus apex Albanesi and Zeballo, Acodus triangularis (Ding), Acodus zeballus n. sp., Gothodus andinus (Rao et al.), Gothodus vetus n. sp., and Paltodus cf. inaequalis (Pander) are described herein. The conodont genus Zentagnathus is diagnosed including two previously known species: Zentagnathus argentinensis (Rao et al.) and Zentagnathus primitivus (Voldman et al.). The Tetragraptus akzharensis and Baltograptus cf. deflexus graptolite zones were identified as well in the ∼1800-m-thick stratigraphic section. The incertae sedis Phosphannulus universalis Müller et al. is discussed for the Cordillera Oriental for the first time. The lower part of the Chulpíos section that involves the contact between the Santa Rosita and the Acoite formations is not able to be dated with precision either as upper Tremadocian or lower Floian because the ranges of the index taxa recorded in that interval of the study section span the stage boundary. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A total of 5,918 conodonts have been recovered from the upper Hulo Formation and the lower Yenwashan Formation in the Hengdu section, Jiangshan County, Zhejiang Province, south‐eastern China, spanning the interval from the middle Darriwilian to the early Sandbian. Thirty‐three species, belonging to 24 genera, have been identified with three biozones (i.e., the Dzikodus tablepointensis Biozone, the Histiodella kristinae Biozone, and the Pygodus anserinus Biozone) recognized in the region. Using multivariate analysis, the Periodon–Protopanderodus biofacies is recorded from the upper Hulo Formation, and the Periodon–Pygodus biofacies and the Protopanderodus–Baltoniodus biofacies are recorded from the lower Yenwashan Formation. The Periodon–Protopanderodus biofacies and the Periodon–Pygodus biofacies represent a deep‐water environment, such as the margin of the platform and/or slope environment, deeper than that of the Protopanderodus–Baltoniodus biofacies. [ABSTRACT FROM AUTHOR]

The Middle Ordovician Rosroe Formation consists of some 1350 m of coarse, mainly siliciclastic to volcaniclastic sedimentary rocks, deposited in a submarine fan environment, and is restricted to the southern limb of the South Mayo Trough, western Ireland. Discrete allochthonous blocks, reaching 5 m in size, are present in the formation at several localities. Conodonts recovered from these blocks, collected from two separate locations, are of late Early and mid Mid Ordovician age. The conodonts have high conodont-alteration indices (CAI 5) indicative of temperatures as high as 300o to max. 480 °C; some found in the Lough Nafooey area have abnormally high indices (CAI 6), which correspond to temperatures of about 360o to max. 550 °C. The oldest fauna is dominated by Periodon aff. aculeatus and characterized by Oepikodus evae typical of the Oepikodus evae Zone (Floian Stage; Stage Slices Fl2-3, Lower Ordovician). The younger conodont assemblage, characterized by Periodon macrodentatus associated with Oistodella pulchra, is referred to the P. macrodentatus conodont Biozone (lower Darriwilian; Stage Slices Dw1-2). The Rosroe conodont assemblages are of Laurentian affinity; comparable faunas are well known from several locations along the east to south-eastern platform margin of Laurentia and the Notre Dame subzone of central Newfoundland, Canada. The faunal composition from the limestone blocks suggests a shelf edge to slope (or fringing carbonate) setting. The faunal assemblages are coeval with, respectively, the Tourmakeady Formation (Floian-Dapingian) and Srah Formation (Darriwilian) in the Tourmakeady Volcanic Group in the eastern part of the South Mayo Trough and probably are derived from the same or similar laterally equivalent short-lived carbonate successions that accumulated at offshore 'peri-Laurentian' islands, close to and along the Laurentian margin. During collapse of the carbonate system in the late Mid Ordovician, the blocks were transported down a steep slope and into deep-water by debris flows, mixing with other rock types now found in the coarse polymict clastics of the Rosroe Formation. The faunas fill the stratigraphical 'gap' between the Lower Ordovician Lough Nafooey Volcanic Group and the upper Middle Ordovician Rosroe Formation in the South Mayo Trough and represent a brief interval conducive to carbonate accumulation in an otherwise siliciclastic- and volcaniclastic-dominated sedimentary environment. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

There are numerous K‐bentonites interlayered with black shales from the Late Ordovician‐Early Silurian that are widely distributed in South China. In this paper, we carried out mineralogical and geochemical investigations on K‐bentonite samples collected from 6 sections in South China. The petrological features of thin sections, X‐ray diffraction data, and major element results show that in addition to clay minerals, which are dominated by illite/smectite mixed layer and illite, the K‐bentonites also contain quartz, microcline, albite, pyrite, and zircon. Zircon U–Pb dating for two K‐bentonite beds (WXP‐BT2 and LBP‐BT1) by the LA‐ICP‐MS method yielded two weighted mean 206Pb/238U ages of 443.5 ± 1.9 and 440.4 ± 5.6 Ma, respectively. The concentrations of rare earth elements (REEs) range from 141.28 to 854.44 ppm, chondrite‐normalized REE patterns display a negative Eu anomaly and an enhanced enrichment in light REE. Samples plot in the fields of trachyte, trachyandesite, rhyodacite (dacite), and andesite in a plot of Nb/Y against Zr/TiO2 suggest that the K‐bentonites are most probably derived from felsic magmas with subalkaline to alkaline affinities. The discrimination diagrams (Y‐Nb, Y + Ta‐Rb, Y + Nb‐Rb) show that the tectonic setting of the source volcanoes ranges from a volcanic arc to within‐plate setting. The widely distributed bentonites suggest intensified volcanic ash eruptions in the early Late Ordovician, which released huge amounts of volcanic ash. The SO2 emission and the weathering of the volcanic ashes probably resulted in global climate cooling and indirectly caused the Hirnantian glaciation and the mass extinction at the end of the Ordovician Period. [ABSTRACT FROM AUTHOR]

Richly fossiliferous Hirnantian shelly strata of near‐shore facies in northern Guizhou, South China, known as the Kuanyinchiao Formation, superbly record glacioeustatic sea‐level fluctuations and benthic faunal turnover. Recent studies of the temporal and spatial distribution of these carbonates and shelly fossils permit a critical stratigraphic revision and establishment of a robust regional stratigraphic correlation. The formation is revised to include three informal subdivisions, that is, units A, B, and C, in ascending order. Unit B of the formation typically is dominated by peloidal or oolitic grainstones, and unit C is composed of skeletal wackestone and calcareous mudstone, both units sharing distinctive coral and brachiopod faunas. This contrasts sharply with unit A of the formation, consisting of mudstone, silty mudstone, or calcareous mudstone, that yields the cool‐water Hirnantia fauna and associated coral fauna. In view of the presence of carbonate ooids and peloids, rugose corals, and a distinctive brachiopod assemblage, all indicative of warm‐water conditions, unit B, as well as unit C yielding the same shelly fauna, is interpreted as representing postglacial sedimentation immediately following the major Hirnantian glaciation, thus marking a significant climatic shift. Similar warm‐water carbonate rocks have been recognized in a number of regions along the margin of the Qianzhong Oldland, including Bijie, Renhuai, Tongzi, and Fenggang of northern Guizhou. Such a vast distribution area of these rocks indicates that postglacial carbonates are more widespread on the Yangtze Platform of South China than previously thought, providing a rare window into rocks and fossils of the survival interval immediately following the extinction event associated with the Hirnantian glacial episodes. [ABSTRACT FROM AUTHOR]

A large sample of coronates (over 90 specimens) from a narrow horizon in the Upper Ordovician, Sholeshook Limestone, at Talfan Farm, Llanddowror, South Wales allows assessment of variation and growth in a population of these rare Palaeozoic echinoderms. Variation is extensive and we synonymize two previously described species. This occurrence extends the stratigraphic range of Cupulocorona rugosa Donovan and Paul down to Cautleyan, Zone 2. Internal moulds reveal new morphological features, especially of the coronal canals. The flattened blade-like and kite-shaped portions support the idea that the coronal canals functioned in respiratory gas exchange by increasing the surface area. We suggest that internal currents flowed up the inner (adoral) canal and down the outer (aboral) canal. Quantitative estimates of flow rate suggest that a volume of coelomic fluid equivalent to the entire body cavity could be flushed through the coronal canals in 10 seconds at most. These coronates probably lived attached by a relatively long stem with a simple, conical holdfast and bent over in gentle currents. They seem to have been characteristic of relatively high-energy environments and are not generally distributed in the Sholeshook Limestone of South Wales. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

New articulated specimens of the British Ordovician cystoid first mentioned under the name ' Hemicosmites rugatus Forbes' in 1848 allow its morphology and systematic affinities to be established for the first time. Despite being based on isolated plates, ' H. rugatus Forbes' has been reported from England and Wales, Belgium, France, Spain and Thailand, and has been attributed to four genera. It is characterized by a heteromorphic, circular stem, a theca with four basal, six infra-lateral and eight lateral plates, all with sharp-crested ridges running to plate angles, multiple arms in each ambulacrum and an extensive tegmen. These characters indicate it belongs in the family Caryocrinitidae and genus Caryocrinites. Caryocrinites rugatus had arms with lateral brachioles that folded in against the main arm axis, as in the type species C. ornatus Say. It is the first Ordovician species known to possess this character. Isolated plates show sorting and a few may represent other species of Caryocrinites s.l. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Pelmatozoans diversified primarily during the Middle and Late Ordovician Period, with Early Ordovician records being much more limited, resulting in many gaps in our knowledge of the early stages of their diversification. Dissociated pelmatozoan ossicles have been found abundantly in one section in the Tonggao Formation ( Tetragraptus approximatus Biozone, Floian, Early Ordovician). Most of the ossicles are thecal plates and stem ossicles from hemicosmitoid and glyptocystitoid cystoids. Thecal plates of ' Cheirocrinus' sp., Polycosmites sp., and other plates of uncertain affinity are described. A different ossicle type, Pentagonopentagonalis (col.), may represent crinoid remains; this would be one of the earliest occurrences of the class. The thecal ossicles and columnals are all considered, as both sets of data are desirable to determine the most complete estimate of generic diversity. The echinoderm ossicles may have been transported in from shallower water palaeoenvironments and clusters of ossicles may represent coprolites or regurgitates. Estimates of Early Ordovician palaeogeography that place this site at 30°S or near the palaeoequator are supported by the physiological requirements of the primitive echinoderms described herein. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Buqingshan Tectonic Mélange Belt in the south margin of the East Kunlun Orogen, located in west section of Buqingshan-A'nyemaqen Suture Zone, is one of the key areas to understand continental tectonics and continental dynamics of China. This paper reports zircon U-Pb dating results and geochemistry of the Manite granodiorite (rock mass) in the Buqingshan Tectonic Mélange Belt. Zircons from the granodiorite show oscillatory zoning structures and relatively high Th/U ratios, indicating that they are magmatic zircons. Zircon LA-ICP-MS U-Pb dating for the Manite granodiorite yields ages of 487 ± 11 Ma (MSWD = 2.3) and 479 ± 2 Ma (MSWD = 0.56), implying that the Manite granodiorite were formed in the Late Cambrian to Early Ordovician. Geochemical analyses show that the rocks have high contents of SiO2 (66.06 wt.%-68.60 wt.%) and Al2O3 (14.84 wt.%-16.54 wt.%), and low alkaline (6.17 wt.%-7.43 wt.%), belonging to the middle-K calc-alkaline series. The A/CNK (Al2O3 /(CaO + Na2O + K2O)) ratios are 1.02-1.15, indicating that the granodiorite is weakly peraluminous. The contents of rare earth elements (REEs) are lower (89.64-130.41 ppm), with weakly negative to weakly positive Eu anomalies ( δEu = 0.83-1.12). The primitive mantle-normalized trace elements are characterized by evidently negative anomalies of Nb, Ta, P, Hf, Ti, etc., and positive anomalies of Th, La, Nd, Zr, Eu, etc. Moreover, the rocks show features of typical I-type granite. This leads us to conclude that the Manite granodiorites is derived from the partial melting of crust and formed in an island-arc environment. Combined with previous studies, we believe that the subduction of the Proto-Tethyan Ocean in the Buqingshan area was ongoing during 487 to 479 Ma and formed island-arc-type granites represented by the Late Cambrian to Early Ordovician Manite granodiorite. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]