Well-preserved and diverse radiolarian assemblages were recovered from a continuous 95 m-thick Lower Jurassic succession of grey siliceous limestone and marl on Mount Rettenstein (Northern Calcareous ...Alps, Austria). A total of seven radiolarian samples across the Late Sinemurian–Early Pliensbachian boundary were studied – five samples were assigned to the Upper Sinemurian and two samples to the Lower Pliensbachian. In total, 188 radiolarian species have been identified. In this article, we present 90 species and 33 genera belonging to the order Nassellaria. One genus and five species are described as new: Katroma hasta Cifer nov. sp., Tipiforma missoniae Cifer nov. gen. nov. sp., Trexus rotundus Cifer nov. sp., Wrangellium mediterraneum Cifer nov. sp., and Zhamoidellum spinosum Cifer nov. sp. In the Sinemurian, the most abundant nassellarian genera are Droltus, Parahsuum and Saitoum. The Pliensbachian yields an entirely different nassellarian assemblage dominated by the genera Zhamoidellum and Lantus. Compiled stratigraphic and geographic ranges as well as a synonymy, descriptions and remarks are provided.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The Nain and Ashin ophiolites consist of Mesozoic mélange units that were emplaced in the Late Cretaceous onto the continental basement of the Central-East Iran microcontinent (CEIM). They largely ...consist of serpentinized peridotites slices; nonetheless, minor tectonic slices of sheeted dykes and pillow lavas - locally stratigraphically associated with radiolarian cherts - can be found in these ophiolitic mélanges. Based on their whole rock geochemistry and mineral chemistry, these rocks can be divided into two geochemical groups. The sheeted dykes and most of the pillow lavas show island arc tholeiitic (IAT) affinity, whereas a few pillow lavas from the Nain ophiolites show calc-alkaline (CA) affinity. Petrogenetic modeling based on trace elements composition indicates that both IAT and CA rocks derived from partial melting of depleted mantle sources that underwent enrichment in subduction-derived components prior to melting. Petrogenetic modeling shows that these components were represented by pure aqueous fluids, or sediment melts, or a combination of both, suggesting that the studied rocks were formed in an arc-forearc tectonic setting. Our new biostratigraphic data indicate this arc-forearc setting was active in the Early Cretaceous. Previous tectonic interpretations suggested that the Nain ophiolites formed, in a Late Cretaceous backarc basin located in the south of the CEIM (the so-called Nain-Baft basin). However, recent studies showed that the CEIM underwent a counter-clockwise rotation in the Cenozoic, which displaced the Nain and Ashin ophiolites in their present day position from an original northeastward location. This evidence combined with our new data and a comparison of the chemical features of volcanic rocks from different ophiolites around the CEIM allow us to suggest that the Nain-Ashin volcanic rocks and dykes were formed in a volcanic arc that developed on the northern margin of the CEIM during the Early Cretaceous in association with the subduction, below the CEIM, of a Neo-Tethys oceanic branch that was existing between the CEIM and the southern margin of Eurasia. As a major conclusion of this paper, a new geodynamic model for the Cretaceous evolution of the CEIM and surrounding Neo-Tethyan oceanic basins is proposed.
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•The volcanic rocks of the Nain-Ashin ophiolites are Early Cretaceous in age.•These rocks and related sheeted dykes were formed in a volcanic arc-forearc setting.•The Nain-Ashin ophiolites formed between the Central-East Iran plate and Eurasia.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Cherty limestones, marls and radiolarites are widespread in the Hallstatt Mélange of the Northern Calcareous Alps. The mélange was formed during the Neotethyan orogeny in a series of deep-water ...basins that progressively developed in front of the advancing nappe front. The low thermal overprint of these rocks favors the good preservation of radiolarians (polycystines) that have been used for dating and reconstructing the Jurassic tectonostratigraphy of the area. This paper describes rich Middle—Late Jurassic radiolarian faunas from four localities in the Hallstatt Mélange near Bad Mitterndorf in Austria. Two different successions, both spanning from the Bathonian to the Oxfordian, are dated. In the first succession, the radiolarites are intercalated between or occur as matrix in mass-flow deposits originating from the accretionary wedge. The second succession is nearly 100m thick but is devoid of mass-flow deposits and documents a continuous radiolarite deposition in greater distance from the nappe stack. Both successions are ascribed to the Sandlingalm Basin, which evolved on a relatively distal continental margin during early stages of the orogeny. The highly diverse and well-preserved radiolarian assemblages have been used for a detailed taxonomic study. Two new families are described: Minocapsidae n. fam. and Xitomitridae n. fam.; six new genera are described Doliocapsa n. gen., Crococapsa n. gen., Parvimitrella n. gen., Xitomitra n. gen., Campanomitra n. gen., and Mizukidella n. gen. In addition, one new replacement name, Takemuraella (pro Triversus), is introduced, the diagnoses of 6 genera are emended, and two new species are described: Hemicryptocapsa nonaginta n. sp. and Mizukidella mokaensis n. sp.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The radiolaritic facies (red/green cherts with radiolarians) is a very characteristic feature of the Tethyan realm. For a long time, its presence has been interpreted as a consequence of depth of an ...oceanic environment. It is now preferable to consider it as high productivity sediment. We here underline the interpretation inferring the role of monsoons for such productivity according to the relative position of lands at that time.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Bąk et al. (2018) presented a model of global palaeoclimatic changes during the Bajocian–Oxfordian based on an analysis of millimetre-thick microlaminae in the radiolarian-bearing deposits of the ...Fatricum Domain exposed in the Filipka Valley in the Tatra Mountains, southern Poland. The authors claim that changes in microfacies and microfossil assemblages recorded in such microlaminae are a proxy for climatic changes and for decadal- to millennial-scale fluctuations of nutrient level in the upper water column. Major shortcomings of this study include: (1) a sparse and poorly documented field database; (2) ignoring of the potential effects of sediment bioturbation; (3) over-interpretation of radiolarian abundances and incorrect taxonomical determination of some microfossils; (4) imprecise stratigraphic framework, unsuitable for a high-resolution modelling of oceanic circulation and climatic changes; (5) improperly calculated duration of hypothetical cycles with a formidably high resolution; and (6) non-objective selecting of references. This comment is a cautionary warning against an uncritical use of the model presented in the disputed paper.
•The model of Bajocian–Oxfordian marine productivity cycles driven by climatic changes by Bąk et al. (2018) cannot be accepted•The database for this model is insufficient and poorly documented•The purported ‘microlamination’ and ‘cycles’ ignored bioturbation•Authors over-interpreted abundance of radiolaria and misidentified some microfossils•Authors used imprecise stratigraphic framework, unsuitable for a high-resolution modelling of palaeoenvironment
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
One of the best preserved Early Pliensbachian radiolarian assemblages from the Western Tethys is described from the grey marly limestone exposed at Mount Rettenstein in the Northern Calcareous Alps, ...south of the Dachstein Massif. Fourty-five genera and 71 species are documented and illustrated here. Four species are newly described: Tozerium filzmoosense Cifer sp. nov., Loupanus pliensbachicus Cifer sp. nov., Thurstonia? robusta Cifer sp. nov., and Ares rettensteinensis Cifer sp. nov. Radiolarian age is in accordance with ammonoid data from the overlying red marly limestone, which was assigned to the upper part of the Lower Pliensbachian. The best equivalent for the radiolarian-bearing lithology is the Dürrnberg Formation, characteristic of the open-marine Hallstatt facies zone. Previously published radiolarian data from the Dürrnberg Formation were re-evaluated and the originally proposed age assignments revised. At two localities, the published Hettangian–Sinemurian age was emended to the early Early Pliensbachian that is in accordance with the age of radiolarians from Mount Rettenstein. We compared the studied fauna from Mount Rettenstein also with two other rich radiolarian assemblages, one from another locality in the Dürrnberg Formation and one from the Gümüslü Allochthon in Turkey, which were assigned to the late Early Pliensbachian and are somewhat younger than the assemblages studied herein.
A bulk carbon-isotope stratigraphy, based on high-resolution sampling of five stratigraphic ammonite-dated sections from pelagic swells of the Subbetic basin (External Zones of the Betic Cordillera, ...southern Spain) is presented. The studied sections are characterized by Callovian–Oxfordian stratigraphic successions located in the South Iberian palaeomargin, a key area connecting the Central Atlantic to the Tethys oceans. The rocks are mainly nodular limestones with common extreme condensation (rosso ammonitico facies). Discontinuities with hiatuses of variable duration, submarine “hardgrounds”, Fe-Mn ooids, limonite crusts, and neptunian dykes are observed around the Callovian/Oxfordian boundary. The stratigraphic record, although very time-averaged, allows for a consistent and accurate ammonite chronostratigraphy. The carbon isotopes of marine carbonates show a marked trend towards high δ13C values from Lower Oxfordian to the Middle Oxfordian (~4.3‰, near the Plicatilis/Transversarium boundary). The isotopic values stand between 2.7 and 3.0‰ at the Upper Oxfordian (Bifurcatus and Hypselum Zones) and lowermost Kimmeridgian (Bimammatum Zone); afterward δ13C values decrease and reach a relative minimum (~2.3–2.5‰) in the Lower Kimmeridgian (Bimammatum/Planula boundary). Finally, isotopic values increase again (~2.6–2.7‰) in the lower Kimmeridgian (mid part of the Planula Zone). Comparison of carbon-isotope stratigraphy between Subbetic and other Tethyan areas shows similar trends. The replacement of thin-shelled bivalves by planktonic foraminifers and radiolarians that took place in the Callovian/Oxfordian boundary can be associated to the widening of the trans-Pangaean seaway. This, in turn, triggered the global warming which increased nutrients concentration in upper water column due to intensified nutrient input by river plumes. These phenomena are concomitant with the major Oxfordian δ13C positive excursion and with a transgressive cycle.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Mesozoic radiolarian biochronologic scales have been developed since the 1970s and most of them reached their present day status in the 1990s. The degree of temporal resolution, on average, ...corresponds to substage level and is sufficient to provide a meaningful framework for general geological studies. The great majority of zonal schemes were elaborated in low-latitude sections but are applicable in high latitudes as well because an adequate number of species occur worldwide. This paper presents a short historical review and a synthesis of currently used zonations developed in North America, Europe and Asia. The advantages and the shortcomings of the existing zonations are discussed. As a general rule, the zonations including a high number of taxa in each zone have a much greater applicability for global correlations than those defined exclusively with marker taxa. In the forthcoming years, particular studies will focus on zonal division of under-explored time intervals and on improved calibration to chronostratigraphy. Two joint objectives for future research are briefly introduced. The first objective, achievable in a relatively short time, is to compile a composite Mesozoic zonation that would provide a single reference standard for radiolarian dating at a global scale. The second objective is to refine the radiolarian zonal schemes, which, in certain intervals, have already attained the resolution comparable to that of the standard ammonite zones. To increase the degree of precision and accuracy to this level through the entire Mesozoic is a long-term goal that requires additional high-resolution sampling and emphasis on detailed documentation of evolutionary first and last appearances in different phylogenetic lineages.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This work aims to unveil the origin, geodynamic significance, and diagenetic history of pyroclastites and associated chert documented within the Upper Anisian volcano‐sedimentary succession of the ...Ivanščica Mt. in Central Europe. An abundance of pyroclastic material points to polyphase volcanic activity and deep‐water sedimentation along the rim of an oceanic realm. Radiolarian‐based dating revealed Illyrian age of chert intercalated with pyroclastites. The latter are largely vitro‐crystalloclastic and were emplaced as airborne tuff. The crystalloclasts of sanidine, plagioclase, altered pyroxene, and amphibole are principal tuff constituents merged in the altered glassy matrix consisted of palagonite, clay minerals, and calcite. Variations in alteration assemblages reflect an extensive in situ eogenesis in an open hydrologic system that gradually evolved toward a restricted fluid percolation environment. Mineralogy, chemistry, and occurrence of andesitic tuff clearly denote an explosive volcanic activity formed at the top of suprasubduction zone. Such scenario presumes a complex genesis outlined in following steps: (a) partial melting and dehydration of down‐going Palaeotethyan slab which gave rise to the subduction‐related magmatism {LILE, Th, and LREE (La/Lu)cn = 6.51−9.42 enrichment; negative anomalies of Nb‐Ta, P, and Ti e.g., (Nb/La)n = 0.31−0.44}; (b) magma contamination via interaction with continental crust during magma uplift along tectonically weakened zones of upper crust positive Pb spikes, negative εNd (−4.18 to −4.44), and 147Sm/144Nd ≤ 0.113175. This is in favour of geodynamic evolution that hypothesizes the existence of an active, ensialic, and mature volcanic arc developed along the southern active continental margins of Euramerica (Laurussia) during Late Anisian subduction of Palaeotethyan lithosphere.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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