We investigated Permian strata in the Ota area of the Kosado Hills, Sado Island, central Japan, and their depositional ages were determined based on radiolarian biostratigraphy and zircon U–Pb ...dating. We also focused on the geology of the region and its lithologic correlation with other geological units in the Inner Zone of Southwest Japan. The radiolarian analysis identified the presence of Follicucullus porrectus and F. dilatatus in mudstone exposed on the coastline of Ota, indicating a middle–late Capitanian to early Changhsingian age. Mudstone exposed along the forest road in the Ota area contained Cariver charveti, suggesting a late Capitanian–early Changhsingian age. Zircon U–Pb dating of the tuff layer intercalated within the Follicucullus-bearing mudstone yielded a weighted-mean age of 259.9 ± 2.0 Ma, corresponding to a Capitanian–Wuchiapingian age. The tuffaceous sandstone interbedded with mudstone containing C. charveti yielded a weighted-mean age of 264.1 ± 6.3 Ma, which covers the Roadian to Wuchiapingian ages. The youngest model peak age (256.6 ± 2.6 Ma; Wuchiapingian) provides the most reliable estimate of the maximum depositional age. The Paleozoic strata in the Kosado Hills have previously been correlated with the Ultra-Tamba and Maizuru belts in Southwest Japan based on fossil occurrences. Our findings indicate that the Permian rocks in the Kosado Hills exhibit differences in lithology from those in the Ultra-Tamba belt but share similarities with the upper Guadalupian–Lopingian strata in the Maizuru belt.
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•Microfossils constrained the Alaunian-Sevatian boundary in the Baoshan terrane.•A positive correlation between δ13Ccarb and δ18Ocarb values was due to diagenesis.•The CIEs of the ...δ13Corg record can be used for global correlation.•The eruption of Angayucham flood basalts may has disrupted Norian carbon cycles.
The biostratigraphy and carbon stable isotopes of the Norian Stage (Upper Triassic) are well studied in the western Tethys, but little information is available from the eastern Tethys. Therefore, we studied the Hongyan-B (HYB) section in the Baoshan terrane, western Yunnan Province, SW China, which was located in the eastern Tethys during the Late Triassic. The HYB section was investigated for conodonts, radiolarians, total organic carbon, carbonate carbon and oxygen stable isotopes (δ13Ccarb and δ18Ocarb), and carbon isotopes of organic matter (δ13Corg). The Mockina slovakensis and Mockina bidentata conodont biozones proposed in the HYB section are associated with two radiolarian zones of the Sevatian substage, the Praemesosaturnalis multidentatus and Praemesosaturnalis pseudokahleri zones (TR8A and TR8B Sugiyama zones). This biostratigraphy places the Alaunian-Sevatian substage boundary (middle-upper Norian) at meter 23 of the HYB section. Unfortunately, the δ13Ccarb and δ18Ocarb values suggest that they might have been influenced by diagenesis. However, the δ13Corg record preserves multiple carbon-isotope excursions across the Alaunian-Sevatian boundary that can be correlated with other coeval global sections. The carbon-isotope excursions registered at this middle-upper Norian boundary are perhaps related to the major outgassing of light carbon during the emplacement of Angayucham flood basalts.
•Recognition of the transition from chert to siliceous mudstone in Zedong siliceous mélange.•Geochemical results show biogenic origin and an increase of terrestrial inputs during sedimentation.•The ...earliest accretion time of the Zedong siliceous mélange has been determined for the first time.•This study indicates complex subduction and accretion systems along the Neo-Tethys.
Widely distributed siliceous mélanges in the Yarlung-Tsangpo suture zone preserve significant information of the Neo-Tethys and subduction-accretion processes. Similar ophiolites and siliceous mélanges are well exposed in the Xigaze and Zedong areas, however, their relationship including age assignments, depositional environments, and accretionary process remains vague. Based on radiolarian biostratigraphy (56 species belonging to 35 genera), black cherts from the Carnian to the Norian (Late Triassic), red cherts from the Aalenian to Bathonian (Middle Jurassic), and siliceous mudstones of the Berriasian (Early Cretaceous) are distinguished from siliceous mélange in the Zedong area. Values of Al/(Al + Fe + Mn) indicate that the siliceous rocks are biogenic silica derived. The diagrams of Al2O3/(Al2O3 + Fe2O3) vs Fe2O3/TiO2 and Al2O3/(Al2O3 + Fe2O3) vs LaN/CeN indicate siliceous rocks were deposited far from the ridge. Weak positive Ce anomaly and low ratio of LaN/CeN indicate that siliceous rocks were deposited in a deep-sea basin proximal to terrigenous sources. Comprehensive summary of studies on Bainang siliceous mélange, Xigaze ophiolite, Zedong ophiolite, and Zedong siliceous mélange reconstructs the Ocean Plate Stratigraphy (OPS) and the evolution of the Neo-Tethys since the Late Triassic till the Early Cretaceous. Mélanges in Xigaze and Zedong were formed in different intra–oceanic subduction-accretion systems at different times in the Neo-Tethys Ocean during the Cretaceous.
Radiolarians are planktonic protozoon that play an important role in marine ecosystem and paleoenvironmental construction. The South China Sea (SCS) and Malacca Strait (MLS), strongly influenced by ...the East Asian monsoon, are the key gateway between the Pacific and Indian Oceans. However, few studies of radiolarians in the water column are performed during winter and spring in the SCS and MLS due to the adverse sea conditions. In this study the use of a ship-board plankton net rendered it possible to obtain shallow water samples (~5 m depth) along transects from the northern SCS to MLS during the spring of 2017 and winter of 2017–2018. The results show that partitioning among Spumellaria, Nassellaria and Collodaria radiolarians differed spatially and seasonally. The high partition of Collodaria and low partition of Nassellaria are potential indicators of the strongly stratified waters with low nutrients for paleoceanographic studies in the slope and basin SCS. The radiolarian assemblages in the MLS are quite different from those in the SCS, that is, the two communities are largely independent, suggesting that advective transport between the MLS and SCS is rare. There are obvious seasonal variations in species diversity and abundance in both the MLS and SCS, generally with higher biodiversity and maximum abundances in winter. The results of Q-mode cluster analysis showed that radiolarian assemblages during winter were grouped together in the slope and basin SCS, and their distributions had moved to the southwest relative to those in spring. The results demonstrate the East Asian monsoon has a significant controlling effect on radiolarian diversity and geographic distribution in the studied areas. We also established five candidates for weakly stratified waters with high nutrients: Archiperidium hexacantha, Acanthodesmia vinculatus, Peromelissa phalacra, Dictyocoryne muelleri, and Tetrapyle octacantha. Thus, this study increases the knowledge of radiolarian geographic distribution in the tropics as a whole, as well as revealing the sensitive response of radiolarians to the regional environments, a fact which may prove useful for reconstructing the paleoceanographic changes.
•Increasing the new knowledge of radiolarian diversity along a transect from the northern SCS to MLS.•Revealing the biogeographic distribution pattern of polycystine radiolarians and their seasonal changes (spring and winter).•Highlighting the obvious significance of East Asian monsoon on radiolarian diversity and flux.•Establishing some potential indicators of the weakly stratified and high-nutrient waters for paleoceanographic studies.
Forty-six species of radiolarians recovered from the Upper Cretaceous Smoking Hills and Mason River formations in the Northwest Territories represent the first assemblage of this age from mainland ...Arctic Canada. Four interval zones and two subzones, calibrated to radiometric ages, are proposed based on the lowest and highest occurrence of index radiolarian species. These are 1) the Santonian/early Campanian Kuppelella aff. cayeuxi Zone, 2) the middle Campanian Diacanthocapsa aff. rotunda Zone (subdivided into the Kreuzstella vierkantiga and Lithostrobus borealis subzones), 3) the late Campanian Canadasphaera inuita Zone, and 4) the early Maastrichtian Stichomitra cf. communis-Xitus sp. B Zone. Integration of these radiolarian biozones with previously reported diatom, silicoflagellate, palynological and foraminiferal biozones and new radiometric ages indicate a middle Coniacian-middle Campanian age for the Smoking Hills Formation and a middle Campanian-late Maastrichtian (probably Paleocene) age for the Mason River Formation. The radiolarian assemblages reported here resemble those of the North Slope of Alaska and western Siberia, allowing for biostratigraphic correlations within the Arctic Realm.
•Highly diverse Cretaceous radiolarian assemblage recovered from the Canadian Arctic.•Four radiolarian biozones identified, spanning Santonian to lower Maastrichtian.•Age refined using correlation with siliceous microfossils and radiometric dating.•Potential for an Upper Cretaceous radiolarian biozonation in the Arctic Realm.
•Adsorption of radiolarian-rich shale is greater than non-radiolarian shale.•Interaction between methane and organic matter surrounding radiolarians is strong.•Trimethylsilane formed in the ...radiolarian-rich shale is conducive to adsorption.•Abundant radiolarian fossils are significant indicators for shale gas enrichment.
Understanding the methane adsorption mechanism in shale, especially for shale with abundant microfossils, is significant for guiding the exploration and development of shale gas. In this study, two groups of organic-rich shale samples derived from the Wufeng-Lungmachi formations were selected for methane adsorption experiments: one core sample contains abundant radiolarian fossils, while the other core sample does not contain any radiolarian fossils. Through a series of calculations and comparisons of thermodynamic studies between radiolarian-rich shale and non-radiolarian shale, the results show that the absolute adsorption of methane in radiolarian-rich shale is greater than the absolute adsorption of methane in non-radiolarian shale at the same pressure and temperature. In addition, the difference in the thermodynamic parameters such as the isosteric heat of adsorption (Qst), enthalpy change (ΔH), standard entropy change (ΔS0) and Gibbs free energy change (ΔG) between radiolarian-rich shale and non-radiolarian shale indicates that the interaction between radiolarian-rich shale and methane molecules is strong, and that radiolarian-rich shale is likely to have more adsorbed methane than non-radiolarian shale under similar geological conditions. Two plausible explanations are proposed to explain the methane adsorption mechanisms in radiolarian-rich shale. On the one hand, the biological pores developed in radiolarian fossils provide some adsorption sites for methane molecules. On the other hand, the amorphous silica in the radiolarian fossils can combine with organic molecules to form a new functional group called trimethylsilane, which possesses a hydrophobic character. The organic-inorganic pore surface provides a new perspective for interpreting methane adsorption mechanisms in shale.
•First detection of ophiolite components in a Hallstatt mélange in the eastern Alps.•Mélange analysis and reconstruction of the middle-late Jurassic geodynamic history.•Middle Jurassic ophiolite ...obduction in the eastern Alps.•Example of a deep-water trench-like basin fill.•Evaluation of how many triassic-jurassic oceans in the western Tethys realm.
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The Northern Calcareous Alps in the Western Tethys realm were affected in Middle to Late Jurassic times by a mountain building process triggered by ophiolite obduction similar to that in the Inner Western Carpathians or Inner Dinarides. In contrast to these other mountain ranges, in the Northern Calcareous Alps the obducted ophiolites or ophiolite derived components in the Bathonian-Oxfordian mélanges are missing. Cr-spinels in Kimmeridgian basinal deposits are the oldest known relics of a Jurassic ophiolite obduction. This study reveals new data from a newly detected Hallstatt Mélange below the Late Jurassic Plassen Platform in the southeastern Northern Calcareous Alps (Raucherschober/Schafkogel area). Upper Triassic Hallstatt Limestone blocks from the former distal northwestern continental margin of the Neo-Tethys Ocean, as well as ophiolite and radiolarite blocks from the Neo-Tethys Ocean floor rest within an upper Middle to lower Upper Jurassic radiolaritic-argillaceous matrix. Ophiolitic blocks show calc-alkaline volcanic arc affinity, defining the rocks as the product of intra-oceanic subduction and the formation of an early arc during stacking of the oceanic crust. Resedimented ribbon radiolarite blocks deposited above the newly formed suprasubduction (SSZ) ophiolites in the Neo-Tethys Ocean east of the island arc have a Middle Jurassic age. Later, at a time of decreasing tectonic activity, the Hallstatt Mélange was sealed by the Kimmeridgian-Tithonian Plassen Carbonate Platform, showing a shallowing-upward trend.
Radiolarian-bearing cherts are widely exposed in the volcanic-sedimentary sequences associated with the Purang ophiolitic mélange in the western segment of the Yarlung Tsangpo suture zone. Highly ...diverse and well preserved Lower Cretaceous (Valanginian–Hauterivian) radiolarian assemblages that correlate to the Cecrops septemporatus Zone occur in bedded cherts in the Peiersanggangmu section of the southern Purang ophiolitic mélange. Fifty-five species belonging to 38 genera, including characteristic species: Archaeodictyomitra apiarium (Rüst), Cecrops septemporatus (Parona), Hemicryptocapsa capita Tan, Pseudodictyomitra carpatica (Lozyniak), and Svinitzium pseudopuga Dumitrica, have been recognized.
Geochemistry of the cherts reveals high SiO2 contents (average: 92.23 wt%), Al/(Al + Fe + Mn) ratios, and low LaN/CeN ratios. Post Archean Australian Shale (PAAS) normalized rare earth element (REE) abundance patterns exhibit moderately positive Ce anomalies (mean Ce/Ce* =1.35) with relative enrichment in light rare earth elements (LREEs). These features are indicative of deposition in an oceanic basin close to a continental margin environment. Lithological characteristics and geochemical results suggest that the paleogeographical location for these radiolarian-bearing bedded cherts closely matches northern regions of the Indian continent, where existed enhanced upwelling activity and surface mixing resulting from monsoon activities.
•Well-preserved Early Cretaceous Cecrops septemporatus Zone radiolarians were recovered.•The geochemistry of the cherts reveals an oceanic basin near a continental margin environment.•Accumulation of bedded cherts was likely affected by monsoon-driven upwelling activity.
