Late Jurassic and Early Cretaceous Radiolarians from Zhilong,Gyangse,Tibet

Abundant well-preserved Late Jurassic-Early Cretaceous radiolarian fossils were extracted from 31 bedded green chert samples collected from Zhilong section,Gyangse,southern Tibet.This

New Discovery of Radiolarians in the Pomulong Mélange, Middle part of the Yarlung Zangbo Suture Zone, Tibet

Objective The Pomulong mélange was established in the regional geological survey of Lhaze County at the scale of 1:250000 by the Geological Survey Institute of Hubei Province.

First Report of Redeposited Cretaceous Radiolarians in the Eocene Sand-Shale Member of Zhepure Formation, Tüna, Yadong, Tibet

Cretaceous radiolarians were firstly reported from the Eocene Sand-Shale Member of Zhepure Formation in the Gulupu section, Tüna, Yadong, Tibet. In spite of poor preservation, 24 species of 14 radiolarian genera have still been identified, clearly indicating an age, ranging from early Aptian–Maastrichtian, and therefore should have occurred in the Eocene as a result of redeposition. The study of the stratigraphic origin of these radiolarians will shed light on the paleoenvironment and late evolutionary history of the Tibet-Tethys.

Micropalaeontological and Geochemical Evidence of the Late Jurassic Radiolarians Cherts of Naga Ophiolite Hill, Nagaland, Northeast-India

We analyzed the radiolarian assemblages (pelagic sediments) and geochemical studies of 15 samples collected from Meluri district Nagaland, Naga Hills Ophiolite belt (NHO) and it consists of the Flysch Naga-Arakan-Yoma trough beyond the Indo-Myanmar border. It reflects one of the many components of the Himalayan Orogenic systems of Tethyan oceanic crust discovered in Nagaland at Meluri district of India and they have very well-preserved studies and can be identified to Upper Jurassic (Kimmeridgian-mid-Tithonian). As well as a continuous sequence of Kimmeridgian-mid-Tithonian, five radiolarian assemblages have been identified in this study. This is so far the first recovery of pelagic sediment assemblages (Radiolarians) from the Naga Hills Ophiolite complex. Samples of Naga Hills Ophiolite belts fell in the Sublitharenite, Litharenite, and Fe-shale Fe-sand area, and the A-CN-K diagram indicates that these sediments in the source region were exposed deep to moderate weathering conditions. In the discriminant plot, the Naga Hill-Ophiolite-Chert samples occupy the field of origin of the sediment quartzose, and the log (K2O/Na2O) versus SiO2 samples fall into the active continental marginal field, and only one sample falls into an island arch, suggesting that the tectonic framework of the Naga Hills-Chert samples was deposited in the active continental margin and the diagrams K2O/Al2O3 and MgO/Al2O3 illustrated the tectonic setting of the marine environment from Naga Hill Ophiolite Chert. Such findings have been consistent with the current geology of Naga Hills in the province of Nagaland.

Evolutionary Significance of Pylentonemid Radiolarians and Their Late Devonian Species from Southwestern Tianshan,China

A group of radiolarian fossils with a complete morphological gradient of increasing polarization are reported from upper Devonian successions in southwestern Tianshan, China. Specifically, the important transitional mophotypes, Pylentonema transitorum sp. nov., Archocyrtium medium sp. nov. and Quadrapesus transitivus sp. nov, were found. Based on the fact that the new transitional radiolarian fossils resemble more closely to pylentonemids （cyrtoid nassellarians） than to entactinids （spumellarians） in morphology, they are assigned to pylentonemids. Pylentonemids share characters of both the Nassellaria （e.g., horned cephalis, basal opening with pylome） and Spumellaria （e.g., system of trabecular spicules）, and they are thus of evolutionary significance. The evolutionary trend from spumellarians to nassellarians is characterized by （1） internal spicule： from simple trabecular spicules to complicate components （A;Ir,II;D;V;Lr,Li;MB）; （2） polarization of the radiolarian tests due to rearrangment of spine, from radial to an axial symmetry; （3） the gradual formation of a basal opening （aperture, pylome, or podome）; and the transition from a pseudopylome, a primative pylome with a narrow margin on the outer shell, to a true pylome rimmed with a narrow, elevated impermite wall.

Late Olenekian Radiolarians from Bedded Chert of Ashio Terrane, Northeast Japan, and Faunal Turnovers in Western Panthalassa during Early Triassic

Late Olenekian assemblages in the western Panthalassa have been recovered from bedded radiolarian chert sequences of an accretionary complex, the Ashio belt. These faunas are documented and considered in terms of radiolarian diversity and faunal turnover during the latest Permian to Middle Triassic time. The fauna includes 30 radiolarians belonging to Spumellaria or Entactinaria, with two relicts from the Late Permian. This late Olenekian fauna is markedly different from Permian and Anisian faunas, respectively, and is herein named the Minowa fauna. Study of the literature indicates that radiolarian provinces were significantly disconnected between the western Panthalassa and eastern Tethys during late Olenekian time. Furthermore, 121 of 143 species disappeared during late Olenekian time, and in turn 118 new species appeared in the western Panthalassa around the Olenekian Anisian boundary. It is concluded that faunal turnover occurred at least three times between the latest Permian and Middle Triassic. The first turnover is the Paleozoic type radiolarian extinction at the Permian Triassic boundary, the second is the diversification of spheroidal Spumellaria and Entactinaria between early and late Olenekian time, and the third is a faunal turnover from the Minowa fauna to the true Mesozoic type radiolarian faunas that are characterized by multi segmented Nassellaria.

Radiolarians from the Pohang Basin,Southeast Korea and Paleoceanographic Implications

We identified a total of 101 species and two subspecies of radiolarians belonging to 56 genera from 95 samples collected from the Hagjeon and Duho Formations in the Pohang Basin of the southeastern Korean Peninsula. On the basis of the biostratigraphic range of Cyrtocapsella cornuta and Theocorys redondoensis, the depositional period of the upper Hagjeon and lowest Duho Formations was determined to be early to late Middle Miocene. The occurrence of deep-dwelling radiolarians indicates that the paleobathymetry seems to become gradually progressing toward an upper bathyal environment in the middle part of the Hagjeon Formation. However, we prefer to accept another interpretation for the occurrence of deep-sea indicators in the Hagjeon and the lowest part of the Duho Formations, and consider the presence of a region of upwelling cold water that might have simulated a deep-water environment in relatively shallow water. This interpretation is based on the present upwelling of a cold-water mass off the southeast coast of Korea, the occurrence of upwelling microfossils from the Pohang Basin, and the effect of the closing of the Korea Strait approximately 15 Ma. We also considered that the uppermost part of the studied section represents a shallow-water environment.

Middle Triassic Radiolarians from Cherts/Siliceous Shales in an Extensional Basin in the Sukhothai Fold Belt,Northern Thailand

More than thirty species of radiolarians are described from maroon chert and siliceous shales from the Den Chai and Santisuk sections in the east of the Sukhothai fold belt. The fauna obtained from Den Chai comprises Muelleritortis cochleata cochleata, M. cochleata tumidospina, M. expansa, Triassocampe deweveri, T. coronata, T. scalaris, Annulotriassocampe companilis, A. multisegmantatus, A. sulovensis, Pseudostylosphaera coccostyla coccostyla, P. imperspicua, Canoptum inornatus, C. levis, Corum kraineri, Spongoserrula rarauana, Orbiculiforma karnica and others. The assemblage may be correlated with those reported in the Fang-Chiang Dao and Lumphun areas in the north of Thailand and in the ChangningMenglian belt of western Yunnan, South China and suggests a late Ladinian（Middle Triassic） age. The radiolarian fauna from the Santisuk Section comprises Muelleritortis cochleata cochleata, M. sp., Striatotrissocampe nodosoannulata, Triassocampe. deweveri, T. sp., Pseudogodia？ sp., Pseudostylosphaera coccostyla coccostyla, Archaeocenosphera sp., Annulotriassocampe multisegmantis, Pseudostylosphaera sp., and others which indicates a late Ladinian age. Middle Triassic radiolarian chert and siliceous shale from Den Chai and Santisuk are interpreted as having been deposited in an extensional continental margin within the Sukhothai fold belt and not in the Devonian–Permian back-arc basin of the Nan suture. These deep marine sequences were deposited in a subsiding continental margin in the Lampang-Phrae Basin. We consider these sequences to be part of the Hong Hoi Formation（Anisian–Ladinian） of the Lampang Group which, in turn, may be compared to the Choushui Formation and other associated Middle Triassic formations in the Simao Basin of South China.

Upper Darriwilian(Middle Ordovician) Radiolarians and Ostracods from the Hulo Formation, Zhejiang Provicnce, South China

Considerable research has been done on the Ordovician marine fossils from South China, including macrofossils such as brachiopods, graptolites, bivalves, trilobites, some microfossils like conodonts and acritarches. However, radiolarians and ostracods that are also important consti- tuents of the Ordovician marine ecosystem have been paid little attention in this region. In this study, ten radiolarians species belonging to four genera and sixteen ostracods species grouped into nine genera were found from the Hulo Formation at the Hengdu Section of the Jiangshan District, west- ern Zhejiang Province, South China. The fossil-bearing strata belong to the graptolite Pterograptus elegans Zone which indicates the Late Darriwilian Age. This radiolarian fauna is the first record of the Middle Ordovician radiolarian body fossils and also the earliest Ordovician radiolarian fauna reported from South China. The occurrence of Beothuka in this fauna extends the stratigraphic range of the genus to the Upper Darriwilian. Reviews of previous literatures suggest that the diversity of Beothuka was greater during the Early Ordovician, and then declined gradually from the Early Ordovician to the Middle Ordovician before its extinction. The co-occurring ostracod fauna belongs to a shallow-water ecotype. This is contrary to the host lithofacies of the ostracod fauna which represent a deep-water environment. Therefore, these ostacods may have been transported from the shallow-water environment, most likely from the Yangtze carbonate platform. If this conjecture is the truth, then the Jiangshan District was near the shallow-water carbonate platform and received its sediments during the Darriwilian. It is still essential to do more work in the future to better understand the ecology of the Ordovician ostracod fanuas and their role in the sedimentary system of South China.

Application of radiolarians and other fossils in non-Smith strata——Exemplified by the A'nyemaqen melange belt in East Kunlun Mts.

The main character of melange strata in an erogenic belt is the integration of mixed materials due to the superposition, displacement or loss of various tectonic slices (blocks) of different origins and environments, different scales, different grades of deformation and metamor-phism, and different stages of tectonic evolution. The approach to non-Smith strata in an erogenic belt is to focus on the understanding of the age, facies, tectonic setting of the original formation and the process of deformation-metamorphism of each tectonic slice, reconstruct the history of dispersal and integration of these tectonic slices in time and space, i.e. 4-dimensional. This paper studies the age and facies of the original formation of tectonic slices in the A’nyemaqen melange belt based on new data of radiolarians, sporo-pollen and trace fossils, and cast new lights on the research of the evolution process of that belt.

Discovery and its significance of late Paleozoic radiolariansilicalite in ophiolitic melange of northeasternJiangxi deep fault belt

Metamorphic basement is widespread in northeastern Jiangxi Province withcomplicated geological structure and enriched polymetallic deposits. It is one of the impor-tant areas for geological research in China, especially for study of deep fault belt

Late Changhsingian (Latest Permian) Radiolarians from Chaohu,Anhui

This article reports a radiolarian fauna from the upper Dalong（大隆） Formation,Ping-dingshan（平顶山）,Chaohu（巢湖）,Anhui（安徽） Province,which includes 15 genera and 23 species.One new species,Copicyntra tongi Gui and Feng n.sp.,is described.Comparison of the fauna,lithology and biotic associations with those from Meishan（煤山） D and Dongpan（东攀） sections shows that the Dalong Formation in the Pingdingshan Section is deposited in a deep-water shelf basin,about 60-200 m in depth.On the basis of the biotic composition,diversity and morphology,the microfossil fauna from the Pingdingshan Section can be divided into three sedimentary assemblages and the extinction proc-esses of the assemblages are discussed.

Slab rollback and microcontinent subduction in the evolution of the Zambales Ophiolite Complex(Philippines):A review

New radiolarian ages show that the island arc-related Acoje block of the Zambales Ophiolite Complex is possibly of Late Jurassic to Early Cretaceous age.Radiometric dating of its plutonic and volcanichypabyssal rocks yielded middle Eocene ages.On the other hand,the paleontological dating of the sedimentary carapace of the transitional mid-ocean ridge-island arc affiliated Coto block of the ophiolite complex,together with isotopic age datings of its dikes and mafic cumulate rocks,also yielded Eocene ages.This offers the possibility that the Zambales Ophiolite Complex could have:(1)evolved from a Mesozoic arc(Acoje block)that split to form a Cenozoic back-arc basin(Coto block),(2)through faulting,structurally juxtaposed a Mesozoic oceanic crust with a younger Cenozoic lithospheric fragment or(3)through the interplay of slab rollback,slab break-off and,at a later time,collision with a microcontinent fragment,caused the formation of an island arc-related ophiolite block(Acoje)that migrated trench-ward resulting into the generation of a back-arc basin(Coto block)with a limited subduction signature.This Meso-Cenozoic ophiolite complex is compared with the other oceanic lithosphere fragments along the western seaboard of the Philippines in the context of their evolution in terms of their recognized environments of generation.

菲律宾Zambales蛇绿岩套的再研究:对其特提斯来源的启示(英文)

A number of geological studies have already been conducted on the Zambales Ophiolite Complex(ZOC), a north-south trending complete ophiolite sequence exposed in the western portion of Central Luzon, Philippines.Previous works recognized the ZOC as being made up of two blocks,

On the Age of the Ophiolitic Complexes in Northeastern Jiangxi:A Micropaleontological Analysis

The age assignment of cherts from ophiolitic/metamorphic complexes in northeastern Jiangxi is widely regarded as one of the crucial issues in the tectonic interpretation of South China. The ophiolitic and metamorphic complexes in northeastern Jiangxi have been traditionally regarded as part of the Proterozoic “Banxi (=Penhsi) Group” of the Jiangnan Uplift. However, recent reports of Late Paleozoic radiolarians from the rock complexes have caused some researchers to question the traditional interpretation of the tectonic and paleogeographic framework in the region; but other workers are suspicious about these findings. In order to test the validity of the putative radiolarians, we, an interdisciplinary study group including micropaleontologists, tectonic specialists and regional geologists, conducted field investigations and multiple re-samplings of the localities where the reported fossils were collected. Our comprehensive study shows that the chert of the ophiolitic complex and the associated low-grade metamorphic slate yield Mesoproterozoic and Neoproterozoic acritarchs, confirming the traditional view of their age assignment (Proterozoic); on the other hand, no recognizable radiolarian fossils have been discovered therein, thus raising questions about the recently published result of Paleozoic radiolarian findings. Probable causes for the putative radiolarian findings are thus discussed herein. Geochemical characteristics indicate that the chert sedimentation most probably occurred under a continental margin setting.

西南日本黒濑川带的解剖:晚二叠世和早侏罗世增生混杂岩的构造-地层学与浅变质作用(英文)

The Kurosegawa belt forms a relatively narrow terrane that can be traced continuously throughout southwest and central Japan.The major constituent continental fragments of the Kurosegawa belt include Early Paleozoic granitic rocks,high-grade

Middle Jurassic-early Cretaceous radiolarian assemblages of the western Yarlung Zangbo Suture Zone: Implications for the evolution of the Neo-Tethys

Cherts in the Zhongba melange of the western Yarlung Zangbo Suture Zone(YZSZ) contain well preserved radiolarian assemblages. These radiolarian assemblages indicate that the Zhongba melange has middle Jurassic-early Cretaceous remnant, are coeval with those from the central and eastern parts of the YZSZ. Cherts from the Najiu area yield Aalenian to Aptian radiolarians, while cherts interbedded with siliceous mudstones from the Bielongjiala area yield Aptian radiolarians, indicating that terrigenousderived sediments were deposited during early Aptian. The above observations indicate that the entire YZSZ have a similar geochronological framework and thus they underwent similar geological evolution:(1) during the Jurassic, the Neo-Tethys was a wide ocean with pelagic sediments distal from continents;(2) during the Cretaceous(around 130-120 Ma), the Neo-Tethys started to subduct along the southern margin of the Lhasa block, and terrigenous-derived siliceous mudstone began deposition.

Discovery of Radiolarian Fossils from the Aiketik Group at the Western End of the South Tianshan Mountains of Chinaand Its Implications

The Aiketik Group, distributed at the western end of the South TianshanMountains, China, is an important lithostratigraphic unit involved in the South Tianshan orogen. Itis separated from the adjacent rocks by faults. Generally, the geologists ascribed it to the UpperCarboniferous according to Pseudostaffella sp., Profusulinella sp. and Fusulinella sp. found fromthe limestone and sandy limestone of Aiketik. Our radiolarian fossils were obtained from the chertsamples collected from the Haladaok section located at the upper Tuoshihan River. The fossils mainlyinclude Albaillella undulata Deflandre, Albaillella paradoxa Deflandre, Albaillella sp. aff. A.paradoxa Deflandre, Albaillella sp. cf. A. deflandrei Gourmelon, Albaillella sp., Albaillellaexcelsa Ishiga, Kito and Imoto (?), Belowea variabilis (Ormiston et Lane), Callella cf. C.parvispinosa Won, Entactinia cf. E. tortispina Ormiston et Lane, Entactinia aff. E. tortispinaOrmiston et Lane, Entactinia variospina Won, Entactinia sp., Eostylodictya rota (Won),Latentifistula impella (Ormistone et Lane) (?), Latentifistula turgita Omiston et Lane,Latentifistulidae gen. et. sp. indet. and Polyentactinia cf. aranea Gourmelon. Among them,Albaillella excelsa Ishiga, Kito and Imoto (?) is a Late Permian species with some elementsuncertain as there is only one poorly-preserved fossil of this species found so far. And tworadiolarian assemblages can be identified from the other fossils. One is the early EarlyCarboniferous assemblage represented by Albaillella undulata Deflandre, Albaillella paradoxa andAlbaillella sp. cf. A. deflandrei Gourmelon. And the other is the late Early Carboniferousassemblage represented by Eostylodictya rota (Won). This is the first discovery of radiolarianfossils in the Aiketik Group, also the first discovery of Late Permian radiolarian fossils in theSouth Tianshan Mountains. Meanwhile, this is the current westernmost sampling site of radiolarianfossils in the South Tianshan Mountains.

Early Eocene Radiolarian Fauna from the Sangdanlin, Southern Tibet: Constraints on the Timing of Initial India-Asia Collision

This is a new report on the early Eocene radiolarian fauna from the Sangdanlin section in the Gyirong region, along the southern margin of the Yarlung Zangbo Suture Zone. The Sangdanlin section measured in this study is divided into three lithostratigraphic units from bottom to top： the Zongzhuo, Sangdanlin, and Zheya formations. Abundant radiolarian fossils were obtained from the Sangdanlin section and 54 species of 30 genera were identified and assigned as follows： Cryptamphorella conara-C. macropora the late Cretaceous Zone and Amphis_phaera coronate, Bur）ella tetradica-Bekoma campechensis, and B.bidartensis-B. divaricata the Paleocene-early Eocene Interval Zones. The Paleocene- early Eocene radiolarian zones are comparable to the radiolarian zones RP4-RP8 in New Zealand. Based on the data of radiolaria and lithofacies, it is suggested that the Zongzhuo Formation should be deposited along the base of the north-facing, continental slope of the Greater Indian continental margin, and the Sangdanlin Formation should be a deep marine, sedimentary sequence located in a foreland basin. The early Eocene radiolarian fauna in the Sangdanlin Formation constrains the initial age of the India-Asia collision to no later than 53.6 Ma.

Geochronology and Geochemistry of the Radiolarian Cherts of the Mada'er Area,Southwestern Tianshan:Implications for Depositional Environment

In the southwestern Tianshan,the geologic ages of many strata and their depositional environments are still poorly constrained because of complex structures.The Mada＇er area is located in the Kuokesaleling belt,Southwestern Tianshan.The cherts from the former Wupata＇erkan Group contain abundant radiolarian fossils,including 10 species which are identified as late Devonian to early Carboniferous in age.Eleven chert samples have SiO_2 contents ranging from 88.80 wt%to 93.28 wt%, and 2.02 wt%to 3.72 wt%for Al_2O_3.The SiO_2/Al_2O_3 ratios of all samples vary from 23.84 to 46.11, much lower than those of the pure cherts（80-1400）.These values suggest that the cherts contain high ratios of terrigenous materials.The Al_2O_3/（Al_2O_3＋Fe_2O_3）ratios vary between 0.64 and 0.77,whereas V and Cu concentrations range from 10.92 ppm to 26.7 ppm and from 2.15 ppm to 34.1 ppm respectively. The Ti/V ratios vary from 25.53 to 44.93.The total REE concentrations of the cherts are between 30.78 ppm and 59.26 ppm,averaging 45.46 ppm.The（La/Ce）_N ratios range from 0.81 to 1.12,and 0.88-1.33 for（La/Yb）_N,averaging 1.09,which suggests a continental margin environment.Consequently,it is inferred that the cherts formed in a residual sea environment during the late Devonian to early Carboniferous time,which suggests that the collision between the Karakum-Tarim and Kazakhstan-Junggar plates did not occur at the time.In addition,the regional geological information indicates that the study area experienced a post-collision stage during the early Permian,and thus it is likely that the collision between the two plates took place in the late Carboniferous.