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Early Pliocene calcareous and siliceous microfossils of the Sawai Bay Formation, Car Nicobar Island, northern Indian Ocean

Chakraborty Arindam, Ghosh Amit K., Mccartney Kevin, Saxena Stuti, Dey Rikee, Roy Lopamudra

Acta Geologica Polonica

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2021

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Vol. 71, no. 2

175--198

EN

The present contribution provides a study of calcareous nannofossils and siliceous microfossils from the Sawai Bay Formation on Car Nicobar Island, northern Indian Ocean. Two stratigraphically short sediment intervals near Sawai Bay have been examined. Qualitative and quantitative microfossil analyses show the Sawai Bay ‘A’ Section to be devoid of siliceous microfossils, while 24 well-preserved calcareous nannofossil taxa are identified. The Sawai Bay ‘B’ Section yields 18 calcareous nannofossil, 33 radiolarian and 25 diatom taxa. The calcareous nannofossil index taxa (Ceratolithus armatus Müller, 1974a and C. cristatus Kamptner, 1950) indicate both sections to be from zones NN12 (CN10b) and NN13 (CN10c) of early Pliocene (Zanclean) age. The radiolarian taxa, i.e., Didymocyrtis avita Riedel, 1953, Euchitonia spp., Siphocampe lineata (Ehrenberg) Nigrini, 1977, Stichocorys peregrina Riedel, 1953, Semantis spp. and Stylochlamydium sp. are common in the Sawai Bay ‘B’ Section, which is assigned to Zone RN9. Most of the diatom taxa are represented by rep-resentatives of the genera Actinocyclus Ehrenberg, 1837, Azpeitia Peragallo in Tèmpere and Peragallo, 1912, Coscinodiscus Ehrenberg, 1839a, Grammatophora Ehrenberg, 1841 and Triceratium Ehrenberg, 1839b, with the benthic diatom species Triceratium favus Ehrenberg, 1839b being predominant (~35% of the total diatom count). Siliceous microfossils are also represented by silicoflagellates dominated by Dictyocha spp. and sponge spicules dominated by astrophorids.

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Biostratigraphy, geochemistry and sedimentology of Middle to Late Jurassic strata in the Strážovce section (Strážovské vrchy Mts), Krížna Nappe of the Central Carpathians, Slovakia

Michalík J., Bąk M., Lintnerová O., Méres Š

Volumina Jurassica

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2017

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Vol. 15, no 1

161--178

EN

The Jurassic / Lower Cretaceous sequence of the Strážovce section has been deposited in the central, axial part of the Zliechov Basin. Its most characteristic part – the Ždiar Formation consists of bedded siliceous radiolarian limestones and radiolarites. The radiolar¬ian assemblage typical of the North Tethyan Bioprovince lived during mid Oxfordian – Early Kimmeridgian in a warm upper part of the well stratified water column, partially near to the thermocline. Radiolarian abundance decreases upwards. Productivity decrease is quanti¬fied by the share of biogenic SiO2 as well as by high EFSi values during sedimentation of both the Ždiar and Jasenina formations. The geochemical data indicate relatively stable volume of the siliciclastic component of the rocks and a felsic character comparable to the Average Shale. The chemically homogeneous sedimentary signal indicates values of both CPA and EF ≤ 1 of Ti, Zr, Fe, Na, K, Rb, V and U. The values of EF > 1 signal enrichment of elements with affinity to carbonate minerals (Sr, Mn, P, Y, and Mg). Metal enrichment (Cu, Zn and Ni) indicates metal mobilization from other sources or due to carbonate diagenesis. In comparison to the Average Shale, decreased ΣREE´s and negative Cech and Euch anomalies could be regarded as a typical deep sea water signal. The differentiated REE record of higher calcareous beds of the Jasenina Fm. suggests basinal dysoxic conditions. The “bell-shape” of curves (normalized to shale) indicate that REEs were slightly affected by carbonate diagenesis. The Oxfordian / Kimmeridgian siliceous sedimentation in the Zliechov Basin was influenced probably more by monsoon-controlled input of land derived weathered material than by hydrothermal fluids from the bottom rifts.

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Radiolarians of the uppermost Oxfordian (Hypselum Zone) of the Wieluń Upland (central Poland)

Smoleń J.

Volumina Jurassica

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2016

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Vol. 14, no. 1

51–-64

EN

Radiolarian assemblages from the uppermost Oxfordian (Hypselum Zone) deposits of two sections (Katarowa Góra and Bobrowniki) in the Wieluń Upland (central Poland) are studied for the first time. The overall composition of the assemblages is characterized by low taxonomic diversity, with many individuals of spherical morphotypes, with dominance of the family Williriedellidae and Gongylothoracidae, among the nassellarians. The radiolarians show features mostly of the Northern Tethyan fauna. Additionally, more cosmopolitan forms consisting of spumellarians and of cold water representatives of the family Parvicingulidae appear in the middle and upper parts of the Hypselum Zone. This change in the character of the radiolarian assemblages suggests Boreal influences into the Submediterranean basin related to activity of sea currents, which have been stimulated by climatic changes during the latest Oxfordian.

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Late Ladinian radiolarians from the Tahtalidag Nappe of the Antalya nappes, SW Turkey : remarks on the late Middle and Late Triassic evolution of the Tahtalidag Nappe

Tekin U., Sonmez I.

Acta Geologica Polonica

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2010

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Vol. 60, no. 2

199-217

EN

The late Ladinian to Late Triassic succession of the Tahtalidag (upper) Nappe of the Antalya nappes was studied in the Egregindere section, north of the city of Antalya, SW Turkey. The chert bands in the central part of the section have yielded poorly to moderately preserved radiolarians documenting the Late Ladinian Muelleritortis firma and Muelleritortis cochleata radiolarian zones. Based on the Egregindere succession, a major deepening event, evidenced by radiolarian cherts, took place between the middle and late Late Ladinian. The Late Triassic thick-bedded neritic limestones represent a shallowing-upward sequence, which formed as a result of the horst-like rising of the Tahtalidag Nappe during the Late Triassic block faulting. Fifty-nine radiolarian taxa have been determined from the Upper Ladinian of the Egregindere section. One species (Muelleritortis elegans) and two subspecies (Muelleritortis firma equispinosa and Muelleritortis firma globosa) are described as new.

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Mikrofauna oksfordu w północno-wschodnim obrzeżeniu Górnośląskiego Zagłębia Węglowego

Smoleń J.

Biuletyn Państwowego Instytutu Geologicznego

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1998

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nr 378

207-223

PL

W wapieniach gąbkowych i marglistych oksfordu dolnego oraz wapieniach cienkopłytowych niższej części oksfordu środkowego, wyróżnionych w rejonie Częstochowa-Zawiercie stwierdzono występowanie licznej mikrofauny. Oznaczono zespół otwornic z indeksowymi gatunkami Spirillina tenuissima Gumbel i Paalzowella feifeli seibaldi Lutae. Na przełomie poziomów Cardioceras bukowskii i C. excavatum wyróżniono horyzont z radiolariami, które miejscem występują w dużym nagromadzeniu, a ich występowanie świadczy o silniejszym wpływie morza Tetydy w tym okresie.

EN

In the sponge and marly limestones of the Lower Oxfordian and in the thin-platy limestones of the lower part of the Middle Oxfordian, distinguished in the Częstochowa-Zawiercie region, the presence of abundant microfauna was stated. The foraminifer assemblage was determined, with the index species Spirillina tenuissima Gumbel and Paalzowella feifeli seiboldi Lutze. In turn of the Cardioceras bukowskii and C. excavatum zones one distinguished the horizon with radiolarians, which locally occur as large accumulations and their presence evidences a stronger influence of the Tethys sea in that period.