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1

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.

2

Identification of the Oligocene-Miocene boundary in the Central Iran Basin (Qom Formation) : Calcareous nannofossil evidences

Parandavar Mohammad, Hadavi Fatemeh

Geological Quarterly

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2019

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Vol. 63, No. 2

215--229

EN

A diverse Late Oligocene to Early Miocene calcareous nannofossil assemblage was examined from the Qom Formation in the Central Iran Basin, and the Oligocene-Miocene boundary was identified based on the quantitative analysis of the assemblages in 303 smear slides. Eleven well-established calcareous nannofossil bio-events are delineated in the Upper Oligocene through Lower Miocene. The results clearly show that the Highest Occurrence (HO) of Sphenolithus delphix is the closest bio-event to the boundary as traditionally delineated on the lithostratigraphic criteria, and provides a distinct biohorizon below it. The Lowest Occurrence (LO) of the species Discoaster druggii is the oldest Miocene bio-event that is observed shortly after the HO of S. delphix, showing that calcareous nannofossils are well suited for approximating the Oligocene-Miocene boundary in the Qom Formation. The Oligocene-Miocene boundary is placed in the upper part of Sub-member “c1” in all three sections studied here and it is traceable throughout the Central Iran Basin, which makes a potentially reliable marker horizon for sequence stratigraphic and hydrocarbon studies in the area.

3

Calcareous nannofossils from the uppermost Oxfordian and lowermost Kimmeridgian of Staffin Bay, Isle of Skye, northern Scotland

Ustinova M. A.

Volumina Jurassica

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2018

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Vol. 16, no 1

63--72

EN

Twenty six samples from the sections at Flodigarry and Digg at Staffin Bay, Isle of Skye, northern Scotland, spanning the stratigraphical interval from the uppermost Oxfordian to the lowermost Kimmeridgian were examined for their calcareous nannofossil content. The study revealed the presence of an assemblage typical of the nannofossil zone NJ15 of the northern European zonation.

4

Biostratigraphy and magnetostratigraphy of the uppermost Tithonian–Lower Berriasian in the Theodosia area of Crimea (southern Ukraine)

Bakhmutov V. G., Halásová E., Ivanova D. K., Józsa Š., Reháková D., Wimbledon W. A. P.

Geological Quarterly

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2018

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Vol. 62, No. 2

197--236

EN

We present evidence for the uppermost Jurassic-lowest Cretaceous interval in Crimea, coastal southern Ukraine. Three facies zones are distinguished in the upper Dvuyakornaya and the Mayak formations of the eastern Crimean Peninsula: basinal, slope and toe-of-slope zones. In this interval we identify the lowest Berriasian Jacobi and Grandis subzones of authors, in expanded form, exceeding 160 metres in thickness. We present new magnetostratigraphic interpretations, and identify two normal and two reversed polarity intervals, assigned to M19n, M18r, M18n and M17r, with M19n2n, M19n1r and M19n1n identified in the uppermost Dvuyakornaya Formation. In the Mayak Formation we record the top of M19n.1n, with M18r, M18n and a thick M17r above. In these two formations component calpionellid species have been identified which characterise the Alpina, Ferasini and Elliptica subzones (Calpionella Zone). In M19n, the FADs of the calcareous nannofossils Hexalithus strictus, Cruciellipsis cuvillieri, Nannoconus wintereri, N. steinmannii minor and N. kamptneri minor are found, which is consistent with other Tethyan regions. N. steinmannii steinmannii and N. kamptneri kamptneri first appear in M18r at Ili Burnu . Specimens of the apparently Tithonian foraminiferan index Anchispirocyclina lusitanica are found, but in the Berriasian lower Mayak Formation.

5

Integrated biostratigraphy of the Jurassic strata of the Wagad Uplift, Kachchh, western India

Rai J., Garg S., Gupta M., Singh A., Pandey D. K., Fürsich F. T., Alberti M., Garg R.

Volumina Jurassica

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2015

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Vol. 13, no. 2

55--80

EN

An integrated study based on calcareous nannofossils, organic-walled dinoflagellate cysts, and ammonites from the Washtawa and Kanthkot formations of the Wagad Uplift have allowed a detailed documentation of the stratigraphic position of these formations within the Oxfordian and Kimmeridgian sediments of the Kachchh Basin, western India. The nannofossil assemblages from the lower part of the Nara Shale Member exposed in the Nara and Washtawa domes, the Kanthkot Ammonite Beds along the Trambau River section, and the Patasar Shale Member exposed along the Trambau River section and the Patasar Tank section in the eastern part of the Wagad Uplift belong to the NJ 14 Cyclagelosphaera margerelli Zone of the Early Oxfordian, the NJ 15a Lotharingius sigillatus Zone of the Middle Oxfordian, and the NJ 15b Cretarhabdus conicus of Early Kimmeridgian age, respectively. Zonation schemes, based on calcareous nannofossils, dinoflagellate cysts, and ammonites were calibrated highlighting their biostratigraphic potential. These studies may represent a reference biochronology for Oxfordian–Kimmeridgian age strata applicable to the Tethyan realm of which India was a part during Late Jurassic times.

6

Fossil karst in the Jurassic of Kościuszko Mound in Kraków (southern Poland)

Wójcik A., Garecka M., Olszewska B., Wódka M.

Geological Quarterly

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2015

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Vol. 59, No. 1

61--70

EN

Study of four boreholes (each 100 mdeep) drilled in the St. Bronisława Hill (a part of the horst of the Wolski Forest, Kraków area) indicated that within the Oxfordian limestone occur claystones with calcareous rubble (detritus), filling the fossil karst forms. The claystones, that in some cases show planar stratification, contain assemblages of Late Cretaceous (Campanian–Maastrichtian) foraminifers. The Middle Miocene planar laminated limestones have also been found in cavities formed in the Middle Oxfordian limestones. Miocene deposits of this type, filling the fossil karst, were not previously known from the area of Kraków. Both the Upper Cretaceous and the Middle Miocene deposits document probably marine sedimentation that resulted in the filling of the karst system. This type of karst was probably formed before the transgression of the Upper Cretaceous sea and the subsequently before the transgression of the Middle Miocene sea into the area of present horst of the Wolski Forest.

7

Nanoplankton wapienny i okrzemki środkowego miocenu w rejonie Buska i Kazimierzy Wielkiej (północna część zapadliska przedkarpackiego)

Gaździcka E.

Biuletyn Państwowego Instytutu Geologicznego

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2015

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nr 461

153--177

PL

Na podstawie wyników szczegółowej analizy zespołów nanoplanktonu wapiennego występującego w profilach badawczych otworów wiertniczych wykonanych w rejonie Buska, w północnej części zapadliska przedkarpackiego, określono pozycję stratygraficzną przewierconych sekwencji osadowych. W profilu otworu wiertniczego Busko (Młyny) PIG-1 iły margliste górnej części formacji skawińskiej zaliczono do poziomu nanoplanktonowego NN5 Sphenolithus heteromorphus odpowiadającego środkowemu badenowi Paratetydy i górnemu langowi/ dolnemu serrawalowi w prowincji medyterańskiej. Serie z ewaporatami (przeławicenia gipsów i iłów), wyróżnione jako formacja krzyżanowicka, oraz osady ilaste formacji z Machowa reprezentują poziom nanoplanktonowy NN6 Discoaster exilis. Przez analogię do innych basenów Paratetydy Środkowej granicę pięter badeńskiego i sarmackiego w profilu tego otworu wskazano bezpośrednio poniżej 20-metrowej miąższości sekwencji zawierającej skały bogate w okrzemki. W zespołach nanoplanktonu wapiennego dolny sarmat wyznacza pojawienie się gatunków Rhabdosphaera poculi Bóna et Kernerne i Rhabdosphaera procera Martini. W profilu otworu wiertniczego Kazimierza Wielka (Donosy) PIG-1, w osadach formacji z Machowa, wyróżniono poziom nanoplanktonowy NN6 Discoaster exilis. Masowy rozwój okrzemek udokumentowany w profilu otworu wiertniczego Busko (Młyny) PIG-1 świadczy o położeniu tego obszaru w pobliżu ujścia większej rzeki dostarczającej związki azotu, fosforu oraz krzemionkę. Zachowanie delikatnych frustul okrzemek było możliwe dzięki szybkiej sedymentacji osadów klastycznych w nadkładzie skał bogatych w okrzemki.

EN

The results of detailed analysis of calcareous nannoplankton in Miocene deposits from the northern part of the Carpathian Foredeep enabled stratigraphic conclusions. Marly clays of the uppermost part of the Skawina Formation in the Busko (Młyny) PIG-1 borehole section are correlated with the NN5 Sphenolithus heteromorphus Zone that corresponds with the Middle Badenian in the Paratethys and the upper Langhian/ Lower Serravalian in the Mediterranean region. The Krzyżanowice Formation, which includes evaporites (gypsum and clay intercalations), and the Machów Formation represent the NN6 Discoaster exilis Zone. By a comparison with other Paratethyan basins, the Badenian/ Sarmatian boundary is proposed just below a 20-metres thick set of diatomaceous siltstone layers. Among the calcareous nannofossil species, the appearance of Rhabdosphaera poculi Bóna et Kernerne and Rhabdosphaera procera Martini may point to the Lower Sarmatian transgression. Clayey sequences of the Machów Formation in the Kazimierza Wielka (Donosy) PIG-1 borehole correspond with the NN6 Discoaster exilis Zone. Abundance of diatom floras observed in the Busko (Młyny) PIG-1 borehole suggests a proximity of a river mouth that supplied water with nitrates, phosphates and silica. Preservation of delicate siliceous diatom frustules was possible due to rapid deposition of clastic sediments above diatomaceous siltstone.

8

Integrated stratigraphy of the Oxfordian global stratotype section and point (GSSP) candidate in the Subalpine Basin (SE France)

Pellenard P., Fortwengler D., Marchand D., Thierry J., Bartolini A., Boulila S., Collin P., Enay R., Galbrun B., Gardin S., Huault V., Huret E., Martinez M., Smith C.

Volumina Jurassica

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2014

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Vol. 12, no. 1

1--44

EN

An integrated biostratigraphic approach, based on ammonites, calcareous nannofossils, dinoflagellates, combined with sedimentology, carbon-isotope and physical stratigraphy, is proposed for the Subalpine Basin (Thuoux and Saint-Pierre d’Argençon sections). Within the expanded marl deposits of the Terres Noires Fm., the Callovian-Oxfordian boundary is particularly well defined by ammonite taxa from different families (i.e. Cardioceratidae, Oppeliidae, Aspidoceratidae and Perisphinctidae), calcareous nannoplankton (first occurrence of large-sized Stephanolithion bigotii) and dinoflagellate cysts (first occurrence of Wanaea fimbriata). This precise biostratigraphy and diversity of ammonites permit long-range correlations with Boreal and Pacific domains. The exceptional outcrop conditions and continuous sedimentation allow high-resolution chemostratigraphy and cyclostratigraphy to be used. Variations of the δ13C record (1.5‰ increase during the Lamberti Zone), consistent with data from other sections of the Subalpine Basin and with the Paris Basin, provide additional markers to characterise the Callovian-Oxfordian boundary. Promising results from cyclostratigraphy should serve to constrain the duration of biostratigraphic units and thus improve the Late Jurassic Geologic Time Scale. Comparisons are made with the two other candidates for an Oxfordian GSSP, Redcliff Point (UK) and Dubki (Russian Platform). Finally, the advantages of the Subalpine Basin sections support the proposal of Thuoux as a suitable GSSP candidate for the base of the Oxfordian Stage

9

Calcareous nannofossils from the Upper Cretaceous of northern James Ross Island, Antarctica : a pilot study

Švábenická L., Vodrážka R., Nývlt D.

Geological Quarterly

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2012

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Vol. 56, No. 4

765--772

EN

The Czech scientific expedition to northern James Ross Island, Antarctica has tested the use of calcareous nannofossils as a possible tool for stratigraphic correlation of Cretaceous and Neogene strata. Only a few samples with poor nannofossil content gave useful information for biostratigraphy. The Lower Campanian Chiastozygus garrisonii Zone and Gephyrobiscutum diabolum Subzone, respectively, was established in the lower part of the Santa Marta Formation, Lachman Crags Member, from the common occurrence of Gephyrobiscutum diabolum associated with Broinsonia parca parca and Acuturris scotus. Deposits of the Late Miocene Mendel Formation yielded exclusively reworked nannofossils from the older Upper Cretaceous deposits. Nannofossils indicate at least two distinct stratigraphic levels: Middle Coniacian and Santonian–basal Campanian, and these must have been sourced from the immediate area. The majority of the marine deposit samples studied were barren of nannofossils, probably due to late diagenetic secondary decalcification.

10

Calcareous nannofossil biostratigraphy and sedimentary environment of Valanginian–Hauterivian rhythmites (Silesian Nappe, Polish Carpathians)

Kędzierski M., Ochabska A.

Annales Societatis Geologorum Poloniae

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2012

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Vol. 82, No. 3

225–-237

EN

The results of semi-quantitative and qualitative studies of nannofossil assemblages in dark to light grey, rhythmically bedded, calcareous mudstones of the Upper Cieszyn Beds, Silesian Nappe of the Outer Carpathians are presented. The vertical variation in the carbonate content of these mudstones and changes in the composition of nannofossil assemblages, as well as the Shannon diversity index (SI), result from humid-arid climate changes, driving the trophic conditions of surface waters and nannoplankton biocalcification. These changes were control- led by the variable influences of both the Tethyan and Boreal provinces. The light grey mudstones were deposited during the dominance of warm waters from the Tethyan realm and some nannoconids, typical of the warm, stratified water of lower palaeolatitudes, occur here. The dark grey mudstones represent influences of the Boreal province, indicated by the appearance of Crucibiscutum sp. and a generally higher biodiversity demonstrated by SI. Climatic changes affected the stratification of surface water, expressed also by different linear fits for pairs of SI, Watznaueria barnesiae and Rhagodiscus asper. On the basis of the presence of Eiffellithus striatus, E. windii and signals of both Tethyan and Boreal influences. the section studied represents the uppermost Valanginian– lowermost Hauterivian boundary interval, i.e., the upper part of the BC5/BC6 nannofossil zones, related to the furcillata-radiatus ammonite zones.

11

Calcareous nannofossils from the Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn as palaeoenvironmental indicator, Kraków-Silesia Homocline, Poland

Kędzierski M.

Acta Geologica Polonica

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2012

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Vol. 62, no. 3

421-437

EN

Qualitative and quantitative studies on calcareous nannofossils have been carried out on the Middle-Upper Bathonian succession of Gnaszyn (Kraków-Silesia Homocline, Częstochowa region). The nannofossil assemblages are moderately or well-preserved and are dominated by Watznaueria britannica; also common are Staurolithites lumina and Zeugrhabdotus erectus. The presence of delicate nannofossil forms together with dissolution-resistant taxa shows that the changes in composition of some of the nannoplankton assemblages reflect original variations. The frequency and diversity changes of the calcareous nannofossil assemblages have been interpreted in relation to fluctuations of sedimentation rate versus changes in trophic conditions within the photic zone. The highest diversity assemblages contain a high percentage of palaeofertility indicators, and are impoverished in the genus Watznaueria. This is interpreted as a reflection of a lower sedimentation rate and more stable, possibly mesotrophic conditions within the photic zone. On the other hand, W. britannica-dominated assemblages with low species diversity may represent more unstable environments with a high influx of terrestrial material related to a high sedimentation rate and a high nutrient influx, i.e. eutrophic conditions in the photic zone.

12

Lower Toarcian organic-rich sediments from the Tuscan Succession (Northern Apennines, Italy): preliminary results

Perilli N., Rodrigues R., Veiga de Oliveira L., Catanzariti R.

Volumina Jurassica

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2009

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Vol. 7, no. 1

55-65

EN

For the first time is here documented the presence of Lower Toarcian black shales in the lower portion of the Calcari e marne a Posidonia (Posidonia Marls auctt.) belonging to the Tuscan Nappe. It consists of alternations of 30 cm to 5 m thick black laminated marlstone and marly claystone, with TOC values ranging from 0.43% to 2.49%. Based on calcareous nannofossils, the basal portion of the Calcari e marne a Posidonia spans the Lotharingius hauffii to Carinolithus superbus zones, and the organic-rich interval lies within the Carinolithus superbus Zone.

13

Palaeoenvironmental reconstruction of the Karpatian-Badenian (Late Burdigalian-Early Langhian) transition in the Central Paratethys. A case study from theWagna Section (Austria)

Spezzaferri S., Ćorić S., Stingl K.

Acta Geologica Polonica

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2009

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Vol. 59, no. 4

523-544

EN

The Karpatian-Badenian (Burdigalian-Langhian, Early-Middle Miocene) transition is a key interval in the evolution of the Paratethys and the proto-Mediterranean Sea. We present here, based on the Wagna section (Styrian Basin, Central Paratethys), a study of a quantitative analysis of the microfossils (foraminifera and calcareous nannofossils) and a statistical treatment of data to reconstruct the palaeoenvironmental condition during this time. During the Karpatian, relatively deep water, cool conditions with a relatively high nutrient input prevailed in the Styrian Basin, as suggested by the high abundance of cool-water foraminifera and calcareous nannofossils. The Badenian was generally warmer, with a lower availability of nutrients, and was characterized by carbonate units and patch reefs and associated microfossil assemblages (e.g., Eponides spp.). Riverine plumes brought fresh water into the Styrian Basins during the Badenian and induced high productivity and the proliferation of species highly tolerant of low salinity such as Ammonia tepida. The passage from calcareous nannofossil Zone NN4 to NN5 is characterized by a reorganization of water masses and the transition from cooler and nutrient-rich to warmer and nutrient-poorer waters. Based on the microfossil abundance trends we interpret the planktonic foraminiferal species Globigerina tarchanensis as preferring cooler nutrient-rich waters and Reticulofenestra minuta as preferring warmer and nutrient-poor waters. The application of cluster analysis based on the Bray-Curtis Similarity and non-metric MultiDimensional Scaling (nMDS) adds important information to that obtained only from microfossil abundance curves, enabling identification of cryptic trends and correlation with sequence stratigraphy. This method may even complement biostratigraphic interpretation and support age attribution in the Paratethyan area, where marker species are missing.

14

First record of the late Campanian heteromorph ammonite Nostoceras hyatti from the Alpine Cretaceous (Grunbach, Gosau Group, Lower Austria)

Summesberger H., Machalski M., Wagreich M.

Acta Geologica Polonica

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2007

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Vol. 57, no. 4

443-451

EN

The heteromorph ammonite Nostoceras (Nostoceras) hyatti is described for the first time from the Piesting Formation (Gosau Group; Upper retaceous) at Grunbach along the eastern margin of the Northern Calcareous Alps, Lower Austria. This record significantly extends the geographic range of this late Campanian marker species; it was not previously known from the Alpine Cretaceous. Moreover, it corroborates earlier age assignments as late Campanian of the (lower) part of the Piesting Formation. A matrix sample taken from the specimen studied has yielded taxa whose range covers zones CC20 to CC23, or UC 15[^tp] to UC18, of the standard nannofossil zonation.

15

An integrated study (inoceramid bivalves, ammonites, calcareous nannofossils, planktonic foraminifera, stable carbon isotopes) of the Ten Mile Creek section, Lancaster, Dallas County, north Texas, a candidate Global boundary Stratotype Section and Point

Gale A.

Acta Geologica Polonica

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2007

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Vol. 57, no. 2

113-160

EN

The WalMart section on Ten Mile Creek, Lancaster, Dallas County, Texas, exposes a 23 metre section of Austin Chalk that can be integrated into a more than 60 m composite sequence for the Dallas area on the basis of bed-by-bed correlation. The section was proposed as a possible candidat e Global Boundary Stratotype at the 1995 Brussels meeting on Cretaceous Stage boundaries, with the first occurrence of the inoceramid bivalve Cladoceramus undulatoplicatus (ROEMER, 1852) as the potential boundary marker. An integrated study of the inoceramid bivalves, ammonites, planktonic foraminifera, and calcareous nannofossils places the first occurrence of Cl. undulatoplicatus in a matrix of ten ancillary biostratigraphic markers. The candidate Global boundary Stratotype Section and Point (GSSP) is located within a composite stable carbon isotope curve for the Austin Chalk as a whole. This shows it to lie 3.5 m below the Michel Dean stable carbon isotope event, originally recognised in the English Chalk. The first occurrence of Cl. undulatoplicatus lies in the same position in relation to stable carbon isotope events in both Texas and England that can in principle be recognised globally in marine sediments. The WalMart section satisfies many of the criteria required of a GSSP for the base of the Santonian Stage, although ownership and access require clarification.

16

The Pliensbachian/Toarcian boundary in the Almonacid de la Cuba section (Iberian Range, Spain)

Goy A., Comas-Rengifo J., Gomez J., Gonzales J., Herrero C., Palencia A., Perilli N., Rodrigo A.

Volumina Jurassica

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2006

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Vol. 4, no. 1

164-166

EN

The Almonacid de la Cuba section, representative of the Pliensbachian-Toarcian transition in the Iberian Range (Fig. 1), is reviewed. It is an expanded section where no important discontinuities have been detected. Four successive assemblages of ammonites, which are characterized by the presence of Pleuroceras (BH14-CU14), Canavaria (CU16-CU32), Dactylioceras (E.) (CU35.2-CU44) and Dactylioceras (O.) (CU44-CU87), are distinguished. The Pliensbachian/Toarcian boundary is located at the base of level CU35.2 with the first record of Dactylioceras (Fig. 2). These assemblages are mainly constituted by taxa typical of the NW European Province, such as Pleuroceras, Dactylioceras (O.) and P. paltum. However, frequent Mediterranean Province taxa such as Emaciaticeras, Canavaria, Lioceratoides, Neolioceratoides, Dactylioceras (E.) and P. madagascariense, are also recorded. In the Tenuicostatum Zone, dactylioceratidae are dominating with respect to harpoceratinae. In the Mirabile Subzone, species of Dactylioceras (E.) are coexisting with P. paltum. Brachiopods show two successive assemblages. The lower one is composed generally of the Pliensbachian taxa and the upper assemblage includes more endemic taxa. Coinciding with the Early Toarcian OAE, almost all these species disappeared at the end of the Tenuicostatum Chron. Foraminiferal assemblages are rich and diversified. Calcareous hyaline taxa are dominated by suborder Lagenina, agglutinated foraminifera are scarce, the suborders Spirillinina and Miliolina are represented by few specimens and taxa, and specimens of Robertinina have been recovered throughout the whole stratigraphic interval. The main biostratigraphical foraminiferal events can be recognized and compared with other sections of the Iberian Range and with another ones of selected NW European Basins. Ostracod assemblages of the Spinatum Zone are dominated by healdiids and cytheraceans, which decrease at the base of the Tenuicostatum Zone, where the cypridaceans are better represented. In the Semicelatum Subzone, coinciding with the disappearance of the healdiids, the cytheraceans become dominants.Calcareous nannofossils assemblages are rich and well preserved. This allowed locating precisely the biochronostratigraphical position of the main markers and events and comparing them with these recorded in other basins of Western Tethys. A magnetic polarity column for the Pliensbachian/Toarcian boundary has been constructed on the basis of the polarities of the 2C Component (Fig. 2). The lower boundary of the Toarcian is located within the R2 magnetozone. A relatively large magnetozone N3 of normal polarity is located within the Tenuicostatum Zone.

17

Pliensbachian calcareous nannofossil zones vs ammonite zones along the western and northern margins of the Iberian Massif and biostratigraphical potential of nannobiohorizons

Perilli N., Veiga de Oliveira L., Comas-Rengifo M., Duarte L.

Volumina Jurassica

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2006

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Vol. 4, no. 1

202-203

EN

Calcareous nannofossils, one of the main components of Lower Jurassic marly/limestone alternations, were studied along the western and northern margins of the Iberian Massif. Consequently, they were used to date the lithological successions as well abiotic signals (e.g. isotope or TOC profiles). Our work focuses on the main changes of calcareous nannofossil record and the biohorizons recognized in some reference Pliensbachian sections from Basque-Cantabrian area (Spain) and Lusitanian Basin (Portugal). The remarkable changes in composition are the appearances and abundance increases of the Biscutaceae (Similiscutum) and of Watznaueriaceae (Lotharingius). The appearances of large Biscutum (B. grande and B. finchii) and of medium-sized Lotharingius species (L. sigillatus) are also clearly detectable though their occurrence is discontinuous. The other events include the appearances of Biscutum dubium, Bussonius prinsii, Biscutum novum and Crepidolithus impontus and the disappearance of Parhabdolithus robustus. The reconstructed distribution pattern of the age-significant species supports the identification and description of the nannofossil zones and subzones proposed for NW Europe. The NJ3/NJ4, NJ4/NJ5 zone boundaries are easily identified by the FO of Similiscutum cruciulus (Lower Pliensbachian) and the FO of Lotharingius hauffii (Upper Pliensbachian), respectively. The subzone boundaries should be carefully checked because the zonal markers are rare and occur discontinuously. However, the other events are helpful to correlate the biostratigraphic frames outlined for the investigated areas and to calibrate the NJ4a/NJ4b, NJ5a/NJ5b zone boundaries with respect to the ammonite zones. Based on the achieved data, the main differences between the two schemes are related to the very low abundance and discontinuous occurrence of the some species in their initial (e.g., B. grande, B. finchii) or final (e.g., P. robustus) ranges. Since for the Basque-Cantabrian area ammonite zone and subzones are well constrained, some discrepancies should be related with a discontinuous or incomplete ammonite record from the Lusitanian Basin. Nevertheless, the biostratigraphic frames proposed for both areas could improve biochronocorrelation between the Pliensbachian successions cropping out along the western and northern margin of the Iberian Massif.

18

Lower Toarcian organic-rich sediments from the Tuscan Succession (Northern Apennines, Italy)

Perilli N., Veiga de Oliveira L., Rodrigues R., Catanzariti R.

Volumina Jurassica

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2006

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Vol. 4, no. 1

203-204

EN

This work is aimed to improve lithostratigraphy and biostratigraphy, based on calcareous nannofossils, of the deep-marine Lower Toarcian sediments belonging to Tuscan Nappe (Northern Apennines). The sampled lower part of the Calcari e marne a Posidonia (Posidonia Marls) correlates with the Marne del Monte Serrone of the Umbria-Marche Basin, which is characterized by the presence of the Lower Toarcian black shales. The Calcari e marne a Posidonia consists of grey to greenish hemipelagic to pelagic bivalves-bearing marlstones and limestones with interbedded grey to grey dark, sometimes reddish, clayey marlstones and marly claystones. In some localities, in the lower portion of this formation is recognized a thin to medium thick organic-rich interval of black marlstones and marly claystones. The recovered calcareous nannofossil assemblages allow to assigne the basal portion of the Marne a Posidonia to the Lower Toarcian with the thin organic-rich interval comprised between the appearances of the genera Carinolithus and Discorhabdus.

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Integrated stratigraphy (radiolarians and calcareous nannofossils) of the Middle to Upper Jurassic Alpine radiolarites (Lombardian Basin, Italy):constraints to a genetic interpretation

Chiari M., Cobianchi M., Picotti V.

Volumina Jurassica

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2006

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Vol. 4, no. 1

152-153

EN

New biostratigraphic data obtained by integrating radiolarian and calcareous nannofossil stratigraphy document a depositional history for the Middle to Upper Jurassic radiolarites of the Southern Alps characterized by strong fluctuations in the sedimentation rates, associated with shifts from turbiditic to hemipelagic sedimentary processes. The radiolarites were studied in four sections located in different settings of the Lombardian Basin, a rifted basin of the northern Adriatic Plate, where this interval is known as Selcifero Lombardo Formation. The latter consists of two members, the Radiolarite and the Rosso ad Aptici, respectively, and passes, gradually, upwards to the Maiolica Formation. The sections studied were sampled in detail to obtain data on their lithology (using facies and microfacies analyses and calcimetry) and their nanno- and microfossils content (especially radiolarians, and calpionellids). An almost complete record of radiolarians was detected throughout the Selcifero Lombardo Formation, so that the Radiolarian Zonation (UAZones) for the Middle to Upper Jurassic interval, partially integrated with calcareous nannofossils and calpionellid biostratigraphic data, was successfully applied. Accordingly, the Radiolarite unit correlates with the Lower Bathonian (UAZ. 5) to the Kimmeridgian (UAZ. 11) interval, and the Rosso ad Aptici member displays an age spanning from Kimmeridgian to the base of Upper Tithonian (from the UAZ. 10-11 to nannofossil NJK zone). The base of the Maiolica Formation is assigned to Upper Tithonian, in agreement with the previous authors. We interpret the radiolarites as pelagic sediments relatively enriched in radiolarian during a long time span of basin starvation, due to the near absence of periplatform exportation. Because the very low sedimentation rates equally imply low radiolarian productivity, it is not necessary to claim for high water fertility during Middle to Late Jurassic, even if this latter condition likely played a role in development of the carbonate platforms.

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Calcareous nannofossils biostratigraphy and oxygen isotope composition of belemnites: Pliensbachian – lowermost Toarcian of Peniche (Lusitanian Basin, Portugal)

Veiga de Oliveira L., Duarte L., Rodrigues R., Perilli N.

Volumina Jurassica

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2006

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Vol. 4, no. 1

219-219

EN

The Lusitanian Basin is located in the western Iberian margin, opened during the Triassic.The Lower Jurassic is particularly well represented at Peniche, which exhibits a continuous seriesof carbonate sediments, more than 450 m thick and aged between Sinemurian and Toarcian.In lithostratigraphic terms it corresponds to the Agua de Madeiros, Vale das Fontes, Lemede and CaboCarvoeiro formations. In this study, 145 m thick section (from the Jamesoni to the Levisoni ammonite zones),was analyzed in terms of calcareous nannofossils biostratigraphy and oxygen isotopes of belemnite rostra.The nannofossil biozones NJ4a, NJ4b, NJ5a (Pliensbachian; upper part of Jamesoni to Spinatumammonite zones), NJ5b (uppermost Pliensbachian - lowermost Toarcian; upper part of Spinatumto Levisoni ammonite zones) and NJ6 (lowermost Toarcian; upper part of Levisoni ammonite Zone) wereidentified based on proposed NW European schema and correlated with ammonite zones. Additionally,the secondary biostratigraphic events were registered which will be useful to refine the nannofossilsbiozonation: the first occurrences (FO) of Biscutum grande and B. finchii were found in the upper part ofthe NJ4a biozone (lower part of Margaritatus ammonite Zone); the FO of Lotharingius frodoi wasidentified at the same stratigraphical level as L. hauffii; the FO of L. sigillatus was found in the upper partof the NJ5a biozone (Spinatum Zone); the first common occurrence (FCO) of Calyculus spp. was recognizedin the NJ5b base, near the Pliensbachian/Toarcian boundary; the FO of Carinolithus spp. was identifiedwithin NJ5b biozone, correlated with the lower part of the Levisoni ammonite Zone and below the extinctionlevels of Calcivascularis jansae and B. grande which are other nannofossil secondary events.The oxygen-isotope profile of the Peniche section seems to reflect primary signals and can be usedto interpret the sea water paleotemperatures variations. In the Early Pliensbachian the temperature showsa gradual cooling trend (NJ3 and the lower part of the NJ4a; Jamesoni ammonite Zone). Afterward,there is a warm period (NJ4a and NJ4b; Jamesoni to lower part of Spinatum ammonite Zone) correlatedwith high TOC values interval (up to 15%), suggesting a relative sea level rise and concomitant high surfacewaterproductivity. In fact, the Margaritatus ammonite Zone corresponds, in the Lusitanian Basin,to 2nd-order flooding interval. In the Late Pliensbachian and Early Toarcian (NJ5a and lowermost partof NJ5b; Spinatum to Polymorphum ammonite zones), the isotopic values show slight variations.However, they suggest a small cooling trend in the upper part of Spinatum ammonite Zone and a warmtendency in the lower part of Polymorphum ammonite Zone.