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The present study focuses on calcareous nannofossil biostratigraphy of the last 23 Myr in the Mediterranean region and is intended as a review paper in which an updated zonation is presented. This includes the improvements in biostratigraphic classification achieved in the last decades. The proposed biozonal scheme incorporates the biochronologic data derived from the integration of biostratigraphically useful events with radiometric datings, magnetostratigraphy and astronomically tuned cyclostratigraphy. This biochronology directly derives by previous compilations and includes improved data and ages derived from recent studies based on high resolution quantitative analysis of nannofossil assemblages. The presented zonal scheme consists of 21 biozones and 35 subzones spanning the last 23 Myr, named according to the well-established code-system MNN (Mediterranean Nannofossil Neogene) for the Miocene and Pliocene time interval and MNQ (Mediterranean Nannofossil Quaternary) for the Pleistocene and Holocene. In addition, a revision of the nannofossil biostratigraphy at the Oligocene/Miocene transition is given, with the introduction of Zone MNP26 (Mediterranean Nannofossil Paleogene), as a result of the different age assigned to the Oligocene/Miocene chronostratigraphic boundary. This zonation provides a significant bio-chronostratigraphic resolution of about 0.5 Myr, corresponding to a degree of precision functional for dating sedimentary successions and, therefore, useful for geological studies (e.g. geological mapping, temporal scanning of geological phasis). The biostratigraphic resolution can be furtherly improved through integration with the analogous scheme recently established for planktonic foraminifers. [ABSTRACT FROM AUTHOR]

This review paper has been thought to emphasize the role of Biostratigraphy in Geosciences and, specifically, of calcareous nannofossils as dating tool. This group of calcareous plankton occurs in Mesozoic and Cenozoic carbonate-bearing marine sediments in all depositional settings and is routinely used for stratigraphic purposes. The importance of calcareous nannofossils in relative dating of marine sediments is due to their abundance, taxonomic diversity, rapid evolution and wide distribution in marine environments. Nannofossil biostratigraphy improved over the last few decades due to the use of accurate methods for data gathering, including acquisition of semiquantitative census data on high-resolution samples. These microfossils contribute to obtain reliable biostratigraphic classification in various time-intervals in the last 66 m.y. and often provide the key to the interpretation of other stratigraphic records. Nannofossil biohorizons can be used as control points for constructing cyclostratigraphic composite sections, and for identification of magnetostratigraphic intervals, and have provided a basis for age models subsequently developed into orbitally tuned cyclostratigraphies or used for chronological revision of polarity timescale. [ABSTRACT FROM AUTHOR]

Copyright of Visnyk of Karazin Kharkiv National University. Series "Geology-Geography-Ecology" is the property of V.N. Karazin Kharkiv National University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents the results of a biostratigraphic and paleoenvironmental study of the Dalichai Formation (Talu Section), eastern Alborz mountain range, northern Iran, based on calcareous nannofossils. The base of the section comprises red sandstone which is overlain by a thick layer of marl and a nodular limestone layer proceeded by alternations of sandy limestone, shale and calcareous shale in the middle part, and a layer of nodular limestone and alternations of shale and limestone on the top of the section, transitioning to the limestone of the Lar Formation. The Dalichai Formation overlies the siltstones of the Shemshak Formation. Sixty-five samples were analyzed for calcareous nannofossils resulting in the identification of 9 genera and 20 species and the identification Berriasian to Early Barremian CC1-CC5 biozones of Sissingh (1977). The findings of the study show that the sedimentary basin of the Dalichai Formation of the Talu Section was located in low latitudes of the Tethyan realm and was characterized by warm surface waters that represents a marine transgression upsection, and nutrient supply decreased and paleoenvironmental conditions became increasingly stable. [ABSTRACT FROM AUTHOR]

This paper presents the fluctuation of the calcareous nannoplankton species Emiliania huxleyi and Braarudosphaera bigelowii identified in four cores sampled from the NW Black Sea, at various water depths, between 160.9 and 1.031 m. Unit 1 (Coccolith Mud) and 3 (Lacustrine Lutite) are present in all studied cores, the former showing a variable thickness. Unit 2 (Sapropel Mud) was not observed in the shallowest studied cores, i.e., above 200 m water depth. At the deepest levels of the studied cores, a red-brownish succession, composed of clays and muds, was identified. Calcareous nannoplankton assemblages in situ are present only in the youngest Holocene units 1 and 2, being composed of Emiliania huxleyiand Braarudosphaera bigelowii. These two calcareous nannoplankton species, very abundant especially in Unit 1, show a negative correlation in their abundance pattern. [ABSTRACT FROM AUTHOR]

The analysis of water samples collected during the MD218 CROTALE expedition (February-March, 2019), and the 4th Indian Southern Ocean Expedition (SOE) (January-February, 2010) (re-visited samples) resulted in the occurrence of a new coccolithophore species belonging to the genus Alisphaera, and is named Alisphaera crostae sp. nov. This new species appears monomorphic and shows distinctive morphological differences in terms of its coccolith size, flange structure, and nodules, compared to other known Alisphaera species. In this study, morphological differences between A. crostae and other Alisphaera species are illustrated and compared. We suggest that the genus Alisphaera may have a higher diversity and may possess a wider distribution than previously evidenced, which requires more careful observation [ABSTRACT FROM AUTHOR]

Background: Calcareous nannofossils are minute microfossils widely present in marine strata. Their identification holds significant value in studies related to stratigraphic dating, paleo-environmental evolution, and paleoclimate reconstruction. However, the process of identifying these fossils is time consuming, and the discrepancies between the results obtained from different manual identification methods are substantial, hindering quantification efforts. Therefore, it is necessary to explore automated assisted identification of fossil species. This study mainly focused on 18 key fossil species from the Miocene era. Five convolutional neural network (CNN) models and 10 data augmentation techniques were compared. These models and techniques were employed to analyze and collectively train two- and three-dimensional fossil morphologies and structures obtained from three different fossils observed under single-polarized light microscopy, orthogonal polarized light microscopy, and scanning electron microscopy. Finally, the model performance was evaluated based on the predictive outcomes on the test set, using metrics such as confusion matrix and top-k accuracy. Result: The results indicate that, for the calcareous nannofossil images, the most effective data augmentation approach is a combination of four methods: random rotation, random mirroring, random brightness, and gamma correction. Among the CNN models, DenseNet121 exhibits the optimal performance, achieving an identification accuracy of 94.56%. Moreover, this model can distinguish other fossils beyond the 18 key fossil species and non-fossil debris. Based on the confusion matrix, the evaluation results reveal that the model has strong generalization capability and outputs highly credible identification results. Conclusion: Drawing on the identification results from CNN, this study asserts a robust correlation among extinction photographs, planar images, and stereoscopic morphological images of fossil species. Collective training facilitates the joint extraction and analysis of fossil features under different imaging methods. CNN demonstrates many advantages in the identification of calcareous nannofossils, offering convenience to researchers in various fields, such as stratigraphy, paleo-ecology, paleoclimate, and paleo-environments of ancient oceans. It has great potential for advancing the development of marine surveys and stratigraphic recognition processes in the future. [ABSTRACT FROM AUTHOR]

We investigate a new event of accelerated environmental change that was recorded during the late Barremian in the pelagic Subbetic Basin (Western Tethys). Two pelagic sections have been studied using a multi-proxy approach based on C-isotope stratigraphy and a high-resolution quantitative study of nannofossil assemblages, along with major and trace elements and biomarkers. Our results provide a detailed biostratigraphy and C-isotope stratigraphy, and outline the paleoenvironmental conditions recorded during the early stages of the Taxy Episode. A disturbance has been identified in the C-isotope record, called the IFeNE (Intra-Feradianus negative C-excursion), which is coeval with environmental and biotic changes that predate the well-known ISNE (Intra-Sarasini negative C-excursion). The combined analysis of nannofossil associations, C-isotopes, major and trace elements, and biomarker distributions indicates a separate episode of warming heralding the ISNE, resulting in the acceleration of the hydrological cycle and a consequent increase in continental inputs and the fertilization of surface waters. The origin of the Taxy Episode (the IFeNE and ISNE) has been related to orbital factors (high-eccentricity cycles), and to a global increase in volcanism, probably related to the early phases of the Ontong Java Plateau. [ABSTRACT FROM AUTHOR]

This research offers a comprehensive examination of calcareous nannofossils, isotopic ratios (δ18O and δ13C), and carbonate content spanning the critical Paleocene-Eocene transition at Gebel Nukhul. The study covers three lithostratigraphic formations: Tarawan, Esna, and Thebes. By meticulous analysis, we've identified five distinct calcareous nannofossil zones, including NP7/8 and NP9-12. Zone NP9 is further divided based on the lowest occurrences of specific nannofossils (Discoaster anartios, D. araneus, and/or Rhomboaster spp.), while Zone NP10 is subdivided using Tribrachiatus contortus as a marker. We discussed the significance of various calcareous nannofossil taxa in biostratigraphy, highlighting their role as valuable stratigraphic markers. Our research precisely locates the base of the Eocene at the onset of Subzone NP9b within the Esna Formation, revealing no discernible lithological changes coinciding with this boundary. Additionally, our findings align with the global record, indicating significant decreases in δ13C, δ18O, and calcium carbonate (CaCO3) content during the Paleocene–Eocene transition. These changes underscore the climatic and environmental perturbations during this pivotal geological phase. This study provides valuable insights into the stratigraphy and paleoclimatology of the Paleocene–Eocene transition, contributing to our understanding of past climatic variations on Earth. [ABSTRACT FROM AUTHOR]

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This paper focuses mainly on the representatives of calcareous nannofossils and invertebrates from the Hrvaćani section of the Middle Miocene (Badenian) (Prnjavor Basin, southern margin of Pannonian Basin), and it defines the time of Badenian transgression in this area. Rich resources of fossil mollusk species, isolated parts of coral colonies, and other invertebrate remains were found in the investigated section. Moreover, turtle remains from marine sediments at the southern margin of Central Paratethys were recorded for the first time. Calcareous nannofossil biostratigraphy has established an NN5 Zone by the presence of Sphenolithus heteromorphus and the absence of Helicosphaera ampliaperta. The foraminifera associations from the analyzed sandstones belong to the Lower Badenian, namely the older zones of Ammonia viennensis and Elphidium crispum (the equivalent of Lagenidae Zone of Vienna Basin). The specimen of a turtle is currently attributed to order Testudines (suborder Pleurodira). From a stratigraphic and paleoecological point of view, all the fossil assemblages showed similar patterns for the subject of study, reflecting favorable conditions for developing a subtropical fauna in the open shallow marine environment. Consequently, by combining nannofossils, foraminifers, corals, malacological, and herpetological data, we can conclude that the early Middle Miocene (Badenian) in Hrvaćani (Bosnia) corresponds to the Lagenidae Zone (NN5 Zone) and was characterized by a relatively warm climate. [ABSTRACT FROM AUTHOR]

We present the interpretation of tectono-sedimentary evolution of the West Sudetic area (central Europe) during the latest Turonian–middle Coniacian as recorded by deposits of the NW part of the Bohemian Cretaceous Basin. This paper provides the first strontium isotope curve from the Upper Cretaceous of the Bohemian Massif. The exact stratigraphic framework was provided by combining of macrofossils (inoceramids) and calcareous nannofossils. Six inoceramid zones were distinguished, from Cremnoceramus deformis erectus Zone to Volviceramus koeneni Zone. Biostratigraphic data were combined with XRF curves and geophysical logs which allowed for correlation of several key sections within the study area. Using the genetic stratigraphy, contrasting parts of the depositional system interpreted as nearshore to deltaic were successfully correlated. Six elementary sequences were defined within the studied succession. These are TUR 7 (latest Turonian), backstepping, aggradation-dominated, with a short-term progradational episode and CON 1 to 5 (early–middle Coniacian), deposited during a period of increasing depth through time. The progradational pattern is most typical for the CON 4 sequence. Intensified sediment supply resulting in pronounced progradation is also evidenced by increased siliciclastic influx to the offshore zone and resulting changes in calcareous nannofossil assemblages. Three major transgressive events are interpreted at the base of sequences: (1) CON 1 (close to the Turonian–Coniacian boundary); (2) CON 2 (near FO of Cremnoceramus crassus crassus); (3) CON 5. The transgressions were predominantly driven by basin-floor subsidence, although the transgression at the Turonian–Coniacian boundary and at the base of sequence CON 2 likely carried a component of eustatic sea-level rise. The accelerated basin-floor tectonic subsidence and source uplift in the NW part of BCB falls within the early Ilsede phase of the Late Cretaceous ('Subhercynian') deformation of the Alpine foreland. • Integrated stratigraphic model of the Coniacian of NW Bohemian Cretaceous Basin. • The first 87Sr/86Sr isotope data from the Bohemian Cretaceous Basin. • Sedimentary record evidences changing tectonic regime during the Coniacian. [ABSTRACT FROM AUTHOR]

Lower Miocene sediments from a previously not investigated outcrop of the Qom Formation (Central Iranian Basin) were studied for their foraminiferal and calcareous nannofossil content. The studied stratigraphic record is assigned to the upper part of calcareous nannofossil NN2 Zone/CN1c Subzone and to the benthic foraminiferal Borelis melo melo Zone of Burdigalian age. The diversity indices, benthic foraminiferal morphogroups, and quantitative investigation of assemblages (principal component and cluster analysis) suggest an overall shallow-marine depositional environment. This interpretation is well constrained based on the dominance of the B1 benthic foraminifera morphotype with biconvex, trochospiral calcareous test, and epifaunal habitat. The identified six cluster groups of benthic foraminiferal assemblages are confirmed by the principal component analysis too, and their distribution along the studied section argue for dynamic changes of the environment. This is well exemplified by a more or less constant shallowing, then deepening trend of the environment as revealed by the shifting from the high diversity, shallow-shelf assemblages of Cluster 5 and 6 toward the low diversity, near-shore Ammonia tepida and Porosononion subgranosus assemblage (Cluster 1), and back. [ABSTRACT FROM AUTHOR]

The present study reports on the distribution and occurrence of Braarudosphaera bigelowii in the surface sediments of the western part of the South China Sea (SCS), along the coast of Vietnam. This part of the SCS is a known upwelling region, characterized by low salinity conditions due to high annual rainfall and river run-off, confirming the results of earlier studies regarding the occurrence of B. bigelowii in shallow bays, nearshore, low salinity marine waters and upwelling areas. Morphometric analysis of B. bigelowii pentaliths in the western SCS revealed the presence of the 3 morphotypes proposed by Takano et al. (2006) based on the pentalith side lengths from coccospheres encountered in surface water samples. This paper also reports the occurrence of a new B. bigelowii morphotype in the SCS, corresponding to specimens with a pentalith side length of 3.5-4.0µm. An attempt to relate the distribution of these morphotypes with temperature and salinity proved to be inconclusive, suggesting the possibility that other factors could be influencing the occurrence of the morphotypes in the study area. [ABSTRACT FROM AUTHOR]

Abstract The Essaouira-Agadir Basin (EAB) of Morocco contains the most extensive exposure of Aptian to Lower Albian strata onshore the NW African Atlantic Margin. This paper documents the first high-resolution, multi-disciplinary stratigraphic approach for the Aptian to Lower Albian on the NW African Atlantic Margin. Previous biostratigraphic work almost exclusively relied on long-distance correlation of ammonoids to the Mediterranean – Caucasian Realm. Recent biostratigraphic work has questioned some of the previous interpretations, highlighting significant faunal endemism and complications with correlation to other key Aptian sections. This study focuses on 5 key sections: Tiskatine, Id Amran, Assaka, and DSDP 416/370. Distribution of ammonoids, foraminifera, and calcareous nannofossils are reported from a bed-by-bed collection made at Tiskatine. The analysis of foraminiferal and calcareous nannofossil assemblages enable correlation to standard zonation schemes; but also highlights the urgent need of revision and future work on the integration of these schemes across disciplines. The study, further, includes δ13C carb , δ13C org , and total organic carbon (TOC) data that is compared to reference material from the Vocontian Basin. The combined litho-, bio-, chemo-, and sequence stratigraphic analysis establishes a robust chronostratigraphic framework for regional and super-regional correlations and a type section is proposed for the Aptian of NW Africa at Tiskatine. [ABSTRACT FROM AUTHOR]

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Copyright of Ameghiniana is the property of Argentine Paleontological Association / Asociacion Paleontologica Argentina and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To reconstruct the paleoclimate in North Africa during the Paleocene, the calcareous nannofossils were quantitatively analyzed at higher resolution from the stratigraphic succession of Gebel Nezzazat (west central Sinai, Egypt). The studied interval extends from NP4 to NP8. Zone NP4 can be subdivided into four subzones from base to top: NTp7B, NTp8A, NTp8B, and NTp8C. The base of the Selandian age is located at the base of NTp8B (Second Radiation of Fasciculithus). The Selandian/Thanetian boundary (S/T) is tentatively placed at the base of Zone NP7/8. The identified nannofossil zones were compared with that of the Tethyan region for the Danian/Selandian boundary. The calcareous nannofossil assemblages were used as indicators for medium-term climatic fluctuations. The pre-Danian (LDE) is dominated by the cool-water Zeugrhabdotus sigmoides and Neochiastozygus modestus, while the post-Danian interval is dominated by Coccolithus pelagicus and Ericsonia subpertusa. Before the onset of the Selandian-Thanetian boundary, a marked shift in the nannofossil species was observed, where Fasciculithus increased significantly, while marker Danian-Selandian genera (e.g., Lithoptychius Neochiastozygus, Chiasmolithus, and Cruciplacolithus) decreased dramatically. Non-Metric Multidimensional Scaling (nMDS) and permutational analysis of variance (PERMANOVA) in addition to the Temperature and Nutrient indices (TI and NI) indicated a marked difference between the warm eutrophic nannofossil assemblages at the Danian/Selandian (D/S) and the Selandian/Thanetian (S/T) transitions and the eutrophic cold-water assemblages during the background sedimentation. A sharp increase in sea surface temperature and decrease in nutrients was observed at D/S and represents the Latest Danian Event (LDE), while the second warming event was started prior to the Selandian and may represent the Early Late Paleocene Event "ELPE." The sea-level lowstand may have limited water circulation, where surface water fertility decreased significantly. Consequently, nannofossil diversity decreased. The rapid recovery after the LDE was attributed to the radiation of warm-water taxa. [ABSTRACT FROM AUTHOR]

The middle Eocene Cibrone Formation of Brianza (central-western Lombardy) represents an important stratigraphic record to understand a key step of the tectonic evolution of the Alpine range poorly recorded elsewhere. Quantitative petrographic analysis of turbidite arenites, well-constrained in age by the biostratigraphy of interlayered marlstones based on calcareous foraminifera and nannoplankton, allowed us to identify a possible vertical compositional trend within the Cibrone Fm. and to document the NP17 nannofossil Zone (Bartonian) in central Lombardy exposures, east of the Ternate Formation outcrop area. Variable arenite compositions are interpreted to reflect contributions from different source areas, i.e., recycled orogen, island arc, and starved continental shelf. In a paleogeographic scenario still open to different interpretations, the proposed reconstruction supports a classical plate tectonics model for arc-trench systems. The stratigraphic gap, recorded everywhere in Lombardy, between the Eocene succession and the base of the Gonfolite Lombarda Group (upper NP24 nannofossil Zone, early Chattian), corresponds to the earliest stage of continental collision, uplift and erosion that climaxed in the Neo-Alpine Phase. [ABSTRACT FROM AUTHOR]

This paper presents a biostratigraphic revision and a quantitative study of the calcareous nannofossils from DSDP Leg 80 – Hole 550B. A total of 42 samples were analyzed, revealing 78 species whose preservation varied from slightly to moderately dissolved with slight to severe overgrowth. Biostratigraphy indicates deposition during the late Campanian to late Maastrichtian, incorporating zones UC15d to UC20b. The quantitative nannofossil data recovered shows that Watznaueria barnesiae and Micula staurophora dominate the assemblages, which can be attributed to a low preservation potential for the depositional environment. Cold-water taxa ( Kamptnerius magnificus , Ahmuellerella octoradiata, and Arkhangelskiella cymbiformis ) are present in very low percentages, with their maximum values occurring inside the UC17 biozone. [ABSTRACT FROM AUTHOR]

Copyright of Iraqi National Journal of Earth Sciences is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Three key Paleocene deep-sea sections cropping out in northern Italy contain intercalations of calciturbiditic, larger foraminifera-bearing beds derived from shallow water environments. The reconstructed Southern Alps record obtained by splicing the three sections allowed a direct correlation of the shallow benthic SB and calcareous nannofossils CN Zones, leading new data about the Shallow Benthic biozonation for the Danian-Thanetian interval and proposing four new SBP (Shallow Benthic Paleocene) Zones (SBP1-4). Such revision relies on an innovative biostratigraphic approach based on larger foraminiferal biohorizons instead of marker species according to the traditional approach used since the introduction of the SB Zones. Based on our study, the SBP1/SBP2 boundary turns out to be about 2 Ma after the K/Pg crisis, highlighting a quite fast recovery of the complexity among foraminifera. [ABSTRACT FROM AUTHOR]

Studies of geochemical proxies, such as carbonate δ18O and TEX 86 , show that the Earth's climate has changed significantly during the Cretaceous Period. However, knowledge about the sea surface temperature (SST) history of the eastern Tethys is limited. Based on the calcareous nannofossil record of the Nirang section, Tethys Himalayas, this paper attempts to establish the biostratigraphic framework and SST evolution of the Cretaceous Period in the southern Tibet. A total of 131 species were identified from the studied succession. Twelve bioevents were recognized, allowing for early Albian to the early Campanian (CC8 to CC18 biozones) in the section. Meanwhile, a disconformity within 81–71 Ma was also identified. The SST evolution was analysed by the calcareous nannofossils modified temperature index (mTI), and the results reveal that the long-term SST changes in the Tethys Himalayas of southern Tibet experienced progressive warming from the early Albian to the early Turonian and the warm interval persisted until the early Campanian. Short-term warming and cooling events, e.g., rapid warming in the early and late Albian, subsequent cooling in the latest Albian and peak warmth at the Cenomanian–Turonian transition, are also recorded in the study area. The SST history of the Albian-Cenomanian in the eastern Tethys can be well correlated to the western Tethys (central Italy). However, the compilation of TEX 86 data indicates substantial global cooling during the Coniacian to Campanian. This study suggests that the northward drift of the Indian continent towards the equator is likely to be responsible for the sustained warmth in the Tethys Himalayas from the middle Turonian to the early Campanian. • Calcareous nannofossil biozones of Albian-early Campanian in Tethys Himalaya of southern Tibet is defined. • Based on mTI of nannofossils, long term history of Cretaceous palaeoclimate of eastern Tethys is reconstructed. • The SST history in Tethys Himalaya is controlled by changes of global palaeotemperature and regional palaeolatitude. [ABSTRACT FROM AUTHOR]

Copyright of Iraqi Journal of Science is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Human-induced carbon emissions are altering the modern climate, with severe repercussions on ecosystems. Among others, anthropogenic pressure is causing deoxygenation of the bottom water, with the widespread establishment of hypoxic zones in several Mediterranean areas. The geological archives allow investigating past deoxygenation dynamics (sapropel events) and their impact on marine ecosystems. Here, we compare the causes and the evolution of deoxygenation dynamics which occurred during two different time periods (Messinian and Holocene) in different paleoceanographic settings based on their micropaleontological content. The Messinian sapropel events are the result of increased export productivity during a relatively cold and arid context, triggering bottom anoxic conditions. The Holocene sapropel formed in response to weakening/stopping of the thermohaline circulation due to increasing temperature and freshwater input. Our results suggest that the deoxygenation dynamics in the Mediterranean in the near future will not follow the trend characteristic of the Holocene deep-sea sapropel because of the predicted drying trend. Differently, the paleoceanographic setting triggering the Messinian shallow-sea sapropels is comparable with the modern situation in different Mediterranean areas, where human-induced eutrophication is promoting deoxygenation. Based on these results, we suggest that the patchy deoxygenation trend in the Mediterranean Sea caused by climate warming may lead to a drastic change in the ecosystem services which would likely impact human activities. [ABSTRACT FROM AUTHOR]

The results of a study of calcareous nannofossils found for the first time in the lower part of the Stolbovaya Group of the Kamchatsky Mys Peninsula in Eastern Kamchatka are presented. Two assemblages of different age are identified, with one assigned to the Upper Cretaceous and the other to the Paleogene (not older than the Lutetian Stage of the Middle Eocene). These data make it possible to refine the age of terrigenous–tuffaceous sequences in the lower part of the Stolbovaya Group, which are poor in organic remains. [ABSTRACT FROM AUTHOR]

New field observations and discovery of calcareous nannofossils and planktonic foraminifera from the 'shallow-marine' Çayraz Formation (Haymana Basin, Central Anatolia), a contributing Eocene section to the shallow benthic zonation (SBZ) in the Tethys, allow us to revise its stratigraphy and establish an integrated biostratigraphic scheme for the first time. The hemipelagic marls in the uppermost part of the Eskipolatlı Formation that underlies the Çayraz Formation yielded nannofossil assemblages of Zone CNE3, pinning down the initiation of the Çayraz shelf system into the 'middle' Ypresian. The prominent marly part (Member B) between the carbonate-clastic packages of the Çayraz Formation with prolific occurrences of larger benthic foraminifers (LBFs) (Members A below and C above) yielded calcareous nannofossils suggesting Zone CNE6 (late Ypresian). We show that the mixed carbonate-siliciclastic sequence with abundant LBFs in the upper part of the formation (Member C) is overlain by newly discovered hemipelagic marls (here named as Member D). These marls yielded calcareous nannofossils indicating Zone CNE9 and CNE10 for the lower and Zone CNE12(?Lutetian) for the upper samples. The same beds yielded planktonic foraminifers indicating Zone E8 for the lower and Zone E9 for the upper samples. We conclude that shallow-marine sedimentation in the Çayraz section ended in the 'middle' Lutetian, challenging the previous Bartonian records by LBFs. A new lithostratigraphic scheme consisting of four members with distinctive lithological and biotic characteristics is proposed for the Çayraz Formation: two main shelf systems (Members A and C), each followed by deep-marine sedimentation (Members B and D). [ABSTRACT FROM AUTHOR]

The Upper Cretaceous succession (Coniacian to lowermost Maastrichtian, with focus on the Campanian) at Petrich, Central Srednogorie Zone in Bulgaria, is described and calibrated stratigraphically based on nannofossils, dinoflagellate cysts and inoceramids. The following standard nannofossil zones and subzones are identified: UC10–UC11ab (middle to upper Coniacian), UC11c–UC12–UC13 (uppermost Coniacian to Santonian), UC14a (lowermost Campanian), UC14bTP–UC15cTP (lower Campanian to ‘middle’ Campanian), UC15dTP– UC15eTP (upper Campanian), UC16aTP (of Thibault et al. 2016; upper part of the upper Campanian), and UC16b (Campanian–Maastrichtian boundary). The base of the Campanian is defined by the FO of Broinsonia parca parca (Stradner) Bukry, 1969 and Calculites obscurus (Deflandre) Prins and Sissingh in Sissingh, 1977 (a morphotype with a wide central longitudinal suture). The Areoligera coronata dinoflagellate cyst Zone (upper lower Campanian to upper upper Campanian) is identified, corresponding to the UC14bTP–UC16aTP nannofossil subzones. The inoceramid assemblage indicates the ‘Inoceramus’ azerbaydjanensis–‘Inoceramus’ vorhelmensis Zone, correlated within the interval of nannofossil subzones UC15dTP–UC15eTP. The composition of the dinoflagellate cyst assemblages and palynofacies pattern suggest normal marine, oxic conditions and low nutrient availability within a distal shelf to open marine depositional environment during the Campanian. [ABSTRACT FROM AUTHOR]

Late Albian -- early Cenomanian calcareous nannofossil assemblages from five mid-latitude localities (23-35°) were analyzed using probabilistic and deterministic methods to produce comprehensive and quantitative biostratigraphic sequences that were compared to the widely used 'CC' and 'UC' calcareous nannofossil zonation schemes. This was done to examine their fidelity and general applicability for mid-latitude biostratigraphy and determine whether these quantitative methods can increase the resolution of said schemes. Four biozones spanning the upper Albian through middle Cenomanian were determined using unitary associations (UAs) and ranking and scaling (RASC) optimumsequence from which last appearance datum (LAD) of -- Gartnerago stenostaurion, first appearance datum (FAD) -- Lithraphidites eccentricus, and LAD -- Staurolithites mutterlosei were determined to be reliable early Cenomanian markers at mid-latitudes, while the FAD and LAD of Calculites anfractus are unreliable bioevents and should not be used as a secondary marker for the Albian -- Cenomanian boundary. In addition, we have revised the stratigraphic position of the FAD of L. eccentricus, which was previously assigned to the middle-Cenomanian. The proposed FAD was shortly after the Albian -- Cenomanian boundary, before the FAD of Corollithion kennedyi. We conclude that UAs are more robust than RASC bioevents for this time sequence; however, both methods do not account for the asynchronicity of depositional and biotic chances. Despite these caveats, combining the results for both methods has proven to be a powerful quantitative biostratigraphic tool. [ABSTRACT FROM AUTHOR]

A continuous outcrop of the neritic sediments ranging from the Cretaceous/Paleogene to Eocene/Oligocene boundary is exposed along the Kheu R., Kabardino-Balkaria Republic, southern Russia. High calcareous nannofossil abundance and species diversity in Kheu section make possible the application of various standard calcareous nannofossil zonations for the investigated interval. This provides a direct correlation of the biohorizons used as zonal markers in these zonations and recognition of the stage boundaries in this complete succession, which represents the reference Paleogene section of the NE Peri-Tethys. The carbon and oxygen isotope records revealed a series of excursions correlated to peculiar Paleogene paleoecological events on the basis of nannofossil biostratigraphy. The continuous Maastrichtian/Danian transition displays ca. 1 m thick interval containing only scarce Cretaceous survivors between the highest occurrence (HO) of the most Cretaceous nannofossil taxa and the lowest occurrence (LO) of the Paleogene taxa; this interval is characterized by prominent positive δ13C and δ18O excursions. The Late Danian Event (LDE) is identified as minor δ13C and δ18O excursions in the upper Danian. The base of Selandian stage is defined by the 2nd radiation of fasciculiths, followed by negative δ13C and δ18O shifts corresponding to the Danian/Selandian Transition Event. Mid-Paleocene Biotic Event (MPBE), A, B1/B2, C1/C2 and D1/D2 events are pronounced in the upper Paleocene C and O isotope record. Wide expansion of Discoasterales (Fasciculithus, Heliotrochus, Heliolithus, Discoaster), served as a basis for nannofossil zonations, is featured for this time span. The base of Ypresian (lower Eocene) corresponds to the onset of the carbon isotope excursion (CIE) documented at the base of the TOC-rich bed. This 0.6 m thick sapropelitic bed corresponds to the Paleocene–Eocene Thermal Maximum (PETM) and contains specific nannofossil assemblage known as "excursion taxa". The high sedimentation rate and completeness of the early Eocene sedimentary succession allowed to record the evolution of Tribrachiatus bramlettei–T. digitalis–T. contortus–T. orthostylus lineage spanning the interval of NP10–NP12 zones. Multiple δ13C and δ18O excursions, occurred in the lower Ypresian sediments, correspond to the early Eocene hyperthermals E1/E2, F1, F2, G, ETM2, I1/I2 and J. The intercalations of a series of TOC-rich layers in the interval ranging the upper NP12 to lower NP13 zones correspond to ETM3 and individual episodes (L-T) of the Early Eocene Climatic optimum (EECO). Long-term cooling trend in the Caucasian basin begins in the uppermost Ypresian (upper NP13 zone). The middle Eocene δ18O record demonstrates a succession of negative excursions occurred against the background of relatively high values. The hyperthermal C21r–H6 is recognized at the base of Lutetian stage defined by the LO of Blackites inflatus. Two later excursions of this time interval corresponding to the Late Lutetian Event (LLE) and Middle Eocene Climatic Optimum (MECO) occur in the enriched in TOC Kuma Fm. (late Lutetian to Bartonian) and fall at the levels with highest TOC concentrations. Nannoplankton assemblages are widely dominated by eurytopic reticulofenestrids during both events, while Chiasmolithus and Discoaster become oppressed that can indicate lower salinity caused by enhanced humidity. The base of Priabonian is defined by the LO of Chiasmolithus oamaruensis and the base of Cribrocentrum erbae acme. These bioevents are preceded by the negative δ13C excursion and very positive δ18O values, possibly correlated to the Priabonian Oxygen Maximum (PrOM). The relatively warm Priabonian time, characterized by recovery of Chiasmolithus, Discoaster and Sphenolithus, gives way to a new cooling phase known as Late Eocene Event (LEE). The base of Clausicoccus subdistichus acme, approximated to the base of Oligocene, falls at the level ca. 0.5 m below the facial change corresponding to the large-scale sea-level fall and, thus, slightly precedes the accumulation of low-calcareous oil-bearing Oligocene-lower Miocene Maikop Fm. The prominent positive δ13C and δ18O excursions occur at the base of this formation. [ABSTRACT FROM AUTHOR]

We obtained material from the Puerto Escano section (southern Spain) to study the Jurassic/Cretaceous (J/K) boundary interval. The same samples had already been processed for magnetostratigraphic studies and biostratigraphic zonation based on calpionellids and ammonites (Pruner et al. 2010), but not for calcareous nannofossils. The aim of this study was to process the samples using micropalaeontological analysis and to compare and calibrate results for calcareous nannofossils with existing magnetostratigraphic and other biostratigraphic data. The calcareous nannofossil assemblage was dominated by the genera Watznaueria, Cyclagelosphaera, Nannoconus, Conusphaera and Polycostella. Several nannofossil bioevents were recorded on the basis of the distribution of stratigraphically important taxa, including zonal and subzonal markers. Based on the lowest occurrences (LO) of M. chiastius, N. globulus minor, N. wintereri, N steinmanii minor, N. steinmannii steinmannii, N. kamptneri minor and N. kampteri kamptneri, two nannofossil subzones (NJT 15b, NJT 17a) and two nannofossil zones (NJT 16, NK-1) were recognized. The paper introduces new palaeoecological data based on geochemical analysis and macrofauna occurrences. [ABSTRACT FROM AUTHOR]

Oceanic Anoxic Event 2, spanning the Cenomanian/Turonian boundary (93.9 Ma), was an episode of major perturbations in the global carbon cycle. To investigate the response of biota and the paleoceanographic conditions across this event, we present data from International Ocean Discovery Program sites U1513 and U1516 in the Mentelle Basin (offshore SW Australia; paleolatitude 59°–60°S in the mid‐Cretaceous) that register the first complete records of OAE 2 at southern high latitudes. Calcareous nannofossils provide a reliable bio‐chronostratigraphic framework. The distribution and abundance patterns of planktonic and benthic foraminifera, radiolaria, and calcispheres permit interpretation of the dynamics of the water mass stratification and provide support for the paleobathymetric reconstruction of the two sites, with Site U1513 located northwest of the Mentelle Basin depocenter and at a deeper depth than Site U1516. The lower OAE 2 interval is characterized by reduced water mass stratification with alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer as indicated by the fluctuations in abundance of the intermediate dwelling planktonic foraminifera. The middle OAE 2 interval contains lithologies composed almost entirely of radiolaria reflecting extremely high marine productivity; the low CaCO3 content is consistent with marked shoaling of the Carbonate Compensation Depth and ocean acidification because of CaCO3 undersaturation. Conditions moderated after deposition of the silica‐rich, CaCO3‐poor rocks as reflected by the microfossil changes indicating a relatively stable water column although episodes of enhanced eutrophy did continue into the lower Turonian at Site U1516. Key Points: Documentation of first complete record of the Late Cretaceous Oceanic Anoxic Event 2 (OAE 2) at southern high latitudes (60°S) in the Indian OceanDynamics of the water mass stratification inferred from distribution patterns of foraminifera, radiolaria, calcispheresOAE 2 is characterized by alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer [ABSTRACT FROM AUTHOR]

The use of calcareous nannofossils for provenance analysis is a new-old topic for cultural heritage. Several studies have already mentioned it for ceramic, but less for paintings. Preparatory layers of the paintings are often made with chalk, which is composed of microfossils. To extract a calcareous nannofossils assemblage from a painting layer, we need to disaggregate it. The method is to plunge the micro-samples into water and heat it if water alone does not work. The disaggregation process takes a long time and is not efficient in terms of quantitative results. In this work, we aimed to develop a disaggregation method that increases the number of determinable nannofossils extracted from a painting micro-sample. As these samples are valuable and unique, we decided that a combination of analyses on the disaggregated micro-sample should be tried to extract the most information from it. We studied the possibility of binder determination by gas chromatography–mass spectrometer after the nannofossils assemblage extraction on the residual liquid from the disaggregation. The method we are presenting is easy to apply, has a high disaggregation rate for most paintings, and a low impact on binders fatty acids for their determination. [ABSTRACT FROM AUTHOR]

The application of wellsite biostratigraphic technique has aided the reconstruction of the subsurface geology in the Nigerian deepwater region. It has further aided decision making during drilling operations including the planning of well paths. Critical decisions regarding casing setting, coring point selection, overpressure zone determination and total depth picks, are easily achieved through confirmation of well prognosis and correlation to offset wells. This technique is very important in the tectonically active Nigerian deepwater region which is characterized by varying degrees of both syn-depositional and post-depositional deformation. Accurate interpretation of basin architecture, lateral variation and facies change is required before drilling. Confirmation of well prognosis during drilling operation is equally important. It has been proved that wellsite biostratigraphic technique helps to “get it right at first” when integrated with the traditional lithologic description, log signature correlation and seismic profile interpretations. The modern and rapid processing technique of calcareous nannofossil, for instance, provides ‘real time’ result for the exploration team for confirmation of, or adjustment to, the drilling program. The attendant contribution in saved time, cost and safe and successful drilling operation makes the technique beneficial for all operators. This paper presents practical experience of wellsite biostratigraphy application in three oil prolific Nigerian deepwater regions: the Niger Delta, Joint Development zone of Nigeria/Sao Tome and Principe area (JDZ) and Benin (Dahomey) Basin. [ABSTRACT FROM AUTHOR]

The mid-Valanginian Weissert Event represents one of the most significant paleoceanographic events of the Early Cretaceous and is characterized by a major perturbation of the carbon cycle testified by a positive carbon isotope shift, a crisis of both neritic and pelagic carbonate producers, and climatic fluctuations. Here we propose a paleoreconstruction of paleoenvironmental changes that occurred in the reference Vergol and La Charce sections (Vocontian Basin, SE France) during the Weissert Event based on the analysis of calcareous nannofossil absolute abundance and assemblages. These latter are compared to newly acquired and already published sedimentological and organic geochemical analyses. Our approach is novel for the time interval considered. Indeed, Principal Component Analysis was applied for the first time to the entire nannofossil assemblage to reconstruct environmental conditions, instead of using paleoecological preferences of single species. The comparison of calcareous nannofossils and biomarker analyses indicates that a phase of severe sea–water stratification occurred prior to the carbon positive excursion of the Weissert Event in the Vocontian Basin. This was followed by a raise in fertility of surface waters, as attested by increased nannofossil abundances, in particular, of meso–eutrophic taxa, and biomarkers likely produced by dinoflagellates. This increase in fertility was likely triggered by a humid climate and enhanced continental input of clays and nutrients to surface oceanic waters. Calcareous nannofossils also proved to react to sea-level changes that occurred in the Valanginian, as inferred by previous works. Species likely inhabiting proximal areas were recorded in higher proportions during a major sea-level drop in the Peregrinus Ammonite Zone, Late Valanginian. The results of this study also permit to revise previously proposed paleoecological affinities of some nannofossil species. We suggest that Watznaueria barnesiae , one of the most-widely used species in the literature, should be used cautiously because of its high plasticity with respect to environmental conditions. Also, nannoconids that are usually regrouped in papers with paleoceanographic purposes should be analyzed separately because they show distinct species-specific ecological preferences. [ABSTRACT FROM AUTHOR]

Detailed lithostratigraphic and calcareous nannofossil biostratigraphic studies were carried out across the Paleocene–Eocene (P-E) that outcrops at Gebel Nezzazat (G. Nezzazat) in West Central Sinai (Egypt). The study interval spans from the upper part of the Tarawan Formation to the lowermost Thebes Formation covering the whole Esna Formation in between them. The Esna Formation had been subdivided into four members: the Hanadi, Dababiya Quarry, Mahmiya, and Abu Had Members. Five calcareous nannofossil biozones (NP7/8, NP9 to NP12) and four subzones (NP9a and NP9b and NP10a and NP10b) were recognized. The lowest occurrences (LOs) of Fasciculithus alanii group, Neochiastozygus junctus, Sphenolithus radians, and Blackites herculesii as well as the highest occurrence of F. alanii group and the increased frequency of N. junctus are biostratigraphically significant. On contrast, the LOs of Discoaster binodosus, Discoaster mahmoudii, Discoaster diastypus, Zygrhablithus bijugatus, and Campylosphaera dela as well as the LOs of Fasciculithus tympaniformis are unreliable bioevents. Calcareous nannofossils increase in abundance close to the P-E transition. Ericsonia subpertusa suddenly increases above the base of Eocene, whereas the diversity of Fasciculithus drops close to this level. The P-E boundary at G. Nezzazat was placed at the base of the Dababiya Quarry Member in coincidence with the base of Subzone NP9b that was delineated by the LOs of Discoaster araneus, Rhomboaster cuspis, Rhomboaster calcitrapa, Rhomboaster spineus, and Rhomboaster bitrifida. A small gap was recorded across the P-E boundary as indicated by the lack of the four beds of the Dababiya Quarry Member. The changes in calcareous nannofossil assemblages reveal warm-water and oligotrophic conditions prevailed during the transition at G. Nezzazat. [ABSTRACT FROM AUTHOR]

The first data on the distribution of calcareous nannofossils in the Behbehan section, the Kuh-e-Rish, are considered. According to the distribution of nannofossils, the Upper Cretaceous deposits of the section are subdivided into nine biostratigraphic zones. CC17 ( Calculites obscurus zone) indicate the Late Santonian. Biozones CC18 ( Aspidolithus parcus zone), CC19 ( Calculites ovalis zone), CC20 ( Ceratolithoides aculeus zone), CC21 ( Quadrum sissinghii zone), and CC22 ( Quadrum trifidum zone) represent the Campanian. Biozone CC23 ( Tranolithus phacelosus zone) indicate the Late Campanian-Early Maastrichtian. Biozones CC24 ( Reinhardtites levis zone) and CC25 ( Arkhangelskiella cymbiformis zone) suggest the Middle and Late Maastrichtian, respectively. In the late Late Maastrichtian, due to decreasing in water depth at the study area, Nephrolithus frequens zone (CC26) defined in Tethysian domain was not recognized. The boundary between Gurpi-Pabdeh Formations represented a non-depositional period from the late Late Maastrichtian to the end of Early Paleocene. Also, it seems that predominant conditions of the sedimentary environment of Neotethys basin with the presence of index species calcareous nannofossils specified, which itself indicates that the warm climate and high depth of the basin in Late Santonian to Late Maastrichtian, in low latitudes has been prevalent. [ABSTRACT FROM AUTHOR]

This paper discusses the results of a study of the Le Chouet section, its lithologies, facies, magnetic properties and fossil record (ammonites, calcareous nannofossils, calpionellids and calcareous dinoflagellates). Data obtained have been applied to give a precise biostratigraphy for this carbonate sequence as well as a paleoenvironmental reconstruction. Its relationship to magnetostratigraphy, based on a modern study of a French site, is important. Investigation of the micro- and macrofossils shows that the site comprises a sedimentary sequence in the Microcanthum to Jacobi ammonite Zones, and the Chitinoidella, Crassicollaria and Calpionella Zones. Several calpionellid and nannofossil bioevents have been recorded on the basis of the distribution of stratigraphically important planktonic organisms. The site allows us to calibrate the levels of various biomarkers and biozonal boundaries, and correlate them with the magnetozones M20n, M19r and M19n. [ABSTRACT FROM AUTHOR]

An integrated study including magnetostratigraphy, larger benthic foraminifera and calcareous nannofossil biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised, the taxa found are enough to support the chronostratigraphic attribution. Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulites and Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs. These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ 13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary occurs in SBZ 12. [ABSTRACT FROM AUTHOR]

In support of the ongoing temporal palaeoenvironment and palaeoclimatic reconstructions of the Neogene sediments, this study attempts to detail the paleo-proxies recovered from DEL-1 Well, western offshore Niger Delta. The standard smear slide method enabled the recovery of well-preserved calcareous nannofossils that depict early to mid-Miocene (NN4-NN5) sediments. The up-hole relationships between the nannofossil accumulation rate (NAR), the relative abundance of Discoaster and coccolith size of Reticulofenestra show step by step collapse of sea surface stability from early to middle Miocene. The lower horizons (8000-9460 ft) exhibit a low NAR, relatively high Discoaster abundance and relatively large Reticulofenestra size to suggest a deep thermocline and nutricline that characterise oligotrophic conditions in less warm-water induced climate. Conversely, upper horizons (5225-6550 ft) exhibit a high NAR, relatively low Discoaster abundance and relatively small Reticulofenestra size to suggest a shallow thermocline and nutricline that characterise eutrophic conditions in warm-water induced climate. The relative abundance of Helicosphaera carteri within the mid-NN5 suggests mesotrophic conditions within a stressed environment, with the possible occurrence of carbonate crash events. The combined parameters indicate gradual eutrophication and collapse of sea surface stability favouring nutrients and influx of terrestrial sediments in the ocean water as it progressed from early to middle Miocene. The abundance of the palaeo-proxies assemblages suggests hyposaline waters in a neritic environment that prevailed during the warm climatic condition. [ABSTRACT FROM AUTHOR]

This paper presents a detailed calcareous nannofossil biostratigraphy of the entire Lutetian of the Agost section ( Betic Cordillera, SE Spain). This investigation integrates and improves on previous study performed through the Ypresian/ Lutetian boundary by the authors on this succession. The new revision of the integrated bio-magnetobiochronology of the Early/ Middle Eocene interval revealed highly diversified calcareous nannofossil assemblages, characterizing more than 8 Myr of climatic variability. The studied interval spans from Zone CP11 to Subzone CP14a and from the upper part of Zone NP13 to the base of Zone NP16 of calcareous nannofossil standard zonations. The revision of the calcareous nannofossil content enabled the identification of numerous secondary events which greatly improved the stratigraphic resolution of this time interval. An important re-organization of the nannoflora was observed during the Y/L transition, when Reticulofenestra and Dictyococcites ( Noelaerhabdaceae) became the most important genera in terms of abundance and dispersal, dominating the Middle Eocene nannofossil assemblages and replacing Toweius and Discoaster taxa characteristic of the lower Eocene. Pentaliths and Blackites experience a great expansion and diversification, whereas Discoaster and Chiasmolithus which are well diversified but never abundant during the Lutetian show a slow turnover. A reassessment of the major bio-events observed in the Noelaerhabdaceae family as well as revision and correlation of these events with the classical Italian sections ( Contessa and Bottaccione) are presented. The new results show that biostratigraphic problems related to the Middle Eocene chronology are not limited to the correlation between calcareous nannofossils and planktonic foraminiferans at the Y/L transition but extend to calcareous nannofossil events commonly used for correlating the Bartonian. [ABSTRACT FROM AUTHOR]