Planktonic Foraminifers Research Articles

Evaluation of oxygen isotopes and trace elements in planktonic foraminifera from the Mediterranean Sea as recorders of seawater oxygen isotopes and salinity

Abstract. The Mediterranean Sea is characterized by a relatively strong west to east salinity gradient, which makes it an area suitable for testing the effect of salinity on foraminiferal shell geochemistry. We collected living specimens of the planktonic foraminifer Globigerinoides ruber albus to analyse the relation between element ∕ Ca ratios, stable oxygen isotopes of their shells, and surface seawater salinity, isotopic composition and temperature. The oxygen isotopes of sea surface water also correlate with salinity in the Mediterranean during winter, which is when sampling for this study took place. Seawater oxygen and hydrogen isotopes are positively correlated in both the eastern and western Mediterranean Sea, although the relationship differs from previously reported values, especially in the eastern region. The slope between salinity and seawater oxygen isotopes is lower than previously published results. Still, despite the rather modest slope, seawater and foraminiferal carbonate oxygen isotopes are correlated in our dataset, albeit with large residuals and high residual variability. This scatter could be due to either biological variability in vital effects or environmental variability. Numerical models backtracking particles show that ocean-current-driven mixing of particles of different origins might dampen sensitivity and could result in an offset caused by horizontal transport. Results show that Na ∕ Ca is positively correlated with salinity and independent of temperature. As expected, foraminiferal Mg ∕ Ca increases with temperature, which is in line with earlier calibrations, and in the high salinity environment. By using living foraminifera during winter, the previously established Mg ∕ Ca–temperature calibration is extended to temperatures below 18 ∘C, which is a fundamental prerequisite of using single foraminifera for reconstructing past seasonality.

Millennial-scale variability of Indian summer monsoon during the last 42 kyr: Evidence based on foraminiferal Mg/Ca and oxygen isotope records from the central Bay of Bengal

Studying marine sedimentary archives from the Indian Ocean have provided great opportunities to assess the forcing/response relationship between the Indian monsoons, millennial-scale climate variability as revealed in Greenland ice cores, and possible roles of the Atlantic meridional overturning circulation (AMOC) changes that are most likely responsible for driving both. Here we present new evidence of sea surface temperature (SST) estimates and δ18O of seawater (δ18Osw, presumably salinity-driven) from the paired data of Mg/Ca and δ18O measured from planktonic foraminifer Globigerinoides ruber (white) in core BoB-24 collected from the central Bay of Bengal (BoB), tropical Indian Ocean. Eleven accelerator mass spectrometry (AMS) radiocarbon dates on planktonic foraminifera Neogloboquedrina dutertrei from the core provide a reliable age model. Our results indicate a gradual surface warming with several short-lived fluctuations since ~42 kyr ago, and a ~3 °C cooling during the Last Glacial Maximum (LGM) and a ~3 °C warming from the last glacial to the Holocene. Our δ18Osw revealed an increased salinity during the Marine Isotope Stage (MIS) 2, which is likely attributable to a weakening of Indian Summer Monsoon (ISM) precipitation and associated river discharge in the BoB. Our record also indicates clearly a phase of strengthening ISM during the mid-MIS 3 (37.5–32 ka) as evidenced by low foraminiferal δ18Osw values of ~0.2‰. Lower than present δ18Osw values during the Bølling/Allerød (B/A) event (14.5–12.6 ka) and the early Holocene (10–5 ka) in core BoB-24 indicate lower salinity that in turn suggest enhanced ISM precipitation and increased freshwater output from the Ganges-Meghna-Brahmaputra-Irrawaddy (GMBI) rivers together with peninsular rivers and Irrawaddy-Salween rivers from Myanmar. This study brings data evidence that implies weakened ISM was linked with Northern Hemisphere cooling events, especially during the MIS 2. Furthermore, the millennial-scale hydroclimate changes in the BoB presented in this study support the dynamic role of AMOC in driving a teleconnection between the North Atlantic and Indian Ocean monsoon regions.

Planktonic Foraminiferal Endemism at Southern High Latitudes Following the Terminal Cretaceous Extinction

AbstractAustral planktonic foraminiferal assemblages from immediately above the Cretaceous/Paleogene (K/Pg) boundary at Ocean Drilling Program Hole 690C (Maud Rise, Weddell Sea) and International Ocean Drilling Program Hole U1514C (southeast Indian Ocean) show a much different record of post-extinction recovery than anywhere outside the circum-Antarctic region. Species of Woodringina and Parvularugoglobigerina, genera with well-documented evolutionary successions within the early Danian P0 and Pα biozones at tropical/subtropical and mid-latitude localities, are absent from southern high latitude sequences. This study proposes new criteria for biostratigraphic correlation of the lowermost Danian Antarctic Paleocene AP0 and AP1 Zones using stratophenetic observations from Scanning Electron Microscope images of lower Danian planktonic foraminifera at deep-sea sites in the southern South Atlantic and southern Indian Ocean. The small but distinctive species Turborotalita nikolasi (Koutsoukos) is a highly reliable index species for the lowermost Danian as it consistently occurs immediately above the K/Pg boundary at multiple southern high latitude sites, which is consistent with its distribution at middle and low latitudes. Also useful for cross-latitude correlation is Parasubbotina neanika n. sp., which first appears within the lowermost Danian worldwide. The geographic distribution of the New Zealand species Antarcticella pauciloculata (Jenkins) and Zeauvigerina waiparaensis (Jenkins), as well as Eoglobigerina maudrisensis n. sp. from just above the K/Pg in the southern South Atlantic and southern Indian Ocean, helps define the extent of the Austral Biogeographic Province and provides evidence for marine communication via marine seaways across Antarctica. While An. pauciloculata was previously considered a benthic species, new stable isotope evidence demonstrates that it lived a planktonic mode of life. It is possible this species evolved from a benthic ancestor and that the benthic to planktonic transition occurred through an intermediate tychopelagic lifestyle at a time when calcareous plankton were less abundant as a result of the terminal Cretaceous mass extinction.

Key Environmental Factors Controlling Planktonic Foraminiferal and Pteropod Community’s Response to Late Quaternary Hydroclimate Changes in the South Aegean Sea (Eastern Mediterranean)

A multidisciplinary study was conducted in order to investigate the environmental factors affecting the planktonic foraminiferal and pteropod communities of the south Aegean Sea. Aspects of the Late Quaternary paleoceanographic evolution were revealed by means of quantitative analyses of planktonic foraminiferal and pteropod assemblages (including multivariate statistical approach; principal component analysis (PCA)), the oxygen (δ18O) and carbon (δ13C) isotopic composition of planktonic foraminifera and related paleoceanographic (planktonic paleoclimatic curve (PPC), productivity (E-index), stratification (S-index), seasonality) indices, extracted by the gravity core KIM-2A derived from the submarine area between Kimolos and Sifnos islands. Focusing on the last ~21 calibrated thousands of years before present (ka BP), cold and eutrophicated conditions were identified during the Late Glacial period (21.1–15.7 ka BP) and were followed by warmer and wetter conditions during the deglaciation phase. The beginning of the Holocene was marked by a climatic amelioration and increased seasonality. The more pronounced environmental changes were identified during the deposition of the sapropel sublayers S1a (9.4–7.7 ka BP) and S1b (6.9–6.4 ka BP), with extremely warm and stratified conditions. Pteropod fauna during the sapropel deposition were recorded for the first time in the south Aegean Sea, suggesting arid conditions towards the end of S1a. Besides sea surface temperature (SST), which shows the highest explanatory power for the distribution of the analyzed fauna, water column stratification, primary productivity, and seasonality also control their communities during the Late Quaternary.

Cretaceous/Palaeogene boundary transition induced lattice defects in illite and kaolinite associated with the Um-Sohryngkew river section, Meghalaya, India

Cetaceous-Palaeogene Boundary (KPB) transition records restricted to a unique, continuous, late Maastrichtian-early Danian, shallow marine Um Sohryngkew river succession (bearing planktonic foraminifers' CF4 to P1a biozones) have not been studied in detail. Earlier studies sub-divided it into lower, middle and upper parts, defined by the dominance of illite> illite/smectite; illite>kaolinite> montmorillonite and kaolinite > montmorillonite assemblages, respectively. However, limited studies were carried out on the KPB transition events, particularly for those reproduced in the illite (C2/m) and kaolinite (P1) lattice structures. Thus, illite and kaolinite cell parameters and interatomic distances have been studied to understand KPB transition events. For this purpose, layer-wise clay (0.2–2 μm) separates were analyzed by X-ray diffraction method and subjected to Rietveld refinement. Obtained data show substantial expansion in the c-axis of the kaolinite grains associated with the shaly marlite (P0 biozone) layer. Also, b- and c- axes of the kaolinite associated with the yellowish brown (CF3 biozone) layer indicate expansion and contraction, respectively. Moreover, Al–O bond in the kaolinite reflects contraction. Obtained cell parametric data and interatomic distances when plotted across the stratigraphic succession show notable contraction along b- and c- axes of the illite associated with the yellowish brown and shaly marlite layers of the CF3 and P0 biozones, respectively. The illite containing 26 atoms, linked to 38 and 34 bonds present in the intensely weathered lower and middle parts of the CF4 biozone, respectively. The illite in the moderately weathered upper part of the CF4 – CF1 biozones bearing 32 atoms and 44 bonds, represent Si–K and Al–K bond distortions together with the loss of Si4+ and K+. The coprolite-bearing shaly marlite layer (between the CF1 and P0 biozones) shows drastic changes in the illite structure, containing 48 atoms and 44 bonds, characterized by K–O, Si–K and Al–O bond contractions along with the retention of K+ and Al3+. Moreover, Al–O, Si–K, Al–K and Al–Al bonds connected strongly due to reinforcement of Al ions. A very low degree of alteration is noticed in case of preceding yellowish brown (CF3 biozone) layer. Owing to the weakening of the Al–O and Si–O bonds in the intensely weathered illite lattices of this layer show distortion as well as Al3+ and Si4+ losses, suggest incidence of thermal high. Sudden degeneration of illite lattices noticed in the shaly marlite layer is also marked with the planktonic foraminifers’ extinction, signifying biostratigraphic boundary. Thus, contraction in the c- axis as well as notable decrease in the bond lengths of illite (in this layer) is linked to KPB transition which includes major tectonic events, sea level changes and global-climatic changes caused environmental stress in the sea shelf. The substantial distortion in the illite lattices of the biozone CF2 corresponds to the most vigorous second phase of the Deccan volcanic eruption that occurred during 65.4–65.2 Ma.

Paleoenvironments of Coniacian Age Outcrops in the Congo Coastal Sedimentary Basin

The study of the Turonian formations outcropping along the Congolese coast was undertaken in the order of to understand the sequential organization of the deposits as well as the evolution of the paleoenvironments. The study consisted of a detailed description of the lithofacies in the field and in the laboratory. This study shows that these formations are essentially made up of silty dolomites, formed in a littoral environment where the waters were favorable to the multiplication of planktonic foraminifers, Lamellibranchs and Brachiopods. The sedimentological characteristics indicate a sudden retreat from the shore, witnessed by the various regressive elementary sequences. These elementary sequences each begin with a layer of thanatocenosis which would be due to a sudden change of environment, consequence of an important arrival of detrital terrigenous sediments. This terrigenous detrital contribution disrupts each time the physicochemical characteristics of the environment (oxygen deficiency, absence of light, high turbidity). The fauna of these formations exhibits a coniacian affinity. The sequential evolution of the deposit shows a large ravine unconformity on the top of the mega sequence. The composition of the fauna and the sedimentological characteristics confirm the existence of a regressive sedimentation model of the Lower Coniacian age.

An Approach to the Paleoceanographic Characteristics of the Sea-Surface at the Western Mediterranean (Balearic Area) during the Pliocene and Gelasian

From the study of the planktonic foraminifer assemblages of the sediments of the Ocean Drilling Program (ODP)-Site 975 (Baleares), sea-surface temperature, seasonality and salinity for the Pliocene and Gelasian of the Western Mediterranean were estimated. The estimates were carried out by the modern analog technique (MAT) using PaleoUma, a calibration dataset of 735 North-Atlantic and Mediterranean core-tops. In order to compare Pliocene–Gelasian and present-day analog assemblages, the necessary reduction of the taxonomic variables leads to statistically insignificant increases in estimation error, assessed on the calibration dataset itself. In addition, the correlation with δ18O results as an independent proxy, supports the use of MAT in order to establish the dominant paleoceanographic frameworks during the Pliocene and Gelasian. The SST curve shows an increase trend of the average value since the Early Zanclean (19.7 ± 1.8 °C) to the Late Piacenzian (20.9 ± 1.7 °C) and a decrease until the Late Gelasian (18.1 ± 1.4 °C). The seasonality offers permanently lower estimates than the current value (9.8 °C), reaching the closest values during the Late Gelasian (8.6 ± 0.8 °C). The salinity estimates are overall slightly lower during the Zanclean (36.7‰ ± 0.5‰) than today (37.3‰), whereas they reach up to more than 38.5‰, in the Early Piacenzian. The paleoceanographic frameworks deduced from the combination of the paleoceanographic parameters suggest that the current water-deficit regime in the Mediterranean was clearly predominant throughout the Pliocene and Gelasian. However, since the Piacenzian this regime alternates with stages of water surplus, which are especially frequent in the late Piacenzian. By the middle of the Early Gelasian the regime becomes more predominantly in deficit again.

Bioerosion on Late Quaternary Planktonic Foraminifera Related to Paleoproductivity in the Western South Atlantic

AbstractPlanktonic Foraminifera are widely used in paleoceanographic reconstructions, although studies of their trophic interactions are still rare, especially those focusing on predation. Drilling holes are the most frequent traces of bioerosion in foraminifer tests, but environmental factors that control bioerosion are not yet understood. To determine if paleoceanographic variables are associated with bioerosion rates in late Quaternary planktonic foraminifers of the western South Atlantic, geochemical and assemblage analyses were made on a 46 kyr record from a piston core. An age model was constructed based on 10 AMS 14C dates. To reconstruct the paleoproductivity, δ13C, benthic/planktonic foraminifer and the relative abundances of Globigerina bulloides and Globigerinoides ruber (high and low productivity, respectively) were used. Bioeroded tests were counted and found in 21 of the 25 identified species, with frequencies ranging from 8.84% to 16.7%. Bioerosion was different in two groups identified by cluster analysis, with a higher intensity during glacial times, showing a strong correlation with paleoceanographic fluctuations. Paleoproductivity estimates and bioerosion rates show a significant correlation, suggesting that bioerosion is more frequent in eutrophic environments and more inhibited in oligotrophic conditions. However, even with a strong correlation between bioerosion and productivity, there is also a negative correlation with sea surface temperature in the study area. Since conditions that promote higher productivity are accompanied by a decrease in surface temperature, the precise distinction between the influence of both variables is hampered. Further research will allow us to explore the potential of planktonic foraminiferal bioerosion as a tool in paleoceanographic studies.

First report of the Eocene bivalve Schedocardia (Mollusca, Cardiidae) from Cuba

Herein we provide the first report of the cardiid bivalve Schedocardia from Cuba. The single, partial, valve external mold was derived from the Madruga Formation which is characterized by a richly diverse marine fauna including echinoderms, brachiopods, benthic and planktonic foraminiferans, but from which bivalves were not previously reported. The unit is considered late Paleocene in age (Thanetian), but the presence of Schedocardia supports a possible age extension of the formation into the early Eocene (Ypresian). Moreover, we provide a reconsideration of the historical factors that affected the accepted type locality of the outcrop, which allows for an alternative interpretation of the fauna found therein.

Zooplankters in an oligotrophic ocean: contrasts in the niches of Globigerinoides ruber and Trilobatus sacculifer (Foraminifera: Globigerinida) in the South Pacific

ABSTRACT Distributions of the planktonic foraminifers Globigerinoides ruber (d’Orbigny) and Trilobus sacculifer (Brady) from the tropical-subtropical South Pacific Ocean are related to sea surface temperature (SST), chlorophyll-a, nitrate, phosphate, salinity and oxygen to determine whether their niches overlap. Their distributions in the ForCenS database of species in seafloor sediment are studied as proxies for upper ocean data. In the occurrence analysis (MaxEnt) SST is the strongest predictor of niche suitability followed by chlorophyll-a; environments between 0–20° S are the most suitable for both species: niches are undifferentiated. Contrarily, abundance analysis (Random Forests) identifies nitrate and chlorophyll-a as primary variables for Globigerinoides ruber, and SST and chlorophyll-a for Trilobatus sacculifer. Maximum abundances of the former are predicted in the subtropical hyper-oligotrophic zone while maxima of the latter are predicted at its margins and near the West Pacific Warm Pool. The high relative abundance of Globigerinoides ruber in the hyper-oligotrophic zone is attributed to its photosymbiotic relation with on-board dinoflagellates; this compensates for the low primary productivity in the zone. It is the best-adapted planktonic foraminifer in this huge marine ‘desert’ and is a proxy for hyper-oligotrophic environments. The photosymbiotic relation is weaker in Trilobatus sacculifer which primarily depends on particulate nutrition.

Biostratigraphy of Campanian—Maastrichtian sequences and facies analysis in Anaran and Samand Anticlines, Zagros, Iran

Gurpi Formation is an important sedimentary sequence in the Zagros area of southwest Iran. It provides effective cap rock at the top of the Bangestan reservoirs and acts as a possible source for younger hydrocarbon reservoirs. Integrated facies analysis and paleontological study of this formation are presented in two surface sections located on the Samand and Anaran anticlines of Lorestan Province. The formation has mainly composed of 203–298 m of argillaceous limestones with two clean limestone members of “Seymareh” and “Imam Hassan.” In the biostratigraphic part of this study, 51 species related to 16 genera of planktonic foraminifers in the Dareh Vorazan section and 44 species belong to 16 genera of planktonic foraminifera in Pahleh section were distinguished. Accordingly, four biozones have been determined in the Dareh Vorazan and the Pahleh sections which are Globotruncana aegyptiaca, Gansserina gansseri, Contusotruncana contusa, and Abathomphalus mayaroensis. Consequently, the Gurpi Formation has an age of Late Campanian–Late Maastrichtian. The location of the Cretaceous–Paleogene (K-Pg) boundary is detected at the top of this formation. Macroscopic field observations integrated with microscopic studies have resulted in the recognition of four microfacies types that belong to open lagoon, shoal, proximal, and distal open marine environments of shallow inner to deep basinal settings. Depositional facies and environments of studied sections are interpreted in a regional depositional model.

Persistent warm Mediterranean surface waters during the Roman period

Reconstruction of last millennia Sea Surface Temperature (SST) evolution is challenging due to the difficulty retrieving good resolution marine records and to the several uncertainties in the available proxy tools. In this regard, the Roman Period (1 CE to 500 CE) was particularly relevant in the socio-cultural development of the Mediterranean region while its climatic characteristics remain uncertain. Here we present a new SST reconstruction from the Sicily Channel based in Mg/Ca ratios measured on the planktonic foraminifer Globigerinoides ruber. This new record is framed in the context of other previously published Mediterranean SST records from the Alboran Sea, Minorca Basin and Aegean Sea and also compared to a north Hemisphere temperature reconstruction. The most solid image that emerges of this trans-Mediterranean comparison is the persistent regional occurrence of a distinct warm phase during the Roman Period. This record comparison consistently shows the Roman as the warmest period of the last 2 kyr, about 2 °C warmer than average values for the late centuries for the Sicily and Western Mediterranean regions. After the Roman Period a general cooling trend developed in the region with several minor oscillations. We hypothesis the potential link between this Roman Climatic Optimum and the expansion and subsequent decline of the Roman Empire.

Ammonium is the preferred source of nitrogen for planktonic foraminifer and their dinoflagellate symbionts.

The symbiotic planktonic foraminifera Orbulina universa inhabits open ocean oligotrophic ecosystems where dissolved nutrients are scarce and often limit biological productivity. It has previously been proposed that O. universa meets its nitrogen (N) requirements by preying on zooplankton, and that its symbiotic dinoflagellates recycle metabolic ‘waste ammonium’ for their N pool. However, these conclusions were derived from bulk 15N-enrichment experiments and model calculations, and our understanding of N assimilation and exchange between the foraminifer host cell and its symbiotic dinoflagellates remains poorly constrained. Here, we present data from pulse-chase experiments with 13C-enriched inorganic carbon, 15N-nitrate, and 15N-ammonium, as well as a 13C- and 15N- enriched heterotrophic food source, followed by TEM (transmission electron microscopy) coupled to NanoSIMS (nanoscale secondary ion mass spectrometry) isotopic imaging to visualize and quantify C and N assimilation and translocation in the symbiotic system. High levels of 15N-labelling were observed in the dinoflagellates and in foraminiferal organelles and cytoplasm after incubation with 15N-ammonium, indicating efficient ammonium assimilation. Only weak 15N-assimilation was observed after incubation with 15N-nitrate. Feeding foraminifers with 13C- and 15N-labelled food resulted in dinoflagellates that were labelled with 15N, thereby confirming the transfer of 15N-compounds from the digestive vacuoles of the foraminifer to the symbiotic dinoflagellates, likely through recycling of ammonium. These observations are important for N isotope-based palaeoceanographic reconstructions, as they show that δ15N values recorded in the organic matrix in symbiotic species likely reflect ammonium recycling rather than alternative N sources, such as nitrates.

Calcification of planktonic foraminifer Pulleniatina obliquiloculata controlled by seawater temperature rather than ocean acidification

Abstract Planktonic foraminifera represent a major component of global marine carbonate production, and understanding environmental influences on their calcification is critical to predicting marine carbon cycle responses to modern climate change. The present study investigated the effects of different environmental influences on calcification of the planktonic foraminifer Pulleniatina obliquiloculata. By correcting the dissolution effect on the size-normalized weight (SNW) of P. obliquiloculata from deep-sea sediments, we provide a means of estimating initial size-normalized weight (ISNW) from which to assess secular changes in the degree of calcification of P. obliquiloculata. Core-top ISNW in P. obliquiloculata from the global tropical oceans is significantly positively correlated with calcification temperature, suggesting that temperature is the dominant control on calcification. Using Neogloboquadrina dutertrei SNW as an independent deep-water Δ[CO32−] proxy, we present an ISNW record for P. obliquiloculata from the western tropical Pacific since 250 ka. The response of ISNW to past seawater temperature variations further confirms the dominant influence of temperature on P. obliquiloculata calcification. A potential increase in calcification as a result of ocean warming may have reduced oceanic uptake of CO2 from the atmosphere and increased atmospheric pCO2, generating a positive feedback for global warming.

Past and future decline of tropical pelagic biodiversity

A major research question concerning global pelagic biodiversity remains unanswered: when did the apparent tropical biodiversity depression (i.e., bimodality of latitudinal diversity gradient [LDG]) begin? The bimodal LDG may be a consequence of recent ocean warming or of deep-time evolutionary speciation and extinction processes. Using rich fossil datasets of planktonic foraminifers, we show here that a unimodal (or only weakly bimodal) diversity gradient, with a plateau in the tropics, occurred during the last ice age and has since then developed into a bimodal gradient through species distribution shifts driven by postglacial ocean warming. The bimodal LDG likely emerged before the Anthropocene and industrialization, and perhaps ∼15,000 y ago, indicating a strong environmental control of tropical diversity even before the start of anthropogenic warming. However, our model projections suggest that future anthropogenic warming further diminishes tropical pelagic diversity to a level not seen in millions of years.

Cleaning method impact on the Mg/Ca of three planktonic foraminifer species: A downcore study along a depth transect

We performed a downcore comparison of Mg/Ca ratios obtained using reductive and non-reductive cleaning methods applied to Globigerinoides ruber, Pulleniatina obliquiloculata and Globorotalia menardii picked along two nearby sediment cores retrieved at 2100 m and 3875 m in the eastern equatorial Indian Ocean. At the shallower site, our results show statistically significant discrepancies in averaged relative Mg/Ca loss induced by the reductive cleaning compared to non-reductive cleaning: G. menardii (8.5%) > G. ruber (6.2%) > P. obliquiloculata (4.4%), suggesting that reductive cleaning impact on relative Mg/Ca loss is species-specific. At the deeper site, differences between the relative Mg/Ca losses for the three species are smaller: G. menardii (3.7%), G. ruber (4.1%) and P. obliquiloculata (6.3%), suggesting the clear impact of in situ preservation state on the cleaning related Mg/Ca loss. The Mg/Ca loss in both relative (%) and absolute (mmol/mol) value of species G. ruber and G. menardii are significantly smaller at the deeper site than the shallower site, implying that these two species which have experienced intense dissolution on the sea-floor are less prone to lose further Mg during the reductive cleaning. P. obliquiloculata, however, show non-significant difference in Mg/Ca loss between the two sites, indicating that the cleaning related Mg/Ca loss in this species is somewhat insensitive to the preservation state at our two sites. Our data reveal that Mg/Ca loss results from partial dissolution induced by the reductive step. We conclude that the non-reductive cleaning approach should be preferred for building inter-laboratory homogeneous datasets of Mg/Ca-derived temperatures, whereas the reductive step should be only included when severe oxide coating is observed.

Late pleistocene paleoceanographic changes in the Ross Sea – Glacial-interglacial variations in paleoproductivity, nutrient utilization, and deep-water formation

The outer Ross Sea continental shelf has experienced large variations in ice sheet extent over the Pleistocene that are theorized to be largely driven by changes in the westward-flowing Antarctic Slope Current (ASC) at the continental shelf break. This current regulates southward incursions of warm modified Circumpolar Water, and it is thought to have triggered past marine ice sheet retreat. Additionally, expansions of grounded ice sheets on the continental shelf have fundamentally altered the Ross Sea water mass formation processes, influencing surface water salinity, sea ice cover, nutrient utilization, deep-water ventilation, and primary productivity. Here, we report the geochemical, physical properties, grain size, bulk δ15N, and diatom records during the late Pleistocene from two sediment cores from the Iselin Bank on the outermost continental shelf in the Ross Sea. These core sites were not overridden by grounded ice sheets during the late Pleistocene glacial-interglacial cycles, allowing for a continuous archive of glacimarine environments that were influenced by the ASC. Interglacial periods are typically characterized by high surface water productivity and nutrient utilization, with Chaetoceros resting spores indicating nutrient limitation under open ocean conditions, and glacial periods are typically characterized by low surface water productivity and nutrient utilization, with sea ice diatoms and planktonic foraminifers indicating light limitation under extensive sea ice/ice margin proximal conditions. A grain size analysis indicates coarse-skewed distributions and winnowing in the Iselin Bank region during cold periods. The winnowing may be related to enhanced ASC flow instead of density driven shelf water outflow.

Rétablissement total des conditions marines après la phase "Lago Mare" du Messinien supérieur de la Mer Méditerranée dans les régions de Licodia Eubea et Villafranca Tirrena (Sicile orientale)

After the Upper Messinian Mediterranean Lago-Mare phase, at the end of the Messinian salinity crisis, the Mediterranean basin was characterized by a return to normal marine conditions starting with the Lower Pliocene (Zanclean). In this period, remarkably thick layers of calcareous pelitic sediments, very rich in planktonic foraminifers and nannofossils, were widely deposited in the Mediterranean basin. The calcareous pelitic deposits of Sicily (Trubi Formation), as well as in other Mediterranean regions, were deposited conformably on the pre-Pliocene substrate, which is mainly represented by Messinian evaporites or by the post-evaporitic Lago-Mare facies. We have analysed samples taken from the lower portion of the Trubi Formation (Zanclean), just above the Messinian facies, collected from Licodia Eubea and Villafranca Tirrena areas (eastern Sicily). Micropalaentological assemblages consist of benthic and planktonic foraminifers and a typical deep-water ostracod fauna. The microfossil association and the stratigraphy of the Messinian-Pliocene transitional layers, supported by calcareous nannoplankton data, demonstrate not only rapid sea-level rise in this sector of the Mediterranean region, but also that this event, occurred without producing erosional features, unlike at other sites (e.g., Strait of Gibraltar).

New biostratigraphic framework for the Triassic–Paleogene in the Neo-Tethys realm of southern Xizang (Tibet), China

Abstract Multifaceted biostratigraphic work on Triassic to Paleogene strata in southern Xizang (Tibet), western China, in the last decades allows a new, refined biochronostratigraphic framework in the Qinghai–Xizang plateau region. Synthesis of the latest biostratigraphic progress is carried out in this paper to build a new integrated biostratigraphic scheme comparable to the international Geological Time Scale. The scheme incorporates key fossils as many of each system, such as ammonites, calcareous nannofossils, conodonts and foraminifers. Other fossil groups that are helpful for stratigraphic division and interregional correlation are also contained. These include bivalves, miospores and radiolarians, some of which, e.g. radiolarians and miospores, not previously well explored, are now utilised for new zones. Biostratigraphic zones of this new integrative system, especially the Lower Triassic conodonts and ammonites, uppermost Triassic–Lower Jurassic ammonites, Upper Cretaceous planktonic foraminifers and calcareous nannofossils, correlate well with the international standards. The results are tabulated as four new comprehensive biostratigraphic charts, which, we hope, will provide a new and more reliable chronostratigraphic foundation for study of Neo-Tethys.

PRELIMINARY OBSERVATIONS ON THE UPPER CRETACEOUS CORAL-RUDIST FACIES OF OSTUNI (SOUTH-EASTERN MURGE, APULIA)

The Upper Cretaceous carbonate platform deposits of Ostuni have been studied from a stratigraphical, palaeontological and palaeoecological point of view.
 ln the sequence studied two parts can be distinguished: the Iower one consists of stratified biomicritic limestones with clusters of rudists, other pelecypods and microfauna, represented by ostracods algae and benthonic foraminifers; the upper one consists of a sequence of coral—rudist buildups with banks of calcarenites and calcirudites characterized by trace fossil assemblages, gastropods, rudists, other pelecypods and benthonic and planktonic foraminifers.