Marine Micropaleontology最新文献

Coccolithophores are an ecologically and biogeochemically important group of calcifying marine plankton, contributing globally to both the organic carbon pump and the carbonate counter pump. Understanding their distribution in today's ecosystems is crucial for both paleoenvironmental reconstruction and for predicting their fate under climate change and environmental pollution. Traditionally regarded as open ocean dwellers, more recent studies have highlighted their importance in coastal systems.

Here we describe the coccolithophore community in the Catalan Sea (Northwestern Mediterranean), off the Ebro River Delta, based on an oceanographic survey conducted in autumn 2019. We identify three environmentally distinct regimes: mixed (mostly shallow), transition (upper photic layers offshore), and stratified deep waters (below 75 m). Total coccolithophore density is driven by Emiliania huxleyi and peaks in the mixed zone where nutrient concentrations are low, but nitrite concentrations are high. We propose that peak cell densities are partly explained by a switch from nitrate to nitrite usage similar to the behavior of diatoms. Species diversity peaks in deeper offshore waters due to vertical stratification. Helicosphaera carteri and Algirosphaera robusta benefit from E.huxleyi decrease both in coastal and offshore environment.

Crystal overgrowth on fossil remains is well-documented in the literature. Attention has specifically focused on bioapatite (i.e., an apatite of biochemical origin regardless of post-mortem changes) configurations, in order to decipher any possible relation to fossilization/diagenesis. This study investigates the Rare Earth Element (REE) and other High-Field-Strength Element (HFSE) composition of euhedral crystals formed on the surface of conodont elements compared with that of crystal-free surfaces. Euhedral crystals are by definition crystals characterized by sharp faces, developing solids that, for apatite, assume the form of hexagonal prisms, reflecting its crystal symmetry. Late Ordovician (Amorphognathus ordovicicus Zone) conodonts from two localities in Sardinia and the Carnic Alps (Italy) are herein investigated. Conodont elements reveal the occurrence of smooth surfaces and surfaces partially covered with euhedral crystals. Since euhedral crystals did not reasonably grow during the organism's lifetime, the REE and HFSE analysis can provide important insights into the crystal growth process. The experimental results indicated a substantial contribution of diagenetic imprinting for all the analyzed material, although more evident on euhedral crystals that are significantly enriched in middle and, subordinately, in heavy REE with respect to smooth surfaces. The positive correlations between La + Th vs log[ΣREE] and Ce + Th vs log[ΣREE] could support the hypothesis that the neoformed euhedral crystals grew also by depleting the pristine bioapatite of the conodont elements. Nevertheless, the occurrence of two types of apatite cannot be ruled out: euhedral crystals as neoformed products of diagenetic processes and smooth surfaces as remains of the pristine conodont bioapatite after diagenesis.

The present review of published data as well as the new results demonstrate the versatility of conodonts in documenting and explaining global environmental fluctuations related to the Kačák Episode (KE) in the latest Eifelian. Although the conodont zonation of the KE interval is ambiguous and requires revision, the compilation of conodont stratigraphic ranges shows their potential for a precise worldwide correlation of relevant marine strata. Conodont biofacies may serve to document environmental changes connected with KE, in particular the sealevel rise at its beginning, followed by a regressive trend. Nevertheless, the familiar Icriodus/Polygnathus ratio should be carefully applied as an indication of water depth and nearshore vs. offshore position, being controlled also by other factors, such as paleolatitude and/or climate. Oxygen isotopes in conodont apatite, studied using secondary ion mass spectrometry technique evidence a warming at the onset of KE, based on the new data from the open marine facies of the Prague Basin. At the same time, they indicated climate-controlled salinity fluctuations in the epeiric Belarusian Basin. The present investigations as well as previous results suggest caution when analyzing thermally altered conodonts which may result in biased oxygen isotope signatures. The present experience suggests the conodont colour alteration index CAI 3 as a boundary value above which the caution is necessary.

Comprehensive field, litho-, biostratigraphy, and paleoenvironmental studies of the upper Paleocene–lower Eocene (P–E) boundary interval in the Gabal El-Gir area were conducted. Two selected sections El-Gir-1 and El-Gir-2 were investigated. The prevailed paleoenvironmental conditions were discussed in the frame of the nannofossils, planktonic, and benthic foraminiferal assemblages. Benthic foraminifera assemblages indicate a remarkable turnover across the PETM. The extinction of Angulogavelinella avnimelechi at the base of the PETM represents a significant marker for the base of the benthic foraminifera extinction event at this site and other neritic sites in the Tethyan region. The dominance of calcareous planktonic excursion taxa at the base of the PETM indicates adaptation to extremely warm sea surface temperatures and low nutrient levels. Also, our data suggests that the biotic responses to environmental change in the early Eocene resembled those observed in the early Eocene hyperthermals at the nearbay Dababiya and El-Ballas sections. This could indicate that similar processes characterized the Egyptian sedimentary basin during the early Eocene. Stratigraphically, despite the limited distance between the studied sections, the Dababiya Quarry Member (DQM) in El-Gir-1 resemble those of the Global Stratotype Section and Point (GSSP) but reduced in thickness. While in El-Gir-2, the lower part of the DQM was missing. These findings could indicate that the DQM was deposited in a submarine channel. Three third-order depositional sequences were recognized covering the P–E interval. The reconstructed sea level curve shows the presence of eustatic similarities with the global sea level.

Automated microscopy, image processing, and recognition using artificial intelligence is getting a growing interest from the scientific community, as more and more research centres are actively working on building datasets of images for training convolutional neural networks (CNNs) to identify microscopic objects. However, images acquired between institutes might show differences in light and contrast intensity leading to potential bias in identification when using datasets or CNNs from another institute.

One might then question if combining datasets acquired in different conditions is likely to improve the efficiency of the resulting CNN by increasing the number of images and integrating lighting variability into the learning process, or on the contrary introduce bias in the CNN training by adding a recurrent noise, common to all classes, through a substantial light and contrast variability.

In order to ease collaboration between laboratories, two datasets of middle Eocene radiolarian images, acquired separately at GNS Science (NZ) and the University of Lille (France), were generated to assess the accuracy of CNNs trained on both datasets individually, and also when combined into a third dataset. The performance of the three resulting CNNs was then evaluated on new images acquired at both institutions.

Finally, the new radiolarian dataset generated at GNS allowed to easily detect unknown taxa, which are otherwise abundant in the studied material. Seven new species are described: Ceratospyris metroid n. sp., Ceratospyris okazakii n. sp., Desmospyris biloba n. sp., Botryostrobus lagena n. sp., Buryella apiculata n. sp., Lophocyrtis cortesei n. sp., and Cromyosphaera fulgurans n. sp.

The complete lifecycle of the planktonic foraminifera has continued to remain obscure. Benthic foraminifera exhibit an obligate alternation of generations between haploid gamonts and diploid agamonts, yet despite years of observation, the fusion of gametes to form a zygote, gamont or agamont has never been observed in the planktonic groups. Recent evidence from Neogloboquadrina pachyderma culture confirms that they do have a biphasic reproductive cycle and the agamonts may exhibit dimorphism in coiling direction. In this study we examine the morphology of normal and aberrant coiling tests of both N. pachyderma and N. incompta from three Arctic and North Atlantic water masses, to explore whether aberrant coiling is an indicator of a biphasic life cycle in the non-spinose planktonic foraminifera group as a whole. Using a Nano-Computed Tomography scanning approach, we morphologically compared the proloculus and growth trajectories of aberrant and normal coiling tests. Aberrant coiling tests were found to have a slightly larger proloculus and test size, consistent with a left coiling N. pachyderma agamont in the literature. This degree of dimorphism is insufficient to discriminate agamonts in the wild population and coiling direction remains their only distinguishable feature without further morphological investigation. The constant low-level aberrant coiling signature in a range of non-spinose planktonic foraminiferal genera implies that a biphasic life cycle is the principal mode of reproduction in the non-spinose planktonic group.

We present various approaches to distinguish the middle Eocene species Podocyrtis chalara and Podocyrtis goetheana, which are end members of a trajectory of phenotypic change, and their intermediate morphogroups. We constructed a set of thirteen traditional morphological variables to classify the entire morphological variability encompassed by the two morphospecies and their intermediates Podocyrtis sp. cf. P. chalara and Podocyrtis sp. cf. P. goetheana. We used two methods of classification, namely Linear Discriminant Analysis (LDA) and machine learning using artificial neural networks. LDA performed on the morphometric data reveals a good discrimination for P. chalara, P. goetheana and Podocyrtis sp. cf. P. goetheana, but not for Podocyrtis sp. cf. P. chalara. We used three approaches of machine learning based on different neural networks: a Convolutional Neural Network (CNN) and two Spiking Neural Networks (SNNs). Each of these neural networks was trained based on classified images of the two morphospecies and their morphological intermediates, thus constituting a different set of input data than the morphometric dataset for LDA. The neural network approaches identified the same three morphospecies recognized by LDA from a dataset of traditional measurements, i.e. P. chalara, P. goetheana and Podocyrtis sp. cf. P. goetheana, with up to 92% accuracy. Our results highlight the great potential and promising perspectives of machine learning and neural networks in the application of image-based object recognition for morphological classification, which may also contribute to more objective taxonomic decisions.

Phytoplankton assemblages in shallow marine environments are being impacted by anthropogenic climate change, but long-term outcomes of these changes are uncertain. Investigation of past neritic calcareous nannoplankton can help us understand the fate these ecosystems face. In this study, a Canonical Correspondence Analysis (CCA) of calcareous nannofossils and X-ray fluorescence geochemistry was used to determine how past planktonic ecosystems were influenced by paleoenvironmental parameters on the eastern side of the Late Cretaceous Western Interior Seaway in the Cenomanian (ca. 95–93 Ma). Samples were collected every 10 cm from the Graneros Shale Greenhorn Formation at an outcrop in northwestern Iowa to determine high resolution changes in assemblages and paleoenvironments. Nannofossil diversity outside of a few small intervals ranges is high (generally 30–60 species) with abundant small Biscutum constans, confirming other publications that show elevated diversity in Cretaceous nearshore settings. The CCA results imply assemblages were most influenced by terrigenous influence, wet vs. dry climate, and changes in water mass source. Cretaceous nannofossil paleoecology was also revised based on the CCA results. Size differentiation of nannofossil taxa may highlight more complexity in environmental preferences that have been largely overlooked. After the initial transgression of the Greenhorn Sea into the region, the climate became wetter and terrigenous influence in the area was high. The peak of terrigenous influence corresponds with elevated nannofossil diversity but a lack of microfauna, which may indicate a similar oceanographic setting to the modern Gulf of Mexico nearshore dead zone. As sea level continued to rise above this point, nannoplankton assemblages indicate a potential shift to a higher productivity, stratified water column. As the muddy Graneros Shale transitioned to a further offshore chalky Greenhorn Formation, a normal marine, cosmopolitan nannofloral assemblage became established. Nannofossil and geochemical evidence indicates high productivity from upwelling might be related to the change of deposition to chalk in the Greenhorn Formation. While only a single outcrop was investigated, the novel use of an integrated micropaleontological and geochemical analysis has shed light on the dynamics of how phytoplankton ecosystems were established and modified in shallow marine environments of the Cretaceous and could have important implications on modern shallow marine settings.

The temperature-size rule (TSR) states that ectotherms mature at smaller adult body size in warmer conditions. Such a rule may have the potential to explain size response of fossil organisms to past temperature variations, but its validity in deep time has been seldom tested. The generality of this rule was investigated here by compiling data documenting the size record of three conodont genera (Palmatolepis, Ancyrodella and Polygnathus) at different spatial and temporal scales during the Late Frasnian and the Famennian, characterized by short- and long-term temperature variations. Statistical models were used to investigate the relationship between conodont size and oxygen isotope values, considered as paleotemperature proxies. Comparison of evolutionary models further allowed to test alternative modes of size variation such as stasis or punctuation.

The TSR was not validated as a general rule explaining size variation in these fossil records, being only observed as a large-scale geographic trend during a time-slice. The only strong support for temperature being the driver of temporal variations was found regarding the size of Palmatolepis during the Kellwasser period, but the relationship was reverse to the expectation of the TSR. The absence of general TSR pattern is probably due to the interference of many other factors (demography and mortality patterns, temperature tolerance, size reduction due to stress) whose relative importance may depend on the time interval and the genus considered. Rather than a correlation with environmental proxies, evolutionary models suggested the occurrence of a synchronous shift in Palmatolepis size around 369 Ma (Palmatolepis termini conodont Zone) in several outcrops, raising questions about the environmental forcing beyond this shift. Departures from the expected TSR may thus provide relevant insights into the complex interplay of physical, tectonic and eco-evolutionary processes impacting size evolution in deep time.

Analysis of benthic foraminifera in surface samples from 23 sites on the Northeast Greenland continental shelf reveal key assemblage differences between sites. Cluster analysis creates two clear geographical faunal assemblage zones: the 1) inner shelf, and 2) mid and outer shelf sites. These assemblages differ significantly, with the inner shelf sites being characterised by a high percentage and concentration of calcareous species, whilst the mid and outer shelf sites are dominated by agglutinated taxa. At almost all sites, the calcareous assemblages are dominated by Cassidulina neoteretis and Cassidulina reniforme, suggesting that they thrive across the shelf. Stetsonia horvathi, Oridorsalis tener, as well as Glomulina oculus and other miliolid species are found to be key calcareous species at many sites in the inner shelf zone, but they are rare-to-absent on the mid and outer shelf. Canonical correspondence analysis shows that September sea-ice cover and bottom water oxygen content are positively correlated with benthic foraminiferal assemblages at inner shelf sites, whereas organic carbon content is correlated with those in the mid and outer shelf. The formation of seasonal sea-ice and the Northeast Water polynya rejects brine into surrounding waters and transports CO₂ to the seafloor, creating a highly corrosive environment for calcium carbonate. These environments are also highly productive, as indicated by the high organic carbon content and low bottom water oxygen content. The oxidation of this organic material creates CO₂. We propose that these processes are key drivers in the dissolution of calcareous tests. In contrast, extensive sea-ice, high bottom water oxygen content and low primary productivity in the glacier-proximal region facilitates carbonate preservation.