Species Of Planktonic Foraminifera Research Articles

Environmental Controls of Size Distribution of Modern Planktonic Foraminifera in the Tropical Indian Ocean

AbstractPaleoceanographic studies often rely on abundance changes in microfossil species, with little consideration for characteristics such as organism size, which may also be related to environmental changes. Using a tropical Indian Ocean (TIO) core‐top data set, we test the Optimum size‐hypothesis (OSH), investigating whether relative abundance or environmental variables are better descriptors of planktonic foraminifera species' optimum conditions. We also investigate the environmental drivers of whole‐assemblage planktonic foraminiferal test size variation in the TIO. We use an automated imaging and sorting system (MiSo) to identify planktonic foraminiferal species, analyze their morphology, and quantify fragmentation rate using machine learning techniques. Machine model accuracy is confirmed by comparison with human classifiers (97% accuracy). Data for 33 environmental parameters were extracted from modern databases and, through exploratory factor analysis and regression models, we explore relationships between planktonic foraminiferal size and oceanographic parameters in the TIO. Results show that the size frequency distribution of most planktonic foraminifera species is unimodal, with some larger species showing multimodal distributions. Assemblage size95/5 (95th percentile size) increases with increasing species diversity, and this is attributed to vertical niche separation induced by thermal stratification. Our test for the OSH reveals that relative abundance is not a good predictor of species' optima and within‐species size95/5 response to environmental parameters is species‐specific, with parameters related to carbonate ion concentration, temperature, and salinity being primary drivers. At the species and assemblage levels, our analyses indicate that carbonate ion concentration and temperature play important roles in determining size trends in TIO planktonic foraminifera.

Paleocene-Eocene foraminifera from the Tuz Gölü Basin (Salt Lake Basin, Central Türkiye) and their paleoenvironmental interpretations

Paleocene-Eocene aged sediments from the east of Tuz Gölü Basin (Central Türkiye) provide significant data for foraminifera contents and their paleoenvironmental clues. They are important in revealing the stratigraphy of the region and the Paleocene-Eocene geological history of Türkiye. The sediments, composed mainly of carbonates, are known as KarapınaryaylasıFormation. In this formation, benthic foraminifera representing SBZ2 to SBZ12 biozones corresponding to the Selandian-Late Cuisian time interval were identified in ten measured stratigraphical sections. The zonal interval from the E7 Zone (late Ypresian) to the E10 Zone (Lutetian) is characterized by the marker species of planktonic foraminifera defined in the clayey limestones from the uppermost part.The studied formation is divided into four main facies and eleven sub-microfacies types. The clayey limestone levels of the KarapınaryaylasıFormation, which generally starts with a transgressive sequence, contain abundant planktonic foraminifers, while the lithologies of grainstone, packstone and wackestone are rich in benthic foraminifers. Benthic foraminifer assemblages indicate different paleoenvironments from lagoon to back-bank, bank and fore-bank. The obtained foraminiferal data show the Selandian-Lutetian age range and various paleoenvironments from the lagoon to the open sea.

Issues in the identification of the Aptian/Albian boundary in South Atlantic basins and beyond

The use of taxonomic-phylogenetic criteria established for planktonic foraminifera in the 2000's and the definition of the Albian Global Stratotype Section Point (GSSP-Alb) have resulted in a major change in the interpretation of the carbonate sections overlying the giant layer of salt present in basins of the South Central Atlantic (CSA) and their equivalent strata in the Equatorial South Atlantic (ESA), and interior of northeastern Brazil (BNE). These post-salt carbonates have long been considered Albian in age, but they contain a planktonic foraminifera association characteristically Aptian. Great conflicts arise, however, when this faunal association is compared with biostratigraphic successions based on other fossil groups or with lithostratigraphic and geochronological data. Controversies similar to those observed at sites 363 and 364 of the Deep Sea Drilling Project (DSDP) leg 40, drilled almost 45 years ago, have resurfaced. Thus, it is paradoxical that the remarkable disappearance of large species of planktonic foraminifera, associated with the top of the Paraticinella rohri Zone (of the upper Aptian), occurred stratigraphically above a typical Albian calcareous nannofossil succession (as the First Stratigraphic Occurrences of Hayesites albiensis, Tranolithus orionatus, Axopodorhabdus biramiculatus, and Eiffellithus turriseiffelli) or the FOs of three known species of pelagic calcispheres, all assumed to be of Albian age. Another notorious conflict lies in the fact that these carbonates rest directly on the salt layer onlapping the South Atlantic Middle Barrier (SAMB), where trachyandesite has been dated at 113.2 ± 0.1 Ma, identical to the value established for the GSSP-Alb. Detailed examination of 16 stratigraphic sections from around the world shows that the difficulties of fully applying the GSSP-Alb criteria are not limited to the CSA, ESA, and BNE basins. The explanation of these controversies may lie in the specific conditions of the water mass of the primitive South Atlantic that may have influenced morphological alterations or affected the temporal amplitude of taxa. But until geochronological, biostratigraphic, and lithostratigraphic incompatibilities can be clarified, it is here recommended to use the base of the evaporitic layer as the reference for the Aptian/Albian transition in CSA, ESA, and BNE basins.

Upper-ocean flux of biogenic calcite produced by the Arctic planktonic foraminiferaNeogloboquadrina pachyderma

Abstract. With ongoing warming and sea ice loss, the Arctic Ocean and its marginal seas as a habitat for pelagic calcifiers are changing, possibly resulting in modifications of the regional carbonate cycle and the composition of the seafloor sediment. A substantial part of the pelagic carbonate production in the Arctic is due to the calcification of the dominant planktonic foraminifera species Neogloboquadrina pachyderma. To quantify carbonate production and loss in the upper water layer by this important Arctic calcifier, we compile and analyse data from vertical profiles in the upper water column of shell number concentration, sizes and weights of this species across the Arctic region during summer. Our data are inconclusive on whether the species performs ontogenetic vertical migration throughout its life cycle or whether individual specimens calcify at a fixed depth within the vertical habitat. The base of the productive zone of the species is on average located below 100 m and at maximum at 300 m and is regionally highly variable. The calcite flux immediately below the productive zone (export flux) is on average 8 mg CaCO3 m−2 d−1, and we observe that this flux is attenuated until at least 300 m below the base of the productive zone by a mean rate of 6.6 % per 100 m. Regionally, the summer export flux of N. pachyderma calcite varies by more than 2 orders of magnitude, and the estimated mean export flux below the twilight zone is sufficient to account for about a quarter of the total pelagic carbonate flux in the region. These results indicate that estimates of the Arctic pelagic carbonate budget will have to account for large regional differences in the export flux of the major pelagic calcifiers and confirm that substantial attenuation of the export flux occurs in the twilight zone.

A Southern Portuguese Margin Perspective of Marine Isotope Stage 47—An Interglacial in the 41 kyr World

In order to better understand interglacial climate variability within the 41 kyr world, we produced high-resolution climate records for interglacial Marine Isotope Stage (MIS) 47 (1424–1452 ka) at IODP Site U1387 (36°48′ N, 7°43′ W) on the southern Portuguese margin. Using benthic and planktonic foraminifera stable isotope records, Uk’37 sea-surface temperature (SST), and plankton assemblage data we investigated Mediterranean Outflow Water (MOW) and surface water conditions. The MOW-level records indicate a poorly ventilated and sluggish bottom current during the MIS 48/MIS 47 transition in association with the insolation maximum, whereas a well-ventilated MOW formed a contourite layer during the second insolation maximum. The benthic δ18O record shows a fairly abrupt change during the deglaciation of MIS 48, while the surface waters experienced a terminal stadial event that was associated with initial cooling and freshening followed by stepwise warming until interglacial SST was reached at 1450 ka. Interglacial conditions with SST of 24 °C or higher persisted until 1427 ka, although warm SST prevailed into MIS 46. The persistent and prolonged warmth is attributed to a northward expansion of the subtropical gyre during MIS 47 as reflected by the dominance of subtropical-tropical planktonic foraminifera species and the presence of warm water coccolithophores taxa.

Planktonic foraminifera organic carbon isotopes as archives of upper ocean carbon cycling

The carbon cycle is a key regulator of Earth’s climate. On geological time-scales, our understanding of particulate organic matter (POM), an important upper ocean carbon pool that fuels ecosystems and an integrated part of the carbon cycle, is limited. Here we investigate the relationship of planktonic foraminifera-bound organic carbon isotopes (δ13Corg-pforam) with δ13Corg of POM (δ13Corg-POM). We compare δ13Corg-pforam of several planktonic foraminifera species from plankton nets and recent sediment cores with δ13Corg-POM on a N-S Atlantic Ocean transect. Our results indicate that δ13Corg-pforam of planktonic foraminifera are remarkably similar to δ13Corg-POM. Application of our method on a glacial sample furthermore provided a δ13Corg-pforam value similar to glacial δ13Corg-POM predictions. We thus show that δ13Corg-pforam is a promising proxy to reconstruct environmental conditions in the upper ocean, providing a route to isolate past variations in δ13Corg-POM and better understanding of the evolution of the carbon cycle over geological time-scales.

Calcification, Dissolution and Test Properties of Modern Planktonic Foraminifera From the Central Atlantic Ocean

The mass of well-preserved calcite in planktonic foraminifera shells provides an indication of the calcification potential of the surface ocean. Here we report the shell weight of 8 different abundant planktonic foraminifera species from a set of core-top sediments along the Mid-Atlantic Ridge. The analyses showed that near the equator, foraminifera shells of equivalent size weigh on average 1/3 less than those from the middle latitudes. The carbonate preservation state of the samples was assessed by high resolution X-ray microcomputed tomographic analyses of Globigerinoides ruber and Globorotalia truncatulinoides specimens. The specimen preservation was deemed good and does not overall explain the observed shell mass variations. However, G. ruber shell weights might be to some extent compromised by residual fine debris internal contamination. Deep dwelling species possess heavier tests than their surface-dwelling counterparts, suggesting that the weight of the foraminifera shells changes as a function of the depth habitat. Ambient seawater carbonate chemistry of declining carbonate ion concentration with depth cannot account for this interspecies difference. The results suggest a depth regulating function for plankton calcification, which is not dictated by water column acidity.

Planktonic foraminiferal biostratigraphy of the Turonian-Coniacian transition interval in the Kopeh-Dagh sedimentary basin, NE Iran

The Abderaz Formation was analyzed from four stratigraphic sections (Qaleh-Zo, Abderaz village, Mozduran pass (type section of the formation), and Chahchahe) in awest to east transect of the Kopeh-Dagh Basin. The Abderaz Formation is composed of light gray shale and marl alternated with limestone rich in echinoids and inoceramids. Planktonic foraminifera were studied in detail in order to determine the Turonian-Coniacian boundary with more accuracy and to highlight bio-events around this boundary in the Kopeh-Dagh sedimentary basin. Nineteen planktonic foraminifera species belonging to 12 genera were identified in the Turonian-Coniacian transition interval. Four planktonic foraminifera biozones are recognized in all studied sections; they are 1) Whiteinella archaeocretacea Partial Range Zone, 2) Helvetoglobotruncana helvetica Total Range Zone, 3) Marginotruncana sigali-Dicarinella primitiva Partial Range Zone, and 4) Dicarinella concavata Interval Zone. In all studied sections, the Turonian-Coniacian boundary is placed at the base of the Dicarinella concavata Interval Zone. As in our previous work, we confirm that the base of the Coniacian stage in the Kopeh-Dagh sedimentary basin is distinguished based on the first occurrences of Dicarinella concavata, Pseudotextularia nuttalli, and Contusotruncana fornicata, and on the last occurrences of Dicarinella imbricata, Marginotruncana paraconcavata and Marginotruncana schneegansi.

Planktonic foraminiferal biostratigraphy and determination of the Santonian-Campanian boundary in the Zagros sedimentary basin, SW Iran

The carbonate-dominated Upper Cretaceous Ilam Formation is representative of an important reservoir in the Zagros Basin. In this study, planktonic foraminiferal biostratigraphy of the Ilam Formation was investigated in the Kuh-e-Surgah section in western Iran. In the studied section, the 170 m thick Ilam Formation is mainly composed of imestones with shale intercalations. The formation conformably overlies and underlies the Surgah and Gurpi formations, respectively. Twelve genera and 24 species of planktonic foraminifera were identified. The following planktonic foraminiferal biozones were identified: the Dicarinella asymetrica Total Range Zone (latest Coniacian- late Santonian), the Globotruncanita elevata Partial Range Zone (Santonian to early Campanian), the Globotruncana ventricosa Interval Zone (middle to late Campanian.), the Radotruncana calcarata Total Range Zone (late Campanian.), the Globotruncanella havanensis Partial Range Zone (late Campanian) and the Globotruncana aegyptiaca Interval Zone (late to latest Campanian). In general, the biozones show that the Ilam Formation in the studied section is latest Coniacian-late Campanian in age. The Santonian-Campanian boundary in the Kuh-e-Surgah section correlates with the Globotruncanita elevata Partial Range Zone. The recognized biozones in the Ilam Formation are comparable with those recorded in other parts of the Tethyan Realm. The crinoid species Marsupites testudinarius is absent in the studied section. Generally, the last occurrence of this cosmopolitan species indicates the base of the Campanian stage. The Santonian/Campanian boundary was placed in the lower part of the Globotruncanita elevata Partial Range Zone at the base of the Ilam Formation in the studied section.

Drivers of global pre‐industrial patterns of species turnover in planktonic foraminifera

Anthropogenic climate change is altering global biogeographical patterns. However, it remains difficult to quantify how bioregions are changing because pre‐industrial records of species distributions are rare. Marine microfossils, such as planktonic foraminifera, are preserved in seafloor sediments and allow the quantification of bioregions in the past. Using a recently compiled data set of pre‐industrial species composition of planktonic foraminifera in 3802 worldwide seafloor sediments, we employed multivariate and statistical model‐based approaches to study spatial turnover in order to 1) quantify planktonic foraminifera bioregions and 2) understand the environmental drivers of species turnover. Four latitudinally banded bioregions emerge from the global assemblage data. The polar and temperate bioregions are bi‐hemispheric, supporting the idea that planktonic foraminifera species are not limited by dispersal. The equatorial bioregion shows complex longitudinal patterns and overlaps in sea surface temperature (SST) range with the tropical bioregion. Compositional‐turnover models (Bayesian bootstrap generalised dissimilarity models) identify SST as the strongest driver of species turnover. The turnover rate is constant across most of the SST gradient, showing no SST threshold values with rapid shifts in species composition, but decelerates above 25°C, suggesting SST is less predictive of species composition in warmer waters. Other environmental predictors affect species turnover non‐linearly, and their importance differs across regions. In the Pacific ocean, net primary productivity below 500 mgC m−2 day−1 drives fast compositional change. Water depth values below 3000 m (which affect calcareous microfossil preservation) increasingly drive changes in species composition among death assemblages in the Pacific and Indian oceans. Together, our results suggest that the dynamics of planktonic foraminifera bioregions are expected to be highly responsive to climate change; however, at lower latitudes, environmental drivers other than SST may affect these dynamics.

Applicability of the Long Chain Diol Index (LDI) as a Sea Surface Temperature Proxy in the Arabian Sea

AbstractThe long‐chain diol index (LDI) is a relatively new proxy for sea surface temperature (SST) which has been rarely applied in upwelling regions. Here, we evaluated its application by comparison with other SST records obtained by commonly used proxies, that is, the Mg/Ca ratio of the planktonic foraminifera species Globigerinoides ruber and the alkenone paleothermometer UK´37. We focused on the last glacial–interglacial transition of four different sedimentary archives from the western and northern Arabian Sea, which are currently under the influence of monsoon‐induced upwelling and the associated development of an oxygen minimum zone. The and Mg/CaG.ruber SST records revealed an increase of 0.6–3.4°C from the Last Glacial Maximum to the late Holocene with somewhat higher amplitude in the northern part of the Arabian Sea than compared to the western part. In contrast, the LDI SSTs did not reveal major changes during the last glacial–interglacial transition which was followed by a decreasing trend during the Holocene. The LGM versus the Holocene LDI SSTs ranged between −0.2 and −2.7°C. Particularly at one record, offshore Oman, the SST decrease during the Holocene was high in amplitude, suggesting a potential cold bias, possibly related to changes in upwelling intensity. This indicates that care has to be taken when applying the LDI for annual mean SST reconstruction in upwelling regions.

Planktonic foraminiferal quantitative analysis across the Campanian/Maastrichtian boundary at the Pondicherry area, Cauvery Basin, Southern India

The late Campanian/Maastrichtian succession exposed at Pondicherry area affords one of the finest exposed marine sections in Cauvery Basin is examined for their foraminiferal contents. The biostratigraphic distribution of 71 species of planktonic foraminifera has been used to diagnose 11 planktonic zones and subzones and correlated to the worldwide bioevent. During the late Campanian, a great transgression event occurred associated with the global warming (CF8b zone) trend indicated by large double‐keeled foraminifera (Globotruncana aegyptiaca Nakkady) of oligotrophic conditions. The latest zone CF4 records a sharp decrease in Planktonic/Benthic (P/B), globotruncanids, rugoglobigerinids and heterohelicids implying a fall of sea level.

High variability in SSU rDNA gene copy number among planktonic foraminifera revealed by single-cell qPCR

Metabarcoding has become the workhorse of community ecology. Sequencing a taxonomically informative DNA fragment from environmental samples gives fast access to community composition across taxonomic groups, but it relies on the assumption that the number of sequences for each taxon correlates with its abundance in the sampled community. However, gene copy number varies among and within taxa, and the extent of this variability must therefore be considered when interpreting community composition data derived from environmental sequencing. Here we measured with single-cell qPCR the SSU rDNA gene copy number of 139 specimens of five species of planktonic foraminifera. We found that the average gene copy number varied between of ~4000 to ~50,000 gene copies between species, and individuals of the same species can carry between ~300 to more than 350,000 gene copies. This variability cannot be explained by differences in cell size and considering all plausible sources of bias, we conclude that this variability likely reflects dynamic genomic processes acting during the life cycle. We used the observed variability to model its impact on metabarcoding and found that the application of a correcting factor at species level may correct the derived relative abundances, provided sufficiently large populations have been sampled.

Population dynamics and reproduction strategies of planktonic foraminifera in the open ocean

Abstract. It has long been assumed that the population dynamics of planktonic foraminifera is characterised by synchronous reproduction associated with ontogenetic vertical migration. However, due to contradictory observations, this concept became controversial, and subsequent studies provided evidence both in favour and against these phenomena. Here we present new observations from replicated vertically resolved profiles of abundance and shell size variation in four species of planktonic foraminifera from the tropical Atlantic to test for the presence, pattern, and extent of synchronised reproduction and ontogenetic vertical migration in this oceanic region. Specimens of Globigerinita glutinata, Globigerinoides ruber ruber, Globorotalia menardii and Orbulina universa were collected over the first 700 m resolved at nine depth intervals at nine stations over a period of 14 d. Dead specimens were systematically observed irrespective of the depth interval, sampling day and size. Conversely, specimens in the smaller size fractions dominated the sampled populations at all times and were recorded at all depths, indicating that reproduction might have occurred continuously and throughout the occupied part of the water column. However, a closer look at the vertical and temporal size distribution of specimens within each species revealed an overrepresentation of large specimens in depths at the beginning of the sampling (shortly after the full moon) and an overrepresentation of small individuals at the surface and subsurface by the end of the sampling (around new moon). These observations imply that a disproportionately large portion of the population followed for each species a canonical reproductive trajectory, which involved synchronised reproduction and ontogenetic vertical migration with the descent of progressively maturing individuals. This concept is consistent with the initial observations from the Red Sea, on which the reproductive dynamics of planktonic foraminifera has been modelled. Our data extend this model to non-spinose and microperforate symbiont-bearing species, but contrary to the extension of the initial observations on other species of foraminifera, we cannot provide evidence for ontogenetic vertical migration with ascent during maturation. We also show that more than half of the population does not follow the canonical trajectory, which helps to reconcile the existing contrasting observations. Our results imply that the flux of empty shells of planktonic foraminifera in the open ocean should be pulsed, with disproportionately large amounts of disproportionately large specimens being delivered in pulses caused by synchronised reproduction. The presence of a large population reproducing outside of the canonical trajectory implies that individual foraminifera in a fossil sample will record in the calcite of their shells a range of habitat trajectories, with the canonical trajectory emerging statistically from a substantial background range.

Planktonic Foraminiferal biostratigraphy of Jaddala Formation in well (K-152), Northern Iraq

Many species of planktonic foraminifera were identified from the Jaddala Formation from well (K-152)of depth (1010-900 m.) northern Iraq. The recorded planktonic foraminifera assemblages permits the recognition of four biozones these are (from top to bottom):Globigerinatheka subconglobata biozone (p11), Acarinina bullbrooki biozone (p10), Acarinina Pentacamerata biozone (p9) 1- Morozovell aragonensi biozone (p8) and On the basis of biocorrelation with previous works Early to Middle Eocene age confirmed for the Jaddala Formation at the studied section.

Unravelling the evolution of extraordinary long-range planktonic foraminifera species based on image processing analysis

The recent growing interest in Late Cretaceous biserial planktonic foraminifera (heterohelicids) has greatly enhanced their use as paleoceanographic and biostratigraphic markers. Pseudotextularia nuttalli, one of the most common cosmopolitan planktonic foraminifera, has an exceptionally long evolutionary range (Turonian-Maastrichtian). The image processing procedure we developed in this study enabled us to document changes in the growth pattern of Ps. nuttalli over time and between different oceanic provinces, and to identify possible speciation events within this lineage. The analysis was complemented by morphometric measurements of the penultimate chamber and test.The morphometric analyses do not indicate an early speciation event within this lineage, and thus, do not support splitting to Planoheterohelix praenuttalli (Turonian-Coniacian) and Pseudotextularia nuttalli (Coniacian-Maastrichtian). Our results indicate a gradual phyletic increase in mean test size from the Santonian through the Maastrichtian, along with increasing morphological diversification. This trend seems to coincide with the global cooling that culminated in the Late Cretaceous.Comparing between Ps. nuttalli from different oceanic provinces reveals that the Southern Tethys specimens are significantly less developed than their counterparts from the two tropical oceanic localities. This adaptive responsiveness suggests a negative correlation between test size and high productivity conditions in the upper water column.The case of Ps. nuttalli lineage exemplifies how extraordinary long-range species (>30 My) can evolutionarily change over time from “primitive” to “developed” forms, without showing a morphological gap. Such species may also show adaptive morphological diversification in response to different environments and, thus, are valuable for palaeoceanographic and paleoecologic reconstructions.

Biozonation and paleobathymetry of the Gurpi Formation in the Dasht-e Arjan section , Zagros area , based on foraminifera

In this research the Gurpi Formation in the Zagros Basin outcropping in the Dasht-e Arjan section, Shiraz province ,for the purpose of biozonational and Paleobathymetric studies were investigated. The thickness of these sediments is about 130 m and consists of Limestones and Shales.To determine the palaeobathymetry of the Gurpi Formation, Planktonic and benthic foraminifera were investigated . A depth of about 270m to 510m was determined for these sediments based on the ratio of planktonic foraminifera to the total assemblages of foraminifera after omitting infaunal benthic foraminifera (%P*) by using the equation D = e (3.58718+(0.03534 × %P* )).In this study sixty-two species of planktonic foraminifera belonging to eighteen genera were recognised .According to the studied planktonic foraminifera the Upper Cretaceous deposits in this area were divided into nine biozones as following :biozone1- Dicarinella concavata Interval Zone. Biozone2- Dicarinella asymetrica Total Range Zone. Biozone3- Globotruncanita elevata Partial range zone .Biozone4- Globotruncana ventricosa Interval Zone. Biozone5- Radotruncana calcarata Interval zone. Biozone 6- Globotruncanella havanensis Partial Range Zone. Biozone7- Globotruncana aegyptiaca Interval Zone. Biozone 8- Gansserina gansseri Interval Zone. Biozone 9- Contusotruncana contusa Interval Zone Based on the studied planktonic foraminifera the Early Santonian to Maastrichtian ages were determined for the sediments .

Biostratigraphy of planktonic foraminifera in the Abtalkh Formation and determination of the Santonian/Campanian Boundary in the Kopeh-Dagh Sedimentary Basin

ABSTRACT:We studied the Abtalkh Formation from five outcrops (Sheikh, Hajgelichkhan, Qarehso, Muzduran, and Deraz-Ab) in the Kopeh-Dagh sedimentary basin. A total of 30 species of planktonic foraminifera belonging to 21 genera were recorded. These species were used to subdivide the Abtalkh Formation into seven biozones (Dicarinella asymetrica Zone, Globotruncanita elevata Zone, Contusotruncana plummerae Zone, Radotruncana calcarata Zone, Globotruncanella havanensis Zone, Globotruncana aegyptiaca Zone, and Gansserina gansseri Zone). The Abtalkh Formation was deposited during the late Santonian-latest Campanian and the Santonian-Campanian boundary is identified based on the last occurrence of Dicarinella asymetrica. The base of the Campanian stage was delineated by the extinction of the marginotruncanid group, the first occurrences of Pseudotextularia nuttalli and Rugoglobigerina rugosa, and on the last occurrence of Dicarinella asymetrica.

New insights into the taxonomy and evolution of Jurassic planktonic foraminifera

Globuligerina glinskikhae nov. sp. Gradstein & Waskowska and Globuligerina waskowskae nov. sp. Gradstein are new species of Jurassic planktonic foraminifera from the Middle Jurassic of Dagestan and Poland. G. glinskikhae nov. sp. with its remarkable ‘protoglobigerine’ test may be an early evolutionary offshoot of Globuligerina oxfordiana (Grigelis). It may be an index taxon for upper Bajocian through Bathonian strata in Eastern Europe and Southwest Asia, and might be recognizable also in thin sections. We consider G. waskowskae nov. sp. to be a possible forerunner of Conoglobigerina helvetojurassica (Haeusler), the first planktonic foraminiferal species with a reticulate wall texture. Currently, is only known from Poland. In some localities, specimens of G. oxfordiana and of G. glinskikhae nov. sp. posses an additional apertural opening, often lacking a rim; its function is enigmatic. The postulated lineage from Jurassic Globuligerina balakhmatovae (Morozova) to Cretaceous Clavihedbergella eocretacea Neagu is refined with the description of Petaloglobigerina simmonsi nov. gen., nov. sp. Gradstein from the Kimmeridgian of Portugal. The evolutionary transition from G. balakhmatovae to P. simmonsi occurs by means of the ontogenic development of a petaloid test, with a pronounced flattening of the whorl with ovate chambers, the last ones often offset and twisted. Jurassic planktonic foraminifera, now known to consist of three genera and 12+ species underwent long periods of stasis, interrupted by late Bajocian, mid-Oxfordian and early Kimmeridgian evolution. The three ‘stasis and root’ taxa G. oxfordiana, G. bathoniana and G. balakhmatovae are geographically widespread in lower to mid palaeo-latitudes, and stratigraphically long ranging within the Middle and Late Jurassic. Modern digital microscopes, with co-axial and side LED lighting and excellent image stacking software are important tools in the study of Jurassic planktonic foraminifera, and fast and cost-effective communication tools in modern micropalaeontology.

FORAMINÍFEROS PLANCTÓNICOS VIVOS EN EL MAR ECUATORIANO: TAXONOMÍA Y DISTRIBUCIÓN*

The sensitivity to changes of the environment marine of planktonic species, such as planktonic foraminifera, makes them in detection tools of marine ecosystem changes, at any given time. The principal purpose of this paper is about of taxonomy and distribution of planktonic foraminifera species found in the Ecuadorian sea, since 1973 until 1998. Zooplankton samples were collected aboard oceanographic cruises realized between the mainland coast until 92 °W, to west of Galapagos Islands,and in the fxed station “La Libertad” (Santa Elena Peninsula). The total population of planktonic foraminifera comprised 25 species distributed in three families and seven genera: Globigerina,Globigerinoides, Globoquadrina, Globorotalia, Orbulina, Hastigerina and Globigerinita. Of these, Globigerinoides sacculifer and G. ruber predominated in waters with major in?uence of warm waters of the Panama Bay and, Globigerina bulloides in cold waters of the Humboldt Current. G. sacculiferand G. ruber predominated during the event “El Niño” 97-98 all along the Ecuadorian coast