Paleoenvironmental change at the Danian–Selandian transition in Tunisia: Foraminifera, organic-walled dinoflagellate cyst and calcareous nannofossil records

In the present study, we document paleoenvironmental change across the Danian–Selandian transition (planktic foraminiferal interval P2–P3b; calcareous nannofossil Zone NP4, Subzones NTp6–NTp8A; 61–59 Ma) in NW Tunisia. Diversifications of Paleogene planktic foraminifera with the evolution of the muricate and photosymbiotic lineages Morozovella, Acarinina and Igorina and of the biostratigraphically important nannofossils genus Fasciculithus are recorded within this interval. The present study aims to understand early Paleogene environmental changes in the southern Tethys, by analyzing the evolution of surface-water and–to a lesser extent–seafloor conditions. Three localities were investigated: Ain Settara, Elles and El Kef, all representing outer neritic deposition in the same basin, the Tunisian Trough. Paleoenvironmental changes are explored by combining planktic foraminiferal, organic dinocyst and calcareous nannofossils assemblages and several proxy parameters (planktic/benthic ratio, numbers of planktic foraminifera per gram, peridinioid/gonyaulacoid ratio; terrestrial/marine palynomorph ratio). In addition, also some geochemical parameters (calcite content and stable isotopes) are examined. Our records indicate that the environment evolved from an initially oligotrophic, open marine, deep outer neritic setting in P2–P3a towards a shallower and nutrient-rich setting from the base of Subzone P3b. This change is seen in the foraminiferal assemblages, with the substitution of Praemurica by Morozovella among the planktic foraminifera and an upward decrease in deeper benthic taxa. Also the organic-dinocyst assemblages show a peak of peridinioid cysts (Cerodinium and Lejeunecysta). Associated to these dinocyst assemblages, the lowest occurrence of Apectodinium is recorded, which seem to have evolved in this region, possibly in response to enhanced nutrient levels on the shelf. Additionally, a distinct change in calcareous nannofossil assemblages is also described, marked by the lowest appearance of Chiasmolithus edentulus, the lowest consistent occurrence of Fasciculithus and a slight increase in near-shore taxa (essentially Pontosphaera).This project provides an accurate understanding of paleoenvironmental change across the Danian–Selandian transition in Tunisia. Especially, integrating different proxies demonstrates a paleobathymetric shallowing from the Danian to the Selandian, associated to increase surface paleoproductivity. Furthermore, the results are compared with those from other localities along the Southern Tethyan margin (Egypt and Jordan) and a more regional paleoclimatic/paleoceanographic perturbation in the Southern Tethys is suggested.     

Palaeoenvironmental turnover across the Ypresian–Lutetian transition at the Agost section, Southastern Spain: In search of a marker event to define the Stratotype for the base of the Lutetian Stage

Marker events to define the stratotype for the base of the Lutetian Stage are poorly defined. To elucidate such markers and characterize palaeoenvironmental turnovers, we conducted an integrated study of the Ypresian–Lutetian (Y–L; early-middle Eocene) transition at the continuous Agost section (southeastern Spain). This 115-m-thick section, which consists of hemipelagic marls intercalated with hemipelagic limestones and turbidity sandstones, spans from planktic foraminiferal Zones P9 to P12 (E7 to E10) and calcareous nannofossil Zones CP11 to CP14a (NP13 to NP16). We report quantitative analyses of planktic and benthic foraminifera and characterization of trace fossil assemblages that are integrated with mineralogical analyses.Relative to benthic forms, planktic foraminifera constitute more than 80% of the foraminiferal assemblage. We found that the most abundant planktic species belong to the genera Acarinina, Morozovella, Subbotina, and Pseudohastigerina. Benthic foraminiferal assemblages are strongly dominated by calcareous taxa, with bolivinids being the most abundant group. Trace fossils showed the succession Nereites–Zoophycos–Cruziana ichnofacies throughout the Agost section. In addition to changes in palaeobathymetry, we deduced that quantity and quality of organic matter flux influenced by turbidity currents are the main factors controlling benthic assemblages. We distinguished several mineralogical boundaries at the Agost section, each associated with lithological facies changes suggesting a change in provenance rather than changes in weathering conditions. We made three observations that indicate an increase in sea water temperatures or a possible hyperthermal event related to the first occurrence (FO) of hantkeninids (i.e., the P9/P10 boundary): 1) a distinct peak in abundance of the benthic foraminifera Aragonia aragonensis; 2) the low-diversity of benthic foraminiferal assemblages; and 3) the occurrence of the planktic foraminifera Clavigerinella eocenica and Clavigerinella jarvisi. Benthic foraminiferal and trace fossil assemblages also suggest an associated relative fall of sea level from upper-middle bathyal to sublittoral depths. These characteristic indicators point to this boundary as a promising feature for defining the Global Stratotype Section and Point (GSSP) for the base of the Lutetian Stage. However, complementary magnetobiostratigraphic studies carried out at the Agost section point to the FO of calcareous nannofossil Blackites inflatus (base of CP12b), which occurred 3–5 Myr before the P9/P10 boundary, as the most suitable primary marker event. Whatever the marker event chosen, all the successive events recognized at the Agost section allow a complete characterization of the Y–L transition, and thus this section may be a suitable candidate to locate the GSSP for the Ypresian/Lutetian boundary.     

Foraminiferal turnover across the Eocene–Oligocene transition at Fuente Caldera, southern Spain: No cause–effect relationship between meteorite impacts and extinctions

We studied planktic and small benthic foraminifera from the Fuente Caldera section, southern Spain, across the Eocene–Oligocene transition. Benthic foraminifera indicate lower bathyal depths for the late Eocene and earliest Oligocene. Detailed high-resolution sampling and biostratigraphical data allowed us to date precisely layers with evidence for meteorite impact (Ni-rich spinel), which occur in the lower part of the planktic foraminiferal Globigerapsis index Biozone and in the middle part of the small benthic foraminiferal Cibicidoides truncanus (BB4) Biozone (middle Priabonian, late Eocene). Major turnovers of foraminifera occur at the Eocene/Oligocene boundary, only. The impact did not occur at a time of planktic or benthic foraminiferal extinction events, and the late Eocene meteorite impacts did thus not cause extinction of foraminifera. The most plausible cause of the Eocene/Oligocene boundary extinctions is the significant cooling, which generated glaciation in Antarctica and eliminated most of the warm and surface-dwelling foraminifera.     

Stable isotopic study of Oligocene-Miocene sediments from DSDP Site 354, Equatorial Atlantic

The oxygen- and carbon-isotope compositions of planktic and benthic foraminifera and calcareous nannofossils from Middle Oligocene-Early Miocene Equatorial Atlantic sediments (DSDP Site 354) indicate two important paleoceanographic changes, in the Late Oligocene (foraminiferal Zone P.21) and in the Early Miocene (foraminiferal Zone N.5). The first change, reflected by a δ¹⁸O increase of 1.45‰ inGlobigerina venezuelana, affected only intermediate pelagic and not surface, deep or bottom waters. The second change affected surface and intermediate waters, whereas deep and bottom waters showed only minor fluctuations. In the case of the former the isotope effect of the moderate ice accumulation on the Antarctic continent is amplified in the Equatorial Atlantic by changes in the circulation pattern. The latter paleoceanographic change, reflected by a significant increase in¹⁸O in both planktic and benthic forms (about 1.0‰ and 0.5‰, respectively), may have been caused by ice volume increase and temperature decrease. Both oxygen- and carbon-isotope compositions indicate a marked depth-habitat stratification for planktic foraminifera and calcareous nannofossils. Three different dwelling groups are recognized: shallowGlobigerinoides, Globoquadrina dehiscens, Globorotalia mayeri and nannofossils; intermediateGlobigerina venezuelana; and deepCatapsydrax dissimilis. The comparison of foraminifera and calcareous nannofossils suggests that the isotopic compositions of nannofossils are generally controlled by the same parameters which control the isotopic composition of shallow-dwelling foraminifera, but the former are more enriched in¹⁸O.     

Ammonite-benthic Foraminifera turnovers across the Lower-Middle Jurassic transition in the Lusitanian Basin (Portugal)

This paper describes and characterises the co-occurrence of ammonite and benthic foraminiferal assemblages across the São Gião outcrop (Central Portugal), a reference section for the Lower-Middle Jurassic boundary in the Lusitanian Basin. The upper Toarcian-lower Aalenian marls and marly-limestones in this section provide a precise and detailed ammonite-based biostratigraphic zonation, with a mixed assemblage of northwest European and Mediterranean faunal elements, associated with benthic foraminifera assemblages with northern hemisphere affinities, both correlatable with the Aalenian GSSP at the Fuentelsaz section (Iberian Cordillera, Spain). A total of 447 well-preserved ammonite specimens and 13.116 foraminifera have been studied; no evidence was detected of any taphonomic processes that could have changed the original assemblages. From a biostratigraphic point of view, the ammonite record has enabled four biostratigraphic units to be recognised (the Mactra and Aalensis subzones of the Aalensis Biozone in the upper Toarcian, and the Opalinum and Comptum subzones of the Opalinum Biozone in the lower Aalenian). With regard to the benthic foraminifera, the taxa identified have enabled the Astacolus dorbignyi Zone and 11 bioevents to be identified, most of which representing local biostratigraphic proxies. However, the increase in the relative abundance of Lenticulina exgaleata Dieni from the upper part of the Opalinum Subzone to the lower part of the Comptum Subzone has a regional value. The constant and continuous ammonite record of northwest European taxa, together with typical Mediterranean taxa – namely Grammoceratinae – throughout the section, the high relative abundance of Miliolina representatives – generally interpreted as foraminifers typical of shallow waters – and the absence of foraminiferal forms typical of cool waters, do not support the inference of cool seawater temperatures attributed to the Early Aalenian, or the global character of the “Comptum cooling event”, at least with reference to the Lusitanian Basin.     

Palaeogeographic and stratigraphic distribution of mid-late Oxfordian foraminiferal assemblages in the Prebetic Zone (Betic Cordillera, Southern Spain)

Middle-Upper Oxfordian assemblages of foraminifera in the Prebetic Zone (Betic Cordillera, SE Spain) were analysed at the genus level to determine their composition, relative abundance, diversity, and dominance, as well as the size of the specimens. A relationship has been established between lithofacies, palaeogeography and composition of foraminiferal assemblages, the former two also determining the stratigraphic record of these microfossil assemblages. Two assemblages of foraminifera serve to identify relatively distal and proximal areas in the Prebetic shelf. The distal assemblage is characterized by higher diversity, specimens of greater size, and more abundant planktic and agglutinated forms. Benthic forms include Ophthalmidium, Epistomina and colonies of encrusting foraminifera. The proximal assemblage shows lower diversity, lower abundance of planktic forms, Epistomina and encrusting nubeculariids, and a greater abundance of spirillinids and Reofax. On the whole, planktic foraminifera decrease upwards in the studied succession, which, together with decreasing nodularity, could be related to system tract conditions previously proposed for Oxfordian deposits in the southern palaeomargin of Iberia.     

Planktonic foraminiferal succession in late Cretaceous to early Palaeocene strata in Meghalaya, India

A roughly 10.5-m-thick succession within the Langpar Formation of the Um Sohryngkew River section, Meghalaya, India, constrained by the last occurrence of Globotruncanita stuarti and the first occurrence of Parasubbotina pseudobulloides , spans the K/T (Cretaceous–Tertiary) transition. The unit is divisible into three parts with the lower consisting of shaly limestone, weakly calcareous shale and silty shale with coal streaks. The middle part is dominated by calcareous shale with mud flakes, coprolites, burrows and pyrite nodules, followed by alternating limestone and marlite at the top. Planktonic foraminifera are rare to frequent within the unit. Based on the distribution of zonal indices, seven successive planktonic foraminiferal zones are recognized from across the K/T boundary. From base to top, these are CF4, CF3, CF2 and CF1 in the upper Maastrichtian part and Zone P0, Zone Pα and Subzone P1a in the lower Danian part. The biozones indicate that the section is biostratigraphically continuous across the K/T boundary. A similar foraminiferal succession and K/T transition is observed in the Langpar of the Cherrapunji-Mahadeo road section at a distance of over 5km. These K/T outcrops from Meghalaya provide the first record of a continuous K/T sequence in the Indian subcontinent with respect to planktonic foraminifera.     

New latest Coniacian to middle Campanian foraminiferal data from the lower Zongshan Formation in the Chaqiela section,Gamba, southern Tibet

A first and detailed foraminiferal biostratigraphic work on the lower part of the Zongshan Formation (Limestone I and Calcareous Marl I sequence) in the Chaqiela section, Gamba, southern Tibet, allows the recognition of three latest Coniacian to middle Campanian planktic foraminiferal biozones: Dicarinella asymetrica Total Range Zone, Globotruncanita elevata Partial-Range Zone, and Contusotruncana plummerae Interval Zone. The base and top of the Santonian Stage in the Chaqiela section were placed at the lowest occurrence (LO) of Globotruncana linneiana and the highest occurrence (HO) of Dicarinella asymetrica, respectively. The deposition of the latest Coniacian to middle Campanian sediments of the lower Zongshan Formation in the Chaqiela section seems to have been continuous or at least without any major gap based on the planktic foraminiferal biozones and events.     

Experimental dissolution of a fossil foraminiferal assemblage (Paleocene–Eocene Thermal Maximum,Dababiya, Egypt): Implications for paleoenvironmental reconstructions

Dissolution experiments were carried out on a foraminiferal assemblage from the Paleocene–Eocene Thermal Maximum (PETM) at Dababiya, Egypt, in order to: 1) reveal the effects of differential dissolution on the composition of the foraminiferal assemblage and 2) develop objective criteria for the evaluation of dissolution in foraminiferal assemblages used in early Paleogene paleoenvironmental reconstructions, particularly with respect to neritic Midway-type assemblages from the Paleocene/Eocene transition. Our results confirm two general observations on modern foraminifera: 1) planktic foraminifera are much more vulnerable to dissolution than benthic foraminifera, leading to depressed P/B ratios and 2) dissolution susceptibility differs between size fractions, with the smaller specimens dissolving more rapidly than the bigger ones, leading to a larger average size of the remaining assemblage. Within a size fraction, wall structure and thickness are considered to be the main factors controlling differential dissolution susceptibility. We propose a ranking scheme for taxa with respect to dissolution resistance. Among the benthic taxa, Lenticulina is most resistant, followed by the agglutinated Gaudryina cf. ellisorae and Alabamina midwayensis. Biserial and triserial hyaline taxa and the porcelaneous Spiroloculina sp. are most susceptible to dissolution, whereas rotaliines, such as Cibicidoides and Anomalinoides have an intermediate susceptibility. This implies that mild dissolution of a Midway-type benthic assemblage leads to a relative enrichment in Lenticulina, Gaudryina and rotaliines. Amongst planktic foraminifera, the muricate taxa Acarinina and Morozovella are most resistant, followed by the cancellate Subbotina. The smooth and generally small Globanomalina and Zeauvigerina are least resistant to dissolution. Our data enable to objectively evaluate various degrees of dissolution in benthic and planktic foraminiferal assemblages retrieved from the lower Paleogene Tethyan outcrops. In this way taphonomic artifacts can be readily distinguished from paleoenvironmental signals affecting the primary composition of the assemblages. More generally, we propose that the combined use of foraminiferal numbers, P/B ratio and relative abundances of non-calcareous agglutinated taxa and Lenticulina may provide a powerful proxy for assessing dissolution in hemipelagic assemblages from Cenozoic and upper Cretaceous continental margins. In order to achieve more robust pre-Quaternary paleoenvironmental reconstructions based on quantitative foraminiferal data, application of dissolution proxies, like proposed here, or in slightly modified form, should become a more widely used micropaleontologic procedure. Particularly continental margin studies dealing with major biotic events (e.g. PETM) or employing P/B ratios for sea-level reconstructions should benefit from such an approach.     

Extinction,survivorship and evolution of planktic foraminifera across the Cretaceous/Tertiary boundary at El Kef,Tunisia

An expanded sediment record at El Kef shows that the K/T boundary extinctions of planktic foraminifera extend over an interval from 25 cm below the geochemical boundary (Ir anomaly) to 7 cm above. Species extinctions appear sequential with complex, large, ornate forms disappearing first and smaller, less ornate, forms surviving longer. The 14 species extinctions below the boundary appear unrelated to an impact event.Cretaceous species survivorship is greater than previously assumed. About 10 species survive (22%) into Subzone P1a (Globigerina eugubina). All Cretaceous survivors are small primitive forms which are generally smaller than their ancestors in Cretaceous sediments.Species evolution after the K/T event occurs in two pulses. The first new Paleocene species evolve in the basal black clay (Zone PO) immediately after the major Cretaceous extinctions. Evolving species are small and primitive similar to Cretaceous survivors. The second pulse in species evolution occurs in the lower part of Subzone P1b with the appearance of larger more diverse species. The first major increase in carbonate sedimentation and productivity occurs at this time and signals the recoveyr of the ecosystem nearly 300,000 years after the K/T event. The species extinctions prior to the generally assumed impact event implied by the Ir anomaly, and the long recovery period of the ecosystem thereafter cannot be explained by a single impact, but suggest that multiple causes may be responsible such as climatic changes, volcanism, a sea level drop, production of warm saline bottom water and the chemical consequences associated with increased salinity.     

Integrated biostratigraphy for the Santonian/Campanian boundary interval,the Kurdistan Region,northeast Iraq

The first high-resolution integrated biostratigraphic study for Santonian/Campanian sediments of the Tabin section in the Kurdistan Region, northeast Iraq is provided. The study, based on 28 closely spaced samples, combines data from planktic foraminifers (25 species), calcareous nannofossils (32 species) and two ammonite genera in the Kometan Formation, marking the Santonian/Campanian boundary (S/C boundary) in the Kurdistan Region. In the absence of the crinoid Marsupites testudinarius, the proposed boundary marker, secondary markers such as calcareous nannofossils, planktic foraminifers and ammonites, have been used to establish a multi-stratigraphic biozonation for the late Santonian–early Campanian duration. Based on the occurrences of calcareous nannofossils, three biozones are identified — Lucianorhabdus cayeuxii (late Santonian), Calculites obscurus (latest Santonian–earliest Campanian), and Broinsonia parca parca (early Campanian). Seven calcareous nannofossil bioevents and three planktic foraminiferal bioevents are also identified. The Santonian/Campanian boundary is marked by: (a) the LO (Last Occurrence) of the planktic foraminifera D. asymetrica, (b) the FOs (First Occurrence) of the calcareous nannofossil species B. parca parca and B. parca constricta, (c) the extinction of several planktic foraminiferal species of Dicarinella and Marginotruncana, (d) the abundance and diversification of the planktic foraminifera genera, Globotruncana and Globotruncanita at the beginning of the Campanian, and (e) the disappearance of the ammonite genus Texanites, 0.5 m below (i.e., at 19 m) the disappearance of all Dicarinella and Marginotruncana species in the study section. Similar to several other Tethyan sections, the FO of B. parca parca is above the LOs of D. concavata and D. asymetrica; the LO of D. asymetrica is used here to mark the S/C boundary     

Benthic foraminiferal paleoenvironmental reconstruction from the Upper Coniacian-Lower Campanian succession in north-western Tunisia

Quantitative analysis of benthic foraminifera is used to characterize the paleoenvironments of the Upper Coniacian-Lower Campanian succession in the Jbil section of north-western Tunisia. Foraminiferal parameters and benthic foraminiferal assemblages show that the studied section includes four distinct paleoenvironmental phases. From oldest to youngest, these are as follows: (1) an interval with a Praebulimina reussi assemblage with infaunal ratios as high as 96.1%. High abundances of P. reussi, reflecting an increase in organic matter flux to the seafloor (meso-to eutrophic) under oxygenated bottom-water conditions. (2) An interval characterized by a Gavelinella costulata assemblage with mixed infaunal/epifaunal foraminifera with higher Fisher's alpha values (ranging from 4 to 15.2), reflecting mesotrophic conditions in an outer shelf environment. (3) An interval with a Gaudryina laevigata assemblage indicative of a middle to outer shelf environment; there is a considerable increase in infaunal agglutinated foraminifera, as well as a relatively abundant and moderately diversified oxic/suboxic foraminifera. (4) The final interval occurs in the lower Campanian (the Globotruncana ventricosa Zone) and includes a Bolivinoides decoratus assemblage reflecting an outer shelf to upper bathyal environment. It contains a higher planktonic percentage and biodiversity with a slight increase in dysoxic species; the mixed infaunal/epifaunal content (57.6 to 73.3%) reflects mesotrophic conditions. Four well-recognized major sea-level falls are matched by the dual signatures of eustatic sea-level changes. These are coincident with the results of this study, which represent the first documentation of these events in Tunisian faunal and paleoenvironmental changes, at the following boundaries: Coniacian/Santonian, intra-Santonian, Santonian/Campanian, and intra-early Campanian.     

西藏定日县贡扎上白垩统浮游有孔虫与桑顿阶/坎潘阶界线的厘定

白垩纪是大洋缺氧及生物灭绝等重大地质事件频发的一个时期,也是全球气候变暖的重要时期。因此,白垩纪研究对于探讨地质历史时期地球的系统演化,尤其是生物与环境之间的协同演化关系,具有十分重要的意义。西藏定日贡扎剖面保存着上白垩统较为完整的地层序列,文中对上白垩统岗巴村口组和宗山组剖面岩石样品中获得的有孔虫化石进行研究,鉴定出有孔虫化石8属22种,识别出Dicarinella asymetrica、Globotruncanita elevata、Globotruncana ventricosa、Radotruncana calcarata等4个有孔虫化石带。根据有孔虫化石确定贡扎剖面的地层时代为晚白垩世桑顿期(Santonian)至坎潘期(Campanian),桑顿阶/坎潘阶界线位于Dicarinella asymetrica带与Globotruncanita elevata带之间。     

Middle Eocene–Early Pliocene Subantarctic planktic foraminiferal biostratigraphy of Site 1090, Agulhas Ridge

The analysis of planktic foraminiferal assemblages from Site 1090 (ODP Leg 177), located in the central part of the Subantarctic Zone south of South Africa, provided a geochronology of a 330-m-thick sequence spanning the Middle Eocene to Early Pliocene. A sequence of discrete bioevents enables the calibration of the Antarctic Paleogene (AP) Zonation with lower latitude biozonal schemes for the Middle–Late Eocene interval. In spite of the poor recovery of planktic foraminiferal assemblages, a correlation with the lower latitude standard planktic foraminiferal zonations has been attempted for the whole surveyed interval. Identified bioevents have been tentatively calibrated to the geomagnetic polarity time scale following the biochronology of Berggren et al. (1995). Besides planktic foraminiferal bioevents, the disappearance of the benthic foraminifera Nuttallides truempyi has been used to approximate the Middle/Late Eocene boundary. A hiatus of at least 11.7 Myr occurs between 78 and 71 m composite depth extending from the Early Miocene to the latest Miocene–Early Pliocene. Middle Eocene assemblages exhibit a temperate affinity, while the loss of several planktic foraminiferal species by late Middle to early Late Eocene time reflects cooling. During the Late Eocene–Oligocene intense dissolution caused impoverishment of planktic foraminiferal assemblages possibly following the emplacement of cold, corrosive bottom waters. Two warming peaks are, however, observed: the late Middle Eocene is marked by the invasion of the warmer water Acarinina spinuloinflata and Hantkenina alabamensis at 40.5 Ma, while the middle Late Eocene experienced the immigration of some globigerinathekids including Globigerinatheka luterbacheri and Globigerinatheka cf. semiinvoluta at 34.3 Ma. A more continuous record is observed for the Early Miocene and the Late Miocene–Early Pliocene where planktic foraminiferal assemblages show a distinct affinity with southern mid- to high-latitude faunas.     

Biostratigraphie,paléoécologie et zones d’acmé des foraminifères planctoniques au passage Crétacé-Paléogène dans la Téthys (Tunisie et Espagne) et l’Atlantique (France)

Biostratigraphical high-resolution analyses and quantitative data confirm that deposition is continuous across the K-Pg transition in several sections in Tunisia (El Kef, stratotype section) and Spain (Agost and Caravaca sections) located in the Tethyan realm and the Bidart sections in the Atlantic realm, without any relevant hiatus. The Upper Maastrichtian assemblages of planktic foraminifera from these sections are largely dominated by small biserial heterohelicids. They are associated to common species having planispiral test (i.e. globigerinelloids), trochospiral test (i.e. hedbergellids, rugoglobigerinids globotruncanids), to rare triserial heterohelicids (i.e. guembelitriids) and trochospiral species showing tubulospines (i.e. schackoinids). Stratigraphical ranges of these diverse taxa through the late Maastrichtian in the Tethyan and Atlantic realms show very few changes in the planktonic foraminiferal assemblages and most of the species are present in the Abathomphalus mayaroensis biozone. By our high-resolution sampling and the intensive research for the A. mayaroensis index species in the uppermost Maastrichtian samples, we confirm that this species is omnipresent up to the top of the Maastrichtian. Therefore, A. mayaroensis is present in almost all samples which are late Maastrichtian in age, but this species became very scarce in the uppermost Maastrichtian samples. This scarceness could be due to a climate cooling. A sharp decrease in relative abundance of the deep dwellers species, like as Abathomphalus intermedius and A. mayaroensis as well as in other keeled globotruncanids is observed at the studied sections from the Tethyan realm (indicative of low latitude) across the latest Maastrichtian. At the K/Pg boundary, all the globotruncanids disappeared. They are considered specialists living in tropical-subtropical deep seawater habitat. At this boundary, large and ornate heterohelicids also disappeared. Therefore, all the studied sections show that about 90 % of the Maastrichtian species became extinct according to a catastrophic mass extinction pattern. Only about 10 % crossed the K/Pg boundary and survived during the earliest Danian. The minor difference in the number of disappeared taxa is related to their latitude location or environment paleodepth. The changes in the species relative abundance, observed in the successive planktic foraminiferal assemblages, make it possible to recognize the Acme-stage 0 typical of the upper Maastrichtian interval. It is characterized by the highest species richness of Globotruncanids and heterohelicids specialists of tropical to subtropical marine conditions, the Acme-stage 1 typical of the Guembelitria cretacea Zone, and in particular of the Hedbergella holmdelensis Subzone dominated by “opportunists” species belonging to Guembelitria, the Acme-stage 2 which corresponds to the Pv. eugubina Zone dominated mainly by specimens belonging to Palaeoglobigerina and Parvularugoglobigerina and the Acme-stage 3 which characterizes mainly the Ps. pseudobulloides Zone dominated by biserial species belonging to Chiloguembelina and Woodringina.     

Correlation between the Paleocene/Eocene boundary and the Ilerdian at Campo, Spain

The Ilerdian is a well-established Tethyan marine stage, which corresponds to an important phase in the evolution of larger foraminifera not represented in the type-area of the classical Northwest-European stages. This biostratigraphic restudy of its parastratotype in the Campo Section (northeastern Spain) based on planktic foraminifera, calcareous nannofossils, dinoflagellate cysts and the distribution of the stable isotopes ∂¹³C and ∂¹⁸O is an attempt to correlate the Paleocene/Eocene boundary based on a characteristic carbon isotope excursion (CIE) marking the onset of the Initial Eocene Thermal Maximum (IETM) and the Ilerdian stage. The base of this ∂¹³C excursion has been chosen as the criterion for the recent proposal of the Global Stratotype Section and Point (GSSP) of the base of the Eocene (= base of the Ypresian) in the Dababiya Section (Egypt) to which an age of 54.9 Ma has been attributed. This level is also characterized by a marked extinction among the deep-water benthic foraminifera (Benthic Foraminifera Extinction Event, BFEE), a flood of representatives of the planktic foraminiferal genus Acarinina and the acme of dinoflagellate cysts of the genus Apectodinium. In the Campo Section, detailed biozonations (planktic foraminifera, calcareous nannofossils, dinoflagellate cysts) are recognized in the Lower and Middle Ilerdian. The correlation with the Ypresian stratotype is based on dinoflagellate cysts and calcareous nannofossils. The base of the Ilerdian is poor in planktic microfossils and its precise correlation with the redefined Paleocene/Eocene boundary remains uncertain.     

Benthic foraminiferal bioevents in lower to upper Toarcian strata of Southern Beaujolais (SE France)

This paper documents changes in benthic foraminiferal assemblages compared with high resolution ammonite biozonation along the lower Toarcian to upper Toarcian marine succession of Southern Beaujolais in southeastern France. Eight ammonite and three benthic foraminiferal zones including five subzones are distinguished based on the occurrence of twelve foraminiferal events. Each benthic foraminiferal subzone is characterized by its taxonomic and morphogroup composition, which represents the paleoecological response of these taxa and morphotypes of benthic foraminifera in the Early Jurassic and early Middle Jurassic. Major changes in abundance and diversity occur at the end of the Toarcian Oceanic Anoxic Event (T-OAE) and near the Early-Middle Jurassic transition. The low-abundance foraminiferal assemblages recorded in the Serpentinus ammonite Zone are interpreted as reflecting adverse environmental conditions after the T-OAE. The later recovery and development of the foraminiferal assemblages is documented in the Bifrons up to the Aalensis zones and is attributed to improved bottom water oxygenation. Common occurrences of agglutinated foraminifera represented mostly by Trochammina pulchra Ziegler in the Dispensum Zone point to an influx of cooler water masses during the late Toarcian. The morphogroup analysis carried out on the foraminifera and their paleoecological interpretations shed light on the changes in the stratigraphic record at the end of the T-OAE up to the Toarcian/Aalenian boundary.     

Environmental perturbation in the southern Tethys across the Paleocene/Eocene boundary (Dababiya,Egypt): Foraminiferal and clay mineral records

Foraminiferal and clay mineral records were studied in the upper Paleocene to lower Eocene Dababiya section (Egypt). This section hosts the GSSP for the Paleocene/Eocene boundary and as such provides an expanded and relatively continuous record across the Paleocene/Eocene Thermal Maximum (PETM). Deposition of illite–smectite clay minerals is interpreted as a result of warm and arid conditions in the southern Tethys during the latest Paleocene. Benthic foraminiferal assemblages are indicative of seasonal variation of oxygen and food levels at the seafloor. A sea-level fall occurred in the latest Paleocene, followed by a rise in the earliest Eocene. Foraminiferal diversity and densities decreased strongly at the P/E boundary, coinciding with the level of global extinction of benthic foraminifera (BEE) and start of the Carbon Isotope Excursion (CIE) and PETM. In the lower CIE, the seafloor of the stratified basin remained (nearly) permanently anoxic and azoic. A sudden increase in mixed clay minerals (kaolinite and others) suggests that warm and perennial humid conditions prevailed on the continent. High levels of TOC and phosphathic concretions in the middle CIE are evidence for increased organic fluxes to the sea floor, related to upwelling and to augmented continental runoff. Low densities of opportunistic taxa appeared, indicating occasional ephemeral oxygenation and repopulation of the benthic environment. The planktic community diversified, although conditions remained poor for deep-dwelling taxa. An increase in illite–smectite dominated clay association is considered to mark the return of a seasonal signature on climatic conditions. During the late CIE environmental conditions changed to seasonally fluctuating mesotrophic conditions and diverse and rich benthic and planktic foraminiferal communities developed. Post-CIE planktic faunas consisted of both deep and shallow-dwelling taxa and buliminid-dominated benthic assemblages reflect fluctuating mesotrophic conditions.The frequent environmental perturbations during the CIE/PETM at Dababiya provided a rather specialized group of foraminiferal taxa (i.e., Anomalinoides aegyptiacus) the opportunity to repopulate, survive and subsequently dominate by a hypothesized capacity to switch to an alternative life strategy (population dynamics, habitat shift) or different metabolic pathway. The faunal record of Dababiya provides insight into the cause and development of the BEE: various severe global changes during the PETM (e.g., ocean circulation, CaCO₃-dissolution, productivity and temperature changes) disturbed a wide range of environments on a geologically brief timescale, explaining together the geographically and temporally variable character of the BEE. This allowed a number of specific but different foraminiferal assemblages composed of stress-tolerant and opportunistic taxa to be successful during and after the periods of environmental perturbations associated with the PETM.     

Extinction pattern of marine Ostracoda across the Pliensbachian-Toarcian boundary in the Cordillera Ibérica, NE Spain: Causes and consequences

This paper discusses the extinction pattern of the Pliensbachian-Toarcian boundary (PTB) ostracod assemblages at the Almonacid de la Cuba section (Cordillera Ibérica, NE Spain), which has been recently proposed as auxiliary boundary stratotype for the PTB. The ostracod record shows that the main Early Jurassic ostracod extinction event occurred not at the end of the Pliensbachian, but near the top of the Mirabile ammonite Subzone, Tenuicostatum ammonite Zone (Early Toarcian). On the basis of the evaluation of PTB ostracod record, a new causal explanation for the Early Toarcian ostracod turnover is proposed. This paper suggests that a reorganization of surface and deep-water circulations caused by the opening of the Hispanic Corridor could have generated a mild cooling episode, finally affecting the survival of healdioid ostracods.     

Integrated biostratigraphy based on planktonic foraminifera and dinoflagellates across the Cretaceous/Paleogene (K/Pg) transition at the Izeh section (SW Iran)

The present work is based on semi-quantitative study carried on detailed sampling (samples are spaced by 5, 10 and 15 cm close to the boundary) of an essentially continuous and expanded section crossing the Cretaceous–Paleogene (K/Pg) boundary in Iran. By this work, we attempt to detail biostratigraphy based on planktonic foraminifera biozones and correlate biozones and subzones with dinocyst events. The entire Cretaceous–Paleogene interval contains rich, diversified and well-preserved planktonic foraminifera and dinoflagellate cyst assemblages. Four planktonic foraminiferal biozones have been recognized across the Cretaceous–Paleogene transition (K/Pg): Abathomphalus mayaroensis Biozone including Plummerita hantkeninoides Subzone from the Late Maastrichtian and Guembelitria cretacea (including Hedbergella holmdelensis and Parvularugoglobigerina longiapertura subzones), Parvularugoglobigerina eugubina Biozone and Parasubbotina pseudobulloides Biozone belonging to the Early Danian. These biozones have been correlated with four dinocyst biozones: the Manumiella seelandica Biozone belonging to the Late Maastrichtian and the Alisocysta reticulata, Senoniasphaera inornata and Damassadinium californicum biozones from the Early Danian. At this section, like at the El Kef section (GSSP for the K/Pg) and the auxiliary sections, an Ir anomaly is detected indicating the K/Pg boundary. This geochemical anomaly coincides also with mass extinctions of planktonic foraminifera species. The extinct species are in particular the large, complex tropical and subtropical taxa dwelling in subsurface and lower photic water. The mass extinctions at the Izeh section occurred over a succinct period of time similar to the K/Pg type section at El Kef (Tunisia). These sudden mass extinctions indicate a catastrophic pattern event occurring at the Maastrichtian/Danian boundary. In contrast the organic-walled dinocysts were less affected by the mass extinction and most species crossed the K/Pg boundary without showing mass and sudden extinctions. Nevertheless, they showed changes in their assemblages’ structure beyond the K/Pg boundary. Especially, Manumiella seelandica and M. druggii, typical species of Antarctic Maastrichtian dinocysts assemblages, occur in coeval deposits at the Izeh section; they persist through the Lower Danian and, like in Tunisia (e.g., El Kef section, Ellès section) show an obvious increase in relative abundance.