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。     

The genetic diversity of planktic foraminifera and the global distribution of ribosomal RNA genotypes

Fossil planktic foraminifers in the ocean sediments play an unparalleled role in our understanding of the oceanographic environment in the past. An in depth knowledge of their diversity, ecology and biogeography in the modern ocean lies central to the interpretation of the fossil assemblages. In comparison with their benthic counterparts, planktic foraminifera have a very limited diversity of around fifty extant morphospecies. Their morphospecies diversity peaks in the sub-tropics and decreases steeply towards the poles. Traditional species concepts have partitioned morphological types into distinct species (morphospecies) based on test shape, but genetic studies show that individual morphospecies are actually complexes of several discrete genetic types (genotypes). Many of these genotypes have distinct ecologies and novel adaptations that are consistent with species-level classification, indicating that the true diversity of planktic foraminifers has been greatly underestimated. Although planktic foraminifera are clearly capable of long-distance dispersal, they may be constrained by both physical and ecological barriers that vary according to the evolutionary history and ecology of the individual genotypes within a morphospecies. These differences lead to diverse biogeographies. Here, we provide an overview of the genetic and biogeographic data available to date for the planktic foraminifera and present global biogeographies highlighting the distribution of genetic types in the eight planktic foraminiferal morphospecies for which detailed molecular evidence is available.     

Oxygen isotopic evidence for the depth stratification of tertiary and cretaceous planktic foraminifera

Oxygen isotope analyses of Tertiary and Cretaceous planktic foraminifera indicate that species have been stratified with respect to depth in the water column at least since Albian time. There is a relationship between morphology and depth habitat. Species with globigerine morphology have consistently occupied shallower depths than have species with globorotalid morphology. Biserially arranged species occupied both shallow and deep levels in the water column. On the average, it appears that ancient species with shallow habitats have been more susceptible to dissolution and have been preserved less well than species dwelling in deeper habitats. This relationship is similar to that observed for Recent planktic foraminifera. Comparison of carbon isotope ratios of adult and juvenile forms indicates that either the source of the carbon found in the shell or the carbon isotopic fractionations which occur during calcite secretion change during the development of individual foraminifera. The carbon isotopic ratios do not provide a reliable means for reconstructing the depth habitats of ancient species. Temperature-depth profiles for tropical Tertiary oceans have been reconstructed from the isotopic temperatures of planktic and benthic foraminifera. The vertical thermal structure of Oligocene oceans resembled that of modern oceans most closely. Those of Paleocene and Maastrichtian times differed most from that of modern oceans.     

Age of the latest marine sedimentation in the western Kunlun area constrained by planktic foraminifera

Surface uplift of the Tibetan Plateau in the Cenozoic has dramatically affected evolutions of climate, environment, and biota in East Asia. The onset time of plateau uplift can be roughly constrained by the termination of the latest marine sedimentation, which shows large spatial differences in the Tibetan Plateau. In the northwest Tibetan Plateau of the western Kunlun area, the Tielongtan Group represents the latest marine sedimentation. However, the age of its depositional cessation is still unknown. For the first time, we conduct taxonomic, paleoecologic and paleogeographic studies of planktic foraminifera in the limestones of the Tielongtan Group. Despite poor preservation and low abundance, ten planktic foraminiferal species are identified, including Globotruncana falsostuarti, G. cf. linneiana, G. cf. ventricosa, Planohedbergella prairiehillensis, P. cf. yaucoensis, Pseudotextularia nuttalli, Planoheterohelix globulosa, P. cf. praenuttalli, Muricohedbergella holmdelensis and Whiteinella brittnensis. The foraminiferal assemblages suggest an age of late Campanian to Maastrichtian, indicating a shallow, neritic marine environment. Combining available research data from other regions, we show that these planktic foraminifera were widely distributed in the Tarim basin, southern Tibet, and the Mediterranean area during the latest Cretaceous. Our result of planktic foraminifera in the Tielongtan Group implies that the surface uplift of the western Kunlun area did not begin until after ∼76–66 Ma.     

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.     

Evolution of early planktic foraminifers

The evolution of Mesozoic species of planktic foraminifers, particularly the succession of their morphotypes and the variation in their diversity and their abundance, is shown to be related to the adaptation of evolutionary strategy to fluctuations in the oceanic environment.During periods of stress (“oligotaxic period”) the more primitive species tend to invade the oceanic surface waters by means of r-selection. During stable “polytaxic” conditions, the same species engage in an adaptive radiation colonizing progressively deeper water through K-selection.The succession of morphotypes from the middle Jurassic to the end of the Cretaceous is compared with living planktic foraminifers and related to the biogeographic (cold arctic, warm equatorial faunas) and bathymetric distribution. A general model for the evolution of early planktic foraminifers is made with reference to the preceding observations, and in relation to the pattern of variation of trophic resources.     

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.     

Deep-sea palaeoceanography of the Maldives Islands (ODP Hole 716A), equatorial Indian Ocean during MIS 12-6

Deep-sea benthic foraminifera, planktic foraminifer Globigerina bulloides and pteropods have been quantitatively analysed in 451 samples from Ocean Drilling Program (ODP) Hole 716A, to understand both surface and deep-sea palaeoceanographic changes in the equatorial Indian Ocean basin during the late Quaternary (∼444–151 Kyrs). Benthic foraminifera were analysed from >125 μm size fraction whereas Globigerina bulloides and pteropods were analysed from >150 μm size fraction. Factor analysis of most dominant benthic foraminiferal species over the studied time span made it possible to identify three biofacies characterizing distinct deep-sea environmental settings at Hole 716A. The environmental interpretation of each species is based on the ecology of recent deep-sea benthic foraminifera. The faunal record indicates fluctuating deep-sea conditions including changes in surface productivity, organic food supply and deep-sea oxygenation linked to changing wind intensities. These changes are pronounced on glacial-interglacial time scales driven by summer monsoon winds.     

Planktic foraminiferal molecular evolution and their polyphyletic origins from benthic taxa

Phylogenetic analyses based on partial sequences of the small subunit (SSU) ribosomal (r) RNA gene have shown that the planktic and benthic foraminifera form a distinct monophyletic group within the eukaryotes. In order to determine the evolutionary relationships between benthic and planktic foraminifers, representatives of spinose and non-spinose planktic genera have been placed within a molecular SSU rDNA phylogeny containing sequences of the benthic suborders available to date. Our phylogenetic analysis shows that the planktic foraminifers are polyphyletic in origin, not evolving solely from a single ‘globigerinid-like’ lineage in the Mid-Jurassic, but derived from at least two ancestral benthic lines. The benthic ancestor of Neogloboquadrina dutertrei may have entered the plankton later than the Mid-Jurassic, and further investigation of related extant species should provide an indication of the timing of this event. The evolutionary origin of the non-spinose species Globorotalia menardii remains unclear. The divergences of the planktic spinose species generally support recent phylogenies based on the fossil record, which infer a radiation from a globigerinid common ancestor in the Mid- to Late Oligocene. The branching pattern indicates that there are possibly four distinct groups within the main spinose clade, with large evolutionary distances being observed between them. Globigerinoides conglobatus clusters strongly with Globigerinoides ruber and are divergent from Globigerinella siphonifera, Orbulina universa and Globigerinoides sacculifer.Conserved regions of the SSU rRNA gene show sufficient variation to discriminate foraminifers at the species level. Large genetic differences have been observed between the pink and white forms of Gs. ruber and between Ge. siphonifera Type I and II. The two types of Ge. siphonifera cannot be discriminated by traditional palaeontological methods, which has considerable implications for tracing fossil lineages and for the estimation of molecular evolutionary rates based upon the fossil record. The conserved regions show a high degree of sequence identity within a species, providing signature sequences for species identification. The variable regions of the gene may prove informative for population level studies in some species although complete sequence identity was observed in G. sacculifer and O. universa between specimens collected from the Caribbean and Western Pacific.     

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.     

Molecular evidence for an independent origin of modern triserial planktonic foraminifera from benthic ancestors

Gallitellia vivans is the only Recent representative of the triserial planktonic foraminiferal family Guembelitriidae. The origin and evolution of this interesting albeit poorly known family are enigmatic. To elucidate the phylogenetic relationships between G. vivans and other planktonic foraminifera, we sequenced the small subunit ribosomal DNA (SSU rDNA) for comparison to our extensive database of planktonic and benthic species. Our analyses suggest that G. vivans represents a separate lineage of planktonic foraminifera, which branches close to the benthic rotaliids Stainforthia and Virgulinella. Both genera resemble Gallitellia in general morphological appearance, having elongate triserial tests at least in their early ontogenic stages. The divergence time of G. vivans is estimated at ca. 18 Ma (early Miocene), suggesting an origin independent from the Cretaceous and Paleogene triserial planktonic foraminifera. Our study thus indicates that modern triserial planktonic foraminifera are not related to the Cretaceous–Paleogene triserial species, and that the sporadic occurrences in the fossil record are not the result of poor preservation, but reflect multiple transitions from benthic to planktonic mode of life.     

Catastrophic mass extinction and assemblage evolution in planktic foraminifera across the Cretaceous/Paleogene (K/Pg) boundary at Bidart (SW France)

A high-resolution biostratigraphic analysis of planktic foraminifers confirms that the Bidart section at the eastern margin of the Atlantic Ocean exhibits a continuous and complete Cretaceous/Paleogene (K/Pg) transition interval. The biozones and subzones recorded in this section are less expanded than their equivalent in Tunisian sections: El Kef (Global Stratotype Section and Point: GSSP for the K/Pg boundary) and Ellès (auxiliary section), but they are sufficiently thick to allow a detailed analysis of the evolution of the planktic foraminiferal assemblages across the K/Pg transition.Throughout the uppermost 4 m Maastrichtian, the planktic foraminiferal assemblages are highly diversified, containing up to 72 species. These Maastrichtian assemblages are rich in cosmopolitan taxa (70%), dominated by small biserial morphotypes which belong mainly to the genus Heterohelix which coexist with less abundant but highly diverse tropical and subtropical species.The extinction pattern at the Bidart section suggests a sudden catastrophic mass extinction at the K/Pg boundary which affected at least 53 out of 72 species. The species becoming extinct include globotruncanids (e.g. Contusotruncana spp., Globotruncana spp., Globotruncanita spp.) and complex heterohelicids (e.g. Racemiguembelina spp., Pseudotextularia spp., Gublerina spp.). At the Bidart section, only Archaeoglobigerina cretacea disappears 2 m below the K/Pg boundary event. Specimens of 18 small and even tiny Maastrichtian species, are found at the lowermost Danian. Only a few of these species belonging to the genera of Guembelitria, Hedbergella and Heterohelix are considered to be real “Cretaceous survivor species”, whereas the specimens belonging to the rest, are most probably reworked, because they differ in their preservation.Throughout lowermost Danian, the planktic foraminiferal assemblages are dominated by “opportunistic” species of the genus Guembelitria. These opportunists are associated to small and poorly diversified pioneer globigerinids (Palaeoglobigerina spp. and Parvularugoglobigerina spp.). These assemblages became progressively more diversified across the early Danian containing species with cancellate walls (Eoglobigerina spp., Parasubbotina spp., Subbotina triloculinoides and Praemurica spp.) and new taxa of biserial heterohelicids (Woodringina spp. and Chiloguembelina spp.) suggesting a paleoenvironmental recovery.     

Benthic foraminiferal fauna during the time of the Indian-Asian contact, in southern Balochistan, Pakistan

Cretaceous and early Paleocene benthic foraminifera were studied from one section along the western Gaj River, southern Balochistan, Pakistan, to reconstruct the paleoenvironment of the Tethys Sea during the Indian-Asian contact. We recognize three lithostratigraphic units in ascending order: the Mughal Kot Formation, the Pab Sandstone, and the Jamburo Group. Both the Maastrichtian Mughal Kot Formation, which consists of shale with grey marly limestone, and the Maastrichtian Pab Sandstone, which consists of quartzose sandstone, indicate an open ocean environment as they have diversified planktic and benthic foraminiferal assemblages. The Maastrichtian-Paleocene Jamburo Group, consisting of dark grey, calcareous shale and marlstone with some sulfide grains, is characterized by low diversities of benthic assemblages. The change to the lower diversities may be associated with the development of poor circulation of deeper water that was caused by narrowing of the Tethys Sea.The Trochammina spp. Assemblage from the Jamburo Group, which can be correlated with flysch-type agglutinated foraminiferal assemblages, has a low benthic species diversity, indicating an unfavorable condition for calcareous foraminifera because of the development of oxygen-depleted water. The absolute abundance of agglutinated specimens shows a remarkable change from low numbers in the Maastrichtian to high ones in the Paleocene. The benthic foraminiferal evidence supports the hypothesis that the collision of the Asian and Indian plates occurred near the end of the Cretaceous.     

Morphological abnormalities in Late Cretaceous and early Paleocene foraminifer tests (northern Patagonia, Argentina)

Morphological abnormalities are common in Late Cretaceous and early Paleocene foraminifer tests at two localities in northern Patagonia, Argentina. Protelphidium sp. in the Auca Mahuevo section (late Campanian–early Maastrichtian) exhibit abnormal size or shape of the later chambers, with the last chamber commonly larger than normal or inflated and variably extending onto one of the lateral sides of the test; modification of the coiling plane; protuberances near the proloculus or on one or more chambers; a double last chamber, and complex forms. Protelphidium hofkeri Haynes in the Cerro Azul section (Danian) exhibit abnormal size or shape of one or more chambers, producing peripheral irregularities. In addition, there are rare multiple tests in planktic species from the Cerro Azul section, probably teratological specimens. The sedimentology of the sections and the character of the accompanying faunas indicate that the abnormalities in the two benthic foraminiferal taxa were most probably caused by hypersalinity and/or fluctuations in salinity. The fossil occurrence of assemblages with abundant deformed specimens suggests that investigators should carefully look at many aspects of the environment before concluding that anthropogenic pollution is the only cause of deformations of living benthic foraminifera.     

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.     

Aptian to Maastrichtian paleobathymetric reconstruction of the Eastern Venezuelan Basin

The objective of this study is a paleobathymetric reconstruction of the depositional environment during the Cretaceous (Aptian-Maastrichtian) on the northern flank of the Eastern Venezuelan Basin. The model is based on the presence of benthic foraminifera in 17 well sections, spread across the paleoslope in a passive margin. Cluster analysis separates five distinct assemblages of foraminifers. The analysis is based on the assumption that the species must occur in 10% or in at least two wells of the area. The R-mode for each well provides clusters of species that are similar in distribution and abundance trends. These clusters together with the diversity and abundance of planktic foraminifers, dinoflagellates, pollen, spores, calcareous nannofossils, and sedimentological data help to delineate the biofacies. The biofacies are distributed in a pattern from the updip position (southwest) to the downdip position (northeast). The shallowest biofacies (0–50 m) is represented by Ammobaculites sp., Haplophragmoides sp., Lituolidae, with abundant terrestrial palynomorphs and dinoflagellates. Abundant species in depths greater than 100 m are Praebulimina carseyae, Epistomina lacunosa, Gavelinella sp., Buliminella sp., and Pullenia cretacea. This biofacies interpretation allows us to establish a paleocoast orientation during the Aptian-Maastrichtian.The establishment of the age-paleobathymetry relationships in this area provides the basis for the stratigraphic reconstruction of the Cretaceous in the Eastern Venezuelan Basin, thus reducing the risk for oil exploration.     

Stability and change in Tethyan planktic foraminifera across the Paleocene–Eocene transition

Examination of planktic foraminifera in the Tethys basin during the Paleocene–Eocene transition reveals two stasis intervals that are separated by a major saltation event coincident with the P–E short-term perturbation in global climate and oceanography. Changes occurred at many spatial and temporal scales as well as many taxonomic and ecologic hierarchical levels, though with various rates and magnitudes. The stasis intervals are marked by slow changes at the species level and account for 50% of the observed first and last appearances during a 2.5 Myr interval. The saltation event is marked by rapid changes at the species and morpho-guild levels and accounts for the remaining 50% of first and last appearances during an interval of about 100–200 kyr. Despite these changes, many taxonomic and ecologic units, such as the depth assemblages and genera, and faunal parameters, such as species richness and turnover rates, are stable with respect to the P–E perturbation. This coexistence of change and stability marks the crisis of Tethyan planktic foraminifera across the P–E transition and reveals the possible dynamics of ecological evolution.     

Benthic origin and earliest evolution of the first planktonic foraminifera after the Cretaceous/Palaeogene boundary mass extinction

There are several hypotheses on the origin and evolution of the earliest Danian planktonic foraminifera. Most experts suggest that they descended from a few opportunist planktonic foraminifera species, mainly of the genera Guembelitria and Hedbergella, which are usually considered to be survivors of the Cretaceous/Paleogene (K/Pg) boundary mass extinction. Nevertheless, early Danian specimens of Guembelitria and Hedbergella remained morphologically well separated from the associated parvularugoglobigerinids (i.e. Parvularugoglobigerina and Palaeoglobigerina), the first trochospiral planktonic foraminifera appearing after the K/Pg boundary event. The most likely alternative is a benthic origin for the parvularugoglobigerinids, which would be consistent with molecular phylogenetic studies that have suggested several episodes of benthic-planktonic transitions in the evolutionary history of planktonic foraminifera. A review of material from the El Kef section and other Tunisian sections supports the previous hypothesis that the buliminid genus Caucasina is the ancestor of the first parvularugoglobigerinids (i.e. Parvularugoglobigerina longiapertura and Palaeoglobigerina alticonusa), on the basis of similarities in test and apertural morphologies and wall texture. The intermediate morphotypes between caucasinids and parvularugoglobigerinids, which appeared approximately 3–5 kyr after the K/Pg boundary, are assigned to Pseudocaucasina antecessor gen. nov. sp. nov.     

Molecular evidence for an independent origin of modern triserial planktonic foraminifera from benthic ancestors

Gallitellia vivans is the only Recent representative of the triserial planktonic foraminiferal family Guembelitriidae. The origin and evolution of this interesting albeit poorly known family are enigmatic. To elucidate the phylogenetic relationships between G. vivans and other planktonic foraminifera, we sequenced the small subunit ribosomal DNA (SSU rDNA) for comparison to our extensive database of planktonic and benthic species. Our analyses suggest that G. vivans represents a separate lineage of planktonic foraminifera, which branches close to the benthic rotaliids Stainforthia and Virgulinella. Both genera resemble Gallitellia in general morphological appearance, having elongate triserial tests at least in their early ontogenic stages. The divergence time of G. vivans is estimated at ca. 18 Ma (early Miocene), suggesting an origin independent from the Cretaceous and Paleogene triserial planktonic foraminifera. Our study thus indicates that modern triserial planktonic foraminifera are not related to the Cretaceous–Paleogene triserial species, and that the sporadic occurrences in the fossil record are not the result of poor preservation, but reflect multiple transitions from benthic to planktonic mode of life.