Development of modern benthic ecosystems in eutrophic coastal oceans: The foraminiferal record over the last 200 years,Osaka Bay,Japan

The ecosystem dynamics of a modern benthic community in Osaka Bay was studied by analyzing sediment cores and fossil foraminifera deposited during the past 200 years. The results suggest that the high-density/low-diversity assemblage has appeared in the early 1900s, coinciding with the eutrophication of the bay resulting from the Japanese industrial revolution. This assemblage proliferated during the period 1960 to 1970 when the eutrophication and bottom-water hypoxia were most pronounced. The development of the assemblage has been characterized by an increase in the relative and absolute abundance of eutrophication-tolerant species (Ammonia beccarii, Eggerella advena, and Trochammina hadai) and a decrease in many other foraminiferal species, such as Ammonia tepida, Elphidium, Miliolinella subrotunda, and Valvulineria hamanakoensis, that are unable to tolerate low-oxygen conditions. Approximately thirty years after the imposition of discharge restrictions in the 1970s, this assemblage continues to predominate in the inner part of the bay, and E. advena is currently found across the entire bay. These records make a significant contribution to understanding the long-term relationship between anthropogenic impact and ecosystem change.     

Distribution of Antarctic benthic foraminifers settling on the pecten Adamussium colbecki

Summary Some benthic foraminifers in Explorers Cove, Antarctica, occur both in the sediment and on hard objects such as rocks and invertebrates. The abundances of four of these foraminiferal species have been measured from sediment samples and from the upper valve of the pecten Adamussium colbecki. The two calcareous species, Cibicides refulgens and Rosalina globularis were more abundant on the pecten shells than the sediment: the agglutinated species, Trochammina ochracea and T. malovensis were more abundant in the sediment. A zone of low foraminiferal density was observed around the outer margin of each shell, but no evidence of an influence of pecten feeding currents on the foraminiferal distributions was found. The size of the pecten shell influenced the density of epizoic foraminifers colonizing it; large shells (area >43 cm²) supported much higher densities than smaller ones.     

Postmortem transport and resedimentation of foraminiferal tests: relations to cyclical changes of foraminiferal assemblages

Cyclical changes in microfossil (mainly foraminiferal) assemblages were analysed for sixteen boreholes from three stratigraphical levels in the Lower and Middle Miocene of the Central Paratethys. The following characteristics of assemblages were quantified and used for interpretation of cyclical changes in assemblages: (1) abundance of foraminifers, calcareous nannoplankton, sponge spicules and diatoms; (2) similarity, diversity and epifauna/infauna ratio of benthonic foraminiferal assemblages; (3) planktic/benthic ratio of foraminiferal assemblages. The palaeoecology (mainly palaeobathymetry) fluctuations were interpreted from the species composition of assemblages. Values of the mentioned quantitative characteristics as well as palaeoecological interpretations may be influenced by postmortem transport and resedimentation of foraminiferal tests. Therefore, prior to the interpretation of cyclical changes of quantitative characteristics, the studied sections were classified on the basis of the intensity of taphonomical changes in foraminiferal assemblages. Three different categories of sections were obtained. For every category, those quantitative characteristics of foraminiferal assemblages were chosen which reflect cyclical changes most efficiently: (1) cyclical changes of abundance of foraminifers, calcareous nannoplankton and sponge spicules, as well as the fluctuations in palaeobathymetry for sections dominated by indigenous foraminifers; (2) percentage of indigenous, suspension-transported, bedload-transported and reworked foraminiferal tests and changes in the abundance of indigenous tests for sections dominated by transported tests; (3) different modes of test preservation used for the identification of a cycle boundary for sections with only transported or reworked tests. The distinguished cycles were interpreted predominantly as manifestations of relative sea-level changes. If comparable data exist from other Paratethys regions, the determined cycles can be correlated with the other basins.     

Effect of seasonal hypoxia on the benthic foraminiferal community of the Louisiana inner continental shelf: The 20th century record

A species census in sediment core samples reveals significant changes in the composition of the Louisiana-shelf benthic foraminiferal community in the past century; these changes can be explained by an increase in the severity of seasonal hypoxia in bottom waters. Agglutinated and porcelaneous orders living in water depths less than 60 m suffered a noticeable decline during this time. In particular, the genus Quinqueloculina was severely affected by the progression of hypoxia, and nearly disappeared from parts of the study area. In contrast, several hyaline taxa, especially Nonionella basiloba, Buliminella morgani, and Epistominella vitrea, tolerated the progressive oxygen depletion well. Results of cluster and principal components analyses of the foraminiferal assemblage data match the observed species distribution trends and indicate that seasonal hypoxia on the Louisiana shelf, related to eutrophication and water stratification, worsened in the past century, even near the outer edge of the present-day zone of spring and summer oxygen depletion. The temporal trends in the foraminiferal record correspond to that of fertilizer use in the U.S. and nitrogen loading in the Mississippi River, suggesting that the anthropogenic factor has been particularly strong in the development of coastal hypoxia since the early 1940s.     

Modern planktic foraminifera

Planktic foraminifers are marine protozoans with calcareous Shells and chambered tests. They first appeared in the mid-Jurassic and spread since the mid-Cretaceous over all the world’s oceans. Modern planktic foraminifers evolved since the early Tertiary, when the first spinose species occurred. Most species live in the surface to sub-thermocline layer of the open ocean, and in marginal seas like the Mediterranean, Caribbean, South China Sea, and Red Sea. Planktic foraminifers are absent in shallow marginal seas, for example, the North Sea. Planktic foraminifers respond to food, temperature and chemistry of the ambient seawater. Species abundance varies according to seasons, water masses, and water depths. Symbiont-bearing species depend on light and are restricted to the euphotic zone. Planktic foraminifers constitute a minor portion of total Zooplankton, but are major producers of marine calcareous particles (shells) deposited on the ocean floor where they form the so-called foraminiferal ooze. Planktic foraminifers contribute substantially to the fossil record of marine Sediments and are of high ecologic, paleoceanographic, and stratigraphic significance since the mid-Cretaceous. Radiocarbon (¹⁴C) gives an absolute age of shell formation within late Pleistocene and Holocene Sediments. Factors that determine the modern faunal composition are applied to Interpretation of the fossil assemblages, for example, by multiple regression techniques (transfer functions) to yield an estimate on ancient environmental parameters. The chemical composition of the calcareous shell (stable isotopes and trace elements) holds clues to the chemical and physical State of the ambient seawater and is useful in the reconstruction of temperature, chemical State, and biological productivity of the ancient marine environment.      

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     

Ammonia beccarii and Ammonia tepida (Foraminifera): morphofunctional arguments for their distinction

New observations from Yeu Island and the Bay of Bourgneuf on the Atlantic coast of France show that Ammonia beccarii s.s. and Ammonia tepida have different morphofunctional adaptations to their habitats and environments. Adult A. beccarii s.s. may be epiphytic, living on the calcareous alga Corallina officinalis or on the red alga Gigartina acicularis along rocky shores, while A. tepida is endopelic, living in sediments of brackish environments. Rapid 3-D emission of pseudopodia from interlocular spaces on both umbilical and spiral sides of adult A. beccarii s.s. can support its test within the seaweed framework. This behaviour is characteristic of phytal species. Thus, it appears that the major difference between A. beccarii s.s. and A. tepida is the presence of large interlocular spaces on spiral side of the former, corresponding to a potential morphofunctional adaptation to the epiphytic mode of life. We believe that these observations could help to solve the long-lasting A. beccarii problems of specific distinction.     

Foraminiferal distribution on the continental margin off Nova Scotia

Q-mode factor analysis of total foraminiferal abundance data (living plus dead) from 250 grab samples taken from the continental margin off Nova Scotia allows the determination of eight factor assemblages. On the northeastern shelf, an exclusively agglutinated assemblage dominated byAdercotryma glomerata occupies both banks and basins. Central shelf basins contain a predominantly calcareous assemblage dominated byGlobobulimina auriculata andNonionellina labradorica. Transitional between these two factor assemblages is an agglutinated assemblage dominated bySaccammina atlantica. Consistently present along the shelf edge is aTrifarina angulosa assemblage. In northeastern bays and a few samples near Sable Island, an agglutinatedEggerella advena assemblage is found. A relict and transport affected assemblage dominated byElphidium excavatum occurs in the southwestern approaches to Emerald Basin. Sandy/gravelly areas of the inner shelf and outer bank regions are characterized by aCibicides lobatulus assemblage.The statistical relationships of these defined assemblages to various aspects of the marine environment (depth, temperature, salinity, percent gravel, sand and mud) were investigated through multiple regression techniques. Results indicate that the present foraminiferal distribution patterns off Nova Scotia are influenced by the prevailing watermass characters and substrate. TheAdercotryma glomerata assemblage is influenced by the presence of cold, (0–4°C) low salinity waters (32–33‰) of arctic, Labrador Current origin. The central basin assemblage (G. auriculata) is related to warmer (8–12°C) more saline waters (35‰) of slope origin. The transition between these two bottom waters is marked by the opportunisticSaccammina atlantica assemblage. Preferred substrate character possibly determines the occurrence of theCibicides lobatulus, Islandiella islandica andEggerella advena assemblages.Trifarina angulosa shows a significant relationship to salinity and depth.Although the surficial sediments on the Nova Scotian Shelf are largely the product of reworking of glacial deposits during late glacial and early Holocene times, all but theE. excavatum factor assemblage appear to be in equilibrium with the modern oceanographic regime.     

Foraminifera may structure meiobenthic communities

The cosmopolitan benthic foraminiferan, Ammonia beccarii, is a fervent microfloral predator which often forms densely-populated 2–4 cm² aggregates in the field. Sediments within aggregate patches become extensively pelletized, mucus bound and depleted in microfloral food. On a West German Wattenmeer mudflat, copepodite and naupliar densities of a predominant harpacticoid copepod, Amphiascoides limicola, were significantly depressed in sediments containing>100 A. beccarii·3 cm^-2 suggesting a possible foraminiferal: copepod amensalism. Therefore, I cultured A. beccarii and A. limicola separately in sediment microcosms and then tested if A. limicola's seemingly negative reaction to sediments containing A. beccarii occurs under controlled conditions, how various life stages of A. limicola are affected, and what the repulsive mechanisms of A. beccarii may be. In natural field sediments seeded with a latin-square dispersion of sterile sediment patches containing 0 or 100 A. beccarii, mean A. limicola naupliar and copepodite densities were 2 to 6 times lower in Ammonia-rich patches than Ammonia-poor patches (i.e. patches containing <100 A. beccarii·3 cm^-2). Choice experiments directly testing potential A. beccarii inhibitory mechanisms were conducted with A. limicola copepodites: Cubic microcosms containing a latin-square patch dispersion of (1) sterile sediments (SS) seeded with 100 A. beccarii (low microflora), (2) SS bound with sterile mucus (0.0001%) (low microflora), (3) SS seeded with pelletized sediments (high microflora), and (4) SS seeded with mucus and pellets (high microflora), showed that copepodites colonized 12 & 3, but 1 & 4 were not significantly different. Mucus addition by itself, in the absence of pelletization and microflora, strongly facilitated colonization—as did addition of microfloral-rich pelletized sediments. Pelletization and mucousbinding combined, but with low microflora, were least attractive to A. limicola. Pelletization and mucous-binding combined, but with high microflora, were more attractive to A. limicola than its complement, but not significantly so. Thus A. beccarii's inhibition of A. limicola is probably not caused by sediment pelletization and simple mucous exudates but by local microfloral depletion within aggregate foraminiferal patches.Contribution No 774 of the Belle W. Baruch Institute for Marine Biology and Coastal Research     

The last 1000 years of natural and anthropogenic low-oxygen bottom-water on the Louisiana shelf, Gulf of Mexico

The relative abundance of three species of low-oxygen tolerant benthic foraminifers, the PEB index, in foraminiferal assemblages from sediment cores is used to trace the history of low-oxygen bottom-water conditions on the Louisiana shelf. Analyses of a network of box cores indicate that the modern zone of chronic seasonal hypoxia off the Mississippi Delta began to develop around 1920 and was well established by 1960. The pattern of development over the last century is consistent with the interpretation that the formation of modern chronic hypoxia is related to anthropogenic activities resulting in increased transport of nutrients to the Louisiana shelf.The PEB index in two gravity- and box core pairs (MRD05-4 and 05-6) indicates that low-oxygen bottom-water events have occurred periodically on the Louisiana Shelf for at least the last 1000 ¹⁴C years. The pre-1900 low-oxygen bottom-water events are likely caused by intervals of increased Mississippi River discharge and widespread wetland export. The PEB record in gravity cores indicates that the pre-1900 low-oxygen bottom-water events were not as well developed or as geographically extensive as the modern hypoxia zone. We conclude that the development of low-oxygen bottom-water on the Louisiana shelf is a natural process that has been negatively modified by human activities in the last 100 years.     

Invasion by a Japanese marine microorganism in western North America

The earliest record in western North America of Trochammina hadai Uchio, a benthic foraminifer common in Japanese estuaries, is from sediment collected in Puget Sound in 1971. It was first found in San Francisco Bay in sediment samples taken in 1983, and since 1986 has been collected at 91% of the sampled sites in the Bay, constituting up to 93% of the foraminiferal assemblage at individual sites. The species is also present in recent sediment samples from 12 other sites along the west coast of North America. The evidence indicates that T. hadai is a recent introduction to San Francisco Bay, and is probably also not native to the other North American sites. Trochammina hadai was probably transported from Japan in ships' ballast tanks, in mud associated with anchors, or in sediments associated with oysters imported for mariculture. Its remarkable invasion of San Francisco Bay suggests the potential for massive, rapid invasions by other marine microorganisms.     

Paleoecology of the cenozoic reefal foraminifers and algae — A brief review

The paleoecology of reefal foraminifers and algae assumes a considerable importance in determining and delineating sub-environments of ancient reefs, especially those of non-coral origin.A review of the ecologic distribution of the Cenozoic larger foraminifers in different biofacies of the reef-complex environment has revealed the following: (1) a prolific growth of “Alveolina” was possible in the back-reef region near the reef core; (2) Orbitolites and Marginopora preferred sheltered waters on the reef-flat and in the back-reef zones; (3) nummulitids and Discocyclina thrived in both fore- and back-reef shoal areas, but the species living in the former are much stouter than those living in the latter; (4) Heterostegina is and, in the geologic past, was a form, preferring quieter waters of the back-reef lagoons and reef-flat pools; (5) Pellatispira was a typical fore-reef form.Smaller foraminifers, as a whole, are dominant in back-reef lagoons. An abundance of miliolids indicates a sheltered environment prevailing in the reef-flat pools and back-reef zones, whereas reef flats, in general, are characterized by a paucity of smaller foraminifers. An increase in the number of nodosariids and globigerinids points to a fore-reef environment, the depth of which is indicated by the relative abundance of the latter group. Encrusting foraminifers are characteristic of the reef core and are important constituents of for-algal (foraminiferal + algal) reef complexes.Of the algae, the calcarous chlorophyte Halimeda is relatively more abundant in the sheltered parts of a reef-complex, especially the lagoons, where water is moderately agitated and clear; its sudden abundance in the geologic record indicates the advent of a reefal environment. An abundance of the calcareous chlorophyte Dasycladaceae indicates the shallow back-reef areas adjacent to the reef core. Articulated coralline algae are associated with reef-complexes but are varied in their adaptability and, hence, are widely distributed in different parts of the complex. Abundant crustose coralline algae almost certainly indicate a reef-core sub-environment; their skeletons are among the chief constructional units of the core. They increase in abundance towards the outer edge of the reef core and decrease away from it.     

The benthic foraminiferal communities of the northern Adriatic continental shelf

Off the Po Delta in the northern Adriatic, three different foraminiferal associations were identified in the fraction >0.125 mm of 25 sediment samples. The first association concerns sample stations between depths of 5 and 13.5 m in the shallow, nutrient-rich belt and is characterised by dominant Ammonia beccarii. The second occupies the 29.5–38.5-m-deep, nutrient-rich zone of clay-rich sediment, where inputs from the Po are concentrated, and is dominated by Nonionella opima. The third association, in the 21–46-m-deep and nutrient-poor zone, is dominated by Textularia agglutinans. The same distribution of communities was obtained using total associations (living and dead specimens) and biocenosis (stained individuals). The good correspondence with the foraminiferal distributions described in the past indicates that, in spite of the occurrence of anoxic and dysoxic events, the environmental state in the northern Adriatic may be considered stable.     

Late Holocene pollution in the Gernika estuary (southern Bay of Biscay) evidenced by the study of Foraminifera and Ostracoda

The Arketas pier in the Gernika estuary (southern Bay of Biscay) has during summer periods waters with strong hypoxia (1 ml l^–1) but curiously bears the richest assemblages of foraminifers and ostracods in the whole estuary. The most abundant species in Arketas are: Ammonia beccarii, Cribroephidium williamsoni, Haynesina germanica and Lobatula lobatula (foraminifers) Loxoconcha elliptica and Leptocythere castanea (ostracods). The benthic foraminifer sub-species A. beccarii tepida exhibits in this estuary three different morphotypes, whose distributions are controlled by changes in the salinity, dissolved oxygen and nutrient content of the waters, and thus could be used as a good indicator of environmental alteration caused by those parameters. To determine whether this environmental alteration is due to natural causes or is anthropogenic, micropalaeontologic and sedimentologic contents of a sediment core 140 cm thick have been analysed. The study of Foraminifera and Ostracoda assemblages, species diversity, and A. beccarii tepida morphotypes allows us to reconstruct the evolution of this part of the estuary over the last 3800 years. To examine anthropogenic effects at this site, we compared the occurrence of heavy metals Pb, As, with the record of A. beccarii tepida morph C in Arketas. The maximum concentration of heavy metals coincides with the maximum occurrence of A. b. tepida morph C, in the 1970s (date calculated according to the estimated rate of sedimentation in this area). This indicates that distribution of A. b. tepida morph C is, at least partially, caused by heavy metal pollution. Nevertheless, the fact that we have found no deformed tests of this taxa in Arketas induces us to think that another factor, such as dysaerobia caused by eutrophization of nutrient inputs in several areas of this estuary, might have been responsible for at least of part of the anomalous shift of A. b. tepida morph C at that time. In recent times, an increase in this anthropogenic activity was evident, reaching its maximum in the 1970s and decreasing from the 1980s. During the late Holocene period (up to 3500 years BP), this site was a middle-outer estuarine settlement, euryhaline with low to moderate salinity. This episode ends with a marine transgressive pulsation. After depositional hiatus of unknown duration, recent sediments suggest a modern palaeogeographic position of Arketas located in a lower estuary environment. The study of A. beccarii through the Holocene sediments of Arketas indicates that dysaerobic/pollution conditions were not a singular event. At the same time, the increase of A. b. tepida morph C were particularly strong over several years of the 20th Century, at precisely the time that a noticeable decrease of richness and diversity of calcareous microfauna is detected in the estuary.     

Distribution and abundance of the planktic foraminifer Neogloboquadrina pachyderma in sea ice of the Weddell Sea (Antarctica)

Summary Sea ice cores were obtained from eleven fast ice stations and one floe in the Weddell Sea, Antarctica in January–February 1985. All cores from the north eastern part of the Weddell Sea contained numerous living and dead planktic foraminifers of the species Neogloboquadrina pachyderma (Ehrenberg), while cores drilled in southern parts were barren of foraminifers with one exception. Foraminiferal abundances were variable, with numbers up to 320 individuals per liter melted sea ice. Distribution of foraminifers appears to be patchy, parallel cores taken less than 30 cm apart contained numbers which varied considerably. On the other hand, three cores taken on a transect each more than 3 km apart showed striking similarities. In general, small dead tests were found in the upper parts of the sea ice cores while large living individuals mainly occurred in lower sections. Abundant diatoms probably serve as a food source for the foraminifers. Correlation of foraminiferal abundance with salinity, chlorophyll and nutrient profiles are inconsistent. The possible mechanism of incorporation of N. pachyderma into the ice is discussed.     

Grazing of intertidal benthic foraminifera on bacteria: Assessment using pulse-chase radiotracing

Although foraminifera are a dominant component of many marine benthic communities, quantification of their predation on prokaryotes remains an experimental challenge. We have developed an approach that allows us to study grazing by adult specimens of the calcareous species Haynesina germanica and Ammonia beccarii, and the single-chambered agglutinated species Psammophaga sp., on bacteria (Halomonas sp.), pulse-chase-labelled with ³H- and ¹⁴C-Leucine. The bacterivorous ciliate Uronema sp. and flagellate Pteridomonas sp. were used as positive controls. The rate of release of ³H when protozoa were incubated with the labelled bacteria indicated the predator's grazing rate; the proportion of ¹⁴C found in the foraminiferal biomass and shell indicated the prey assimilation rate. All three foraminiferal species grazed bacteria at a rate of 3.2-5.7 ng C ind⁻¹ h⁻¹ depending on bacterial concentrations. About 23% of the biomass of the ¹⁴C-labelled prey was most likely assimilated into foraminiferal pseudopodia, 12% was expelled in dissolved waste material, about 62% was respired and only 0.1% was incorporated into the carbonate shell. Extracellular digestion associated with pseudopodia could explain the very low proportion of the labelled food assimilated in the cell body and the significant proportion located in pseudopodial networks. These experiments also suggest that very little of the carbon ingested by adult calcareous foraminifera is incorporated into the shell. However, we cannot conclude that diet has no influence on the stable isotope composition of the shell since none of our calcareous specimens grew new chambers during the experiments.     

Paleoceanographic implications of smaller benthic and planktonic foraminifera from the Eocene Pazin Basin (Coastal Dinarides,Croatia)

Summary Smaller benthic and planktonic foraminifera from the clastic sediments of the Pazin Basin (Istria, Croatia) were studied in order to obtain more data about paleoceanographic conditions that existed in the Middle Eocene Dinaric foreland basin. The succession investigated corresponds to the Middle Eocene planktonic foraminiferal zones Globigerapsis kugleri/Morozovella aragonensis (P11), Morozovella lehneri (P12), and Globigerapsis beckmanni (P13). Benthic foraminiferal assemblages from the clastic succession are dominated by epifaunal trochospiral genera suggesting oligotrophic to mesotrophic conditions and moderately oxygenated bottom waters. Planktonic foraminiferal assemblages indicate mesotrophic to eutrophic conditions of the surface waters, with increased eutrophication in the upper part of the section. Water depth, based on the ratio between planktonic and epifaunal benthic foraminifera and on the recognized species of cosmopolitan benthic foraminifera, was estimated to have been between about 900 and 1200 m. The basin was elongated and open to marine currents on both sides allowing good circulation and ventilation of the bottom water.     

Evolution of a Maastrichtian–Paleocene tropical shallow-water carbonate platform (Qalhat,NE Oman)

The biostratigraphy (larger foraminifers, dasycladaleans), microfacies, sedimentology, and geochemistry (δ ¹³C, strontium-isotope stratigraphy) of a continuous, 148-m-thick section of shallow-water platform carbonates that contain the Cretaceous/Paleogene (K/P) boundary were analyzed. The boundary is constrained within a 7-m-thick interval, between the last occurrence of Maastrichtian larger benthic foraminifers and the first occurrence of Danian benthic foraminifers. Although this interval is intensively dolomitized, there is no sedimentological evidence of a major hiatus at the K/P boundary. The correlation of bulk rock δ ¹³C values with stable isotope data from DSDP Site 384 (NW Atlantic Ocean) supports this interpretation and indicates a Selandian age for the top of the section. The Qalhat section is a unique example of a carbonate platform that has recorded persisting open marine environmental conditions across the K/P boundary (Maastrichtian–Selandian), as indicated by the abundance of rudists, larger benthic foraminifers (Maastrichtian), calcareous algae and scleractinian corals.     

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.     

Cluster analysis of recent benthic foraminifera from the northwestern Mediterranean coast of Egypt

A suite of 74 surface sediment samples, collected from two areas along the Egyptian Mediterranean coast (the Western Harbor of Alexandria and its environs, and the area comprising the Gulf of Kanayis and the Abu Hashafa Bay), have been examined for their benthic foraminiferal faunas. A total of 82 species were identified. Census data were obtained for different species in each sample and the statistically significant fractional abundances values (≥5%) were analyzed using a Q-mode cluster analysis. Samples were segregated into four clusters, each having its peculiar benthic faunal assemblage (biotope), reflecting particular environmental conditions. These clusters are: (1) the Ammonia beccarii forma tepida Biotope, found in samples located in areas with waters of low energy, characterizing semi-closed basin conditions, with muddy or sandy mud bottom sediments (Harbor Proper); (2) the Quinqueloculina spp. Biotope, found in samples collected from depths bathed by turbid inner shelf conditions with some fresh water inflow and sandy bottom sediments (Harbor’s environs); (3) the Peneroplis-Amphistegina Biotope, found in samples collected from depths characterizing marine shelf environments with calcareous algae, and medium to very coarse calcareous sands (the Gulf of Kanayis and the Abu Hashafa Bay); (4) the Triloculina trigonula-Adelosina laevigata Biotope was represented by only one sample (at the far eastern part of the Gulf of Kanayis), collected from a site exhibiting very restricted environmental conditions. The study suggests that nutrients, turbidity, light intensity, type of substrate, and salinity are the main ecological factors controllingthe distribution of benthic foraminifera.