Showing papers on "Foraminifera published in 1990"

Distribution of rose bengal stained deep-sea benthic foraminifera from the Nova Scotian continental margin and Gulf of Maine

Abstract: Analysis of Rose Bengal stained benthic foraminifera in six boxcores taken from the Nova Scotian margin and Gulf of Maine reveals that foraminifera are vertically stratified within surficial sediments raised from 200 to 3000 m water depth. The consistent presence of infaunal taxa within the sediments demonstrates that these tolerant of a range of low-oxygen conditions as determined by pore-water manganese profiles. The habitat depth of foraminiferal populations, defined as the depth within which 95% of the fauna is found in a subcore, varies between the stations. A shallow habitat depth of 3 cm exists in shallow water (a 202 m core) in the Gulf of Maine. The habitat depth gradually increases on the continental slope with increasing water depth, reaching 11–13 cm in cores at 2225 and 3000 m, and then shoals to 4 cm in a core taken from 4800 m water depth. We suggest that the habitat pattern is related to the flux of organic carbon to the seafloor. At shallow depths, relatively high organic carbon flux results in a shallow oxic layer. The inferred oxic layer gradually increases on the continental slope and rise with increasing water depth, due to decreased organic carbon flux to the sediment-water interface. Carbon fluxes in the deep ocean are so low that pore waters are oxic and the organic carbon content is low, creating a food-limiting environment best suited to epifaunal taxa and reflected in a shallow habitat depth.

The influence of microhabitats on the carbon isotopic composition of deep-sea benthic foraminifera

Abstract: We report δ13C and δ18O values for Rose Bengal-stained benthic foraminifera from a set of box cores from continental margin environments in the Atlantic and Pacific oceans. These isotopic results are compared with foraminiferal distribution data and pore water δ13C profiles to evaluate the importance of environmental (microhabitat) effects on the carbon isotopic composition of benthic foraminifera. The δ13C values of infaunal taxa are consistently lower than those of epifaunal taxa, suggesting that microhabitat effects on test composition do exist. The δ13C differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the δ18O differences between benthic foraminifera tests and equilibrium calcite, but they do correlate with variations in the chemistry of sediment pore waters. However, interspecific δ18O differences as well as δ13C differences between species with similar vertical distributions in the sediments indicate that taxon-specific “vital” effects also influence test composition.

Late Cretaceous through Neogene deep-sea benthic foraminifera(Maud Rise, Weddell Sea, Antarctica)

Abstract: Upper abyssal to lower bathyal benthic foraminifers from ODP Sites 689 (present water depth 2080 m) and 690 (present water depth 2941 m) on Maud Rise (eastern Weddell Sea, Antarctica) are reliable indicators of Maestrichtian through Neogene changes in the deep-water characteristics at high southern latitudes. Benthic foraminiferal faunas were divided into eight assemblages, with periods of faunal change at the early/late Maestrichtian boundary (69 Ma), at the early/late Paleocene boundary (62 Ma), in the latest Paleocene (57.5 Ma), in the middle early Eocene to late early Eo­ cene (55-52 Ma), in the middle middle Eocene (46 Ma), in the late Eocene (38.5 Ma), and in the middle-late Miocene (14.9-11.5 Ma). These periods of faunal change may have occurred worldwide at the same time, although specific first and last appearances of deep-sea benthic foraminifers are commonly diachronous. There were minor faunal changes at the Cretaceous/Tertiary boundary (less than 14°7o of the species had last appearances at Site 689, less than 9% at Site 690). The most abrupt benthic foraminiferal faunal event occurred in the latest Paleocene, when the diversity dropped by 50% (more than 35% of species had last appearances) over a period of less than 25,000 years; after the extinction the diversity remained low for about 350,000 years. The highest diversities of the post-Paleocene occurred during the middle Eocene; from that time on the diversity de­ creased steadily at both sites. Data on faunal composition (percentage of infaunal versus epifaunal species) suggest that the waters bathing Maud Rise were well ventilated during the Maestrichtian through early Paleocene as well as during the latest Eocene through Recent. The waters appeared to be less well ventilated during the late Paleocene as well as the late middle through early late Eocene, with the least degree of ventilation during the latest Paleocene through early Eo­ cene. The globally recognized extinction of deep-sea benthic foraminifers in the latest Paleocene may have been caused by a change in formational processes of the deep to intermediate waters of the oceans: from formation of deep waters by sinking at high latitudes to formation of deep to intermediate water of the oceans by evaporation at low latitudes. Benthic foraminiferal data (supported by carbon and oxygen isotopic data) suggest that there was a short period of in­ tense formation of warm, salty deep water at the end of the Paleocene (with a duration of about 0.35 m.y.), and that less intense, even shorter episodes might have occurred during the late Paleocene and early Eocene. The faunal record from the Maud Rise sites agrees with published faunal and isotopic records, suggesting cooling of deep to intermediate waters in the middle through late Eocene.

Reconstructing tropical Atlantic hydrography using planktontic foraminifera and an ocean model

Abstract: In the tropical Atlantic, planktonic foraminfera species are vertically distributed with highest abundances occurring in the photic zone (approximately 0–100 m). The tropical Atlantic thermocline dips from east to west and varies seasonally due to changes in the southeast and northeast trade winds. In the east, the thermocline is in the photic zone, and in the west, the well-mixed surface layer extends below the photic zone most of the year. As expected from species vertical distributions in plankton tows, the species assemblages on the seafloor are correlated to the hydrographic conditions of the overlying surface ocean layer. A new technique to reconstruct past tropical Atlantic (20°N to 20°S) photic zone hydrography and surface wind field uses faunal assemblage data from deep-sea cores. Planktonic foraminifera abundances in core tops correlate with observations of modern photic zone hydrography defined here as seasonal temperature variation and mixed layer depth. The hydrography is mathematically described using empirical orthogonal function (EOF) analysis of annual temperature range as a function of depth. Factor analysis of 29 species of planktonic foraminifera from 118 core tops produces three factors. The factors correlate to mixed layer depth and the two EOF modes. The ocean model of the Atlantic ocean produces similar map patterns of the EOF modes. Therefore the model can be used to simulate hydrographic changes to compare with faunal predicted past hydrographic changes. Since the ocean model is wind driven, this approach provides a way of evaluating the validity of estimates of past wind stress changes and the contribution of these changes to the faunal changes in the past. A double wind stress run indicates that the central and eastern equatorial and southeast regions of the study area are most sensitive to wind stress increases. Factor analysis of the foraminifera abundances from the last glacial maximum (LGM) shows that species associations change downcore and demonstrates how the methods developed in this study can be applied. Comparison of the double wind stress experiment and the LGM faunal changes indicates some areas of significant agreement suggesting that faunal changes may reflect thermocline structure response to the LGM wind field. Discrepancies may reflect the fact that uniform changes in the north and south trade wind strengths did not occur at the LGM.

Evidence for two-step deglaciation and its impact on North Atlantic deep-water circulation

Abstract: Oxygen and carbon isotope records from benthic and planktonic foraminifera are presented for the past 35,000 years in the northeastern Atlantic. The results support the idea that the last deglaci­ation took place in two major steps1–4, and conflict with theories calling for a strong reduction in North Atlantic deep-water formation to explain the abrupt cooling of the Younger Dryas cold period5–7.

Paleoecology, biostratigraphy, paleoceanography and taxonomy of agglutinated foraminifera

Abstract: Agglutinated Foraminifera: An Introduction.- Why are Foraminiferida Foraminifers ?.- Composition and Microstructure of Agglutinated Foraminifer Wall.- Wall Structures of Palaeotextulariid Foraminifers and Discussion of Microgranular Test Walls.- Partitions and Fistulose Chamberlets in Textulariina.- Abyssal Agglutinates: Back to Basics.- On the Way to the Optimal Suprageneric Classification of Agglutinating Foraminifera.- Revision of the Trochamminacea and Remaneicacea of the Plymouth District S.W. England, Described by Heron-Allen and Earland (1930).- Agglutinated Foraminifera from the Palaeogene of the North Sea.- Gerochammina N.G. and Related Genera from the Upper Cretaceous Flysch-Type Benthic Foraminiferal Fauna, Eastern Carpathians - Romania.- Recent Deep-Sea Agglutinated Foraminifera: A Brief Review.- The Ecology, Distribution and Taxonomy of Crithionina Hispida Flint, 1899.- High Latitude Agglutinated Foraminifera: Prydz Bay (Antarctica) vs. Lancaster Sound (Canadian Arctic).- Biostratigraphy and Paleoecology of Deep-Water Agglutinated Foraminifera at ODP Site 643, Norwegian-Greenland Sea.- Danian Deep-Water (Bathyal) Agglutinated Foraminifera from Bavaria and Their Comparison with Approximately Coeval Agglutinated Assemblages from Senegal and Trinidad.- Paleoecology of Late Cretaceous to Paleocene Deep-Water Agglutinated Foraminifera from the North Atlantic and Western Tethys.- Deep Water Agglutinated Foraminiferal Assemblages from Upper Cretaceous Red Shales of the Magura Nappe / Polish Outer Carpathians.- The Oldest Assemblages of Agglutinated Foraminifers of the Polish Flysch Carpathians.- Faunal Trends and Assemblages of the Northern South China Sea Agglutinated Foraminifera.- Agglutinated Foraminifera in Organic-Rich Neritic Carbonates (Upper Cretaceous, Israel) and Their Use in Identifying Oxygen Levels in Oxygen-Poor Environments.- Agglutinated Foraminifera from the Albian and Cenomanian of Jordan.- Facies Controlled Distribution of Foraminifera in the Jurassic North Sea Basin.- Variations in Estuarine Foraminiferal Biofacies with Diminishing Oxygen Conditions in Drammensfjord, SE Norway..- Seasonality in the Benthic Foraminiferal Community and the Life History of Trochammina Hadai Uchio in Hamana Lake, Japan..- Recent Marsh Foraminifera from the East Coast of South America: Comparison to the Northern Hemisphere.- Estuarine and Marsh Foraminifera from the Lower Cretaceous of the Lusitanian Basin, West Portugal.- Recent Marsh-Type Agglutinated Foraminifera from Inland Salt Springs, Manitoba, Canada.- Biogeographic Distribution of Modern Thecamoebians in a Transect Along the Eastern North American Coast.- Thecamoebians from the Early Cretaceous Deposits of Ruby Creek, Alberta (Canada).- Fossil Thecamoebians: Present Status and Prospects for the Future.- Stratigraphically Important Agglutinated Foraminifera in the Badenian (Miocene M4) of Poland.- Foraminiferal Biostratigraphy and Seismic Sequences - Examples from the Cenozoic of the Beaufort-Mackenzie Basin, Arctic Canada.- Deep-Water Agglutinated Foraminifera from the Massignano Section (Ancona, Italy), a Proposed Stratotype for the Eocene-Oligocene Boundary.- Agglutinated Foraminifera, Biostratigraphy and Intraregional Correlation of Upper Cretaceous Deposits of Eastern Urals.- Cretaceous Agglutinated Foraminifera of the UK: A Review.- Agglutinated Foraminiferida from the Albian / Cenomanian Boundary in SE England.- The Application of Middle Jurassic-Early Cretaceous Agglutinated Foraminifera to the Offshore Correlation of Humber Group Sediments in the North Viking Graben.- Agglutinated Foraminiferal Stratigraphy of Middle Jurassic to Basal Cretaceous Shales, Central Spitsbergen..

Foraminiferal reconstruction of barium distributions in water masses of the glacial oceans

Abstract: Foraminiferal Ba can be used to reconstruct the distribution of deeply regenerated chemical components in past oceans. The Ba contents of benthic foraminifera recovered from cores in the Atlantic Ocean indicate that waters deeper than 2900 m had ∼30–60% higher Ba during the last glacial maximum (LGM). These changes are consistent with previously observed glacial nutrient enrichments based on foraminiferal Cd and δ13C. Increases in deepwater nutrient contents in the Atlantic can be explained by reductions in North Atlantic Deep Water formation during the LGM. Ba/Ca of benthic foraminifera from the glacial sections of intermediate depth Atlantic cores are equal to or lower than Holocene values. This Ba evidence argues against the Mediterranean as a greatly increased source to Atlantic intermediate waters during the LGM, since the Mediterranean is enriched in Ba today and apparently remained enriched during the LGM. Benthic foraminiferal Ba from the glacial sections of cores from the eastern equatorial Pacific suggest that deep waters of the Glacial Pacific were about 25% lower in Ba (at ∼3000 m). Taken together, the foraminiferal evidence indicates that the Ba content of deep waters of the Atlantic, Antarctic, and Pacific were similar at the LGM. Since foraminiferal Cd distributions indicate that Cd remained significantly lower in the deep Atlantic relative to the Pacific at the last glacial maximum, a seven-box ocean model is used to explore several scenarios for reconciling LGM Ba and Cd distributions. While the changed distribution of both tracers suggests diminishment in the flux of nutrient depleted waters to the deep Atlantic during the LGM, increased Atlantic upwelling rates and consequently enhanced Ba particle fluxes can account for the the lack of Ba fractionation between the deep Atlantic and Pacific. The model suggests that Ba can be transferred efficiently to the deep Atlantic by enhanced upwelling because the vast majority of the Ba is regenerated in the deep Atlantic box.

The distribution of radiocarbon in the glacial ocean

Abstract: Accelerator mass spectrometric radiocarbon measurements on benthic foraminifera shells, picked from samples on which concordant ages were obtained on the shells of two species of planktonic foraminifera, reveal that the age of deep water in the equatorial Atlantic during glacial time was 675±80 years (compared to today's age of 350 years) and that the age of deep water in the South China Sea was 1670±105 years (compared to today's value of 1600 years). These results demonstrate that the 1.3 to 1.5 times higher radiocarbon content of carbon in glacial surface waters of the Caribbean Sea reconstructed by Bard et al. [1990] was primarily the result of a higher global inventory of radiocarbon rather than a decrease in rate of mixing between surface and deep waters of the ocean. The results are also consistent with the conclusion by Boyle and Keigwin [1987] that the flow of North Atlantic Deep Water was considerably weakened during glacial time, allowing deep waters of Antarctic origin to push much further north into the Atlantic than they do today.

Atlantic Ocean thermohaline circulation of the last 150,000 years: Relationship to climate and atmospheric CO2

Abstract: The high-resolution δ18O and δ13C records of benthic foraminifera from a 150,000-year long core from the Caribbean Sea indicate that there was generally high δ13C during glaciations and low δ13C during interglaciations. Due to its 1800-m sill depth, the properties of deep water in the Caribbean Sea are similar to those of middepth tropical Atlantic water. During interglaciations, the water filling the deep Caribbean Sea is an admixture of low δ13C Upper Circumpolar Water (UCPW) and high δ13C Upper North Atlantic Deep Water (UNADW). By contrast, only high δ13C UNADW enters during glaciations. Deep ocean circulation changes can influence atmospheric CO2 levels (Broecker and Takahashi, 1985; Boyle, 1988a; Keir, 1988; Broecker and Peng, 1989). By comparing δ13C records of benthic foraminifera from cores lying in Southern Ocean Water, the Caribbean Sea, and at several other Atlantic Ocean sites, the thermohaline state of the Atlantic Ocean (how close it was to a full glacial or full interglacial configuration) is characterized. A continuum of circulation patterns between the glacial and interglacial extremes appears to have existed in the past. Subtracting the deep Pacific (∼mean ocean water) δ13C record from the Caribbean δ13C record yields a record which describes large changes in the Atlantic Ocean thermohaline circulation. The δ13C difference varies as the vertical nutrient distribution changes. This new proxy record bears a striking resemblance to the 150,000-year-long atmospheric CO2 record (Barnola et al., 1987). This favorable comparison between the new proxy record and the atmospheric CO2 record is consistent with Boyle's (1988a) model that vertical nutrient redistribution has driven large atmospheric CO2 changes in the past. Changes in the relative contribution of NADW and Pacific outflow water to the Southern Ocean are also consistent with Broecker and Peng's (1989) recent model for atmospheric CO2 changes.

Variations in Estuarine Foraminiferal Biofacies with Diminishing Oxygen Conditions in Drammensfjord, Se Norway

Abstract: Distribution of recent, benthic foraminifera in the silled, partly anoxic Drammensfjord, reflects the prevailing hydrographic conditions, and reveals different intra basin responses to depleted oxygen conditions. The redox cline dips from about 35 m in the northern to about 60 m in the southern part of the fjord. Sediment surface samples are strongly dominated by agglutinated taxa except in the most oxygen depleted areas (O2 <2 ml/1) in middle and southern parts. The water masses are subdivided into three units: 1) Brackish surface layer dominated by Miliammina fusca; 2) Transitional water masses with Astrammina sphaerica, Eggerelloides scabrus, Spiroplectammina biformis, and Ammodiscus? gullmarensis as frequently occurring species; and 3) Oxygen depleted water masses (salinity max. 31.2 ‰) dominated by Stainforthia fusiformis. The thin-shelled S. fusiformis shows adaption to low oxygen (<2 ml/1) conditions and muddy, organic rich substrate as long as salinity exceeds about 30 ‰. Species diversity decreases towards the redox cline, and no foraminifera are found in oxygen depleted areas with salinities less than about 30 ‰.

Stable isotope evidence for gradual environmental changes and species survivorship across the Cretaceous/Tertiary Boundary

Abstract: High-resolution δ13C and δ18O records have been generated from analyses of the planktonic foraminiferal species Heterohelix globulosa and the benthonic foraminiferal taxon Lenticulina spp from 3 m of a cored section spanning the Cretaceous/Tertiary (K/T) boundary at Brazos River, Texas. These are the first stable isotope records across the K/T boundary based on monospecific and monogeneric foraminiferal samples. They show a gradual decrease in δ13C values of about 2.5 permil beginning at the K/T boundary, as defined by the first appearance of Tertiary planktonic foraminifera, and continuing 17–20 cm above the boundary, approximately 40,000 years later. Gradual 13C depletion contrasts with the sudden δ13C drop at the K/T boundary observed in many deep-sea sections. The surface-to-bottom δ13C gradient decreased to less than zero approximately 25,000–30,000 years after the K/T boundary and remained negative for at least the next 140,000 years. Concomitant with change in δ13C values is a gradual decrease of about 2.5 permil in δ18C values which has not been observed at other localities. This 18O depletion suggests changes in temperature and/or salinity in the earliest Paleocene Gulf of Mexico. No extinction of foraminiferal species is associated with the K/T boundary or the onset of 18O and 13C depletions. Instead, two phases of Cretaceous species extinctions occur. One extinction phase is below the K/T boundary and below the tsunami bed of Bourgeois et al. [1988] and may be linked to sea level regression and environmental perturbations. The second extinction phase coincides with the minimum in δ13C and δ18O values in the Early Danian (Zone P0/Pla) and appears directly related to environmental changes reflected in the isotopic record. H. globulosa, which is commonly present in Maastrichtian and Danian sediments, exhibits significantly lower 18O/16O and 13C/12C ratios in Tertiary sediments relative to specimens from Maastrichtian sediments, demonstrating the survival of this important Cretaceous taxon after the K/T boundary event.

The impact of seasonally deposited phytodetritus on epifaunal and shallow infaunal benthic foraminiferal populations in the bathyal northeast Atlantic: the assemblage response

Abstract: The impact of phytodetritus on deep-sea benthic foraminiferal assemblages was studied before and after a detritus drop in 1982 at about 1350 m in the Porcupine Seabight. Assemblage data from the top cm of sediment were analysed by diversity and species distribution methods. Despite its relatively modest organic content, the phytodetritus had a significant impact on the foraminiferal communities. The mix of species changed significantly after the phytodetritus drop, as indicated by species distribution analysis. A number of species displayed a disproportionate population growth in the detritus itself, which was readily detectable by neutral model analysis. In so far as could be determined by the methods employed in this study, the phytodetritus had less impact on those organisms that did not colonize the detritus, but it appeared to be responsible for changes in species composition and may have caused their populations to become more heterogeneous.

A 210,000-year record of barium variability in the deep northwest Atlantic Ocean

Abstract: THE deep ocean is the storehouse for most of the carbon and nutrients in the ocean–atmosphere system; together with its out-crops at high latitudes, the deep ocean is of great importance in driving glacial–interglacial changes in the carbon dioxide content of the atmosphere1–3. The chemical and physical structure of the deep glacial oceans can be reconstructed by means of palaeochemical tracers; for example, the cadmium and carbon isotope contents of benthic foraminifera have been used to reconstruct the phosphate (or labile nutrient) compositions of deep waters4–14. Recently, it was proposed15 that barium in benthic foraminifera could be used to reconstruct the distribution of refractory, deep-regenerated chemical properties in the water masses of the glacial oceans. A reconstruction of barium concentra-tions in the oceans at the time of the Last Glacial Maximum revealed the greatest changes in the North Atlantic, where barium concentrations in deep water were up to 50% higher than at present16. Here we present a record of the benthic Ba/Ca ratio in the deep northwest Atlantic stretching back to interglacial stage 7 (∼210 kyr ago), encompassing two full glacial cycles. A comparison of the barium record with that of the other nutrient-like tracers lends confidence in the general agreement between these tracers while showing some spectral variability unique to barium, thus underscoring its utility as an additional palaeoceanographic tracer.

The record of deglaciation in the Sulu Sea: Evidence for the Younger Dryas Event in the tropical western Pacific

Abstract: A high-resolution, accelerator mass spectroscopy 14C dated sediment record from the Sulu Sea clearly indicates that the Younger Dryas event affected the western equatorial Pacific. Planktonic foraminiferal δ18O and abundance data both record significant changes during Younger Dryas time. In particular, a 0.4‰ increase in the δ18O value of Globigerinoides ruber and the reappearance of the cool water planktonic foraminifera, Neogloboquadrina pachyderma, occur during the Younger Dryas at this location. These isotopic and faunal changes are a response to either surface water temperature or salinity changes, or some combination of the two. Changes in surface salinities could have been accomplished through either local or global processes. Intensification of the monsoon climate system and increased precipitation at approximately 11 ka is one mechanism that may have resulted in local changes in salinity. A meltwater pulse derived from the Tibetan Plateau is another mechanism which may have caused local changes in salinity. The presence of the Younger Dryas in the tropical western Pacific clearly indicates that this climatic event is not restricted to the North Atlantic or high latitudes, but rather is global in extent.

Morphotype analysis of deep-sea benthic foraminifera from the Northwest Gulf of Mexico

Abstract: An analysis of benthic foraminiferal morphotypes, based on test shape, mode of coiling and presence or absence of surface pores, was carried out on benthic foraminiferal data collected from the Gulf of Mexico by Phleger (1951). The morphotypes show distinct depth patterns and are used to determine the depth distribution of foraminiferal microhabitats in the Gulf of Mexico. The plano-convex morphotype has generally low values ({le}10%) in relatively shallow depths ( 1,000 m). The biconvex morphotype has values of 2,000 m, with the 1,300-2,000 m interval being transitional with variable values. The infaunal-epifaunal depth pattern is similar to that observed in the Norwegian Sea. The infaunal-epifaunal transition between 1,300 and 2,000 mmore » is close to the upper or lower depth limits of many species, and the authors suggest that these depth limits are related in part to the microhabitat preferences of the taxa.« less

Facies, fossil record, and age of pleistocene reefs from the Red Sea (Saudi Arabia)

Abstract: Facies patterns within the Pleistocene reef terraces along the Red Sea coast exhibit lateral changes over short distances. These changes reflect either transitions within the depositional environment or they are related to minor or major sea level fluctuations. On the basis of quantitative distributions of biota in the field as well as in thin section it is possible to establish and map these lateral patterns. Important biota are framebuilders and secondary reef encrusters (foraminifers, coralline algae). Frequency distributions of sessile foraminifera and scleractinians are strikingly similar to those of the recent environment within diagenetically unaltered terraces. The marine reef terraces occur in different elevated levels above the present sea level. Morphological steps are caused by onlap during different sea levels, by tectonics, or by erosion during transgression. Although several morphological steps exist which obscure the terrace stratigraphy, only three reef units can be distinguished. Each unit exhibits a lateral facies development, which begins at the shore, covering the whole lagoonal facies and ends at the upper reef slope. Besides this lateral facies pattern vertical patterns occur as well, showing a transgressive sequence in the youngest (lower) and oldest (upper) unit and a regressive one in the middle unit. In top quality outcrops, like wadi sections, it is possible to differentiate within the youngest reef unit between three onlaping reef cycles. Such cycles, however, can not be seen in the middle and oldest formations. The three reef cycles within the youngest unit and the three units as well, exhibit different degrees of diagenetic alterations, which are strongly reflected by a gradual reduction in the number of biota. This reduction may be best described as a process of “sieving”. Where these differences in diagenesis are recorded, they correspond to the age of the reef units. U/Th datations of the investigated terraces reveal an age for the youngest unit between 86,000 and 118,000 years B.P.. During this time three major sea level high stands have occurred, which explain the existence of the three reef cycles. The age of the middle formation is around 205,000 years, while the age for the oldest formation can only be assumed to fit in the time span between 290,000 and 340,000 years B.P.. All these data correspond to other published datations along the Red Sea coast.

Benthic foraminifera of Puerto Rican mangrove-lagoon systems; potential for paleoenvironmental interpretations

Abstract: Recent foraminiferal assemblages from four traverses across mangrove-lagoonal environments off Puerto Rico exhibit patterns of distribution that should be useful in paleoenvironmental interpretations. Variations in sediment substrate type, abundance and distribution of marine vegetation, and degree of exposure to wave and current activity appear to be important factors related to foraminiferal distributions and abundances. Cluster analysis of foraminiferal abundance data distinguishes four major assemblages. Other generally recognizable trends in foraminiferal assemblages include: offshore increase in species diversity; offshore increase in percent miliolids while percent rotaliids remain more or less constant; small peaks in percent textulariids immediately adjacent to mangrove growth; almost 100% agglutinated assemblages in fully mangrove environments; offshore increase in foraminiferal number except in areas of abundant Halimeda plate production where numbers of foraminifera are diluted; restriction of high abundances of Fissurina, Nonionella, Fursenkoina and Helenina to lagoons behind mangrove islands; restrictions of high abundances of Rosalina, Cibicides, Discorbis, Spiroloculina, Cyclogyra, Quinqueloculina, Amphistegina, Peneroplis and Archaias to lagoons seaward of mangrove islands. These trends provide a micropaleontological link between a potential petroleum source, mangrove swamps, and the potential petroleum reservoir, reef rocks.

Stable isotope evidence for foraminiferal habitats during the during of the Cenomanian/Turonian ocean anoxic event

Abstract: Oxygen and carbon isotope analyses of several species of size-controlled planktonic and benthic foraminifera from the Plenus Marls of Dover (Kent, England) show a clear separation in oxygen and carbon isotope ratios consistent with different habitats; the analyses indicate the existence of vertical gradients of temperature and 13 C in dissolved CO 2 in the Chalk Sea. Whereas sequential ontogenetic stages of planktonic foraminifera do not show systematic variations in δ 18 O or δ 13 C values (implying no systematic change in depth habitat during the growth of individual species), species of the genera Hedbergella and Dicarinella are interpreted to have lived nearer to the surface than Rotalipora . Because vertical 13 C gradients in the Chalk Sea remained stable during the late Cenomanian, the oxygen-minimum zone is unlikely to have impinged on this area.

Taphonomic Process and Species Microhabitats in the Living to Fossil Assemblage Transition of Deeper Water Benthic Foraminifera

Abstract: A detailed analysis was made of living and death assemblage abundances of benthic foraminiferal species in the top 10 cm of three high quality box cores from the Gulf of Mexico (water depth=1170, 1050, and 1020 m). These data, combined with sedimentological studies and analysis of the biotic activity in the sediments (using Pb-210 profiles), were used to examine the processes controlling the transformation of living to fossil assemblages. These results have implications for the paleoceanic interpretation of benthic foraminiferal assemblage and isotopic data

Agglutinated Foraminifera from the Palaeogene of the North Sea

Abstract: The bulk of this paper consists of taxonomic notes on 146 species (67 genera) of agglutinated foraminifera from the Palaeogene of the North Sea. These include not only those representing agglutinate- dominated “Rhabdammina” or “flysch-type” faunas but also those that form a component of predominantly calcareous benthonic foraminiferal assemblages and those associated with volcaniclastic sediments. Thirty-eight species are left in open nomenclature. Forty-eight of the remainder are named on the basis of comparison with type or topotype material, most importantly in the cases of the Brady collection in the British Museum (Natural History), London and the Grzybowski collection in the Jagiellonian University, Krakow, Poland.