Showing papers on "Foraminifera published in 1982"

Vertical distribution and isotopic fractionation of living planktonic foraminifera from the Panama Basin

Abstract: A model1,2, which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western North Atlantic and is comprised of three tenets: (1) The conditions in the photic zone (upper 80–100 m) exclusively dictate planktonic foraminifera species composition and abundance throughout the water column. (2) Species are vertically stratified within the photic zone according to their temperature preference. Depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments. Due to seasonal temperature variations, seasonal variations in the δ18O composition of seawater, and species-specific isotope fractionation, rigorous proof of this hypothesis cannot be provided from sediment analyses alone. (3) The chlorophyll maximum is a major food source zone, which is preferentially exploited by foraminifera. Our data from the Panama Basin, which are presented here, are confirmation of this model. The Panama Basin in the eastern equatorial Pacific, which has a shallow and steep thermocline, was sampled for living planktonic foraminifera. A multiple opening–closing net and environmental sensing system (MOCNESS)4 was used to collect 13 sets of eight vertically stratified oblique samples. We report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four MOCNESS tows taken over 5 days, during August 1979 (RV Knorr cruise 73) at 5°20′ N, 8°50′ W. Each tow consisted of eight samples which integrated ∼12.5-m intervals from 0 to 100 m for MOC 126, 25-m intervals from 0 to 200 m for MOC 127, 100–150-m intervals from 0 to 1,000 m on MOC 128 and 250-m intervals from 0 to 2,000 m on MOC 131.

Isotopic Paleoceanography of the Caribbean and East Pacific: Role of Panama Uplift in Late Neogene Time

Abstract: Comparisons of carbon isotopic data on benthic foraminifera from Deep Sea Drilling Project sites 502 (western Caribbean) and 503 (eastern Pacific) indicate that the difference between the Atlantic and the Pacific in the per mil enrichment in carbon-13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago, when the difference reached the modern level (1 per mil). Comparisons of planktonic foraminiferal oxygen isotopic data for the Caribbean and the Pacific suggest that the salinity of Caribbean surface waters began increasing 4 million years ago, possibly in response to shoaling of the Panama isthmus. These results suggest that modern circulation patterns in the Caribbean and eastern Pacific developed by 3 million years ago in concert with changing tectonic, climatic, and biogeographic patterns.

Deep Circulation of the North Atlantic over the Last 200,000 Years: Geochemical Evidence

Abstract: Variations in the cadmium/calcium ratio of North Atlantic Deep Water are recorded in the fossil shells of benthic foraminifera. The oceanic distribution of cadmium is similar to that of the nutrients, hence the cadmium/calcium ratio in shells records temporal variations in nutrient distributions. Data from a North Atlantic sediment core show that over the past 200,000 years there has been a continuous supply of nutrient-depleted waters into the deep North Atlantic. The intensity of this source relative to nutrient-enriched southern waters diminished by about a factor of 2 during severe glaciations. This evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested.

Glacial to interglacial contrasts in the northern Indian Ocean

Abstract: Differences between the 18O/16O ratios of planktonic foraminifera deposited during the last glacial maximum, about 18,000 yr ago, and those deposited during the Holocene show that in the Indian Ocean, the south-west monsoon was weaker than today but that the north-east monsoon was stronger. The upwelling observed in modern conditions along the southern coast of Arabia had disappeared because of the low speed of the southwestern winds during glacial summers. The reduction in rainfall and runoff over the continent caused a reduction of the salinity gradient in the Bay of Bengal and along the western coast of India. Increased precipitation fell on the sea south of 10° N, while strong evaporation over the northernmost Arabian Sea produced an enhanced salinity gradient in that area.

Environmental distribution of Recent benthic foraminifera on the northeast United States continental slope

Abstract: Several bathymetrically consistent Recent benthic foraminiferal biofacies have been recognized from the continental slope south-east of Cape Cod. Faunal assemblages are dominated by Globobulimina / Bulimina (upper slope; less than 1,000 m) and Uvigerina peregrina (lower slope-uppermost rise; water depths between 1,000 and 2,500 m). The Globobulimina / Bulimina assemblage coincides with the oxygen minimum zone; this agrees with the occurrence of Globobulimina in Mediterranean sapropels, organic-rich sediments deposited under anoxic conditions. Previous studies have noted the association of U. peregrina with bathyal water depths, deep-water temperatures of 3 to 4 ° C, and water of low oxygen content. However, correlations between abundance of U. peregrina and water depth or temperature are not the same everywhere, and no correlation with dissolved oxygen in the water column is seen on the United States continental slope and rise. The highest abundances of U. peregrina coincide with maxima of organic carbon and silt within the slope sediments. This suggests that the distribution of U. peregrina in this region may be influenced more by low oxygen in the sediments, rather than by low oxygen content of the overlying water.

Evidence for primary control of the distribution of certain Atlantic Ocean benthonic foraminifera by degree of carbonate saturation

Abstract: The distribution of certain Atlantic Ocean benthonic foraminifera is most consistently correlated with the degree of saturation of seawater with respect to calcium carbonate. Based on this relationship it may be possible to recognize changes in “paleosaturation” in the deep sea from fossil benthonic foraminifera.

Paleoecology of late miocene mediterranean foraminifera

Abstract: Qualitative and quantitative analyses were made of the benthic and planktonic foraminiferal associations derived from about 400 samples of the Cretan and Sicilian Upper Miocene (Tortonian and Messinian). The quantitative data were analyzed by means ofR- and Q-mode computer programs, which resulted in clusterings of benthic and of planktonic foraminiferal species and the grouping of the samples. Oxygen and carbon isotope data were collected from the foraminiferal carbonate of some 150 samples. The combination of these data with the data from sedimentological analyses and with paleogeographic reconstructions made it possible to arrive at fairly refined estimates of the Late Miocene Mediterranean paleo-oceanography. The foraminiferal distribution and abundance patterns were compared with the paleo-oceanographic interpretation in order to trace the Late Miocene preference and tolerance patterns of the foraminiferal species. Nutrient abundance and, to a lesser extent, salinity were probably the main parameters controlling the Late Miocene distribution patterns. Temperature, type of substrate, depth and pH apparently played only a subordinate role. The various existing models of the Messinian salinity crisis are discussed. The roles of structural evolution, climate and oceanographic factors are considered. Special attention is paid to the genesis of the laminated and diatomaceous sediments. It is concluded that the laminated sediments are the result of changes in the inflow-outflow balance of the Atlantic and Mediterranean waters. The diatomites are ascribed to the same processes but with the additional characteristic that they were formed in the western Mediterranean, against shoals and landmasses, during periods of upwelling. It is suggested that the laminated sediments were deposited during eustatic sea-levellowerings. The ecology and paleoecology of planktonic and benthic foraminifera are discussed extensively. It is concluded that the distribution of both groups of foraminifera is mainly dependent on the distribution of water-masses; each water-mass contains a characteristic faunal association. The abundance of both groups of foraminifera is mainly linked to nutrient abundance, whereas physical/chemical factors are of lesser importance. A calibration of the Late Miocene distribution and abundance patterns and those described from Recent environments suggests that the niches of many foraminiferal species, in particular benthic taxa, changed considerably during the last 5 to 6 m.y. This implies that the Recent distribution patterns cannot simply be applied for the interpretation of fossil associations and for the reconstruction of paleo-environmental conditions. A tentative model is presented which might account for the inferred changes in habitats.

Water chemistry control of cadmium content in Recent benthic foraminifera

Abstract: The micropalaeontology and isotopic chemistry of foraminifera and other fossils have provided a detailed picture of the surface ocean environment during glaciation1,2. Less is known about climate-related changes in the deep ocean, although Weyl3 and Newell4 have proposed significant variations on theoretical grounds. It is clear that significant variations in the population assemblages and δ13C of benthic foraminifera occur5,6 but these changes do not yet constrain a unique hydrographical solution. Adsorption of phosphate onto calcite and unfavourable solid solution behaviour7,8 preclude direct palaeonutrient determination. Because CdCO3 and CaCO3 form a continuous solid-solution series9 it has been suggested that the trace cadmium variability in foraminifera may provide an additional tool for probing changes in deep ocean circulation10. Here we demonstrate that certain benthic foraminifera, Uvigerina spp. and C. kullenbergi, show a consistent relationship between the Cd/Ca of the bottom water and of their calcite shells.

Holocene history of Bedford Basin, Nova Scotia: foraminifera, dinoflagellate, and pollen records

Abstract: Three piston cores from Bedford Basin, a silled coastal inlet, provide the basis for a micropaleontological study of postglacial to recent sediments. Five faunal units (four foraminiferal, one arcellacean) are found in core 79-11: a surface assemblage, followed by deep estuarine, marginal marine, transition, and freshwater (arcellacean) assemblages. The other cores contain only expanded marine sequences. The top of the transition zone in core 79-11 has a C-14 age of 5830 ± 230 years BP, indicating a rise in sea level of at least 20 m (the sill depth) during the Holocene.Four dinoflagellate assemblage zones are found in core 79-11. The first (O. centrocarpum – B. tepikiense) is typical of a silled basin with marine water of near-normal salinity; the second (P. conicoides – Cyst C) indicates a temperate marine environment with strong fluvial influence (marginal marine); the third (P. limbatum) is dominated by freshwater cysts, and the fourth (Dinocyst sp. A) is dominated by subarctic brackish water cysts.Fo...

Middle miocene foraminiferal biochronology and ecology of se poland

Abstract: Midd~e and Late Miocene (Late Badenian and Sarmatlan) foraminifera of the epicontinental deposits of SE Poland (Roztocze area) h ave been examined. These deposits, referred to the Late Badenlan are correlated with NI3-N14 s t a n da r d b io stratigraphic zones, based on planktonic foraminifera . Sarmatlan, therefore, especially it s deeper wate r deposits, appears to represent younger zones. Changes in water depth appe ared to control distribution of benthonic forms, whereas climatic changes and water depth controlled d istribution of pl anktonic forms. The Mlddle/Late Badenlan boundary probably r epresents an e cos t r a ti g r a p hi c event. A correlation is su ggested r elating the Middle Miocene deposits of the Roztocze area with those of .the Polish Fore-Carpathian Depression. Bolboforma badenensis sp . n., a planktonic form of uncertain taxonomic affinity Is described. Key w 0 r d s : Foraminifera, problematic pl anktonic form, Miocene, Poland, biochronology, ecology, taxonomy.

Ecologic Atlas of Benthic Foraminifera of the Gulf of Mexico

Abstract: Because of their importance as indicators of petroleum deposits, the benthic foraminifera of the Gulf of Mexico are one of the most intensely studied groups of animals in the world. This is especially true of the foraminifera inhabiting the shallow shelf region of the northern and eastern Gulf; much less is known about the animals of the southern shelf, continental slope, and abyssal plains. The author spent 10 years examining collections from various not well-known areas of the Gulf; this atlas is a synthesis of distributional data from approximately 4500 previously known stations, plus new information from 400 additional stations.

Holocene and latest glacial benthic foraminifera from the slope and rise off eastern North America

Abstract: Benthic foraminifera from sediments of Holocene age exhibit a consistent bathymetric zonation along the continental slope and rise from the Grand Banks to Cape Hatteras. Slumping, gravity flow, and contour currents have not destroyed this pattern, although displaced benthic faunas can occur locally. Consistently recognizable faunas are dominated by Bulimina (less than 1,000 m), Uvigerina (1,000 to 2,600 m), Hoeglundina (2,600 to 3,800 m), and Osangularia (deeper than 3,800 m). The Holocene faunal pattern may reflect the position and intensity of contour-following currents, the physical and chemical nature of the bottom water, and the sediment type; all are interrelated. In cores from the slope and rise (2,200 to 3,900 m), uppermost Pleistocene faunas are dominated by Uvigerina , while Hoeglundina is dominant or subdominant in the Holocene. This faunal transition is dated by radiocarbon. At 3,000 m, it occurs at about 12,000 yr B.P., and at 4,000 m it occurs at about 8,000 yr B.P. Below 4,000 m, the glacial to modern faunal shift is subtle, but it clearly occurs later than on the upper rise. The faunal turnover seems to coincide with the initiation of the modern North Atlantic circulation pattern. If so, the North Atlantic became an increasingly important source of deep water around 12,000 yr ago, and this dense water came to dominate the pattern of Atlantic circulation over a period of some 4,000 to 5,000 yr.

Salinity reduction of the end‐Triassic sea from the Alpine region into northwestern Europe

Abstract: A palaeoecological analysis of the Penarth Group (=‘Rhaetic’) of southern England and Wales is undertaken in terms of a species-richness comparison with the Zlambach and Kossen Beds of the Austrian Alps. The three groups studied, bivalves, foraminifers and ostracodes, comprise the most important invertebrate faunas occurring in the deposits cited. All show significant diversity from the Alps into northwest Europe. Coupled with the disappearance of stenohaline elements including ammonites, and taking into account other facies information, the evidence suggests a transgression of a shallow epicontinental sea in northwest Europe at the end of the Triassic. The salinity of this sea (˜25–30%□) was appreciably below that of the Tethyan ocean.

Eocene to Oligocene benthic foraminiferal isotopic record in the Bay of Biscay

Abstract: We present here oxygen and carbon isotopic records of Eocene to Oligocene benthic f oraminif era from two Bay of Biscay Deep Sea Drilling Project (DSDP) sites (119 and 401). δ18O of benthic foraminifera increases 1.9‰ from a middle Eocene minimum (Zones P10–P11) to an earliest Oligocene maximum (Zone NP21). Approximately 1.4‰ of the increase in benthic foraminiferal δ18O occurs during the late Eocene to earliest Oligocene (Zones P15/16–NP21). Previous results from other North Atlantic DSDP sites (400A and 398) have significantly lower δ18O values of benthic foraminifera, some by as much as 2‰ (refs 1–3). We believe that these differences result from diagenetic alteration of the sediments in the deeper-buried Sites 400A and 398.

Stable isotopic evidence for latest Miocene sea-level fall in the Mediterranean region

Abstract: The discovery of a marked isochronous decrease of carbon isotope ratio values (∼0.5–0.8‰ in marine carbonates at about 6.2 Myr has stimulated several speculations regarding the origin of this event1–3. Here we report stable isotope studies of planktonic and benthic foraminifera from the late Miocene Carmona–Dos Hermanos section in southwestern Spain which suggest that (1) the carbon shift at 6.2 Myr is directly associated with a eustatic sea-level lowering recorded in the same section; (2) the shift in δ13C at 6.2 Myr and other times may be related to an increased flux of marine and terrigenous organic matter depleted in 13C and eroded from the continental shelves during sea-level lowstands; and (3) the sea-level fall at 6.2 Myr triggered the rapid shift towards hypersaline conditions in the Mediterranean well before the deposition of the Messinian evaporites.

Temperature control of oxygen-isotope fractionation of cultured planktonic foraminifera

Abstract: The palaeotemperature equation of Epstein et al.1. relates the oxygen-isotope composition of mollusc carbonate shells to the temperature in which it has been deposited. This equation has been applied extensively to derive palaeotemperatures and other palaeoenvironmental parameters for the Pleistocene epoch, based on the isotopic composition of planktonic foraminifera in deep sea cores2–11. Recently, doubt has been expressed as to whether planktonic foraminifera fractionate oxygen isotopes according to the known palaeotemperature equation12–18, and thus the validity of many palaeoenvironmental studies has been questioned. We present here experimental data demonstrating that planktonic foraminifera of the species G. sacculifer deposit calcite skeletons that have an oxygen-isotope composition very close to that predicted by the well-known palaeotemperature equation1.

Temperate carbonate sediments of Northern Spencer Gulf, South Australia: a high salinity ‘foramol’ province

Abstract: Cool-water skeletal carbonate sediments are forming in Spencer Gulf, South Australia, an area of high salinity and moderate tidal range. Four environments can be distinguished: deeper marine areas (10–20 m); shallow subtidal platforms and banks (2–10 m); intertidal and supratidal zones; and coastal springs and lakes fed by saline continental groundwaters. The sediments are predominately bioclastic carbonate sands; muddy sediments occur in protected intertidal environments. The most common grain types are gastropods, bivalves, foraminifera, coralline algae and quartz. Indurated non-skeletal carbonate grains have not been seen. Composition of the sediment varies little between environments, but considerable textural variation results from variation in the stability of the substrate, hydrodynamic conditions, depth of water, period of tidal inundation, supply of terrigenous grains, temperature, and salinity. The Spencer Gulf data suggests that temperature, and particularly minimum temperature, controls the distribution of skeletal and non-skeletal grain associations in high-salinity environments. The textures of the sedimentary facies of Spencer Gulf closely parallel those of equivalent environments in warm-water carbonate provinces.

Linkage of North Atlantic and Southern Ocean deep-water circulation during glacial intervals

Abstract: The Antarctic Circumpolar Current (ACC) is one of the major current systems in the world ocean, affecting circulation in all of the major ocean basins. The ACC flows eastwards around Antarctica from the surface to ∼4,000 m depth with a transport on the order of 125 Sverdrups1. Deep-sea benthic foraminifera from one piston core (E49–18) from the south-east Indian Ocean sector of the Southern Ocean were analysed to determine deep-water-mass-circulation conditions within the ACC during the late Quaternary. I report here that benthic foraminiferal faunal patterns closely match Northern Hemisphere ice-volume changes shown by planktonic foraminiferal oxygen-isotopic stratigraphy. The glacial–interglacial faunal oscillations are interpreted to reflect the presence of a deep-water mass in the ACC during glacial times which differs from modern Circumpolar Deep Water. I suggest that deep-water circulation changes within the ACC during the interval 440,000 to the present are directly linked to changes in North Atlantic Deep Water (NADW) circulation.

Foraminifera in Late Saalian, Eemian, Early and Middle Weichselian of the Skærumhede I boring

Abstract: A foraminiferal stratigraphy primarily based on the late Axel Norvangs material from the Skaerumhede I boring has been made. Foraminifera from the marine Skaerumhede sequence show a faunal succession from an arctic environment (zone N4) to deep water boreal and boreo-lusitanian conditions (zone N3). This is succeeded by a zone (N2) containing a faunal transition from a shallow water boreal assemblage in its lower part through to boreo-arctic conditions in its upper part, and finally a zone (Nl) reflecting mainly arctic environment. It is argued that zone N4 represents the Late Saalian, zone N3 the Eemian and zones N2 and Nl the Early and Middle Weichselian.

Late glacial to recent cores from the eastern Mediterranean

Abstract: Variations in the planktonic foraminiferal population in sediment cores from the eastern Mediterranean indicate a slow warming from about 24,000 y BP to the climatic optimum at 4700 y BP; there is evidence of an earlier warm phase in two cores. Globorotalia truncatulinoides and G. pachyderma are not found in sediments younger than 10,400 y BP. Dates are confirmed by 14 C dating at 10,438 and 4722 y BP. G. sacculifer becomes more abundant than G. ruber for a short interval at 1200 y BP. A dark olive green microburrowed horizon in the cores coincident with a reduction in the benthonic foraminferal population between 9300 and 6700 y BP represents the sapropel found in the deeper basins. Planktonic foraminiferal productivity was highest at 9000 and 4700 y BP; benthonic productivity was highest in the late Glacial between 12,000 and 10,000 y BP. 18 O composition of the foraminifera shows a rapid depletion of 18 O from 13,000 to 10,000 y BP, caused by melting ice and temperature increase, indicating the end of glacial conditions. The magnetic fabric of three cores is similar to that of British lake cores and in conjunction with the 14 C dates and foraminiferal changes can be used to date eastern Mediterranean sediments. The overall mineralogy and sedimentation rates in the area are controlled by proximity to Cyprus; part of the fine clay fraction ( μ m) are believed to be derived from the Turkish mainland. A decrease in the relative amount of montmorillonite, which commenced at 12,000 y BP in the deep-water cores, coincides with the introduction of ice melt-water from the Black Sea into the eastern Mediterranean; at 6700 y BP (the end of the sapropel) the amount of montmorillonite increases to that of glacial times.