Showing papers on "Foraminifera published in 1983"

Biotic Interactions in Benthic Foraminifera

Abstract: Foraminif era have a long geologic record, extending back perhaps to the Cambrian, and they are both abundant and diverse during most of the Phanerozoic. Over 40,000 species now have been described, of which approximately 4000 are living today (Tappan, 1971). They occur in all modern marine communities, and have also been found living in brackish and fresh water (Arnal, 1958; Boltovskoy and Lena, 1971; Resig, 1974). Foraminifera are especially diverse and abundant in deep-sea, coral reef, and many soft-bottom, shallow-water habitats (Hessler, 1974; Smith et al., 1978; Thiel, 1975; Murray, 1973; Wefer and Lutze, 1976), making them one of the most important animal groups on earth. Yet little is known about their interactions with other organisms, although much has been published on their distributional patterns. Successful use of foraminifera in paleobiology and paleoenvironmental interpretations requires more detailed ecologic knowledge (Lipps, 1981).

Geochemistry of Namibian Shelf Sediments

Abstract: The modern sediments accumulating on the Namibian shelf between 20° and 26°S latitude are composed predominantly of biogenous material: organic matter, diatomaceous silica and calcium carbonate. A belt of anoxic, organic-rich diatom ooze, containing fish debris and Recent and pre-Recent phosphorite, occurs in a coastal zone up to 70 km wide off Walvis Bay in water depths shallower than 140 m. A blanket of foraminiferal and skeletal calcarenites, containing reworked phosphorite, and calcareous muds covers the central and outer shelf. The diatom ooze is a modern equilibrium facies reflecting the intensity of coastal upwelling in the Benguela Current; sedimentation rates range between 30 and 120 cm/103 yr. Seaward of the diatom ooze, benthic and planktonic carbonate is mixed with a reworked, shelly transgressive facies on the middle part of the shelf, the sediment becoming richer in foraminifera and more fine-grained towards the shelf edge, where sedimentation rates are on the order of 5 cm/103 years.

Evidence for Oligocene–Middle Miocene abyssal circulation changes in the western North Atlantic

Abstract: Previous studies of benthic foraminiferal isotopic composition have demonstrated that a latest Eocene–earliest Oligocene benthic foraminiferal δ18O increase occurred in the Pacific, Southern and Atlantic Oceans1–9. A Middle Miocene δ18O increase has been noted in the Pacific, Southern and South Atlantic Oceans1–3,7,10,11 and tentatively identified in the North Atlantic12,13. Due to the incomplete nature of the North Atlantic stratigraphical record14,15, however, the Oligocene to Middle Miocene isotopic record of this ocean is poorly understood. In the modern ocean, the North Atlantic and its marginal seas has a critical role in abyssal circulation, influencing deep- and bottom-water hydrography as far away as the North Pacific16–18. We now report oxygen isotope measurements on Oligocene to Middle Miocene (12–36 Myr BP) benthic foraminifera in the western North Atlantic which show two periods of enriched 18O values: early Oligocene and early Middle Miocene. These enriched intervals are interpreted as resulting, in part, from the build-up of continental ice sheets. The Oligocene to Middle Miocene δ13C record shows three cycles of enrichment and depletion of large enough magnitude to be useful for time–Stratigraphical correlations. Within the biostratigraphical age resolution, δ18O and δ13C records correlate with records from other oceans, helping to establish a useful Tertiary isotopic stratigraphy. An Atlantic–Pacific δ13C contrast of 0.3–0.9‰ during the latest Oligocene to Middle Miocene (12–26 Myr BP) indicates North Atlantic deep and bottom-water production analogous to modern North Atlantic deep water (NADW).

Distribution of Holocene deep-sea benthonic foraminifera in the southwest Indian Ocean☆

Abstract: The distribution of deep-sea benthonic foraminifera in core top samples from the southwest Indian Ocean is examined. Principal component analysis reveals two major assemblages. One assemblages between 3600 and 4800-m water depth is dominated by Episominella umbonifera and is associated with cold (θ = −0.3 to 0.8°C), low salinity (34.66 to 34.72 × 10−3) Antarctic Bottom Water in the Crozet Basin, in fracture zones, and on the flanks of the Southwest Indian Ridge. A second assemblage, dominated by Planulina wuellerstorfi, Globocassidulina subglobasa, Astrononion echolsi and Pullenia bulloides, is between 1600 and 3800 m on the Crozet Plateau, Madagascar Ridge, Central Indian Ridge, and Southwest Indian Ridge and is associated with relatively warm (θ = 0.8 to 2.6°C), high salinity (34.72 to 34.76 × 10−3) North Atlantic Deep Water. The third principal component divides the P. wuellerstorfi assemblage into two subgroups. One is dominated by Epistominella exigua, P. bulloides, P. wuellerstorfi, and A. echolsi and a second is dominated by G. subglobosa. The distribution of the E. umbonifera assemblage and previous hydrographic studies suggest that AABW flows as a western boundary contour current in the Crozet Basin and penetrates fracture zones in the Southwest Indian Ridge between 55 and 57°E and near 66°E as it travels northward into the Madagascar and Mascarene basins. The faunal-water mass associations from the southeast Indian Ocean are compared; the most notable faunal difference is the absence of Uvigerina as a dominant taxon in the southwest Indian Ocean. A comparison of dissolved oxygen and Uvigerina data shows that oxygen is not a major influence upon the distribution of Uvigerina. A correlation analysis of the faunal data and water depth, potential temperature, in situ temperature, salinity, dissolved oxygen, and 1 − Ω , an index of calcium carbonate undersaturation, was carried out to determine the relationships between fauna and hydrography. The second principal component has a significant positive correlation at the 99.9% level with temperature and negative correlations with water depth and 1 − Ω . A general faunal-water mass correlation exists, but it is not possible to determine which variable controls the faunal distributions.

Late Oligocene–early Miocene glacial record of the Ross Sea, Antarctica: Evidence from DSDP Site 270

Abstract: Foraminifera from Deep Sea Drilling Project Site 270, Ross Sea, Antarctica, are used to trace an early phase of glaciation during the late Oligocene–early Miocene. The central Ross Sea underwent significant bathymetric and oceanographic evolution with the inception of glaciomarine sedimentation, resulting in the sequential development of four contrasting foraminiferal populations (assemblage zones). Gradual climatic change in the Ross Sector during latest Paleogene-early Neogene time culminated in major ice build-up by the late early Miocene. Conclusions derived from our microfaunal studies reaffirm climatic and oceanographic trends interpreted from oxygen-isotope data for sub-Antarctic deep sea sites north of the Ross. Sea. Intensification of glaciation within the Ross Sea area may be responsible for the increase in production of Antarctic Bottom Water and associated development of widespread early Neogene deep-sea hiatuses reported from lower latitude regions.

Calcification Rates, Photosynthesis and Light in Planktonic Foraminifera

Abstract: Two processes that are of major importance in the global carbon cycle, photosynthesis and calcification, are widely associated in the marine environment This association can be direct, as in coccolithophores and calcareous algae, or in the form of symbiosis, as found in hermatypic corals, planktonic and benthonic foraminifera These groups of organisms are the major calcifiers in the ocean and precipitate the bulk: of CaCO3 in the pelagic and the neritic environments

Late Pleistocene Eucampia antarctica abundance stratigraphy in the Atlantic sector of the Southern Ocean

Abstract: A stratigraphy based upon abundance changes in the marine diatom Eucampia antarctica (Castr.) Mangin is presented for Late Pleistocene sediments of the Atlantic sector of the Southern Ocean south of the Polar Front. This stratigraphy is directly tied to lithology and concentrations of ice-rafted detritus. We find a positive correlation between E. antarctica abundance, increased ice-rafted detritus, and silty diatomaceous sediment. Low E. antarctica counts are associated with little or no ice-rafted detritus and diatomaceous ooze. Tentative correlation with the oxygen isotope record indicates that low E. antarctica abundances are associated with Oxygen Isotope Stages 1, 5a, 5c, and 5e. Late Pleistocene Eucampia antarctica abundance stratigraphy in the Atlantic sector of the Southern Ocean INTRODUCTION The Antarctic region plays a significant role in the world climate system (Fletcher, 1969). Fletcher pointed out that ice cover in the Southern Ocean influences ocean/atmosphere heat exchange and that yearly variations in ice cover may be important in enhancing the climatic effects of minor changes in global heating. It is therefore important to be able to identify both shortand long-term climatic fluctuations in the Southern Ocean recorded in deep-sea sediments. Central to this theme is the development of high resolution stratigraphic schemes. Since foraminifera and coccoliths are largely absent from high southern latitude sediments, the responsibility for a suitable stratigraphic scheme rests with the radiolarians and diatoms. Regional stratigraphies in the deep-sea sediments based upon abundance changes of individual species (Ericson, 1961; Ericson et al., 1961; Hays et al., 1976; Morley and Hays, 1979) or morphologic changes of selected species [e.g. coiling direction in Globorotalia truncatulinoides (d'Orbigny) (Ericson and Wollin, 1956), size change in Coscinodiscus nodulifer A. Schmidt (Arrhenius, 1952; Burckle and McLaughlin, 1977)] have been used to resolve time intervals of less than 50,000 years. Within the past few years it has been possible to further refine the resolution of some of these stratigraphies by correlating them with the globally synchronous oxygen isotope record (Shackleton and Opdyke, 1973, 1976). Using such an approach, Hays et al. (1976) and Morley and Hays (1979) have resolved time intervals of less than 10,000 years with a stratigraphy based upon changes in abundance of the radiolarian Cycladophora davisiana Ehrenberg. In the Southern Ocean, and particularly south of the Polar Front, a number of diatom species show abundance variations during the Late Pleistocene (unpublished data L.H.B.). These include such well-known forms as Coscinodiscus lentiginosus Janisch, Nitzschia kerguelensis (O'Meara), and Eucampia antarctica (Castr.) Mangin. This paper describes variations in abundance of this latter species which is found in the Antarctic and sub-Antarctic regions of the Southern Ocean and is also a constituent of the displaced diatom flora entrained in the Antarctic Bottom Water (Burckle and Stanton, 1975). Five cores in the South Atlantic were selected for this study (see table 1). Four were located south of the Polar Front and one (V29-105) north of it. Although we have studied E. antarctica abundances in other sectors of the Southern Ocean, we have not yet assured ourselves that the fine details of each abundance curve are indeed correlative around the Antarctic. micropaleontology, vol. 29, no. 1, pp. 6-10, 1983 6 This content downloaded from 157.55.39.45 on Tue, 19 Jul 2016 05:50:29 UTC All use subject to http://about.jstor.org/terms

Late Quaternary marine stratigraphy southeast of New Zealand

Abstract: Sediment cores of late Quaternary age from the continental margin and deep sea (Bounty Trough) southeast of New Zealand reveal an alternating sequence of glacial and interglacial sediments. During glacial episodes of lowered sea level, glaciation in the Southern Alps was at its peak, and east coast rivers delivered enormous volumes of terrigenous sediments to the shelf edge. At these times, sediments of the deep adjacent basins were dominated by micaceous hemipelagic deposits with a low biogenic component consisting mostly of siliceous remains (radiolaria and sponge spicules). Planktonic foraminifera, although present, were much reduced in abundance because of increased dissolution, as in deeper water subantarctic cores farther to the south. Cool-water forms dominated. During interglacial episodes, terrigenous sediment supply to the deep basins was reduced in response to higher sea levels and as glaciers retreated and deposited much of their loads in newly formed glacial lakes and on the plains. Terrigenous sediment dilution of the biogenic portion was thus much reduced. Calcium carbonate dissolution also was reduced. These processes, in combination, led to the deposition of foraminifera-rich hemipelagic sediments. Siliceous biogenic productivity decreased. Thus, the late Quaternary marine sediment record in the area adjacent to southeast New Zealand is dominated by paleoclimatic influences that control terrigenous input, calcium carbonate dissolution, biogenic productivity, and the migration of planktonic assemblages.

Changes in Glacial-Marine Sedimentation in Core HU77-159, Frobisher Bay, Baffin Island, N.W.T: A Record of Proximal, Distal, and Ice-Rafting Glacial-Marine Environments

Abstract: Core HU77-159 from Frobisher Bay, Baffin Island, Canada records the sedimentologic and biologic conditions associated with three distinct glacial-marine sediment types that can be correlated to a 14C dated terrestrial glacial chronology. The chronology of events recorded at the core site is controlled by five 14C dates and by paleomagnetic studies. During the Hall glacial advance in Frobisher Bay at shortly before 10,760± yr B.P., proximal glacial-marine conditions are recorded in HU77-159. The proximal glacial-marine sediments consist of clay, rich in detrital carbonate and other clay-sized minerals, which suggest erosion of bedrock, a low rate of sand influx, but increased quartz grain angularity, and a characteristic low diversity Elphidium excavatum forma clavata foraminiferal assemblage. Distal glacial-marine sediments are found directly above and below the proximal sediments, and these record conditions prior to and after the Hall advance. Ice-distal glacialmarine sediments are typically silty clays, with moderate CaCO3 percentages, sand influx, and grain angularity. Bentnic foraminifera in ice-distal glacial-marine sediments, are more abundant and diverse than in the ice-proximal environment reflecting an improved environment. In the upper portion of HU77-159, ice-rafted glacial-marine sediments have been deposited since the removal of glacier ice from Frobisher Bay. Ice-rafted sediments are noticeably sandier than the lower units and contain maxima of sand influx and grain angularity. Benthic foraminifera in the ice-rafting environment are the most abundant and diverse assemblages in the last 12,000 yr. Marine sedimentological processes have been dominant in middle Frobisher Bay at depths of 500–600 m throughout the Holocene.

Paleoecology and Stratigraphy of Jurassic Abyssal Foraminifera in the Blake-Bahama Basin, Deep Sea Drilling Project Site 534

Abstract: At Site 534, Blake-Bahama Basin, 66 brownish to olive green to gray black shale samples from Cores 127 to 70, of the middle Callovian-Valanginian, contain an assemblage of foraminifers with 36 calcareous taxa in 9 families and 35 agglutinated taxa in 8 families. The average number of taxa per sample is about 5, with a spread of 0 to 19 and a mode of about 8. Sample weight (10-50 g) is not correlated to species diversity and to specimen abundance, which means that a better recovery tool is more rather than bigger samples per core. R-mode cluster analysis using Jaccard and Dice coefficients of variation on 25 taxa occurring in 5 or more samples show a low level of association. One cluster includes the Kimmeridgian, carbonate-rich environment assemblage with Lenticulina quenstedti, Ophthalmidium carinatum, Neobulimina atlantica n. sp., and Epistomina aff. uhligi. Three clusters comprise stratigraphically persistent taxa of the genera Reophax, Bigenerina, Bathysiphon, Glomospira, Glomospirella, Lenticulina, Rhizammina, Psammosphaera, Dentalina, Lagena, Marginulina, Pseudonodosaria, and Trochammina. Strikingly similar Jurassic assemblages at other Atlantic and Indian oceans sites, which also backtrack to ~ 3-km water depth, show that the Jurassic abyssal fauna principally consists of small-sized agglutinated taxa in 8 or so families, small-sized nodosariids in a dozen or so genera, and variable numbers of epistominids, ophthalminids, spirrilinids, and turrilinids. There is high (< 100) species and high (<50) generic diversity, patchy specimen representation, and low species communality between stratigraphically successive samples. The fauna is accompanied by radiolarians, calcispherulids, aptychi, Saccocoma, and largely continues in the Early Cretaceous. Coeval shallow-marine (neritic) Jurassic assemblages have a much more limited representation of agglutinated taxa. Miliammina, Trocholina, Patellina, Paalzowella, Citharina, Tristix, and large Ammobaculites and Ammomarginulina may be exclusive of this niche, which in general contains larger and more sculptured forms. At Site 534,18 taxa group in 3 stratigraphically successive assemblages. The co-occurrence of Conorboidesparaspis, Gaudryina heersumensis, Textularia hauesleri, Trocholina nodulosa, and Globuligerina aff. oxfordiana in Core 110, although possibly transported in part, has no oceanic correlative at other sites, which agrees with the interpretation that this Oxfordian assemblage geomagnetically correlates to M-25, not penetrated at other DSDP sites. The co-occurrence of Lenticulina quenstedti and Epistomina aff. uhligi at DSDP Sites 534, 391, 105, and 367 may be a Kimmeridgian event; it correlates to M-22 to M-19. The co-occurrence of Dorothia praehauteriviana and Lenticulina nodosa at Sites 534, 391, 101, 105, 370, and 416 can be used to correlate late Valanginian strata. Multiple biostratigraphic comparison at Site 534, Cores 127 to 91, shows Oxfordian-Kimmeridgian-Tithonian stage assignments to be 1 to 5 cores apart.

Foraminifera and microfacies of the type-Priabonian

Abstract: The Priabonian is generally recognized and accepted as a stage name for the uppermost Eocene. The name is derived from the small village ofPriabona in the North Italian province of Vicenza (fig. 1). Since the underlying and overlying stages of the idealized chronostratigraphic scale are based on sections in completely different sedimentation areas in northwest Europe which are remote from each other and from Priabona, the correlation between the type sections, especially at the Eocene-Oligocene boundary has been a subject of much discussion. The predominantly carbonate facies of the Priabonian deposits contain abundant larger foraminifera, and were therefore of great interest to paleontologists at the beginning of the 20th century. Unfortunately the groups represented belong to poorly defined lineages without distinct or sufficiently well-known evolutionary trends. In addition, the scarcity of planktonic organisms means that the type Priabonian is not very promising as a basis for establishing modern biostratigraphic correlations. The primary object of this study is to provide an illustrated record of the smaller foraminifera, both benthonic and planktonic. The widest possible range of habitats was obtained by investigating the contents of three sections: the Buco della Rana section, thought to lie close to the Late Eocene shallow carbonate platform; the off-shore Bressana section; and the Priabona section, paleogeographically situated in an intermediate position on the slope between platform and off-shore area. An additional study has been carried out involving microfacies analysis of the carbonates ~nd quantitative investigations of the benthonic faunas from intercalated marls. The purpose of this study was to obtain a better appreciation of the environments of the deposition and a correct biostratigraphic correlation of the three sections. The original intention was to give a thorough account of biometrical data on the larger foraminifera, but this had to be restricted to a detailed study of certain assemblages of the Discocydinidae.