Benthic Foraminiferal Tests Research Articles

Factors influencing recent benthic foraminifera distribution on the Guadiana shelf (Southwestern Iberia)

Benthic foraminiferal assemblages in 24 sediment surface samples collected at water depths ranging from 9 to 103 m on the continental shelf off Guadiana River were analysed, leading to the identification of a total of 270 species. Cluster analyses performed on species with a relative abundance higher than 5% led to the identification of four assemblages. The shallowest assemblage, down to 12 m water depth, is represented by Ammonia beccarii, Asterigerinata mamila, Eggerelloides scaber, Mississipina concentrica, Planorbulina mediterranensis, Elphidium crispum and Quinqueloculina laevigata. A second assemblage between 12 and 40 m water depth is characterised by Bulimina elongata, Cribrononion gerthi and Nonion fabum. The assemblage between 40 and 95 m water depth is characterised by Bolivina dilatata, Epistominella vitrea, Bulimina aculeata, Bolivina ordinaria, Spiroloxostoma croarae and Nonionella iridea. Finally, below a depth of 95 m on the upper outer shelf, an assemblage exists characterised by Brizalina spathulata, Bulimina marginata, Cassidulina minuta, Brizalina subaenariensis, Cassidulina laevigata and Uvigerina peregrina. The spatial distribution of assemblages is closely associated with sea-bottom sedimentary environments and bathymetry. The number of benthic foraminiferal tests, and the distribution of several nearshore species within the two shallowest assemblages are clearly influenced by the outflow of the Guadiana Estuary and by local hydrodynamic conditions. The deeper water assemblages, on the other hand, were found to be more related to low levels of tidal energy, low oxygen environments associated to fine-grained sediments, and cold-water filaments related to seasonal upwelling.

The Cretaceous‐Tertiary extinction: Modeling carbon flux and ecological response

It is widely recognized that a significant negative excursion in carbon isotopic (δ13C) differences between planktic and benthic foraminiferal tests occurred at the Cretaceous‐Tertiary (K‐T) boundary. We applied parametric and nonparametric breakpoint tests and statistical comparisons of different recovery models to assess the timing and pattern of recovery from this negative excursion at South Atlantic Deep Sea Drilling Project (DSDP) Site 528 and equatorial Pacific DSDP Site 577. Our results indicate a two‐stage recovery with an initial recovery to an intermediate state of planktic‐to‐benthic δ13C differences followed by a discontinuous shift to a final state with planktic‐to‐benthic δ13C differences similar to preextinction values. The final discontinuous shift in both the Pacific and Atlantic Ocean sites occurred several million years after the K‐T collapse of planktic‐to‐benthic δ13C differences. Both the first and second stages of recovery are best described by damped exponential relaxations. The pattern and timing of this carbon cycle recovery may have been contingent on the occurrence of key biological events.

Relationship between surface-water temperature and ice-sheet expansion during the middle Miocene

A three-fold expansion of the Antarctic ice sheet at 13.60, 12.82, and 11.60 Ma has been inferred from δ 18O maxima analyzed in planktonic and benthic foraminiferal tests, although accompanying changes in sea surface temperature have not been detailed. We present estimated changes in middle Miocene surface-water temperatures based on analysis of δ 18O in planktonic foraminifera collected at mid-latitude Deep Sea Drilling Project sites in the North Atlantic and South Pacific oceans. We also identify periods of ice-sheet growth based on comparisons of benthic and planktonic foraminiferal δ 18O values. Our results indicate: (1) a distinct cooling of the sea surface from 13.6 to 13.5 Ma immediately following a peak in ice volume at 13.6 Ma, (2) a cooling of the sea surface during a period of increasing ice volume from 13.2 to 13.0 Ma, and (3) a development of the Antarctic ice sheet during a period of cooling of the sea surface centered at 11.6 Ma.

Glacial–interglacial deep-water changes in the NW Pacific inferred from single foraminiferal δ 18O and δ 13C

Oxygen and carbon isotope values of single benthic foraminiferal tests in a core from the Shatsky Rise, NW Pacific Ocean, show greater intra-horizon variance during the Holocene than during the Last Glacial Maximum (LGM). This greater variance is caused by the introduction of glacial specimens some 20 cm upward from their original deposition layer due to bioturbation. In contrast, foraminiferal populations belonging to glacial layers do not include Holocene specimens. The difference in direction of bioturbation greatly modifies climate information in horizons formed during and after deglacial events. After omitting glacial specimens from Holocene sediments, the glacial–interglacial difference in δ 18O suggests that Pacific deep-water temperature changed by 2.4–3.8°C at the most. The δ 13C values suggest that nutrient concentration was higher during the LGM than the Holocene. The glacial deep North Pacific Ocean apparently was influenced by cold deep waters of southern origin.

Holocene Sedimentation History in the Southern Novaya Zemlya Trench

It is shown that sediments accumulated in the Southern Novaya Zemlya Trench at both deglaciation and marine stages. Permanent sea ice sheet existed during the deglaciation, and glacier meltwater was intensely delivered to the bottom layer. Along with the dominant sediment supply from the Southern Island of Novaya Zemlya, southern continental sources also played a noticeable role at that stage. Seasonal sea ice freezing led to the formation of cold brines at the marine stage. Like paleoproductivity, these processes were irregular. Dissolution of calcareous benthic foraminiferal tests considerably intensified after about 7 ka BP owing to a stronger Atlantic water advection into the Western Arctic and consequent increase in paleoproductivity, whereas the relative role of southern sedimentary provenances decreased. Sedimentation rates were constant (45 cm/ka) during the entire marine stage.

Foraminiferal and molluscan evidence for the Holocene marine history of two breached maar lakes, Auckland, New Zealand

Drillhole records of fossil Foraminifera and Mollusca, together with sparse tephra age control, document similar Holocene marine histories of two of Auckland's breached maars—Pukaki Lagoon, Manukau Harbour, and Onepoto Lagoon, Waitemata Harbour. Following eruption, both maars slowly accumulated carbonaceous mud in freshwater lakes, until they were breached by rising sea level in the early Holocene (c. 8100 cal. yr at Onepoto, c. 7600 cal. yr at Pukaki). Following breaching, both became saltwater tidal lagoons with silled, subtidal basins rapidly accumulating marine mud as the underlying sediment compacted. Onepoto Lagoon may have had deeper water than Pukaki, because it was colonised by a foraminiferal fauna (Bolivina, Bulimina, Buliminella, Spiroloxostoma) that prefers quiet, dysoxic bottom conditions. Both fossil groups identify where the lagoons shallowed from subtidal to low tidal depths. This occurs c. 15 m downhole (6900 cal. yr) in Pukaki and c. 9.5 m downhole in Onepoto, after sea‐level rise had levelled off at about its present height (7000 cal. yr). Marine mud sedimentation slowed in the intertidal, accumulating largely in response to 12 m and 5 m compaction of the maar fill, respectively. Subtidal and low tidal fringe foraminiferal faunas of both lagoons are characterised by Ammonia‐Haynesina associations, whereas intertidal faunas above mean low water are dominated (>90%) by Ammonia. Pukaki Lagoon foraminiferal faunas differ from Onepoto by their higher subtidal diversity of benthic foraminiferal tests and the presence of planktic tests in the subtidal section. These differences are inferred to relate to the significantly more exposed conditions outside the entrance to Manukau Harbour, where juvenile benthic tests were lifted into suspension and, together with the planktics, carried by the strong tidal currents up the harbour channels into Pukaki Lagoon. These introduced tests settled out of suspension in the quiet subtidal waters and accumulated in the sediment. Once Pukaki Lagoon had been filled with mud to intertidal depths, most introduced tests were apparently flushed away by the outgoing tides and did not accumulate. The presence in the Onepoto sequence (9.8–8.7 m) of the gastropods Micrelenchus huttonii and Notoacmea helmsi f. scapha indicate that Zostera seagrass once grew in the lagoon at around spring low tide level.

Morphological abnormalities of foraminiferal tests in Brazilian environments: comparison between polluted and non-polluted areas

We investigated morphological abnormalities of Recent benthic foraminiferal tests in paralic environments of Brazil from two estuaries (Rio Guaraú and Rio Una located in the tropical forest) which are not affected by human activities in comparison to one polluted estuary (Baixada Santista), and one hypersaline lagoon (Araruama). The highest percentage of abnormal tests occurred in Rio Una (29%) and was caused by decalcification/recalcification processes resulting from natural periodical acidification. In the Rio Guaraú, percentages of abnormal tests reached 10%. The strong hydrodynamics in this estuary induced damage in living foraminiferal tests and the shape of the tests resulting from the regeneration of a damaged chamber, was often abnormal. In the lagoon of Araruama, percentages of abnormal tests reached 24%. Here, hypersalinity and strong salinity variations seem to perturb the test construction of foraminifers. In the most polluted estuary (Baixada Santista), lower percentages of abnormal tests occurred (0–7% with only one station reaching 12%). In this paralic environment, it is difficult to distinguish between the effect of natural stress and anthropogenic impact. Our study shows that higher percentages of abnormal tests occur in non-polluted areas than in polluted areas. Thus, the relative abundance of abnormal tests used as a bio-indicator of pollution in paralic environments, which are subject to strong natural stress, must be handled with care. Nevertheless, the relative abundance of abnormal tests is a useful proxy for the reconstruction of paleoecological changes in stressed paleoenvironments.

Anatomy of a Modern Coral Reef Flat: A Recorder of Storms and Uplift in the Late Holocene

ABSTRACT Cores from Kabira Reef, Ishigaki Island, southwest Japan, reveal the internal structure and temporal changes in sedimentary process of a complete coral reef flat. The reef crest caught up with sea level at about 4000 yr BP. Since then, it expanded oceanward and the reef pavement has grown landward. The backreef structure is composed of bioclasts derived from the reef framework. Of all the bioclasts, corals and coralline algae are most abundant. Coral fragments coarser than -3.0 o have dominated the backreef sediments since about 2000 yr BP. Benthic foraminiferal tests first occurred at about 4000 yr BP, and their abundance increased significantly starting around 2000 yr BP. Shallowing of the reef crest is also indicated by the presence of the shallow-water benthic Foraminifera Baculogypsina sphaerulata tests after 2000 yr BP. The date 2000 yr BP is coincident with tectonic uplift at Kabira Reef (Kawana 1989). We consider this uplift to have caused a relative sea-level fall that aided the deposition of coral fragments transported from the reef pavement by storms. The relative sea-level fall also caused subaerial exposure of the reef crest during low tides and the transition of reef-building organisms from corals to shallow-water species of benthic Foraminifera, resulting in a change noticeable in the constituents of backreef sediments. The results of this study suggest that the coral reef flat, and especially the backreef, can be a faithful recorder of relative sea-level changes.

Effect of organic carbon flux and dissolved oxygen on the benthic foraminiferal oxygen index (BFOI)

Variations in oceanic primary productivity, flux of organic carbon to the sediments, and dissolved-oxygen levels in the water column are thought to be important in the control of benthic foraminiferal test size, wall thickness, morphology, and species composition of assemblages by many foraminiferal paleontologists. Aspects of these processes should be reflected by the benthic foraminiferal oxygen index (BFOI) based on these foraminiferal characteristics. However, analyses indicate that the BFOI correlates most strongly with dissolved-oxygen levels in overlying water ( R 2=0.81), weakly with oceanic primary productivity ( R 2=0.55), and weakly with organic carbon flux to the sediments ( R 2=0.51). Although both dissolved oxygen and organic carbon flux are main controlling factors for benthic foraminiferal assemblages, the BFOI is a useful indicator extracted from benthic foraminiferal assemblages for estimating the condition of dissolved oxygen in Cretaceous and Cenozoic oceans.

Differential rates of benthic foraminiferal test production in surface and subsurface sediment habitats in the southern Adriatic Sea

Live communities and corresponding dead assemblages of benthic foraminifera recovered in box cores from the southern Adriatic Sea differ significantly with respect to the relative abundances of species and higher-order groups of foraminifera. Taphonomic destruction of disintegration-prone arenaceous species is held responsible for the observed strong reduction in relative abundance of arenaceous foraminifera in the dead assemblage. Systematic differences in live and dead relative abundances of calcareous and calcite-cemented arenaceous species may be due to differential rates of test production rather than selective taphonomic destruction. We observed that epifaunal or shallow-infaunal foraminifera are often overrepresented in the dead assemblage, compared to their relative number in the live community, whereas deeper-infaunal species tend to be underrepresented. On this basis we hypothesize that test production rate of benthic foraminiferal species may be related to their living depth in the sediment.

Production of lime mud by breakdown of foraminiferal tests

Many sources of lime mud have been discussed in the literature. However, foraminifers, despite their abundance and importance in recent as well as in ancient sediments, have been generally disregarded. This study is based on stereo microscope observations and on a detailed SEM study of modern carbonate sediments from New Caledonia and French Polynesia, and of foraminiferal tests. Many particles of the mud fraction have a morphology and composition similar to particles observed in benthic foraminiferal tests. The particles are calcitic or Mg-calcitic needles, or are columns composed of crystallites less than 0.5 μm in size. In tropical environments, foraminifers can produce as much as 1 kg m −2 of carbonate annually, and their tests may form more than 80% of the sediment. These observations show the genetic link from mud back to foraminiferal tests and show that at least a noticeable part of the carbonate mud can result from the breakdown of foraminiferal tests. The role of foraminifers for the production of calcitic mud may be as important as the role of Halimeda for the production of biogenic aragonite.

Global climatic forcing of deep-sea benthic foraminiferal test size during the past 120 m.y.

Research Article| June 01, 1998 Global climatic forcing of deep-sea benthic foraminiferal test size during the past 120 m.y. Kunio Kaiho Kunio Kaiho 1Institute of Geology and Paleontology, Tohoku University, Sendai 980, Japan Search for other works by this author on: GSW Google Scholar Author and Article Information Kunio Kaiho 1Institute of Geology and Paleontology, Tohoku University, Sendai 980, Japan Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1998) 26 (6): 491–494. https://doi.org/10.1130/0091-7613(1998)026<0491:GCFODS>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kunio Kaiho; Global climatic forcing of deep-sea benthic foraminiferal test size during the past 120 m.y.. Geology 1998;; 26 (6): 491–494. doi: https://doi.org/10.1130/0091-7613(1998)026<0491:GCFODS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Stratigraphic distribution of the maximum diameter of the largest deep-water (> 1500 m water depths) calcareous trochospiral benthic foraminiferal tests in samples representing the past 120 m.y. shows that average values of the maximum diameter have doubled since Early Cretaceous time. Fluctuations in test size show six minima and six maxima. It is significant that the fluctuations correspond to changes in global climate and in deep-water dissolved oxygen conditions. This latter synchronism indicates that deep-sea foraminiferal test size was likely controlled by fluctuations in the level of dissolved oxygen or related factors in the deep ocean caused by global climatic changes. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Foraminiferal associations in the upper Waitemata Harbour, Auckland, New Zealand

Census data on 68 benthic foraminiferal tests in 56 seafloor sediment samples from the upper Waitemata Harbour, Auckland, New Zealand (36° 50' S, 174° 40' E) are analysed by Cluster Analysis. The faunal samples, taken from extreme high tide to 8 m depth, and from strongly brackish to normal marine salinities, are grouped into 7 associations. Characterising species of each association are found by calculating Association Scores for each species, based on its mean abundance, relative abundance, fidelity, persistence, and dominance within each association. The foraminiferal associations are: JE, Jadammina macrescens‐Elphidium excavatum f. clavata – high tidal, sandy mud, in salt meadow and dwarf mangrove swamp, with near normal marine salinity; Tn, Trochammina inflata – around mean high water springs in salt marsh and salt meadow, with variable salinity; M, Miliammina fusca – subtidal channels and intertidal mud banks, mangrove swamp, and salt marsh with reduced salinity; H, Haplophragmoides wilberti – above mean high water, in salt meadow and salt marsh, with slightly reduced salinity; Tr, Trochamminita salsa – intertidal sandy mud banks at head of estuary, with lowest salinity; AM, Ammonia beccarii‐Miliammina fusca – intertidal and shallow subtidal mud fiats and channels, with near normal marine to slightly reduced salinity; A, Ammonia beccarii – intertidal and subtidal (to 8 m+ depth) muddy sand, with near normal marine to slightly reduced salinity. In the cluster analysis dendrogram of samples, the first‐order division produces a three‐way split of: (1) near‐normal marine salinity agglutinated associations (JE,Tn); (2) low‐salinity, agglutinated associations (M,H,Tr); and (3) near‐normal marine salinity, calcareous associations (AM,A). The dominant foraminiferal species are grouped by cluster analysis into five species associations; these correlate closely with the sample associations. There is an overall trend of increasing species diversity from brackish to saline and from intertidal to subtidal. This study supports earlier conclusions that salinity and tidal exposure are the two most influential factors in determining foraminiferal distribution patterns in sheltered tidal harbours and estuaries. A common species in the near‐normal salinity subtidal channels, Siphogenerina striata, may have been introduced into the harbour with foreign shipping.

Net Sand Transport Direction in a Tidal Inlet, using Foraminiferal Tests as Natural Tracers

The relationship between the flux of exotic benthic foraminiferal tests (i.e. tests which are supplied from open-sea sources alone) in a tidal inlet and that of bulk sediment was analysed, which can be expressed as two first-order linear equations. According to this relationship, in order to determine net sediment transport directions in the entrance, the test concentration in surficial sediments of the tidal basin can be compared against a ‘critical level’. The critical level is determined for the conditions that no net transport of bulk sediment is present within the entrance. If the observed concentration (averaged over the tidal basin) is higher than the simulated critical level, then the net sediment transport is directed to landward. This method is applied to the analysis of net sand transport at Christchurch Harbour, a tidal inlet system located in southern England. In this investigation, concentrations of exotic foraminiferal tests in the surficial sediments of the tidal basin and ebb tidal delta area were obtained from the analysis of sea-bed sediment samples. A series of probable critical levels were calculated based upon the data sets with regard to: (1) sediment discharge from the rivers; (2) magnitude of sediment discharge within the entrance during the ebb; (3) the test concentration outside the harbour; (4) the thickness of the moving layer; and (5) two parameters associated with dispersive processes. The results show that the concentration in the tidal basin sediment is higher than a number of simulated critical concentrations for representative cases. Consequently, the high level of the concentration of exotic benthic foraminiferal tests within the harbour should be explained as a result of landward net transport of sands within the entrance.

Fossil indicators of nutrient levels. 1: Eutrophication and climate change

Abstract Both phosphorus and nitrogen are elements essential to life. Availability of these biolimiting nutrients therefore exerts a major control on the carbon cycle through ocean productivity, bringing about changes in ocean-atmosphere chemistry and climate. This review begins with a brief account of the biological importance of phosphorus and nitrate to the cell, and introduces current terminology relating to the interlinked carbon-nutrient cycles in the oceans. Nitrate-limited, eutrophic ecosystems are associated with modern upwelling zones, characterized by high rates of delivery of new phosphorus, high rates of new primary production and export production. Fossil indicators include high accumulation rates of biogenic silica, apatite, baryte and organic matter, plus non-spinose, smaller planktonic foraminifera. Examples from biomineral chemistry include indications of high Ba/Ca, high Cd/Ca and increased differences between δ 13 C in planktonic and benthic foraminiferal test calcite. Such eutrophic indicators are shown to have peaked during glacial phases in the Quaternary, supporting a model in which Milankovitch-related reductions in solar isolation influenced the availability of nutrients, increasing primary productivity and lowering the levels of atmospheric carbon dioxide.

Computer analysis of benthic foraminiferal associations in a tidal New Zealand inlet

Abstract. Census data on benthic foraminiferal tests in 45 surface sediment samples from Pauatahanui Inlet, Wellington, New Zealand, are analysed by Correspondence Analysis and Non-Hierarchical classification techniques. The faunas are grouped into 7 associations: (A) Trochamminita irregularis/Miliammina fusca - at high tide level in a small tidal creek at the limits of salt water influence; (B) Trochammina inflata/Jadammina macrescens - in an extreme high tidal pool, close to the mouth of a small stream; (C) Miliammina fusca/Haplophragmoides wilberti/Trochammina inflata - intertidal and shallow subtidal (to 0.6 m depth), muddy sand over a large area in the upper reaches of the inlet, where most freshwater runoff enters; (D) Elphidium excavatum/Miliammina fusca - intertidal muddy sand associated with shelly beaches on the fringe of association C; (E) Ammonia beccarii/Haynesina depressula - in a wide variety of intertidal and shallow subtidal (to 3 m depth) sediments that form a belt between the more brackish associations (A–D) and the more normal salinity associations (F–G); (F) Bolivina cf. translucens/Textularia earlandi/Bolivina subexcavata - in mud to muddy, very fine sand in a shallow basin (1–2.5 m deep) in the middle of the inlet and in a small, sheltered backwater; (G) Elphidium charlottensis/Patellinella inconspicua/Quinqueloculina seminula - in sandy mud and muddy fine sand, intertidal to 10 m depth, in the mouth, entrance channel and adjacent outer and middle parts of the inlet, where a flush of normal salinity water enters during each tidal cycle.Using Canonical Correspondence Analysis, the factors most influential in determining the faunal distribution are, in decreasing importance: freshwater influence (salinity), exposure to the air during tidal cycles, proximity to the open sea, tidal current strength and percentage of mud in the substrate.

Sediments in Arctic sea ice: Implications for entrainment, transport and release

Despite the Arctic sea ice cover's recognized sensitivity to environmental change, the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood. Sea ice sediment inclusions were studied in the central Arctic Ocean during the Arctic 91 expedition and in the Laptev Sea (East Siberian Arctic Region Expedition 1992). Results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central Arctic Ocean. This study documents the regional distribution and composition of particle-laden ice, investigates and evaluates processes by which sediment is incorporated into the ice cover, and identifies transport paths and probable depositional centers for the released sediment. In April 1992, sea ice in the Laptev Sea was relatively clean. The sediment occasionally observed was distributed diffusely over the entire ice column, forming turbid ice. Observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment. In the central Arctic Ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes. The surface sediment accumulation in central Arctic multi-year sea ice exceeds by far the amounts observed in first-year ice from the Laptev Sea in April 1992. Sea ice sediments are generally fine grained, although coarse sediments and stones up to 5 cm in diameter are observed. Component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles. The biogenous components, namely shells of pelecypods and benthic foraminiferal tests, point to a shallow, benthic, marine source area. Apparently, sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing. Clay mineralogy of ice-rafted sediments provides information on potential source areas. A smectite maximum in sea ice sediment samples repeatedly occurred between 81°N and 83°N along the Arctic 91 transect, indicating a rather stable and narrow smectite rich ice drift stream of the Transpolar Drift. The smectite concentrations are comparable to those found in both Laptev Sea shelf sediments and anchor ice sediments, pointing to this sea as a potential source area for sea ice sediments. In the central Arctic Ocean sea ice clay mineralogy is significantly different from deep-sea clay mineral distribution patterns. The contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms.

Foraminiferal associations in Port Pegasus.Stewart Island, New Zealand

Abstract Census data on benthic foraminiferal tests in 56 seafloor sediment samples (high tide to 45 m depth; slightly brackish to normal marine) in Port Pegasus, south‐east Stewart Island, are analysed by cluster analysis. The faunal samples are grouped into six associations: A. Trifarina angulosa/Textularia proxispira/Miliolinella subrotundata—current‐swept passages and adjacent port; B. Notorotalia finlayi/Quinqueloculina delicatula/Nonionella flemingi—muddy fine sand at 22–30 m; C. Notorotalia zelandica/Elphidium novozealandicum—sheltered bays at 2.5–26 m; D. Rosalina bradyi—shallow subtidal amongst rocky reefs; E. Ammonia beccarii/Elphidium advenum depressulum/Haynesina depressula—0.5–6 m, sheltered bays and channels of Cooks Arm; F. Miliammina fusca—brackish, intertidal. In the entrance passages and exposed shelf (5–45 m depth) planktics comprise 15–30% of the total foraminiferal tests. Directly inside the passages in Port Pegasus, planktics comprise 30–65% of the fauna. These are dominated by small species that have been swept inshore by the predominant onshore swells and winds and carried into the port by strong tidal currents before settling out of suspension. The small, calcareous tests of benthic Cassidulina carinata and Trifarina angulosa also have distribution patterns consistent with some current transport into Port Pegasus.

温帯浅海域の炭酸塩堆積システム オーストラリア，ビクトリア州南部，第三系上部漸新統・下部中新統

With the purpose to envisage depositional systems of the temperate shelf carbonates with respect to sea level changes in a tectonically inactive region, eight sedimentary facies (facies A to H) are differentiated in a sedimentary sequence which occurs within the Jan Juc Formation (Late Oligocene to Early Miocene) along the sea cliff at Torquay area, southern Australia. The sequence ranges from 1 to 6m in thickness and over 3.5 m.y. in duration and their spatio-temporal relationship is restored.While the lower sequence boundary (25.5Ma) formed during a lowstand period varies basinward from karstified surface into a conformable surface within the heavily burrowed beds, the upper sequence boundary (22Ma) is traced along just below the well-indurated “Bird Rock Cap (BRC)”, which was deposited during the subsequent lowstand period.The sequence is unevenly divided into two packages of sediments by MFS (maximum flooding surface), which is traced within the interval less than 1m above the shell bed (facies E); the thick TST (transgressive systems tract) below MFS and the less developed HST (highstand systems tract) above it. The TST sediments of especially very fine packstone-mudstone of which fossils are largely made up of benthic foraminiferal tests and shell fragments (facies C) are best developed, onlapping onto the lower sequence boundary. The transgressive lag characterized with profusion of glauconitic minerals and shell fragments of gravel size (facies A) occurs basinward just above the sequence boundary. Sediments of the HST are mainly composed of fine packstone with bivalve fragments and benthic foraminiferal tests (facies F) and relatively thin as progradation took place only landward.It is concluded, therefore, that the most salient characteristic of the temperate carbonate depositional systems for a complete cycle of sea level change is low influx of sediments at early transgression and highstand periods, as evidenced by grain composition, especially abundance of glauconitic minerals, and difference in thickness between the TST and HST.

Vent activity in a subduction area (Nankai wedge): The foraminiferal test records

We have collected 41 sediment samples from the depths of about 2000 m and 4000 m in the Nankai Trough area using the submersibleNautile. Study of these samples has enabled recognition of two main preservation states of planktonic and benthic foraminiferal tests: dissolution in all the samples and superimposed encrustation in some of them. The distributional pattern of planktonic foraminifera reveals a strong rate of dissolution of the tests. Among the benthic foraminifers, the aragonitic speciesHoeglundina elegans shows, below 2000 m, a corrosion of test surfaces, removing parts of growth layers, and breakage of last chambers. On the basis of pore water chemistry the high rates of dissolution are related to unusual aragonite undersaturation in pore water at the sediment-water interface and to expulsion of pore water in open sea water. Furthermore, a peculiar etching of the whole test ofH. elegans and encrusted calcitic tests are observed, but only in the samples collected near fluid venting manifestations (clams, worms, and “shell concretions”), suggesting a possible relationship between diagenesis and fluids.