Foraminiferal Content Research Articles

Benthic foraminiferal assemblages from the eastern Weddell Sea between 68 and 73°S: Distribution, ecology and fossilization potential

Surface sediment samples taken with a vented ☐ corer from the eastern Weddell Sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content. The live fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Based on the dead assemblages, potential fossil assemblages were calculated to facilitate the analogy with late Neogene core material. Five distinct live assemblages inhabit the continental margin today. Six dead assemblages and five potential fossil assemblages, respectively, correspond to these biocoenoses. A predominantly calcareous live fauna dominated by Trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope. Below this, on the upper slope down to 2000 m water depth, the predominantly calcareous Bulimina aculeata assemblage coincides with the core of warm (>0°C) Weddell Deep Water and with fine and more organic-rich sediments. These calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment, which depends largely on the grain size distribution of the sediment and the fluxes of organic matter. Therefore, a still calcareous T. angulosa-dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope, whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by Martinottiella nodulosa, the characteristic arenaceous fossil remnant of the former predominantly calcareous live B. aculeata fauna. On a continental terrace between 2500 and 3500 m water depth Cribrostomoides subglobosus dominates the live fauna, but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by Oridorsalis umbonatus and Epistominella exigua comprises the dead assemblage and the potential fossil assemblage, respectively. On the lower continental slope, between the carbonate lysocline (3500 m) and the carbonate compensation depth (4000 m), tests of Nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna, which is associated with the lower part of the Antarctic Bottom Water (AABW). This corroborates earlier investigations suggesting a relationship between the carbonate-corrosiveness of water masses and the distribution of N. umbonifer. This is important for inferring paleo-routes and estimates of paleo-production rates of AABW during the Neogene.

Foraminiferal stratigraphy of Quaternary deposits in boring no. 51.12 Anholt, Kattegat

Material from a 229 m deep boring on the island of Anholt in the central part of the Kattegat has been stratigraphically analysed on the basis of its foraminiferal content. Due to the lack of casing in the main part of the bore hole, only very few core samples and some samples from the drilling bit were not contaminated. The results of the foraminiferal analyses have, therefore, to be treated with some reservation. The boring did not penetrate the Quaternary. The bottom 143 m of the boring represents deposits of pre-Eemian, possibly Saalian age. This interval seems to contain three marine interstadials, Anholt 1, 2 and 3, of which the upper interstadial is the warmest. Tills and glaciofluvial sediments are found between the marine sequences. The Eemian is represented by 13 m of marine deposits, which can be correlated with Eemian deposits known from other localities in the Vendsyssel-Kattegat region. They correspond to the Lower Turritella terebra Zone of the Skærumhede Series. The Early Weichselian and the lower part of the Middle Weichselian are missing, while the upper part of the Middle Weichselian, 32 m in all, is represented by marine deposits corresponding to foraminiferal zones known from the Vennebjerg Stadial and the Sandnes lnterstadial in the Vendsyssel-Kattegat region. These Middle Weichselian zones correspond to the upper part of the Portlandia arctica Zone of the Skærumhede Series. The non-marine sequence on top of these deposits is considered to be glacial, belonging to the main Weichselian glacial event. Holocene littoral sands and gravels terminate the Quaternary sequence at Anholt.

Recent and fossil benthic foraminifera and late cenozoic palaeobathymetry of Seram, eastern Indonesia

Analyses of the benthic foraminiferal content of two middle Pliocene-Pleistocene sections on the Island Seram showed the species composition to remain more or less constant throughout both sections. A palaeodepth of 400 to 1100 m is concluded, based on quantitative correlation of the late Cenozoic benthic foraminiferal associations with the bathymetric distribution of modern benthic foraminifera in 35 selected box-core top samples from the Australian-Irian Jaya continental margin. The depth-positions of maximum positive Z-score values of selected autochtonous species and their overlapping depth-ranges allow for a more precise interpretation falling within the depth-interval of 600 to 900 m. The autochtonous fossil species are tolerant to oxygen depletion. Laminated silty-clayey intervals within the sections, lacking bioturbation, also suggest low-oxygen bottom conditions. High P/B ratios indicate enhanced productivity in the surface waters, implying a high trophic level.

Quaternary forminiferal stratigraphy in boring 81/29 from the central North Sea

A 140.2 m deep boring (BH 81/29) from the central North Sea (British sector) has been investigated for its foraminiferal content. Fourteen assemblage zones are identified, and these are correlated with other records from the North Sea region. The stratigraphical interpretation of BH 81/29 is supported by palaeomagnetic data and by amino acid dates and thermoluminescence dates from the same boring. Foraminiferal zones 14 to 8, from the bottom of the core, have been referred to the Early Pleistocene. Zones 7 to 4, which occur above the Bruhnes/Matuyama boundary, seem to belonged in the Middle Pleistocene, and zones 3 to 1 are referred to the Late Pleistocene. A characteristic feature of the present sequence is that a major part of the Quaternary record seems to be missing. As is also known from other areas of the North Sea, interglacial deposits are especially badly represented.

A Late Saalian, Eemian and Weichselian marine sequence at Nørre Lyngby, Vendsyssel, Denmark

A 120 m thick marine Quaternary sequence resting on Upper Cretaceous chalk at Nørre Lyngby has been stratigraphically analysed on the basis of its foraminiferal content. The foraminiferal zones in the Nørre Lyngby boring are compared with corresponding zones from borings and outcrops in adjacent areas in Vendsyssel and Kattegat, and a general zonation covering the whole area is proposed. The lower part of the marine sequence at Nørre Lyngby represents deposits of pre‐Eemian, possibly Saalian, and Eemian age. The Early Weichselian seems to be missing, while most of the Middle and Late Weichselian foraminiferal zones known from Vendsyssel occur. The foraminiferal zones and the corresponding macrofossil zones are correlated with the oxygen isotope stratigraphy. A cross‐section through deposits from the Saalian‐Eemian‐Weichselian marine basin in North Jutland and the Kattegat illustrates the development of the basin through this period of time. The centre of basin subsidence shifted from the southwest in the pre‐Eemian to the northeast in the Eemian, and remained there throughout the Weichselian.

Storm-generated, episodic sediment movements off Kahe Point, Oahu, Hawaii

The area off Kahe Point, Oahu, Hawaii, has been the focus of recent oceanographic research in preparation for a large-scale Ocean Thermal Energy Conversion (OTEC) Project. Underwater instrument arrays moored to the bottom in this area were damaged, shifted or lost during Hurricane Iwa in 1982. Four underwater telephone cables located at greater depths were severed during the same period. SeaMARC II images show that most of the sea floor in this area is represented by light gray tones. Cores collected from this smooth sediment cover contain thick sequences of hemipelagic silt and clay. Darker acoustic reflection patterns trend downslope across this light gray background. Cores containing coarse sands and gravels and displaced shallow benthic foraminifera were collected from rough bottom represented by these patterns. The pattern configurations, sediment types within them and their benthic foraminiferal content indicate that these darker tones represent downslope sediment flow. Telephone cables were damaged and instrument arrays moved during Hurricane Iwa in places and along trajectories coincident with the orientation of the dark tones.

The distribution of living benthic foraminifera on the continental slope and rise off southwest Norway

Surface sediment samples taken by ☐ corer from 45 stations on the Norwegian continental margin and in the Norway Basin have been investigated for their benthic foraminiferal content. Unlike previous studies, the living benthic foraminiferal fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Factor analysis of both the living and dead faunal data reveals six living species assemblages and five corresponding dead assemblages. The additional living assemblage is characterized by the arenaceous species Cribrostomoides subglobosum that dominates between 1400 and 2000 m water depth, but is rare in the dead faunal data. Trifarina angulosa and, to a lesser extent, Cibicides lobatulus characterize the shallowest foraminiferal assemblage from 200 to 600 m water depth, where it is associated with strong bottom currents and warm, saline Atlantic water of the North Atlantic Drift. On the slope between 600 and 1200 m water depth, the Melonis zaandami Species Assemblage dominates, particularly in areas characterized today by rapid sedimentation of terrigeneous material. Between 1000 and 1400 m depth, where the slope is covered by fine grained, organic-rich, terrigeneous mud, the living foraminiferal assemblage is characterized by Cassidulina teretis and Pullenia bulloides. Below 1400 m, three foraminiferal assemblages are found: C. subglobosum is found from 1400 to 2000 m, Cibicidoides wuellerstorfi and Epistominella exigua predominantly live from 2000 to 3000 m water depth, and below 3000 m, Oridorsalis umbonatus and Triloculina frigida dominate the fauna. All of the Elphidium excavatum tests found in this study and the Cassidulina reniforme tests found above 500 m water depth were found to be reworked. Analysis of the sediment grain-size distribution and the organic carbon content in surface samples from the deepest stations suggest that the abundance of C. wuellerstorfi and E. exigua is positively correlated to relatively coarse (caused by planktic foraminifera) and organic-rich sediments, whereas high frequencies of O. umbonatus and T. frigida coincide with low organic carbon content. We suggest that C. wuellerstorfi is adapted to deep-sea environments with relatively high food supply, tolerating relatively low interstitial water oxygen content, whereas O. umbonatus may tolerate lower food supply prefering well-oxygenated interstitial waters.

Foraminiferal Paleoenvironments and Biostratigraphy of Eocene Nanjemoy Formation, Virginia and Maryland: ABSTRACT

Foraminiferal and sedimentologic data from 80 spot samples collected in Virginia and Maryland were used to investigate the paleoenvironments and biostratigraphy of the lower Eocene Nanjemoy Formation. The predominant lithology of the Nanjemoy Formation is variably glauconitic fossiliferous muddy sands, with foraminiferal abundance decreasing up section. The sediments of the lower Potapaco member are typically fine to medium-grained muddy sands containing abundant lignite and sparse glauconite. The upper Woodstock member is characterized by fine to coarse-grained sands with a decreased mud content and increased glauconite abundance. Distributions of individual foraminiferal taxa, planktonic-benthic ratios, foraminiferal suborder ratios, and species diversity patterns were used to determine variations in the Nanjemoy paleoenvironment throughout the lower Eocene Salisbury embayment. Planktonic foraminifera place the samples sections within established biostratigraphic schemes. Supplemental evidence of paleoenvironmental variations was obtained from grain size and composition data of all samples collected. Cluster and canonical variate analyses were used to investigate further similarities and differences in the foraminiferal content between samples, locations, and members. End_of_Article - Last_Page 314------------

Foraminiferal stratigraphy in a marine Eemian­Weichselian sequence at Apholm, North Jutland

Undisturbed core material is investigated for the first time from a marine Quaternary sequence through the Eemian of North Jutland. Core samples were examined from 86 m-190 m depth in a 202.6 m deep boring at Apholm. The marine sequence from that interval was subdivided into 4 biozones based on its foraminiferal content. Zone AP3 (190-140 m) contains boreal and boreal-lusitanian faunas indicating a water depth of at least 60-100 m. This zone is referred to the Eemian Interglacial. The Late Saatian/Eemian transition is identified at 190.2 m depth (AP4). The faunas of zone AP2 (140-113 m) record the onset of a major deterioration in climate and a considerable shallowing of the marine environment. The climate is then seen to fluctuate between arctic and boreal-arctic in zone APl (113 m to at least 86 m). This indicates the succeeding stadia! and interstadial periods. Zones AP2 and APl are referred to the Early and Middle Weichselian. The foraminiferal zones at Apholm are compared with the marine sequence at Skrerumhede. In addition, an attempt is made to relate these zones to the oxygen isotope chronology and to the Late Quaternary climatic regimes of the Norwegian Sea.

Foraminiferal Biostratigraphy and Paleoenvironments of Eastover Formation (Late Miocene), Virginia: ABSTRACT

Foraminifera from 50 samples taken from the Eastover Formation (Miocene) in Virginia are used in a study of biostratigraphy and paleoecology. The Eastover Formation contains two members: the lower Claremont Manor Member, a clayey, silty, poorly sorted, fine-grained sand which contains abundant foraminifera; and the upper Cobham Bay Member, a well-sorted, shelly, fine-grained sand that contains less abundant foraminifera. Planktonic species are used to establish a biochronology of the Eastover, while benthic species are used to interpret paleoecology, using the distribution of modern foraminifera as a basis. Evidence of changes in environments through time and varying sea margins is searched for by examination of samples taken from vertical sections and samples taken from different geographic locations within the study area. Additional evidence of paleoenvironments is gained by a grain size analysis of sediments from the formation. Synthesis of this information allows for reconstruction of the geologic history of the Eastover Formation in terms of environments changing through time and space. Cluster analysis and canonical variate analysis are used to clarify differences in foraminiferal content between and within the two members and to identify the taxa which cause such differences. Analysis of this type is helpful in revealing any foraminiferal assemblage zones present as well as quantifying data derived from the study. End_of_Article - Last_Page 481------------

The Middle Eocene-Oligocene of the Northern Hafit Area, South of Al Ain City (United Arab Emirates)

The measurement, field description and study of the foraminife-ral content of the Paleogene rocks exposed in the area enable to recognize three formations and several time stratigraphie units and lacunes of sedimentation. The formations are from base to top : the Hafit Formation (including three members, belonging to the Middle Eocene), the Senaiya Formation (including five members, ranging in age from latest Middle Eocene to Early Oligocene) and the A1 Jaww Formation (including two members of Middle Oligocene age). The relations of the major structures recognized in the geologic map with the unconformities (detected by both field observations and studies on the stratigraphical distribution of Foraminifera) enables to detect four periods of tectonic activity during the Paleogene. It seems that the Hafit and A1 Jaww Formations has been laid down under dry climatic conditions, while the Senaiya Formation reflects less arid climates.

Reworked Hantkenina Specimens at Little Stave Creek, Alabama: ABSTRACT

ABSTRACT The Eocene-Oligocene boundary in Mississippi and Alabama has been traditionally placed between the Member of the Yazoo Formation and the overlying Red Bluff Formation (or its carbonate facies equivalent, the Bumpnose Formation). Consequently, the presence of Eocene planktonic foraminifers in the Red Bluff and Bumpnose has long been attributed to reworking. To test the validity of this hypothesis, samples were collected on both sides of the boundary from the upper Shubuta and Bumpnose units at Little Stave Creek, Alabama, and were examined for both calcareous nannofossil and planktonic foraminiferal content. The calcereous nannofossil assemblage, preserved in the matrix from inside handpicked specimens of Hantkenina from both units, was demonstrably older than the calcareous nannofossil assemblage from the surrounding sediment. Thus, at least some of the Hantkenina specimens in both the Shubuta and Bumpnose are indeed reworked, which not only confirms the original hypothesis regarding reworking within the Red Bluff and Bumpnose, but also indicates that the last occurrence of Hantkenina, the Shubuta-Bumpnose contact, and the Eocene-Oligocene boundary in the U.S. Gulf Coast may not be equivalent.

Foraminiferal zonation of a boring in Quaternary deposits of the northern North Sea

The foraminiferal content of samples from a 122 m deep borehole in the Statfjord Field of the northern North Sea permitted a biostratigraphical subdivision of the sequence into 11 units. The paleoecology of these units is discussed. Most of them reflect High-Arctic ice age conditions, whereas two of them are of interstadial character. Distinctly ameliorated assemblages occur 20 m below sea floor. They correlate with late Statfjord Interglacial assemblages from a previously described boring and probably originate from the end of the Eemian. An attempt has been made to correlate the units of the present boring with published deep sea oxygen isotope stages.

Coexistence of deep- and shallow-water foraminiferal faunas off Panama City, Florida

Benthic box core sampling along a transect off Panama City, Florida, in the vicinity of the DeSoto Canyon, from 37-m to 200-m depths, were run throughout the Bureau of Land Management's Outer Continental Shelf environmental assessment program for the Mississippi-Alabama-Florida (MAFLA) area from 1974 through 1978. Seasonal samples were taken and analyzed for benthic distribution, abundance, diversity, and faunal affinities. The most striking feature brought out by foraminiferal analyses was the mixture of foraminifera from different depth zones. Species normally found in abundance only at depths of > 100 m in adjacent areas were living at all shallower depths, including 37 m. Coexisting with the deeper assemblage were all of the species normally encountered at the shallow depths. Species diversity, normally showing a progressional increase from inner to outer shelf, either remained constant or decreased due to the decrease of shallow-water species with depth. Along with this mixed assemblage, there was a planktonic foraminiferal content in the shallowest assemblage of as much as 25%. Normally, planktonic percentage of similar water depths is 0%. Seasonality had minor effects on the assemblages. The planktonic content is attributed to Loop Current water providing open-Gulf water to the inner shelf. Because the Loop Current is intermittent, the consistently high percentages of deeper-water species on the inner shelf must be attributed to up-welling currents providing cooler, deeper water to the inner shelf. However, since this deeper water did not restrict survival of shallow-water species, multiple factors must be considered for controlling benthic foraminiferal distribution.

Pleistocene foraminifera from Botany Bay, New South Wales

Unconsolidated sediments from a borehole in Botany Bay have been analyzed for their foraminiferal content. Faunas from between 41 and 54 m below sea level are interpreted as Pleistocene in age. The foraminiferal assemblage from 54 m indicates marine conditions of moderately deep water (25–30 m), and a climate warmer than at present. The higher assemblages indicate a more brackish environment The foraminifera, belonging to 123 species in 67 genera, are tabulated and 24 are discussed and illustrated. Three species, Oolina bifidocostata, Fissurina alatoquadrata and Elphidium botaniensis and one subpecies, Quinqueloculina affinis atrata, are described as new.

INTERPRETAÇÃO ECOLÓGICA DOS FORAMINÍFEROS DE SEDIMENTOS MODERNOS DA BAÍA DE SEPETIBA E ADJACÊNCIAS, RIO DE JANEIRO

In Sepetiba bay (State of Rio de Janeiro), a semi-confined, 305 km2 salt-water body, the present sedimentation is essentially elastic. From these sedimentary deposits, 92 samples have been collected and analysed which have allowed us to investigate the following parameters: benthonic foraminifera / planktonic foraminifera ratios, physical conditions of the foraminifera (size, wall thickness and abrasion degree), and the diatom content of the samples. Six dominant species of foraminifera have been identified in the studied area: Ammonia beccarii Line in thirty-eight samples, Buliminella elegantissima Orbigny in seventeen samples, Textularia sp. in fourteen samples, Bulimina marginata Orbigny ii, two samples, Reophax sp. and Arenoparrella mexicana Kornfeld in one sample. Thus, three principal biofacies and three less important biofacies are characterized by foraminiferal content of the sediments. These results confirm the importance of foraminiferal synecological studies in understanding water circulation dynamics and sedimentary dispersion on a regional level. Moreover, it has been verified that the water-oxygen content of the ecosystem is reflected by the foraminiferal content of the sediments.

Nearshore Glacial-Marine Sedimentation; Preliminary Modeling Based on Pliocene-Pleistocene Deposits of Puget Lowlands: ABSTRACT

Environmental interpretations based on combined sedimentologic and micropaleontologic analyses together with field relations have enabled preliminary modeling of processes of nearshore glacial-marine sedimentation in the Puget Sound region (Washington and British Columbia). Although these processes are active today in the Arctic and Antarctic, ice cover makes direct observations of them difficult. Therefore, uplifted Pliocene-Pleistocene deposits were examined, using various criteria for the recognition of similar deposits in the ancient record. Forty-six whole or partial sections from the Puget Lowlands have been measured, described, and sampled, and over 200 samples have been analyzed for foraminiferal content. These data, in conjunction with detailed textural (settling tube) analyses and available radiocarbon dates from the area, have enabled the delineation of sedimentary environments and their associated facies. Modeling is based on the interaction of such parameters as thermal regime of the ice sheet, eustatic sea-level fluctuations, circulation patterns as delineated by the microfaunas, and changes in bathymetry resulting from isostatic loading and rebound and from regional tectonics. Thermal regime of the ice appears to be the major controlling factor, determining both the kinds of sediments deposited and the extent to which marine processes are able to act on them. Microfaunas show strong evidence of the mixing of a restricted shallow-water ice-shelf fauna with mid-shelf and outer-shelf forms which must be explained by any subsequent models. Glaciotectonic structures appear to be an important consideration for interpreting these sequences and may possibly be used to explain some of the pr sent problems with regional stratigraphic correlations. End_of_Article - Last_Page 434------------

Quaternary sedimentary environments in comprida Island, state of São Paulo, Brazil

The coastal plain between the towns of Cananéia and Iguape is very important as it contains the most extensive Quaternary coastal sedimentation in the State of São Paulo, Brazil. Comprida Island, the most prominent physiographic feature in this geological context, is essentially formed of shallow marine sands. Sedimentological analysis made it possible to characterize the texture and mineralogy of 126 samples of sediments from the different sub-environments of Comprida Island. Grain size analysis of the sands, treated by the SAHU method (1964), indicates high-energy and low-viscosity deposition in beach, shallow marine and eolian environments. Morphometric and heavy-mineral studies suggest that Holocene sands are derived from the Cananéia Formation (Pleistocene), the Precambrian Crystalline Complex, and the Upper Precambrian Açungui Group. The combined foraminiferal content of 26 of the samples consists of twenty-six species belonging to twenty-one genera, where Ammonia beccarii (Linné) and Nonionella atlantica (Cushman) are the dominant species. Data on these micro-organisms emphasize the importance of foraminifera in the interpretation of beach zone dynamics and show the necessity of considering the relations of these assemblages to the pattern of circulation of water masses and to such biological controls as the ecological succession of benthonic communities.

Winnowing of Recent and Late Quaternary Deep-Sea Sediments: Colombia Basin, Caribbean Sea

ABSTRACT Sediments of the Colombia Basin, Caribbean Sea, contain evidence of current winnowing. Although bottom photographs reveal a relatively tranquil bottom over most of the basin, current smoothing of the seafloor is observed on and adjacent to the Hess and Beata Escarpments. Current scour is observed at one location on the Hess Escarpment. The proportion of foraminiferal, coccolith, and clay components in 52 surface sediment samples suggests that fine particles (including coccolith carbonate) are being sorted and removed. The foraminifera to total CaCO3 ratio (F/C) is highest on and adjacent to the major escarpments and reflects the increased foraminiferal content relative to total CaCO3 caused by partial removal of the fine fraction coccolith carbonate. The increased currents associated with the escarpments are caused by streamlining and acceleration of water masses as they pass around the obstructions. The lack of erosional bed forms as revealed by bottom photographs and absence of fractionation towards larger foraminifera shows that only fine particles are being sorted and removed. The erosion a sociated with current smoothing of the bottom is probably responsible for the observed winnowing. Sediment cores from winnowed areas (F/C > .60) have irregular carbonate curves, more small-scale CaCO3 variation, hiatuses, and mixed faunas when compared to cores from unwinnowed areas (F/C < .50). Thus, areas near escarpments which are being winnowed today have been winnowed throughout the past 150,000 years. Therefore, the geographic extent and intensity of winnowing must be known to interpret properly sediment cores in these areas.

Foraminifera in Eemian deposits at Stensigmose, southern Jutland

The foraminiferal content of 57 samples from two sections in interglacial Eemian deposits of the cliff at Stensigmose, Broagerland in southern Jutland, have been investigated. Saalian glaciofluvial deposits and Eemian freshwater clay, underlying the marine sequence, were examined in order to check a contamination by reworked specimens from older deposits. The foraminiferal assemblages indicate that the marine sediments were deposited in shallow water. As the lower part of the strata was deposited, the water depth was increasing, but later on it was constantly decreasing. The lower part of the marine sequence was deposited during rising temperature conditions, reaching probably a little higher than today. Salinity was low throughout the deposition of these sediments, but higher than that of the present Baltic Sea.