Planktonic Foraminiferal Assemblages Research Articles

Sedimentation and climate-induced sediments on Feni Ridge, Northeast Atlantic Ocean

Feni Ridge has been studied in detail in the area between 54 and 56°N and 12 and 16°W by using high-resolution profiling, water column sampling with transmissometer and CTD, and by piston and box core sampling. The crest of Feni Ridge is absent in the north of the study area, but on passing towards the south it begins to take shape and to increase in height; its distance from the Rockall slope also increases towards the south. On the lower southeastern flank a secondary ridge crest has locally developed, and sediment waves along the flanks have amplitudes of up to 45 m. The highest and steepest waves are found in the south, the waves in the north being somewhat lower. Bottom nepheloid layers of 175 m near the foot of Rockall Plateau and 125 m near the crest are attributed to a Norwegian Sea Overflow Water current with a core at 2100 m. Bottom nepheloid layers of 75–100 m on the lower flanks of the ridge are thought to have been caused by Northeast Atlantic Deep Water. Piston cores reflect alternations of glacial and interglacial periods. Interglacials have a high carbonate and C org content, a positive Eu anomaly and negative Ce anomaly, and a low Rb La ratio. They are dominated by a subpolar and transitional foraminiferal assemblage. Glacials show a low carbonate and C org content, a reduced Eu anomaly and a high Rb La ratio, suggesting increasingly continental sediment sources. These deposits are dominated by a polar planktonic foraminiferal assemblage characterized by N. pachyderma (s) and G. quinqueloba. Sedimentation rates reflect differential deposition. At crestal station NA 87-25 rates are 17.1 cm/k.y. for stage 1, 14.6 cm/k.y. for stage 2, 3.4 cm/k.y. for stage 3 and 5.4 cm/k.y. for stage 4. Stage 5a–e has a mean sedimentation rate of 6.1 cm/k.y. Over the last 125 k.y. the development of Feni Ridge has taken place under a relatively low energy current regime.

Lamprophyric volcanism of Cenozoic age on the Sierra Leone Rise: Implications for regional tectonics and the stratigraphic time scale

Igneous and sedimentary rocks have been recovered by dredging the upper slopes of Krause Seamount, a feature lying on the Sierra Leone Rise near 9°N, 20°W in the eastern Equatorial Atlantic. The igneous samples consist of lamprophyres and an ankaramite, which are rarely encountered in an oceanic setting. Associated with these rocks are breccias made up of lamprophyric fragments set in a lithified calcareous matrix containing a rich planktonic foraminiferal assemblage of early Eocene (Ypresian Subzone P8a) age. Whole-rock K-Ar dating of the igneous samples proved unsuccessful owing to advanced alteration and consequent argon loss. However, within the breccias are numerous, fresh crystal clasts of Ti-rich amphibole, pyroxene and biotite which have compositions closely similar to phenocrysts observed in the lamprophyric rocks, suggesting that they are derived directly from them. K-Ar dating of separates of the three minerals yielded ages in the range 53.3–55.4 Ma. The concordant results provide a maximum age for the Ypresian Subzone P8a and are consistent with its position within recently established Cenozoic time scales. They indicate that Krause Seamount is appreciably younger than the adjacent Gambia and Sierra Leone Basins. In common with other occurrences of lamprophyric rocks in the oceans, those exposed on Krause Seamount are located in an area of old oceanic basement close to a large fracture zone which has been reactivated by late-stage volcanic activity. These relatively rare alkaline rocks may be generated by remelting of a volatile-rich metasomatized layer which is present in the upper mantle beneath Mesozoic ocean floor.

Upwelling signals at the northeastern Walvis Ridge during the past 500,000 years

Qualitative and quantitative analyses of planktonic foraminiferal assemblages from Deep Sea Drilling Project site 532 shed light on hydrographic changes over the Walvis Ridge during the past 500,000 years. From changes in distribution of foraminiferal assemblages, two major hydrographic regimes (coastal and geostrophic branches of the Benguela Current and the Angola Current) can be distinguished at site 532. It is suggested that the hydrographic situation on the northeastern Walvis Ridge was characterized by intensified upwelling and a westward expansion of the coastal upwelling cells during several global cooling pulses. During glacial stages 2–4, the middle part of stage 6, sporadically from the lower stage 8 through upper stage 10, and during stage 12, site 532 was located beneath the coastal branch of the Benguela Current because faunal distribution patterns indicate intensified upwelling. The Angola Current probably intruded the area of study during the lower stages 5, sporadically 6–8, and 11, as documented by the increased abundance of Neogloboquadrina dutertrei.

Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico

A relatively extended Oligocene pelagic sequence with good to medium recovery, drilled during DSDP Leg 77 in the Gulf of Mexico, yielded rich and well diversified planktonic foraminiferal faunas. Planktonic foraminifera recorded in Hole 538A span the interval from Zone P19 through P22. Evolutionary lineages were observed among the globoquadrinids, the globigernitids, and the “ Globigerina” ciperoensis and Globigerinoides primordius groups. Quantitative analysis of planktonic foraminiferal assemblages shows that faunas fluctuate in abundance and species diversity throughout the sequence. A few of these fluctuations that could be related to selective dissolution are mainly confined to the early-mid Oligocene. A climatic curve was constructed using a warmer indicators, Turborotalia pseudoampliapertura, Globoquadrina tripartita, Dentoglobigerina globularis, Dentoglobigerina baroemoenensis, “Globigerina” ciperoensis and Globigerinoides groups, and Cassigerinella chipolensis; and as cooler indicators, Catapsydrax spp., Globorotaloides spp., Subbotina angiporoides group, Globigerina s. str., and the tenuitellids. Three major intervals are identifiable in the climatic curve: Interval 1 (lower) up to Zone P20 predominantly cooler; Interval 2 (intermediate) up to the upper part of Zone P21a with warm and cool fluctuations; and Interval 3 (upper), warmer, with large positive peak, due to abundant “ G” angulisuturalis, at the beginning of Zone P21b with recooling midway in Zone P22. In intervals 1 and 2 planktonic foraminiferal faunas are dominated by temperate forms. Interpretation of planktonic foraminiferal data suggests that cooler water conditions characterize the early-mid Oligocene; during the mid Oligocene (most of Zone P21a) water masses exhibit peculiar characteristics transitional to the warmer waters prevailing during the late Oligocene. Warmer conditions were not definitely settled in Zone P22, however, as indicated by the cooler episode following the warmest peak. These climatic trends are inconsistent with those inferred from oxygen isotopes except at small scale. In fact, oxygen isotope values for Oligocene Atlantic Ocean are too heavy (thus too cool) in comparison with the high abundance and diversity of warm taxa, especially in Zone P22. When values are lighter (warmer), as in Zone P19, abundance and diversity of warm indices are too low. To explain such a cool isotope values in presence of highly diversified and abundant warm planktonic foraminifera, we suggest (1) that the oxygen isotope ratio used for estimating Oligocene paleotemperatures might be 1/%. heavier than Eocene values and further increased for the late Oligocene. This hypothesis implies the presence of a relatively extended ice cap in Antarctica in the early and mid Oligocene, and probably an increase in ice volume during the late Oligocene; (2) heavier isotope values might be related to an increase in salinity, or (3) by a combination of both ice cap and increase in salinity.

High-Resolution Biostratigraphy: Providing a Framework for Correlating Reservoir Sands

Correlating individual sands is critical to field development and reservoir management. High-resolution biostratigraphy can provide this correlation by supplementing standard paleotops with local bioevents, recognized in thin hemipelagic units. These events provide an additional framework for calibrating and refining well logs and seismic record sections. This high-resolution data set can be used to reduce the risk in development drilling. Detailed studies in the United States Gulf of Mexico and Indonesian Neogene reveal local and semiregional signals between those regional extinctions. These signals, or events, are caused by physical and chemical fluctuations in the oceanic water masses through time. Planktonic foraminiferal and calcareous nannofossil assemblages imprint these events onto the accumulating sediments and yield a reproducible signal that can be interpreted and correlated. Identifying and documenting these events is the principle behind high resolution biostratigraphy. When integrated with electric logs and transferred to seismic sections, such signals produce a more refined correlation and subdivision of sediment packages. This paper discusses data generation, integration, interpretation and display using specific computer software. The authors present three field studies where local high-resolution biostratigraphic zonations have permitted a finer subdivision of sediment packages and correlations of sands.

Age and origin of Cretaceous planktonic foraminifers from limestone of the Franciscan Complex near Laytonville, California

Detailed planktonic foraminiferal biostratigraphy from eight measured sections of Cretaceous limestone near Laytonville, California, indicates a composite sequence that extends in age from late Albian to early Turonian. The sequence contains seven biozones and two subzones based on the first and last appearance datums of planktonic foraminifers examined in thin section. Unequivocal biostratigraphic facing directions show four sections are right side up and four are reversed, and confirm the stratigraphic polarity employed in the paleomagnetic studies of Alvarez et al. (1980) and Tarduno et al. (1986). Temporal changes in the microfauna deviate from the global trend. Early Albian through early Cenomanian planktonic foraminiferal assemblages dominated by opportunistic, eurytopic species of Hedbergella and Globigerinelloides give way in the late Cenomanian to assemblages containing more abundant larger, heavily ornamented stenotopic species of Rotalipora and Praeglobotruncana typical of stratified Tethyan oceans. Radiolarian replacement chert increases slightly in the late Albian to early Cenomanian part of the Laytonville sequence and then decreases in the late Cenomanian and early Turonian. Benthic foraminifers show a similar decrease in abundance and diversity. We propose that this complex of biogenic and lithogenic patterns records transit via oceanic plate motion from a depositional site in the southern part of the paleoequatorial zone of high productivity, characterized by pronounced upwelling and habitat destabilization, perhaps augmented by topographic upwelling, to the central part of the equatorial zone dominated by biogenic calcite deposition. Our model of northward transit from below the equator supports the paleomagnetic determinations of Alvarez et al. (1980) and Tarduno et al. (1986). Arrival at the paleoequator coincided with the onset of stratification in the world ocean during the middle Cenomanian, indicated by the diversification of the more complex rotaliporids, and the subsequent intensification of oxygen‐depleted intermediate waters in the latest Cenomanian to early Turonian. Two pulses in heterohelicid abundance signify the onset or intensification of an oxygen‐minimum layer if Cretaceous heterohelicids occupied habitats analagous to Tertiary biserial heterohelicids. The first pulse beginning in the middle Cenomanian Rotalipora reicheli Zone may indicate a minor expansion of the oxygen‐minimum zone or regional upwelling due to transit of the site beneath the equatorial divergence. The second pulse in the late Cenomanian Dicarinella algeriana Subzone signals the onset of upwelling of deeper oceanic water masses that characterized the succeeding Whiteinella archaeocretacea Zone. Organic‐rich black shales typical of the Whiteinella archaeocretacea Zone are missing at Laytonville, although samples do contain the low‐diversity, partially dissolved, planktonic assemblages that characterize this zone. The lack of black shales suggests that deposition occurred at depths greater than the oxygen‐depleted intermediate water depths or alternately indicates paleoceanographic conditions unique to the Pacific.

Contribution of foraminifera to the study of Recent sedimentation in the Gulf of Lions (western Mediterranean Sea)

The spatio-temporal evolution of benthic and planktonic foraminiferal assemblages during the Holocene is studied on the margin of the Gulf of Lions, which is characterized by the indentation of several canyons. The analysis of modern thanatocenoses, sampled in various physiographical areas of four canyons (Lacaze-Duthiers, Petit-Rhoˆne, Marseille and Aude), reveals the importance of geomorphological and hydrologic factors on faunal composition. There is an evident link between the distribution of associations and the topography of the area: larger specimens ( Globorotalia inflata, G. truncatulinoides, Orbulina universa, Uvigerina mediterranea and Cibicidoides sp.) always decrease in abundance in the canyon axis, whereas smaller forms (such as globigerinids) follow the opposite trend, as a result of lateral transports. An increase of species diversity and the occurrence of littoral species in the canyon axis show evidence of channelled sedimentological transport; some littoral specimens with large and black or rusted tests originate from sediments reworked by progradation of the canyon. A comparative study of foraminiferal distribution in six box cores, obtained by Flucha box corers, contributes to the understanding of sedimentary processes in various parts of the Lacaze-Duthiers Canyon during the Holocene. The influence of geomorphological and hydrodynamic factors on planktonic foraminiferal distribution hides the climatic record in the upper canyon, whereas in the upper fan the climatic trend of the Holocene is clearly detectable.

Quaternary planktonic foraminiferal assemblage zones of the northeast Gulf of Mexico, Colombia Basin (Caribbean Sea), and tropical Atlantic Ocean: Graphic correlation of microfossil and oxygen isotope datums

Sediments of Ocean Drilling Program's hole 625B (northeast Gulf of Mexico) represent a virtually continuous record of Pleistocene paleoceanographic development associated with the Florida Loop Current. Utilizing relative abundances of the Globorotalia menardii complex and G. inflata, supplemented by left‐ and right‐coiling varieties of G. truncatulinoides, we have subdivided the prezone W Pleistocene of core 625B into 17 subzones, resulting in an average duration of approximately 100,000 years per unit. This is substantially better resolution than for the Ericson and Wollin [1968] zones alone (average duration ∼300,000 years per unit). The subzones recognized in core 625B can be recognized in Eureka core E67‐135 (northeast Gulf of Mexico) and extended to cores 502B (Colombia Basin, Caribbean Sea) and V16‐205 (tropical Atlantic). Subzonal boundaries are largely coeval between sites based on graphic correlation of paleomagnetic, biostratigraphic, and oxygen isotope datums. The subzonation reveals relatively abrupt changes in sediment accumulation rate which probably decrease the signal to noise ratio in spectral analysis and tuning of oxygen isotope curves. In some cases, accumulation rate changes correspond to core breaks. Abundances of Globorotalia inflata and G. truncatulinoides are damped in the tropical cores (V16‐205 and 502B) but amplified in the subtropical Gulf of Mexico (625B), an observation which is consistent with previously published biogeographic models.

Neogene planktonic foraminifera and events in Japan

The warm-water constituents of successive Neogene planktonic foraminiferal assemblages in Japan are identified and expressed as percentages of the total planktonic fauna. By this means five major events have been recognized: (1) a marine temperature optimum in the earliest Middle Miocene (Zone N8b); (2)an abrupt cooling since early Middel Miocene time; (3) a rise in temperature culminating in latest Miocene to earliest Pliocene time (Zones N17b and N18); (4) an accelerated “evolutionary” event during the early Pliocene (Zone N19b–N21a); (5) a short warm episode in the early Pliocene (Zone N21a).

Late Quaternary paleoceanography of the South China Sea: Glacial‐interglacial contrasts in an enclosed basin

The sea surface paleotemperature of the South China Sea (SCS) is estimated quantitatively, based on the quantitative analysis of planktonic foraminiferal faunas recovered from piston cores V36‐06‐3, V36‐06‐5, and SO49‐KL8 on the northern continental slope. The results lead to a reconstruction of the history of paleocirculation patterns during the last 200,000 years. The postglacial and interglacial transbasinal circulation pattern was replaced by a semienclosed basin flow pattern during glacial episodes. Lowered sea level transformed the SCS into a semienclosed basin with the only passageway to the open ocean in its northeastern corner. The East Asian Monsoon, which governs circulation patterns in the SCS both today and during the late Quaternary, created both clockwise (summer) and counterclockwise (winter) surface gyres during glacials. The inflow of tropical surface water‐masses from both the Pacific and Indian oceans decreased or was completely cut off from this marginal sea, causing a greater decrease in glacial sea surface temperature than in the open ocean of the same latitude. Inferred increased influence of Pacific Temperate Waters and decreased influence of Tropical‐Subtropical Waters are confirmed by changes in the planktonic foraminiferal assemblages. Glacial‐interglacial fluctuation in sea surface temperature (SST) (6.8–9.3°C for winter and 2–3°C for summer), as well as the seasonality (4–6°C for postglacial and interglacials and 9–10°C for glacials), are much greater than the adjacent open western Pacific, reflecting the amplification of the climatic signal in the marginal sea.

Planktonic foraminifera in recent bottom sediments of the Flores, Lombok and Savu Basins, eastern Indonesia

The distribution of Recent planktonic Foraminifera in the surface sediments of the Flores, Lombok and Savu Basins has been studied, based on box-core samples obtained during the Snellius-II Expedition. The planktonic foraminiferal assemblages are different in the Flores Basin and the Lombok and Savu Basins, and the distribution of the most abundant species is discussed. In the Flores Basin Neogloboquadrina dutertrei is dominant followed by Globorotalia menardii, Pulleniatina obliquiloculata s.l., Hastigerina siphonifera and Globigerina bulloides. The Lombok and Savu Basins are characterized by the dominant species Globorotalia menardii, which is associated with Pulleniatina obliquiloculata, Globigerinoides ruber and Globorotalia tumida. These different distribution patterns and abundances of planktonic foraminiferal species are discussed in the light of differences in oceanography and dissolution effects (lysocline/CCD).

Assemblages de foraminifères planctoniques en Mer tyrrhénienne et en Mer Adriatique pendant les derniers 130 000 Ans. Implications Paléoécologiques

The planktonic foraminiferal assemblages found in three cores from the Tyrrhenian Sea and in one core from the Adriatic Sea provide a climatic sequence ranging from the last interglacial to the Holocene. The data have been treated by the Correspondence Factor Analysis method. We propose an interpretation of the three first factors: • - Factor I is thermal. Its influence is clearer in the Tyrrhenian Sea than in the Adriatic Sea where the warm maxima are always less important. • - Factor II probably depends on salinity. • - Factor III seems to be linked with an Atlantic water property and may reflect the influence of this water mass in the different Mediteranean areas. The alternating occurrence of Atlantic subtropical species (in interstadial periods) and of an Atlantic temperate form (at the beginning of the cooling periods) is interpreted as reflecting circulation changes in the Atlantic Ocean (gyre diameter, polar front location). In the Tyrrhenian Sea, the planktonic microfauna is very homogeneous in the different sectors during the Postglacial. However, during stage 5, there are some differences between southern and northern assemblages. This fact suggests that the circulation was different during these two warm periods. In the Adriatic Sea, we note a hydrological shift at about −25,000 yr B.P.

Estimates of sea surface temperature in the Coral Sea at the Last Glacial Maximum

The CLIMAP [1981] reconstruction of the Coral Sea found relatively little cooling (2°C) in the low latitudes (10°S) but a warming off Australia at about 25°S. The small low‐latitude changes are of interest because terrestrial pollen and snowline data from the New Guinea highlands imply that surface temperatures may have been 6° to 9°C colder at the last glacial maximum (LGM). The purpose of this paper is to evaluate these conclusions on the basis of additional core sites, new oxygen isotope stratigraphy, and new sea surface temperature (SST) estimates using the modern analog technique (MAT). In the northern Coral Sea, planktonic foraminifer assemblages consist of tropical‐subtropical species that show little change over the past 20 kyr. Quantitative estimates of SST using the modern analog technique (MAT) confirm the CLIMAP [1981] conclusion that little or no temperature change occurred in this tropical region at the LGM, thus reinforcing the conflict with terrestrial evidence. In the southern region (25°S), two cores indicate that foraminifer faunas became more subtropical at the LGM. The MAT estimates for the LGM are 3° to 4°C colder than modern, producing a steeper thermal gradient in the southern Coral Sea. These data remove the warm SST anomaly along the eastern coast of Australia and indicate that during the LGM, cool high‐ latitude waters were displaced northward along the coast of Australia into the southern Coral Sea.

Distributional pattern of planktonic foraminifers and pteropods in surface waters and top core sediments of the Red Sea, and adjacent areas controlled by the monsoonal regime and other ecological factors

Living planktonic foraminiferal and pteropod distribution patterns in the western Arabian Sea, Gulf of Aden and Red Sea, collected during two summer cruises (1984, 1985), reflect the hydrographical system that is mainly controlled by a combination of monsoonal winds and evaporation rates. Spinose species constitute the majority of the planktonic foraminiferal assemblages in the Red Sea during both monsoonal seasons. The non-spinose species Globorotalia menardii, Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, which are always abundant in the Arabian Sea, are present only during winter inflow. The intensity and duration of these inflowing surface currents control their distribution pattern. Stable oxygen isotope ratios show that G. menardii survives but ceases to grow north of Bab el Mandeb, while N. dutertrei continues to grow. Trends in the foraminiferal distribution in surface waters compare well with those of the sea floor, as far as larger specimens (>250 μm) are concerned, but differ for the small ones. Surface distribution patterns of small-sized specimens and juvenile/neanic stages of large-sized fully grown species do not correspond to those in the core top samples. The distribution pattern of living pteropods in the Red Sea is closely related to distinct water masses and corresponds to the distribution in top core sediments. Pteropods are absent in the sediments of the Gulf of Aden and the western Arabian Sea due to dissolution. Peak abundances of various pteropods and foraminifers indicate the presence of local upwelling processes in the Bab el Mandeb area. Determining these dynamics allows for the reconstruction of ancient oceanic environments and climatic interactions in the area.

Sedimentology of the Neogene to Modern glauconite-goethite-phosphate system : east australian continental margin between 29° and 32° south latitude. Le système sédimentaire glauconite-goethite-phosphate du Néogène à l'Actuel : la marge continentale orientale de l'Australie entre 29° et 32° de latitude sud

Outer shelf and upper slope environments (250 to 525 m) on the East Australian continental margin off northern New South Wales, represent an important iron-rich sediment province. The dominant (up to 30 9c) authigenic-diagenetic components are glauconite and associated goethite, with minor concentrations of carbonate fluorapatite (mean P₂O₅ content = 0.37 %) within a muddy foraminiferal fine sand. The outer shelf and shelf-slope break (250 to 425 m depth) contain a series of small scarp features interpreted to be outcrops of indurated subsurface units. Sedimentologic and biostratigraphic data from these features suggest that they are Miocene hardgrounds composed of ferruginous-phosphate pavements and gravels. Plank tonic foraminiferal assemblages in unconsolidated surface sediments overlying the hardgrounds range in age from late Pliocene through Holocene and are draped across the continental margin as a veneer covering older strata which only locally crop out. Relative concentrations of glauconite and goethite change downslope and downsection as follows. (1 ) Surface sediments at depths from 250 to 340 m are dominated by goethite with subordinant amounts of weathered glauconite grains. (2) Sediments underlying (1) and constituting the surface sediments from 340 to 465 m are dominated by glossy dark green glauconite with subordinant amounts of goethite. (3) Sediments underlying both of the above and constituting the surface sediments from water depths of 465 to 525 m are dominated by glossy dark green glauconite with subordinant concentrations of light green glauconite within foraminiferal tests. Glauconite forms within foraminiferal tests as light green grains and is subsequently altered to glossy dark green grains with accompanying dissolution of the tests. Above the shelf-slope break, dark green glauconite is altered to goethite within the surface sediment. Goethite occurs at the top of multiple depositional cycles in some sediments between 375 and 465 m depth, suggesting either periods of upper slope oxidation or off-shelf sediment transport during sea-level lowstands. Two types of phosphate occur within the sediments of outer shelf and upper slope. Type I (dark reddish-brown, ferruginous phosphate) is found in water depths from at least 200 to 425 m where it forms hardground pavements and associated nodules and lag gravels. Type I phosphates contain 7 9c to 12 9c P205, 10 % to 50 % Fe₂O₃, and are in radioactive equilibrium indicating uranium-series ages in excess of 800 ka (O'BRiENand Veeh, 1980 ; O'Brien et al., 1986). Type II (gray phosphate) occurs in water depths from 340 to 525 m as irregularly shaped nodules and internal molds within macrofossils in muddy sediments with unweathered light and dark green glauconite. Type II phosphates contain 4% to 19 9c P205, 2 9c to 4 9c Fe₂O₃, negligible goethite, and yield uranium-series ages that range from 250 ka to 2.5 ka (O'Brien and Veeh, 1980 ; O'Brien et ai, 1986).

The later Eocene transgressions in southern Australia

Correlations based mostly on planktonic foraminiferal assemblages indicate four continent-wide transgressions: two in the late Middle Eocene (high Zone PI2; near Zone P14/P15 boundary) and two in the Late Eocene (near top Zone P15; low Zone P17). The first (Wilson Bluff) is part of the Indo-Pacific Khirthar Transgression at the boundary between the Laramide and Himalayan global tectonic regimes; the Khirthar was an ‘immediate“ response to renewed seafloor spreading (geomagnetic Anomaly 19) after India/Asia collision. However, the later transgressions were more widespread in this region. Although data are patchy and correlations are somewhat strained, there is some evidence that transgressions fall between lowstands in the incomplete global curve and that they are coeval with isotopic and biological (oceanic, neritic, continental) evidence for warming. The later Eocene as a whole marks a significant intervening reversal of the global climatic deterioration that occurred across the Early/Middle Eocene and E...

Lower Eocene Benthic Foraminifera and Paleoenvironment of the Outer Vøring Plateau, Norwegian Sea (DSDP Site 338)

Analysis of early Eocene benthic foraminifers of DSDP Site 338 (Outer Voring Plateau, Norwegian Sea) revealed three benthic foraminiferal assemblage zones: a lower barren Zone; a middle Nodosariid Assemblage Zone, characterized by Midway-type benthic foraminifers; and an upper Vagulinopsis decorata Assemblage Zone, divided into a lower Pullenia quinqueloba Subzone and an upper Haplophragmoides Subzone. The V. decorata Assemblage Zone is also characterized by Midwaytype faunas, but benthic foraminiferal assemblages show an increasing proportion of deep water Velasco-type faunal elements. The fauna closely resembles age-equivalent benthic foraminiferal faunas from the North Atlantic (e.g. Rockall Plateau). From the poverty of planktonic foraminiferal assemblages and nannofloras it seems that similarities in benthic foraminiferal assemblages were probably not the result of an open marine connection across the Iceland-Faroe Ridge, but rather of migration through the epicontinental seas of NW Europe. The early Eocene subsidence history of Site 338 as inferred from benthic foraminiferal assemblages and lithostratigraphy confirms independent paleodepth estimates from backtracking and seismic stratigraphy and shows that this site has subsided during a maximum of 2.8 Ma from near sea level to upper bathyal depths. The maximum water depth must have been less than 500 m at the top of early Eocene and probably was in the order of 250 m.

A stratigraphic study of Late Quaternary sediments on the Vøring-Plateau, eastern Norwegian Sea

Four gravity cores from the Vøring Plateau, west of the Nordland coast in Northern Norway have been studied. About 250,000 yrs of continuous hemipelagic sedimentation is represented in the cores. This period has been divided into seven lithostratigraphic units and four planktonic foraminiferal assemblage zones. To improve the reliability and precision of the isotopic stratigraphy, a graphic comparison with several isotopic records previously described in the literature has been performed. A taxonomy of 36 isotopic events is established following Prell's ∗ ∗ Prell et al. (1986). technique. The majority of these events seem to be recognizable in the isotopic records from the Norwegian Sea. During the glacial stages, however, several local events are caused by influxes of isotopically light meltwater. Comparisons between the records indicate a general trend toward decreasing sedimentation rates with increasing distance from the continental margins for isotope stages 2, 3, 4 and 6. Only small variations in sedimentation rates are observed during stages 5 and 7. Comparisons with the land-based stratigraphy of Northwest Europe indicate that the main glacials and interglacials as well as the Fana and the Torvaldstad interstadials are recognizable in the marine sequences. Correlations to the Bølling and Allerød interstadials and the Younger Dryas stadial is obscured by a period of rapid influx of meltwater at about 15-14 Ka, followed by a period of high influx of clastic material.

Late pleistocene to recent sediment deposition in the central and western Mediterranean

Examination of the planktonic foraminiferal fauna in cores from the Mediterranean indicates that the present and probably the past populations do not reflect the water temperatures as in the Atlantic Ocean. Variation in the planktonic foraminiferal assemblage and the oxygen isotope values of some species of foraminifera during Late Würm to Recent times indicate changes in the water circulation pattern of the Mediterranean. The proportions of quartz and clay group minerals have an inverse relationship, quartz being more abundant during Würm times and clays during Post-Glacial and interglacial times. Calcite is essentially of biogenic origin, pyrite is found in sapropels and near stratigraphic breaks. Sapropel formation is attributed to high terrigenous and marine organic input sluggish circulation and high freshwater input from the Black Sea and the Nile. Initiation of sapropel conditions may have been triggered by the re-introduction of Atlantic water into the Mediterranean.

Antarctic marine temperatures: Late Campanian through Early Paleocene

An oxygen isotope paleotemperature study of benthic foraminifera from the upper Campanian through lower Paleocene section at Seymour Island, near the coast of Antarctica, was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation. The isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that Campanian through Paleocene high‐latitude shelf waters near Antarctica had temperatures between approximately 4.5° and 10.5°C. Temperatures during early and middle Maastrichtian time were slightly higher than those of either the late Campanian or late Maastrichtian. The inference of temperate climatic conditions in Antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera, as well as with published conclusions based upon paleobotanical evidence. The Maastrichtian and Campanian water temperatures at Seymour Island are similar to those inferred from published isotope ratios of Pacific Late Cretaceous benthic foraminifera from low latitudes, indicating that Campanian through early Paleocene deep ocean waters, at least in the Pacific and perhaps elsewhere as well, could have formed by sinking of surface waters in polar regions.