Planktonic Foraminiferal Faunas Research Articles

Planktonic foraminiferal turnover across the Cretaceous-Tertiary boundary in the Vajont valley (Southern Alps, northern Italy)

Planktonic foraminiferal analysis of the Erto section in the Vajont valley (Southern Alps, northern Italy) reveals a relatively complete succession across the Cretaceous–Tertiary (K–T) boundary. The turnover of planktonic foraminiferal fauna was studied for a stratigraphic interval spanning the Abathomphalus mayaroensisZone p.p., Pseudotextularia deformisZone, Guembelitria cretaceaZone, Parvularugoglobigerina eugubinaZone, Eglobigerina eobullioidesSubzone, and Parasubbotina pseudobulloidesZone p. p.The extinction of most large, ornate, late Maastrichtian species occurs below a black ‘boundary clay’ (2–4 cm thick); however, part of the Late Cretaceous species, mainly heterohelicidids and hedbergellids, were found over an interval of more than 100 cm above the boundary. Although a relatively high number of species occur for the last time in the main extinction phase, the abundance of these outgoing species is less than 20% of the total population; unkeeled or weakly keeled, simple-shaped forms (heterohelicids, globotruncanellids, hedbergellids) constitute the bulk of the planktonic foraminiferal population both in uppermost Maastrichtian and lowermost Danian beds. The first Tertiary species (‘ Globigerina’ minutulaand ‘ Globigerina’ fringa) appear just above the ‘boundary clay’; Parvularuglobigerina eugubinaoccurs a few centimeters above. A marked increase in abundance and diversity in the Tertiary planktonic foraminiferal population occurs at the base of the Eoglobigerina eobulloidesSubzone.

Late Quaternary palaeoceanography near Tasmania, southern Australia

Abstract This study of the palaeoceanographic record south of Australia is based on two cores taken from lower Circumpolar Deep Water depths: core E27-30, located south of Tasmania in water depth of 3552 m, to the north of the present location of the Subtropical Convergence, and core E55-6 from the continental margin off Victoria at 2346 m depth, in a region of very low surface productivity. A preliminary examination of planktonic foraminiferal faunas in core E27-30, located south of Tasmania, provides a record of movement of the Subtropical Convergence through the late Quaternary that is consistent with records elsewhere in the Southeast Indian Ocean. The Convergence has been located equatorward of its present position through much of the late Quaternary, with poleward excursions in the Holocene and at oxygen-isotope stage 5e. Benthic foraminiferal faunas contrast strongly in the two cores, despite their location at similar depths within the same water mass. Core E55-6 is largely dominated by deep infaunal taxa, while core E27-30 has a high proportion throughout of epifaunal taxa. The benthic foraminiferal fauna in core E27-30 is dominated by Epistominella exigua, known to feed directly on phytoplankton detritus in the modern deep-sea. Abundances of that species coincide with the presence of the Subtropical Convergence at or near the site, indicating that surface phytoplankton production has had a major influence on benthic productivity. Dissolution records in the two cores also differ markedly. Core E55-6 records a strong dissolution event in oxygen-isotope stage 4. The cause of the event is not clear, although it appears to be associated with increased productivity levels. This pronounced dissolution event is not evident in core E27-30, suggesting either the event is localised or that the record in core E27-30 has been overprinted by the Convergence. The extent to which the records in the two cores vary emphasises the influence of frontal structures on core records in this region and the need to take this into account when investigating Southern Ocean history.

Eemian and Early Weichselian (140–60 ka) Paleoceanography and paleoclimate in the Nordic Seas with comparisons to Holocene conditions

Paleoceanographic and paleoclimatic time series were extracted from Norwegian, Iceland, and Greenland Sea (the Nordic seas) sediment sequences covering the time intervals 60–140 ka and 0–15 ka on the basis of stable isotope stratigraphy, planktonic foraminiferal faunas, and sedimentological methods. The proxy temperature records from the Norwegian‐Iceland Sea display a number of high‐frequency and high‐amplitude variations within the last interglacial (the Eemian) indicating marked changes in heat flux at high northern latitudes. Eemian‐Holocene comparisons document that the climate of the Norwegian‐Iceland Sea in the last interglacial was less stable than that of the present interglacial and that the distribution of surface water masses in the Eemian differed from that of the Holocene. Within the Greenland Sea, uniform cold conditions prevailed throughout both interglacials. Cooling of the Nordic seas, as well as the initial growth of the surrounding ice sheets, began within the Eemian interval, before the main increase in global ice volume. Heat flux to the Nordic seas was significantly higher during the interglacials than at any time during the early Weichselian (60–113 ka), and no marked stadial‐interstadial changes in sea surface temperature and deep water ventilation are documented in the early Weichselian records, contrary to the pattern found in North Atlantic sediment records. However, fluctuations in planktonic foraminiferal content, planktonic δ13C, and ice rafting on suborbital timescales, mostly comparable in number and age to the stadial‐interstadial fluctuations in the Greenland ice cores, are demonstrated in our records. The ice‐rafted detritus records provide a more detailed account of ice sheet variability than previously known for the early Weichselian period and demonstrate that glaciers advanced to sea level somewhere around the Nordic seas several times during this interval.

Comparison of Imbrie‐Kipp Transfer Function and modern analog temperature estimates using sediment trap and core top foraminiferal faunas

We evaluate the reliability of statistical estimates of sea surface temperature (SST) derived from planktonic foraminiferal faunas using the modern analog method and the Imbrie‐Kipp method. Global core top faunas provide a calibration data set, while modern sediment trap faunas are used for validation. Linear regression of core top predicted SST against atlas SST generated slopes close to one for both methods. However, the Imbrie‐Kipp transfer function temperature estimates had an intercept 1.3°C warmer than modern analog estimates and 1.7°C warmer than recorded atlas SST. The RMS error for the core top data set using the modern analog method (1.5°C) was smaller than that of the Imbrie‐Kipp method (1.9°C). SST errors for the sediment trap faunas were not statistically different from those of the core top data set, regardless of method. Developing Imbrie‐Kipp transfer functions for limited regions reduced the RMS variability but introduced residual structure not present in the global Imbrie‐Kipp transfer function. Dissolution simulations with the sediment trap sample which generated the warmest SST residual for both methods suggests that the loss of delicate warm water foraminifera from midlatitude sediments may be the cause of this thermal error. We conclude that (1) the faunal structure of sediment trap and core top assemblages are similar; (2) both methods estimate SST reliably for modern foraminiferal flux assemblages, but the modern analog method exhibits less bias; and (3) both methods are relatively robust to samples with low communality but sensitive to selective faunal dissolution.

Abrupt hydrographic change in the Alboran Sea (western Mediterranean) around 8000 yrs BP

This paper discusses planktonic foraminiferal fauna results from the Alboran Sea, western Mediterranean. In this new record, as well as in previously published records, a rather abrupt faunal change occurs around 8000 BP, from dominance of Neogloboquadrina pachyderma (dextrally coiled) with Globigerina bulloides, to dominance of Globorotalia inflata with Globigerina bulloides. The paper argues that this change marks the onset around that time of more or less modern conditions with distinct geostrophic fronts separating the jet of Atlantic inflow from ambient Mediterranean waters. According to a previously published hydraulic control model for the Strait of Gibraltar with variable sea level, the inflow volume of Atlantic water around 8000 BP (sea level at about −30 m) may have amounted to a maximum of about 86% of its present value. Our reconstruction suggests, therefore, that the modern front-dominated conditions in the Alboran Sea prevail only when the inflow volume is at least 86% of the present volume, which should be confirmed in realistic models of the circulation through the Strait of Gibraltar and in the Alboran Sea.

Planktonic foraminiferal faunas across the Cretaceous-Tertiary succession of Mexico: Implications for the Cretaceous-Tertiary boundary problem

Four consecutive planktic foraminiferal faunas characterize the planktic transformation recorded from continuous Cretaceous-Tertiary boundary successions of Mexico; from older to younger, these are mayaroensis , aegyptiaca , relict, and cancellate. The mayaroensis fauna, containing the nominal taxon and lacking gansseri , is followed by the aegyptiaca fauna, characterized by the absence of mayaroensis , indicating that this taxon disappeared before the major extinction of Cretaceous Hedbergellacea. The relict (“small globigerinas”) fauna contains taxa whose wall structure and umbilical apparatuses are directly linked to Cretaceous Hedbergellacea rather than Tertiary Globigerinacea. The cancellate fauna represents the first appearance of true Tertiary forms. The mayaroensis and aegyptiaca faunas are found immediately below the spherulite and clastic units attributed to the asteroid impact in Yucatan. The relict fauna is found immediately above the clastic unit, whereas the cancellate fauna is usually found ∼30 cm above this unit. The stratigraphic positions of the four consecutive faunas indicate that (1) the faunal changes observed started before the physical features attributed to the impact, and (2) the major evolutionary planktic event, i.e., the appearance of the cancellate wall, is the only unequivocal feature that defines the entry of the Tertiary planktic foraminiferal fauna.

Fossil Foraminifera from four active mud volcanoes in the Gulf of Mexico

Samples were collected for foraminiferal studies by the Johnson Sea-Link I and II manned submersibles on the Louisiana continental slope. This paper documents that the mud, extruded onto the sea floor from depth by four mud volcanoes, ranges in age from Miocene to Pleistocene based on studies of the planktonic foraminiferal fauna. The vents are in water depths ranging from 300 to 690 m located in Garden Banks Block 382, Green Canyon Blocks 143 and 272, and Mississippi Canyon Block 929. Two mud volcanoes in GB 382 and MC 929 also have rich fossil foraminiferal microfaunas. We suggest that the extrusion of fossil sediments onto the sea floor during the Quaternary is a reasonable explanation for frequent occurrences of displaced fossil microfaunas encountered at depth in wells drilling on the flanks of salt diapirs in the slope environment. Results of this study have important implications for age dating subsurface sediments in bathyal locations.

Planktonic foraminiferal biostratigraphy and palaeoceanography of the Cretaceous-Tertiary boundary section at Bidart, south-west France

A planktonic foraminiferal biostratigraphy of the relatively complete Cretaceous-Tertiary (K/T) boundary section at Bidart, south-west France, is given. With the exception of Rugoglobigerina hexacamerata Brönnimann and Guembelitria cretacea (Cushman), all Cretaceous planktonic foraminifera became extinct at the K/T boundary. Thanetian age strata are for the first time reported from Bidart, and a significant hiatus representing 350-750 kyr I is detected at the Danian/Thanetian boundary. Population changes within the Maastrichtian planktonic foraminiferal faunas are generally similar to those of other K/T boundary sections but large 'globotruncanids' increase in numbers close the boundary, rather than decrease as elsewhere. This change in faunal composition 2.5 m below the boundary correlates with changes in lithology (from grey to red micrite) and 87 Sr/ 86Sr ratio, an increase in δO 18 and a decrease in δ 13C. This evidence suggests that the palaeoceanography of the Bidart region changed from a Tethyan to a North Atlantic dominated setting towards the end of the Cretaceous.

Eocene-Miocene high latitude biostratigraphy

Abstract Studies of high-latitude planktonic foraminiferal faunas indicate that certain biostratigraphic problems may be resolved by the application of bioevents among the three microperforate families, Guembelitriidae, Chiloguembelinidae and Tenuitellidae. With the aid of the scanning electron microscope, these small tests appear to be useful stratigraphic markers in the condensed sequences of deep-sea cores, where their evolution can be correlated with magnetostratigraphy. In the early-mid-Eocene, the Jenkinsina-Cassigerinelloita lineage assists the recognition of zones based on the larger, muricate Acarinina . Four zones are proposed in a revised lineage zonation of the tenuitellids, presented as a complementary biostratigraphic scheme for differentiating the Eocene-Oligocene boundary interval in high latitudes: (1) the Praetenuitella insolita Zone in the late Eocene; (2) the Tenuitella gemma Zone in the early Oligocene; (3) the Tenuitella munda Zone in the mid-Oligocene; (4) the Tenuitellinata angustiumbilicata Zone in the late Oligocene.

Paleontological evidence for early exposure of deep oceanic crust on the Vema Fracture Zone southern wall (Atlantic Ocean, 10°45'N)

We present the results of a paleontological study of samples collected during the Vemanaute cruise on the Vema Fracture Zone southern wall where an almost complete section of oceanic crust is exposed. The three studied samples are poorly lithified yellowish calcareous sediments lying horizontally over gabbros. They contain abundant, generally well-preserved, and relatively diverse tropical late Neogene calcareous nannofloras and planktonic foraminiferal faunas, and yield a few poorly preserved radiolarians. The estimated ages are 8.8–10 Ma; 5.6–6.4 Ma (late Miocene); 4.5–4.2 Ma (early Pliocene), derived from deepsea correlations between microfossil zonations and magnetic stratigraphy. Our results are compared to theoretical ages proposed for the crust in the surveyed area. This leads us to discuss the timing and location of mechanisms responsible for the exposure of the observed section and allows us to emphasize that early morphologies and structures may be preserved during the transform walls migration.

Late Quaternary Surface Circulation of the Southern Indian Ocean and its Relationship to Orbital Variations

The paleoceanographic history of the Southern Indian Ocean is reflected by the movement of two prominent dynamical features of the Southern Ocean: the Subtropical Convergence (STC) and the Antarctic Polar Front (APF). These fronts, and their associated sea surface temperature (SST) signatures, are well delineated by planktonic foraminiferal faunas in surface sediments of the southern Indian Ocean. Using a transect of piston cores between 42°S and 48°S at about 90°E, we have reconstructed the latitudinal distribution of planktonic foraminiferal faunas over the past 500,000 years. These faunal variations imply changes in the paleolatitudes of the STC and APF and the surface isotherms associated with the fronts. Stratigraphic and chronologic control is provided by δ18O, %CaCO3, and biostratigraphy. Our reconstruction indicates that the STC has been equatorward of its present position (∼40°S) for most of the past 500,000 years and has been poleward of that position for only four relatively brief (∼10,000‐year) intervals during that time. We estimate six equatorward excursions of the APF over the same period, with a maximum total range of about six degrees of latitude. The average paleo‐position of the APF is about 46°S, about 4°north of its present position (∼50°S). Ice‐rafted debris, another indicator of APF position, occurs as far north as 45°S during glacial intervals. Latitudinal gradients in SST show little glacial‐interglacial change between 42° and 48°S, suggesting that surface isotherms were displaced uniformly or that compression of SST gradients occurred outside the transect. Time series analyses of the SST records in this transect reveal statistically significant concentrations of variance in the primary orbital frequency bands. SST variations in these bands are coherent with orbital variations and with changes in δ18O. SST in the subantarctic Indian Ocean slightly precedes changes in δ18O occurring in the eccentricity, obliquity, and precession bands, and lag orbital variations in the obliquity and precession bands. These results place important constraints on possible mechanisms of interhemispheric climatic timing. The similarities in temporal patterns and timing among Southern Ocean SST, atmospheric CO2, and relative flux of North Atlantic Deep Water implicate atmospheric carbon dioxide and deep water circulation as possible interhemispheric pacing mechanisms.

Planktonic Foraminiferal Assemblage of the Yorktown Formation, Virginia, USA

Planktonic foraminifers from Coastal Plain deposits in southeastern Virginia provide biochronologic control and paleoceanographic information for the lectostratotype of the Yorktown Formation and type localities of its four members. Faunas recovered from six localities are consistent with faunas reported from the Yorktown in North Carolina and Yorktown correlatives (Duplin and Raysor Formations) from Georgia to North Carolina and support an age assignment between 3.0 and 4.0 Ma. Quantitative estimates of surface temperature based upon the planktonic foraminifer assemblages indicate winter conditions 3? to 5?C warmer than today and summer conditions essentially equivalent to today during Yorktown deposition. PURPOSE AND SCOPE The Yorktown Formation is an unconformity bounded package of fine grained sandy clays and shell marls exposed along the Atlantic Coastal Plain from Virginia to North Carolina. Originally thought to be Late Miocene in age, deposits now referred to as Yorktown Formation were placed in the Chesapeake Group with all other rocks of Miocene age between the Chesapeake Bay area and Florida by Dall and Harris (1892). The Yorktown Formation was originally described by Clark and Miller (1906). As redefined by Ward and Blackwelder (1980), the Yorktown Formation consists of four members: a basal Sunken Meadows Member, overlain by the Rushmere, Morgarts Beach and Moore House Members. The geographic distribution of these members in the mid-Atlantic Coastal Plain suggests three transgressive pulses. The first pulse is represented by the Sunken Meadows Member, the second pulse by the Rushmere and Morgarts Beach Members, and the third pulse by the Moore House Member (Ward and Strickland 1985). The Morgarts Beach-Rushmere transgression was the most extensive of the three pulses and deposited marine sediments directly on crystalline rocks over 130km inland of the present shoreline (Gibson 1983; Ward and Strickland 1985). Recent biostratigraphic studies focusing on marine ostracodes, planktonic foraminifers and calcareous nannofossils have firmly placed the Yorktown Formation in the Pliocene (Akers 1972; Hazel 1983; Gibson 1983; Snyder et al. 1983; Cronin et al. 1984). Most of this work has been done on the Yorktown at Lee Creek Mine, North Carolina, or correlative units to the south. Relatively little has been published on the planktonic foraminiferal faunas found in Virginia where the lectostratotype of the Yorktown Formation is at Rushmere, Virginia. This study was undertaken to provide biostratigraphic control from the northern outcrop area and assess the paleoceanographic/paleoclimatic significance of the planktonic foraminiferal faunas found in this region. We have analyzed a series of samples from six outcrops of the Yorktown, including the lectostratotype of the Yorktown Formation and type localities of the Moore House, Morgarts Beach, Rushmere and Sunken Meadows Members (text-figs. 1, 2). Semi-quantitative and quantitative analyses of these samples reveal important biostratigraphic and paleoclimatic information as well as documentation of the taxa that exist in this region. MATERIALS AND METHODS Twenty three samples were collected from six localities of the Yorktown Formation in southeastern Virginia (text-figs. 1, 2). Approximately 500 grams from each sample was washed through >850gim and >63gm sieves. The 850gm portion was discarded. The remaining 63gm fraction was transferred to filter TEXT-FIGURE 1 Map showing location of study area and Yorktown Formation localities investigated for planktonic foraminifers. micropaleontology, vol. 38, no. 1, pp. 75-86, pls. 1-3, text-figs. 1-6, table 1, 1992 75 This content downloaded from 157.55.39.127 on Sun, 26 Jun 2016 07:12:50 UTC All use subject to http://about.jstor.org/terms H. J. Dowsett and L B. Wiggs: Planktonicforaminiferal assemblage of the Yorktown Formation, Virginia, USA

Isotopic evidence for the depth stratification of fossil and recent globigerinina: A review

Stable isotopic evidence for the depth stratification of the planktonic foraminifera is collected and reviewed. The aim is to establish the validity of the hypothesis that keeled (Globorotaliid‐like) forms have consistently lived deep in the water column relative to unkeeled (Globigerinid‐like) forms during the history of the Globigerinina. General trends in the distribution of δ18O and δ 13C across morphotypic spectra are clear, and suggest that keeled globorotaliids were the deep‐dwelling foraminiferal component of planktonic foraminiferal faunas only in the Pleistocene and Holocene. Earlier in the Neogene the deep water dweller was the globoquadrinid form Globoquadrina venezuelana while during the Oligocene the deep water forms were members of the genus Catapsydrax. In the earlier Palaeogene, members of the globorotaliid‐like genera Morozovella and Acarinina were surface dwelling forms while the deep water. dwellers were members of the genus Subbptina. The data available for the mid‐Cretaceous suggest a surface water dwelling habit for the globigerinid‐like genus Hedbergella while representatives of the keeled genus Rotalipora apparently lived deeper in the water cojumn.

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.

A high‐resolution Late Quaternary upwelling record from the anoxic Cariaco Basin, Venezuela

Results are presented of a high‐resolution study of the planktonic foraminiferal faunas from two piston cores recovered from the Cariaco Basin in the southern Caribbean Sea. The Cariaco Basin is a small anoxic marine basin on the northern continental margin of Venezuela in an area today characterized by both seasonal trade wind‐induced upwelling and pronounced dry and wet seasons. Our data indicate that large changes in the intensity of upwelling, and hence trade wind strength, occurred in this region during the last glacial‐interglacial transition and throughout the Holocene. During the last glacial lowstand of sea level, the Cariaco Basin was effectively isolated from the open Caribbean along its northern margin by the then largely emergent Tortuga Bank. Oxic conditions existed in the deep Cariaco Basin at this time, and surface productivity was low. About 12,600 years ago, the abrupt initiation of strong upwelling over the basin and the onset of permanent anoxia in the deep waters are coincident with the rapid rise of sea level that accompanied the peak interval of meltwater discharge from the Laurentide Ice Sheet into the Gulf of Mexico. Strong upwelling between 12,600 and about 10,000 years ago may be related to intensified trade winds resulting, in part, from cooler sea surface temperatures in the Caribbean and Gulf of Mexico. After about 10,000 years ago, upwelling intensity was reduced, though highly variable. A preliminary frequency domain analysis of the Holocene portion of the Cariaco Basin time series suggests that solar forcing may explain a significant component of the century‐scale variability observed in the record of upwelling and trade wind strength.

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.

Kau Bay, Halmahera, a late quaternary palaeoenvironmental record of a poorly ventilated basin

Kau Bay is a small marine basin in between the two northern arms of the Island of Halmahera (Indonesia), separated from the adjacent Philippine Sea by a sill of 40 m deep. Microfossil and radiocarbon data of piston cores indicate that Kau Bay was a freshwater lake in Weichselian times. At 10 ka BP, the Bay became reconnected with the open ocean. Present-day deep water in Kau Bay is poorly ventilated because the sill limits water exchange with the adjacent ocean. Ventilation occurs through occasional inflow of denser oceanic water, but when this fails oxygen depleted conditions rapidly arise. The permanent presence of oxygen tolerant deep water benthic foraminifers over the past 10 ka indicates that dysoxic conditions prevalied and that anoxic conditions, as observed during the Snellius-I Expedition (May 1930), apparently existed for a short time only and left no trace that could be resolved with our time-resolution of 35 years. Slight and long-term variations in the degree of oxygen deficiency most likely are caused by long-term changes in the density of inflowing oceanic water, possibly in consequence of climatic oscillations. The homothermal surface water of Kau Bay shelters a low-diversity planktonic foraminiferal fauna of primarily shallow-dwelling species. This specific association extends back over the past 8 ka indicating that surface waters remained homothermal over much of the Holocene. Surface water productivity most likely changed with variations in river discharge.

Dinoflagellate cysts, sea level changes and planktonic foraminifers across the Cretaceous-Tertiary boundary at El Haria, northwest Tunisia

Dinoflagellate cysts and planktonic foraminifers have been studied from the Cretaceous/Tertiary (K/T) boundary interval at El Haria (northwest Tunisia). A high-resolution integrated biostratigraphy is presented. The K/T boundary is drawn at the level of extinction of Cretaceous planktonic foraminifers and is coincident with the first occurrence of the dinoflagellate cyst species Danea californica. The final extinction of planktonic foraminifers is foreshadowed by a reduction in their total abundance some 5 kyr earlier at the base of the boundary clay. This reduction is coeval with reported anomalies in siderophyle elements and δ13C-values in the same area. Dinoflagellate cysts do not show accelerated rates of extinction at K/T time. Associations of dinoflagellate cysts, however, change drastically and parallel changes in relative numbers of sporomorphs (spores and pollen) and in the quantity of land-derived organic matter. Jointly, these changes reflect a rapidly falling sea level during the final 17 kyr of the Mesozoic which culminates at the level of the K/T boundary. This steep sea level fall at K/T time represents a peak regressive pulse at the end of the well-documented latest Cretaceous regressive trend. This short-term sea level fall might show to be a wide-spread phenomenon which could have caused an excess shrinking of the already reduced areal extent of marginal seas. Since deep waters in Cretaceous oceans were primarily produced in shallow marginal seas, the rate of formation of deep water might have been minimized at K/T time. Minimum rates of formation of deep water might have curtailed the slow upward mixing of relatively cool and nutrient-rich deeper water through which the thermocline weakened and surficial waters became depleted in nutrients. Consequently, phytoplankton productivity rapidly diminished which, in combination with a weakened thermal gradient, pushed the highly depth-stratified Cretaceous planktonic foraminiferal fauna to extinction over a period of time of some 5 kyr. Guembelitria cretacea was the sole planktonic foraminifer which could accommodate to the low productivity conditions. The oscillating rise in sea level at the beginning of the Cenozoic reinforced the upward mixing of relatively cool and nutrient-rich deeper water, steepened the thermocline and replenished the photic layer with nutrients. Concomitant niche-differentiation in the photic layer progressively stimulated morphological innovation amongst early Cenozoic planktonic foraminifers. The final return of normally-sized planktonic foraminifers and of stable and well-balanced dinoflagellate cyst associations at about 125 kyr after the K/T boundary seems to indicate that primary productivity and niche differentiation in the photic layer begin to revert to optimum levels. The earliest Cenozoic planktonic foraminiferal species Globoconusa minutula and Parvularugoglobigerina fringa are thought to have developed from a benthic foraminiferal species rather than having a planktonic ancestry.

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.

Geographical distribution of living planktonic foraminifera (Protozoa) off the east coast of Australia.

Major water masses found off eastern Australia can be identified by their planktonic foraminiferal faunas. A total of 83 surface and oblique plankton samples from two cruises, in spring (October) and summer (January), between Hobart at 44� S. and Townsville at 18� S. yielded 27 species belonging to four distinct faunas: 'tropical', 'warm subtropical', 'cool subtropical' and 'transitional'. The tropical fauna is characterized by Globigerinoides sacculifer at an abundance greater than 42% and the co- dominance of Globigerinoides conglobatus, and is associated with Coral Sea water of equatorial origin. The subtropical fauna can be subdivided into warm and cool elements. The warm-subtropical fauna, with G. sacculifer more abundant than Globigerinoides ruber, inhabits Coral and Tasman Sea waters. The cool-subtropical fauna is a mixture of the warm subtropical and the transitional faunas. The transitional fauna is dominated by Globorotalia inflata and Globigerina bulloides in the south Tasman Sea subantarctic waters. It characterizes the South West Tasman water as defined by Rochford (1957). These water masses can be clearly separated, and the extent of mixing determined by their foraminiferal fauna. The shifts in the boundaries between the faunal zones was evident between spring and summer. The boundary between the tropical and subtropical water corresponds to the tropical convergence and the subtropical/transitional boundary is the Tasman Front. During the spring cruise, a warm core eddy was identified by its warm subtropical foraminiferal fauna surrounded by a transitional fauna to the south and cool subtropical fauna to the north. This water body was near 32� S., which is consistent with the reported positions of eddies shed by the East Australian Current. The distribution patterns of individual species are discussed.