Paleoceanographic Events Research Articles

Ecological structuring and evolution of deep sea agglutinated foraminifera — a review

Recent agglutinated foraminiferal communities exhibit both simple and complex ecological structuring within habitats. Simple ecological structuring (i.e. a limitation of the entire fauna at or close to the sediment-water interface and absence of erect suspension feeding forms) is mainly observed under low oxygen conditions and high organic flux or after severe substrate disturbance. Oligotrophic deep sea conditions with low vertical particle flux and little substrate disturbance as in the central areas of the modern oceans lead to the development of complex ecological structuring with various highly adapted “specialists” (i.e. mobile infaunal forms, a variety of epifaunal suspension feeders, and epifaunal deposit feeders with special mechanisms to avoid energy loss and use food resources not exploitable by other organisms). The paleontologic record of species diversity and habitat preferences since the late Jurassic exhibits two trends: (1) a general trend from simple to complex ecological structuring within habitats leads to an overall increase in diversity; (2) fluctuations in this trend coinciding with major paleoceanographic events, i.e. changes in deep water oxygenation and paleoproductivity. From a comparison of Recent and fossil communities from various trophic situations we conclude, that the ecological structuring of agglutinated foraminifera within habitats may have been one of the most important driving forces (selection mechanisms) in the evolution of this special group of protists.

Ferromanganese crusts as indicators for paleoceanographic events in the NE Atlantic

Ferromanganese crusts as indicators for paleoceanographic events in the NE Atlantic

Modern Carbonate Sediments and Environments of the La Paz Region, Baja California Sur, Mexico: ABSTRACT

The Gulf of California represents one of the most productive and unique marginal seas in the world. The mouth of the Gulf captures warm equatorial water while annual wind patterns assure major upwelling of nutrient-rich water leading to a rich marine biota. These conditions have created a wide array of tropical through warm temperate carbonate environments. The most unusual of these environments is located in the La Paz region of Baja California Sur where tropical-subtropical water temperatures and low rainfall have allowed growth of corals, calcareous red algae, and other shelled invertebrates to form a carbonate bank environment. Sampling and mapping transacts in shallow bays north of La Paz and on the adjacent Espiritu Santo island have revealed a full spectrum of subenvironments including mangrove bordered, terrigenous mud dominated coastal zones, which grade into carbonate tidal flats. In addition, single coral heads as well as incipient reef structures constructed by Porites and Pocillopora coral are present in deeper water areas. Coralline red algae, which are increasingly utilized for paleoenvironmental reconstructions, grow in high abundance on coral debris and in soft sediments and turn out to be main contributors to the La Paz carbonates. Analysis of siliciclastic admixtures, grain size andmore » organic carbon content allow a classification of distinct environments. These data are supplemented by an evaluation of benthic foraminiferal zonations and the varying abundance of biogenic constituents. This Baja California Sur carbonate environment holds special relevance for the interpretation of analogous Neogene and Paleogene paleoenvironments marking major paleoclimatic and paleoceanographic events along the Pacific Coast of North America.« less

Ferromanganese crusts as indicators for paleoceanographic events in the NE Atlantic

Hydrogenetic ferromanganese crusts reflect the chemical conditions of the sewater from which they formed. Fine-scale geochemical analysis of crust layers in combination with age determinations can therefore be used to investigate paleoceanographic changes which are recorded in geochemical gradients in the crusts. At Tropic seamount (off northwest Africa), uniform crust growth influenced by terrigenous input from the African continent occurred during approximately the past 12 Ma. Phosphatization of these crusts is minor. In contrast, crusts from Lion seamount, located between Madeira and the Portuguese coast, display a much more variable growth history. A pronounced increase in Ni, Cu, and Zn is observed in some intervals of the crusts, which probably reflects increased surface productivity. A thick older phosphatized generation occurs in many samples. Hydrographic profiles indicate that Mediterranean outflow water (MOW) may play an important role in the composition of these crusts.10Be dating of one sample confirms that the interruption of the MOW during the Messinian salinity crisis (6.2–5 Ma ago) resulted in changes in element composition. Sr-isotope dating of the apatite phase of the old crust generation has been carried out to obtain a minimum age for the older generation of Atlantic crusts and to determine whether crust phosphatization in the Atlantic can be related to phosphatization episodes recorded in Pacific crusts. The preliminary data show that the old phosphatized crust generation might be as old as approximately 30–40 Ma.

Biostratigraphy and paleoceanographic significance of the radiolarians from the protomouth of the Gulf of California

The presence of radiolarians in the diatomitic strata of subunit C of the Trinidad Formation (McCloy, 1984) in Baja California Sur, Mexico, is analyzed with a graphic-multivariate model in order to define a biostratigraphic frame and infer paleoceanographic events. Stichocorys peregrina and Didymocyrtis penultimus are the only index species present in the diatomites. Nevertheless, the total faunistic composition indicates that their deposition was principally promoted by upwelling processes which occurred approximately 8 to 5 million years ago, i.e., during the latest Miocene. As time elapsed in this stage, the California Current intensified until it was very evident in the protomouth of the Gulf of California. The age of the Trinidad Formation diatomites indicates that the Pacific Ocean invaded the gulf-mouth region before the tectonic processes (sea-floor accretion and spreading) were established, processes that have opened and outlined the present morphology of the Gulf of California; consequently, the basin which harbored said invasion can be called protomouth.

Allometric heterochrony in the Pliocene-Pleistocene planktic foraminiferal cladeGloboconella

Allometric analysis of the size-shape relationships in the Pliocene-Pleistocene planktic foraminiferalGloborotalia(Globoconella)puncticulata-inflataplexus reveals several heterochronic modes underlying the morphological evolution of the clade. The ancestral lineage,G. puncticulata,is a peramorphocline, showing a pre-displacement mode of heterochrony between 3.5 Ma and 3.0 Ma and an acceleration mode from 3.0 to 2.7 Ma. A different peramorphosis process, isometric giantism (hypermorphosis), in the ontogeny of the ancestral stocks ofGloboconellaoccurred at about 3.5 Ma and gave rise to theG. inflatalineage. The descendant lineage,G. inflata,appears to have adopted a paedomorphosis trend by delaying the onset of the neanic stage in ontogeny during the period of 3.5 to 2.35 Ma, resulting in a series of transposition allometries. During the interval of 2.4 to 1.73 Ma, the allometries shifted to the opposite direction, signifying a pre-displacement trend. Evolutionary stasis marks the evolution during 1.73 to 0.25 Ma. Neoteny concluded the final evolutionary stage of theG. inflatalineage during the latest Quaternary (0.26 to 0.05 Ma). The enormous plasticity and fluctuations in morphology ofG. inflataare attributed to the highly positive allometric growth during the ontogeny and the wide-range transposing allometries in the phyletic history. The major changes in heterochronic mode coincide with paleoceanographic events, suggesting that the morphological evolution in theGloboconellaclade has been modulated by changes in paleoceanographic conditions.

南米太平洋側の新第三紀海洋イベントの検討

南米太平洋側の新第三紀海洋イベントの検討

Neogene oceanographic variations recorded in manganese nodules from the Somali Basin

A detailed study of a nodule from the Somali Basin dated by 230Th excess was correlated with the paleoceanographic events recorded in Site 236 (Leg 24) Deep Sea Drilling Project (DSDP) cores. Tentative indications are that the phase of nodule accretion starting with the development of pillar structure at a depth of 20 mm in the nodule around 13 Ma coincides with increased Antarctic Bottom Water (AABW) flow and an elevated calciumcarbonate compensation depth (CCD). The Late Miocene lowering of the CCD is represented by the mottled zones between 8 and 18 mm in the nodule is characterised by an abundant silicate component (>20%) of aeolian origin. The Miocene/Pliocene boundary (5 Ma) occurs at a depth of about 8 mm and is represented by the development of pillar structure and a minimum of aeolian dust (10.3%). The increased biological productivity of the Somali surface water since the Middle Miocene is demonstrated by the increasing C org content of the nodule (from 0.11 to 0.19%) towards its surface.

Biotic response to a Middle Ordovician paleoceanographic event in eastern North America

Global paleontological events such as mass extinctions have been the focus of attention in recent years, yet regional biotic events account for a greater proportion of extinction in the fossil record and should receive greater attention if we are to fully understand extinction processes over the Phanerozoic. We use a sequence stratigraphic framework to document a major extinction and migration episode that occurred in the Middle and Late Ordovician of North America. This event is characterized in eastern North America by coordinated changes in faunal assemblages, carbonate lithologies, siliciclastic influx, and phosphatization. We ascribe these changes to a regional paleoceanographic event brought on by thrust-driven flexural subsidence and sea-level fluctuations that lowered water temperature and increased turbidity and nutrient input.

Downhole Logging as a Paeoceanographic Tool on Ocean Drilling Program Leg 138: Interface Between High‐Resolution Stratigraphy and Regional Syntheses

On Ocean Drilling Program (ODP) Leg 138, standard shipboard procedures were modified to allow for the real‐time monitoring of several laboratory core‐scanning systems that provide centimeter‐scale measurements of saturated bulk density, magnetic susceptibility and digital color reflectance. These continuous, high‐resolution data sets were used to ensure the proper offset of multiple holes and to splice together complete sedimentary sections. Typically, the spliced, continuous sediment sections were found to be about 10% longer than the section drilled, as measured by the length of the drill string. While the source of this elongation is not yet fully understood, it must be compensated for in order to property determine sediment fluxes and mass accumulation rates. Downhole logging, in conjunction with inverse correlation techniques provided a means to determine where the distortion occurred and to correct back to true in situ depths.Downhole logging also provides a means, through the generation of synthetic seismograms, of precisely relating the paleoceanographic events found in the core record to the high‐resolution seismic record. Once correlated to the seismic record, the spatial and temporal extent of paleoceanographic events can be traced well beyond the borehole. Most seismic events in the equatorial Pacific are related to rapid changes in carbonate content that, in turn, are related to both productivity events (often expressed as monospecific laminated diatom oozes) and times of enhanced dissolution. While many of these events may have oceanwide extent, others, like the absence of carbonate in the late‐Miocene to Recent in the Guatemala Basin have been shown to be regional and confined to only the deeper portions of the Guatemala Basin. As we identify and trace specific paleoceanographic events in the seismic record, we can begin to explore the response of the ocean through gradients of latitude, productivity, and depth.

The record of Ontong Java Plateau: Main results of ODP Leg 130

The drilling campaign of ODP Leg 130 on Ontong Java Plateau resulted in the recovery of complete Neogene sections at several depths, providing materials for detailed biostratigraphic and paleoceanographic studies in the western equatorial Pacific. The acquisition of extensive logging records and high-resolution physical-property data allow detailed correlation from hole to hole and from site to site and provide the basis for a paleoceanographic interpretation of acoustic reflectors. We drilled 16 holes at 5 sites on the north-eastern flank of the plateau (Sites 803 through 807). All sites are close to the equator, at water depths ranging from 2,500 m to 3,900 m. Sites 803 and 807 penetrated into basement (26 m and 149 m, respectively). The K/T boundary was recovered at both of these sites. Neogene sedimentation rates decrease with depth, as expected, but this decrease is much greater than calculated from carbonate content, under the assumption that carbonate dissolution is the sole cause of the decrease. At any one site, sedimentation rates vary by a factor of more than two, with a striking maximum in the latest Miocene to early Pliocene, and strong minima in late early to early middle Miocene and in the Pleistocene. Many acoustic reflectors correlate between sites, within the limits of stratigraphic resolution. This suggests paleoceanographic events as a cause, generating changes in physical properties of sediments at the time of deposition. Many of the reflectors occur at carbonate reduction events (CRE's). Some apparently are the product of diagenetic enhancement of property changes, as, for example, within the ooze/chalk transition (which is diachronous). The interval corresponding to the Cretaceous/Tertiary (K/T) transition in the area is characterized by the presence of a deep CCD. The sequence at one site is calcareous; that at the other, is not. The fact that the two K/T sections recovered occur in sequences with major hiatuses suggests special conditions for preservation during the transition. We propose early cementation caused by high silicate concentrations in an ocean with greatly reduced productivity. The basalt cored at Sites 803 and 807 is predominantly aphyric to sparsely olivine or plagioclase phyric; the last flows are Albian to Aptian in age. At Site 807, pillow lavas buried sediments. One very thick flow (∼28 m) was penetrated here, possibly a flood basalt, indicative of massive outpourings on Ontong Java Plateau during the middle Cretaceous.

Aspects of Middle-Late Jurassic-Cretaceous Tethyan brachiopod biogeography in relation to tectonic and paleoceanographic developments

Important tectonic and paleoceanographic events during the Middle to Late Jurassic and Cretaceous resulted in modifications to the biogeographic distributions of Tethyan brachiopod genera from Europe. The development of the Central Atlantic Ocean during the Jurassic-Early Cretaceous led to an increase in the number of brachiopod genera common to both the Mexico/Eastern Pacific and Northwestern Europe/Tethyan regions. Brachiopod genera recorded from Tethys in Europe show evidence of migration via at least four major routes as a consequence of tectonic developments (dates in parentheses indicate stages where evidence exists for generic links): (1) Northwestern Europe via Mexico/Caribbean region (Oxfordian) to South America (Valanginian, Hauterivian, Cenomanian); (2) Eastern Tethys via Eastern Africa (East African Seaway) to the South Atlantic Ocean (Late Turonian-Early Coniacian, Santonian-Campanian); (3) Northwestern Europe via the Central Atlantic to the opening South Atlantic, reaching the Antarctic Peninsula region (late Albian, Santonian, Campanian); (4) Europe northward to higher latitudes (Russian Platform to Barents Sea, Berriasian-Valanginian; Europe to East Greenland, Valanginian; Europe-Canadian Arctic Islands, Albian and also earlier during the Jurassic). For routes (1)–(3) direction of dispersal may prove to have been in either direction, at times it appears to have been in a southerly direction for route (3). Stratigraphic age relationships suggest a south to north dispersal for routes considered under (4) (except for the link to the Canadian Arctic Islands, which is inconclusive). By the Late Cretaceous the low-latitude faunas of Europe and America had become isolated by the increasing width of the Central Atlantic Ocean although some genera appear to be cosmopolitan.

Continental-shelf progradation by sediment-drift accretion

Multi-channel seismic profiles from the Canterbury Basin on the eastern margin of the South Island of New Zealand reveal the importance of current activity in shaping a Neogene shelf sediment prism. The shelf prism prograded across a broad, near-horizontal platform in water depths of 1,000 to 1,750 m. The platform was formed above a condensed section of late Eocene to late Oligocene limestones which overlie Cretaceous to Paleogene rift-fill and transgressive sediments. The Neogene sediment prism contains sediment drifts which are as much as 25 km long and 15 km wide and extend up to 1,600 m (uncompacted) vertically. Individual drifts migrated westward and can be traced between dip profiles, revealing that the long axes of most are subparallel to the present coastline and shelf-edge. Channel-like features at the landward edges of the drifts correspond to residual space left between the landward-prograding off-shelf sediment drift and the adjacent shelf foreslope. Erosion or slow deposition characterized the foreslope. Progradation of the shelf was by the accretion of successive sediment drifts. Before ca. 11.5 Ma (= Pink Horizon), the shelf-edge-parallel drifts were distributed across the central part of the basin, whereas subsequently they were concentrated to the northeast. The seismic architecture of the Neogene sediment prism results from the interplay of an abundant western sediment source and an offshore boundary current system. Present-day ocean circulation involves northward flow along the east coast of the South Island. The basin may have been subjected to a middle Miocene to late Pliocene phase of intensified flow, caused by local topographic enhancement and/or global paleoceanographic events. Current activity has played a crucial role in the sedimentary evolution of the Canterbury Basin Neogene shelf prism.

Application of Image Analysis to Neogene Planktonic Foraminiferal Bioseries

The morphological characteristics of fossil foraminiferal tests are the basis for making phylogenetic and taxonomic, as well as paleoecological inferences about fossil species. A complete understanding of the taxonomic and paleoenvironmental information contained in morphology of foraminifera depends heavily on quantitative methods to describe phenotypic and ecophenotypic variation. Automated image analysis is used to quantify the shape characteristics of planktonic and benthic foraminifera. There are three main components to the authors' quantitative image analysis system: (1) computer based image digitizer; (2) Fourier series analysis in closed form; and (3) multivariate statistical analysis. The advantages of such a system are that shape characteristics can be objectively determined and that large numbers of specimens can be analyzed. The focus of their research has been to improve the utility of foraminifera in paleoenvironmental and biostratigraphic application. The Globorotalia menardii/Globorotalia tumida group and the Globigerinoides obliquus/Globigerinoides extremus complex from Neogene sediments from DSDP Site 502 in the Caribbean have been examined via image analysis. In both groups they were able to determine distinct morphotypes that change relative proportion with time. This information is utilized to define morphotypes within each group that are independent of taxonomically defined zones. Changes in the proportions of each endmore » member are also correlated with paleoceanographic events of the Neogene such as the initiation of Northern Hemisphere glaciation and the Messinian event. Signal processing techniques, such as cross correlation, spectral analysis, and cross spectral analysis are also used in their investigations. Applying these techniques to the data in conjunction with stable isotope record for Site 502 allows them to determine correlations with the isotopic record and the similarities in the frequencies in the morphological records.« less

Neogene paleoceanographic events recorded in an active-margin setting: Humboldt basin, California

Recognition of North Pacific paleoceanographic events in the marginal Humboldt (Eel River) basin of northern California enables correlation of stratigraphic sections and development of a chronostratigraphy. Paleoclimatically related coiling shifts in Neogloboquadrina pachyderma (Ehrenberg) and benthic foraminiferal datums form the basis of the chronostratigraphy. Benthic foraminiferal datums are defined by the occurrence of selected benthic species and abundance maxima of benthic biofacies. The compiled chronostratigraphy is used to refine reconstructions of the depositional history of Humboldt basin. Paleoceanographic events, recognized by the distribution of benthic foraminiferal biofacies, are used to infer paleoceanographic history along the northeastern Pacific margin. The similarity in coiling curves of N. pachyderma from the marine sequence at DSDP Site 173 and the coastal Centerville Beach section of Humboldt basin and at other independently dated sites along the northeastern Pacific margin demonstrates that matching records of climatic oscillations is a reliable method of correlating marine sequences. Benthic fauna from the Centerville Beach section vary in phase with climatically related coiling shifts in N. pachyderma. In particular these data show an increase in displaced neritic fauna during inferred warm intervals and resurgence of deeper bathyal fauna during inferred cool events. Similar data are observed from the inland Eel River section, demonstrating that benthic foraminiferal trends recognized at Centerville Beach can be identified elsewhere in Humboldt basin. This in-phase benthic response to climatic fluctuations probably results from changes in vertical depth range of many benthic species in response to paleoclimatically related vertical changes in water-mass position. Depositional histories reconstructed for two key sites in southern Humboldt basin indicate low rates of sediment accumulation during early basin filling with hemipelagic sediments. Initiation of turbidite sedimentation in the early Pliocene resulted in a sharp increase in rate of sediment accumulation. This increase in rate of sediment accumulation is partially a response to tectonic uplift in the northern Coast Ranges and may be an effect of realignment of motion between the Pacific and North American plates at about this time. The inland site shoaled more rapidly during turbidite sedimentation as a result of a higher rate of sediment accumulation. The rate of sediment accumulation increased again at this site in the late Pliocene during deposition of shelf and nearshore facies. The Eel River region subsided concurrent with deposition of these shallow-water deposits.

Leg 124 of the Ocean Drilling Program

Leg 124 of the Ocean Drilling Program drilled five sites in the Sulu and Celebes Seas (Figure 1). The papers presented in this issue provide an overview of some of the preliminary results of the shipboard science. They represent a team effort, and all are co‐authored by the entire scientific party. Our objectives were to determine the age and origin of these basins, and their stratigraphic histories, as indicators of the complex tectonic and paleoceanographic events that have affected the western Pacific region during the Cenozoic. Numerous competing hypotheses have been put forward to explain the array of marginal basins and island arcs in the western Pacific, and these basins are all potential recorders of the complex history of the western Pacific history.

Nonlinear response of Pliocene climate to orbital forcing: Evidence from the eastern equatorial Pacific

A high‐resolution radiolarian record from the eastern equatorial Pacific is used to examine paleoceanographic events during the Pliocene, from 1.8 to 4.9 Ma. These data provide a means to evaluate the response of the equatorial Pacific to the onset of northern hemisphere glaciation near 2.47 Ma and to the closure of the Isthmus of Panama near 3.2 Ma. Responses are recorded both as long‐term trends and as variations within the Milankovitch band (104 to 105 years). Radiolarian‐based sea surface temperature (SST) estimates indicate a mean cooling from lower to upper Pliocene, but no significant changes occur near the onset of northern hemisphere glaciation, and no abrupt changes are observed before or after the closure of the isthmus. Spectral and cross‐spectral analyses of this SST time series indicate concentrations of variance within the precession (23‐kyr) and obliquity (41‐kyr) bands in several but not all time intervals. Variance is commonly concentrated at lower frequencies. Cross spectral analysis of SST time series and calculated orbital variations indicates that the SST record is not coherent with, and therefore not linearly related to, orbital variations. Detailed time series analysis of the SST and δ18O time series indicates the absence of a direct linear relationship but rather the presence of a strongly nonlinear relationship between Pliocene climatic variables and Earth's orbit. High coherence is seen between the amplitude of the 23‐kyr component of SST and the amplitude modulation of precession. The amplitude modulation of the 41‐kyr component of the SST record is dissimilar to the amplitude modulation of obliquity but is extremely similar to and coherent with the amplitude of the 23 kyr component of SST. The amplitude modulations of SST and δ18O at a range of frequency bands have the same features, features that roughly follow the modulation of precession. This suggests a strongly nonlinear response of equatorial Pacific SST and planktonic δ18O to orbital forcing in the Pliocene. Such a response, extending over a number of frequency bands, has not previously been seen in a paleoclimatic data set but may be consistent with proposed models describing paleoclimatic variability. Although the reasons for this response are still unclear, it is evident that strong nonlinearities in climate are present during this time.

Growth rate variations of manganese nodules and crusts induced by paleoceanographic events

Time markers at about 3 Ma., 6.5 Ma., and 14 Ma. are common to 16 manganese nodules and crusts from different localities in the world oceans. These time markers correspond to variations in the growth rates, in the inner structure, and in the chemistry of the samples. The observed time markers could be related to (1) changes of the bottom water velocity and (2) variations in the manganese and iron contents in the deep ocean. The time markers were determined by high‐resolution 10Be dating, applying the accelerator mass spectrometry facility at the Eidgenössische Technische Hochschule Zürich.

Paleocene-Pleistocene benthic foraminiferal evidence of major paleoceanographic events in the eastern South Atlantic (DSDP Site 525, Walvis Ridge)

Benthic foraminifers in the size-fraction greater than 0.073 mm were studied in 88 Paleocene to Pleistocene samples from Deep Sea Drilling Project Site 525 (Hole 525A, Walvis Ridge, eastern south Atlantic). Clustering of the samples on the basis of the 86 most abundant foraminifers (in total, 331 taxa were identified) allowed separating two major assemblage zones: the Paleocene to Eocene interval, and the Oligocene to Pleistocene interval. Each of these, in turn, were subdivided into three minor subzones as follows: lower upper Paleocene (approx. 62.4 to 57.8 Ma); upper upper Paleocene (56.6 to 56.2 Ma); lower and middle Eocene (55.3 to 46.8 Ma); upper Oligocene to middle Miocene (25.3 to 16 Ma); middle Miocene to Pliocene (15.7 to 4.2 Ma); and lower Pleistocene (0.4 to 0.02 Ma), with only minor differences with the previous zone. Some very abundant taxa span most of the column studies ( Bolivina huneri, Cassidulina subglobosa, Eponides bradyi, E. weddellensis, Gavelinella micra, Oridorsalis umbonatus, etc.). Several of the faunal breaks recorded coincide with conspicuous minima in the specific diversity curve, thus suggesting that the corresponding turnovers signal the final stages of periods of faunal impoverishment. At least one major bottom-water temperature drop (as derived from δ 18O data) is synchronous with a decrease in the foraminiferal specific diversity. On the other hand, a specific diversity maximum in the middle Miocene might be associated with a δ 13C increase at approx. 16 to 12 Ma. Highest foraminiferal abundances (up to 600–800 individuals per gram of dry sediment) occurred in the late Paleocene and in the early Pleistocene, in coincidence with the lowest diversity figures calculated. The magnitude of the most important faunal turnover recorded, between the middle Eocene and the late Oligocene, is magnified in our data set by the large hiatus which separates the middle Eocene from the upper Oligocene sediments. Considerably smaller overturns occurred within the late Paleocene (in coincidence with changes in the specific diversity, absolute abundance of foraminiferal tests, and δ 13C), and in the middle Miocene (in coincidence with a specific diversity maximum and a δ 13C excursion). New information on the morphology and the stratigraphic ranges of several species is furnished. For all the taxa recorded the number of occurrences, total number of individuals identified and first and last appearances are listed.

Late Cenozoic environments in the Barents Sea

We examine the paleoceanography and paleogeography of the Barents Sea during the late Cenozoic glacial regime by seismostratigraphy and core analysis. During the smaller glaciations which probably dominated the first period of the glaciogenic regime (approximately 2.5–0.8 Ma?), glaciomarine processes with sediment influx from the adjacent mainland prevailed. The Barents Sea has been covered by grounded ice sheets several (five to 10) times during the late Cenozoic. We speculate that these glaciations occurred during the last 0.8 Ma. During these larger glaciations the margin of the ice sheet expanded to the shelf edge, and the continental shelf break and slope acted as a depocenter and prograded rapidly. Frequent sediment gravity flows accumulated on the lower continental slope. During interglacials, the Barents Sea was converted to a starved continental margin. Most of the Barents Sea was glaciated during the maximum of the last glaciation (19–16 ka). A two‐stepped deglaciation, 16 to 13 ka and 13 to 10 ka, occurred. Incipient Atlantic water reached the western areas about 13 ka and totally replaced the Arctic water by 10 ka. These paleoceanographic events were delayed in the eastern Barents Sea.