Dinoflagellate cyst distribution along a shelf to slope transect of an oligotrophic tropical sea (Sunda Shelf, South China Sea)

From 51 surface samples collected along a shelf to slope transect of the Sunda Shelf, South China Sea, 36 taxa of organic‐walled dinoflagellate cysts are identified. Oligotrophic tropical shelf assemblages on the Sunda Shelf are dominated by gonyaulacoids such as Spiniferites species, Operculodinium centmcarpum and Operculodinium israelianum. Concentrations of dinoflagellate cysts in the shelf sediments are generally low and correlate well with the content of fine‐grained (clay and silt fraction) sediments. Detailed comparisons of sediment grain‐size distributions to concentrations of dominant dinoflagellate taxa (Spiniferites species, 0. centmcarpum and 0. israelianum) in the shelf sediments indicate that these taxa behave in water like sediment particles with size range φ 5.75–6.25 (13–18 μm). In contrast, slope assemblages in fine‐grained sediments are dominated by protoperidinioids. This may reflect higher nutrient availability as a result of weak winter upwelling. The concentrations of dinoflagellate cysts in the shelf sediments are mainly controlled by transport and winnowing processes and are probably not representative of surface water conditions.     

Facies of a Lower Ordovician carbonate shelf (Mungok Formation: Taebaeksan Basin,Korea)

Summary The lithologic associations within the Lower Ordovician Mungok Formation in Korea define four depositional facies that formed across a continental margin fringing the Sino-Korean block: these facies represent lagoonal/restricted marine, shoal, inner shelf, and outer shelf environments. The stacking pattern of these facies reveals two systems tracts composed of five depositional sequences. The lower highstand systems tract consists of the lagoonal/restricted marine and shoal facies, whereas the upper lowstand systems tract comprises, in ascending order, inner shelf, outer shelf, and inner shelf facies. Three trilobite biofacies are recognized in the Mungok Formation: i.e.,Yosimuraspis, Kainella, andShumardia biofacies in ascending order. TheYosimuraspis Biofacies is dominated byYosimuraspis but also containsJujuyaspis andElkanaspis. The predominance of the endemic eponymous taxon suggests a lagoonal/restricted marine environment. The nearly monotaxicKainella Biofacies, which comprises pandemic genera such asKainella and occasionallyLeiostegium, may represent a less restricted environment than theYosimuraspis Biofacies. TheShumardia Biofacies occurs in the marlstone/shale lithofacies through relatively thick stratigraphic interval and is dominated by cosmopolitan trilobite taxa with some endemic species. The lithofacies and cosmopolitan trilobite assemblage of theShumardia Biofacies indicate that it occupied an outer shelf environment. The vertical succession of lithofacies and trilobite biofacies in the Mungok Formation records in general a shift from a restricted, shallow water environment to deeper-water environment.     

Thanetian–Ilerdian coralline algae and benthic foraminifera from northeast India: microfacies analysis and new insights into the Tethyan perspective

Thanetian–Ilerdian carbonate deposits from the Lakadong Limestone in Assam Shelf, Meghalaya, northeast India, are studied with respect to microfacies distributions and controlling ecological factors on dominant biogenic components. Palaeoenvironmental implications are inferred following the detailed analysis of microfacies characterized by rich assemblages of coralline red algae and benthic foraminifera. The carbonate sediments have been interpreted as lagoonal to outer shelf facies. It is envisaged that the analysed benthic communities thrived in a meso‐oligotrophic regime above the fair‐weather wave base. The Lakadong Limestone constitutes a well‐preserved record of Late Palaeocene–earliest Eocene shallow marine carbonate ecosystem and has high potential to decipher its response to an interval of distinct changes in climate and tectonic settings. The abundance of oligotrophic larger benthic foraminifera in the Lakadong Limestone is comparable to the foraminiferal assemblages of west Tethys. The phylogenetic changes (‘Larger Foraminiferal Turnover’, LFT) and subsequent rapid radiation of typical Eocene larger benthic foraminifera (Alveolina, Nummulites) usually observed in the west Tethys have also been observed in the upper part of the Lakadong Limestone. The eastward migration of Eocene foraminifera from the west coincided with the India‐Asia collision and global warming events at the Palaeocene–Eocene boundary that may have produced a wide array of modifications in biogeography, seasonal run‐offs and ocean circulation pathways. The data indicate that rapid rate of migration from west before the onset of geographic barriers and/or timely restoration of pan‐Tethyan environmental conditions ensured the incidence of these forms in the earliest Eocene sediments.     

Sedimentary environments of the Central Region of the Great Barrier Reef of Australia

The sediments and calcareous organisms on the outer reefal shelf of the Central Region of the Great Barrier Reef were collected and observed by SCUBA diving and research vessel techniques (including underwater television) to understand the production and processes of deposition of the sediment. The carbonate grains are mainly sand and gravel size and solely of skeletal origin. Over the whole area the major CaCO₃ producers, in order of decreasing importance are: benthic foraminiferans (chiefly Operculina, Amphistegina, Marginopora, Alveolinella and Cycloclypeus), the calcareous green alga Halimeda, molluscs and corals. Coral abundance is high only close to reefs and submerged rocky substrates. Benthic foraminiferal sands dominate the inter-reef areas i.e. the bulk of the shelf, and Halimeda gravels form an outer shelf band between 60 and 100 m depths. Seven distinct facies are recognised after quantitative analyses of the sediments. These are: A. Shelf edge slope (>120 m depth); B. Shelf edge (with rocky outcrops); C. Outer shelf with high Halimeda (>40%); D. Inter-reef I; E. Inter-reef II ( 100 m depth but >2% pelagics); F. Lee-ward reef talus wedge (<2 km from sea level reefs); G. Lagoonal.     

Living benthic foraminifera of the Okhotsk Sea: Faunal composition, standing stocks and microhabitats

Live (Rose Bengal stained) benthic foraminifera were investigated in surface sediment samples from the Okhotsk Sea to reveal the relationship between faunal characteristics and environmental parameters. Live benthic foraminifera were quantified in the size fraction > 125 µm in the upper 8 cm of replicate sediment cores, recovered with a multicorer at five stations along the Sakhalin margin, and at three stations on the southwestern Kamchatka slope. The stations are from water depths between 625 to 1752 m, located close or within the present Okhotsk Sea oxygen minimum zone, with oxygen levels between 0.3 and 1.5 ml l^- 1. At the high-productivity and ice-free Kamchatka stations, live benthic foraminifera are characterized by maximal standing stocks (about 1700-3700 individuals per 50 cm²), strong dominance of calcareous species (up to 87-91% of total live faunas), and maximal habitat depths (down to 5.2-6.7 cm depth). Vertical distributions of total faunal abundances exhibit a clear subsurface maximum in sediments. At the Sakhalin stations, which are seasonally ice-covered and less productive, live benthic foraminifera show lower standing stocks (about 200-1100 individuals per 50 cm²), lower abundance of calcareous species (10-64% of total live faunas), and shallower habitat depths (down to 2.5-5.4 cm depth). Faunal vertical distributions are characterized by maximum in the uppermost surface sediments. It is suggested that 1) lower and strongly seasonal organic matter flux, caused by the seasonal sea ice cover and seasonal upwelling, 2) lower bottom water oxygenation (0.3-1.1 ml l^- 1), and 3) more pronounced influence of carbonate undersaturated bottom water along the Sakhalin margin are the main factors responsible for the observed faunal differences. According to species downcore distributions and average living depths, common calcareous species were identified as preferentially shallow, intermediate and deep infaunal. Foraminiferal microhabitat occupation correlates with the organic matter flux and the depth of the oxygenated layer in sediments.     

Integrating phylogenetic and taxonomic evidence illuminates complex biogeographic patterns along Huxley’s modification of Wallace’s Line

Aim Nearly 150 years ago, T. H. Huxley modified Wallace’s Line, including the island of Palawan as a component of the Asian biogeographic realm and separating it from the oceanic Philippines. Although Huxley recognized some characteristics of a transition between the regions, Palawan has since been regarded primarily as a peripheral component of the Sunda Shelf. However, several recent phylogenetic studies of Southeast Asian lineages document populations on Palawan to be closely related to taxa from the oceanic Philippines, apparently contradicting the biogeographic association of Palawan with the Sunda Shelf. In the light of recent evidence, we evaluate taxonomic and phylogenetic data in an attempt to identify the origin(s) of Palawan’s terrestrial vertebrate fauna. Location The Sunda Shelf and the Philippines. Methods We review distributional and phylogenetic data for populations of terrestrial vertebrates from Palawan. Using taxonomic data, we compare the number of Palawan taxa (species and genera) shared with the Sunda Shelf and oceanic Philippines. Among widespread lineages, we use phylogenetic data to identify the number of Palawan taxa with sister relationships to populations or species from the Sunda Shelf or oceanic Philippines. Results Although many terrestrial vertebrate taxa are shared between Palawan and the Sunda Shelf, an increasing number of species and populations are now recognized as close relatives of lineages from the oceanic Philippines. Among the 39 putative lineages included in molecular phylogenetic studies with sampling from the Sunda Shelf, Palawan and the oceanic Philippines, 17 of them reveal sister relationships between lineages from Palawan and the oceanic Philippines. Main conclusions Rather than a simple nested subset of Sunda Shelf populations, Palawan is best viewed as having played multiple biogeographic roles, including a young and old extension of the Sunda Shelf, a springboard to diversification in the oceanic Philippines, and a biogeographic component of the Philippine archipelago. Palawan has a long, complex geological history, which may explain this variation in pattern. Huxley originally noted transitional elements in Palawan’s fauna; we therefore suggest that his modification of Wallace’s Line should be recognized as a filter zone, reflecting both his original intent and available taxonomic and molecular evidence.     

Human‐mediated introduction of introgressed deer across Wallace's line: Historical biogeography of Rusa unicolor and R. timorensis

In this study we compared the phylogeographic patterns of two Rusa species, Rusa unicolor and Rusa timorensis, in order to understand what drove and maintained differentiation between these two geographically and genetically close species and investigated the route of introduction of individuals to the islands outside of the Sunda Shelf. We analyzed full mitogenomes from 56 archival samples from the distribution areas of the two species and 18 microsatellite loci in a subset of 16 individuals to generate the phylogeographic patterns of both species. Bayesian inference with fossil calibration was used to estimate the age of each species and major divergence events. Our results indicated that the split between the two species took place during the Pleistocene, ~1.8 Mya, possibly driven by adaptations of R. timorensis to the drier climate found on Java compared to the other islands of Sundaland. Although both markers identified two well‐differentiated clades, there was a largely discrepant pattern between mitochondrial and nuclear markers. While nDNA separated the individuals into the two species, largely in agreement with their museum label, mtDNA revealed that all R. timorensis sampled to the east of the Sunda shelf carried haplotypes from R. unicolor and one Rusa unicolor from South Sumatra carried a R. timorensis haplotype. Our results show that hybridization occurred between these two sister species in Sundaland during the Late Pleistocene and resulted in human‐mediated introduction of hybrid descendants in all islands outside Sundaland.     

Recent benthonic ostracod assemblages as indicators of the Tsushima warm current in the southwestern sea of Japan

One hundred and sixty-seven species of podocopid ostracods are reported from 26 recent surface sediment samples collected on the shelf of the Tsushima Strait in the southwestern Sea of Japan. Four biofacies (A–D) are recognised based on Q-mode cluster analysis. Among these, biofacies B is distributed along the Tsushima Warm Current and includes typical East China Sea species. This fact suggests that the migration of the shelf-living ostracods between the open sea and the adjacent semi-enclosed marginal sea mainly occurs in association with the inflow of this sea current. The distribution of the recent ostracod assemblages from the Tsushima Strait are expected to be a sensitive indicator of past and future changes in the Tsushima Warm Current. One new ostracod species of the family Trachyleberididae, Trachyleberis ikeyai, is described and illustrated herein. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

Productivity events of the marine diatom Thalassiosira tumida (Janisch) Hasle recorded in deglacial varves from the East Antarctic Margin

During the last deglaciation calving bay reentrants formed over several deep inner shelf basins around Antarctica as the ice sheets retreated. Marine diatoms flourished in spring and summer within the bays, providing exceptionally high silica flux rates to the basins on an annual basis. As a result, several hundred years of the late deglaciation are archived in many of these deep basins as continuously laminated diatom-rich marine sediments. The laminae are excellently preserved and offer a unique opportunity to study deglacial processes over the Antarctic shelf at very high resolution (subseasonal to seasonal at best). Annual palaeoenvironments from these sediments have been recently reconstructed. However, finer sedimentary detail is also apparent by the preservation of sublaminae of single diatom species, which represent discrete productivity events (blooms). In this paper, we focus on Thalassiosira tumida (Janisch) Hasle sublaminae preserved in the  5 m thick deglacial laminated sequence of NBP01-01 Jumbo Piston Core (JPC) 43B from Iceberg Alley ( 67°S, 63°E) on the Mac.Robertson Shelf, East Antarctic Margin. These T. tumida sublaminae are distinctive, occur several times throughout the deglacial sequence and are always preserved within summer laminae. Importantly they carry ecological and paleoceanographic information for deglacial Iceberg Alley and possibly the entire East Antarctic Margin. We describe and illustrate the T. tumida sublaminae using scanning electron microscope backscattered electron imagery of highly polished thin sections and secondary electron imagery of sublamina fracture surfaces. T. tumida sublaminae range in thickness from 0.57 to 21.07 mm (mean = 5.12; σ = 4.49) and are defined as discrete sedimentary intervals within a summer lamination where T. tumida is the dominant diatom species (abundance > 50%; but frequently > 80%) or is very abundant (abundance 40% to 49%). Based on the stratigraphic position of these sublaminae in the annual/seasonal succession and on published morphological, ecological and distributional data of living specimens in culture and in the field, we surmise an open-water, late summer bloom for T. tumida in deglacial Iceberg Alley, at sea-surface temperatures of 0 to − 1.69 °C, under low or fading light levels just prior to significant sea-ice formation. We suggest that the sublaminae formed by a combination of episodic T. tumida blooms (surface concentration), followed by rapid deposition (high flux) and optimal frustule preservation on the sea floor. Increased sublaminae frequency upcore suggests a lengthening of the summer season, while their complete cessation 43 years prior to the end of lamination deposition in outer Iceberg Alley (JPC43B) may be due to a coastward population shift.     

Benthic foraminiferal distributions in Chilean fjords: 47°S to 54°S

Surface sediment samples collected from the fjord region of southern Chile (47° to 54° South) were analyzed for benthic foraminifera. A total of 175 species were identified including agglutinated and calcareous benthic taxa. Hierarchical cluster analysis of the foraminiferal data resulted in the recognition of three distinct biofacies: inner-fjord, intermediate fjord and channel, and oceanic biofacies, geographically controlled by relative position between the Pacific Ocean and fjord heads. Similarity percentage (SIMPER) analysis identified key taxa in the definition of the biofacies that include Globocassidulina rossensis, Cassidulina laevigata and Bulimina notovata. Principal components analysis resulted in two principal components representing sediment size, and bottom water temperature and salinity.Regional distributions are strongly controlled by the oceanographic conditions influenced from the Pacific in the west and the glacial/freshwater input from the east. Localized distributions of foraminifera are controlled by conditions influenced by the physiography of the individual fjords and channels. The distribution of Chilean fjord foraminifera and their environmental associations are consistent with results from other temperate to high latitude fjord foraminiferal studies.     

Spatial distribution of live benthic foraminifera in the Rhône prodelta: Faunal response to a continental–marine organic matter gradient

Benthic foraminifera were collected in the Rhône prodelta (Gulf of Lions, Mediterranean Sea), an enriched zone with high organic matter content. In June 2005, sediment cores were sampled at depths ranging from 20 to 100 m. Four distinct foraminiferal assemblages were determined in the study area, reflecting the geographical distribution of the impact of river supply. The living foraminiferal faunas present a typical picture, with strongly impoverished faunas composed exclusively of stress-tolerant taxa (Fursenkoina fusiformis, Bulimina aculeata, Leptohyalis scottii, and Adelosina longirostra) in the immediate vicinity of the river mouth. This assemblage is well adapted to a high input of continental organic matter and a minimum oxygen penetration depth into the sediment. To the southwest, under the main corridor followed by the river plume, high organic input with a dominantly terrestrial signature (more refractory) may be stressful for many taxa which need organic matter of a more labile quality. In this area, Nonion scaphum, Nonionella turgida and Rectuvigerina phlegeri are present in low densities. On the edge of this area, these taxa show much higher densities. A greater proportion of marine organic carbon could explain their increasing abundances in this area. Towards the east and towards the deepest stations, in the outer part of the enriched zone, biodiversity increases. Faunas at these stations have intermediate densities and contain a number of taxa (Cassidulina carinata, Epistominella vitrea, Valvulineria bradyana, Nonionella iridea/bradyi) at the deepest stations; Bolivina dilatata/spathulata and Textularia porrecta at the eastern stations) that seem to benefit from more marine organic matter. The comparison of geochemical measurements and foraminiferal data strongly suggests that the spatial distribution of foraminifera in the Rhône prodelta is mainly governed by the quality and the quantity of organic matter reaching the sediment–water interface. Since bottom waters are well oxygenated (215–260 µmol/L), and oxygen penetration into the sediment is less than 1 cm at all stations, benthic ecosystem oxygenation appears to have only a minor impact on regional differences in faunal distribution.     

Deep-sea palaeoceanography of the Maldives Islands (ODP Hole 716A), equatorial Indian Ocean during MIS 12-6

Deep-sea benthic foraminifera, planktic foraminifer Globigerina bulloides and pteropods have been quantitatively analysed in 451 samples from Ocean Drilling Program (ODP) Hole 716A, to understand both surface and deep-sea palaeoceanographic changes in the equatorial Indian Ocean basin during the late Quaternary (∼444–151 Kyrs). Benthic foraminifera were analysed from >125 μm size fraction whereas Globigerina bulloides and pteropods were analysed from >150 μm size fraction. Factor analysis of most dominant benthic foraminiferal species over the studied time span made it possible to identify three biofacies characterizing distinct deep-sea environmental settings at Hole 716A. The environmental interpretation of each species is based on the ecology of recent deep-sea benthic foraminifera. The faunal record indicates fluctuating deep-sea conditions including changes in surface productivity, organic food supply and deep-sea oxygenation linked to changing wind intensities. These changes are pronounced on glacial-interglacial time scales driven by summer monsoon winds.     

The Cenomanian of northern Germany: facies analysis of a transgressive biosedimentary system

A facies analysis of the epicontinental marine Cenomanian sediments of northern Germany shows the presence of 17 facies types (FTs, including several subtypes) which can be assigned to three facies associations: 1) an inner shelf facies association (FT 1–8) with high amounts of terrigenous material and/or high-energy depositional features, 2) a middle shelf facies association (FT 9–15) of predominantly calcareous sediments with moderate amounts of generally fine siliciclastics, and 3) an outer shelf facies association (FT 16–17) of low-energy, fine-grained, pure limestones. These three facies associations roughly correspond to the well-known lithological units of the Cenomanian of northern Germany, i.e., the Essen Greensand/Cenomanian Marls complex, the Pläner Limestones, and the Poor rhotomagense Limestones. The sediments were deposited on a northward-dipping homoclinal ramp with more-or-less shoreline-parallel facies belts. The sediment composition on this ramp-like shelf was a function of the varying importance of three different sediment sources: 1) terrigenous input from the south (Rhenobohemia), generally fining/decreasing in a proximal–distal (i.e., S–N) direction; 2) production of skeletal grains, mainly by macrobenthic organisms; and 3) settling of planktic carbonate (mainly calcispheres and calcareous nannofossils). In response to decreasing water energy with increasing water depth, the seaward decreasing terrigenous influence, and increasing planktic carbonate production, increasingly finer and more calcareous sediments were deposited in a proximal–distal transect. This rather straightforward picture was slightly modified by highest carbonate accumulation rates (planktic and benthic) on the middle shelf, forming a mid-shelf depocenter (fossiliferous, calcisphere-rich Pläner Limestones). Time-transgressive, southward-directed onlap of this biosedimentary system during the Cenomanian caused a significant retreat of the coastline towards the south and a retrogradational stacking of facies belts, explaining the broadly similar facies development and lithology of Cenomanian successions across northern Germany. The boundaries of the lithological units, however, tend to be considerably diachronous in a distal–proximal transect. In the late Middle and early Late Cenomanian, a final drowning and facies levelling (“oceanization”) is indicated by the widespread deposition of uniform calcareous nannofossil mudstones (Poor rhotomagense Limestones).     

Polychaete distribution on the southwestern Atlantic continental shelf

Diversity and distribution of polychaetes on the southeastern Brazilian Shelf (SBS) adjacent to the city of Santos were studied. The study area is situated in the vicinity of Santos Bay with its estuarine complex and other small rivers along the coast. A total of 16,274 specimens belonging to 214 polychaete species were found at 21 sampling stations during two different periods. Two communities occur along the shelf and were related firstly to sediment characteristics. Prionospio dayi (Spionidae) was dominant in the inner shelf community that was characterized by well-sorted, very fine sand. The outer shelf community was found in muddy sediments with high organic matter content and was dominated by subsurface deposit feeders, like Petersenaspis capillata (Sternaspidae) and Leitoscoloplos kerguelensis (Orbiniidae), and by large carnivores such as Aglaophamus sp. (Nephtyidae) and Sigambra sp. (Pilargidae). A transition zone of mixed sediments presenting high diversity and richness was found between these communities. The characteristics of bottom water and food quality in the sediment were important to divide the inner shelf into two sub-areas. Nearshore sampling stations (A group) were more influenced by freshwater input, mainly during summer. This influence is not conspicuous at stations close to 30?m depth (B group). However the effect of South Atlantic Central Water mass (SACW) intrusion on the benthic system was observed on the inner shelf – B group during the summer. The summer intrusion of SACW onto the inner shelf may explain the higher quality of organic matter that resulted in an increase in polychaete abundance and richness.     

Paleoceanographic changes during the past 1.9 Myr at DSDP Site 238, Central Indian Ocean Basin: Benthic foraminiferal proxies

Deep-sea benthic foraminifera have been quantitatively analyzed in samples (> 125 μm size fraction) from Ocean Drilling Program (ODP) Site 238, to understand paleoceanographic changes in the Central Indian Basin over the past 1.9 Myr. Factor and cluster analyses of the 25 highest-ranked species made it possible to identify five biofacies, characterizing distinct deep-sea environmental settings. The environmental interpretation of each biofacies is based on the ecology of recent deep-sea benthic foraminifera. The benthic faunal record indicates fluctuating deep-sea conditions in environmental parameters including oxygenation, surface productivity and organic food supply. These changes appear to be linked to Indian summer monsoon variability, the main climatic feature of the Indian Ocean region. The benthic assemblages show a major shift at ∼ 0.7 to 0.6 Ma, marked by major turnovers in the relative abundances of species, coinciding with an increased amplitude of glacial cycles. These cycles appear to have influenced low latitude monsoonal climate as well as deep-sea conditions in the Central Indian Ocean Basin.     

Geochemical investigation of gametogenic calcite addition in the planktonic foraminifera Orbulina universa

Several species of planktonic foraminifera precipitate a final layer of calcite onto the shell surface immediately prior to gamete release at the end of the foraminifera life cycle. Here, we present the results of carbon-13, oxygen-18 and thermal labeling experiments conducted under high (HL) and low light (LL) regimes that vary symbiont photosynthetic activity. Mean experimental group data show that gametogenic (gam) calcite contributes between 4–17% and 14–20% to final shell mass for high and low light experiments respectively. These data indicate that past studies of gam calcite addition have overestimated the amount of gam calcite on foraminifera shells by ~ 30–55%. Calculations indicate that the mass of gam calcite added to the O. universa shell, 4.2 ± 2.0 μg and 4.0 ± 2.4 μg, is constant in the HL and LL groups respectively. We propose that the production of gam calcite may be the result of the discharge of a relatively constant-volume cytoplasmic pool of either Ca²⁺ or alkalinity (carbon pool) that increases the calcite saturation state in the microenvironment adjacent to the foraminifera shell just prior to gamete formation and release. Results from these experiments indicate that the geochemistry of thin-walled O. universa from deep sea sediments is composed of > 80% ontogenetic calcite that was precipitated in the primary, near surface habitat of this species.     

Planktonic foraminiferal turnover, diversity fluctuations and geochemical signals across the Eocene/Oligocene boundary in Tanzania

A major turnover in planktonic foraminifera occurred across the Eocene/Oligocene (E/O) boundary. New drill holes through the E/O boundary in southern Tanzania contain extremely well-preserved and diverse assemblages of planktonic foraminifera. Here we document a 1.2 million year record of assemblages, diversity and stable isotope fluctuations through this critical interval, which is often dissolved and/or recrystallised in carbonate-rich facies. The E/O boundary is marked by the abrupt extinction of all five remaining species of the family Hantkeninidae and a distinct size reduction in the genus Pseudohastigerina. The boundary is preceded over a short stratigraphic interval by the extinction of Turborotalia cerroazulensis, Turborotalia cocoaensis and Turborotalia cunialensis. Quantitative analysis of planktonic foraminiferal assemblages reveals significant changes in the abundance of certain species and the composition of the assemblages. We compare diversity fluctuations to the stable isotope record of Pseudohastigerina naguewichiensis and use multispecies stable isotope analyses to determine the life habitats of the most important species. A major shift in the evenness occurs at ~ 33.8 Ma associated with the extinction of the T cerroazulensis group suggesting acute ecological disturbance. We propose that the extinction of the T. cerroazulensis group at ~ 33.8 Ma was directly related to cooling of sea surface temperatures, while the extinction of Hantkeninidae was due to modifications in the thermal structure of the oceans and associated productivity changes. After the extinctions, renewed origination and diversification occurred, leading to a characteristic Oligocene planktonic foraminifer assemblage.     

Aptian to Maastrichtian paleobathymetric reconstruction of the Eastern Venezuelan Basin

The objective of this study is a paleobathymetric reconstruction of the depositional environment during the Cretaceous (Aptian-Maastrichtian) on the northern flank of the Eastern Venezuelan Basin. The model is based on the presence of benthic foraminifera in 17 well sections, spread across the paleoslope in a passive margin. Cluster analysis separates five distinct assemblages of foraminifers. The analysis is based on the assumption that the species must occur in 10% or in at least two wells of the area. The R-mode for each well provides clusters of species that are similar in distribution and abundance trends. These clusters together with the diversity and abundance of planktic foraminifers, dinoflagellates, pollen, spores, calcareous nannofossils, and sedimentological data help to delineate the biofacies. The biofacies are distributed in a pattern from the updip position (southwest) to the downdip position (northeast). The shallowest biofacies (0–50 m) is represented by Ammobaculites sp., Haplophragmoides sp., Lituolidae, with abundant terrestrial palynomorphs and dinoflagellates. Abundant species in depths greater than 100 m are Praebulimina carseyae, Epistomina lacunosa, Gavelinella sp., Buliminella sp., and Pullenia cretacea. This biofacies interpretation allows us to establish a paleocoast orientation during the Aptian-Maastrichtian.The establishment of the age-paleobathymetry relationships in this area provides the basis for the stratigraphic reconstruction of the Cretaceous in the Eastern Venezuelan Basin, thus reducing the risk for oil exploration.     

Neogene stratigraphy,foraminifera, diatoms,and depositional history of Maria Madre Island,Mexico: Evidence of early Neogene marine conditions in the southern Gulf of California

Foraminifera and diatoms have been analyzed from an upper Miocene through Pleistocene(?) sequence of marine sediments exposed on Maria Madre Island, largest of the Trés Marias Islands off the Pacific coast of Mexico. The Neogene stratigraphic sequence exposed on Maria Madre Island includes a mid-Miocene(?) non-marine and/or shallow marine sandstone unconformably overlain by a lower upper Miocene to uppermost Miocene upper to middle bathyal laminated and massive diatomite, mudstone, and siltstone unit. This unit is unconformably overlain by lower Pliocene middle to lower bathyal sandstones and siltstones which, in turn, are unconformably overlain by upper Pliocene through Pleistocene(?) upper bathyal to upper middle bathyal foraminiferal limestones and siltstones. These beds are unconformably capped by Pleistocene terrace deposits. Basement rocks on the island include Cretaceous granite and granodiorite, and Tertiary(?) andesites and rhyolites. The upper Miocene diatomaceous unit contains a low diversity foraminiferal fauna dominated by species of Bolivina indicating low oxygen conditions in the proto-Gulf Maria Madre basin. The diatomaceous unit grades into a mudstone that contains a latest Miocene upper to middle bathyal biofacies characterized by Baggina californica and Uvigerina hootsi along with displaced neritic taxa. An angular unconformity separates the upper Miocene middle bathyal sediments from overlying lower Pliocene siltstones and mudstones that contain a middle to lower bathyal biofacies and abundant planktonic species including Neogloboquadrina acostaensis and Pulleniatina primalis indicating an early Pliocene age. Significantly, this Pliocene unit contains common occurrences of benthic species restricted to Miocene sediments in California including Bulimina uvigerinaformis. Pliocene to Pleistocene(?) foraminiferal limestones and siltstones characterize submarine bank accumulations formed during uplift of the Trés Marias Island area, and include abundant planktonic foraminifera such as Pulleniatina obliquiloculata and Neogloboquadrina duterteri. Common benthic foraminifera in this unit are indicative of upper bathyal water depths. The Neogene depositional history recorded on Maria Madre Island involves an early late Miocene subsidence event marking formation of the Trés Marias Basin with relatively undiluted diatomaceous sediment deposited in a low oxygen setting. Subsidence and deepening of the basin continued into the early Pliocene along with rapid deposition of terrigenous clastics. Uplift of the basinal sequence began in late Pliocene time accompanied by deposition of upper Pliocene-Pleistocene foraminiferal limestones on a rising submarine bank. Continued episodic uplift of the Neogene deposits brought the island above sea level by late Pleistocene time.