Distribution Of Benthic Foraminifera Research Articles

Recent shallow-water benthic foraminifera from a tropical estuary, SW Nigeria

This paper presents a comprehensive survey of benthic foraminifera from shallow waters of the Apapa-Badagry Creek estuary in southwestern Nigeria. Sediments of the Apapa-Badagry Creek, an important estuary surrounded by sprawling estates and industrial parks, yielded diverse assemblages of benthic foraminifera with a total of eighty-eight species. They include hyaline-perforate taxa which dominated the inner western sites around the Lagos Harbor in the Apapa Creek with Ammonia aoteana, A. tepida, A. convexa, Ammonia sp. 1, Ammonia sp. 2. Agglutinated taxa are well established in the westernmost areas in the Badagry Creek, where there is seamless fresh-water mixing, with high populations of Ammotium salsum and few occurrences of Milliamina fusca and Ammobaculites species. The miliolids, represented mainly by species of Quinqueloculina, occupy sample stations in the Commodore Channel which flourish under conditions of marine and tidal influences. Cribroelphidium mirum, Pararotalia sarmientoi, Bolivina striatula and Rosalina species are also found within the Commodore Channel sediments. Our study widely extends and completes previous studies from the tropical eastern Atlantic, especially within the Gulf of Guinea and provides new information on the distribution, diversity, and species richness of shallow-water benthic foraminifera fringing the Atlantic coast of Africa.

Study of current benthic foraminifera as environmental bioindicators in the mediterranean coasts, northwest Morocco

In this project, we introduce a novel methodology for analysing the environmental conditions in the coastal area of Martil (Tétouan, Morocco) using benthic foraminifera as bio-indicators of marine ecological status. Benthic foraminifera have emerged as reliable indicators of environmental pollution, Their sensitivity to environmental changes, wide geographic presence, and short life cycle make them ideal for indicating the ecological status. Our study focused on the Mediterranean coastal region, along a radial perpendicular to the coast, at different depths, at the mouth of the Martil River, in addition to a control sample collected in the Azla region at a depth of 25 meters. Abiotic parameters like pH, temperature, and dissolved oxygen were measured on-site, complemented by detailed sedimentary analyses in the laboratory. A meticulous protocol was followed for the study of microfauna, particularly benthic foraminifera, involving washing, extraction, sorting, species identification, statistical counting, and microscopic imaging. Utilizing CA and AHC analyses, we identified factors influencing benthic foraminifera distribution, such as sediment depth and grain size variations. Specific indices derived from foraminifera data allowed us to assess stress levels accurately. This comprehensive approach provides valuable insights into evaluating the ecological health of Morocco's coastal marine ecosystems, paving the way for informed conservation efforts and sustainable management practices.

Abundance and distribution of recent benthic foraminifera from the southwestern part of the Bay of Bengal

Foraminifers are ubiquitous and abundant organisms in the marine environment, sensitive to different environmental variables such as pH, dissolved oxygen, salinity, temperature, organic matter and substrate. In the present study, environmental variables and benthic foraminiferal assemblages from 32 surface sediment samples belonging to different water depths were studied to understand the shelf and slope environment of the southwestern Bay of Bengal. Statistical methods such as cluster and principal component analysis (PCA) were used to infer the relationship existing among various foraminiferal assemblages, bathymetry, sediment and bottom water characteristics. Statistical analysis yielded four assemblages, of which assemblage-I is dominated by Nonion faba, Rotalidium annectens, Asterorotalia pulchella, Elphidium crispum, and Amphistegina radiata, and is confined to the shallowest inner shelf region (5 to 35 m water depth) with sandy sediments indicating high-energy condition. Assemblage-II is marked by the abundance of Cibicidoides wuellerstorfi, Hanzawaia concentrica, Quinqueloculina agglutinans, Quinqueloculina seminula, Quinqueloculina lamarckiana, Ammonia beccarri, and Ammonia tepida which are associated with the middle shelf region (water depth 35 to 70 m) with sandy to slightly muddy sand sediments. Assemblage-III is dominated by Asterorotalia dentata, Quinqueloculina venusta, Cancris communis, Cassidulina laevigata, and N. costiferum which occur at a depth of 70 to 170 m in the outer shelf, and are highly associated with slightly muddy sand to muddy sand. Whereas, assemblage -IV includes Uvigerina mediterranea, Bolivina dilatata, Bolivina robusta, and Bulimina marginata foraminiferal species that are abundant in the upper slope (170–244 m water depth) and are confined to muddy sand and sandy mud with low dissolved oxygen in the bottom water. The above assemblages depict that the abundance and distribution of foraminifera are largely controlled by substrate, energy conditions and environmental variables such as temperature, salinity, organic matter and dissolved oxygen.

Impact of submarine karst sulfur springs on benthic foraminiferal assemblage in sediment of northern Adriatic Sea

PurposeThis work highlights the sedimentary characteristics and the role of submarine sulfur-rich karstic springs in the distribution of benthic foraminifera in the northern part of the Adriatic Sea (Bay of Koper). Little is known about how local conditions such as temperature and sulfur bursts may influence sediment properties, benthic habitat variability, and composition of foraminiferal assemblages. Here we compare the distribution of total and living benthic assemblages in surface sediment samples collected from a funnel-shaped depression created by submarine sulfur springs.Materials and methodsSampling was performed at water depths between 24.6 and 32.2 m in fine-grained sandy silt to silty sand (partially washed). Sedimentological, mineralogical, and geochemical analyses of the sediment were carried out and the distribution of benthic foraminifera living around the springs was studied.Results and discussionIn general, sediment characteristics (i.e., mineralogical, geochemical, and organic content) around the sulfur springs do not show prominent deviations from the marine surface sediment of the area; however, some differences exist among depressions of different depths. Deeper depressions in the lower parts probably extend to older continental sediments of Late Pleistocene age with alluvial features, while shallower depressions were formed entirely in Holocene marine sediments typical of a wider area. Only one of the five samples (M05) contained living foraminifera in sufficient abundance for biocenosis research. The benthic foraminiferal assemblages of moderate diversity are composed of opportunistic species. Elphidium translucens, Ammonia ex gr. tepida, Haynesina depressula, and Porosononion granosum dominate, while A. neobeccarii, Reussella spinulosa, and Textularia bocki are subordinate.ConclusionsThe distribution and diversity of foraminifera in the sediment near sulfur springs can be explained by several factors and their interactions. The intensity of the spring discharge affects the mixing/oxygenation of the sediment, the shape of spring depressions, and the granulometry of the coarser sediment around the springs. Sediment characteristics indicate different types of sediment origin. This is related to and can be explained by the depth of spring depressions.

The Benthic Foraminiferal Assemblages in the Seagrass Bed of Tanjung Berakit Waters, Bintan Island

Seagrass is the most common ecosystem in Tanjung Berakit waters. Therefore, Tanjung Berakit waters have a very important role as a benthic foraminiferal habitat. This study was conducted to describe the distribution of benthic foraminifera relating to the environmental condition of the waters. The samples were collected from eight stations by handling garb in November 2017. This study collected 18 species of shallow water benthic foraminifera dominated by Amphistegina and Heterostegina. This study recorded a correlation between the sediment texture and foraminiferal assemblages. The most common foraminifera were inhabiting fine-textured sediments, especially very fine sand and silt. Only a few foraminifers are collected from extremely fine sediments such as clay sediments, or extremely coarse including pebbles.

Diversity and Distribution of the Benthic Foraminifera on the Brunei Shelf (Northwest Borneo): Effect of Seawater Depth

The marine benthic diversity of the Palawan/North Borneo ecoregion is poorly known, despite its implied unique high species richness within the Coral Triangle. The present study investigated the diversity and distribution of benthic foraminifera on the Brunei shelf. The objectives were to determine the species composition of sediment samples collected from 11 sites, extending ~70 km from the Brunei coastline and along a depth gradient of 10–200 m. We retrieved a total of 99 species, belonging to 31 families and 56 genera, out of which 52 species represented new records for Brunei and probably the ecoregion. Using presence/absence data, analyses were also performed to compare species diversity patterns (species richness, occupancy, taxonomic distinctness) and species assemblage similarity across the sites. For further insight into the relationship between distribution and depth-associated environmental conditions, we undertook stable isotope analyses of selected species of Rotaliida, Miliolida, and Lagenida. Oxygen isotope values were positively correlated with depth and species distribution, confirming cooler temperatures at greater depth. The carbon isotope data revealed species differences relating to habitat and food source specificity and a biomineralization effect. Close to one-third of the species were recorded from single sites, and species richness and taxonomic distinctness increased with depth and were greatest at the second deepest site (144 m). Together, these findings suggest data underrepresentation of diversity, habitat disturbance in shallower water, and species specialization (adaptation) in deeper water. Importantly, assemblage similarity suggests the occurrence of at least three marine biotopes on the Brunei shelf (10–40 m, 40–150 m, and >150 m). This study contributes significantly to our understanding of the local and regional patterns of foraminiferal diversity and distribution.

Benthic foraminiferal response to the Oceanic Anoxic Event 2 (Late Cretaceous) and evidence of bottom water re‐oxygenation during the Plenus Cold Event at Clot Chevalier (Vocontian Basin, SE France)

The Cenomanian-Turonian boundary interval is characterized by environmental perturbations related to the Oceanic Anoxic Event 2 (OAE 2) that severely affected the marine biota, including benthic and planktonic foraminifera. We present a continuous high-resolution benthic foraminiferal record in combination with published planktonic foraminiferal and geochemical data across the Cenomanian-Turonian boundary interval in the Clot Chevalier section (Vocontian Basin, SE France) with the aim to interpret paleoceanographic changes in bottom waters. Benthic foraminiferal assemblages are characterized by low diversity and indicate an outer shelf-upper bathyal environment. Changes in composition and abundance of the benthic assemblages throughout the stratigraphic section allow identification of seven distinct environments. In the middle Cenomanian, below the OAE 2, benthic foraminifera show high species diversity and abundance of infaunal and epifaunal taxa, suggesting an environment characterized by oxic conditions at the seafloor. The microfossil assemblages in the upper Cenomanian within the OAE 2 interval are dominated by radiolaria (> 50%) followed by benthic calcareous taxa (Gavelinella sp., Gyroidinoides sp., Praebulimina elata, Tappanina laciniosa). Benthic agglutinated taxa (Ammobaculites sp., Ammodiscus cretaceus, Gaudryina sp., Textulariopsis bettenstaedti) show high abundance in the lowest part of the OAE 2 and disappear close to the top of the interval. The assemblage composition and the highest values of Total Organic Carbon (TOC) registered in this interval suggest eutrophication and suboxic conditions at the seafloor. However, at ∼1 m above the onset of the OAE 2, the repopulation by inferred oxic benthic foraminiferal taxa (i.e., Frondicularia sp. and Ramulina aculeata) suggests ventilation of bottom water masses, recording the Plenus Cold Event (PCE). In the lowermost Turonian, the assemblages exhibit high species diversity and abundance with the re-appearance of calcareous taxa, indicating oxic conditions, and of agglutinated taxa associated to moderate oxygen concentrations. Results show that the distribution of benthic foraminifera follows fluctuations in oxygenation and carbon export flux at the seafloor interpreted as the environmental changes associated to the onset of the OAE 2 and of the PCE across the Cenomanian-Turonian boundary interval.

Sub-surface foraminifera distribution and preservation in short core samples from the Strait of Malacca

Abstract
 The Strait of Malacca—a shallow and hyposaline strait—is one of the busiest shipping routes in the world. It divides Sumatra and Peninsular Malaysia. This study assessed the sub- surface distribution of benthic foraminifera, their preservation, and their relationship with the sediment characteristics of the Strait of Malacca. One short sediment core sample was collected from the southern part of the Strait of Malacca. The core was then divided into 10 subsamples at every 2 cm interval. The samples were used for foraminifera identification and grain size and organic matter analysis. From the approximately 3000 benthic foraminifera that were selected and identified, 17 species exhibited ≥ 2% occurrence in at least one subsample along the core. Out of the 17 species identified, 4 species (Asterorotalia pulchella (57%), Cavarotalia annectens (13%), Discorbinella bertheloti (7%), and Pseudorotalia schoerteriana (6%)) exhibited an average relative abundance of >5% in all core intervals. Cluster analysis subdivided the core intervals into two groups: BF1 and BF2. Both the groups were dominated by A. pulchella. The PCA biplot indicated that BF1, which represented the upper sub-surface intervals, had relatively more agglutinated species than BF2. Despite being common in surface samples along the Strait of Malacca, species such as Textularia sp. were absent further down the core. This study indicated that in the sub-surface sediment of the Strait of Malacca, calcareous hyaline species, especially those belonging to Rotaliida, were abundant and readily preserved compared to the agglutinated or calcareous porcelaneous groups. The loss of several agglutinated groups down the cores indicated that a more discreet approach to paleoenvironmental interpretation using benthic foraminifera assemblages should be adopted in this region to avoid bias in the interpretation.

The influence of submarine canyons-related processes on recent benthic foraminiferal distribution, Espírito Santo Basin, Southeastern Brazil

The complex topography of submarine canyons may result in different composition of benthic foraminifera assemblages. To understand how trophic, hydrological and sedimentological conditions in submarine canyons can influence the distribution of benthic foraminifera, and to use this information to corroborate paleoenvironmental interpretations for the Holocene, we investigated recent benthic foraminiferal assemblages (total fauna >63 μm) and sedimentological data in two canyons (CANWN and CAND) in the Espírito Santo Basin (ESB) between 18°20′ and 21°20′ S. Surface sediment samples (0–2 cm) were collected inside the canyons (150 to 1300 m water depth) and in shelf-slope adjacent transects (50 to 1300 m water depth). The density, taxonomic diversity, and assemblage composition of benthic foraminifera change with depth and location. The distinct ecological preferences of the most abundant taxa allowed us to recognize five benthic foraminiferal groups. Three groups (V, III, and I) are present in different bathymetric sectors; Group V: outer shelf (50 m), Group III: upper, and middle – lower slope (150 to 400 m), and Group I: middle – lower slope (1000 to 1300 m). Groups II and IV show no characteristic bathymetric distribution and are present only in CAND and in CANWN, respectively. Group V consists of Hanzawaia boueana, Peneroplis planatus, and Quinqueloculina lamarckiana; Group III is dominated by Globocassidulina rossensis and Trifarina spp.; Group I consists of Globocassidulina crassa, Bolivina lowmani, Gavelinopsis versiformis, Alabaminella weddellensis, and Epistominella exigua. The main species in Group II (CAND, 150, 1000 to 1300 m) are Trifarina angulosa, Globocassidulina subglobosa, and Discorbis vilardeboanus. Group IV (middle – lower CANWN, 1000 to 1300 m), consists mainly of agglutinated species Glomospira charoides, Rhabdammina abyssorum, and Psammosphaera fusca. Our data suggest that the quantity (and quality) of food supply, hydrodynamic conditions and sediment properties are the main drivers controlling the bathymetric distribution of benthic foraminiferal assemblages in both canyons. The middle – lower CANNW revealed unstable trophic conditions, related to terrigenous sediment input due to turbidity currents. In CAND, the foraminiferal assemblages ecology indicated sufficient organic matter supply that favors species establishment and diversity, indicating a more productive and less unstable environment than in CANWN.

Understanding the Distributions of Benthic Foraminifera in the Adriatic Sea with Gradient Forest and Structural Equation Models

In the last three decades, benthic foraminiferal ecology has been intensively investigated to improve the potential application of these marine organisms as proxies of the effects of climate change and other global change phenomena. It is still challenging to define the most important factors affecting foraminiferal communities and derived faunistic parameters. In this study, we examined the abiotic-biotic relationships of foraminiferal communities in the central-southern area of the Adriatic Sea using modern machine learning techniques. We combined gradient forest (Gf) and structural equation modeling (SEM) to test hypotheses about determinants of benthic foraminiferal assemblages. These approaches helped determine the relative effect of sizes of different environmental variables responsible for shaping living foraminiferal distributions. Four major faunal turnovers (at 13–28 m, 29–58 m, 59–215 m, and >215 m) were identified along a large bathymetric gradient (13–703 m water depth) that reflected the classical bathymetric distribution of benthic communities. Sand and organic matter (OM) contents were identified as the most relevant factors influencing the distribution of foraminifera either along the entire depth gradient or at selected bathymetric ranges. The SEM supported causal hypotheses that focused the factors that shaped assemblages at each bathymetric range, and the most notable causal relationships were direct effects of depth and indirect effects of the Gf-identified environmental parameters (i.e., sand, pollution load Index–PLI, organic matter–OM and total nitrogen–N) on foraminifera infauna and diversity. These results are relevant to understanding the basic ecology and conservation of foraminiferal communities.

New biostratigraphy and microfacies analysis of Eocene Jahrum Formation (Shahrekord region, High Zagros, West Iran). A carbonate platform within the Neo-Tethys oceanic realm

The Eocene Jahrum Formation in High Zagros was studied in Kuh-e- Soukhteh and North Gahrou sections (southwest of Shahrekord region, Chahar-mahal Bakhtiari Province). This formation, composed of limestone, marl, and dolomitic limestone (dolostone), accumulated on a marine platform within the Neo-Tethys ocean realm. It yields a rich foraminiferal fauna, in which three larger benthic foraminiferal assemblage zones were identified. Two assemblage zones in the North Gahrou section were correlated to the Ypresian and Bartonian, and one assemblage zone is represented in the Kuh-e- Soukhteh section and assigned to the Bartonian. In addition, three other groups of benthic foraminiferal associations have been identified based on test wall type (porcellaneous, agglutinate, hyaline) and paleogeographical significance. A discontinuity marked by a hiatus from Cuisian to Lutetian in the North Gahrou section was most probably due to a concealed fault. According to microscopic textures and distribution of benthic foraminifera and other components (peloids, intraclasts, etc.), a gentle depth gradient from the inner ramp to the proximal outer ramp may be reconstructed.

Spatial Distribution of Benthic Foraminifera in the Neretva Channel (Croatia Coast): Faunal Response to Environmental Parameters

Benthic foraminiferal assemblages have been studied at 11 sediment surface samples located in the Neretva Channel covering the delta habitat and the adjacent open sea areas. The major objective of the investigation was to explore the main environmental parameters affecting the benthic foraminifera compositional changes. To this end, a statistical approach was applied that integrates micropaleontological data with physical, geochemical and sedimentological parameters (total organic carbon and grain size). Statistical analyses identified four distinct groups (cluster A1, A2, B1, B2) corresponding to different environmental settings. Cluster A1 groups samples under Neretva river influence and is characterized by Aubignyna perlucida, Nonionella turgida, Eggerelloides scaber and Rectuvigerina sp.; species able to live in organic-matter-rich sediments and in a wide range of oxygen content. Cluster A2 includes samples distant from the fluvial outlet and samples along the NW coast partially influenced by the Neretva river plume. In these environmental conditions, Ammonia beccarii, Bulimina marginata, Nonionella turgida and Textularia sp. resulted as the most characteristic taxa. Cluster B1 distinguishes the deepest stations which are in connection with the open Adriatic Sea. Here Asterigerinata mamilla, Buccella granulata, Cibicides group, Reussella spinulosa and Textularia sp. reach their maximum abundance associated with coarse-grained sediments. Cluster B2 groups samples collected in the inner bay of the southernmost sector of the studied area characterized by silt and clay and a negligible influence by river inputs. The benthic microfauna is principally composed of Miliolids, Porosononion granosum and Textularia sp.

Distribution of larger benthic foraminifera from Miocene carbonates in the Center and Southeast of the Nam Con Son basin

In biostratigraphical studies, the planktonic foraminifera, nannofossils, and palynomorphs are recorded rarely in shallow water limestones. Meanwhile, larger benthic foraminifera (LBF) have an important role in defining the stratigraphic range and the depositional environment of carbonate formations is recorded abundantly. The precise identification of LBF’s taxonomy depends on the recognition of its internal structures using polarised microscopes.
 Results from the study in the Central and South-eastern Nam Con Son basin show that LBF occurred frequently in the Miocene and, especially, became extremely dominant in the Middle Miocene. In the Early Miocene (Te5 - lower Tf1), they appeared sparsely in the Te5 but became abundant in the lower Tf1. In the Middle Miocene (middle Tf1 - Tf3), they were predominant and diverse in many genera and species, marked by the disappearance of Miogypsina, Miogypsinoides, Katacycloclypeus, and most of the species of Lepidocyclina and Cycloclypeus at the top of the sub-epoch. In the Late Miocene (Tg), LBF was not varied, mainly Amphistegina and Operculina. However, some significant species of the genus Lepidocyclina were extant and dwelled on the isolated carbonate platforms in the Southeast area of the basin. The association of larger benthic foraminifera with small millioids and rotalids, planktonic foraminifera, coral, and/or algae, crinoids, bivalves, etc., may implicate the palaeoenvironmental zone of the carbonate deposits in the wells of the studied region, ranging from the lagoon, shelves surrounding reef to relatively deep, open marine conditions. The occurrence of LBF in carbonate deposits is the key to defining the age, identifying the stratigraphy and depositional environment, and correlating the carbonates.

Distribution and Diversity of Benthic Foraminifera in the Coastal Area of Al-Bawadi Island, Southern Red Sea

ABSTRACT The coastal areas of the southern Red Sea islands are non-urbanized, relatively pristine environments and are located on the main migration pathway of Indo-Pacific foraminiferal species to the northern Red Sea and to the Mediterranean Sea via the Suez Canal. Studying the foraminiferal composition, structure, and distribution in the Red Sea is essential to understanding how Indo-Pacific species can migrate to and survive in the Mediterranean Sea. Al-Bawadi, an uninhabited island located in the southern Red Sea, is an ideal location for such study. The coastal waters are oligotrophic, hypersaline, and very warm, overlying carbonate-rich, sandy-bottom and coral-reef substrata. In 25 sediment samples collected from water depths <6 m, 79 foraminiferal species were recorded. Rotaliids dominated the assemblages, followed by miliolids; agglutinated foraminifers were scarce, and planktic species were not found. The larger-benthic, symbiont-bearing Neorotalia calcar dominated except in very shallow water, where smaller, free-living miliolid species dominated. The FoRAM Index (FI) was calculated for all samples; the symbiont-bearing group included seven genera comprising more than half of the total assemblage such that the FI>4 for most samples from depths >3 m, indicating that water quality is suitable for coral-reef growth and recovery. Diversity indices reflected prevailing normal marine to hypersaline conditions. Depth, presence of coral reefs, and hydrodynamics are the main factors controlling the spatial distribution of the foraminiferal assemblages. Occurrences of aberrant tests in the tidal flat area could be related to naturally occurring stresses, such as rapid changes in temperature and salinity, or to breakage and repair. Monitoring studies of unthreatened environments are essential to understand reef-related assemblages and to predict the migration pathways of thermo-tolerant and thermo-sensitive foraminiferal species.

Co-occurrence patterns and community assembly mechanisms of benthic foraminiferal communities in South Chinese bays

Benthic foraminifera are among the most important components of marine benthic communities and can provide valuable information about the structure and activity of those communities. The distribution and diversity of benthic foraminifera have been well documented, but their co-occurrence patterns and community assembly processes have rarely been elucidated. To fill this gap, we used network analysis and null/neutral model approaches to benthic foraminiferal communities in five bays in South China to evaluate the influences of environmental factors and interspecies interactions on species co-occurrence and the relative importance of deterministic and stochastic processes in shaping community structure, respectively. The spatial heterogeneity of foraminiferal communities across bays was characterized by nonmetric multidimensional scaling analysis. Variation partitioning analysis showed that heavy metals (Cr, Co, Cu, As, Sb, and Hg) were the most important factor influencing community structure, while less importance was attributed to organic matter and grain sizes, which was likely due to the low TOC contents and small variations in TOC and grain size across sites. Network analysis showed that closely related species tended to co-occur with each other, which may be mediated by environmental filtering. The network was divided into three distinct clusters: one cluster consisted of miliolid, and two were dominated by rotaliids, each of which represented a special niche according to the habitat preference of the dominant taxa. The structure of the network was highly informative, as illustrated by the fact that the observed structure was denser than that of randomly constructed networks with the same size or the same degree sequence. The frequency of occurrence of most species (70%) met neutral model expectations, indicating that neutral processes were important for the assembly of benthic foraminiferal communities. However, PER-SIMPER analysis revealed that niche-assembly processes were more important than dispersal-assembly processes in shaping species abundance. Overall, this study provides the first insight into the mechanisms maintaining the community structure and diversity of benthic foraminifera.

Distribution and ecology of benthic foraminifera in the Santoña estuary, Spain

The living and dead assemblages in the Santoña estuary were studied seasonally in order to determine the distribution and abundance of the benthic foraminifera in this area. Samples were collected from Winter 1983 to summer 1985 to document the seasonal variation of the faunas and various ecological factors in the intertidal zone. Salinity is thought to be the main control of the living assemblages and two different biofacies characterising the upper and lower areas have been defined. Ammonia beccarii and Haynesina germanica are the most dominant forms throughout the estuary with Miliammina fusca as co-dominant in the upper estuary and Quinqueloculina seminulum as co-dominant in the lower estuary. The dominant living species are also dominant in the dead assemblages but in the latter the agglutinated indigenous component is much more abundant. This compositional difference is thought to be caused by production rates and change in the environmental conditions within the estuary. The living and dead assemblages have been analysed and compared using the Fisher a diversity index, Triangular plot of wall types and Sanders similarity index.

Biotic and Paleoceanographic Changes Across the Late Cretaceous Oceanic Anoxic Event 2 in the Southern High Latitudes (IODP Sites U1513 and U1516, SE Indian Ocean).

Oceanic Anoxic Event 2, spanning the Cenomanian/Turonian boundary (93.9 Ma), was an episode of major perturbations in the global carbon cycle. To investigate the response of biota and the paleoceanographic conditions across this event, we present data from International Ocean Discovery Program sites U1513 and U1516 in the Mentelle Basin (offshore SW Australia; paleolatitude 59°–60°S in the mid‐Cretaceous) that register the first complete records of OAE 2 at southern high latitudes. Calcareous nannofossils provide a reliable bio‐chronostratigraphic framework. The distribution and abundance patterns of planktonic and benthic foraminifera, radiolaria, and calcispheres permit interpretation of the dynamics of the water mass stratification and provide support for the paleobathymetric reconstruction of the two sites, with Site U1513 located northwest of the Mentelle Basin depocenter and at a deeper depth than Site U1516. The lower OAE 2 interval is characterized by reduced water mass stratification with alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer as indicated by the fluctuations in abundance of the intermediate dwelling planktonic foraminifera. The middle OAE 2 interval contains lithologies composed almost entirely of radiolaria reflecting extremely high marine productivity; the low CaCO3 content is consistent with marked shoaling of the Carbonate Compensation Depth and ocean acidification because of CaCO3 undersaturation. Conditions moderated after deposition of the silica‐rich, CaCO3‐poor rocks as reflected by the microfossil changes indicating a relatively stable water column although episodes of enhanced eutrophy did continue into the lower Turonian at Site U1516.

DISTRIBUTION OF BENTHIC FORAMINIFERA IN THE CORAL REEFS ECOSYSTEM OF PULAU BIDONG, TERENGGANU, SOUTHERN SOUTH CHINA SEA

A study on the distribution of benthic foraminiferal species in the surface sediments of coral reefs was carried out in Pulau Bidong in the southern South China Sea (SCS). Samples were collected at 12 sites around Pulau Bidong at water depths ranging from 5 m to 30 m. Live (rose bengal stained) and optimally preserved empty tests of benthic foraminifera were analysed based on their chamber and apertural characteristics observed under binocular microscope (Leica Zoom 2000). The results revealed that 32 genera of benthic foraminifera were found in the coral reefs sediments. Amphistegina was the most abundant genus with relative abundance of 68% and frequently recorded at depths of between 10-15 m and 25-30 m. Other common genera that were found were Calcarina, Elphidium, Heterolepa, Heterostegina, Quinqueloculina, Peneroplis and Triloculina. These genera showed depth distribution preference in the shallow water zone (5 m depth). The highest diversity index (2.3) and number of taxa (26 genera) were recorded at station W2, located at the western part of Pulau Bidong. The lowest diversity index (0.2) and number of taxa (seven genera) were recorded at station S3, located at the southern part of Pulau Bidong. The frequency distribution and diversity of benthic foraminifera in the study area were related to water depth.

The early middle Eocene transition at the Esera valley

An integrated study including magnetostratigraphy, larger benthic foraminifera and calcareous nannofossil biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised, the taxa found are enough to support the chronostratigraphic attribution. Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulitesand Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs. These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ 13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary occurs in SBZ 12.

Diversity and Depth Distribution of Modern Benthic Foraminifera Offshore Brunei Darussalam

ABSTRACT The distribution of modern benthic foraminifera is studied from offshore mixed carbonate-siliciclastic settings of Brunei Darussalam located in northwestern Borneo (South China Sea). The sediments were collected from 17 sites (i.e., shallow reefs, sunken wrecks, and two depth transects). A total of 231 species were identified from 8 to 63 m water depth. We conducted several analyses to understand the patterns of faunal composition, including: (1) Cluster analysis and Principal Component Analysis together with correlation to define relation among the sites; (2) Diversity indices, such as Shannon Index and Fisher's Alpha Index to assess diversity patterns at sites; and (3) Foram Index (FI) to determine whether the water quality indicates conditions that support reef growth. The most abundant foraminiferal groups from the reef and most wreck samples are larger benthic foraminifera (LBF), especially Calcarinidae and Amphisteginidae, whereas in the muddier sites the most abundant are smaller benthic foraminifera (SBF) with the genera Pseudorotalia and Asterorotalia. Certain species from the groups have shown patterns that do or do not correlate with depth and clay content.