Modern Benthic Foraminifera Research Articles

Seasonal variability of modern benthic foraminifera assemblages in a mangrove ecosystem from northeast coastal Bay of Bengal

Benthic foraminifera assemblages, nutrient dynamics of surface and porewater from 10 intertidal sites spanning over two years (2019–2020) covering two major estuaries in Sundarbans mangrove were evaluated to understand role of seasonal precipitation and primary production (driven by eddy nutrients) with a focus on standing crop. Benthic foraminifera abundance ranged between 280 individuals/10 cc in pre-monsoon (2019), 415 individuals/10 cc in post-monsoon 2019 and 630 individuals/10 cc in post-monsoon (2020). Standing crop was highest in post-monsoon coinciding with eddy nutrients driven stoichiometry and increase in abundance of large diatom cells. Calcareous and agglutinated foraminifer taxa Ammonia sp.1, Quinqueloculina seminulum, Entzia macrescens and Textularia sp. respectively were frequent. Entzia macrescens was found in dense mangrove vegetation sites; exhibited strong relationship with sediment texture and pore water total organic carbon. One of the major findings is mangroves with pneumatophores improves oxygen availability in sediment and leads to an increase in standing crop.

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.

Groundwater Salinity and Particulate Organic Carbon Flux Control Benthic Habitats in Anchialine Environments on Millennial Timescales

The environmental conditions and habitats in Bermudian underwater caves have responded to vertical aquifer migration and groundwater salinity changes associated with sea-level rise since the last glacial maximum. Recently, a large database of modern benthic foraminifera in Bermudian caves were found to be highly sensitive to both the amount and source of particle organic carbon (POC) transported to the sediment-water interface, consistent with similar timewise analysis of foraminifera in a Mexican flooded cave. Here we provide evidence that while benthic meiofaunal communities in Bermuda’s underwater caves are primarily controlled by groundwater salinity changes on millennial timescales from sea-level change, they are secondarily controlled by the POC source and supply deposited in the cave through time. Benthic foraminiferal assemblages were evaluated in the best-preserved stratigraphic succession currently known from an underwater cave. In the case of Palm Cave, POC flux changes were driven by changes in seawater-groundwater circulation dynamics caused by flooding on the carbonate banktop, and the inherited geometry of the cave system itself. These results demonstrate that benthic meiofaunal communities in anchialine environments are highly sensitive to changes in the source and quantity of POC through time. This work also enables a better understanding of the environmental conditions associated with preserved meiofaunal remains in global cave sediment. These results indicate that if the POC flux to the subsurface increases from coastal urbanization on karst landscapes, subsurface anchialine communities are likely to respond.

Fast and pervasive diagenetic isotope exchange in foraminifera tests is species-dependent

Oxygen isotope compositions of fossil foraminifera tests are commonly used proxies for ocean paleotemperatures, with reconstructions spanning the last 112 million years. However, the isotopic composition of these calcitic tests can be substantially altered during diagenesis without discernible textural changes. Here, we investigate fluid-mediated isotopic exchange in pristine tests of three modern benthic foraminifera species (Ammonia sp., Haynesina germanica, and Amphistegina lessonii) following immersion into an 18O-enriched artificial seawater at 90 °C for hours to days. Reacted tests remain texturally pristine but their bulk oxygen isotope compositions reveal rapid and species-dependent isotopic exchange with the water. NanoSIMS imaging reveals the 3-dimensional intra-test distributions of 18O-enrichment that correlates with test ultra-structure and associated organic matter. Image analysis is used to quantify species level differences in test ultrastructure, which explains the observed species-dependent rates of isotopic exchange. Consequently, even tests considered texturally pristine for paleo-climatic reconstruction purposes may have experienced substantial isotopic exchange; critical paleo-temperature record re-examination is warranted.

Systematics of Modern Benthic Foraminiferal Assemblages From the Deltaic Mangrove Ecosystem of Sundarbans

The contemporary intertidal foraminifera and estuarine environment information were collected from the four sites adjoining the deltaic mangrove environment in the Sundarbans. The marsh zones of the south-western coastal region of Bangladesh were examined for modern benthic foraminifera and to expound on the relationship of the foraminiferal assemblages with the environment. Due to high inaccessibility and remoteness, the taxonomic study of foraminifera and its depositional environment remains largely overlooked in the Sundarbans of Bangladesh. This study includes a detailed survey of depositional environment of these fluvio-deltaic to shallow marine sediments. The seventeen species belonging to fourteen genera representing nine families were recorded from surficial sediment of supratidal, intertidal, and dune environment of Kotka, Jamtala, Kochikhali, and Dimer char area. In the present study, these foraminiferal assemblages are characterized calcareous and agglutinated foraminifera. The Kotka beach is recognized as Nonionina assemblage zone, Jamtala beach designated as Ammonia assemblage zone, Kochikhali as Nonionina assemblage zone and Dimer char as Rosalina-Nonionina-Nonionella assemblage zone. The deposition of foraminifera is restricted to Sundarbans’ low to high marsh zone. J. Asiat. Soc. Bangladesh, Sci. 47(2): 121-136, December 2021

Environmental Controls on the Distribution of Modern Benthic Foraminifera in the Florida Everglades and Their Use as Paleoenvironmental Indicators

ABSTRACT This study examined the environmental factors that control the distribution of modern foraminiferal assemblages in the Everglades in order to provide baseline data for a paleoenvironmental study. Total assemblages from the surface 2 cm of 30 sites across the marsh and mangrove environments of southwest Florida were investigated. Eight environmental variables, including average salinity, salinity range, pH, total phosphorus, temperature, and dissolved oxygen, and total organic carbon and total inorganic carbon measured on bulk sediments, as well as the elevation and distance from the coastline were determined for each of the 30 sampling locations. In total, 82 species were identified, the majority of which were calcareous. Diversity decreases, dominance increases, and agglutinated taxa increase from the coastline inland. Rotaliina are equally abundant across the intertidal environment, whereas Miliolina are common near the coast and in lagoons or inland lakes. The most important factor controlling foraminiferal distribution is total organic carbon, followed by total inorganic carbon, distance from coastline, total phosphorus, and salinity. Jadammina macrescens and Miliammina fusca indicate lower salinities (<15 psu). Good indicators for higher salinities are Haplophragmoides wilberti (10–20 psu) and Arenoparrella mexicana (10–20 psu and 28–30 psu). Ammonia spp. prefer salinities >15 psu and Elphidium spp. >20 psu. Ammonia tepida, Helenina anderseni, Trochammina inflata, and A. mexicana prefer organic-rich sediments. Thus, the benthic foraminifera from Everglades sediments are excellent salinity proxies and can be used to determine the history of habitat change in this area as well as to assess past trends in the rate of sea level rise.

Fossichnus solus and Oichnus simplex, two peculiar ichnospecies in modern benthic foraminifera from a polluted area in SW coast of Sardina, Italy

The modern benthic foraminiferal tests collected from a coastal area of south-western Sardinia (Portoscuso-Portovesme) that is heavily polluted by industrial activity reveal intense and widespread bioerosional structures induced by diversified microborers. A large number of the foraminifera reveals microscopic round holes (1-60 μm in diameter) and roundish concavities (25x40 μm in external diameter) on their surface that belong, respectively, to the ichnospecies Oichnus simplex Bromley, 1981, and Fossichnus solus Nielsen et al., 2003. These traces just occur in the tests of the foraminifera which are heavily infested by microendolithic cyanobacteria, algae and fungi suggests comparable ethological behaviour between the ichnospecies Fossichnus and Oichnus and the microbial euendoliths that are ascribed to individual biological taxa. The greater occurrence of F. solus and O. simplex in the high-Mg foraminiferal porcelanaceous tests than in the low-Mg foraminiferal hyaline tests reveals that the bioerosional processes seem to be related to the Mg/Ca ratio, as well as to morphological structures of the taxa

Mg/Ca-Temperature Calibration of Polar Benthic foraminifera species for reconstruction of bottom water temperatures on the Antarctic shelf

Benthic foraminifera Mg/Ca is a well-established bottom water temperature (BWT) proxy used in paleoclimate studies. The relationship between Mg/Ca and BWT for numerous species has been determined using core-top and culturing studies. However, the scarcity of calcareous microfossils in Antarctic shelf sediments and poorly defined calibrations at low temperatures has limited the use of the foraminiferal Mg/Ca paleothermometer in ice proximal Antarctic sediments. Here we present paired ocean temperature and modern benthic foraminifera Mg/Ca data for three species, Trifarina angulosa, Bulimina aculeata, and Globocassidulina subglobosa, but with a particular focus on Trifarina angulosa. The core-top data from several Antarctic sectors span a BWT range of −1.7 to +1.2 °C and constrain the relationship between Mg/Ca and cold temperatures. We compare our results to published lower-latitude core-top data for species in the same or related genera, and in the case of Trifarina angulosa, produce a regional calibration. The resulting regional equation for Trifarina angulosa is Temperature (°C) = (Mg/Ca −1.14 ± 0.035)/0.069 ± 0.033). Addition of our Trifarina angulosa data to the previously published Uvigerina spp. dataset provides an alternative global calibration, although some data points appear to be offset from this relationship and are discussed. Mg-temperature relationships for Bulimina aculeata and Globocassidulina subglobosa are also combined with previously published data to produce calibration equations of Temperature (°C) = (Mg/Ca-1.04 ± 0.07)/0.099 ± 0.01 and Temperature (°C) = (Mg/Ca-0.99 ± 0.03)/0.087 ± 0.01, respectively. These refined calibrations highlight the potential utility of benthic foraminifera Mg/Ca-paleothermometry for reconstructing past BWT in Antarctic margin settings.

Distribution of Benthic Foraminifera off Kelantan, Peninsular Malaysia, South China Sea

Abstract We investigated the distribution of modern benthic foraminifera from Kelantan waters in the western part of the Sunda Shelf, South China Sea. Twenty-nine benthic foraminiferal species were identified from seven samples collected along a ∼250 km-long transect perpendicular to the Kelantan coastline. Calcareous hyaline species made up 57% of the overall assemblages collected in the study area, followed by calcareous porcelaneous (23%) and agglutinated (20%) species. Cluster analysis recognised two distinctive groups. Group A represented the shallow inner-shelf area (19–35 m water depth) with a coarse sand-dominated substrate where Amphistegina papillosa (13.37%) and Assilina ammonoides (11.04%) were highly abundant. Group A had lowest diversity with no agglutinated species. Group B, occurred at 40–60 m water depth, had higher foraminiferal diversity and was characterised by a very fine sand substrate. The foraminiferal assemblages here were dominated by calcareous hyaline species in group B followed by calcareous porcelaneous and agglutinated species. Group B was characterised by Assilina ammoinodes (11.04%), Heterolepa dutemplei (10.29%), and Discorbinella bertheloti (10.03%). The dominant agglutinated species in Group B were Textularia agglutinans (4.93%) and Cylindroclavulina bradyi (3.55%). Shallow-water species, such as Amphistegina spp., were absent from Group B. Our study shows that the distribution of benthic foraminiferal assemblages from the western Sunda shelf off Kelantan, is closely associated with changes in seafloor sediment, distance from the shore, and water depth.

Inner Shelf Benthic Foraminifera of the South China Sea, East Coast Peninsular Malaysia

Abstract The distributional patterns of modern benthic foraminifera from the inner shelf of the southern South China Sea, off the east coast of peninsular Malaysia, are documented for the first time. The study area from Tanjung Sedili, Johor in the south to Marang, Terengganu, in the north was selected for a sand-resource study by the Minerals and Geoscience Department, Malaysia in 1993. Twenty-four surface sediment samples from <50 m water depth contained 266 foraminiferal species belonging to 6 orders, 49 families, and 117 genera, including 32 agglutinated, 130 calcareous hyaline, and 104 calcareous porcelaneous species. Two biofacies were distinguished by cluster analysis. Biofacies A was characterized by high relative abundance of Amphistegina papillosa and few other larger benthic foraminiferal (LBF) taxa in sandier sediments. Biofacies B was characterized by Pseudorotalia schroeteriana and other small rotaliids that were found in muddy sediments. The following features of foraminiferal assemblages and sediments reflect the strong fluvial/terrestrial influence on this tropical shelf environment: the overall moderate foraminiferal diversity, dominance of rotaliids over miliolids, overall dominance of smaller foraminiferal assemblages by Elphidium crispum, the limited diversity of LBF, the limited abundance of A. lessonii and the dominance of LBF assemblages by A. papillosa at relatively shallow depths. These features indicate at least intermittently turbid waters with limited light penetration and the dominance of the shelf sediments by siliciclastics, with mean percent carbonates <35%.

Atlas of benthic foraminifera from coral reefs of the Raja Ampat Archipelago (Irian Jaya, Indonesia)

Raja Ampat (Indonesia) is a remote archipelago west of Papua mainland and situated at the eastern edge of the Coral Triangle. The archipelago is considered one of the species-richest and most pristine localities and home to the world’s most diverse coral reefs. For centuries, reefs of Raja Ampat have enjoyed natural protection and remained largely untouched due to their isolated location. The region represents a key area for evaluating richness and biogeographic patterns of tropical shallow-water organisms, yet the foraminiferal fauna of Raja Ampat is virtually unexplored. Benthic foraminifera are an integral part of the reef fauna, prolific carbonate producers and essential for reefal accretion and substrate stability. Previous studies on Indo-Pacific benthic reef foraminifera indicate that diversity is highest in the Central Indo-Pacific and broadly correlates with diversity patterns of other tropical marine taxa. This report presents the first illustrated catalog and comprehensive analysis of the structure, composition, and diversity of the species-rich benthic foraminiferal biotas of the Raja Ampat Archipelago including an assessment of local reef vitality with the Foraminifera in Reef Assessment and Monitoring (FoRAM) Index. We examined shallow-water sediment samples from fringing reefs, reef platforms, sheltered bays and reef-associated environments to cover the full range of existing micro- and macrohabitats. Atotal number of 421 species were recovered, among them five new species and one newly described genus of the porcelaneous Miliolida. The fauna is dominated by hyaline taxa but the Miliolida represent the species-richest order and are especially diverse in fine-grained sediments of deep fore-reef slopes. Extraordinary high diversity of the benthic foraminiferal communities indicates that the waters of Raja Ampat probably represent one of the world’s biologically richest locations in reefs.We identified a total of 35 species of larger symbiont-bearing benthic foraminifera, a number that is among the highest reported so far for reefs in modern oceans. The analysis of the FoRAM Index revealed that water quality at all sites examined is suitable for reef growth and recovery. The results of our study show that the Raja Ampat Archipelago harbors unique and particularly diverse assemblages of modern benthic foraminifera and provides a protistan perspective for the hotspot of diversity in the Central Indo-Pacific.

Testing the applicability of a benthic foraminiferal-based transfer function for the reconstruction of paleowater depth changes in Rhodes (Greece) during the early Pleistocene.

We present paleo-water depth reconstructions for the Pefka E section deposited on the island of Rhodes (Greece) during the early Pleistocene. For these reconstructions, a transfer function (TF) using modern benthic foraminifera surface samples from the Adriatic and Western Mediterranean Seas has been developed. The TF model gives an overall predictive accuracy of ~50 m over a water depth range of ~1200 m. Two separate TF models for shallower and deeper water depth ranges indicate a good predictive accuracy of 9 m for shallower water depths (0–200 m) but far less accuracy of 130 m for deeper water depths (200–1200 m) due to uneven sampling along the water depth gradient. To test the robustness of the TF, we randomly selected modern samples to develop random TFs, showing that the model is robust for water depths between 20 and 850 m while greater water depths are underestimated. We applied the TF to the Pefka E fossil data set. The goodness-of-fit statistics showed that most fossil samples have a poor to extremely poor fit to water depth. We interpret this as a consequence of a lack of modern analogues for the fossil samples and removed all samples with extremely poor fit. To test the robustness and significance of the reconstructions, we compared them to reconstructions from an alternative TF model based on the modern analogue technique and applied the randomization TF test. We found our estimates to be robust and significant at the 95% confidence level, but we also observed that our estimates are strongly overprinted by orbital, precession-driven changes in paleo-productivity and corrected our estimates by filtering out the precession-related component. We compared our corrected record to reconstructions based on a modified plankton/benthos (P/B) ratio, excluding infaunal species, and to stable oxygen isotope data from the same section, as well as to paleo-water depth estimates for the Lindos Bay Formation of other sediment sections of Rhodes. These comparisons indicate that our orbital-corrected reconstructions are reasonable and reflect major tectonic movements of Rhodes during the early Pleistocene.

Annual changes in Arctic fjord environment and modern benthic foraminiferal fauna: Evidence from Kongsfjorden, Svalbard

The relationships between modern Arctic benthic foraminifera and their ecological controls, along with their sensitivity to rapid environmental changes, is still poorly understood. This study examines how modern benthic foraminifera respond to annual environmental changes in the glaciated Arctic fjord Kongsfjorden, western Svalbard. Large environmental gradients due to the inflow of warm and saline Atlantic Water and the influence of tidewater glaciers characterise the fjord hydrography. A transect of six multi-corer stations, from the inner to the outer fjord, was sampled in the late summers of 2005 to 2008 to study the distribution of living (rose Bengal stained) benthic foraminifera. Physical properties of the water masses were measured concurrently. In general, nearly the entire Kongsfjorden region was dominated by ubiquitous N. labradorica foraminiferal assemblage that successfully exploited the local food resources and thrived particularly well in the presence of Atlantic-derived Transformed Atlantic Water (TAW). Further, the annual investigation revealed that Kongsfjorden underwent large interannual hydrological changes during the studied years related to variable inflow of warm and saline Atlantic Water. This led to a strong fauna variability particularly at the two marginal sites: the glacially influenced inner fjord and marine influenced shelf region. We also observed significant species shift from the ‘cold’ to ‘warm’ years and an expansion of widespread and sub-arctic to boreal species into the fjord.

An updated classification of rotaliid foraminifera based on ribosomal DNA phylogeny

Abstract Rotaliida is the most diversified order of modern benthic foraminifera, comprising 73 extant families. The current classification of Rotaliida is based exclusively on morphological characters of their calcareous tests. Previous molecular phylogenetic studies partly confirmed morphological classifications but they were based on relatively limited taxon sampling and SSU rRNA gene sequences only. Here, we investigate phylogenetic relationships of rotaliid foraminifera by sequencing complete or partial SSU and LSU rRNA genes for 80 phylotypes representing 70 genera. The analysis of 87 sequences of concatenated genes enabled us to recognize seven rotaliid superfamilies, four of them being established ones (Planorbulinoidea, Discorboidea, Rotalioidea, Nummulitoidea) and three new ones (Glabratelloidea, Calcarinoidea, Serioidea). Although some of these superfamilies were not strongly supported in phylogenetic trees, due to a weak signal of ribosomal genes, they comprise genera and families of distinctive morphological features that have been often united in previous morphology-based classifications. A total of 34 families has been recognized, 10 of them being newly established ones. The placement of three families (Rubratelliidae, Cymbaloporidae, Murrayinelliidae), which occupied isolated branches among the seven superfamilies, could not be determined and they are considered here as incertae sedis. An assemblage of 22 genera representing several morphologically different families of small rotaliids (Clade 3) was not raised to superfamily level because of the lack of molecular and/or morphological support. The phylogenetic relations within this assemblage as well as within the superfamily Rotalioidea have been examined in detail by analyzing partial SSU rDNA sequences for large taxon sampling.

Latitudinal change in benthic foraminiferal fauna by ITCZ movement along the ~131°W transect in the equatorial Pacific Ocean

Modern and fossil benthic foraminifera were examined from nine surface sediments and two piston cores along the ~131°W transect in the equatorial Pacific Ocean. This study was conducted to clarify the biotic response of abyssal benthic foraminifera during the last 220 ka to changes in the seasonal extent of the Intertropical Convergence Zone (ITCZ). The abundance of modern benthic foraminifera was high at stations between the equator and 6°N, whereas it was low at stations north of 6°N, which is generally consistent with the latitudinal CaCO3 distribution of surface sediments. The northward increase of Epistominella exigua from the equator to ~6°N is similar to the seasonal variations in chlorophyll-a concentrations in the surface water and ITCZ position along ~131°W. This species was more common at core PC5103 (~6°N) than at core PC5101 (~2°N) after ~130 ka, when the Shannon-Wiener diversity (H’) between the two cores started to diverge. Hence, the presentday latitudinal difference in benthic foraminifera (E. exigua and species diversity) between ~2°N and ~6°N along ~131°W has been generally established since ~130 ka. According to the modern relationship between the seasonality of primary production and seasonal ITCZ variations in the northern margin of the ITCZ, the latitudinal divergence of benthic foraminiferal fauna between ~2°N and ~6°N since ~130 ka appear to have been induced by more distinct variations in the seasonal movement of ITCZ.

Shallow-water nearshore benthic foraminifera assemblages from Gabon

The Gulf of Guinea is a hotspot of marine diversity, with unique biotas. We provide the first survey of shallow-water foraminifera from nearshore coastal waters of Gabon, an area from which modern benthic foraminifera are virtually unknown. We document the composition of benthic assemblages and assess their biogeographic relation to adjacent faunal provinces. Our analysis survey documents that shallow-water sediments harbor abundant and relatively diverse assemblages of symbiont-bearing and other smaller foraminifera. The 39 species recorded from nearshore coastal waters off Gabon contrast with lower diversity assemblages previously documented from offshore hydrocarbon drilling waste disposal sites. The assemblages of benthic foraminifera recovered suggest a deeply-rooted species diversity, where the true number of foraminiferal taxa present in Gabonese’s pristine waters remains yet to be discovered. The composition of foraminiferal biotas found off Gabon shows them to be distinct from faunas recorded from off Namibia and South Africa, indicating the presence of a marine biogeographic barrier.

Sediment characterization of the highly impacted Augusta harbour (Sicily, Italy): modern benthic foraminifera in relation to grain-size and sediment geochemistry

The Augusta harbour is affected by high anthropogenic impact due to intense harbour activity and a large chemical and petrochemical pole. Thirty-seven sediment samples were collected during an environmental characterization project and analyzed for grain size, chemical parameters (Al, As, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Zn and V) and foraminifera, the last one generally being used as ecological indicators of environmental quality. Anthropogenic enrichment was recognized for As, Cu, Hg, Pb and Zn and, among these, Hg showed very high concentrations (up to 191 mg kg(-1) d.w.) often associated in the southern sector of the study area to very high PCB levels (up to 0.83 mg kg(-1)). In this area, an assemblage dominated by Rosalina bradyi and Quinqueloculina lata was recognized. This assemblage shows a clear decrease of foraminiferal density and diversity and, at the same time, increased dominance with respect to the assemblage characterizing the central and northern less polluted sectors, in which Miliolinella subrotunda prevails. Quinqueloculina lata was demonstrated to be a stress-tolerant species because it was not influenced by sediment texture, but positively correlated with the concentration of Hg, PCBs and PAHs. The environmental stress shown by the high-dominance of the Ammonia tepida assemblage was attributed mainly to the influence of stream mouths, which determine environmental instability. Foraminiferal assemblages showed a clear response to environmental degradation in the most polluted area but, at the same time, they demonstrated a high adaptation to pollution.

Distribution of Foraminifera of the Poverty Continental Margin, New Zealand: Implications for Sediment Transport

ABSTRACT Foraminiferal assemblages were used to investigate the nature of sedimentation on the tectonically active Poverty continental margin (PCM) of New Zealand. Recent research around the world has been focused on understanding the sedimentary functioning of small mountainous rivers to the global sediment budget, and this study is part of a greater effort to define the processes that link sediment source and sink of such a system in New Zealand. Fifty-five surface samples from box, gravity, and multi-cores from the shelf and slope of the PCM were used to document the distribution of modern benthic foraminifera. Also, twenty samples from two gravity cores retrieved from Poverty Canyon, a hypothesized conduit of sediment to the deep ocean, were analyzed to evaluate the record of down-slope sediment transport. Seven biofacies, recognized by cluster analysis of benthic foraminiferal abundance data from surface and core samples, are strongly related to water depth and continental margin morphology: inner-shelf biofacies (26–43 m), shelf biofacies (~30–130 m) (this biofacies contained all samples from a canyon-head core taken at 359-m water depth), outer-shelf biofacies (60–250 m), upper-slope biofacies (230–350 m), shallow lower-slope biofacies (870–1255 m), Lachlan Anticline biofacies (40–63 m on the PCM shelf), and a mid-canyon thalweg biofacies from a core taken at 891-m water depth. Foraminiferal assemblages of the Lachlan Anticline biofacies are characterized by the largest foraminifera (mostly inner-and mid-shelf species), the most diverse assemblages, and the highest percentage of reworked planktonic tests in the dataset. Many planktonic and benthic specimens have probably been derived from the outcropping Miocene-Pliocene rock of the anticline. A high percentage of reworked (fossil) planktonic foraminifera at the mouth of Poverty Bay likely results from sediments shed from rapidly uplifting Plio-Pleistocene strata within the Waipaoa River drainage basin. Assemblages throughout the canyon-head (359 m) and mid-canyon (891 m) cores from Poverty Canyon contained higher percentages of shallower-water indicator taxa than other samples at similar depths outside the canyon, thus supporting the hypothesis that Poverty Canyon is channeling sediment from the shelf and upper slope to the deep ocean. However, different patterns of down-core distributions between the canyon head and mid-slope thalweg sites indicate that the nature of sedimentation varies down canyon. Abundances of shallower-water foraminifera suggest that shelf taxa are being supplied from a more consistent source to the canyon head, while shelf and upper-slope taxa are more variably supplied to the deeper-canyon thalweg. The effects of bioturbation appear to be greater in the canyon head.

Antarctic glaciation recorded in Early Miocene New Zealand foraminifera

Abstract New Zealand sedimentary sequences are important repositories of southern temperate palaeoenvironmental data, as may be interpreted from biogenic chemical signals preserved in marine microfossils. Calibration curves for Mg/Ca ratios versus water temperatures were established using modern benthic foraminifera, Notorotalia and Cibicides . Notorotalia is a long-ranged endemic benthic genus with a good record in shelf sediments, while Cibicides allows comparisons with similar studies elsewhere. The resulting correlations were T (°C) = ln(Mg/Ca [mmol/mol] / 1.64) × 10.89 for Cibicides spp., and T (°C) = ln(Mg/Ca [mmol/mol] / 0.44) × 5.71 for Notorotalia spp. Well-preserved Early Miocene Notorotalia and Cibicides were collected for paired Mg/Ca and δ 18 O analysis from a 3.6 m section of the Mount Harris Formation spanning an estimated 60 ka and dating from about 17.7 Ma ( Globoconella zealandica zone, roughly middle Burdigalian, Early Miocene) within the local Altonian Stage (15.9–18.7 Ma). Mg/Ca bottom-water palaeotemperature estimates from Cibicides and Notorotalia gave concordant results: 13.3 ± 1.0 °C for Notorotalia spinosa , 15.5 ± 3.0 °C for Cibicides spp. Estimates of oxygen isotopic composition for Altonian sea water (δ 18 O palaeo-sw ) were − 0.4 ± 0.4‰, suggesting the presence of small ice sheets on Antarctica. The method used to generate such results has far reaching implications for reconstructing δ 18 O palaeo-sw , and should allow Antarctic ice volume history to be finely resolved from New Zealand sequences.

Paleoceanographic reconstruction of the late Cretaceous oil shale of the Negev, Israel: Integration of geochemical, and stable isotope records of the organic matter

The Levantine high productivity system was an extensive coastal upwelling that operated in the Late Cretaceous along the SE Tethyan margin. This study focuses on the top Phosphate Member of the Mishash Formation and the Oil Shale Member (OSM) of the Ghareb Formation (latest Campanian-early Maastrichtian), which represent the last phase of this high productivity system in the Negev, Israel. Bulk organic matter (TOC), δ13Corg, δ15Norg, C/N and pristane/phytane (Pr/Ph) ratios, were studied for reconstruction of seafloor and water column depositional environments. Our records indicate a gradual decrease with time in surface water productivity in the OSM and a marked weakening at the overlying Marl Member. High C/N ratio along with relatively low δ15Norg (4‰ to 6‰) and δ13Corg (−29‰ to −28‰) probably reflect significant diagenetic preferential loss of nitrogen-rich organic compounds enriched with 15N and 13C isotopes (e.g. proteins). This along with the low Pr/Ph values (0.11–0.7), indicate oxygen depleted bottom water (anoxia-dysoxia) during the deposition of the top Phosphate Member and the OSM. The moderate gradual upward increase in δ15Norg, and in Pr/Ph values and the decrease of TOC and C/N values from the top Phosphate Member through the OSM indicate transition from anoxic (Phosphate-lower OSM) to dysoxic (middle-upper OSM) conditions. This environmental trend is consistent with co-occurring foraminiferal assemblages in the studied succession and implies that the benthic species in the Negev sequence were adapted to persistent minimum oxygen conditions by performing complete denitrification as recently found in many modern benthic foraminifera.