Diversity Of Benthic Foraminifera Research Articles

Benthic foraminifera diversity from the south Atlantic Ocean: Tierra del Fuego and surrounding waters (South America).

The present study provides a detailed record of foraminiferal fauna and their ecological implications from surface sediments from Atlantic shelf of Tierra del Fuego, Argentina. The foraminiferal assemblage is mostly composed by four main hyaline genera, such as Cibicidoides, Cibicides, Globocassidulina and Buccella, which allowed the identification of three environmental zones. Zone 1 (Z1, 37 to 90 m) encompasses the eastern Beagle Channel and San Sebastian Bay. The assemblage reflected well-oxygenated marine inner shelf habitat, adapted to cold temperate waters. Zone 2 (Z2, up to 98.4 m), is located around the southern tip of Tierra del Fuego. The assemblage suggested a deeper marine environment, well oxygenated and with higher energy, probably due to the effect of tides and mainly by the influence of Malvinas Current. Finally, Zone 3 (Z3, up to 195 m) is located furthest from the Atlantic coast and the assemblage suggested an environment characteristic of outer shelf, with well-oxygenated cold waters and high-energy environment, reflected by species adhered to the substrate and coarse sediments. The distribution and abundance of certain species showed the influence of the Malvinas Current, while others evidenced a contribution of the Cape Horn waters.

Benthic foraminifera across the Albian–Cenomanian transition and their paleoceanographic significance during OAE1d in the western Tethys (Umbria–Marche Basin, Italy)

The benthic foraminiferal assemblages from the upper Albian-lower Cenomanian interval of the Scaglia Bianca Formation in the Monte Petrano (MP) and Le Brecce (LB) sections (Umbria–Marche Basin; Italy) provide a detailed record of the faunal changes across the Oceanic Anoxic Event 1d (OAE 1d). Fluctuations in abundance, diversity, and species composition reflect variations in bottom-water oxygenation and organic carbon fluxes. Benthic foraminifera are integrated with planktonic foraminifera, calcareous nannofossils, and geochemical proxies to reconstruct the bottom and surface water conditions across the OAE 1d in the Umbria–Marche Basin.The pre-OAE 1d interval was characterized by benthic foraminifera that thrived under stable mesotrophic condition in bottom waters. In surface waters, planktonic foraminifera indicate dominant mesotrophic conditions in agreement with calcareous nannofossil assemblages suggesting a regime of higher fertility under cooler conditions.During the OAE 1d interval, benthic foraminifera display an increase in the abundance of infaunal taxa, suggesting mesotrophic conditions in bottom waters. Nevertheless, within the Pialli Level, the six laminated black-to-dark grey shale horizons (MP1/LB1 to MP6/LB6), benthic foraminifera are absent or highly impoverished (MP1, MP2, MP4, MP6, LB5, LB6), suggesting hypoxic/anoxic conditions in bottom waters. Planktonic foraminifera in this interval reflect mesotrophic to oligotrophic conditions under the presence of an expanded mixed layer and deeper thermocline in the surface waters. Calcareous nannofossils record warm conditions and lower fertility starting just prior to and across the OAE 1d. However, higher values of fertility are recorded in the black-to-dark grey shales MP3/LB3, MP4/LB4 and MP5/LB5 of the Pialli Level.The post-OAE 1d interval is marked by an increase in the diversity of benthic foraminifera, indicating a restoration of the oxygen conditions in a continuous mesotrophic regime in bottom waters. The surface waters experienced oligotrophic conditions based on the planktonic and calcareous nannofossils.A minor discrepancy between benthic foraminifera and geochemical reconstruction of oxygenation levels of bottom waters was recorded, especially in the Pialli Level. The benthic microfaunas appear to be very sensitive to very short-term oxygen depletion at the seafloor when geochemical proxies suggest temporary suboxia. This might indicate that very rapid redox changes are not resolved by bulk elemental data. Otherwise, benthic foraminifera might be much more responsive to very low concentrations of oxygen in bottom waters and temporarily disappear under strong suboxia before reaching fully anoxic conditions.

Radiolarian size and silicification across the Paleocene-Eocene boundary and into the early Eocene

The Paleocene-Eocene Thermal Maximum (PETM) was a major environmental perturbation that drove range shifts, adaptation, and faunal turnover in marine and terrestrial clades. Open ocean planktonic responses—including body size trends—have been characterized for calcareous nannoplankton, dinocysts, and planktonic foraminifera. Relatively little, however, is known about the response of radiolarians, which share life modes and phylogenetic history with planktonic foraminifera but make their tests (i.e., ‘shells’) out of silica rather than calcium carbonate. Here, we compare radiolarian assemblage changes in the Southwest Pacific with assemblages from Atlantic and Indian Ocean sites. We also measured radiolarian test size before, during, and after the PETM in a pelagic sedimentary succession at Mead Stream, South Island, New Zealand. Our results show a substantial positive shift in mean radiolarian test size at Mead Stream at the assemblage level concurrent with the onset of the PETM, primarily due to an increase in the size and relative abundance of spumellarian radiolarians. We investigate oligotrophy, elevated seawater silica concentration, and redeposition as potential drivers for this size shift. Mead Stream radiolarians remain large for 1.3 Myr, long past the recovery of the carbon isotope excursion and a return to baseline in terrigenous sedimentation, bioturbation, and benthic foraminifera diversity, leaving the ultimate cause of the observed changes in test size uncertain. We find little evidence for a uniform morphological response to the event or its aftermath across sites, particularly as relates to the relative extent of silicification of different groups of radiolarians.

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 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.

Assemblages of Benthic Foraminifera in Pujada Island, Davao Oriental, Philippines

The present study investigated the composition, density, abundance, and diversity of benthic foraminifera, and their relationship with various physico-chemical parameters such as pH, salinity, temperature, and sediment grain size. Foraminifera were collected from the intertidal zone using sediment cores and extracted from the sediments through sieving. The extracted foraminifera were stained with Rose bengal solution and preserved with buffered formalin. A total of 9,459 individuals of foraminifera were identified, consisting of 39 species classified into four orders, 16 families, and 21 genera. The top three most abundant genera were Calcarina, Baculogypsina, and Amphistegina. The comparison (ANOVA) of the abundance of foraminifera among the six stations revealed highly significant differences (P= 0.000; df= 38). Station 1 exhibited the highest diversity of foraminifera on Pujada Island, as indicated by an H’ value of 3.06. Conversely, station 6 displayed the lowest diversity, with an H’ value of 1.59. The pH, salinity, and temperature values are all within acceptable limits for seawater. The decreased diversity observed in some stations are attributed by various factors, like site disturbance (accessibility to many tourists and availability of beach resorts) and the variation in sediment grain size composition. The findings suggest that generally, Pujada Island remains an undisturbed coastal area. As a result, this study provides a baseline for future monitoring of the impacts of natural and human-induced activities in the region, thereby recommending the use of foraminifera's as bioindicators for marine health.

Diversity and Paleoenvironmental Signature of Benthic Foraminifera of St. Martin’s Island, Bangladesh

The present research is concerned with the investigations of the paleoenvironment of the benthic foraminifera and their diversity in St. Martin’s Island, Bangladesh. About 300 specimens of foraminifera were collected from three sampling sites of the island. Among them 44 species, 39 genera and 25 families were identified which were mostly benthic in origin. Astrorhiza, Elphidium, Cyclammina, Cibicides, and Eponoide were the most abundant genera all over the island based on their relative abundance and frequency of occurrence. Among the three sections, Uttar Para can be designated as Astrorhiza- Elphidium assemblage zone, Maddhya Para as Astrorhiza- Elphidium assemblage zone and Dakkhin para as Astrorhiza-Cibicides assemblage zone. The relative abundance chart of foraminifera and its correlation with the Saraswati and Srinivasan (2016) model diagram indicates that the paleoenvironment signature of the island belongs to the inner shelf to the middle shelf region. The plot of shell-type ratios on Murray’s ternary diagram also suggests the same paleoenvironment. Gibson’s index of oceanity was 2% which indicates a shelf environment where the diversity of benthic foraminifera is high. Murray’s index of diversity for all three sections was above the range V, which indicates the normal salinity of the ocean.
 The Dhaka University Journal of Earth and Environmental Sciences, Vol. 9(1), 2020, P 25-30

Modern Benthic Foraminiferal Diversity: An Initial Insight into the Total Foraminiferal Diversity along the Kuwait Coastal Water

Kuwait territorial water hosts an important part of national biodiversity (i.e., zooplankton and phytoplankton), but very limited information exists on the overall diversity of benthic foraminifera. On the basis of the integration of publications, reports and theses with new available data from the Kuwait Bay and the northern islands, this study infers the total benthic foraminiferal diversity within Kuwait territorial water. This new literature survey documents the presence of 451 species belonging to 156 genera, 64 families, 31 superfamilies and 9 orders. These values are relatively high in consideration of the limited extension and the shallow depth of the Kuwait territorial water. Kuwait waters offer a variety of different environments and sub-environments (low salinity/muddy areas in the northern part, embayment, rocky tidal flats, coral reef systems, islands and shelf slope) that all together host largely diversified benthic foraminiferal communities. These figures are herein considered as underestimated because of the grouping of unassigned species due to the lack of reference collections and materials, as well as the neglection of the soft-shell monothalamids (‘allogromiids’).

Distribution and Diversity of Foraminifera in the Northwest of Sarawak Offshore Waters, Malaysia

A study on distribution and diversity of benthic foraminifera in surface sediments was carried out in Northwestern Sarawak waters, Malaysia. The range of water depth at the study site was between 43 m and 71 m. A total of seven sediment samples were taken for this study. As a result, 11 genera were identified from a total of 1,222 individuals of foraminifera. 200 individuals were picked out from each sample. The 11 genera that were identified from the study site included Heterolepa spp., Textularia spp., Quinqueloculina spp., Operculina spp. Pseudorotalia spp., Amphistegina spp., Cylindroclavulina spp., Elphidium spp., Ammobaculites spp., Asterorotalia spp. and Bolivina spp.. The common genera found in the sediments of the study areas were Heterolepa, Textularia, Quincoloculina, Operculina and Pseudorotalia. The highest and lowest values of Fisher alpha and Shannon-Wiener indices were shown at Station C287 and Station B482 respectively. The highest value of Fisher alpha was 3.23 and the lowest value was 1.97. The highest and lowest values of Shannon-Wiener were 2.30 and 1.91. The highest index value of diversity was 3.23 at depth 67.76 m and the lowest value was 1.53 at depth 45.54 m and 68.45 m. From this study, depth is not the main factor that influences the diversity of benthic foraminiferal in northwestern Sarawak waters.

The trend of Foraminifera Benthic Assemblages for Comparing Paleo-environmental change: a Case study at Bulu and Wonosari Formation, Indonesia

Basically, the use of foraminifera fossils is used in the exploration of energy resources, especially in the field of petroleum, but as we know foraminifera activities can be a study in monitoring the ancient environment. This study aims to compare the ancient environment of limestone in the Wonosari Formation which is composed of layered limestones that show turbidite symptoms with Bulu Formation characterized by plotted limestones. In this study using a stratified sampling method, abundance and diversity calculation of benthonic foraminifera. From the comparison of the two formations shows the response to changes in environmental changes is seen based on the trend of changes in the diversity of benthic foraminifera.

Discovery of the Late Changhsingian Bivalve Complex and Two Fauna Extinction Episodes in Northeastern Asia at the End of the Permian.

A late Changhsingian bivalve complex including species from the genera Palaeonucula, Dacryomya, Malletia ?, Sarepta ?, Myalina, Pteria, Maitaia, and Unionites is discovered in northeastern Asia for the first time. The transition from the Permian to the Triassic in high-boreal basins has been shown to include two extinction episodes similar to those observed in the low-boreal basins and apparently evoked by trap volcanism activation in Siberia. Changes in benthic foraminifera diversity and vertical distribution of ammonoidea of the genus Otoceras in transitional Permian-Triassic deposits also are considered. Images of bivalves from the most typical taxa are presented.

KEANEKARAGAMAN FORAMINIFERA BENTIK TELUK BALIKPAPAN, PROVINSI KALIMANTAN TIMUR

Balikpapan Bay is one of locations of sampling sediments for the study of benthic foraminifera. The objective of this research was to determine the diversity of benthic foraminifera at different depths at Balikpapan Bay, East Kalimantan. Samples was selected at depth of 0-20 m, then divided into 4 depths, 0-5 m, 6-10 m, 11-15 m, and 16-20 m. A total of 1553 specimens were obtained from 66 species, 7 ordo, and 17 family. Asterorotalia trispinosa is a species with the highest of abundance, that followed by Rotalia sp.1, Rotalia sp.2, and Trichammina nana. The diversity index of each sampling point was different, 8 points have stable diversity, 11 moderate points, and 1 unstable point. This condition were influenced by depth, brightness, temperature, pH, turbidity, salinity, and DO at each sediment sampling point.

Deep-sea trace fossils of the Oligocene–Miocene Numidian Formation, northern Tunisia

Twenty-two ichnogenera and thirty-one ichnospecies have been recorded in the Oligocene–Miocene Numidian Formation of northern Tunisia. Heterolithic successions of thin-bedded turbidite sandstones and interchannel mudstones contain the most diverse trace fossil assemblages. Thick- to very thick-bedded structureless sandstones and conglomerates representing the fill of channel complexes contain a low-diversity trace fossil assemblage. The ichnoassemblage in the lower part of the formation (Oligocene), which includes Paleodictyon isp., Scolicia strozzii, Spirorhaphe isp., ?Cosmorhaphe isp. and Halopoa isp., can be ascribed to the Paleodictyon ichnosubfacies of the Nereites ichnofacies. The ichnoassemblage in the upper part of the formation (Miocene: Aquitanian), including Diplocraterion cf. habichi, Scolicia vertebralis and Ophiomorpha isp., is interpreted as the shallower part of the Ophiomorpha rudis ichnosubfacies of the Nereites ichnofacies. The notable switch in ichnofauna between the Oligocene and lower Miocene reflects variation in environmental and depositional conditions. The common occurrence of trace fossils of the Ophiomorpha rudis ichnosubfacies, and Diplocraterion cf. habichi in the early Miocene, indicates an increase in energy level, greater environmental disturbance and probable shallowing. This is also confirmed by a corresponding decrease in the abundance and diversity of benthic foraminifera. The integration of ichnological, sedimentological and microfossil contents has allowed the distinction of two quite distinct geographical depositional settings within the Numidian Formation. The first domain includes the Numidian succession of the Tabarka, Cap-Negro, Cap-Serrat and Bouhertma areas, which are characterised by “distal” turbidites, showing the Paleodictyon ichnosubfacies that is compatible with a lower bathyal depth in the Oligocene and an upper slope depositional environment during the early Miocene.The second domain includes the NE part of Mogod Mountain (e.g. the Ras El Korane, Jebel Gattous–Zoukar), which exhibit more proximal characteristics compatible with a probable slope canyon interpretation. The southern margin of the Kroumirie (Balta and Zouza areas) and Sejnene area shows a distal setting compared with the Ras El Korane and Jebel Gattous–Zoukar areas. It is ascribed to a mid- to upper slope depositional environment during the Oligocene to early Miocene.

Changes in diversity and assemblages of foraminifera through the Holocene in an atoll from the Maldives, Indian Ocean

Abstract This study presents the first high-resolution Holocene records of diversity and assemblages of benthic foraminifera from tropical reef environments in the Indian Ocean. Two 3.2 m and 4.4 m long cores from the lagoon of Rasdhoo Atoll (4°N/73°W) in the central Maldives, were sampled at ~ 250 yr intervals. Core #16 covers most of the Holocene (10.32–0 kyr BP) and was taken in the deep lagoon of the atoll (35 m water depth). Core #19 covers the time span 7.375–0 kyr BP and is from a sublagoon (14 m water depth) on the northern margin of the atoll. In Core #16, an early colonization phase during Holocene sea-level rise is characterized by an Ammonia sp. 1 dominated assemblage until ~ 7 kyr BP. The slowdown of sea-level rise in the Mid Holocene (~ 4 kyr BP) marks the onset of a phase of stable environmental conditions in the deep lagoon with high diversity. A shift toward lower diversity and the dominance of Textularia foliacea has occurred from ~ 4–1 kyr BP, which may be explained with the Intermediate Disturbance Hypothesis. An environmental change at ~ 1.4 kyr has caused a distinct faunal change, the decrease of T. foliacea and an increased recovery in diversity. In Core #19, a significant faunal change at ~ 4.0 kyr BP from an Ammonia sp. 2 dominated fauna to a fauna with Ammonia sp. 1, miliolid taxa and a higher diversity might be related to the formation of a sand spit that separates the sublagoon from the main lagoonal basin. The westward extension of the sand spit during the Late Holocene could have changed the restricted bottom water circulation in the main lagoon and caused longer residence times of water and the build-up of lower oxygen and higher nutrient concentrations. This study underlines the importance of the factor time on diversity and the significance of lagoon circulation and bottom water residence times on assemblages and diversity of benthic foraminifera.

Late Weichselian deglaciation and early Holocene development of a cold-water coral reef along the Lopphavet shelf (Northern Norway) recorded by benthic foraminifera and ostracoda

Cold-water coral (CWC) settlement in northern Norway is strongly related to the outlet-glaciers of the Fennoscandian Ice-sheet, and dating of known CWC structures show clearly post-glacial ages. Two gravity cores (POS391 559/2,277cm long and POS391 559/3,282cm long) were recovered on a CWC reef in the area of Lopphavet, northern Norway. Detailed investigations on lithology (sediment structures and composition), micropaleontology (foraminifera and ostracoda) and AMS 14C dating on the epibenthic foraminifera Discanomalina coronata were performed on the two cores. Phosphorus analyses were performed only on core POS391 559/3. Results indicate that the whole core POS391 559/2 is representative of a CWC reef environment. The base of the core is dated at 10,600±120cal.yrBP, thus representing one of the oldest ages of a Norwegian coral reef. Core POS391 559/3 documents the passage from a proximal glacier environment characterized by fine silty sediments with intercalation of several dropstone layers to a CWC ecosystem. The transition from the glacial to the interglacial stage is dated as old as 10,725±205cal.yrBP, whereas the base of the core is dated to an age of 15,300±550cal.yrBP. Diversity of benthic foraminifera is higher within the CWC, especially in the intervals containing coral framework. Five clusters are identified based on the Bray–Curtis Similarity Term Analyses and the interpretation of data shows that they are related to different ecological settings, e.g., fluctuations of the sea-ice cover; influence of the warmer and more saline Atlantic water masses; transitional to a fully interglacial environment; well oxygenated, nutrient-rich and high current setting being conducive to CWC.Ostracod assemblages show that these crustaceans may be also used to characterize sedimentary facies on CWC reefs.

Effect of municipal wastewaters on bottom sediment geochemistry and benthic foraminifera of two Red Sea coastal inlets, Jeddah, Saudi Arabia

Al-Arbaeen and Al-Shabab inlets are two Red Sea coastal inlets lying on the mid-coast of Jeddah City, Saudi Arabia. Forty-four surface sediment samples were collected from these inlets and surrounding areas during June 2010. Water depths and the overlying environmental parameters (temperature, salinity, pH and dissolved oxygen) of these samples were measured. Sediment samples were analyzed for variables, such as loss on ignition (LOI, organic matter), CaCO3, heavy metals (Fe, Mn, Cu, Zn, Cd, Ni, Cr and Pb) and benthic foraminifera to assess any changes in the environment of the inlets and surrounding areas. Variables distribution patterns indicated that mud sediments dominated the inlets and enriched by LOI, heavy metals and Ammonia tepida–Quinqueloculina seminula assemblage, whereas coarse (sand–gravel) sediments dominated the substrates of surrounding areas and enriched by CaCO3 and Coscinospira hemprichii–Peneroplis planatus–Varidentella neostriatula assemblage with low values of LOI and heavy metals. Highest concentrations of Cu, Zn, Cd, Ni, Cr and Pb were recorded inside the inlets, especially near the discharge points, and they were positively correlated with the LOI and mud fraction indicating their affinity to anthropogenic materials. However, highest concentrations of Fe and Mn were typically recorded in the whole study area. These metals were positively correlated with the LOI values of the surrounding area, but in the inlets they were negatively correlated with the LOI, indicating an existence of reducing conditions caused by limited dissolved oxygen conditions at bottom waters of the inlets. Changing the environment within the inlets, according to higher concentrations of heavy metals and LOI, is probably responsible for the existence of the low density and diversity of benthic foraminifera and the absence of (reefal) symbiont-bearing species.

Foramíferos Bentónicos de Seno Gallegos y Bahía Brookes (54,5° S - 69,5° S), Chile: patrones de distribución y diversidad

ABSTRACTThis paper describes the distribution pattern and diversity of benthic foraminifera from Gallegos sound and Brookes Bay (XII Region, Chile) and the relationships with the particle size and concentration of the organic matter. Fourteen samples were obtained using a Van Veen grab between 22 and 65 m water depth in January 2010.The sediment at all stations was predominantly sand. Thirty-five species of foraminifera were de-termined from 1601 collected specimens. Mean abundance was 14.8 ind g -1 per station. Diversity, mea-sured using Shannon-Wiener index (H’) varied between 1.7 and 2.8. The highest diversity was recorded in stations at Brookes Bay and the lowest in the stations from Gallegos sound off Ventisquero Garibaldi. Cluster analysis identified two stations groups. Only sediment texture and particle size were significantly related to mean abundance, diversity and eveness. There was no relationship between depth, concentration of organic matter and the community’s parameters. Our results suggest that interstitial space in the sandy habitat play an important role in the establishment of foraminifera communities within Gallegos sound and Brookes Bay.Key words: benthos, microfauna, meiofauna, fjords, marine periglacial.

Composition and distribution of sediments and benthic foraminifera in a submerged caldera after 30 years of volcanic quiescence

Abstract Deception Island (62°59′S, 60°34′W) is an active volcano with a submerged caldera (Port Foster) located northwest of the Antarctic Peninsula. Surveys following the most recent eruption of the volcano in 1970 showed that direct deposition of coarse pyroclastics into Port Foster decimated the benthic communities. The objective of this study is to examine how the submarine sediment distributions and the composition, distribution and abundance of benthic foraminiferal communities in Port Foster have changed after 30 years of volcanic quiescence. Grab, core and settling particulate matter were collected on a series of five cruises during 1999–2000 to monitor seasonal changes in the ecosystem of Port Foster. The caldera floor is covered with a layer at least 15 cm thick of yellowish-brown volacaniclastic sandy mud composed primarily of basaltic-andesitic lithic fragments and volcanic glass with mean and median grain diameters of 26±10 and 32±12 μm, respectively. We suggest that these sandy muds were deposited since the last volcanic eruption in 1970, yielding a minimum sediment accumulation rate of at least 5 mm/year. Settling particulate matter during the fall, winter and spring of 1999 and 2000 were finer grained than the seafloor samples, with mean and median grain diameters of 11±2 and 13±3 μm, respectively. Except for a slight coarsening of the mean grain diameter in the late spring, we observed no temporal changes in either the granulometry or the mineralogy of the settling particulate matter. The concentration of biogenous sediment in Port Foster is relatively low due to dilution by a high volume of lithogenic material being deposited in the bay. The abundance (from foraminifera numbers) and diversity of benthic foraminifera within Port Foster is spatially variable and patchy. Although previous studies of the benthic foraminiferal community following the 1967–1970 eruptions showed an increase in abundance (foraminifera number) of Port Foster's benthic foraminifera community from 1972 to 1976, our data show that these increases did not continue beyond the mid-1970s. The most notable similarities between the mid-1970s and 2000 assemblages are the predominance of Miliammina arenacea and Trochammina malovensis in Port Foster. Since the 1970s, there has been an increase in importance of Globocassidulina (the most abundant genera), a decrease in the relative abundance of Stainforthia fusiformis and Nonionella bradii, and the introduction of Reophax dentaliniformis, and Cassidulinoides parkerianus, which were not abundant in either Port Foster or on the outer slopes surrounding the flanks Deception Island during the 1970s. The later arrival of R. dentaliniformis to Port Foster suggests that it is not a pioneer colonizer following disturbance in all environments.

Paleoenvironmental evolution of the Guercif basin (south Rifain corridor, northern morocco). Implications for the Messinian salinity crisis

Abstract Foraminiferal biostratigraphic and paleoenvironmental results from the MDS1 borehole of the Guercif basin reveal the detailed history of its paleogeographic evolution during the late Neogene. Four biostratigraphic events are recognised based on the study of planktonic foraminifera. In addition to the placement of the Tortonian-Messinian boundary at 798 m depth, they also allow correlation of the MSD1 borehole with other late Miocene sections in the Mediterranean area. The diversity of benthic foraminifera is significant in the studied borehole. 111 species assigned to 55 genera, were identified. Three successive assemblages of benthic foraminifera were recognised, each one conveying a different paleoenvironmental information. They thus recorded a number of fundamental changes in the environmental and water mass characteristics of the Guercif basin. Following the oldest upper Tortonian transgressive marine deposits found at the bottom of the borehole, marls accumulated at lower epibathyal to upper mesobathyal depths (~400 to ~800 m). They recorded sea-floor dysoxia and associated stratification of the water column for the time interval between ~7.5 and ~7.3 Ma. During the latest Tortonian-early Messinian the basin experienced a rapid shallowing, first from the previously bathyal environments to deep neritic (~100 to ~200 m), and to shallow neritic afterwards (0 to ~30 m). The total absence of any foraminifera in the conglomerates situated at the top of the study borehole suggests that these sediments were deposited in subaerial environments. At this time the connection between the Atlantic Ocean and the Mediterranean Sea through the South Rifain Corridor was stopped. This local event contributed to the establishment of the particular conditions of the Messinian salinity crisis.