Main Assemblages Research Articles

Deep-water fish assemblages in the Mediterranean Sea

Data collected during the DESEAS survey carried out in three areas of the Mediterranean Sea (Balearic Sea, western and eastern Ionian Sea) were used to describe the structure and spatial distribution of the fish assemblages at depths between 600 and 4000 m. A total of 55 species (8 chondrichthyes and 47 teleost fish) were sampled, 38 of them in the Balearic Sea, 30 in the western Ionian and 37 in the eastern Ionian. Multivariate analysis showed a clear pattern of zonation with depth and geographic area. Three main assemblages were identified across the vertical gradient investigated: on the upper slope around a depth of 600 m, on the middle slope between 800 and 1300 m, and on the lower slope below 1300 m. The geographic characterisation of the ichthyofauna structure was mainly observed on the upper and middle slope. The highest abundance and biomass values were found at depths of 1000-1200 m due to the presence of larger species with high energy requirements, such as Alepocephalusrostratus, Mora moro and Galeus melastomus. On the middle slope, significant differences in the abundance, biomass and mean fish weight were detected between the three areas. Significant differences for these parameters were also shown between the middle and lower slope assemblages. A significant decrease in species richness and diversity was shown with increasing depth, indicating an impoverishment of the megafauna with depth and a higher similarity between the Balearic Sea and the Ionian Sea with regard to the greatest depths. The dominant species on the deepest bottoms were Bathypteroismediterraneus, Chalinura mediterranea and Coryphaenoides guentheri. On the lower slope, the shark Centroscymnuscoelolepis was also found to be relatively abundant off the Balearic Islands, Etmopterusspinax in the eastern Ionian Sea and the teleost fish Cataetyx laticeps throughout the three study areas. The deepest bottoms of the Mediterranean Sea shelter an ichthyofauna dominated by small-medium species living in a food scarce environment in which some large mobile fishes are widespread. The results are discussed in relation to previous studies mostly carried out in the Atlantic and western Mediterranean.

THE COMPOSITION OF Co-Ni-Fe SULFARSENIDES, DIARSENIDES AND TRIARSENIDES FROM THE SAN JUAN DE PLAN DEPOSIT, CENTRAL PYRENEES, SPAIN

The San Juan de Plan deposit, in the central Pyrenees of Spain, is situated in an ankeritic horizon in Silurian black shales. The main association consists of pyrite, sulfarsenides, diarsenides, and Co triarsenides (skutterudite), as well as a late stage consisting of cobaltite, Fe, Cu and Bi sulfides and native Bi. The sulfarsenides are arsenopyrite, alloclasite, members of the gersdorffite‐ cobaltite solid-solution series, arsenic-rich gersdorffite and cobaltite, whereas the diarsenides range from rammelsbergite to safflorite. Rammelsbergite is characterized by a composition within the range (Ni0.71‐0.97Co0.02‐0.29Fe0.00‐0.02)As1.75‐2.01S0.00‐0.26, exceeding the theoretical value (As1.93S0.07) given by Yund (1962). Two generations of the gersdorffite‐cobaltite solid-solution series have been found on the basis of textural features and chemical composition; the first, (Co0.10‐0.77Ni0.07‐0.80Fe0.03‐0.58)As0.95‐ 1.27S0.75‐1.06, shows a positive correlation between S and Fe contents, and between Co and As contents, whereas the second one, (Co0.02‐0.91Ni0.02‐0.96Fe0.00‐0.28)As0.99‐1.38 S0.67‐1.01, exhibits a considerable compositional field in the Fe-poor region of the system CoAsS‐NiAsS‐FeAsS , providing evidence of extensive substitution of Co by Ni, with a positive correlation between As and Ni contents. Arsenic-rich gersdorffite displays a broad range of As and S mutual substitution, (Ni0.65‐0.98Co0.02‐0.27Fe0.00‐0.06)As1.37‐ 1.83S0.22‐0.64, exceeding the experimental value of NiAs1.77S0.23 reported by Yund (1962). The presence of alloclasite and the extent of the solid-solution fields of the cobaltite‐gersdorffite series suggest that the main assemblage of minerals at the San Juan de Plan deposit formed at temperatures as high as 600°C. Preliminary geothermometric data obtained on graphite support such a high temperature.

P4-238 APP and ACH

Giardia duodenalis is one of the most frequent intestinal parasitic infections in children worldwide. To date, eight main assemblages of G. duodenalis have been described, but only A and B genetic groups are known to infect humans. In Cuba, this parasite has most clinical impact on children. The aim of this investigation was genetic characterization of G. duodenalis isolated from children with giardiasis diagnosed at the Paediatric Hospital “William Soler” between 2010 and 2011, and to compare the genetic results with clinical and epidemiological data. A total of 103 stool samples from 452 children were positive for G. duodenalis and co-infections with other parasites were noted in 5 cases. Assemblage identification was carried out by the amplification of a fragment of the triosephosphate isomerase (tpi) gene. Sub-assemblages of assemblage A (AI and AII) were identified by a nested PCR using the intergenic spacer (IGS) region of ribosomal deoxyribonucleic acid gene as a target. DNA from 90 of 103 (87.4%) samples was successfully amplified by PCR–tpi. The prevalence of assemblages A and B was 40% and 42%, respectively. Infections with both assemblages were reported in 16 cases. No associations between epidemiological information and assemblage was detected, but assemblage B was significantly (P < 0.01) more frequently found in children with diarrhea, flatulence or abdominal pain than assemblage A. Sub-assemblage AII accounted for the majority of cases (86.5%).

Using benthos as a tool for coastal management: The impact of the tidal power station on benthic communities of the Rance basin

The spatio-temporal variability of benthic communities was studied in a modified system whose main physical characteristics are controlled by humans: the Rance basin, with its tidal power station. Soft-bottom communities were sampled in 1976 and 1995 by a quantitative survey of 105 and 113 stations, respectively, to assess spatial and temporal changes, to determine factors involved in benthic assemblage changes and to lay a base for the management of this coastal area. A total of 205 and 240 species were recorded in 1976 and 1995, respectively. Ascendant hierarchical classification and factorial correspondence analysis identified 7 and 6 assemblages in 1976 and 1995, respectively. The main groups are: 1) the Amphioxus lanceolatus-Glycymeris glycymeris; 2) the Abra alba-Corbula gibba and 3) the oligospecific Macoma balthica communities. A large consortium of common species linked the main assemblages described in 1976 as in 1995. From comparison of their distribution and structure, local spatio-temporal changes were identified in response to modifications of the habitats due to 1) silting in the brackish sector; 2) the decrease in the mean low water level and 3) the proliferation of the mollusc Crepidula fornicata. As a consequence, species richness 1) decreased in the brackish part as a result of the ‘homogenisation’ of habitats induced by silting and 2) increased in parts of the basin through the proliferation of Crepidula fornicata and the apparent diversification of the associated habitat. However, despite reduction in species abundances, the structure of the identified assemblages between 1976 and 1995 remained stable at the scale of the Rance basin. This long-term relative stability seems to reflect stable environmental conditions. In the basin, tide is moderate with reduced range variations and benthic communities are preserved from the effects of swells. However, the new balance is entirely dependant upon the mode of the installation: by modifying water levels with appropriate time intervals, managers can chose to favour intertidal or subtidal communities according to their respective ecological interests for avifauna and flatfishes, local socio-economical preoccupations or recreational activities carried out in the basin.

Factors Affecting Macroinvertebrate Communities in Astatic Ponds in Central Italy

ABSTRACT Twenty astatic ponds near Rome were studied in order to define the relationships between physicochemical variables and macroinvertebrate communities. The main abiotic factor differentiating the ponds was the annual hydrologic cycle. Depth, surface area, and sand percentages in the sediment were higher in permanent ponds, whereas silt+clay content was higher in temporary ones. No difference was recorded in pH, conductivity and oxygen content in the water or organic matter in the sediments between the two pond types. Three main ecological assemblages were distinguished: a) generalist taxa common to both pond types; b) taxa associated with and adapted to temporary ponds; and c) taxa which seemed to prefer permanent ponds. Overall, there was no relationship between number of taxa and surface area, except for Odonata and aquatic macrophytes. A positive correlation was observed between number of macrophyte species and macroinvertebrate taxa richness, and particularly of odonates and chironomids, suggesting that an increase in aquatic vegetation species leads to an increase in microhabitats and suitable food, substrate, and/or refuge from predators. Odonata seemed also to prefer more stable and sunny ponds.

Varying depositional environments of gypsum successions in the Upper Miocene Eskisehir-Sivrihisar lacustrine basin, NW Turkiye

The basement rocks of Eskisehir-Sivrihisar basin are made of Upper Paleozoic metamorphic rocks and Upper Cretaceous ophiolite complex. These rocks are overlain by Middle Miocene sedimentary rocks the base. Upper Miocene-Pliocene stratigraphic succession consists of basal conglomerates, sandstones, claystones, limestones, dolomites and tuffs are thinly interbedded with cyclic evaporites. The main clay mineral assemblage consists of smectite, illite and sepiolite that are enriched in different percentage in different horizons. The Upper Miocene-Pliocene stratigraphic succession consists of alterations of gypsum, clayey carbonates and unconsolidated very soft dolomite beds, which are conformably underlain by sepiolite-bearing clayey carbonates and disconformably overlain by alluvium and conglomerate series of Pleistocene age. The Upper Miocene unit includes three different facies, based on sedimentary properties of gypsum from the base to the top; (I) laminated gypsum beds are thinly interbedded with dolomites and green clays; (2) gypsum rosettes within thin reddish and greenish clays and carbonates; and (3) scattered gypsum mainly within carbonates. Gypsums had been deposited in somewhat different depositional conditions in the same basin where multi-periodic evaporative episodes, ranging from saline to schizohaline environments, had been involved. During these episodes, under high Eh-pH intervals and high salinity conditions, three different types of gypsum formations had been developed in a meromictic-type lake under the influence of varying paleoclimatologic conditions and pore water chemistry of brines. All these gypsum morphologies respectively reflect the different conditions of environments of deposition in a Miocene playa lake basin: (1) subaqueous environments in playa lakes with short evaporation episodes; (2) marginal swamps with cyclic fluctuation of lake level; and (3) extended closed-lake with evaporatic lake water. These different gypsum morphologies are associated with distinctive sedimentary subfacies, which are also primarily related to cyclic climatic changes, alternating semi-arid and evaporite conditions, fluctuation of lake water level and sulphate input in the chemistry of lake water from runoff and hydrothermal source adjacent to basin.

Geochemical and rock magnetic records from sediments of the Cenozoic Pagodroma Group, Prince Charles Mountains, East Antarctica: implications for provenance and weathering

Geochemical and magnetic data from glacigenic sediments can be useful indicators of past environments and climate. In this paper, the results of X-ray fluorescence (XRF) and rock magnetic analyses are presented for samples from the Pagodroma Group, an assemblage of pre-Quaternary glacimarine sediments preserved as remnants along the raised flanks of the Lambert Graben, Prince Charles Mountains, East Antarctica. Samples were obtained from four formations: Mount Johnston, Battye Glacier, Fisher Bench and Bardin Bluffs, which range in age from late Oligocene or early Miocene through to Pliocene or early Pleistocene. Principal component analysis of the XRF data indicates the occurrence of two main element assemblages, which we infer are determined by the presence in the Bardin Bluffs formation of a significant component derived from Permo–Triassic sedimentary rocks of the Amery Group. Calculation of chemical indices of alteration suggests that the values reflect provenance differences rather than the syndepositional weathering environment. Multidomain ferrimagnetic grains mainly dominate the magnetic mineral assemblages of the samples, probably magnetite, with varying concentrations of high coercivity material, probably hematite.

Ecology of Freshwater Ostracoda (Crustacea) from Lakes and Reservoirs in Bolu, Turkey

ABSTRACT Freshwater ostracods are important for interpreting the water quality of aquatic habitats. However, using ostracods in this way requires knowledge of their ecology and habitat preferences, particularly because species may show different responses to different ecological conditions. I documented ecological requirements of five ostracod species and their distribution in ten similar-sized lakes and reservoirs in Bolu, Turkey. Five species (Darwinula stevensoni, Cypria ophthalmica, Cypridopsis vidua, Cyclocypris ovum, Fabaeformiscandona fabaeformis) were found from natural lakes, while no ostracods were encountered from reservoirs. A canonical correspondence analysis suggested that salinity, temperature, redox potential, and pH were the four most influential factors on the species habitat preference in these lakes. These results were also supported with unweighted pair group mean averages (UPGMA) that also showed ostracod preference for certain ecological conditions in these lakes was mostly species-specific, depending on the changes in the levels of variables. UPGMA analysis for clustering of species and environmental data revealed three main species assemblages. The first group was represented by a single species, F. fabaeformis, whose occurrence was closely related to water hardness. The second group included two species, D. stevensoni and C. ophthalmica, that were found in relatively alkaline waters with moderate temperature. The third group was represented by two species, C. vidua and C. ovum.

Les Pectinidae miocènes des faluns (Ouest de la France). Intérêts biostratigraphiques des associations

The Miocene Pectinidae from the “faluns” (W France). Biostratigraphical interests of the associations. New sampling was realized throughout neogene outcrops occurring in Western France (mainly, “faluns” of Langhian to Tortonian age from Touraine, Anjou and Blésois). It has been known for long that the species or associations of the representatives of the family Pectinidae vary in each outcrop, but it was still necessary to get original data, which were collected precisely in their original level. Such a work is still in progress in Mediterranean areas. It seems that the systematic framework of several species has still to be detailed; the recently re-discovered species may be 12 in number. The species may characterize four main assemblages: rich and poorly diversified faunas, collected in microconglomerates, deposited in shallow environments; rich and diversified association, corresponding to the bryozoa facies deposited in deeper environments (“savignean” facies Auct.); poor assemblage, collected in shallow water, shelly beds (“pontilevian” facies Auct.); nearly absent Pectinidae in the shallow water Arca facies (“lublean” Auct.). Generally, the species belonging to the genus Pecten are only common in the savignean facies, in which the diversity consequently increases. Actually, the biochronological framework of the “faluns” is correct, mainly related to the mammal zonation. The associations of Pectinidae collected in the “faluns” may be of several interests. • Several memberships of the observed faunas have a long stratigraphical range (Langhian–Pliocene), wide geographical distribution (from Britain to Mediterranean areas), and may be ecologically tolerant. They belong to the Crassadoma multistriata and Aequipecten radians species. In Western France, A. radians may be related to quite shallow environment. Opposite, the species Gigantopecten ligerianus may be related to the deepest environments. • Several species or association may success to each other through time, which may offer a regional stratigraphical interest, in the “faluns” from Western France: P. subarcuatus—P. sp. 1 (Langhian), P. sp. 2 (close to praebenedictus, Serravalian to Tortonian.), P. praebenedictus s. s. (younger Tortonien), P. jacoabeus or maximus (Messinian to Pliocene). G. ligerianus was recently recollected regionally in sediments of Langhian age only, if the local deposition environments are deep enough. Note that numerous shells belonging to this species exist in historical collections, from Doué area (obs. pers. M.B.).

Pattern of distribution and diversity of demersal assemblages in the central Mediterranean Sea

A highly diversified mix of fish species, cephalopods and crustaceans, together with several macro-epibenthic organisms, compose trawl catches in the Mediterranean Sea. Management of Mediterranean trawling needs a multispecies approach that considers the community and not the single species as the basic unit of the analysis. While many studies have correlated several environmental factors to the spatial organizations of demersal organisms, few have focused on the role of macro-epibenthic communities in structuring demersal assemblages. In this paper, the following hypotheses were tested: (1) there are discrete demersal assemblages in the central Mediterranean Sea; (2) the distribution and diversity of demersal communities does not change on small temporal scales (1 year); (3) the demersal assemblages were segregated across both different epibenthic assemblages and depth gradients. Shallow stations were separated into coastal and middle-deep shelf assemblages while stations on the slope formed three main assemblages: slope edge, upper slope and middle slope assemblages. The demersal community did not show a substantial change at the small temporal scale. Sandy, sand-muddy and detritic epibenthic communities characterized coastal shelf assemblages, while epibenthic assemblage on muddy bottoms were dominant in the deeper areas of the shelf. A well-defined difference in macro-epibenthic faunal associations among stations on the slope (depth >200 m) was not found. Depth appeared to affect diversity of the main taxa of demersal organisms in different ways. Teleostean diversity did not show any trend with depth, the number of cephalopod species increased on the shelf and decreased on the slope while crustacean and elasmobranch species richness increased significantly from the shelf to the middle slope. The strong correlation shown in this study between epifaunal benthic communities and demersal fish assemblages requires the formulation of an ecosystem-based management for the Mediterranean Sea trawl fisheries. The existence of such biological diversity certainly contributes to the Mediterranean ecosystem health and its conservation should become one of the main objective of demersal resources management in the future.

Response of the small mammal community to changes in western French agricultural landscapes

We studied the response of the small mammal community (rodents and shrews) to recent changes in agricultural systems of western French landscapes. Work was conducted on twelve sites representative of the diversity of farming systems in this region. The characteristics of small mammal assemblages in each site were assessed using Barn Owl (Tyto alba) pellet analysis. Relationships between small mammal data and landscape descriptors were performed through co-inertia analysis. Richness and specific composition of the small mammal community were not affected by the degree of cultivation but variations in species frequency could be observed. The prevalence of some species allowed us to distinguish three main assemblages which were characteristic of low, medium, and high intensified landscapes. Status and life traits of these species showed that intensification of agriculture has negative effects on density of rare and habitat-specialist species while it favours habitat-generalist species, some of them being known to exhibit fluctuating density. The two main ways of agricultural intensification (maize vs. other crops) did not show any significant relationships with species assemblages. Our results gave us the opportunity to suggest recommendations on agronomical and conservation problems that may arise from these changes of agriculture in western France.

Study on the carbonate ocelli-bearing lamprophyre dykes in the Ailaoshan gold deposit zone, Yunnan Province

Three carbonate ocelli-bearing lamprophyre dykes have been found in the Laowangzhai and Beiya gold orefields in the northern sector of the Ailaoshan gold deposit zone, Yunnan Province. Ocelli in the lamprophyre dykes are carbonates composed mainly of dolomite and calcite. Their trace elements, REE and C isotopic compositions are characteristic of carbonatite and the main mineral assemblages, major elements, trace elements and REE in the matrix are similar to those in the carbonate ocelli-barren lamprophyre dykes in the orefields, which are calc-alkaline lamprophyres that derived from the fertile mantle. The results indicate that the carbonate ocelli-bearing lamprophyre dykes in this area were produced at the time when the Himalayan lamprophyre magma evolved to a relatively late stage of silicate-carbonate liquid immiscibility. In the process of magmatic evolution there took place magmatic degassing with CO2 and H2O as the dominant released gases.

Carbon and water economy of Australian NAD-ME and NADP-ME C4 grasses

C4 grasses are grouped into three biochemical subtypes,NAD malic enzyme (NAD–ME), NADP malic enzyme (NADP&amp;ndash;ME)and phosphoenolpyruvate carboxykinase (PCK), possessingcharacteristic leaf anatomy, biochemistry and physiology. This studyinvestigates the physiological implications of these differences by comparing growth, water use efficiency (WUE, dry matter gain per unit water transpired) and gas exchange characteristics of NAD–MEand NADP–ME C4 grasses belonging to threetaxonomic groups (main Chloroid assemblage, Paniceae and Andropogoneae). Wegrew 28 C4 grasses from seeds for 6 weeks in aglasshouse under ample water and nutrients in winter and summer. Theinter-specific variation in plant dry mass (30-fold) was much greater thanthat in WUE (2-fold). There was no significantdifference in average WUE between NAD–ME andNADP–ME grasses. Average plant dry mass andWUE were highest in the Paniceae (mostlyNADP–ME), lowest in the Andropogoneae (NADP–ME) and intermediate in the Chloroid (NAD–ME). CO2assimilation rate (A), stomatal conductance(g) and the ratio of intercellular to ambient CO2 partial pressure (pi/p a )were measured under standard conditions at high light. AverageA and g were slightly higher inNADP–ME than NAD&amp;ndash;ME grasses, but pi/p awas similar for the two subtypes. A did not differbetween winter and summer experiments in spite of a 3-fold difference inmaximal daily irradiance. Dry matter accumulation correlated positively withleaf area ratio (LAR; plant leaf area per unit plant drymass) and specific leaf area (SLA; leaf area per unitleaf dry mass) in NAD–ME, but not NADP–ME, grasses.Variation in A (expressed on a per area basis) did notcorrelate with biomass accumulation or SLA. Whenexpressed on a dry mass basis, A correlated withSLA in all C4 grasses. This studyshows that there is large inter-specific variation in growth among the C4 grasses, but average WUE andA/g are similar forNAD–ME and NADP–ME species under well-wateredconditions.

Interannual variation in the composition of the assemblages of medusae and ctenophores in St. Helena Bay, Southern Benguela Ecosystem

The assemblages of medusae and ctenophores were examined from samples collected each winter from St Helena Bay, over the 10-year period 1988-1997. A total of 50 hydromedusae, 1 scyphozoan and 2 ctenophore species were identified from 243 samples. Although the data set is characterised by great interannual variability, two main assemblages could be identified each year. These were characterised by either holoplanktonic medusae (e.g. Liriope tetraphylla, Aglaura hemistoma) or meroplanktonic medusae (e.g. Mitrocomella millardae, Chrysaora hysoscella) and ctenophores (e.g. Pleurobrachia pileus). The holoplanktonic medusae were typical of samples at the southern edge of the Bay, and were positively associated with both depth and temperature. Their abundances tended to increase during warm years (1992, 1993 and 1997) as warm surface water flooded the Bay. The meroplanktonic medusae and ctenophores were typical of samples collected within the Bay, and the density of species tended to be negatively correlated with temperature and depth. In spite of the eurythermal nature of the meroplanktonic species, they were more common during cold years (1990 and 1995). This paper represents the first Bay-wide, interannual study of any zooplankton group, and contributes important base line information on the structure of regional pelagic assemblages.

Polychaete Assemblages in the San José Gulf (Chubut, Argentina), in Relation to Abiotic and Biotic Factors

Abstract. The composition and distribution of the polychaete assemblages of the San José Gulf (Chubut, Argentina) are described in relation to environmental variables using indicator species (TWINSPAN) and canonical correspondence analysis (CCA). The polychaetes were collected during a benthic cruise in October 1984. Sediments were collected at 110 sampling sites using a 0.25 m2 van Veen bottom grab or by divers in near‐shore areas and sieved with 1 mm mesh. A total of 73 polychaete taxa were collected and identified. Both analyses revealed the presence of four main assemblages distributed according to depth as well as bivalve and seaweed abundance gradients: ‘Syllis‐Eunice’ and ‘Harmothoe‐Eunice’ assemblages occurred at the same depths (0 –­ 185 m) and substrata (poorly sorted rock and coarse sand), but were separated by bivalve and seaweed abundance, wherby the highest abundances of bivalves and the minimum abundances of seaweeds corresponded to the ‘Syllis‐Eunice’ association. The ‘Ninoe‐Glycera’ and ‘Aglaophamus‐Fabriciinae indet. 6’ assemblages also occurred at similar depths (0 – 60 m) and substrata (very well‐sorted medium‐fine sand), but differed in their composition of bivalves and seaweed abundances; the ‘Aglaophamus‐ Fabriciinae indet. 6’ association corresponded with minimum bivalve and maximum seaweed abundances.

CONTRASTING FLUID TYPES AT THE NEVORIA GOLD DEPOSIT IN THESOUTHERN CROSS GREENSTONE BELT, WESTERN AUSTRALIA: IMPLICATIONS OFAURIFEROUS FLUIDS DEPOSITING ORES WITHIN AN ARCHEAN BANDED IRON-FORMATION

Two main hydrothermal mineral assemblages have been identified in the banded iron-formation-hosted gold mine at Nevoria. The earlier quartz ± garnet ± clinopyroxene ± calcite vein group formed pre- or synmetamorphic, and the later quartz ± pyrrhotite ± pyrite vein group appears to be postmetamorphic and related to gold mineralization. Fluid inclusion characteristics are obviously different in those two vein groups. Microthermometric analysis indicates that the fluids with metamorphic alteration are aqueous, CO2-rich or CO2-absent solutions; no or very small amounts of CH4 were involved in this fluid. Mineralizing fluids were a CH4-CO2-H2O solution. The initial auriferous fluids were CH4 dominant. Heterogeneous trapping, interaction of the hydrothermal fluid with graphite-bearing rocks, or fluid mixing may cause large variations of CH4/CO2 ratios or a XCH4 of CH4-CO2-H2O inclusions, particularly in mineralized quartz-pyrrhotite veins. Phase mixing or separating, resulting in an increase in pH and f O2, together with loss of reduced sulfur by mineral-fluid reactions and precipitation of sulfides, led to the breakdown of the gold-transporting complexes.

Oxidation state of mantle xenoliths from Jeju-do, South Korea

The common upper mantle assemblage of olivine-orthopyroxene-spinel may be used to calculate the oxygen fugacity at which mantle-derived peridotites have equilibrated. Mantle-derived ultramafic xenoliths occur in two alkali basaltic flows of Jeju-do, South Korea: Sangumburi and Sinsanri. They are mostly spinel Iherzolites with minor spinel harzburgites. Main mineral assemblage is olivine-orthopyroxene-clinopyroxene-spinel. The oxygen fugacities of 27 peridotite xenoliths from two locations fall mostly within a narrow range from −1.5 to 0.5 log units relative to FMQ buffer. The range offo2 approaching FMQ buffer indicates that dominant fluid phases in the uppermost mantle beneath Jeju-do are H2O and CO2 instead of CH4 and H2. The overall degree of basaltic element depletion in the xenoliths is independent of thefo2 they record, which implies that partial melting and melt extraction took place under approximately the samefo2 conditions. Oxidation state of the sub-continental lithospheric mantle is somewhat related to the tectonic setting. Published data suggest that hot-spot and recent subduction-related domains are more oxidized than asthenospheric (MORB-like) ones. It is commonly considered that relatively high oxygen fugacity in the mantle above subduction zone results from upward migration of slab-derived hydrous fluid. Oxygen fugacity values for lithospheric mantle beneath Jeju-do fall within the range observed in abyssal peridotites, which is similar to the range of peridotite xenoliths from other continental regions, but more reduced than for hot-spot and recent subduction-related domains. However the meanfo2 values of Jeju xenoliths are slightly higher than those of the typical continental lithospheric mantle xenoliths, suggesting a possible interaction with the fluids emanating from mantle plumes.

The Geology, Mineralogy, and Occurrence of Bedded Sepiolite Deposits in the Akcayir-Yurukakcayir (Eskisehir) Lacustrine Basin, Central Turkey

The Akcayir-Yurukakcayir Miocene-Pliocene basin in the Central Anatolia hosts ancient lacustrine sepiolite deposits. The succession in this basin consists of conglomerate (Yurukakcayir conglomerate), clayey and silty limestone, dolomitic marl, sepiolite beds and lenses, and dolomitic limestone (Kepeztepe formation). The main impurities within the sepiolite rock are dolomite, opal-CT, calcite, smectite and feldspar as sepiolite + dolomite and sepiolite + opal-CT are the main mineral assemblages. Smectite and feldspar are thought to be of detrital origin. Calcite is found as a secondary filling in root tubes and casts. Sepiolite samples studied display root-marks and root tubes, soapy and massive structure indicating direct precipitation. Sepiolite deposits probably formed at a pH of 8 to 9, and Mg+2 and SiO 2 concentrations in moderately saline environments of internal facies of an alkaline lake.

DISTRIBUTION AND PALEOECOLOGICAL SIGNIFICANCE OF FOSSIL DIATOM ASSEMBLAGES FROM THE HOLOCENE SEDIMENTS OF LAKE MANZALA, EGYPT

The diatom distribution pattern in the bottom sediments of Manzala Lake is very variable and is dependent on many factors. The relative abundance of diatom species has evolved over time, reflecting the change in environmental conditions from the pre-Aswan Dam before 1965 when Nile flood water continuously entered the lake, and the post-Aswan Dam, when the lack of Nile water is compensated by drainage and sewage waters entering the lake. The study was carried out on Recent subfossil material from six core sites taken from Manzala Lake. A total of 212 diatom species and varieties belonging to 44 genera were identified and counted from 171 samples. The statistical data derived from the relative frequency of the diatom taxa provide fine resolution for paleoecologic interpretation of the recent sediments of the Lake. There are clear changes regarding alkalinity and salinity. The diatom composition of the sediment cores was analyzed by Twinspan program. This classifies the diatom taxa into six main assemblage zones. Each assemblage is mainly related to a certain environmental conditions and reflects recent environmental change. The paleoenvironmental reconstruction results for the lake are discussed in detail. It is concluded that the post High Dam drainage and seepage waters flowing into the lake have caused a change in the composition and distribution pattern of diatoms in the lake.

Mangrove Conservation and Coastal Management in Southeast Asia: What Impact on Fishery Resources?

This paper focuses on relationships between mangroves and coastal fish resources. A review of the literature highlights the lack of quantified relationships. We show that mangroves can be considered as a particular case of an estuarine environment, and then address the broader issue of the relationships between tropical estuaries and fishery resources. An estuarine fish community is composed of three main assemblages, respectively from continental, strictly estuarine or marine origin. The major characteristics of these assemblages are defined. On this basis we detail the different and sometimes opposite impacts of major rehabilitation actions on each assemblage. The biological approach is then widened by a critical overview of current approaches in economic valuation of mangrove-related fish resources. This provides a rational and scientific foundation for economic analysis of resources and for coastal management decisions, and allows us to define priorities for further scientific and policy research in these areas.