The fish zonation of the Itanha,m river basin in the Atlantic Forest of southeast Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Disentangling the influences of habitat structure and limnological predictors on stream fish communities of a coastal basin, southeastern Brazil

Em ambientes de riacho, fatores relacionados à estrutura dos habitats e limnologia interagem regulando os padrões de transferência de energia e matéria, afetando a composição da comunidade de peixes. Em bacias costeiras do sudeste do Brasil as características limnológicas e estrutura dos habitats diferem entre riachos de águas claras e pretas. Os primeiros são compostos por uma variedade de tipos de substrato, possuem velocidades de corrente mais elevadas e baixa condutividade, enquanto os últimos apresentam substrato arenoso, baixas velocidades de corrente e águas escuras e ácidas. Neste trabalho analisamos a importância relativa da estrutura dos habitats e das variáveis limnológicas como preditores dos padrões de composição em comunidades de peixes de riachos. Oito riachos de primeira a terceira ordem foram amostrados na planície costeira da bacia do rio Itanhaém. Capturamos 34 espécies e verificamos que a composição das comunidades foi influenciada por fatores estruturais e limnológicos, sendo os primeiros mais importantes. Uma fração de variação que não pode ser totalmente decomposta, deve-se à influência conjunta da limnologia e estrutura dos habitats. Algumas das espécies restritas aos riachos de águas pretas provavelmente apresentam adaptações fisiológicas e comportamentais para lidar com os baixos níveis de pH. Quando foram examinados somente os riachos de águas claras, toda a variação explicada na composição da comunidade de peixes foi atribuída aos fatores estruturais, devido a preferências específicas por diferentes características de hábitats.

Updated bathymetric chart of the East Aral Sea

The Aral Sea is located in an arid region with much sand and salt deposits in the surrounding barren open land. Hence, significant displacements of sediments into the lakebed by the action of wind, water, gravity, or snow are likely. The bathymetry of the lake was last observed in the 1960s, and within the last half century, the structure of the lakebed has changed. Based on satellite observations of the temporal changes of shoreline (Landsat optical remote sensing) and water level (multi-mission satellite altimetry) over more than one decade an updated bathymetric chart for the East Basin of the Aral Sea has been generated. During this time, the geometry of the shallow East Basin experienced strong fluctuations due to the occurrence of periods of drying and strong inflow. By the year 2014 the East Basin fell dry. The dynamic behavior of the basin allowed for estimating the lake's bathymetry from a series of satellite-based information. The river mouth made its impression in the present East Aral Sea, because its shrinking led to the inflow of much sediment into the lake's interior. In addition, salt deposits along the shorelines increased the corresponding elevation, a phenomenon that is more pronounced in the reduced lakebed because of increased salinity. It must be noted that height estimates from satellite altimetry were only possible down to a minimum elevation of 27 m above sea level due to a lack of reliable altimetry data over the largely reduced water surface. In order to construct a complete bathymetric chart of the lakebed of the East Aral Sea heights below 27 m were obtained solely from Landsat optical images following the SRB (Selected Region Boundary) approach as described by Singh et al. (2015).

Ictiofauna de riachos na planície costeira da bacia do rio Itanhaém, litorial sul de São Paulo

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

On the origin of the ultradeep East Barents Sea basin

Very large subsidence, with up to 20 km thick sediment layers, is observed in the East Barents Sea basin. Subsidence started in early Paleozoic, accelerated in Permo-Triassic times, finished during the middle Cretaceous, and was followed by moderate uplift in Cenozoic times. The observed gravity signal suggests that the East Barents Sea is at present in isostatic balance and indicates that a mass excess is required in the lithosphere to produce the observed large subsidence. Several origins have been proposed for the mass excess. We use 1-D thermokinematic modeling and 2-D isostatic density models of continental lithosphere to evaluate these competing hypotheses. The crustal density in 2-D thermokinematic models resulting from pressure-, temperature-, and composition-dependent phase change models is computed along transects crossing the East Barents Sea. The results indicate the following. (1) Extension can only explain the observed subsidence provided that a 10 km thick serpentinized mantle lens beneath the basin center is present. We conclude that this is unlikely given that this highly serpentinized layer should be formed below a sedimentary basin with more than 10 km of sediments and crust at least 10 km thick. (2) Phase changes in a compositionally homogeneous crust do not provide enough mass excess to explain the present-day basin geometry. (3) Phase change induced densification of a preexisting lower crustal gabbroic body, interpreted as a mafic magmatic underplate, can explain the basin geometry and observed gravity anomalies. The following model is proposed for the formation of the East Barents Sea basin: (1) Devonian rifting and extension related magmatism resulted in moderate thinning of the crust and a mafic underplate below the central basin area explaining initial late Paleozoic subsidence. (2) East-west shortening during the Permian and Triassic resulted in densification of the previously emplaced mafic underplated body and enhanced subsidence dramatically, explaining the present-day deep basin geometry.

The break-up of East Gondwana along the northeast coast of Oman: evidence from the Batain basin

Recent detailed studies on the Batain nappes (northeast coast of Oman), which represent a special part of the so-called `Oman Exotics', have led to a better understanding of the Neotethyan geodynamic evolution. The Batain Exotics bear witness to volcanic activity, sea-level changes, tectonic instability, rifting and oceanization along the Eastern Oman margin during Late Palaeozoic and Mesozoic times. They allow definition of the Batain basin as an aborted Permian branch of Neotethys. This marine basin was created in Early Permian times extending southward to the East African/Madagascar region and was linked to the Karoo rift system. The presented revised classification of the Batain nappes considers the Batain basin to be no longer a part of the Hawasina basin and the Neotethyan mat-gin proper. We attribute the Batain basin to a Mozambique-Sornali-Masirah rift system (Somoma). This system started in Early Permian, times, creating a marine basin between Arabia and India/Madagascar; rifting in the Late Triassic and oceanization during Late Jurassic times led to the separation of East Gondwana.

Element concentrations and isotopic composition of tholeiite and whole rocks samples from the east Mariana Basin

Studies of seafloor magnetic anomaly patterns suggest the presence of Jurassic oceanic crust in a large area in the western Pacific that includes the East Mariana, Nauru and Pigafetta Basins. Sampling of the igneous crust in this area by the Deep Sea Drilling Program (DSDP) and the Ocean Drilling Program (ODP) allows direct evaluation of the age and petrogenesis of this crust. ODP Leg 129 drilled a 51 m sequence of basalt pillows and massive flows in the central East Mariana Basin. 40Ar/39Ar ages determined in this study for two Leg 129 basalts average 114.6 +/- 3.2 Ma. This age is in agreement with the Albian-late Aptian paleontologic age of the overlying sediments, but is distinctively younger than the Jurassic age predicted by magnetic anomaly patterns in the basin. Compositionally, the East Mariana Basin basalts are uniformly low-K tholeiites that are depleted in highly incompatible elements compared to moderately incompatible ones, which is typical of mid-ocean ridge basalts (MORB) erupted near hotspots. The Sr, Nd and Pb isotopic compositions of the tholeiites (87Sr/86Sr init = 0.70360-0.70374; 143Nd/144Nd init = 0.512769-0.512790; 206Pb/204Pb meas = 18.355-18.386) also overlap with some Indian Ocean Ridge MORB, although they are distinct from the isotopic compositions of Jurassic basalts drilled in the Pigafetta Basin, the oldest Pacific MORB. The isotopic compositions of the East Mariana Basin tholeiites are also similar to those of intraplate basalts, and in particular, to the isotopic signature of basalts from the nearby Ontong Java and Manihiki Plateaus. The East Mariana Basin tholeiites also share many petrologic and isotopic characteristics with the oceanic basement drilled in the Nauru Basin at DSDP Site 462. In addition, the new 110.8 +/- 1.0 Ma 40Ar/39Ar age for two flows from the bottom of Site 462 in the Nauru Basin is indistinguishable from the age of the East Mariana Basin flows. Thus, while magnetic anomaly patterns predict that the igneous basement in the Nauru and East Mariana Basins is Jurassic in age, the geochemical and chronological results discussed here suggest that the basement formed during a Cretaceous rifting event within the Jurassic crust. This magmatic and tectonic event was created by the widespread volcanism responsible for the genesis of the large oceanic plateaus of the western Pacific.

Composition of carbonaceous sediments from the Late Jurassic Volgian Basin of the East European Platform (Kostroma Region, Russia)

Lithological, geochemical, stratigraphic, and paleoecological features of carbonaceous sediments in the Late Jurassic Volgian Basin of the East European Platform (Kostroma Region) are considered. The shale-bearing sequence studied is characterized by greater sedimentological completeness as compared with its stratotype sections in the Middle Volga region (Gorodishche, Kashpir). Stratigraphic position and stratigraphy of the shale-bearing sequence, as well as distribution of biota in different sedimentation settings are specified. It is shown that Volgian sediments show distinct cyclic structure. The lower and upper elements of cyclites consist of high-carbonaceous shales and clayey-calcareous sediments, respectively, separated by transitional varieties. Bioturbation structures in different rocks are discussed. Microcomponent composition and pyrolytic parameters of organic matter, as well as distribution of chemical elements in lithologically variable sediments are analyzed. Possible reasons responsible for appearance of cyclicity and accumulation of organic-rich sediments are discussed.

Investigations on seven sediment cores from the New Ireland Basin, east of Papua New Guinea

Sediment cores were recovered from the New Ireland Basin, east of Papua New Guinea, in order to investigate the late Quaternary eruptive history of the Tabar-Lihir-Tanga-Feni (TLTF) volcanic chain. Foraminifera d18O profiles were matched to the low-latitude oxygen isotope record to date the cores, which extend back to the early part of d18O Stage 9 (333 ka). Sedimentation rates decrease from >10 cm/1000 yr in cores near New Ireland to ~2 cm/1000 yr further offshore. The cores contain 36 discrete ash beds, mostly 1-8 cm thick and interpreted as either fallout or distal turbidite deposits. Most beds have compositionally homogeneous glass shard populations, indicating that they represent single volcanic events. Shards from all ash beds have the subduction-related pattern of strong enrichment in the large-ion lithophile elements relative to MORB, but three distinct compositional groups are apparent: Group A beds are shoshonitic and characterised by >1300 ppm Sr, high Ce/Yb and high Nb/Yb relative to MORB, Group B beds form a high-K series with MORB-like Nb/Yb but high Ce/Yb and well-developed negative Eu anomalies, whereas Group C beds are transitional between the low-K and medium-K series and characterised by flat chondrite-normalised REE patterns with low Nb/Yb relative to MORB. A comparison with published data from the TLTF chain, the New Britain volcanic arc and backarc including Rabaul, and Bagana on Bougainville demonstrates that only Group A beds share the distinctive phenocryst assemblage and shoshonitic geochemistry of the TLTF lavas. The crystal- and lithic-rich character of the Group A beds point to a nearby source, and their high Sr, Ce/Yb and Nb/Yb match those of Tanga and Feni lavas. A youthful stratocone on the eastern side of Babase Island in the Feni group is the most probable source. Group A beds younger than 20 ka are more fractionated than the older Group A beds, and record the progressive development of a shallow level magma chamber beneath the cone. In contrast, Group B beds represent glass-rich fallout from voluminous eruptions at Rabaul, whereas Group C beds represent distal glass-rich fallout from elsewhere along the volcanic front of the New Britain arc.

Whole rock analytical techniques and glas analytical techniques of silicic magmas from the South East Rift, Manus Basin

There has been much recent interest in the origin of silicic magmas at spreading centres away from any possible influence of continental crust. Here we present major and trace element data for 29 glasses (and 55 whole-rocks) sampled from a 40 km segment of the South East Rift in the Manus Basin that span the full compositional continuum from basalt to rhyolite (50-75 wt % SiO2). The glass data are accompanied by Sr-Nd-Pb, O and U-Th-Ra isotope data for selected samples. These overlap the ranges for published data from this part of the Manus Basin. Limited increases in Cl/K ratios with increasing SiO2, La-SiO2 and Yb-SiO2 relationships, and the oxygen isotope data rule out models in which the more silicic lavas result from partial melting of altered oceanic crust or altered oceanic gabbros. Rather, the data form a coherent array that is suggestive of closed-system fractional crystallization and this is well simulated by MELTS models run at 0.2 GPa and QFM (quartz-fayalite-magnetite buffer) with 1 wt % H2O, using a parental magma chosen from the basaltic glasses. Although some assimilation of altered oceanic crust or gabbro cannot be completely ruled out, there is no evidence that this plays an important role in the origin of the silicic lavas. The U-series disequilibria are dominated by 238U and 226Ra excesses that limit the timescale of differentiation to less than a few millennia. Overall, the data point to rapid evolution in relatively small magma lenses located near the base of thick oceanic crust; we speculate that this was coupled with relatively low rates of basaltic recharge. A similar model may be applicable to the generation of silicic magmas elsewhere in the ocean basins.

Sedimentological, mineralogical, biogeochemical and micropaleontological parameters on sediment core PS69/849-2, Burton Basin, MacRobertson Shelf, East Antarctica

A multi-proxy study including sedimentological, mineralogical, biogeochemical and micropaleontological methods was conducted on sediment core PS69/849-2 retrieved from Burton Basin, MacRobertson Shelf, East Antarctica. The goal of this study was to depict the deglacial and Holocene environmental history of the MacRobertson Land-Prydz Bay region. A special focus was put on the timing of ice-sheet retreat and the variability of bottom-water formation due to sea ice formation through the Holocene. Results from site PS69/849-2 provide the first paleo-environmental record of Holocene variations in bottom-water production probably associated to the Cape Darnley polynya, which is the second largest polynya in the Antarctic. Methods included end-member modeling of laser-derived high-resolution grain size data to reconstruct the depositional regimes and bottom-water activity. The provenance of current-derived and ice-transported material was reconstructed using clay-mineral and heavy-mineral analysis. Conclusions on biogenic production were drawn by determination of biogenic opal and total organic carbon. It was found that the ice shelf front started to retreat from the site around 12.8 ka BP. This coincides with results from other records in Prydz Bay and suggests warming during the early Holocene optimum next to global sea level rise as the main trigger. Ice-rafted debris was then supplied to the site until 5.5 cal. ka BP, when Holocene global sea level rise stabilized and glacial isostatic rebound on MacRobertson Land commenced. Throughout the Holocene, three episodes of enhanced bottom-water activity probably due to elevated brine rejection in Cape Darnley polynya occured between 11.5 and 9 cal. ka BP, 5.6 and 4.5 cal. ka BP and since 1.5 cal. ka BP. These periods are related to shifts from warmer to cooler conditions at the end of Holocene warm periods, in particular the early Holocene optimum, the mid-Holocene warm period and at the beginning of the neoglacial. In contrast, between 7.7 and 6.7 cal. ka BP, brine rejection shut down, maybe owed to warm conditions and pronounced open-water intervals.

Drawdown tests on earth cover material placed over an asphalt membrane, East Bench Canal, Missouri River Basin Project, Montana /

Mode of access: Internet.

Shallow ground-water flow and drainage characteristics of the Brown Ditch basin near the East Unit, Indiana Dunes National Lakeshore, Indiana, 1982 /

Mode of access: Internet.

Basin-scale architecture of deeply emplaced sill complexes : Jameson Land, East Greenland

We would like to thank reviewers Steffi Burchadt and Simon Passey for the considerate and careful reviews which improved this paper. Funding for data collection in study was provided from the research council of Norway through the PETROMAKS project 193059 and the Force Safari project. Funding for data analysis was provided from PETROMAKS through the Trias North project (234152). Dougal Jerram is partly supported by research council of Norway Centres of Excellence funding (223272, CEED). The data were acquired by Julien Vallet and Samuel Pitiot of Helimap Systems. Simon Buckley is acknowledged for help with data processing, and Gijs Henstra and Björn Nyberg for assistance in the field. Aka Lynge and Arild Andresen are thanked for logistical support