Possible influence of salinity and temperature on modern shelf carbonate sedimentation

In modern, marine, carbonate sands from shelf areas between the equator and latitudes 60°S and 60°N several major grain associations can be distinguished.On open shelves (< 100 m water depth) there are two skeletal grain associations. One (chlorozoan) is virtually restricted to warm, tropical waters; the other (foramol) characterizes temperate waters but also extends into the tropics. The distribution of these two associations cannot be explained in terms of water temperature alone: salinity is suspected as being a further controlling factor. Indeed, a third skeletal association (chloralgal) appears to be characteristic of areas where salinity is higher than on open shelves.Non-skeletal grains, where present, can be grouped into two associations. In one, pellets are the only non-skeletal grains represented; in the other, ooliths and/or aggregate grains are also present. These non-skeletal associations are restricted to relatively warm waters, but temperature does not determine which one of the associations develops. Again, salinity seems important.As both salinity and temperature apparently influence the grain associations, an attempt is made to present the relationships diagrammatically. By using graph pairs of “maximum temperature/minimum salinity” and “minimum temperature/maximum salinity” (named S.T.A.R. diagrams after Salinity Temperature Annual Ranges), the various grain associations can be classed into separate salinity/temperature fields.Salinity and temperature often seem to have a mutual “compensating” effect. For example, even at high temperatures the chlorozoan association does not develop if the salinity falls below a certain value, but it develops at relatively low temperatures when salinity is sufficiently high.This “compensation” effect also appears on the S.T.A.R. diagram for non-skeletal associations. More striking here, however, is a relationship suggesting that development of the oolith/aggregate association is strongly dependent on salinity.Carbonate muds are not shown on the S.T.A.R. diagrams, but an attempt is made to assimilate them into the model.The S.T.A.R. diagrams have a predictive value. In principle, given salinity and temperature values for an area, the grain associations can be predicted. In fact, the prediction is one of “potential”, i.e. that which is to be expected provided any other necessary environmental conditions are satisfied. Predictions are presented for the shelves of an ideal ocean and of present-day oceans and seas. The S.T.A.R. diagrams thus provide the basis for a tentative global model of present-day shelf carbonate sedimentation.The special problems of land-locked seas are discussed with reference to the Mediterranean Sea and the Persian Gulf. Predictions are presented.To illustrate the possibilities of the S.T.A.R. diagram technique, an attempt at detailed prediction is given for an area — the Gulf of Batabano, Cuba — where the sediments are known and predictions can be checked.In conclusion, the problems inherent in applying the model to ancient sedimentary systems are briefly discussed.     

Tourmaline-rich Rocks Associated with the Submarine Hydrothermal Rosebery Zn-Pb-Cu-Ag-Au Deposit and Granites in Western Tasmania,Australia

Summary The stratiform massive Zn-Pb sulphide Rosebery deposit of western Tasmania is hosted by metamorphosed deformed acid volcanics and sediments of the Cambrian Mt. Read Volcanics. Tourmalinite, a boron-rich siliceous sulphide facies iron formation, overlies and occurs as an exhalite facies equivalent of the massive sulphides. The orebody is partially replaced by post deformation tourmaline-bearing pyrrhotite-pyrite rocks associated with an alteration facies comprising magnetite-pyrite-tourmaline-phlogopite and the host metavolcanics are transgressed by quartz-tourmaline veins and tourmaline-filled joints. Tourmalinite and tourmaline in alteration zones are associated with other base metal deposits in the area. Tourmaline also occurs as fault-fill and in granitic rocks and associated Sn-W mineralization nearby. Tourmaline associated with the Cambrian massive sulphides is schorl > dravite in contrast to schorl in the Devonian granites.It is suggested that boron was an integral part of the ore fluids at Rosebery which precipitated tourmaline in exhalites immediately after and distal to the mineralization event. Tourmaline from the tourmalinite exhalites appears to have derived from submarine hydrothermal precipitation. Joint- and fracture-fill tourmaline could have derived from remobilization from tourmalinites during Devonian tectonism, however, it is more probable that these discordant tourmaline-bearing veins, tourmaline in the post-cleavage Rosebery Fault and tourmaline-bearing pyrrhotite-pyrite replacement of the Rosebery orebody derived from Devonian granite at a shallow depth which has been intersected in drilling. Tourmaline replacement associated with discordant structures is no different in composition from that from tourmalinites associated with the orebody and hence has undergone re-equilibration with the host rocks during multiple events of deformation and metamorphism associated with Devonian tectonism. In contrast, the composition of tourmaline from the Devonian granites is markedly different from that of the Rosebery area.

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Zusammenfassung Die stratiforme, massive Zn-Pb-Sulfidlagerstätte Rosebery in West-Tasmanien sitzt in metamorphen und deformierten sauren Vulkaniten und Sedimenten der Kambrischen Mt. Read Vulkanit-Serie auf. Turmalingesteine treten im Hangenden dieser Serie auf. Sie stellen eine Bor-reiche Eisenformation in silizuiumreicher Sulfidfazies dar und sind als das exhalative Äquivalent der massiven Sulfide anzusehen. Der Erzkörper wird teilweise von postdeformativen Turmalin-fährenden Pyrrhotin-Pyrit-Gesteinen verdrängt, die mit einer Alterationsfazies, bestehend aus Magnetit-Pyrit-Turmalin-Phlogopit, assoziiert sind. Die erzfährenden Metavulkanite werden von Quarz-Turmalin-Gängen und Turmalinadern durchschlagen. Turmalingesteine wie auch Turmalin in Alterationszonen kommen auch mit anderen Buntmetall-Vererzungen des Arbeitsgebietes vor. Turmalin tritt weiters in Störungszonen, in Graniten und in an diese gebundenen Sn-W Mineralisationen auf.Der mit den kambrischen, massiven Vulkaniten assozierte Turmalin ist ein Schörl > Dravit, während in den devonischen Graniten Schörl dominiert. Es ist anzunehmen, daß Bor einen integralen Anteil der Erzlösungen in der Rosebery-Lagerstätte darstellt. Aus diesen ist Turmalin exhalativ, kurz nach der Sulfidmineralisation distal gebildet worden. Es zeigt sich, daß der Turmalin aus submarin hydrothermalen Absätzen herzuleiten ist. Gangturmaline könnten durch Remobilisation der Turmalingesteine während devonischer Deformation entstanden sein. Es scheint jedoch wahrscheinlicher, daß diese diskordanten Gänge, wie auch der Turmalin in der Rosebery-Störung und die Turmalin-führenden Pyrrhotin-Pyrit-Verdrängungen aus dem devonischen Granit stammen. Verdrängter Turmalin, assoziiert mit diskordanten Strukturen, zeigt in seiner Zusammensetzung keinerlei Unterschiede zum Turmalin in Turmalingesteinen aus dem Erzkörper. Im Zuge mehrphasiger, devonischer Deformation und Metamorphose ist es somit zu Reäquilibrierung des Turmalins mit dem Trägergestein gekommen. Die Zusammensetzung des Turmalins in den devonischen Graniten unterscheidet sich deutlich von der des Rosebery-Gebietes.

     

Summer and winter differences in zooplankton biomass,distribution and size composition in the KwaZulu-Natal Bight,South Africa

Zooplankton biomass and distribution in the KwaZulu-Natal Bight were investigated in relation to environmental parameters during summer (January–February 2010) and winter (July–August 2010). Mean zooplankton biomass was significantly higher in winter (17.1 mg dry weight [DW] m^–3) than in summer (9.5 mg DW m^?3). In summer, total biomass was evenly distributed within the central bight, low off the Thukela River mouth and peaked near Durban. In winter, highest biomass was found offshore between Richards Bay and Cape St Lucia. Zooplankton biomass in each size class was significantly, negatively related to sea surface temperature and integrated nitrate, but positively related to surface chlorophyll a and dissolved oxygen. Zooplankton biomass was significantly related to bottom depth, with greatest total biomass located inshore (<50 m). Distribution across the shelf varied with zooplankton size. Seasonal differences in copepod size composition suggest that a smaller, younger community occupied the cool, chlorophyll-rich waters offshore from the St Lucia upwelling cell in winter, and a larger, older community occurred within the relatively warm and chlorophyll-poor central bight in summer. Nutrient enrichment from quasi-permanent upwelling off Durban and Richards Bay appears to have a greater influence on zooplankton biomass and distribution in the bight than the strongly seasonal nutrient input from the Thukela River.     

华北北部中生代岩墙群

岩墙群是深源岩浆浅侵位的产物，它可提供有关壳-幔演化的重要信息。通过华北北部大同早中生代碳酸岩-煌斑岩岩墙群、赤峰早中生代闪长玢岩岩墙群、林西中生代辉绿岩岩墙群、京北晚中生代双峰式岩墙群的对比研究，揭示了华北中生代存在的两次底侵作用及其相关的伸展作用。华北早、晚中生代岩墙群与晋北地区元古代岩墙群的初步对比，从一个侧面反映了华北壳幔的演变。     

Point defects in crystalline zircon (zirconium silicate), ZrSiO<Subscript>4</Subscript>: electron paramagnetic resonance studies

This article outlines the present state of knowledge of paramagnetic defects in crystalline zircon as obtained mainly, but not exclusively, from electron paramagnetic resonance (EPR) studies in crystalline zircon (zirconium silicate, ZrSiO₄). The emphasis is on single-crystal studies where, in principle, unambiguous analysis is possible. Firstly, the crystallography of zircon is presented. Secondly, the relationships between available crystal-site symmetries and the symmetries of observed paramagnetic species in zircon, and how these observations lead to unambiguous assignments of point-group symmetries for particular paramagnetic species are detailed. Next, spin-Hamiltonian (SH) analysis is discussed with emphasis on the symmetry relationships that necessarily exist amongst the Laue classes of the crystal sites in zircon, the paramagnetic species occupying those sites and the SH itself. The final sections of the article then survey the results of EPR studies on zircon over the period 1960–2002.     

Structure and dynamics of demersal fish assemblages over three decades (1985–2012) of increasing fishing pressure in Guinea

In a context of growing fishing pressures and recommendations for an ecosystem approach to fisheries, there is a need to monitor changes in fish communities over time. In this study, we analysed data from scientific trawl surveys carried out on the continental shelf off Guinea between 1985 and 2012. We performed factorial analyses and calculated biodiversity indices to characterise the changes in the structure and composition of fish communities that occurred over the 28-year period in this area, particularly given intensive fishing activities. We show that, over the study period, fish communities on the Guinean shelf were structured primarily according to spatial factors, with temporal changes being less pronounced than expected. However, a temporal analysis of biodiversity indices and species dominance showed that the intensification of fishing had significant effects on the general ecological features of the fish assemblages under study. There was a decrease in fish density and in mean trophic level. In addition, there were changes in species dominance, whereby large, slow-growing species with high commercial value were gradually replaced by smaller, fast-growing species of lesser commercial interest. These results from field observations are in line with some conclusions from previous modelling studies in the same geographical area, and provide further support for the hypothesis of a progressive ‘ecosystem effect of fishing’ occurring in Guinean waters.     

Do predatory fish of benthic crustaceans vary between kelp and barren reef habitats in northeastern New Zealand?

Fish assemblages that included known predators of benthic crustaceans were compared between kelp and barren habitats in northeastern New Zealand using baited underwater video census methods. The benthic-feeding fish were observed in winter, spring/summer and autumn, as well as during night-time in spring/summer. Overall, the fish assemblages varied between barren and kelp habitat, being most marked in winter. Individual benthic-feeding species, such as grey mao mao (Scorpis lineolatus) and leatherjacket (Meuschenia scaber) were associated with barren habitat, while the spotted wrasse (Notolabrus celidotus) was more strongly associated with kelp habitat. The results suggest that changes in habitats on coastal reefs affect populations of species that are benthic predators, which may in turn influence the distribution and abundance of their prey species, such as juvenile spiny lobsters.     

Relationship between eddy viscosity of seawater and eddy diffusivity of suspended particles

A method is described to calculate the relationship (β) between the eddy diffusivity of suspended particles and the eddy viscosity of the fluid. The data were obtained while making suspended sediment concentration measurements near the seabed on the British continental shelf. β was calculated for 0.50 size fractions and varies inversely with the suspended sediment concentration. The values were used successfully to calculate suspended sediment transport rates for separate sand fractions through a spring tidal cycle. Finally, specific values of β are suggested for varying concentrations of sand at a reference height of 100 cm above the seabed.     

Recent earth movements in the Middle East

In many sectors of the Alpine-Himalayan mountain system movement continues into recent times, but the rate of movement is usually uncertain. The Mesopotamian plains show the effect of movement on canal systems and on old culture levels. There is a regional up-warp of the mountains as a whole and a depression of the plains, but there is also continued growth of individual anticlines. The head of the Persian Gulf is now advancing and has inundated extensive areas which were under irrigated cultivation perhaps up to the 13th. century A.D. At Shaur an anticline was crossed by an old Sassanian canal which has since been folded at a rate of one metre per century.