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  • 1
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A new type of animal community has been found near hot vents in the subpolar Atlantic at 100 to 106 m depth off Kolbeinsey on the Jan-Mayen ridge. Incubation of high temperature fluids yielded cultures of undescribed hyperthermophilic eu- and archaebacteria, growing in a temperature range between 70° and 110°C depending on the isolates. Bacteria are closely related to species occurring within deep sea hydrothermal areas. In contrast to deep-sea vent sites of the Mid-Atlantic and other oceans, the Kolbeinsey macro- and meiofauna consists of species reported from non-vent areas in the boreal Atlantic and adjacent polar seas. The most abundant forms are a solitary hydroid polyp and two sponges. Kolbeinsey is an isolated and young area of hydrothermal activity at relatively low depth and in highly productive waters; these findings could indicate a model for an early evolutionary step towards the formation of a genuine specialized vent community.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Mineralium deposita 24 (1989), S. 82-91 
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract New investigations are carried out on the mineralogy and mineral chemistry of sulfide assemblages obtained in samples from one core in the hydrothermally active, southwest basin of the Atlantis II deep, Red Sea. The most abundant sulfide phases are the exsolved intermediate solid solution (ISS) and chalcopyrite. Sphalerite, pyrrhotite, marcasite, mackinawite, and presumably wurtzite are also observed. Two distinct groups of paragenesis were encountered: (a) Intermediate solid solution with sphalerite incrustations and intergrowths, and (b) intermediate solid solution barren of sphalerite intergrowths. The first group is confined to the upper part of the Co zone and the SOAN zone (Bäcker and Richter 1973), and the second is present in the entire core 100-3-7. An optically isotropic chalcopyrite is found for the first time as a natural mineral in Atlantis II, Red Sea. Yet its existence as a novel phase needs x-ray confirmation. It exhibits a lower reflectivity than normal chalcopyrite and is isotropic. Chalcopyrite occurs either as a single phase or in association with tetragonal chalcopyrite. Our investigations indicate that the formation of Atlantis II deposits is a result of complex processes. These processes are characterized by compositional changes in the ore-bearing fluids and the change in sulfur fugacity (especially with depth). The presence of exsolved chalcopyrite lamellae in ISS indicates slow cooling below 450°C. However, it is difficult to understand why the cubic chalcopyrite is not converted to the tetragonal form even though the temperature of transformation lies above 450°C (470° – 500°C, Cabri 1973). The Cu/Fe ratio changes in the exsolved chalcopyrite lamellae from core to rim of the composite grains. The ratio is higher in the rims. This suggests that primary inhomogenous ISS grains formed from solutions with a continuous increase in the Cu/Fe ratio. Slow cooling is also required to account for the exsolution of chalcopyrite lamellae in ISS. The low sulfur content in isotropic chalcopyrite is also suggestive of low fs2. The low S content in the chalcopyrite may be the controlling factor for the sluggish conversion from cubic to tetragonal chalcopyrite. Mackinawite lamellae show the same orientation in ISS and exsolved isotropic chalcopyrite indicating that mackinawite exsolved before the breakdown of ISS. This strongly suggests that mackinawite is stable above 300°C (contrary to experimental results by Zoka et al. 1973). Pyrrhotite was probably formed by the sulfurization of ilvaite. The pyrrhotite grains with several complex successive zones show the sequence of the sulfurization episodes. Metalliferous sediments related to hot brines were discovered in the Red Sea in 1964 (Miller et al. 1966). Since then, several papers have been published on this subject (Degens and Ross 1969, Bäcker and Schoell 1972, Bäcker and Richter 1973, Bignell et al. 1976, Shanks and Bishoff 1977, Weber-Diefenbach 1977, Nöltner 1979, Pottorf 1980, Pottorf and Barnes 1983, Oudin et al. 1984). Complex sulfide phases including intermediate solid solution (ISS), chalcopyrite, and a chalcopyritelike mineral (which exhibits a lower reflectivity than normal chalcopyrite and appears to be isotropic occur in the metalliferous sediments. These phases were found in association with several minerals in different parageneses. In an attempt to understand the origin of the formation of the sulfide-bearing sediments in the Atlantis II deep of the Red Sea, a detailed study of the phase relations of the Cu-Fe sulfide ores of this locality was carried out.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The North Atlantic volcanic province has been attributed to continental rifting about 60 Myr ago over an Iceland plume head with a diameter of 1,000–2,000 km (refs 1, 2). But evidence from a few igneous centres has been used to infer that earlier ...
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 107 (1991), S. 318-327 
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 107 (1991), S. 243-255 
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 121 (1994), S. 111-124 
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 101 (1990), S. 54-62 
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 89 (1988), S. 261-272 
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Mineralogy and petrology 33 (1984), S. 1-23 
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Manganmikroknollen aus 7 verschiedenen Gebieten des Pazifischen Ozeans werden untersucht und miteinander verglichen. In Abhängigkeit von der Sedimentfazies lassen sich deutliche Unterschiede in der Häufigkeit, der Morphologie und inneren Struktur sowie in der Mineralogie und chemischen Zusammensetzung der Mikroknollen beobachten. Die Menge an Manganmikroknollen im Sediment scheint umgekehrt proportional der Sedimentationsrate zu sein. Höchste Gehalte an Mikroknollen finden sich in extrem langsam abgelagerten braunen pelagischen Tonen (z.B. Südwest-Pazifisches Becken). Die Morphologie und die innere Struktur der Mikroknollen hängt entscheidend vom Nukleusmaterial (kieselige, kalkige Organismen, vulkanoklastisches Material) ab. Biogene Anreicherung, hydrogenetische und hydrothermale Metallzufuhr sowie diagenetische Mobilisationsprozesse bestimmen, ähnlich wie bei Manganmakroknollen, die Mineralogie und chemische Zusammensetzung der Manganmikroknollen, wobei diagenetische Prozesse von größter Bedeutung sind. Sie erklären die Unterschiede in der chemischen Zusammensetzung zwischen Mikro- und Makromanganknollen aus dem gleichen Untersuchungsgebiet. Diagenetische Mobilisierung von Mangan und anderen Elementen im Sediment bestimmt Verteilung und Chemismus der Mikroknollen in tieferen Sedimentschichten. Mikroknollen lassen sich nicht durch einen einfachen Bildungsprozeß erklären. Ihr Auftreten wird durch eine Reihe von Einflüssen wie Redoxpotential, Sedimentationsrate, Nukleusmaterial, biogene Anreicherungsprozesse, Diagenese und Tiefenwasserströmungen kontrolliert.
    Notes: Summary The abundance, morphology, internal structure, mineralogy and composition of manganese micronodules from seven areas in the equatorial and South-West Pacific have been evaluated and compared. Micronodule abundance appears to be inversely related to sedimentation rate with highest abundances occurring in dark brown clays where sedimentation rates are low. Morphology and internal structure are dependent on the nature of the seed material in which the micronodule forms, of which calcareous tests, siliceous tests and volcanoclastic material are the most important. SEM studies show quite marked variations in the external and internal characteristics of the micronodules from different areas. The mineralogy and composition of the micronodules tend to follow those of macronodules from the same location with biogenic processes leading to the formation of todorokite and high Ni + Cu contents in equatorial Pacific micronodules, for example. Nonetheless, significant differences are apparent in composition between micronodules and macronodules from the same location. Diagenetic processes lead to remobilization of manganese within the sediment column. This influences the distribution and composition of micronodules within the various sediment size fractions and with depth in the sediment column. The characteristics of the micronodules studied here are strongly influenced by the nature of the sedimentary environment in which they form. Micronodules are therefore seen not to have a uniform mode of formation but rather to reflect a variety of influences on their growth.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    International journal of earth sciences 73 (1984), S. 1055-1080 
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract The mineralogy and composition of sediments and manganese micronodules from the northern and central sectors of the Peru Basin are discussed. Because of the proximity of the basin to the Carbonate Compensation Depth (C.C.D.), surface sediments vary between calcareous oozes and siliceous muds. Besides biogenic components clay minerals are important. By far the most abundant clay mineral is smectite which is thought to be of diagenetic origin. On a carbonate-free basis, the surface sediments are rather uniform in composition throughout the basin and are similar in composition to those of the equatorial Pacific. Sedimentation rates for the uppermost core sections are in the range of 3 to 5 mm/ 1000 yr. Micronodule compositions show significant variations related to the size class of the micronodules and the depth of occurrence within the sediment column. In general, the chemistry of the micronodules can be explained by the reductive mobilization of Mn within the sediment column and by oxic diagenetic reactions between ferromanganese hydroxides and biogenic opal. The dominant mineral phase is todorokite.
    Abstract: Résumé Cette note décrit la minéralogie et la composition des sédiments et des nodules polymétalliques de la partie septentrionale et centrale du bassin de Perou. Les sédiments de surface consistent en dépôts calcaires ou siliceux selon leur situation par rapport à la profondeur de compensation des carbonates (C. C. D.). A côté des composants biogènes, des minéraux argileux (smectites, illites) sont présents en quantité importante. Le minéral argileux le plus fréquent est une smectite diagenétique. La composition chimique de la fraction non carbonatée des sédiments est uniforme, comparable au chimisme de ceux du Pacifique central. Dans les couches les plus élevées, la vitesse de sédimentation, basée sur des datations par230Th, est de 3 à 5 mm/1000 ans. Le chimisme des micronodules polymétalliques est très variable et dépend de leur profondeur dans le sédiment et de leur dimension. Le chimisme est déterminé par des processus de remobilisation en conditions réductrices dans la colonne sêdimentaire, ainsi que par des réactions diagénétiques entre les hydroxydes de Fe-Mn et l'opale biogène. Le minéral dominant est la todorokite.
    Notes: Zusammenfassung Mineralogie und chemische Zusammensetzung von Sedimenten und Manganmikroknollen aus dem nördlichen und zentralen Teil des Peru-Beckens werden beschrieben. Die Oberflächensedimente bestehen je nach der Lage zur Karbonatkompensationstiefe (C.C.D.) aus karbonatischen bzw. kieseligen Ablagerungen. Neben den biogenen Komponenten sind Tonmineralien (Smektit, Illit) von Bedeutung. Das häufigste Tonmineral ist diagenetisch gebildeter Smektit. Auf karbonatfreier Basis ist die chemische Zusammensetzung der Sedimente sehr einheitlich, vergleichbar mit dem Chemismus zentralpazifischer Sedimente.230Th-Datierungen ergeben eine Sedimentationsrate von 3–5 mm/1000 a für die obersten Sedimentschichten. In Abhängigkeit von der Korngrößenklasse und der Tiefe in der Sedimentsäule zeigen die Manganmikroknollen große Schwankungen im Chemismus. Remobilisationsprozesse unter reduzierenden Bedingungen in der Sedimentsäule sowie die diagenetischen Reaktionen zwischen Fe-Mn-Hydroxiden und biogenem Opal bestimmen die chemische Zusammensetzung der Manganmikroknollen. Die vorherrschende Mineralphase ist Todorokit.
    Type of Medium: Electronic Resource
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