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Digitale Medien

The influence of late Quaternary stagnations on clay sedimentation in the eastern Mediterranean sea (1979)

Dominik, Janusz ; Stoffers, Peter

Springer

International journal of earth sciences 68 (1979), S. 302-317

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ISSN: 1437-3262

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie

Beschreibung / Inhaltsverzeichnis: Abstract Late Quaternary sapropels of the eastern Mediterranean differ from normal sediments in their clay mineral composition. Clay minerals in the sapropels studied here are only slightly affected, or are not affected at all by diagenetic alteration. This permits the observation of primary differences. During stagnation periods, the contribution of remote or accessory sources was reduced or even absent. Different circulation patterns and, particularly, a general decline in deeper water currents activity might be held responsible for the observed differences in the clay mineral composition of sapropels and normal sediments.

Kurzfassung: Résumé Les sapropels quaternaires de la Méditerranée orientale se distinguent des vases communes par la composition des minéraux argileux. Les argiles des sapropels examinés sont peu affectés par l'altération diagénétique, ce qui permet l'observation de différences primaires. On a conclu, que pendant les périodes de stagnation, la contribution des argiles provenant des sources éloignées ou secondaires, a été réduite ou même interrompue. Différentes conditions de circulation et, avant tout, la réduction d'activité des courants profonds, sont probablement responsables des différences observées dans la composition des minéraux argilezx des sapropels et des vases communes.

Notizen: Zusammenfassung Die quartären Sapropele des östlichen Mittelmeeres unterscheiden sich von den normal marinen Sedimenten in ihrer Tonmineralzusammensetzung. Die hier untersuchten Tone der Sapropele zeigen nur geringe oder gar keine diagenetischen Veränderungen. Diese Tatsache erlaubt, Rückschlüsse auf primäre Unterschiede zu ziehen. Während der Stagnationsperioden war die Zufuhr von Tonen aus entfernten oder weniger wichtigen Liefergebieten stark vermindert. Unterschiedliche Zirkulation, besonders eine geringere Aktivität der Tiefenströmungen, scheinen die Ursache für die beobachteten Unterschiede in der Tonmineralzusammensetzung zwischen Sapropel- und normal-marinen Sedimenten

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01821133

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Digitale Medien

Clay minerals in Lake Mobutu Sese Seko (Lake Albert) — Their diagenetic changes as an indicator of the paleoclimate (1979)

Stoffers, Peter ; Singer, Arieh

Springer

International journal of earth sciences 68 (1979), S. 1009-1024

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ISSN: 1437-3262

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie

Beschreibung / Inhaltsverzeichnis: Abstract The mineralogy and chemistry of cores from Lake Mobutu Sese Seko (East Africa) were studied. The base of the longest core was14C-dated at 28,000 years B.P. The clay fraction contains smectite (S), illite (I), kaolinite (K) and interstratified illite-smectite (I—S). These clays vary in a cyclic pattern. The following sequence was observed in the longest core from top to bottom: S (I+K) → I—S (S, + I, + K) → I (I—S, +(K)) → I—S (I, +S, +K) → S (I+K). This sequence is related to the Pleistocene evolution of Lake Mobutu Sese Seko. The occurrence of illite is explained as a diagenetic transformation of smectite into illite. During the illite formation (〉 12,500 years B.P.) the lake was in a closed basin stage, a conclusion supported by the presence of phillipsite and chabazite zeolites and the occurrence of protodolomitic oolites together with the illite.

Kurzfassung: Résumé Des carrottes de sondage provenant du Lac Albert ont fait l'objet d'études minéralogiques. L'extrémité inférieure des carrottes les plus longues ont, datées par le C14, un âge de 28.000 années. La fraction argileuse comprend de la smectite (S), de l'illite (I), de la kaolinite (K), et des minéraux à feuillets (I—S). La proportion des minéraux change cycliquement avec la profondeur. Du haut vers le bas, on observe la suite suivante: S (I+K) → I—S (S, + I, + K) → I (I—S, +(K)) → I—S (I, + S, +K) → S (I+K). Cette suite est en liaison étroite avec le développement du Lac Albert au Pléistocène. La présence d'illite s'explique par la transformation diagénétique à partir de la smectite. Au moment de la formation de l'illite (〉 12.5000), le Lac Albert était sans écoulement et était marqué par une forte concentration. Ce fait est souligné par l'association d'illite avec les zéolites, la philippsite et la chabasite. La présence simultanée d'oolites protodolomitiques montre que le niveau du lac était nettement plus bas qu'ajourd'hui.

Notizen: Zusammenfassung Sedimentkerne aus dem Albert-See wurden mineralogisch untersucht. C14-Datierungen ergaben für das Kernende des längsten Kerns ein Alter von 28 000 Jahren v. h. Die Tonfraktion enthält Smektit (S), Illit (I), Kaolinit (K) und Wechsellagerungsmineralien (I—S). Der Anteil der einzelnen Mineralien ändert sich zyklisch mit der Tiefe. Vom Hangenden zum Liegenden läßt sich folgende Abfolge beobachten: S (I+K) → I—S (S, + I, + K) → I (I—S, +(K)) → I—S (I, + S, +K) → S (I+K). Diese Abfolge steht im Zusammenhang mit der Pleistozänen Entwicklung des Albert-Sees. Das Auftreten von Illit wild als diagenetische Umwandlung aus Smektit erklärt. Zum Zeitpunkt der Illitbildung (〉 12500 v. h.) war der Albert-See abflußlos und hochkonzentriert. Diese Tatsache wird unterstrichen durch die Vergesellschaftung von Illit mit den Zeolithen Phillipsit und Chabasit. Das gleichzeitige Auftreten von protodolomitischen Oolithen zeigt, daß der Seespiegel wesentlich tiefer als heute lag.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF02274684

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Magmatic evolution of the Easter microplate-Crough Seamount region (South East Pacific) (1995)

Hekinian, Roger ; Stoffers, Peter ; Akermand, Dietrich ; [weitere]

Springer

Marine geophysical researches 17 (1995), S. 375-397

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ISSN: 1573-0581

Schlagwort(e): Petrology ; structure ; volcanism ; microplate

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract The Easter microplate-Crough Seamount region located between 25° S–116° W and 25° S–122° W consists of a chain of seamounts forming isolated volcanoes and elongated (100–200 km in length) en echelon volcanic ridges oriented obliquely NE (N 065°), to the present day general spreading direction (N 100°) of the Pacific-Nazca plates. The extension of this seamount chain into the southwestern edge of the Easter microplate near 26°30′ S–115° W was surveyed and sampled. The southern boundary including the Orongo fracture zone and other shallow ridges (〈 2000 m high) bounding the Southwest Rift of the microplate consists of fault scarps where pillow lava, dolerite, and metabasalts are exposed. The degree of rock alternation inferred from palagonitization of glassy margins suggests that the volcanic ridges are as old as the shallow ridges bounding the Southwest Rift of the microplate. The volcanics found on the various structures west of the microplate consist of depleted (K/Ti 〈 0.1), transitional (K/Ti = 0.11−0.25) and enriched (K/Ti 〉 0.25) MORBs which are similar in composition to other more recent basalts from the Southwest and East Rifts spreading axes of the Easter microplate. Incompatible element ratios normalized to chondrite values [(Ce/Yb)N = 1−2.5}, {(La/Sm)N = 0.4−1.2} and {(Zr/Y)N = 0.7−2.5} of the basalts are also similar to present day volcanism found in the Easter microplate. The volcanics from the Easter microplate-Crough region are unrelated to other known South Pacific intraplate magmatism (i.e. Society, Pitcairn, and Salas y Gomez Islands). Instead their range in incompatible element ratios is comparable to the submarine basalts from the recently investigated Ahu and Umu volcanic field (Easter hotspot) (Scientific Party SO80, 1993) and centered at about 80 km west of Easter Island. The oblique ridges and their associated seamounts are likely to represent ancient leaky transform faults created during the initial stage of the Easter microplate formation (≈ 5 Ma). It appears that volcanic activity on seamounts overlying the oblique volcanic ridges has continued during their westward drift from the microplate as shown by the presence of relatively fresh lava observed on one of these structures, namely the first Oblique Volcanic Ridge near 25° S–118° W at about 160 km west of the Easter microplate West Rift. Based on a reconstruction of the Easter microplate, it is suggested that the Crough seamount (〈 800 m depth) was formed by earlier (7–10 Ma) hotspot magmatic activity which also created Easter Island.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01227041

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Geochemistry of lavas from Mohns Ridge, Norwegian-Greenland Sea: implications for melting conditions and magma sources near Jan Mayen (1996)

Haase, K. M. ; Devey, Colin W. ; Mertz, Dieter F. ; [weitere]

Springer

Contributions to mineralogy and petrology 123 (1996), S. 223-237

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ISSN: 1432-0967

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie

Notizen: Abstract Mohns Ridge lavas between 71 and 72°30′N (∼360 km) have heterogeneous compositions varying between alkali basalts and incompatible-element-depleted tholeiites. On a large scale there is a continuity of incompatible element and isotopic compositions between the alkali basalts from the island Jan Mayen and Mohns Ridge tholeiites. The variation in isotopes suggests a heterogeneous mantle which appears to be tapped preferentially by low degree melts (∼5%) close to Jan Mayen but also shows its signature much further north on Mohns Ridge. Three lava types with different incompatible element compositions [e.g. chondrite-normalized (La/Sm)N〈1 to 〉2] occur in the area at 72°N and were generated from this heterogeneous mantle. The relatively depleted tholeiitic melts were mixed with a small degree melt from an enriched source. The elements Ba, Rb and K of the enriched melt were probably buffered in the mantle by residual amphibole or phlogopite. That such a residual phase is stable in this region of oceanic mantle suggests both high water contents and low mantle temperatures, at odds with a hotspot origin for Jan Mayen. Instead we suggest that the melting may be induced by the lowered solidus temperature of a “wet” mantle. Mohns MORB (mid ocean ridge basalt) and Jan Mayen area alkali basalts have high contents of Ba and Rb compared to other incompatible elements (e.g. Ba/La 〉10). These ratios reflect the signature of the mantle source. Ratios of Ce/Pb and Rb/Cs are normal MORB mantle ratios of 25 and 80, respectively, thus the enrichments of Ba and Rb are not indicative of a sedimentary component added to the mantle source but were probably generated by the influence of a metasomatizing fluid, as supported by the presence of hydrous phases during the petrogenesis of the alkali basalts. Geophysical and petrological models suggest that Jan Mayen is not the product of hotspot activity above a mantle plume, and suggest instead that it owes its existence to the unique juxtaposition of a continental fragment, a fracture zone and a spreading axis in this part of the North Atlantic.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s004100050152

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Stetteria hydrogenophila, gen. nov. and sp. nov., a novel mixotrophic sulfur-dependent crenarchaeote isolated from Milos, Greece (1997)

Jochimsen, Beate ; Peinemann-Simon, Susanne ; Völker, Horst ; [weitere]

Springer

Extremophiles 1 (1997), S. 67-73

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ISSN: 1433-4909

Schlagwort(e): Key words Hyperthermophilic ; Crenarchaeota ; Hydrogen and sulfur dependence ; Hydrothermal ; Stetteria hydrogenophila

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract A new hyperthermophilic, strictly anaerobic crenarchaeote, Stetteria hydrogenophila DSM11227 representing a new genus within the family of Desulfurococcaceae, was isolated from the sediment of a marine hydrothermal system at Paleohori Bay in Milos, Greece. Cells are gram-negative irregular and disc-shaped cocci, 0.5–1.5 μm in diameter, which are flagellate and can form cytoplasmatic protrusions up to 2 μm in length. The strain grew optimally at 95°C at pH 6.0 and at a NaCl concentration of 3%. The organism grew mixotrophically on peptide substrates. It required elemental sulfur as an external electron acceptor, and in addition, its growth was completely dependent on the presence of molecular hydrogen. Sulfur could be replaced by thiosulfate. H2S, CO2, acetate, and ethanol were identified as products of metabolism. The G + C content of DNA was 65 mol%. Analysis of its phylogenetic position by sequence analysis of 16S rRNA placed this organism in the family of Desulfurococcaceae. The dependence of this organism on both hydrogen and sulfur during growth on peptide substrates distinguishes Stetteria from all previously described species of Crenarchaeota.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s007920050016

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