东西特提斯晚白垩世深水底栖有孔虫生物相和岩相

白垩纪深水古海洋学研究仍处于早期发展阶段,一方面是由于来自钙质底栖有孔虫的稳定同位素和地球化学数据的缺乏,其原因在于白垩纪高碳酸盐补偿深度;另一方面在于深水有机质胶结有孔虫示踪古海洋还没有充分发展起来。深海环境深水胶结有孔虫的分布主要取决于碳酸盐可利用状况、原始生产的输入通量、深水交换、环境波动(深海洋流、浊流和快速沉积事件)和底层沉积类型,因此对于重建深海环境具有非常巨大的潜力。东、西特提斯Campanian Maastrichtian深水底栖有孔虫组合的统计分析揭示出6个生物相,代表着明显不同的沉积环境。包括:深海红色泥岩与矮小深海生物组合(生物相1);红色深海泥灰岩(“Couches Rouges”相),含钙质胶结有孔虫组合(生物相3);深水远洋灰岩(“Scaglia Rossa”相),含易碎的Rhizammina组合(生物相2);绿色灰色半远洋泥灰岩,含适应高输出通量生物组合(生物相4);半远洋泥岩和粉砂岩,含Aschemocella Nothia 组合(生物相5);陆源浊积层序,含“复理石型”Rhabdammina组合(生物相6)。Campanian Maastrichtian红色氧化深水环境动物组合与现今深海类似,而白垩纪贫氧深海环境胶结组合在现今无法找到相类似物。随着古生态信息的增加和数据库的扩展,深水胶结有孔虫有望成为揭示古海洋条件的重要工具,尤?     

Biogene,klastische und evaporitische Sedimentation in einem mesothermen monomiktischen ufernahen See (Golf von Aqaba)

The genesis and development of a monomictic, mesothermal lake and its sediments is demonstrated by the analysis of sediment cores from different parts of the lake and from different stages of development. The compounds which build up the sediments, consist of irregular large particles from the surrounding crystalline rocks, of fine grained silt sediments from catastrophic flud deposits, of evaporitic series, and algae mats. The thickness of the different layers and their distribution in various parts of the lake; the different compounds, absolute age determinations, the carbonate layers and algae mats allow the definition of different stages of development of the lake. Causes and influences of an unusual type of monomixis with summer turnover are discussed and related to the sedimentary environment. Annual fluctuations in physical and biological limnology lead to the development of annual cycles in mat development and evaporites, which are reflected in the varved sediments. Inorganic sedimentation of terrestrial sediments, evaporites and organic matter accumulation are in shifting equilibrium which can be analysed by changes in the sediment types. Within the zone of biologic decay of algae via photosynthetic and other sulfur bacteria and heterotrophic bacteria, biogenic aragonite, Mg-Calcite and sulfides are precipitated. The autigenic dolomite occuring within the algae mats could not be attributed to biological precipitation so far. The lake started out as a lagoon approximately 4500 years B.P. Algae mat development was initiated after the lagoon was separated from the open sea (2400 B.P.). The central parts of the lake subsided at a time between 1900 and 1600 B.P. At this time the algae mat deposition, which until then took place in the whole lake, was restricted to the remaining shallow parts. Years of extremely high precipitation and catastrophic floods are represented by silt layers in the western parts of the lake, while coarser terrestrial sediments are intercalated in the algae mats of the eastern parts. Oöids, carbonate laminae, oncoliths and other types of carbonate particles within the algae mats are defined as biogenic by SEM analyses and laboratory experiments.     

Sedimentmikrobioiogie und ihre geologischen Aspekte

The influence of bacteria on recent sediments was first discussed in 1885, whenFischer andGazert were discussing the cycle of substances in the sea as well as in sediments. The influence of bacteria on the cycling of C, N, S, P in recent sediments and the open sea was soon accepted by marine geologists. Nevertheless, only very few experiments have, so far, shown more than qualitative and quantitative data collection in various restricted areas. This is due to the extensive and complicated chain of reactions on the surface of sediments and in the sediment itself. Biologists are asking for the amount of organic and inorganic matter which is reworked and released to the sea. Geologists usually emphasize the amount of substances which are sedimentated. For biologists the sediment is only part of their dominant ecosystem (the sea). While, for geologists the “sea” is only furnishing and influencing their first range system sediment. How much then, are bacteria involved in the slow process of conversion from a recent sediment to sedimentary rocks? Bacteria influence more or less strongly and to a more or less advanced degree of diagenesis:

1. The organic matter in sediments and the final form in which it is found.
2. The anions CO₃ ^2?, NO₃ ^?, OH-, SO₄ ^2?, PO₄ ^3? as well as their intermediate stages and the resulting minerals.
3. The cations H⁺, NH₄ ⁺, Ca²⁺, Fe²⁺, Fe³⁺, and a series of metals which are dissolved or precipitated by microbial activities as for example Fe, Mn, Cu, Ag, V, Co, Mo, Ni, U, Se, Zn.
4. The equilibrium of silicium. At least diatoms and radiolarians are precipitating silica, while other reactions which have been proved are not yet shown to influence marine sediments.
5. p_H-values and oxidation-reduction potentials of the sediment.
6. The composition of interstitial waters.
7. The surface activity of minerals, since bacteria are growing especially on particle surfaces.
8. The energy content and temperature of sediments.
9. The texture of fine grained sediments.
10. The fossilization of microfauna, macrofauna and trace fossils.

Sedimentology and mineralogy may also influence the bacterial activities and the composition of the microflora within sediments. Methods and problems of sediment microbiology are demonstrated by some investigations in the German Bay (North Sea) in connection with the first German Underwater Station (UWL). Ecological work proves to be difficult in various directions. The main cause of difficulties in microbiological work on sediments are the great variety of different factors influencing the environment (microbial, chemical, physical, mineralogical), the difficulty of taking representative samples, and the small amount of data which has been collected so far.     

Paläogeographie und Tiefseesedimente des Atlantischen Ozeans

Ohne Zusammenfassung     

Age constraints on faulting and fault reactivation: a multi-chronological approach

Movement within the Earth’s upper crust is commonly accommodated by faults or shear zones, ranging in scale from micro-displacements to regional tectonic lineaments. Since faults are active on different time scales and can be repeatedly reactivated, their displacement chronology is difficult to reconstruct. This study represents a multi-geochronological approach to unravel the evolution of an intracontinental fault zone locality along the Danube Fault, central Europe. At the investigated fault locality, ancient motion has produced a cataclastic deformation zone in which the cataclastic material was subjected to hydrothermal alteration and K-feldspar was almost completely replaced by illite and other phyllosilicates. Five different geochronological techniques (zircon Pb-evaporation, K–Ar and Rb–Sr illite, apatite fission track and fluorite (U-Th)/He) have been applied to explore the temporal fault activity. The upper time limit for initiation of faulting is constrained by the crystallization age of the primary rock type (known as “Kristallgranit”) at 325 ± 7 Ma, whereas the K–Ar and Rb–Sr ages of two illite fractions <2 μm (266–255 Ma) are interpreted to date fluid infiltration events during the final stage of the cataclastic deformation period. During this time, the “Kristallgranit” was already at or near the Earth’s surface as indicated by the sedimentary record and thermal modelling results of apatite fission track data. (U–Th)/He thermochronology of two single fluorite grains from a fluorite–quartz vein within the fault zone yield Cretaceous ages that clearly postdate their Late-Variscan mineralization age. We propose that later reactivation of the fault caused loss of helium in the fluorites. This assertion is supported by geological evidence, i.e. offsets of Jurassic and Cretaceous sediments along the fault and apatite fission track thermal modelling results are consistent with the prevalence of elevated temperatures (50–80°C) in the fault zone during the Cretaceous.     

Early Cretaceous rift-related volcanism in the Songliao Basin,NE China – A geochemical study

Following the amalgamation of the Siberian and North China Cratons, NE China, as part of the Central Asian Orogenic Belt (CAOB), underwent Late Mesozoic lithospheric extension that was associated with volcanic activity. The Songliao Basin is the most important rift structure formed during these processes and contains voluminous volcanic rocks interlayered with sedimentary infill. Mafic-to-intermediate lavas are associated with felsic ones. This study focusses on the geochemical compositions of the less-widespread Early Cretaceous mafic-to-intermediate lavas in the Songliao Basin and compares them with the more abundant felsic rocks. Two mafic-to-intermediate magma series, one with alkaline and the other with sub-alkaline affinity, were identified. High MgO and Cr contents, low Th/Nb and La/Nb ratios, and variable but depleted Nd isotope compositions indicate that both magma suites were most likely formed by the melting of enriched upper mantle sources. Sub-alkaline mafic-to-intermediate rocks and I-type rhyolites define a co-genetic magma series. This rock suite was produced by the melting of subduction-modified lithospheric mantle and subsequent magma evolution as well as crustal melting during lithospheric extension. Alkaline mafic-to-intermediate rocks and A-type rhyolites form another co-genetic magma suite that was produced under within-plate conditions from an OIB-type mantle source, supposed to be the heterogeneous shallow asthenosphere and/or the lower lithosphere. Decompression partial melting of this mantle source requires a relatively thin lithosphere. The development of alkaline mafic rocks and A-type rhyolites as typical bimodal volcanic assemblage reflects that lithospheric thinning below the Songliao Basin reached its maximum, whereas basin rifting terminated afterwards.     

Conventional and in situ geochronology of the Teplá Crystalline unit, Bohemian Massif: implications for the processes involving monazite formation

The Teplá Crystalline unit (TCU), western Bohemian Massif, proves highly suitable for studying the effects of differential metamorphic reworking on the U–Th–Pb systematics in monazite, as the overprint of Variscan regional metamorphism onto high-grade Cadomian paragneisses intensifies progressively towards the northwest. Although variably hampered by scarcity, small size, and low uranium contents of monazite, isotope dilution–thermal ionisation mass spectrometry of monazite from paragneisses from the garnet, staurolite, and kyanite zones of the TCU gives a narrow ²⁰⁶Pb/²³⁸U age range from 387 to 382 Ma for Variscan peak metamorphism. These data are supported by 382–373 Ma monazite ages derived from electron microprobe analyses. Inheritance of older components in grains from the central TCU imply major “resetting” of pre-Variscan monazite around 380 Ma, possibly due to widespread garnet growth during Variscan metamorphism, which led to the consumption of pre-Variscan high-Y monazite and subsequent growth of new low-Y monazite. Concordant 498–494 Ma monazite ages in a migmatitic paragneiss close to the adjacent Mariánské Lázně Complex (MLC) grew in response to metagabbro emplacement in the MLC from 503 to 496 Ma and not during either Cadomian or Variscan regional metamorphism. Backscatter imaging and electron microprobe analyses reveal that discordant monazite of the migmatite comprises a mix of various age domains that range from ca. 540 to 380 Ma. Combined evidence presented here suggests that instead of Pb loss by volume diffusion, the apparent resetting of the U–Th–Pb systematics in monazite rather involves new crystal growth or regrowth by recrystallisation and dissolution/reprecipitation.     

Dioritic intrusions of the Slavkovský les (Kaiserwald), Western Bohemia: their origin and significance in late Variscan granitoid magmatism

Mafic and intermediate intrusions occur in the Slavkovsky les as dykes, sills and minor tabular bodies emplaced in metamorphic rocks or enclosed in late Variscan granites near the SW contact of the Western Krušné hory/Erzgebirge granite pluton. They are similar in composition and textures to the redwitzites defined in NE Bavaria. Single zircon Pb-evaporation analyses constrain the age of a quartz monzodiorite at 323.4 ± 4.4 Ma and of a granodiorite at 326.1 ± 5.6 Ma. The P–T range of magma crystallization is estimated at ~1.4–2.2 kbar and ~730–870°C and it accords with a shallow intrusion level of late Variscan granites but provides lower crystallization temperatures compared to the Bavarian redwitzites. We explain the heterogeneous composition of dioritic intrusions in the Slavkovsky les by mixing between mafic and felsic magmas with a minor effect of fractional crystallization. Increased K, Ba, Rb, Sr and REE contents compared to tholeiitic basalts suggest that the parental mafic magma was probably produced by melting of a metasomatised mantle, the melts being close to lamprophyre or alkali basalt composition. Diorites and granodiorites originated from mixed magmas derived by addition of about 25–35 and 50 vol.%, respectively, of the acid end-member (granite) to lamprophyre or alkali-basalt magma. Our data stress an important role of mafic magmas in the origin of late Variscan granitoids in NW Bohemian Massif and emphasize the effect of mantle metasomatism on the origin of K-rich mafic igneous rocks.     

Amateur decision-making in avalanche terrain with and without a decision aid: a stated choice survey

Avalanches pose a serious threat to recreational backcountry travelers in mountainous terrain. This study explores how the three main amateur user groups of avalanche terrain in western Canada (backcountry skiers, out-of-bound skiers, and snowmobile riders) balance recreational goals with safety concerns when choosing backcountry destinations under varying avalanche conditions. Using a discrete choice experiment (DCE), a stated preference technique, the study first examines the strengths and weaknesses in the decision process of the three amateur groups by comparing their responses with the choice patterns of professional mountain guides. The results show that the decision-making strategies employed by the respective amateur groups vary considerably in their level of complexity and the degree to which avalanche safety considerations are incorporated. Second, we examine the effects of a decision aid that preprocesses the most crucial pieces of avalanche hazard information on the decision preferences of the amateur groups in the DCE. The results show that a relatively simple decision aid can influence the decision-making process considerably and steer users towards more avalanche hazard sensitive behaviour.     

Ein Modell zur alpidischen Evolution und Orogenese des Tauernfensters

Zusammenfassung Die drei großen der jüngst vonSchlager &Schöllnberger für die Nördlichen Kalkalpen herausgearbeiteten stratigraphischen Wenden, die jeweils eigene Entwicklungsstadien einleiten, lassen sich auch in den im Tauernfenster vorliegenden Serien des Mesozoikums feststellen.Die Adneter Wende, die zeitlich mit dem Aufreißen der kontinentalen Kruste und der Herausbildung der Bündner Schiefer-Geosynklinale zusammenfällt, die die europäische von der ostalpinen (austroalpinen) Platte trennt, ist für den betrachteten Raum das wichtigste Ereignis zwischen variszischer und alpidischer Gebirgsbildung.Die altalpidische Orogenese setzt in der mittleren Kreide ein und erreicht in der Oberkreide mit der Subduktion der europäischen Platte unter die Sedimente der Geosynklinalfüllung (Bündner Schiefer) sowie derselben unter die ostalpine (austroalpine) Platte ihren Höhepunkt. Der Zuschub der heute im Tauernfenster vorliegenden Serien war im Campan abgeschlossen. Ebenso ist die Deckengliederung in Venedigerdecke (Zentralgneis-Komplexe mit Sedimenthülle und höhere Teildecken), Glocknerdecke (vorwiegend aus Bündner Schiefern mit Ophiolithen bestehend) und Ostalpin bereits auf die kretazischen plattentektonischen Vorgänge zurückzuführen.Die alttertiäre Regionalmetamorphose hat während ihres Höhepunktes am Ende des Eozäns die heute im Tauernfenster aufgeschlossenen Serien bis in Tiefen von 15 km oder mehr versenkt. Die anschließende, durch weitere Einengung verursachte Aufwölbung der Tauernkuppel führt zum Einströmen heißen, tiefkrustalen sauren Materials in den Kern des Antiklinoriums und — in heute noch nicht angeschnittenem Niveau -zur Anatexis.Der Flysch der Ostalpen ist aus einem paläogeographisch nördlich der Zentralgneiszone beheimateten Gebiet abzuleiten.

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The Mesozoic series of the Tauern Window are characterized by three changes in the sedimentation conditions dividing the stratigraphic evolution in four periods.In Middle and Upper Cretaceous time, the European plate is subducted under the Austroalpine plate. In Campanian time, the series of the Tauern Window are wholly covered by the Austroalpine Nappe. Three great tectonic units can be distinguished: i. e., the Venediger Nappe (consisting of Zentralgneis and its cover as well as smaller nappes and schuppen), the Glockner Nappe (mainly consisting of the Bündner Schiefer with ophiolites), and the Austroalpine nappes.The Lower Tertiary regional metamorphism culminates at the end of the Eocene at which time the series of the Tauern Window are brought into depths of 15 km or more. The succeeding arching of the Tauern cupola by continuing compression causes influx of hot acid crustal material and anatexis in the core of the anticlinorium.The flysch of the Eastern Alps derives from a zone situated paleogeographically north of the Zentralgneis zone.

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Résumé Les séries secondaires de la fenêtre des Hohe Tauern sont caractérisées par trois changements dans les conditions de la sédimentation divisant ainsi l'évolution stratigraphique en quatre périodes. Pendant le Crétacé moyen et supérieur la plaque Européenne est subductée sous les Schistes lustrés de la fosse eugéosynclinale qui, de son côté, est subductée sous la plaque Austroalpine. La formation des grandes unités tectoniques s'est achevée pendant le Crétacé supérieur, c'est-à-dire la Nappe de Venediger (constituée par le Zentralgneis et sa couverture aussi que des nappes et des écailles particulières), la Nappe du Glockner (surtout constituée par des Schistes lustrés avec des ophiolites), et les nappes Austroalpines.Le métamorphisme tertiaire culmine à la fin de l'Eocène, au terme duquel les séries de la fenêtre des Hohe Tauern sont enfouies à un profondeur de 15 km ou plus. La formation de la voûte des Hohe Tauern commence immédiatement après par rétrécissement continuel, provoquant l'admission de materiel chaud de la croûte acide et l'anatéxie dans l'intérieur de l'anticlinorium.Le flysch des Alpes orientales dérive d'une zone située paléogéographiquement au nord de la zone du Zentralgneis.

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