Early Cretaceous »events« in the evolution of the eastern and western North Atlantic continental margins

At many North Atlantic continental margins, the early Neocomian is characterized by a major stratigraphic turning point from Late Jurassic-Berriasian carbonate bank/pelagic carbonate deposition to Valanginian-Barremian hemipelagic sedimentation with thick Wealden-type deltaic to deep-sea fan sequences. The stratigraphy and structure of the very old, starved passive margin of the Mazagan Plateau and adjacent steep escarpment off Morocco was studied during the French-German CYAMAZ deep diving campaign. The drowning of the Late Jurassic-early Berriasian carbonate platform was strongly influenced by a global late Berriasian sea level fall which was followed by a rapid late Valanginian sea level rise and/or by a major regional blockfaul ting event with accelerated subsidence rates. Upper Berriasian to (?) Hauterivian quartz-bearing bioclastic wackestones document the transition from the carbonate platform to the hemipelagic deposition on the drowned platform margin. Seawards, these deposits are correlated with a deep sea fan sequence. We discuss also an example from the Tarfaya Basin-Fuerteventura area further south. A 300 m thick succession of organic-rich claystone and sandstone turbidites (including m-thick debris flow units) of Hauterivian to Barremian age was an unexpected discovery at DSDP Site 603 off North Carolina (Leg 93). We discuss a tectonically confined fan model with laterally migrating channels, influenced by sea level fluctuations and varying terrigenous supply. During the Valanginian to Barremian time of high-standing (or rising) sea level, shelf construction (Wealden-type deltas) coincided with subdued, resedimentation-starved turbiditic system on the continental rise. Extensive unconsolidated sands, however, reflect sudden input of shelfal material into the basin during a mid-Aptian sea level lowstand (shelf destruction). The following global late Aptian transgression terminated the clastic fan deposition, raised the CCD and started the deposition of organic-rich shales.     

S- and I-type granitoids of North Victoria Land,Antarctica, and their inferred geotectonic setting

In the context of Gondwana North Victoria Land forms the Antarctic conjugate terrain to the East Australian Lachlan Fold Belt, where the distinction between S- and I-type granitoids was first worked out (Chappell &White 1974). Thus the area was considered a good testing ground for the hypothesis when the German Antarctic North Victoria Land Expedition (Ganovex) resumed fieldwork there in 1979/80.It was known at that time that there existed a Cambro/Ordovician and a Devonian/Carboniferous granitoid generation, which, in analogy to Australia, were taken to be related to two different orogenetic events. Our geological, petrographical and geochemical investigations, together with radiometric age dating, revealed that this is true only for the older granite generation. The younger generation is in fact anorogenic. At the same time, it became obvious that the S- and I-type classification did not completely fit the observed field data. At this pointPitcher's (1982) subdivision of the I-types into a »Cordilleran« and a »Caledonian« suite offered a solution to account for the observed irregularities.At about the same time, plate tectonic models based on evidence independent from the granite classification were developed for this part of the active Gondwana margin. This offers the opportunity to crosscheck the tectonic environment derived from the granite classification:The characteristics of the older, Cambro/Ordovician granitoids allow a perfect accommodation in the model of an active margin above a subduction zone as derived from other evidence.For the younger (Devonian/Carboniferous) granitoids, however, the postulated tectonic setting (post-collisional uplift and faulting) could not be verified in North Victoria Land.It is concluded thatPitchers classification is applicable in its petrographic and geochemical aspects but that the tectonic environment postulated for the production of »Caledonian« I-type granitoids may not be the same in all investigated areas.

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Zusammenfassung Im Gondwana Rahmen bildet Nord Victoria Land das antarktische Pendant zur ostaustralischen Lachlan Mobilzone, wo die Einteilung von Graniten in S- und I-Typen entwickelt wurde (Chappell &White 1974). Deshalb war eine überprüfung dieser neu entwickelten Hypothese eines der Arbeitsziele, als die deutschen Nord Victoria Land Expeditionen (Ganovex) dort 1979 ihre Arbeiten aufnahmen. An den bekannten zwei Granitgenerationen der Region wurden geologische, petrographische und geochemische Untersuchungen sowie Altersbestimmungen durchgeführt, deren Ergebnisse sich folgenderma\en zusammenfassen lassen.Die ältere, kambro-ordovizische Granitfolge steht, analog zur Situation in Australien, in enger Beziehung zu einer bedeutenden Orogenese, während sich zur jüngeren, devonisch-karbonischen Suite kein zugehöriges tektonisches Ereignis finden lie\. Dies steht im Gegensatz zur Situation in Australien/Tasmanien.Die S- und I-Typ Klassifikation, auf Nord Victoria Land angewendet, weist ähnliche Widersprüche auf, wie siePitcher (1982) zur Aufteilung der I-Typen in »kordillere« und »kaledonische« Sippen führten.Plattentektonische Modelle, die in den letzten Jahren für diese Region am mobilen Rand Gondwanas unabhängig von der Granitklassifikation nach geologischen und tektonischen Kriterien entwickelt wurden, erlauben es, die vonPitcher entwickelten tektonischen Bildungsmilieus für verschiedene Granit-Typen zu überprüfen:Die Charakteristiken der älteren (kambro-ordovizischen) Granite erlauben ein widerspruchsloses Einfügen in das aus anderen Kriterien abgeleitete Bild eines aktiven Kontinentalrandes über einer Subduktionszone.Für die jüngeren (devonisch-karbonischen) Granite dagegen, die im Charakter den »kaledonischen« I-TypenPitchers entsprechen, sind die für deren Bildung postulierten Vorgänge, nämlich Hebung und Dehnung nach einer Kollision, in Nord Victoria Land nicht erkennbar.Demnach erscheint zwar die KlassifikationPitchers sinnvoll, da sie in ihrer petrographisch-geochemischen Charakterisierung nachvollziehbar ist, aber das abgeleitete tektonische Milieu für die Bildung der »kaledonischen« Typen bedarf einer weiteren überprüfung.

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Résumé Dans le contexte du Gondwana, la Terre Victoria est le pendant antarctique de la zone plissée de Lachlan, en Australie Orientale, où la distinction entre granites S et I a été établie pour la première fois (Chappel &White 1974). C'est pourquoi la vérification de cette hypothèse a été portée au programme de l'expédition allemande à la Terre Victoria en 1979–80 (Ganovex).On connaissait à cette époque l'existence d'une génération cambro-ordovicienne et d'une génération dévono-carbonifère de granitoÏdes qui, par analogie avec l'Australie, avaient été rapportées à deux événements orogéniques différents. Nos investigations géologiques, pétrologiques, géochimiques et géochronologiques montrent que cette conclusion n'est vraie que pour les granites de la première génération. La seconde génération est, en fait, anorogénique. Il s'est avéré en mÊme temps que la répartition en types S et I ne correspond pas exactement aux observations de terrain. Par contre, la distinction introduite parPitcher (1982) parmi les granites I entre une série »de Cordillère« et une série »Calédonienne« peut expliquer les irrégularités que nous observons.Environ à cette époque, des modèles géodynamiques basés sur des considérations indépendantes de la classification des granites ont été proposés pour cette partie de la marge active du Gondwana. Ces modèles permettent de recouper les considérations sur l'environnement tectonique des granites, déduites de leur classification:Les caractères des granitoÏdes anciens, cambro-ordoviciens, s'accordent parfaitement au modèle d'une marge active surmontant une subduction.Par contre, pour les granitoÏdes jeunes, dévono-carbonifères, la situation tectonique postulée (soulèvement et fracturation post-collision) n'a pas pu Être confirmée sur la Terre Victoria.En conclusion, la classification dePitcher est applicable dans ses aspects pétrographiques et géochimiques, mais l'environnement tectonique qui préside à la formation de granitoÏdes de type »Calédonien I« n'est pas nécessairement le mÊme dans toutes les régions étudiées.

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- Lachlan, S I (Chappell & White, 1974). (GANOVEX) 1979 . , , . : - , , , , - , , - . S I , , (Pitcher, 1982) I . , , , , : — - — , . , - , , , , .. ., , - , , , , .

     

Substitute conductors for electromagnetic response estimates

Various concepts exist to define substitute conductors for empirical response estimates at singular frequencies: Chapman's shell-core model, the Cagniard-Tikhonov apparent resistivity, the Niblett-Bostick and Molochnov transformation, thep ^* —z ^* transformation. They are all interrelated and assign comparable resistivities to the substitute conductor at a given frequency. Applications to synthetic response data of plane and spherical conductors show under which conditions these substitutions come closest to the model and which influence of source dimensions and Earth's sphericity can be expected.p ^* —z ^* transformed global response data forS andDst variations demonstrate how substitute conductors may serve as useful guides in inverse procedures.     

Shock effects in melilite

Shock recovery experiments on melilite samples in the pressure range from 11 to 50.5 GPa have been performed in order to examine the effects of shock waves on this material. The shocked samples were subsequently studied in the transmission electron microscope. All samples displayed the shock-induced amorphous areas, known as diaplectic glass. The amount of diaplectic melilite glass increased from a few percent at 11 GPa to about 85 percent at 50.5 GPa shock pressure. The shock waves also caused deformational effects as planar faults parallel to (001) and dislocations with a density in the order of 10¹⁰ cm^?2. Regarding the present discussion on the origin and nature of diaplectic glass, diaplectic melilite glass is assumed to be the reversion product of a high-density phase produced in the shock front. Deformed melilites in Ca-Al-rich inclusions from chondritic meteorites studied so far do not contain diaplectic glass. It is assumed that the meteoritic melilites were hot (>1,000° C) and thus plastically deformable by shock waves of rather low amplitudes.     

Germination and algal-free laboratory culture of widgeon grass,Ruppia maritima

A methodology for the isolation ofRuppia maritima L. into algal-free laboratory culture is described. Seeds were surface sterilized with 96% ethyl alcohol of pH 2, kept for several months in cold storage at 7°C, and subsequently transferred to 25°C to induce germination. Basic culture conditions are discussed and a vessel of easy maintenance and sterilization forRuppia culture in ground glass sediments is presented. Minor modifications of this methodology might permit contaminant-free laboratory cultures of other estuarine and marine spermatophytes.     

Conceptual study — An improved method to assess acidification in German streams by using benthic macroinvertebrates

The present study is based mainly upon the authors' hydrochemical and hydrobiological studies of small silicate streams in South-West Germany, principally in the Black Forest and the Odenwald.

The aim of the paper is the adaptation of a practically proven four-level biological classification system of different degrees of acidity using benthic maroinvertebrates to a five-level system of acidification of mainly upland streams with low buffer capacity. The main reason for such a five-class system is the Water Framework Directive of the European Union (EU WFD), which lays down a five-level classification system for the assessment of the ecological quality of waters.

The biological method of assessing the state of acidity for evaluation of the degree of anthropogenic acidification under the directive, and principles of the EU WFD, are also described. A list of 278 taxa of the macrozoobenthos has been reclassified from a four-level system to a five-level biological indication system, based upon the authors' scientific expertise and the latest references from literature of different acid sensitive areas in Germany.     

Observation of isotopes in the water cycle—the Swiss National Network (NISOT)

The Swiss National Network for the Observation of Isotopes in the Water Cycle (NISOT) includes eleven precipitation, seven surface water (river) and three groundwater stations, where tritium, deuterium and oxygen-18 are monthly measured in composite samples. The network provides a good overview of the characteristic isotope signatures in recharge waters in Switzerland and of the relations between isotopes and altitude, orography and the amount of precipitation. Mixing of air water vapour and surface waters can be observed along a NW/SE cross section through the Alps. With increasing length of the data series, the network provides a valuable contribution for national and international scientific and practical applications in surface and subsurface hydrology, climatology and biology. The Swiss Geological Survey at the Federal Office for Water and Geology operates the isotope network within the legal framework of the Federal Law on the Protection of Waters and guarantees quality, access and distribution of the isotope data.     

Presolar nanodiamonds: faster, cleaner, and limits on platinum-HL

We have developed a procedure that allows extraction of clean nanodiamond samples from primitive meteorites for isotopic analyses of trace elements on a timescale of just a week. This procedure includes microwave digestion and optimization of existing isolation techniques for further purification. Abundances of trace elements that are difficult to dissolve using standard procedures (e.g., Ir) are lower in the diamond residues prepared using the new technique. Accelerator mass spectrometry (AMS) was explored as a means for isotopic measurements. Results obtained on diamond fractions from Allende and Murchison show the need for suitable matrix-adjusted standards to correct for fractionation effects; nevertheless they allow putting an upper limit on the abundance of ¹⁹⁸Pt-H in nanodiamonds of ∼1 × 10¹⁴ atoms/g. This limit is on the order of what can be expected from predictions of competing nucleosynthesis models and extrapolation of the apparently mass dependent abundance trend of the associated noble gases.Unfortunately, and unexpectedly, presolar silicon carbide is almost quantitatively dissolved during microwave digestion with HCl/HF/HNO₃. Re-evaluation of the standard extraction technique, however, shows that it also may lead to severe loss of fine-grained SiC, a fact not commonly appreciated. A lower limit to SiC abundance in Murchison is 20 ppm, and previous conclusions that Murchison SiC is unusually coarse-grained compared to SiC in other primitive meteorites seem not to be warranted. Graphite and silicon nitride may survive and possibly can be separated after this step as suggested by a simulation experiment using terrestrial analog material, but the detailed behavior of meteoritic graphite requires further study.     

Vegetation response to rapid climate change in central europe during the past 140,000 yr based on evidence from the Füramoos pollen record

The response of Central European vegetation to rapid climate change during the late Quaternary period (Eemian to Holocene) is assessed by data from the new pollen record of Füramoos, southwestern Germany. This record represents the longest late Quaternary pollen record north of the Alps as currently known. Its high degree of completeness allows detailed correlations with Greenland ice cores and sea-surface temperature records from the North Atlantic. Our data show that if climate deteriorations were not long or severe enough to extirpate refugia of arboreal taxa north of the Alps such as during marine oxygen isotope stage (MIS) 5 (i.e., Würm Stadial A, Stadial B, and Stadial C), reforestation with the onset of warmer conditions in Central Europe occurred on a centennial scale. If arboreal taxa became completely extinct north of the Alps such as during MIS 4 (i.e., Würm Stadial D), several thousand years were necessary for the reimmigration from refugia situated in regions south of the Alps. Thus, Dansgaard-Oeschger interstades (DOIS) 24 to 20 and 15 to 11 are expressed in Central European pollen records, whereas DOIS 19 to 16 are not recorded due to migration lags.     

Assessment of Primary Production by Statistical Analysis of Water‐quality Data

Time series of weekly water‐quality data at Schnackenburg on the Elbe River (1985—2000) were subjected to principal component analysis (PCA). Considering the amplitudes of composite patterns of variables is a step towards a process‐oriented interpretation of waterquality data. One specific objective was to investigate the impact of improved water quality after the German reunification in 1990 on primary production and the oxygen budget. To discriminate anthropogenic signals from natural fluctuations a separation of the impact of discharge was attempted based on a linear regression approach. A dominant pattern of co‐variation in the residual data could be attributed to biological activity (primary production). The most relevant variables of this 'biomode' are oxygen saturation, pH, and orthophosphate. We conclude that multivariate statistical analysis of water‐quality data can help to estimate primary production when direct observations of algal concentrations are missing. In the years from 1998—2000 the trend of the ‘biomode’ indicates an increased load of oxygen consuming biomass caused by enhanced primary production in the middle stretches of the Elbe River which corresponds with the observation of more severe oxygen deficits in the tidal section of the river.