Geologische Vorgänge in den Alpen ab Obereozän im Spiegel vor allem der deutschen Molasse

Zusammenfassung Die vorquartäre Geschichte des Molassebeckens nördlich der Alpen läßt sich in 3 Großabschnitte unterteilen, in deren Ablauf sich umrißhaft die jeweils zugehörigen Entwicklungsstadien des aufsteigenden Gebirges widerspiegeln, die bisweilen umgekehrt auch von Ereignissen im Vorland beeinflußt werden. Der 1. Abschnitt (Obereozän bis Aquitan/ Ober-Eger) ist von der in den Westalpen beginnenden Hebung sowie von Bewegungen der savischen Dislokationsphase geprägt, in besonderem Maße ferner an der Rupel/ChattGrenze von der größten Meeresspiegelsenkung seit dem Kambrium. Im 2. Abschnitt (Burdigal/Eggenburg bis Unterpannon) verlagert sich die Hebungsaktivität zu den Ostalpen, womit im Vorland die große, E-W gerichtete Flußschüttung der Oberen Süßwassermolasse ausgelöst wird. In ihr verursacht die gewaltige Erderschütterung des Riesmeteoriten-Einschlags im höheren Baden vermutlich die Flußverlegung der Enns, eines ihrer beiden Hauptzubringer, zum Grazer Becken und damit eine sich u. a. im Schwermineralbestand (als A-Grenze) abzeichnende Änderung der Materialzufuhr aus dem Gebirge. Im 3. Abschnitt (Unterpannon bis Pliozän) geht infolge weiteren Aufsteigens der Alpen samt Vorland bei gleichzeitiger Verlagerung des Hebungszentrums wieder zur Westschweiz die bisherige Akkumulation in Denudation über, die von dem sich nun von Niederösterreich aus ins Molassebecken hineinfressenden Donausystem besorgt wird.Die während des 2. Großabschnitts von der Auflast der vorrückenden kalkalpinen Dekken aus ihrem Ablagerungsraum herausgequetschte ältere Molasse ist zu den alpenparallelen Mulden des gefalteten Bereichs zusammengeschoben, mit einer wohl erst im 3. Abschnitt entstandenen Achsendepression zwischen Iller und Mangfall. In diesen Zeitraum vor allem fällt auch die Verformung der jüngeren ungefalteten Molasse zu einer alpenparallelen Großmulde, deren Achse nach SW und E aushebt.

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The pre-Quaternary history of the Molasse basin north of the Alps can be subdivided into three major phases, in the course of which the respective associated evolutional stages of the rising mountains are reflected in outline. On the other hand, these stages are occasionally also influenced by events in the foreland. The first phase (Upper Eocene to Aquitanian/Upper Egerian) ist characterized by the uplifting beginning in the Western Alps and movements of the Savic dislocation phase, and in particular also at the Rupelian/Chattian boundary by the greatest eustatic lowering of the sea level since the Cambrian period. During the second phase (Burdigalian/Eggenburgian to Lower Pannonian) the uplifting shifts to the Eastern Alps, bringing about in the foreland the large E-W directed fluvial accretion of the Upper Fresh-water-Molasse. During its progress the enormous earth-tremor of the Ries meteoric impact in the upper Badenian presumably leads to the diversion of the Enns river, being one of the two main tributaries, to the Graz basin, resulting in a change in the material supply from the mountains, which is reflected in the heavy mineral content (designated as A-boundary). In the third phase (Lower Pannonian to Pliocene) the previous accumulation, as a result of the continuing uplifting of the Alps and the foreland with simultaneous shifting of the uplift centre back to Western Switzerland, turns to denudation which is effected by the Danube system extending from Lower Austria into the Molasse basin.The older Molasse squeezed out of its deposition area by the overburden of the advancing Austroalpine nappes has been compressed to the throughs of the folded zone along the Alps, with an axis depression between the rivers Iller and Mangfall, which has presumably not developed until the third phase. Above all, during this period the deformation of the younger unfolded Molasse to a large trough paralleling the Alps also took place; its axis rises to the SW and E.

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Résumé L'histoire préquaternaire du bassin molassique au nord des Alpes peut se diviser en trois périodes principales dont le déroulement reflète à grands traits les phases de développement corrélatives de la chaîne en voie de soulèvement. D'autre part, ces phases de développement sont de temps en temps influencées par des événements intervenus dans le bassin. La première période (Eocène supérieur à Aquitanien/Egerien supérieur) est marquée par le soulèvement commençant dans les Alpes occidentales, ainsi que par des mouvements de la phase de dislocation savique et, en particulier à la limite du Rupélien/Chattien, par le plus grand abaissement eustatique du niveau de la mer depuis le Cambrien. Pendant la seconde période (Burdigalien/Eggenburgien à Pannonien inférieur) l'activité de soulèvement se déplace vers les Alpes orientales, provoquant dans le bassin préalpin la grande accrétion fluviale de la Süßwassermolasse (Molasse d'eau douce) supérieure dirigée de l'est vers l'ouest. Le violent ébranlement terrestre produit dans celle-ci par l'impact de la météorite dans le Ries pendant le Badénien supérieur mène probablement le détournement de l'Enns, l'un des deux fleuves tributaires principaux, vers le bassin de Graz, donnant lieu à un changement dans le transport de matériaux venant des montagnes, ce qui se reflète dans la teneur en minerais lourds (dénommé « limite A »). Pendant la troisième période (Pannonien inférieur à Pliocène), l'accumulation antérieure, par suite du soulèvement continu des Alpes et du bassin préalpin, accompagné de la retraite du centre du soulèvement vers la Suisse occidentale, tourne à la dénudation qui est effectuée par le système danubien s'étendant dès lors de la Basse-Autriche au bassin molassique.La Molasse plus ancienne expulsée pendant la seconde période principale de son milieu de sedimentation par la pression des nappes austroalpines susjacentes en progression a été comprimée en auges de la zone pliée le long des Alpes, avec un abaissement axial entre l'Iller et le Mangfall, qui ne s'est probablement formé que dans la troisième période. Dans cette période surtout intervient la déformation de la Molasse plus récente non plissée qui prend la forme d'une grande auge parallèle aux Alpes, dont l'axe s'élève vers le sud-ouest et l'est.

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Herrn Dr. Dr. h. c. Artur Roll (Tübingen) gewidmet

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Nach einem Vortrag auf der 73. Jahrestagung der Geologischen Vereinigung in Berchtesgaden am 25. Februar 1983.     

Structure proof and significance of stereoisomeric 28,30-bisnorhopanes in petroleum and petroleum source rocks

Two C₂₈H₄₈-pentacyclic triterpanes were isolated from Monterey shale. X-ray crystallography of a crystal containing both compounds proved their structures as 17β,18α,21α(H)-28,30-bisnorhopane and 17β,18α,21β(H)-28,30-bisnorhopane. Several differences are found between 28,30-bisnorhopanes and the regular hopanes. Unlike the regular hopane epimers, for practical purposes the three epimeric 28,30-bisnorhopanes [17α,21β(H)-, 17β,21α(H)-, and 17β,21β(H)-]cannot be distinguished by their mass spectra. Special conditions are needed to separate them by gas chromatography. The diagenetically first-formed epimer is thought to be 17α,21β(H)- because it predominates in immature shales. The order of thermodynamic stability is 17β,2lα(H) < > 17α,21β(H) > 17β,21β(H), and all three epimers are present in petroleum. 25,28,30-Trisnorhopanes can be analyzed in similar fashion and are found to have similar thermodynamic characteristics. The percent of the ring D/E cis epimer of 28,30-bisnorhopane and/or 25,28,30-trisnorhopane is a useful maturation parameter similar to the 20S/20R sterane ratio. Evidence indicates 25-demethylation of 28,30-bisnorhopane to 25,28,30-trisnorhopane during advanced stages of biodegradation. Hence, percent ring $\text{D}\text{E}$cis 25,28,30-trisnorhopane has an application to maturation assessment in heavily biodegraded oils.     

Results of a semi-implicit two-step method for the simulation of markedly nonlinear flow in coastal seas

Results of a numerical method for the simulation of nonlinear flow in coastal seas are presented. The method is based on a neutral semi-implicit scheme which is modified into a stability-enhancing two-step algorithm. By means of this method the simulation of highly nonlinear flow patterns is possible in a stable and economic way. Three examples of models of different North Sea coastal regions are discussed under certain aspects to demonstrate the reliability of the method.     

36Cl and53Mn in Antarctic meteorites and10Be-36Cl dating of Antarctic ice

Cosmic-ray-produced⁵³Mn (t_1/2 = 3.7 × 10⁶years) has been measured in twenty Antarctic meteorites by neutron activation analysis.³⁶Cl (t_1/2 = 3.0 × 10⁵years) has been measured in fourteen of these objects by tandem accelerator mass spectrometry. Cosmic ray exposure ages and terrestrial ages of the meteorites are calculated from these results and from rare gases.¹⁴C (t_1/2 = 5740years) and²⁶Al (t_1/2 = 7.2 × 10⁵years) data. The terrestrial ages range from 3 × 10⁴ to 5 × 10⁵ years. Many of the L3 Allan Hills chrondrites seem to be a single fall based on these results. In addition,¹⁰Be (t_1/2 = 1.6 × 10⁶years) and³⁶Cl have been measured in six Antarctic ice samples. The first measurements of¹⁰Be/³⁶Cl ratios in the ice core samples demonstrate a new dating method for ice.     

Hydraulic properties of the crystalline basement

Hydraulic tests in boreholes, up to 4.5 km deep, drilled into continental crystalline basement revealed hydraulic conductivity (K) values that range over nine log-units from 10⁻¹³−10⁻⁴ m s⁻¹. However, K values for fractured basement to about 1 km depth are typically restricted to the range from 10⁻⁸ to 10⁻⁶ m s⁻¹. New data from an extended injection test at the KTB research site (part of the Continental Deep Drilling Program in Germany) at 4 km depth provide K=5 10⁻⁸ m s⁻¹. The summarized K-data show a very strong dependence on lithology and on the local deformation history of a particular area. In highly fractured regions, granite tends to be more pervious than gneiss. The fracture porosity is generally saturated with Na–Cl or Ca–Na–Cl type waters with salinities ranging from <1 to >100 g L⁻¹. The basement permeability is well within the conditions for advective fluid and heat transport. Consequently, fluid pressure is hydrostatic and a Darcy flow mechanism is possible to a great depth. Topography-related hydraulic gradients in moderately conductive basement may result in characteristic advective flow rates of up to 100 L a⁻¹ m⁻² and lead to significant advective heat and solute transfer in the upper brittle crust. An erratum to this article can be found at     

Compaction localization in the Earth and the laboratory: state of the research and research directions

Localized compaction in porous rocks is a recently recognized phenomenon that has been shown to reduce permeability dramatically. Consequently, the phenomenon is relevant to a variety of technologies involving fluid injection or withdrawal. This article summarizes current understanding of localized compaction and impediments to further progress. The article is based on discussions at a small workshop on localized compaction sponsored by the Office of Science, U. S. Department of Energy.     

Jorvik MIST – 2001

The magnetosphere, ionosphere and solar–terrestrial physics community gathered at the Department of Chemistry, University of York from 9–11 April 2001. Neil Arnold and Ian Mann report.     

Microbial–silica interactions in Icelandic hot spring sinter: possible analogues for some Precambrian siliceous stromatolites

Silicified deposits, such as sinters, occur in several modern geothermal environments, but the mechanisms of silicification (and crucially the role of microorganisms in their construction) are still largely unresolved. Detailed examination of siliceous sinter, in particular sections of microstromatolites growing at the Krisuvik hot spring, Iceland, reveals that biomineralization contributes a major component to the overall structure, with approximately half the sinter thickness attributed to silicified microorganisms. Almost all microorganisms observed under the scanning electron microscope (SEM) are mineralized, with epicellular silica ranging in thickness from < 5 μm coatings on individual cells, to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick. Within the overall profile, there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite: ‘microbial’ layers are predominantly consisting of filamentous, intact, vertically aligned, biomineralized cyanobacteria, identified as Calothrix and Fischerella sp.; and weakly laminated silica layers which appear to be devoid of any microbial component. The microbial layers commonly have a sharply defined base, overlying the weakly laminated silica, and a gradational upper surface merging into the weakly laminated silica. These cyclic laminations are probably explained by variations in microbial activity. Active growth during spring/summer allows the microorganisms to keep pace with silicification, with the cell surfaces facilitating silicification, while during their natural slow growth phase in the dark autumn/winter months silicification exceeds the bacteria’s ability to compensate (i.e. grow upwards). At this stage, the microbial colony is probably not essential to microstromatolite formation, with silicification presumably occurring abiogenically. When conditions once again become favourable for growth, recolonization of the solid silica surface by free‐living bacteria occurs: cell motility is not responsible for the laminations. We have also observed that microbial populations within the microstromatolite, some several mm in depth, appear viable, i.e. they still have their pigmentation, the trichomes are not collapsed, cell walls are unbroken, cytoplasm is still present and they proved culturable. This suggests that the bulk of silicification occurred rapidly, probably while the cells were still alive. Surprisingly, however, measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light (PAL) only transmitted through the uppermost 2 mm. Therefore the ‘deeper’ microbial populations must have either: (i) altered their metabolic pathways; (ii) become metabolically inactive; or (iii) the deeper populations may be dominated by different microbial assemblages from that of the surface. From these collective observations, it now seems unequivocal that microstromatolite formation is intimately linked to microbial activity and that the sinter fabric results from a combination of biomineralization, cell growth and recolonization. Furthermore, the similarities in morphology and microbial component to some Precambrian stromatolites, preserved in primary chert, suggests that we may be witnessing contemporaneous biomineralization processes and growth patterns analogous to those of the early Earth.