Albert Heim (1849–1937): Weitblick und Verblendung in der alpentektonischen Forschung

Um 1900 war Albert Heim einer der führenden Al­pentektoniker. 1878 veröffentlichte er eine exzellent bebilderte Studie über die Anatomie der Falten, die auf dem Gebiet der Faltengebirge bald zum Klassi­ker wurde. Die Glarner Alpen interpretierte er darin nicht als überschiebung, sondern als Doppelfalte, eine These, die bereits sein Lehrer Arnold Escher vorsichtig formuliert hatte: Zwei einander gegen­überstehende Falten permischer und mesozoischer Gesteine umschliessen, so die Annahme, eine tabak­beutelförmige Mulde aus tertiärem Flysch. 1884 zeigte der französische Geologe Marcel Bertrand, dass eine einzige nordwärts gerichtete überschiebung plausibler war. Heim jedoch ignorierte diese und jede andere Kritik über Jahre, obwohl ihm schon in den 1880er und 1890er Jahren hätte klar sein können, dass die Idee einer Doppelfalte höchst unwahrschein­liche Schlussfolgerungen nach sich zog. Erst 1901 akzeptierte Heim die dann schon allgemein etablierte Deckenstruktur für die Glarner Alpen. Der Artikel skizziert die Geschichte der alpentektonischen For­schung im 19. Jahrhundert. Er stellt insbesondere die Beiträge Heims heraus. Abschliessend wird überlegt, warum Heim ungeachtet seiner ausserordentlichen geologischen Kenntnisse über 30 Jahre lang an einer beinahe unmöglichen Theorie festhielt

Crustal structure and reflectivity of the Swiss Alps from 3-Dimensional seismic modeling. 2. Penninic Nappes

Surface geological mapping, laboratory measurements of rock properties, and seismic reflection data are integrated through three-dimensional seismic modeling to determine the likely cause of upper crustal reflections and to elucidate the deep structure of the Penninic Alps in eastern Switzerland. Results indicate that the principal upper crustal reflections recorded on the south end of Swiss seismic line NFP20-EAST can be explained by the subsurface geometry of stacked basement nappes. In addition, modeling results provide improvements to structural maps based solely on surface trends and suggest the presence of previously unrecognized rock units in the subsurface. Construction of the initial model is based upon extrapolation of plunging surface. structures; velocities and densities are established by laboratory measurements of corresponding rock units. Iterative modification produces a best fit model that refines the definition of the subsurface geometry of major structures. We conclude that most reflections from the upper 20 km can be ascribed to the presence of sedimentary cover rocks (especially carbonates) and ophiolites juxtaposed against crystalline basement nappes. Thus, in this area, reflections appear to be principally due to first-order lithologic contrasts. This study also demonstrates not only the importance of three-dimensional effects (sideswipe) in interpreting seismic data, but also that these effects can be considered quantitatively through three-dimensional modeling

New specimen of Psephoderma alpinum (Sauropterygia, Placodontia) from the Late Triassic of Schesaplana Mountain, Graubünden, Switzerland

Psephoderma alpinum is an armoured, durophagous placodont known from the alpine Late Triassic. Here we present a new, well-preserved isolated skull discovered in the Alplihorn Member (Late Norian–Early Rhaetian) of the Kössen Formation, Schesaplana Mountain, which straddles the Swiss/Austrian border. Micro-computed tomographic (µCT) scanning was used to create an accurate osteological reconstruction of the specimen, the first time this has been conducted for Psephoderma. We thus clarify disputed anatomical features from previous descriptions, such as a lack of a lacrimal and a pineal foramen that is enclosed by the parietal. We also present the first description based on µCT data of the lateral braincase wall, sphenoid region and some cranial nerve canals for Psephoderma, with the location of the hypophyseal seat, cerebral carotid foramina, dorsum sellae, prootic foramen, lacrimal foramen, as well as all dental foramina being described. This specimen represents the first skull of Psephoderma recovered in Switzerland, and features such as poorly-sutured braincase elements and its relatively small size compared to other known specimens may indicate that it was a sub-adult