THE NORTHEASTERN MARGIN OF THE EASTERN ALPS: FACIES AND TECTONIC DEVELOPMENTS

A complete geological remapping of the northwestern margin of the Eastern Alps has led, together with the results of deep drilling, to new results about facies and tectonic developments of Molasse, Helveticum, Ultrahelveticum, Rhenodanubian Flysch and Calcareous Alps. In the southern Subalpine Molasse compression began with a conjugate shear system which was rotated by consequent folding into its present position. The Subalpine Molasse was then unrooted from its Helvetic underground and thrust more than 30 km northwards. Oil drillings in the unfolded Molasse have revealed that the facies of the rocks of the Helvetic domain (Quinten fm, “Gault”) is shifting northwards in eastern direction. The Landshut – Neuötting high, a Half horst trending NW-SE parallel to the western rim oft the Moldanubian Massif ist terminating the Helvetic domain to the East. The Helvetic domain, which ist E of the Rhine valley the continuation of the Swiss Säntis thrust sheet, shows a distinct telescoping effect in eastern direction with a remarkable decrease in width. The Cretaceous and Tertiary of the southernmost Helvetic was scraped off its underground and dispersed as incoherent Liebenstein thrust sheet with numerous Klippes as far N as the southern Molasse margin. Also the ultrahelvetic Flysch sediments of the Feuerstätter thrust sheet have been unrooted from their underground by the thrust of the Penninic Rhenodanubian Flysch and the sedimentary basin fill was thrust over the Helvetic zone. The Penninic Rhenodanubian Flysch trough was situated originally at the northern flank of the Brianconnais terrane (HESSE). In Vorarlberg and Allgäu the RDF consists of three thrust sheets, the two southern were thrust northwards out of sequence over the deeper Üntschen thrust sheet and the whole Helvetic zone. In a palinspastic section through the Northern Calcareous Alps the sedimentary history is shown and the later tectonic deformation into several thrust sheets is demonstrated, using the age of the Cretaceous clastic sediments to dating the different tectonic thrusting phases.