THE PALEOGEOGRAPHIC ORIGIN OF THE EASTERN ALPS’ RHENODANUBIAN FLYSCH AND RELATED ALPINE GEODYNAMICS: A BASIN ANALYSIS APPROACH

The Rhenodanubian Flysch of the eastern Alps represents Cretaceous deep marine rocks thrust close to the northern margin of the orogen. Paleocurrent indicators and heavy minerals of the Early Cretaceous formations point to a northern (European) source region. A southern (Adriatic) provenance is indicated for the Cenomanian-Turonian Reiselsberger Sandstein’s paleocurrents and heavy minerals. Thus, the flysch basin must have occupied a transitional position between the European and the Adriatic crustal characteristics. It is suggested that the basin formed on the Mid-Penninic microcontinent which is known to have linked the Adriatic plate with Europe before the Adriatic plate rifted off from Europe during the Mid-Jurassic creating the South Penninic Ocean basin. During the late Early Cretaceous, the Mid-Penninic region rifted off from Europe leading to the formation of the partly oceanic North Penninic basin and the closure of the South Penninic ocean basin.

The flysch basin likely represents an aborted Jurassic rift basin. During most of the Early Cretaceous, the South Penninic region, including the adjacent southern Mid-Penninic region, thermally subsided precluding that detritus was shed northward into the flysch basin. Early Cretaceous rifting in the North-Penninic realm caused uplift of the northern Mid-Penninic region from where detritus was transported southward into the flysch basin. At the Albian/Cenomanian transition, thermal subsidence affected the area to the north of the flysch basin causing waning sediment supply from the north. At the same time, subduction of the South Penninic Ocean began causing uplift and formation of the Late Cretaceous Tschera-Kalkberg mélange of the southern Mid-Penninic region, the source of Late Cretaceous flysch.