Eo-Alpine evolution of the Transdanubian Range in the nappe system of the Eastern Alps: revival of a 15 years old tectonic model

Abstract

Recently, several books on the geology of Hungary have reviewed the stratigraphy and structural evolution of the
different megatectonic units using the principle of evolutionary cycles. The Transdanubian Range Unit (TRU) is
considered by some authors to be exceptional, because in this unit a complicated Late Cretaceous to Eocene stratigraphy
is associated with a simple structure. Namely, the unit bordered by two boundary faults (the Rába and Balaton Lines) is
supposed to have been affected only by block-faulting during the Eo-Alpine orogeny.
In this paper the authors reiterate a counter-opinion which they first expressed more than 15 years ago. Based
primarily on the interpretation of data from more than 150 hydrocarbon exploration wells and 2000 km of seismic lines.
It is argued that the TRU is actually characterized by a nappe structure and situated at the top of the Austroalpine nappe
pile, as envisaged by UHLIG (1907) more than a century ago. It is also suggested that the seismically- mapped thrust
planes at the fully sedimentary-covered north-western flank can be tied to the traditionally recognised thrust faults on
the exposed south-eastern flank of the TRU. This leads to a straightforward allochthonous model and provides an
inference about the original (Late Cretaceous to Eocene) continuity of the Transdanubian Range and the Northern
Calcareous Alps.
Finally, the paper argues that the complex Late Cretaceous stratigraphy of the TRU has been controlled by the
development of flexural basins and highs in front of the advancing nappe systems.