SUBDUCTION TECTONIC EROSION AND LATE CRETACEOUS SUBSIDENCE ALONG THE NORTHERN AUSTROALPINE MARGIN (EASTERN ALPS, AUSTRIA)

The Late Cretaceous to Early Tertiary subsidence history of the Northe rn Calcareous Alps (NCA) records the effect of two independent basin f ormation mechanisms at the northern leading margin of the Austroalpine unit. The terrestrial to shallow-marine sediments of the Lower Gosau Subgroup were deposited mainly within small, fault-bound basins during a phase of strike-slip faulting from the late Turonian onwards. After a short period of uplift, deformation and erosion of 1 to 3 Ma, renew ed rapid subsidence followed. During this period the whole NCA subside d into bathyal to abyssal depths. The characteristics of this second e volutionary phase are: (1) a short period of uplift and erosion, follo wed by strong subsidence of the whole NCA with tectonic subsidence rat es up to 700 m/Ma; (2) sedimentation of turbidites and hemipelagites ( Upper Gosau Subgroup (3) northward tilting of the depositional area; ( 4) elimination of an accretionary wedge north of the NCA as the main s ource for the sediments; and (5) a pronounced migration of the subside nce event from the northwest to the southeast from late Turonian/Santo nian to the Maastrichtian. These features can be explained by a model of subduction tectonic erosion along the northern margin of the Austro alpine unit, a part of the Adriatic microplate. Tectonic erosion, as c ompared to recent analogues and fore-are modelling, may be due to the collision and oblique subduction of an oceanic swell or ridge of the P enninic plate beneath the overriding Austroalpine unit with the NCA on its leading northern margin.