Syn-orogenic clastic deposits reveal the thrust propagation of the Oravic units (Pieniny Klippen Belt, Western Carpathians)

The extraordinary Western Carpathian tectonic structure, the Pieniny Klippen Belt (PKB), is characterized by its complex internal structure, particular tectonic units and a range of specific lithostratigraphic formations. Among them, the terminating coarsening-and-thickening upward deep marine clastic formations record the sequential thrust propagation of the principal Oravic tectonic units of the PKB. The Oravic palaeogeographic domain included the southern Kysuca–Pieniny basin (later Pieniny nappe) as a marginal part of the South Penninic oceanic realm (Piemont–Ybbsitz­­–Váh ocean) that separated the Oravic continental ribbon from the Central Carpathian (Austroalpine) realm. The central Czorsztyn ridge and its rifted slopes formed the Subpieniny unit, while the northern ridge foots (Šariš unit) were facing the North Penninic ocean (present Magura units). This pattern resulted from complex rifting and breakup episodes related to opening of the Alpine Atlantic during the Jurassic – Early Cretaceous.

The syn-orogenic clastic sedimentation commenced in the inner Pieniny basin during the Coniacian–Santonian. Material of siliciclastic turbidites and mass-flow conglomerates was derived from advancing fronts of the Central Carpathian Fatric cover nappe system (e.g. Klape nappe). The clastic material was largely recycled from mid-Cretaceous “exotic” conglomerates related to intra-continental subduction that generated the Fatric nappes. Distal northern turbidite lobes reached slopes of the Czorsztyn ridge and bypassed it up to the Šariš depositional area, so forming a large-scale, northward thinning classic wedge.

After elimination of the Váh ocean, shortening progressed by detachment of the Pieniny unit and its thrusting over the Czorsztyn ridge. This event is recorded by deposition of the Maastrichtian–Danian calcareous wildflysch complex that was terminated by olistostromal breccias composed of erosional debris released from the Pieniny nappe fronts. After the basement of the Czorsztyn ridge was thrust under the Central Carpathian orogenic wedge, its variable cover successions were attached to the developing Oravic accretionary complex. Depended on the variable sedimentary settings and resulting heterogeneous composition, sedimentary successions of the Subpieniny unit were partly fragmented and gravitationally transported by mass-wasting mechanisms to the northern Šariš basinal area. Consequently, the Maastrichtian to Lower Eocene calcareous wildflysch of the Šariš unit is inserted by huge bodies of olistostromes and (mega)olistoliths derived predominantly from the Subpieniny successions. As a matter of fact, numerous klippen that gave the name to the entire PKB are olistoliths, in addition to the tectonic klippen that originated by deformational disintegration of competent sedimentary layers and their embedding in incompetent matrix formations.