Deformation of the Dachstein Limestone in the Dachstein thrust sheet (Eastern Alps, Austria)

Abstract

Deformation affecting the Upper Triassic Dachstein Limestone has been analyzed in the Dachstein thrust sheet, the uppermost thrust unit of the central Northern Calcareous Alps (Eastern Alps). Different scales of deformation are discussed, from kilometer-scale thrusting down to folds in the order of tens of meters to meters. Observations are based on both conventional outcrop observations and on digital fieldwork performed on drone-captured virtual outcrops and on GoogleMaps 3D terrain renderizations. The structures observed were formed at different times and document the following events: 1) Late Triassic syn-depositional instability and slumping; 2) Late Triassic syn-depositional growth of the Hallstatt diapir; 3) Late Triassic syn-depositional, salt-driven, extensional faulting; 4) Jurassic-age re-activation of extensional faults; 5) (presumably) Early Cretaceous shortening in both east-west and north-south directions; and 6) (presumably) Late Cretaceous extensional re-activation of faults. The structures and their origin have a bearing on the interpretation of the tectonic evolution of the Dachstein thrust sheet, highlighting the potential relevance of salt tectonics in controlling its structure.

Emplacement and associated sedimentary record of the Jurassic submarine salt allochthon of the Wurzeralm (Eastern Alps, Austria)

“…These faults are interpreted to cut across the entire Triassic stratigraphy, as indicated by the fact that a splay of the Hintersteinerbach juxtaposes the Dachstein Fm against the Wetterstein Fm (Figure 2a), and the panel of Triassic platform they bound may have been tilted down northwards during shortening (Figure 5), guiding the emplacement of the salt sheet. The northern extension of the Hintersteinerbach fault was later activated in extension (possibly during the Late Cretaceous, similar to structures documented further west by Fernandez et al, 2022), dropping the Jurassic Plassen Limestone down to the same elevation as the Dachstein Limestone (Figure 2a,d).…”

Emplacement and associated sedimentary record of the Jurassic submarine salt allochthon of the Wurzeralm (Eastern Alps, Austria)

“…1b). These faults are interpreted to be faults detaching within the Haselgebirge Fm and likely played a protracted role in the development of the diapir: they accommodated variable subsidence during Middle to Late Triassic deposition, and re-activated after allochthony in extension (possibly during the Late Cretaceous, similar to structures documented in a similar setting further west by Fernandez et al, 2022).…”

Architecture and Structure of a Fold-and-Thrust Belt During Initial Inversion of a Salt-Bearing Passive Margin (Jurassic of the Eastern Alps, Austria)

“…2,11). The age for this collapse post-dates the Early Cretaceous emplacement of the Dachstein thrust sheet, and most likely occurred due to the evacuation of Permo-Triassic evaporites (as proposed for the Gosau basin by Fernandez et al, 2022). The TT contractional system resurfaces in the footwall of the Postalm fault (to its west).…”

“…Whereas the Gosau basin is documented to have developed by extension in the Late Cretaceous (Wagreich & Decker, 2001), the age of collapse in other areas is Eocene or younger (Lattengebirge; Herm, 1962;Risch, 1993). In many other locations, timing of collapse is only constrained to be post-Jurassic (e.g., Lofer-Gerhardstein, Lammertal, Sandling, Obertraun, Ramsau, Wurzeralm) (Fernandez et al, 2022(Fernandez et al, , 2024Kurz et al, 2023).…”