Tectonic subdivisions in thrust belts – cleaning up the western Northern Calcareous Alps (NCA)

2020 ◽  
Author(s):  
Hugo Ortner ◽  
Sinah Kilian
Keyword(s):  
Northern Calcareous Alps ◽  
Field Observations ◽  
Southern Germany ◽  
Northern Calcareous ◽  
Thrust Belts ◽  
Formal Framework ◽  
Thrust Sheets ◽  
Comprehensive Mapping

<p>Tectonic subdivisions of larger geologic units reflect the geologic knowledge at the time of creation. In many thrust belts the original subdivisions had been created during the first comprehensive mapping campaigns at the end of the 19<sup>th</sup> to early 20<sup>th</sup> century and reflect the geologic knowledge at that time. Even if many thrusts were identified correctly, no formal framework existed to give guidelines of how to distinguish tectonic units. Nevertheless, these subdivisions are still in use.</p><p>We analyze the thrust sheets of the Northern Calcareous Alps of western Austria and southern Germany and test the implicit assumptions underlying most tectonic subdivisions against field observations:</p><p>Assumption 1: Thrust transport is large and thrusts do not end laterally. However, several major thrusts do loose stratgraphic offset and end laterally.</p><p>Assumption 2: Allochthons are surrounded by thrusts on all sides. Unfortunately, any fault has been used to delimit allochthons.</p><p>Assumption 3: Thrusting should bring old on young rocks. In some cases, allochthons have been delimited by out-of-sequence thrusts, that stack young on old rocks. In other cases, the allochthon is a mountain-size glide block that was buried by younger sediments, and the trace of the thrust is an unconformity in the field.</p><p>As a consequence we propose a revised tectonic subdivision of the western part of the NCA, that avoids some of the problems discussed here, and is entirely based on the emplacement of old-on-young rocks across thrusts.</p>

Prediction uncertainties in salt detached fold and thrust belts – examples from the surface and subsurface of the Northern Calcareous Alps (Austria)

2020 ◽  
Author(s):  
Klaus Pelz ◽  
Pablo Granado ◽  
Michael König ◽  
Elizabeth P. Wilson ◽  
Philipp Strauss ◽  
...  
Keyword(s):  
Northern Calcareous Alps ◽  
Deformation Localization ◽  
Well Control ◽  
Northern Calcareous ◽  
Structural Style ◽  
Thrust Belts ◽  
Fold And Thrust Belts ◽  
Thrust Sheets ◽  
Lateral Extent ◽  
Thickness Variations

<p>As shown for fold and thrust belts worldwide and for the Northern Calcareous Alps (NCA) in particular, the initial thickness and spatial distribution of autochthonous salt exerts fundamental control on deformation localization and structural style. The initial sedimentary geometries of mini-basins formed by downbuilding into or rafting on salt do influence the geometries of thrust sheets during subsequent shortening. The lateral extent and spacing of individual thrust sheets and the overall cylindricity of structures is governed by initial facies changes and thickness variations within and across mini-basins and salt ridges between them. During convergence, remaining inflated salt localizes shortening whereas mini-basins may react as rather rigid blocks. As deformation culminates at these secondary welds that eventually become thrusted and squeezed, apparent structural closures might become exploration targets but potentially yield more complex internal geometries and less predictable facies distribution.</p><p>In this contribution we show several cross sections constrained by surface and subsurface data in the eastern NCA and below the Vienna Basin. We compare areas with abrupt changes in stratigraphic thickness, limited lateral extent of individual thrust sheets and highly non-cylindrical structural style along strike to areas where thrust sheets extend over several tens of kilometers along strike with remarkably cylindrical structures, little thickness variations and less abrupt facies changes. Predictive capabilities in underconstrained areas (i.e., insufficient seismic imaging and/or resolution, lack of well control, bad outcrop conditions) are analyzed and compared to closures with well control and pre-drill expectations. Evidently, culminations can be predicted with more confidence in areas with little variation in facies and sedimentary thicknesses. Reliability of predictions generally degrades with decreasing thrust sheet size, observable non-cylindricity within and in between thrust sheets, and with increased complexities at the edges of mini-basins (e.g., squeezed and thrusted flaps). Internal geometries of mini-basins need to be imaged and analyzed properly to narrow down these uncertainties at potential culminations along the edges.</p>

scholarly journals Structural styles in fold-and-thrust belts involving early salt structures: The Northern Calcareous Alps (Austria)

Geology ◽  
2018 ◽  
Vol 47 (1) ◽  
pp. 51-54 ◽  
Author(s):  
Pablo Granado ◽  
Eduard Roca ◽  
Philipp Strauss ◽  
Klaus Pelz ◽  
Josep Anton Muñoz
Keyword(s):  
Northern Calcareous Alps ◽  
Northern Calcareous ◽  
Thrust Belts ◽  
Fold And Thrust Belts

scholarly journals Structural evidence of in-sequence and out-of-sequence thrusting in the Karwendel mountains and the tectonic subdivision of the western Northern Calcareous Alps

2019 ◽  
Vol 112 (1) ◽  
pp. 62-83
Author(s):  
Sinah Kilian ◽  
Hugo Ortner
Keyword(s):  
Hanging Wall ◽  
Strike Slip ◽  
Northern Calcareous Alps ◽  
Deformation History ◽  
Structural Geometry ◽  
Thrust Sheet ◽  
Northern Calcareous ◽  
Nappe Tectonics ◽  
Thrust Sheets ◽  
History Of

AbstractWe present the results of a field study in the Karwendel mountains in the western Northern Calcareous Alps, where we analysed the boundary between two major thrust sheets in detail in a key outcrop where nappe tectonics had been recognized already at the beginning of the 20th century. We use the macroscopic structural record of thrust sheet transport in the footwall and hanging wall of this boundary, such as folds, foliation and faults. In the footwall, competent stratigraphic units tend to preserve a full record of deformation while incompetent units get pervasively overprinted and only document the youngest deformation.Transport across the thrust persisted throughout the deformation history of the Northern Calcareous Alps from the late Early Cretaceous to the Miocene. As a consequence of transtensive, S-block down strike-slip tectonics, postdating folding of the major thrust, new out-of-sequence thrusts formed that climbed across the step, and ultimately placed units belonging to the footwall of the initial thrust onto its hanging wall.One of these out-of-sequence thrusts had been used to delimit the uppermost large thrust sheet (Inntal thrust sheet) of the western Northern Calcareous against the next, tectonically deeper, (Lechtal) thrust sheet. Based on the structural geometry of the folded thrust and the age of the youngest sediments below the thrust, we redefine the thrust sheets, and name the combined former Inntal- and part of the Lechtal thrust sheet as the new Karwendel thrust sheet and the former Allgäu- and part of the Lechtal thrust sheet as the new Tannheim thrust sheet.

scholarly journals Thrust tectonics in the Wetterstein and Mieming mountains, and a new tectonic subdivision of the Northern Calcareous Alps of Western Austria and Southern Germany

2021 ◽  
Author(s):  
Hugo Ortner ◽  
Sinah Kilian
Keyword(s):  
Eastern Alps ◽  
Northern Calcareous Alps ◽  
Main Body ◽  
Thrust Belt ◽  
Southeastern Part ◽  
Thrust Sheet ◽  
Northern Calcareous ◽  
Lateral Contact ◽  
Thrust Tectonics ◽  
Thrust Sheets

AbstractWe investigate the tectonic evolution of the Wetterstein and Mieming mountains in the western Northern Calcareous Alps (NCA) of the European Eastern Alps. In-sequence NW-directed stacking of thrust sheets in this thin-skinned foreland thrust belt lasted from the Hauterivian to the Cenomanian. In the more internal NCA major E-striking intracontinental transform faults dissected the thrust belt at the Albian–Cenomanian boundary that facilitated ascent of mantle melts feeding basanitic dykes and sills. Afterwards, the NCA basement was subducted, and the NCA were transported piggy-back across the tectonically deeper Penninic units. This process was accompanied by renewed Late Cretaceous NW-directed thrusting, and folding of thrusts. During Paleogene collision, N(NE)-directed out-of-sequence thrusts developed that offset the in-sequence thrust. We use this latter observation to revise the existing tectonic subdivision of the western NCA, in which these out-of-sequence thrusts had been used to delimit nappes, locally with young-on-old contacts at the base. We define new units that represent thrust sheets having exclusively old-on-young contacts at their base. Two large thrust sheets build the western NCA: (1) the tectonically deeper Tannheim thrust sheet and (2) the tectonically higher Karwendel thrust sheet. West of the Wetterstein and Mieming mountains, the Imst part of the Karwendel thrust sheet is stacked by an out-of-sequence thrust onto the main body of the Karwendel thrust sheet, which is, in its southeastern part, in lateral contact with the latter across a tear fault.

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