Abstract
A brief, regional-scale review of the Late Cretaceous – Early Palaeogene inversion-related tectonic structures affecting the Sudetes and their foreland at the NE margin of the Bohemian Massif is presented and complemented with results of new seismic studies. The Sudetes expose Variscan-deformed basement, partly overlain by post-orogenic Permo-Mesozoic cover, containing a wide spectrum of tectonic structures, both brittle and ductile, in the past in this area referred to as young Saxonian or Laramide. We have used newly reprocessed legacy seismics to study these structures at the two main post-Variscan structural units of the area, the North-Sudetic and Intra-Sudetic synclinoria, and discuss the results together with regionally-distributed examples coming from quarries and underground mines as well as those from the literature. The Late Cretaceous – Early Palaeogene tectonic structures in consecutively reviewed Sudetic tectonic units, from the north to south, typically include gentle to moderate buckle folds of detachment type or fault-related, high-angle reverse and normal faults, as well as low-angle thrusts – often rooted in the crystalline basement. The structures hitherto described as grabens, are frequently believed to be bounded by reverse faults (hence we use the term ‘reverse grabens’) and typically reveal strongly synclinal pattern of their sedimentary fill. The crystalline basement top, as imaged by seismic sections in the North Sudetic Synclinorium below the detachment-folded cover, is synformally down-warped with a wavelength of up to 30 km, whereas on the elevated areas, where the basement top is exposed at the surface, it is up-warped (i.e. tectonically buckled). The reviewed compressional structures typically show an orientation fitting the regionally-known Late Cretaceous – Early Palaeogene tectonic shortening direction of NE-SW to NNE-SSW The same applies to the regional joint pattern, typically comprising an orthogonal system of steep joints of c. NW-SE and NE-SW strikes. All the reviewed structures are considered as due to the Late Cretaceous – Early Palaeogene tectonic shortening episode, although some of the discussed faults with a strike-slip component of motion may have been modified, or even produced, by later, Late Cenozoic, tectonism.
Highlights
During Late Cretaceous to Early Palaeogene times, compressional tectonic structures developed over vast areas of western 30 and north-central Europe (e.g. Kley and Voigt, 2008; Navabpour et al, 2017; Kley, 2018; Nádaskay et al, 2019; Malz et al., 2020; Voigt et al, 2021)
To the SW of the Mid-Polish Swell there is the Szczecin-Łódź Trough (Synclinorium), which occurs next to the successive elevated structural element, occurring at the NE margin of the Bohemian Massif, in the borderland between Poland and Czechia. This is the Sudetic area - the principal 40 object to be presented in this paper, whose goal is to briefly overview the wide spectrum of structural effects produced by the Late Cretaceous to Early Cenozoic trans-European compressional event at the NE margin of the Bohemian Massif, in the Sudety Mts and in their northern foreland with a similar geology
In our brief review of the Late Cretaceous – Early Palaeogene tectonic structures affecting the NE margin of the Bohemian 375 Massif we have shown their common and widespread occurrence all over the region and, to some degree, shortly discussed their style and mechanisms of formation
Summary
During Late Cretaceous to Early Palaeogene times, compressional tectonic structures developed over vast areas of western 30 and north-central Europe (e.g. Kley and Voigt, 2008; Navabpour et al, 2017; Kley, 2018; Nádaskay et al, 2019; Malz et al., 2020; Voigt et al, 2021). An important part of the paper, aimed at giving its readers an overall information on the distribution and genetic and geometrical diversity of the tectonic structures that formed or evolved under the Late Cretaceous –Early Palaeogene compressional regime, are depiction and short description of a selection of such structures exposed in natural outcrops and in active mines and quarries 100 throughout the entire Sudetic area or its direct vicinities. This material is either our own or is based on critically evaluated other authors’ accounts. Larger structures appear on mining maps as a complex network of faults, whose pattern reflects reactivation of a few major and numerous minor NW-SE trending fractures propagating upwards from the Variscan basement, which are accompanied by a number of relatively large WSW-ENE en-echelon events (cf. Markiewicz, 2007), the latter most probably formed due to a Late Cretaceous – Early Palaeogene (or Late Cenozoic?) sinistral strike-slip activity of the major NW-SE faults
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