Evidences for pre-orogenic passive-margin extension in a Cretaceous fold-and-thrust belt on the basis of combined seismic and field data (western Transdanubian Range, Hungary)

Abstract

Combined sedimentological and structural analysis was carried out in the field and on 2D seismic reflection profiles to recognize pre-orogenic structures in a Cretaceous fold-and-thrust belt. Detailed field observations were made in the Keszthely Hills, Western Hungary, while 2D seismic interpretation was carried out in the neighbouring Zala Basin. As a result, a fault-controlled intraplatform basin system was identified by a detailed analysis of bounding faults, and related outcropscale structures. The Norian-Rhaetian (227-201.3 Ma) synsedimentary faulting was associated with talus breccia formation, small-scale faulting, and dyke formation, in addition to slumping and other soft-sediment deformations. Based on the distribution of talus breccia, WNW-ESE-trending map-scale normal faults were identified in the Keszthely Hills, which is in agreement with the directly observed outcrop-scale synsedimentary faults. On seismic sections, similar WNW-or NWtrending Late Triassic normal faults were identified based on thickness variations of the syn-rift sediments and the presence of wedge-shaped bodies of talus breccia. Normal faulting occurred already in the Norian, and extensional tectonics was active through the Early and Middle Jurassic. The Late Triassic grabens of the western Transdanubian Range could be correlated with those in western part of the Southern Alps, and the Bajuvaric nappe system of the Northern Calcareous Alps. These grabens were situated on the proximal Adriatic margin, and they represent the first sign of the Alpine Tethys rifting. The locus of extension was laterally migrated westward, towards the distal Adriatic margin during Early and Middle Jurassic.

Results, problems and future tasks of palaeostress and fault-slip analyses in the Pannonian Basin: the Hungarian contribution

“…NW-SE compression characterised both the Bakony and Vértes Hills during the Cretaceous (early Albian) contrac tion (D3a phase of FODOR 2008FODOR , 2010, while a very similar compression reoccurred during the late Oligocene to early Miocene (D7 and D8 phases of the same works). NE-SW tensional stress field was characteristic during several phases, namely during Triassic (HÉJA et al 2018) and Jurassic extension, late Cretaceous (Senonian) extension (KISS 2009), and during the main syn-rift phase of the Pannonian Basin (FODOR et al 1999). Figure 2 shows that similar stress fields occurred during the late Oligocene to earliest Miocene in the Bükk foreland (PETRIK et al 2014(PETRIK et al , 2016PETRIK 2016) prior to or during the first tilting event which pre-dated the main syn-rift phase.…”

“…When the tilting is Cretaceous, like in the TR, the pre-tilt fractures are older than the main folding phase of the range (latest Aptian to early Albian). In this way, Triassic faults were recognised in the Keszthely Hills (HÉJA 2015, HÉJA et al 2018.…”

Dolomitization of Late Norian carbonate deposits of restricted basin facies in the Keszthely Mts., Transdanubian Range, Hungary

“…The northern segment of this fault system is the N-S striking Szent Miklós fault. The southern continuation of this fault is the NW-SE striking Ederics fault (Héja et al 2018). In the eastern part of this fault system, completely or partially dolomitized or non-dolomitized Carnian platform carbonates (Ederics Limestone) and basinal marl and limestone (Veszprém Marl, Sándorhegy Formation) crop out (Csillag et al 1995;Budai et al 1999a, b;Haas et al 2014a, b).…”

Modes of Oblique Inversion: A Case Study From the Cretaceous Fold and Thrust Belt of the Western Transdanubian Range (TR), West Hungary

“…In general, sedimentary transport directions are pointing toward to the NE on the fault controlled slopes. However, transport directions turn toward to the E or SE on relay ramps (Héja et al, 2018(Héja et al, , 2022. The R (Rezi) syncline is bounded by the western segment of the CT fault to the south.…”