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- Author or Editor: Gábor Csillag x
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Three shallowing upward and one deepening upward depositional cycles were described from the Upper Julian to Lower Tuvalian (Carnian) Sándorhegy Limestone Formation from the Balatonhenye – Barnag area. Lithological and microfacies characteristics of the depositional cycles suggest contemporaneous platform and basin sedimentation. Coarsening upward feature is certainly characteristic for Cycle I, yet progradation is doubtful. Cycle II represents platform sedimentation consisting of calcareous peritidal unit that progrades into the adjacent basin. Coeval deeper water sediments were mixed showing a coarsening upward trend from terrigenous mudstones to calcareous wacke-packstones (slope sediments) and grainstones (shoals). These cycles are asymmetric and were driven only by eustatic sea-level changes. Cycle IIIa, developed only in the basin, shows a gradual deepening upward trend. The laterally equivalent cycle on the platform is confined to an erosional hiatus. Tectonic subsidence along with eustatic sea-level rise may controlled the deposition of IIIa. We propose that tectonism may have been one of the plausible causes for the cessation and the following erosion of the Ederics Platform. Consequently, recolonization couldn't take place during the subsequent eustatic sea-level rise thus the source of IIIb prograding carbonate unit shifted to the Sédvölgy Platform.
Abstract
Four paleosol layers indicating wet and moderate periods and five loess layers indicating dry and cold climate were separated by different methods. The following climate cycle model, based on the development of the sediment sequence created by the influence of climatic, geologic and geomorphologic phenomena, was established by detailed paleomagnetic studies (e.g. anisotropy of magnetic susceptibility (AMS), isothermal remanent magnetization (IRM), frequency dependence of magnetic susceptibility (κFD), etc.):
- – A well-foliated magnetic fabric predominantly built up by multi-domain ferromagnetic minerals (magnetite, maghemite) was developed during the semi-arid (350–400 mm/y) and cold loessification period of the Pleistocene. The magnetic fabric can reflect the direction of dust deposition and/or the paleoslope.
- – The accumulation period of dust was followed by the more humid (650 mm/y) pedogenic period indicated by the enrichment of superparamagnetic minerals and by the disturbed or inverse magnetic fabric developed during pedogenesis by different processes (e.g. leaching and/or bioturbation).
- – The third period following the pedogenic period is the humid erosional phase indicated by the finely layered reworked loess. The magnetic fabric built up by multi-domain ferro- and superparamagnetic minerals is characterized by better-aligned directions of principal susceptibilities than in the wind blown material. Sheet wash and other waterlogged surface processes appeared in the fabric of these layers. This process is possibly connected to sudden, rare yet significant events with high precipitation and absence of vegetation.
- – The cycle was closed by the beginning of the next dust accumulation period.
Abstract
We have investigated the deformation history of the Keszthely Hills (Transdanubian Range, W Hungary), which belongs to the uppermost slice of the Austroalpine nappe system. This Upper Triassic to Upper Miocene sedimentary rock sequence documented the deformation of the upper crust during repeated rifting and inversion events. We investigated the structural pattern and stress field evolution of this multistage deformation history by structural data collection and evaluation from surface outcrops. Regarding the Mesozoic deformations, we present additional arguments for pre-orogenic (Triassic and Jurassic) extension (D1 and D2 phases), which is mainly characterized by NE–SW extensional structures, such as syn-sedimentary faults, slump-folds, and pre-tilt conjugate normal fault pairs. NW–SE-striking map-scale normal faults were also connected to these phases.
The inversion of these pre-orogenic structures took place during the middle part of the Cretaceous; however, minor contractional deformation possibly reoccurred until the Early Miocene (D3 to D5 phases). The related meso- and map-scale structures are gentle to open folds, thrusts and strike-slip faults. We measured various orientations, which were classified into three stress states or fields on the basis of structural criteria, such as tilt-test, and/or superimposed striae on the same fault planes. For this multi-directional shortening we presented three different scenarios. Our preferred suggestion would be the oblique inversion of pre-orogenic faults, which highly influenced the orientation of compressional structures, and resulted in an inhomogeneous stress field with local stress states in the vicinity of inherited older structures.
The measured post-orogenic extensional structures are related to a new extensional event, the opening of the Pannonian Basin during the Miocene. We classified these structures into the following groups: immediate pre-rift phase with NE–SW extension (D6), syn-rift phase with E–W extension (D7a) and N–S transpression (D7b), and post-rift phase with NNW–SSE extension (D8).
