3 results
Structural and microstructural analysis of K–Mg salt layers in the Zechstein 3 of the Veendam Pillow, NE Netherlands: development of a tectonic mélange during salt flow
- Alexander F. Raith, Janos L. Urai, Jacob Visser
-
- Journal:
- Netherlands Journal of Geosciences / Volume 96 / Issue 4 / December 2017
- Published online by Cambridge University Press:
- 15 January 2018, pp. 331-351
-
- Article
-
- You have access Access
- HTML
- Export citation
-
In fully developed evaporite cycles, effective viscosity contrasts of up to five orders of magnitude are possible between different layers, but the structures and mechanics in evaporites with such extreme mechanical stratification are not well understood. The Zechstein 3 unit in the Veendam salt pillow in the Netherlands contains anhydrite, halite, carnallite and bischofite, showing this extreme mechanical stratification. The Veendam Pillow has a complex multiphase salt tectonic history as shown by seismic reflection data: salt withdrawal followed by convergent flow into the salt pillow produced ruptures and folds in the underlying Z3-anhydrite–carbonate stringer and deformed the soft Z3-1b layer
We analysed a unique carnallite- and bischofite-rich drill core from the soft Z3-1b layer by macroscale photography, bulk chemical methods, X-ray diffraction and optical microscopy. Results show high strain in the weaker bischofite- and carnallite-rich layers, with associated dynamic recrystallisation at very low differential stress, completely overprinting the original texture. Stronger layers formed by alternating beds of halite and carnallite show complex recumbent folding on different scales commonly interrupted by sub-horizontal shear zones with brittle deformation, veins and boudinage. We attribute this tectonic fragmentation to be associated with a softening of the complete Z3-1b subunit during its deformation. The result is a tectonic mélange with cm- to 10 m-size blocks with frequent folds and boudinage. We infer that these structures and processes are common in deformed, rheologically strongly stratified evaporites.
3D reconstruction of salt movements within the deepest post-Permian structure of the Central European Basin System - the Glueckstadt Graben
- Y. Maystrenko, U. Bayer, M. Scheck-Wenderoth
-
- Journal:
- Netherlands Journal of Geosciences / Volume 85 / Issue 3 / September 2006
- Published online by Cambridge University Press:
- 01 April 2016, pp. 181-196
-
- Article
-
- You have access Access
- Export citation
-
The Glueckstadt Graben is a prominent structure of the Central European Basin System, where the sedimentary patterns are extensively affected by Permian salt movements. The relations of the sedimentary patterns to salt structures have been analyzed through present-day distributions of sediments. In addition, a three-dimensional backward modelling approach has been applied to determine the original salt distribution in response to the unloading due to sequential backstripping of the stratigraphic layers. The results of the modelling reveal the thickness distribution of the Permian salt for 5 time intervals from the end of the Triassic to present day. Spatial agreement has been found between the development of the depleted zone of the Permian salt through time and the observed distribution of the maximum subsidence for the different stratigraphic units above the salt. The sedimentation centres for each time interval are always located above the zone of reduced or depleted Permian salt. In the central part of the Glueckstadt Graben, the depletion occurred already in the Triassic and perfectly correlates with the thickest Triassic. During the Jurassic, Cretaceous and Tertiary, the areas of depleted Permian salt shifted towards the basin flanks, and the same occurred with the centres of maximum sediment deposition. Thus, the results of the modelling strongly support the conclusion that salt withdrawal has played a major role during the Meso-Cenozoic evolution of the Glueckstadt Graben and that the progressive depletion of the Permian salt layer, from the central part towards the margins, created the large part of the accommodation space for sedimentation in addition to tectonic subsidence.
Furthermore, our study has several important implications for salt behaviour in different tectonic settings. In general, the results of modelling indicate a good correlation between the main phases of salt movements and tectonic events in the area under consideration. During the Triassic, the first stage of diapirism in the Glueckstadt Graben occurred within the central part of the basin. Regional extension may have triggered reactive diapirism and caused the formation of the deep primary rim synclines. Once the salt structures had reached the critical size, buoyancy forces supported their continued growth until the Jurassic when extension-induced regional stresses once more affected the Glueckstadt Graben. The results of the modelling indicate very little salt activity during the late Early Cretaceous-early Late Cretaceous when the area of the Glueckstadt Graben was tectonically silent. Therefore, our study supports the concept of tectonically induced salt movements which can be interrupted during the absence of tectonic forces. Salt movements were reactivated in the marginal troughs by compressional forces during the latest Late Cretaceous-Early Cenozoic. Paleogene-Neogene salt withdrawal led to the growth of N-S oriented salt structures mainly at the margins of the basin. This phase of salt tectonics correlates temporally with almost W-E extension. This indicates a renewed change in tectonic regime after Late Cretaceous-Early Cenozoic compression.
3D structural modelling of the southern Zagros fold-and-thrust belt diapiric province
- VINCENT TROCMÉ, EMILY ALBOUY, JEAN-PAUL CALLOT, JEAN LETOUZEY, NICOLAS ROLLAND, HASSAN GOODARZI, SALMAN JAHANI
-
- Journal:
- Geological Magazine / Volume 148 / Issue 5-6 / November 2011
- Published online by Cambridge University Press:
- 05 August 2011, pp. 879-900
-
- Article
- Export citation
-
3D modelling of geological structures is a key method to improve the understanding of the geological history of an area, and to serve as a drive for exploration. Geomodelling has been performed on a large 60000 km2 area of the Zagros fold-and-thrust belt of Iran, to reconcile a vast but heterogeneous dataset. Topography, geological surface data and dips, outcrop surveys, and well and seismic data were integrated into the model. The method was to construct a key surface maximizing the hard data constraints. The Oligo-Miocene Top Asmari layer was chosen, as this formation was regionally deposited before the main Zagros collision phase and because the numerous outcrops allow proper control of the bed geometry in the fold cores. Interpreted seismic data have been integrated to interpolate the surfaces at depth within the synclines. Several conceptual models of fold geometry have been applied to estimate the best way to convert seismic time signal to depth. Several deeper horizons down to Palaeozoic strata were deduced from this key horizon by applying palaeo-thickness maps. During the construction, the 3D interpolated surfaces could be reconverted to time, using a velocity model, and compared with previous seismic interpretations. This exercise obliged us to revise some early interpretations of seismic lines that were badly tied to wells. The 3D modelling therefore clearly improves regional interpretation. In addition, the 3D model is the only tool that allows drawing consistent cross-sections in areas where there are no seismic lines. Emerging Hormuz salt diapirs were added to the model. Dimensions and shapes of the individual diapirs were modelled using a statistical survey on the cropping out Hormuz structures. Modelling reliably demonstrated that the diapirs, when piercing, show a constant mushroom shape whose diameter depends on the stratigraphic depth of observation. This observation allowed us to exemplify relations between the pre-existing diapirs and the anticlines of the area, and to highlight the morphological changes from the inner onshore areas to the coastal and offshore areas. In addition, one of the surprising results of this study was the observation of the increasing diameter of the diapirs at the time of the Zagros collision and folding event, with growth strata and overhangs on the flanks of the diapirs.