Emplacement of “exotic” Zechstein slivers along the inverted Sontra Graben (northern Hessen, Germany): clues from balanced cross sections and geometrical forward modeling

Lens-shaped slivers of Permian (Zechstein) amid Triassic units appearing along the master fault of the Sontra Graben in central Germany on the southern margin of the Central European Basin System (CEBS) were studied by means of detailed map analysis, a semi-quantitative forward model, and two balanced cross sections. We show how partial reactivation of the graben's main normal fault and shortcut thrusting in the footwall during inversion, combined with a specific fault geometry involving flats in low-shear-strength horizons, can produce the observed slivers of “exotic” Zechstein. This conceptual model implies that the Sontra Graben was created by about 1200 m of extension followed by some 1000 m of contraction, resulting in the few hundred meters of net extension observed today. Gentle dips and comparatively extensive exposure of some slivers suggest they are backthrust onto the reactivated normal fault's hanging wall, an interpretation corroborated in one location by shallow drilling. Backthrusting appears to have wedged some Zechstein slivers into incompetent Triassic units of the hanging wall. Based on regional correlation, extension most likely occurred in Late Triassic to Early Cretaceous time, while the contraction is almost certainly of Late Cretaceous age. The main aim of this paper is to describe an uncommon structural feature that we interpret to originate from inversion tectonics in an evaporite-bearing succession with multiple detachment horizons but without the presence of thick salt.

Emplacement of exotic Zechstein slivers along the inverted Sontra Graben (northern Hessen, Germany): clues from balanced crosssections and geometrical forward modelling

Lens-shaped slivers of Permian (Zechstein) amid Triassic units, appearing along the main boundary fault of the Sontra Graben in central Germany on the southern edge of the Central European Basin System (CEBS) were studied by means of detailed map analysis, a semi-quantitative forward model and two balanced cross-sections. We show how partial reactivation of the graben’s main normal fault and shortcut thrusting in the footwall during inversion, combined with a specific fault geometry involving flats in low shear-strength horizons, produce the observed slivers of exotic Zechstein. Based on regional correlation, extension most likely occurred in Late Triassic to Early Cretaceous time while the contraction is of Late Cretaceous age. The kinematic history of the graben, reconstructed through field observations, structural and cross-section analysis is employed to discuss the dynamic evolution of the graben system in the immediate vicinity and to consider implications for the entire CEBS.

The effects of glacial-interglacial loading on the 3D pore pressure evolution in sedimentary basins: case study from the Central European Basin System

<p>This study deals with modelling the distribution of the subsurface pore pressure in space and the respective evolution in time in response to variations in hydromechanical surface loading during a full glacial-interglacial cycle. The aim here is to better understand (i) the feedback mechanisms between the atmosphere and solid earth components, and (ii) to which degree this coupling might be relevant for subsurface hydromechanical modelling studies. The study area is the Central European Basin System (CEBS) in northern and Central Europe and state-of-the-art ice reconstructions for the last glacial-interglacial period have been used to model the surface hydromechanical loading conditions. Thereby, investigations on how transient ice coverage influences the pore pressure distribution with depth and over time within a heterogeneous sedimentary cover were carried out. The subsurface beneath the CEBS consists of more than 10 km thick sediments, which have been heavily restructured by salt movements during the whole Mesozoic evolution. Our 3D geological model resolves all major sedimentary and crustal domains, and we relied on the GLAC1-D (1.0 degree longitude by 0.5 degree latitude spatial resolution) ice sheet chronology. Starting from ice-free initial conditions, transient simulation runs are performed (hydraulic vs hydromechanical) which cover the entire last glacial cycle, i.e. encompassing 122ka BP till present day conditions. Results are discussed in terms of pore pressure evolution over time and space. The focus will lie on quantifying subsurface conditions favourable to the establishment and maintenance of overpressure evolution and the related equilibration time within the sedimentary pile. We also investigate how these transient conditions influence the subsurface hydrodynamics, showcasing representative time steps during the evolution of the system. We will finally attempt to quantify the memory effect of such loading conditions on the basin-wide hydromechanics, a feedback mechanism that has been neglected so far in 3D subsurface studies.</p>

A three-dimensional lithospheric-scale thermal model of Germany

We present a 3-D lithospheric-scale model covering the area of Germany that images the regional characteristics of the structural configuration and of the thermal field. The structural model resolves major sedimentary, crustal and lithospheric mantle units integrated from previous studies of the Central European Basin System, the Upper Rhine Graben and the Molasse Basin, together with published geological and geophysical data. A combined workflow consisting of 3-D structural, gravity and thermal modelling is applied to derive the 3-D thermal configuration. The modelled temperature distribution is highly variable in response to an imposed heterogeneous distribution of thermal properties assigned to the different units. First order variations in the temperature field are mainly attributed to the thermal blanketing effect from the sedimentary cover, the variability in the amount of radiogenic heat produced within the different crystalline crust compartments and the implemented topology of the thermal Lithosphere-Asthenosphere Boundary.