ALBERT

Description: Paleoclimatic effects may still influence the present day subsurface temperature distribution and therefore the heatflow density calculated in affected depth levels. Cooling of several degrees Celsius into depths of up to 1.5 – 2km were reported for areas which were strongly affected by the Pleistocene ice ages (e.g. Canada, Poland, andDenmark). However, although this phenomenon is well known, not much research has been performed to quantifythese processes in Northern Germany, an area where Pleistocene ice margins of the last ice ages are located. Tofill that gap we compiled new data from two boreholes in the eastern part of the North German Basin, one locatedbeneath the former ice shield of the last glaciation, and one located in the foreland. We determined thermal rockproperties (thermal conductivity, thermal diffusivity, and specific heat capacity) on drill core samples and used itas calibrator for well-log based calculations of thermal parameter profiles along the borehole. The results wereused for heat-flow computations with depth and implemented as a base for an analytical solution of the heatequation as well as inversion modelling. By showing the discrepancy of observed and theoretical backgroundtemperature and heat flow density profiles, we aim to improve the understanding of the regional thermal responseto the last glaciations.

Description: This data set compiles the raw data used to evaluate the performance of the Goto & Matsubayashi model for continental sedimentary rocks ( Goto & Matsubayashi, 2009). It reports thermal diffusivity (α) and porosity (φ) data for two suites of rock, quartz sandstones of varying porosity and clastic and carbonate lithologies of variable porosity and modal mineralogy. The rock collection involves roughly 120 samples (from boreholes and outcrops) with porosities between 0 and 35%, on which the operability of the Goto & Matsubayashi modified geometric mean model (mGM) was evaluated and quantified. Our study confirms the operability of the mGM for consolidated quartz-rich sandstones and implies a reasonably good performance of this model also for mineralogically more complex sedimentary rocks. This model was also proven to be an appropriate tool to convert thermal diffusivity data obtained on air-saturated samples into such reflecting water-saturated conditions. Altogether, our study suggests that the mGM is suited to model thermal-diffusivity data of all types of sedimentary rock of whatever porosity and chemistry of the pore fluid. The data reported in this data publication are the basis for tables and plots published by Fuchs et al. (2020). Data are provided in tab-delimited text format and described in detail in the associated data description.

Description: Understanding the thermal behaviour of non‐steady state subsurface geosystems, when temperature changes over time, requires knowledge on the speed of heat propagation and, thus, of the rock's thermal diffusivity as essential thermo‐physical parameter. Mixing models are commonly used to describe thermo‐physical properties of polymineralic rocks. A thermal diffusivity–porosity relation is known from literature that incorporates common mixing models into the heat equation and properly works for unconsolidated, clastic clayey and sandy marine sediments of high porosity (35−80%). We have proofed the relation's applicability for consolidated, isotropic sedimentary rocks of low porosity (〈35%). The performance of this approach was evaluated for consolidated quartz‐dominated sandstones containing air, water, and heptane as pore‐ and/or fracture‐filling medium. For these rocks, the reliability of the relation was confirmed for the entire range of porosity and all three media, with water‐saturated rocks displaying an almost perfect fit between measured and modelled thermal diffusivity. Additional measurements conducted on a larger suite of low‐porous siliciclastic and carbonate rocks imply that it is also suitable to acceptably good to infer the thermal diffusivity of mineralogically more diverse sedimentary rocks. In contrast to other common mixing models, this relation is appropriate to convert thermal‐diffusivity data obtained on air‐saturated samples into such reflecting water‐saturated conditions. This is of particular importance for handling data acquired from methods limited to the measurement of dry samples, e.g., laser‐flash analysis. In conclusion, the applied relation is suited to model thermal‐diffusivity data of isotropic sedimentary rocks of different porosity and independent of the pore fluid.

Description: Fault-propagation folding occurs when a shallow fold is created by an underlying propagating thrust fault. These structures are common features of fold and thrust belts and hold key economic relevance as groundwater or hydrocarbon reservoirs. Reconstructing a fault-propagation fold is commonly done by means of the trishear model of the forelimb, a theoretical approach that assumes simplistic rheological rock properties. Here we present a series of numerical models that elucidate the kinematics of fault-propagation folding within an anisotropic sedimentary cover using complex visco-elasto-plastic rheologies. We explore the influence of different parameters like cohesion, angle of internal friction, and viscosity during folding and compare the velocity field with results from the purely kinematic trishear model. In the trishear paradigm, fault-propagation folding features a triangular shear zone ahead of the fault tip whose width is defined by the apical angle that in practice serves as a freely tunable fitting parameter. In agreement with this framework, a triangular zone of concentrated strain forms in all numerical models. We use our models to relate the apical angle to the rheological properties of the modeled sedimentary layers. In purely visco-plastic models, the geometry of the forelimb obtained can be approximated using a trishear kinematic model with high apical angles ranging between 60° and 70°. However, additionally accounting for elastic deformation produces a significant change in the geometry of the beds that require lower apical angles (25°) for trishear kinematics. We conclude that all analyzed numerical models can be represented by applying the theoretical trishear model, whereby folds involving salt layers require high apical angle values while more competent sedimentary rocks need lower values.

Description: The lithosphere is often assumed to reside in a thermal steady‐state when quantitatively describing the temperature distribution in continental interiors and sedimentary basins, but also at active plate boundaries. Here, we investigate the applicability limit of this assumption at slowly deforming continental rifts. To this aim, we assess the tectonic thermal imprint in numerical experiments that cover a range of realistic rift configurations. For each model scenario, the deviation from thermal equilibrium is evaluated. This is done by comparing the transient temperature field of every model to a corresponding steady‐state model with identical structural configuration. We find that the validity of the thermal steady‐state assumption strongly depends on rift type, divergence velocity, sample location and depth within the rift. Maximum differences between transient and steady‐state models occur in narrow rifts, at the rift sides, and if the extension rate exceeds 0.5‐2 mm/a. Wide rifts, however, reside close to thermal steady‐state even for high extension velocities. The transient imprint of rifting appears to be overall negligible for shallow isotherms with a temperature less than 100°C. Contrarily, a steady‐state treatment of deep crustal isotherms leads to underestimation of crustal temperatures, especially for narrow rift settings. Thus, not only relatively fast rifts like the Gulf of Corinth, Red Sea, and Main Ethiopian Rift, but even slow rifts like the Kenya Rift, Rhine Graben, and Rio Grande Rift must be expected to feature a pronounced transient component in the temperature field and to therefore violate the thermal steady‐state assumption for deeper crustal isotherms.