Hydrogeologic evidence for a continuous basal shear zone within a deep-seated gravitational slope deformation (Eastern Alps, Tyrol, Austria)

The currently inactive deep-seated gravitational slope deformation (DGSD) Sagspitz in Tyrol, Austria, covers an area of 3km2 and originated along a glacially over-steepened slope composed mainly of phyllites belonging to the Innsbruck Quartzphyllite Complex. Past mass movement processes caused the formation of fracture systems and slump bodies which consequently form the aquifers of relatively large springs in a rock type with generally very low permeability and poor porosity. Analysis of water chemistry, oxygen isotope, and field parameters of the springs emerging from the DGSD imply that multilevel aquifers exist and enabled the detection of continuous deep flow paths through the entire length of the mass movement from the main scarp to the toe of the slope. It is shown that the aquifer boundaries and spring emergences throughout the loosened rock mass can be correlated to the internal and basal shear zones of the DGSD so that this hydrogeological approach proved to be useful for evaluating the mass movement structur

Structural evolution and neotectonics of the Rhine-Bresse Transfer Zone

This thesis was carried out within the framework of the international EUCOR-URGENT project and represents a joint study (co-tutelle) between the Universities of Basel and Besançon. It is devoted to the structural evolution and present-day tectonic activity of the region of Franche Comté in Eastern France, a region that is located at the intersection between the Jura fold-and-thrust belt representing the front of the Alpine orogen and the immediately adjacent northwestern foreland, characterized by the intra-continental Rhine-Bresse Transfer Zone (RBTZ). The formation of the RBTZ, that forms a central segment of the Paleogene European Cenozoic Rift System, involved the extensional reactivation of the Late Paleozoic Burgundy Trough System. Substantial extension occurred in Eo-Oligocene times and was achieved by ENE-WSW striking normal faults that are highly oblique to the dominant strike of the Rhine and Bresse grabens. Fission track data suggest that basement reactivation also contributed to the Eo-Oligocene exhumation of the Late Paleozoic La Serre Horst in the context of rifting. Basement reactivation in connection with the formation of the RBTZ resulted in complex fault patterns and local stress field perturbations, especially in the surroundings of the pre-existing Paleozoic horst structure. During Late Miocene to Early Pliocene times the northwestern most segment of the thin-skinned Jura fold-and-thrust belt, the Besançon Zone, encroached onto the RBTZ. Moreover, NW-SE directed foreland compression caused thick-skinned, transpressive reactivation of the RBTZ that started by Late Pliocene times at the earliest. Present-day seismicity in the RBTZ indicates that thick-skinned tectonics are still active and may reflect ongoing tectonic underplating in the northwestern Alpine foreland. Post-Pliocene relative rock uplift is recorded along the RBTZ by differential erosion of the Middle Pliocene Sundgau-Forêt de Chaux Gravels on a regional scale. Uplifted remnants of this gravel plain, identified by heavy mineral analyses, permitted to determine a latest Pliocene to recent minimum regional rock uplift rate of 0.05 +/- 0.02 mm/yr. A reconstruction of the Plio-Pleistocene drainage basin evolution of the Ognon and Doubs Rivers revealed that this relative rock uplift is still ongoing and most likely partly driven by the inversion of the RBTZ. Pleistocene folding near Besançon is evident from differentially up warped paleo-meanders along the Citadelle Anticline. This deformation is apparently enhanced by the bedrock incision of the Doubs River and associated with higher local uplift rates of 0.17 +/- 0.03 mm/yr. The results of this study vividly illustrate the dynamic processes that control the progressive evolution of continental collisional forelands. It appears that while the evolution of the RBTZ was largely controlled by the reactivation of pre-existing structures, its present tectonic activity is to some extent also controlled by surface processes and involves positive feedbacks between large-scale uplift, enhanced erosion and active deformation

Influence of rheologically weak layers on fault architecture: insights from analogue models in the context of the Northern Alpine Foreland Basin

We present a series of analogue models inspired by the geology of the Zürcher Weinland region in the NorthernvAlpine Foreland Basin of Switzerland to explore the influence of rheological weak, i.e. (partially) ductile layers on the 3D evolution of tectonic deformation. Our model series test the impact of varying weak layer thickness and rheology, as well as different kinematics of an underlying “basal fault”. Model analysis focuses on deformation in the weak layer overburden and, uniquely, within the weak layer itself. We find that for low to moderate basal fault displacements, the above-mentioned parameters strongly influence the degree of coupling between the basal fault and the weak layer overburden. Coupling between the basal fault and overburden decreases by reducing the strength of the weak layer, or by increasing the weak layer’s thickness. As a result, basal fault displacement is less readily transferred through the weak layer, leading to a different structural style in the overburden. By contrast, increasing the amount, or rate, of basal fault slip enhances coupling and leads to a more similar structural style between basal fault and overburden. Moreover, dip-slip displacement on the basal fault is more readily transferred to the overburden than strike-slip displacement of the same magnitude. Our model results compare fairly well to natural examples in the Northern Alpine Foreland Basin, explaining various structural features. These comparisons suggest that rheological weak layers such as the Jurassic Opalinus Clay have exerted a stronger control on fault zone architecture than is commonly inferred, potentially resulting in vertical fault segmentation and variations in structural style. Furthermore, the novel addition of internal marker intervals to the weak layer in our models reveals how complex viscous flow within these layers can accommodate basal fault slip. Our model results demonstrate the complex links between fault kinematics, mechanics and 3D geometries, and can be used for interpreting structures in the Alpine Foreland, as well as in other settings with similar weak layers and basal faults driving deformation in the system

Feedback between erosion and active deformation: geomorphic constraints from the frontal Jura fold-and-thrust belt (eastern France)

A regional tectono-geomorphic analysis indicates a Pliocene to recent rock uplift of the outermost segment of the Jura fold-and-thrust belt, which spatially coincides with the intra-continental Rhine-Bresse Transfer Zone. Elevated remnants of the partly eroded Middle Pliocene Sundgau-Forêt de Chaux Gravels identified by heavy mineral analyses allow for a paleo-topographic reconstruction that yields minimum regional Latest Pliocene to recent rock uplift rates of 0.05±0.02mm/year. This uplift also affected the Pleistocene evolution of the Ognon and Doubs drainage basins and is interpreted as being tectonically controlled. While the Ognon River was deflected from the uplifted region the Doubs deeply incised into it. Focused incision of the Doubs possibly sustained ongoing deformation along anticlines which were initiated during the Neogene evolution of the thin-skinned Jura fold-and-thrust belt. At present, this erosion-related active deformation is taking place synchronously with thick-skinned tectonics, controlling the inversion of the Rhine-Bresse Transfer Zone. This suggests local decoupling between seismogenic basement faulting and erosion-related deformation of the Mesozoic cover sequence

Lithologic Effects on Landscape Response to Base Level Changes: A Modeling Study in the Context of the Eastern Jura Mountains, Switzerland

Landscape evolution is a product of the forces that drive geomorphic processes (e.g., tectonics and climate) and the resistance to those processes. The underlying lithology and structural setting in many landscapes set the resistance to erosion. This study uses a modified version of the Channel‐Hillslope Integrated Landscape Development (CHILD) landscape evolution model to determine the effect of a spatially and temporally changing erodibility in a terrain with a complex base level history. Specifically, our focus is to quantify how the effects of variable lithology influence transient base level signals. We set up a series of numerical landscape evolution models with increasing levels of complexity based on the lithologic variability and base level history of the Jura Mountains of northern Switzerland. The models are consistent with lithology (and therewith erodibility) playing an important role in the transient evolution of the landscape. The results show that the erosion rate history at a location depends on the rock uplift and base level history, the range of erodibilities of the different lithologies, and the history of the surface geology downstream from the analyzed location. Near the model boundary, the history of erosion is dominated by the base level history. The transient wave of incision, however, is quite variable in the different model runs and depends on the geometric structure of lithology used. It is thus important to constrain the spatiotemporal erodibility patterns downstream of any given point of interest to understand the evolution of a landscape subject to variable base level in a quantitative framework.Key PointsA landscape evolution model is used to show how topographic history is influenced by regional geologyExhumation of different lithologies modulates the transient response to base level changes over millions of yearsSignificantly different erosion and topographic histories result depending on the stratigraphic architecture, even over a small range in erodibilityPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141336/1/jgrf20766_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141336/2/jgrf20766.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141336/3/jgrf20766-sup-0001-Data_S1.pd

Rinikerfeld Palaeolake (Northern Switzerland) – a sedimentary archive of landscape and climate change during the penultimate glacial cycle

While timing and ice extent of the last glacial maximum are generally well known, the courses of earlier glaciations have remained poorly constrained, with one of the main reasons being the scarcity of sedimentary archives. This study introduces a new palaeolake record from a Mid‐Pleistocene glaciofluvial channel system in the Lower Aare Valley (Northern Switzerland). The record of Rinikerfeld comprises a >40 m long succession of Quaternary deposits that are targeted by multi‐method sedimentological analysis. Sedimentary facies together with geochemical and geotechnical parameters, pollen content, as well as luminescence ages allow the reconstruction of the establishment, evolution and infilling of the early Marine Isotope Stage 6‐aged Rinikerfeld Palaeolake. A drastic change in lake sediment composition and structure indicates cessation of the initial glacially derived input, which is explained by landscape modification and drainage rerouting during the Penultimate (Beringen) Glaciation. Geochemical and palynological data further reveal cold, initially periglacial but slightly ameliorating, climate conditions, while the lake was progressively filled up by local runoff, before being buried by periglacial colluvial diamicts, and potentially overridden by ice. It is therefore concluded that the onset of the Beringen Glaciation was an environmentally as well as geomorphically dynamic time period in the Northern Alpine Foreland

Active Faulting in Lake Constance (Austria, Germany, Switzerland) Unraveled by Multi-Vintage Reflection Seismic Data

Probabilistic seismic hazard assessments are primarily based on instrumentally recorded and historically documented earthquakes. For the northern part of the European Alpine Arc, slow crustal deformation results in low earthquake recurrence rates and brings up the necessity to extend our perspective beyond the existing earthquake catalog. The overdeepened basin of Lake Constance (Austria, Germany, and Switzerland), located within the North-Alpine Molasse Basin, is investigated as an ideal (neo-) tectonic archive. The lake is surrounded by major tectonic structures and constrained via the North Alpine Front in the South, the Jura fold-and-thrust belt in the West, and the Hegau-Lake Constance Graben System in the North. Several fault zones reach Lake Constance such as the St. Gallen Fault Zone, a reactivated basement-rooted normal fault, active during several phases from the Permo-Carboniferous to the Mesozoic. To extend the catalog of potentially active fault zones, we compiled an extensive 445 km of multi-channel reflection seismic data in 2017, complementing a moderate-size GI-airgun survey from 2016. The two datasets reveal the complete overdeepened Quaternary trough and its sedimentary infill and the upper part of the Miocene Molasse bedrock. They additionally complement existing seismic vintages that investigated the mass-transport deposit chronology and Mesozoic fault structures. The compilation of 2D seismic data allowed investigating the seismic stratigraphy of the Quaternary infill and its underlying bedrock of Lake Constance, shaped by multiple glaciations. The 2D seismic sections revealed 154 fault indications in the Obersee Basin and 39 fault indications in the Untersee Basin. Their interpretative linkage results in 23 and five major fault planes, respectively. One of the major fault planes, traceable to Cenozoic bedrock, is associated with a prominent offset of the lake bottom on the multibeam bathymetric map. Across this area, high-resolution single channel data was acquired and a transect of five short cores was retrieved displaying significant sediment thickness changes across the seismically mapped fault trace with a surface-rupture related turbidite, all indicating repeated activity of a likely seismogenic strike-slip fault with a normal faulting component. We interpret this fault as northward continuation of the St. Gallen Fault Zone, previously described onshore on 3D seismic data

Microstructural characterization of natural fractures and faults in the Opalinus Clay: insights from a deep drilling campaign across central northern Switzerland

Abstract The Middle-Jurassic Opalinus Clay is the foreseen host rock for radioactive waste disposal in central northern Switzerland. An extensive drilling campaign aiming to characterize the argillaceous formation resulted in a comprehensive drill core data set. The rheologically weak Opalinus Clay is only mildly deformed compared to the over- and underlying rock units but shows a variety of natural fractures. While these structures are hydraulically indistinguishable from macroscopically non-deformed Opalinus Clay today, their analysis allows for a better understanding of the deformation behaviour in the geological past. Here, we present an overview of the different fracture and fault types recorded in the Opalinus Clay and a detailed microstructural characterization of veins—natural dilational fractures healed by secondary calcite and celestite mineralizations. Macroscopic drill core analysis revealed five different natural fracture types that encompass tension gashes of various orientations with respect to bedding and small-scale faults with displacements typically not exceeding the drill core diameter. The occurrence of different fault types generally fits well with the local tectonic setting of the different drilling sites and with respect to the neighbouring regional fault zones. The microstructural investigations of the various vein types revealed their often polyphase character. Fibrous bedding-parallel veins of presumable early age were found to be overprinted by secondary slickenfibres. The polyphase nature of fibrous bedding parallel veins and slickenfibres is supported by differing elemental compositions, pointing towards repeated fracturing and mineralization events. Direct dating of vein calcites with U–Pb was unsuccessful. Nevertheless, age constraints can be inferred from structural orientations and fault slip kinematics. Accordingly, some of the veins already formed during sediment compaction in Mesozoic times, others possibly relate to Early Cenozoic foreland uplift. The youngest veins are most likely related to Late Cenozoic regional tectonic events, such as the Jura fold-and-thrust belt to the south and the Hegau-Lake Constance Graben to the northeast of the study area. During these latest tectonic events, previously formed veins acted as rheologically stiff discontinuities in the otherwise comparably weak Opalinus Clay along which deformation of the rock formation was re-localized

Climatic and tectonic controls on the development of the River Ognon terrace system (eastern France)

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Post-2.4 Ma to present-day propagation of a hidden anticline at the front of the Jura fold-and-thrust belt, Alpine foreland, France

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