No abstract

No abstract

No abstract

a b s t r a c tTectonics and erosion are the driving forces in the evolution of mountain belts, but the identification of their relative contributions remains a fundamental scientific problem in relation to the understanding of both geodynamic processes and surface processes. The issue is further complicated through the roles of climate and climatic change. For more than a century it has been thought that the present high topography of western Scandinavia was created by some form of active tectonic uplift during the Cenozoic. This has been based mainly on the occurrence of surface remnants and accordant summits at high elevation believed to have been graded to sea level, the inference of increasing erosion rates toward the present-day based on the age of offshore erosion products and the erosion histories inferred from apatite fission track data, and on over-burial and seaward tilting of coast-proximal sediments.In contrast to this received wisdom, we demonstrate here that the evidence can be substantially explained by a model of protracted exhumation of topography since the Caledonide Orogeny. Exhumation occurred by gravitational collapse, continental rifting and erosion. Initially, tectonic exhumation dominated, although erosion rates were high. The subsequent demise of onshore tectonic activity allowed slow erosion to become the dominating exhumation agent. The elevation limiting and landscape shaping activities of wet-based alpine glaciers, cirques and periglacial processes gained importance with the greenhouse-icehouse climatic deterioration at the Eocene-Oligocene boundary and erosion rates increased. The flattish surfaces that these processes can produce suggest an alternative to the traditional tectonic interpretation of these landscape elements in western Scandinavia. The longevity of western Scandinavian topography is due to the failure of rifting processes in destroying the topography entirely, and to the buoyant upward feeding of replacement crustal material commensurate with exhumation unloading.We emphasize the importance of differentiating the morphological, sedimentological and structural signatures of recent active tectonics from the effects of long-term exhumation and isostatic rebound in understanding the evolution of similar elevated regions.

Ramp syncline basins were identified above thick salt in the São Paulo Plateau, Santos Basin  They form by translation over a thick salt detachment with basal relief due to viscous drag and salt flux variations  They record 28-32 km of SE translation during the Late Cretaceous to Paleocene  They form by translation over basinward-dipping and landward-dipping basesalt ramps  Stratal terminations and architecture vary along-dip and strike within these

No abstract

O. R. 2007. A morphometric analysis of tunnel valleys in the eastern North Sea based on 3D seismic data.ABSTRACT: A 1250 km 2 3D seismic volume is used to provide a detailed spatial and geometrical analysis of fifteen Pleistocene tunnel valleys in the Danish North Sea. All the valleys are buried; they are up to 39 km long, 3-4 km wide and up to 350 m deep. The valleys are part of a vast tunnel valley province covering an area of some 0.5 million km 2 of the formerly glaciated lowland areas of North West Europe. The valleys consist of non-branching, non-anastomosing troughs; they exhibit strongly undulating bottom profiles with numerous sub-basins and thresholds, and are characterised by adverse end slopes. Cross-cutting relationships and theoretical considerations suggest the occurrence of seven major episodes of valley incision attributed to ice marginal oscillations within a few glacials. Calculations considering the valley end gradients and theoretical ice-surface profiles suggest that the valleys were formed by pressurised subglacial meltwater erosion. Given a range of theoretical ice-surface profiles, the adverse end slopes are well beyond the supercooling threshold, which suggests that the water was not in thermal equilibrium with the basal ice and that flow was concentrated in substantial conduits with sufficient mass and flux to maintain water temperature well above the freezing point.

Subsurface sediment remobilization and fluid flow processes and their products are increasingly being recognized as significant dynamic components of sedimentary basins. The geological structures formed by these processes have traditionally been grouped into mud volcano systems, fluid flow pipes and sandstone intrusion complexes. But the boundaries between these groups are not always distinct because there can be similarities in their geometries and the causal geological processes. For instance, the process model for both mud and sand remobilization and injection involves a source of fluid that can be separate from the source of sediment, and diapirism is now largely discarded as a deformation mechanism for both lithologies. Both mud and sand form dykes and sills in the subsurface and extrusive edifices when intersecting the sediment surface, although the relative proportions of intrusive and extrusive components are very different, with mud volcano systems being largely extrusive and sand injectite systems being mainly intrusive. Focused fluid flow pipes may transfer fluids over hundreds of metres of vertical section for millions of years and may develop into mud volcano feeder systems under conditions of sufficiently voluminous and rapid fluid ascent associated with deeper focus points and overpressured aquifers. Both mud and sand remobilization is facilitated by overpressure and generally will be activated by an external trigger such as an earthquake, although some mud volcano systems may be driven by the re‐charge dynamics of their fluid source. Future research should aim to provide spatio‐temporal ‘injectite’ stratigraphies to help constrain sediment remobilization processes in their basinal context and identify and study outcrop analogues of mud volcano feeders and pipes, which are virtually unknown at present. Further data‐driven research would be significantly boosted by numerical and analogue process modelling to constrain the mechanics of deep subsurface sediment remobilization as these processes can not be readily observed, unlike many conventional sediment transport phenomena.