The Sognefjord transect through the lower to middle Palaeozoic Caledonian mountain belt in southern Norway provides one of the best and most completely documented examples of late collisional tectonics in an Alpine-type orogen. It exposes a 250km long cross-section from the cratonic foreland, in the east, through the heavily deformed continental margin (Baltica), to the remains of the Caledonian ocean (Iapetus) at the Norwegian west coast. Exceptionally detailed and complete structural data are available along the whole transect, together with good stratigraphic, radiometric, petrological, and geophysical control. In this synthesis, the structural data are analysed, in terms of the kinematics and relative age of the different deformation phases, and correlated along the whole transect. The analysis is then used, in conjunction with the other data, to carry out a retrodeformation, reconstructing the crustal geometry at different stages backward in time. The earliest of the present reconstructions (c. 410 Ma) marks the time of formation of the well-known West Norwegian eclogites, in an over-deepened root of Baltica which had developed in the ductile lower crust as a response to extreme crustal shortening. The brittle upper crust took up the shortening by the SE movement of a rigid sheet of Precambrian basement (Jotun complex) above the low-angle Jotunheimen contractional detachment, across a rigid wedge of the Baltic Shield. During the final stages of contraction (c. 410-395 Ma), the upper crust acted as an orogenic lid, against which the root 'collapsed' upwards by sub-vertical shortening and lateral E-W extension. During this process of inverted gravity spreading, the eclogites were carried upwards from 60-70 km to 40 km (exhumation phase 1, rate 2-3 mm a -1) and retrograded within their deforming gneissic matrix. At the end of this phase, the strain field in the upper crust changed from contraction to extension, concomitant with a broad up-doming (base Devonian unconformity) which caused a further 10 km exhumation by 385 Ma (exhumation phase 2, 1 mm a-l). This was followed by the main phase of crustal extension with the development of low-angle normal top-to-W or NW fault and shear zones, of which the Nordfjord-Sogn detachment was the most important (50 km of normal displacement). Exhumation in this phase took place by rapid uplift and erosion of the footwall of the detachment, causing the currently exposed eclogites in outer Sognefjord to rise the remaining 30 km (exhumation phase 3,1.5 mm a-l), to become juxtaposed against Devonian conglomerates on the hanging wall. The reconstructions confirm the general picture of eclogite exhumation in western Norway, and fill out some of the details. However, they do not support the idea that the process was due to extensional orogenic collapse caused by advective or convective lithospheric thinning. Although gravity played a significant role at various stages in the process, the main phase of crustal extension seems to have been mainly related to changes in Devonian plate...
Seepage water through a lake bottom and the layering of tight and high-permeable layers in the aquifer produce groundwater under greater pressure than the water column of the lake. This results in under-water springs and seepages. When spawning substrata were available, there was a spatial correlation between the degree of groundwater influx and the redd density of brown trout Salmo trutta. In high density spawning areas with >100 observed redds ha 1 , the mean seepage water influx during spring was c. 1200 ml m 2 min 1 compared to a mean flux of 113 ml m 2 min 1 in low density spawning areas with 5-10 redds ha 1 .
At Lacgerdorf, northern Germany, several large quarries provide access to study extensional deformation features in three dimensions, in the chalk overburden of a salt diapir. Numerous individual faults and the intervening blocks have been analyzed with respect to detailed fault morphology and geometry of brittle structures within the blocks. The studied fault zones, with displacements in the range of several metres, display geometries which vary within well defined limits. The fault zones are mostly very narrow (some tens of centimetres), but can widen up to a maximum of 7 m. The fractures composing a fault zone have a dominant length below 3 m. A 3D reconstruction of one quarry shows the rhombohedral shape of the fault blocks with a block width of 100 to 150 metres and the long diagonal parallel to the salt-ridge axis. The block-internal deformation is characterized by fractures which seem to be interconnected in a network. The locality of Lacgcrdorf is comparable with that of the Albuskjell and Ekofisk hydrocarbon reservoirs of the central North Sea in terms both of the structural setting of the deformed chalk on top of a salt diapir and the characteristics of extensional features.
Quantitative descriptions of 3D fracture networks in terms of fracture characteristics and connectivity are necessary for reservoir evaluation, management, and EOR programs of fractured reservoirs. Our research has focused on an analogue to North Sea fractured chalk reservoirs that is excellently exposed near Uigerdorf, northwest Germary. An underlying salt diapir uplifted and deformed Upper Cretaceous chalk; the cement industry now exploits it. The fracture network in the production wall of the quarry was characterized and mapped at different scales, and 12 profiles of a 230-m wide and 35-m high production wall were investigated as the wall receded 25 m. In addition, three wells were drilled into the chalk volume. The wells were cored and the wellbores were imaged with both the resistivity formation micro scanner (FMS) and the sonic circumferential borehole image logger (CBIL). The large amount of fracture data was analyzed with respect to parameters, such as fracture density distribution, orientation, and length distribution, and in terms of the representativity and predictability of data sets collected from restricted rock volumes. Data CollectionAll the data in our investigation were collected in the Saturn quarry, where the production process allows mapping of cross sections of a type similar to 3D seismics offshore. A large excavator running on rails continuously scrapes off a planar wall inclined at 50°, exposing 'Now with Scandpower AS.
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