Well-log correlation using a back-propagation neural network

We present a back-propagation neural network with an input layer in the form of a tapped delay line wich can be trained effectively on one or several well logs to recognize a particular geological marker. Subsequently, the neural network proposes locations of this marker on other wells in the field. Another neural network, similar in architecture to the first one, performs the same task for secondary markers using, in addition to the well logs, a depth reference function to the first marker. This method is shown to have better performance and better discrimination than standard cross-correlation techniques. It lends itself well for an interactive implementation on a workstation.     

On the effective thermal and hydraulic conductivity of binary heterogeneous sediments

Heterogeneity is present in geological sedimentary structures at all scales from pore to basin, and its distribution has an impact on transport processes such as heat and fluid flow. The rock masses at any scale need to be characterized by their effective properties at that scale, based on the individual characteristics of the heterogeneous porous medium. The effective thermal and hydraulic conductivity of sediments characterized by a stochastic distribution of heterogeneity is studied using an inverse approach based on numerical experiments. The simulations, covering a large range of conductivity contrasts, are carried out for actual core-scale cases of shale clasts in a sand matrix, and on a diagrammatic cross-section through a clastic sedimentary group at the basin scale.

The effective conductivity depends primarily on the heterogeneity fraction and on the conductivity contrast between heterogeneities and the embedding matrix, a dependency which can be described by a generalized weighted mean model. This model is better suited to estimate the effective conductivity at any scale than other models like the self-consistent, or any of the arithmetic, geometric or harmonic averages. The effective conductivity has an anisotropic character although the individual components are homogeneous and isotropic. The variation in effective conductivity is significant even for small conductivity contrasts, like in heat flow processes, and exhibits an asymptotic behaviour for large conductivity contrasts characteristic of fluid flow processes. The effective conductivity has a second-order dependence on such heterogeneity characteristics as shape, aspect ratio, orientation, and distribution. Depending on these characteristics, the bounds of effective conductivity values can be narrowed further from the extreme bounds expressed by the arithmetic and harmonic averages.     

A well-preserved Cambrian impact exposed in Central Sweden

The Lockne impact crater south of Östersund formed in the early Middle Cambrian with a diameter of 7 km. It is identified by its rim wall of crushed Precambrian basement granite, by fragments of impact melt, and by grains of shocked quartz. The exceptional preservation, in particular of the rim wall, is due to a complicated geological history, the first stage of which consisted of burial by marine sediments. This stage lasted until the Middle Ordovician, or over 50 million years. An early Caradoc lowering of the sea-level may have induced debris flows that stripped the rim wall of much of its sedimentary cover. Because normal marine sedimentation recommenced soon after this event, the structure was not seriously damaged, as it was buried again. The Caledonian orogeny emplaced an overthrust nappe as ultimate protection, which was removed by a recent erosion episode from all but the center of the structure.Structures formed by the impact of extraterrestrial bodies are very rare throughout much of Europe, because such structures are neither well preserved nor displayed in young mountain belts or sedimentary basins. However, northern Europe has several ascertained structures of this kind (Svensson &Wickman, 1965;Svensson, 1968;Bruun &Dahlman, 1982;Kala et al., 1984;Flodén et al., 1986;Wickman, 1988). Unfortunately, the hitherto known structures are either poorly preserved or hidden by younger deposits. We are reporting the discovery of a well-preserved exposed and accessible impact structure that has escaped the notice of geologists although important features of it have been described and puzzled over by generations of researchers (Wiman, 1900;Hadding, 1927;Thorslund, 1940;Lindström et al., 1983).The structure is located in the Lockne area to the south of Östersund in central Sweden. It has a diameter of 7 km and its center is near Tramsta on the northwest shore of Lake Locknesjön (Fig. 1). Its middle is covered by folded Lower to Middle Ordovician Orthoceratite Limestone with the sheared Lower Ordovician Töyen Shale at its base. This local expanse of deformed rock is the remainder after erosion of an extensive nappe of overthrust rocks emplaced during the Caledonian orogeny. The good preservation of the impact structure is due to the nappe cover, which had to be removed before erosion could attack the underlying structures.The rim of the impact crater is outlined by a wall of strongly shattered fragments of Proterozoic crystalline rocks (Fig. 2), which formed the local bedrock (Strömberg et al., 1984) at the time of impact. The rim wall is best preserved along the western part of the structure. It was referred to as »arkose-like breccia« byThorslund (1940), who interpreted it as the result of continental weathering, but the components rather show evidence of intense crushing than of weathering (Simon, 1987a). The »arkose-like breccia« does not contain components derived from the lower Palaeozoic deposits of the area.     

Pre-Variscan basement rocks in southern Poland: Where is the southeastern margin of eastern Avalonia (Cadomia)?

Summary Pre-Variscan basement in southern Poland is poorly exposed and thus known mostly from subsurface data. The availability of the latter is reviewed for terrains located between the Sudetes and the East European Platform. In these terrains the following relationships have been documented: Cadomian granitoids capped by Variscan flysch, Palaeozoic platform strata, Palaeozic folded and partly thermally altered successions, and low-grade metamorphic rocks overlain by Middle Cambrian strata. In view of their interrelationships the location of the Avalonia-Baltica suture in southeastern Poland is uncertain.     

Enzymological classification of salt lakes in Romania

Sediments of 56 salt lakes from Romania were studied enzymologically. The following 7 enzymatic and nonenzymatic catalytic activities have been measured: phosphatase, H₂O₂-splitting in nonautoclaved (catalase) and autoclaved samples, TTC reduction in nonautoclaved (dehydrogenase) and autoclaved samples, without or with glucose addition. A formula is proposed for the evaluation of the enzymatic potential of salt lake sediments or other habitats. A hierarchy of the studied lakes has been established on the basis of the enzymatic potential of their sediments expressed as enzymatic indicator.     

Rewriting the book of the city: on old signs,new technologies,and reinventing Adelaide

Can a sense of ownership over constantly changing urban places be generated through pedestrian exploration and everyday digital media practice? This paper begins with the author’s visit to the city of Adelaide, where a chance encounter – an intriguing sign painted on the wall of a city building – led to a hunt through the city for ghost signs, the remnants of old hand-painted advertisements. This spontaneous activity, combined with the online exploration and image sharing that followed, generated a renewed feeling of connection to, and ownership over, an erstwhile familiar locale. The experience is analysed through the work of theorists investigating change and belonging in modern cities including Guy Debord, Doreen Massey, Michel de Certeau, Andreas Huyssen, and Mark Crinson, as well as the contemporary growth in both politically inspired urban exploring (“Urbex” or “place hacking”) and the digital documentation and sharing of ghost signs and other urban ephemera.