Relationships between shelf‐edge trajectories and sediment dispersal along depositional dip and strike: a different approach to sequence stratigraphy

Analysis of shelf‐edge trajectories in prograding successions from offshore Norway, Brazil, Venezuela and West Africa reveals systematic changes in facies associations along the depositional dip. These changes occur in conjunction with the relative sea‐level change, sediment supply, inclination of the substratum and the relief of the margin. Flat and ascending trajectories generally result in an accumulation of fluvial and shallow marine sediments in the topset segment. Descending trajectories will generally result in erosion and bypass of the topset segment and deposition of basin floor fans. An investigation of incised valley fills reveals multiple stages of filling that can be linked to distinct phases of deepwater fan deposition and to the overall evolution of the margin. In the case of high sediment supply, like the Neogene Niger and Orinoco deltas, basin floor fans may develop systematically even under ascending trajectory styles. In traditional sequence stratigraphic thinking, this would imply the deposition of basin floor fans during a period of relative sea‐level highstand. Facies associations and sequence development also vary along the depositional strike. The width and gradient of the shelf and slope show considerable variations from south to north along the Brazilian continental margin during the Cenozoic. During the same time interval, the continental shelf may display high or low accommodation conditions, and the resulting stacking patterns and facies associations may be utilized to reconstruct palaeogeography and for prediction of lithology. Application of the trajectory concept thus reveals nuances in the rock record that would be lost by the application of traditional sequence stratigraphic work procedures. At the same time, the methodology simplifies the interpretation in that less importance is placed on interpretation and labelling of surface boundaries and systems tracts.     

Climate change: impacts on electricity markets in Western Europe

This paper studies some impacts of climate change on electricity markets, focusing on three climate effects. First, demand for electricity is affected because of changes in the temperature. Second, changes in precipitation and temperature have impact on supply of hydro electric production through a shift in the inflow of water. Third, plant efficiency for thermal generation will decrease because the temperature of water used to cool equipment increases. To find the magnitude of these partial effects, as well as the overall effects, on Western European energy markets, we use the multi-market equilibrium model LIBEMOD. We find that each of the three partial effects changes the average electricity producer price by less than 2%, while the net effect is an increase of only 1%. The partial effects on total electricity supply are small, and the net effect is a decrease of 4%. The greatest effects are found for Nordic countries with a large market share for reservoir hydro. In these countries, annual production of electricity increases by 8%, reflecting more inflow of water, while net exports doubles. In addition, because of lower inflow in summer and higher in winter, the reservoir filling needed to transfer water from summer to winter is drastically reduced in the Nordic countries.     

A slow-down treatment for close binaries

We present a new method for fast numerical integration of close binaries inN-body systems. The basic idea is to slow down the motion of the binary artificially, which makes a faster numerical integration possible but still maintains correct treatment of secular and long-period effects on the motion. We discuss the general principle, with application to close binaries inN-body codes and in the chain regularization.     

Feldspathoidal rocks from the Cainozoic volcanic province of Ethiopia

A review of the occurrence of feldspathoidal rocks in the Cainozoic volcanic province of Ethiopia is given. Ijolite and melanephelinite are described for the first time from this province. The close relationship between cross-rift transcurrent faults and situation of peralkaline rocks, including the feldspathoidal varieties, is emphasized. No feldspathoidal rocks are known from within the Ethopian rift system, being restricted to the interiors of the Ethiopian and Somalian plateaux.     

Fluid flow and alkali transport within a metamorphic terrane, western North Carolina

This paper presents preliminary results from study of a metasedimentary terrane near the Great Smoky Mountains of North Carolina. Grade of metamorphism ranges from garnet to staurolite-kyanite zone. The stratigraphic section is dominated by metasandstone but contains thick pelitic horizons over the central portion (Anakeesta Formation) of the studied interval. Metasandstone beds contain numerous isolated calcite concretions; these react to form leucocratic calc-silicate rock at variable grade of metamorphism. Metasandstones themselves are unreactive. Study of calc-silicate reaction permits the following statements regarding fluid flow and alkali transport within the studied terrane.Within unreacted concretions, the typical mineral assemblage is quartz-oligoclase-muscovite-biotite-calcite. Reaction between micas and calcite proceeded through several stages, forming as prograde minerals andesine/bytownite, clinozoisite, zoisite, garnet, hornblende, and chlorite. Reaction occurred in the presence of a fluid phase containing a H₂O/CO₂ ratio of 9 and resulted in massive expulsion of Na₂O, K₂O and CO₂. Since postulated reactions would have produced, on average, a fluid phase whose H₂O/CO₂ ratio is only one, flow of water-rich fluid through the concretions accompanied reaction. Rough estimate suggests a volumetric ratio of external fluid to rock of at least 1.1.The metamorphic grade at which concretions undergo reaction is controlled by stratigraphic position of the host metasandstone relative to metashale. Within the Anakeesta Formation and overlying strata, extensive reaction occurs near the pelitic staurolite and kyanite isograds. Within massive metasandstones of the underlying strata, reaction is delayed to the middle staurolite-kyanite zone, 5 km upgrade. Some reaction occurs within the upper garnet zone, but this is restricted to certain thin metasandstone beds interlayered with metashale. Study of dehydration reactions within metashale demonstrates that calc-silicate reaction was coupled to production of H₂O-rich fluids within pelitic strata.Transport of H₂O-rich fluids beyond outcrop scale was by advection. Diffusion was limited to outcrop distance. On most outcrops, all isolated concretions show the same degree of reaction. But at larger scale separate metasandstone packets bounded by metashale show differing degrees of reaction. Also, all rocks underwent some degree of penetrative deformation during time of reaction. The suggestion is made that advective flow was in fact channelized into fractures within metasandstone, and that diffusion between fractures promoted reaction within outcrop-size volumes of rock. Overall direction of fluid transport was in part upsection and in part channelized within metasandstone strata. Downsection flow was limited.For the most part alkalis liberated by calc-silicate reaction appear to have left the terrane. Metasandstones do not appear to constitute a sink for alkalis, and no sink of any sort was found for sodium. Potassium metasomatism of pelitic rock did occur and is marked by conversion of chlorite to biotite. But such K deposition is limited to sections within which metashale and calc-silicate rock are within outcrop distance. No sink is evident for most liberated potassium. It is within conjecture that the liberated elements caused alkali metasomatism elsewhere within the metamorphic belt, but such an event has yet to be demonstrated.     

The sagatu ridge dike swarm, ethiopian rift margin

A swarm of dikes forms the core of the Sagatu Ridge, a 70 km long topographic feature elevated to more than 4000 m above sea level and 1500 m above the level of the Eastern (Somalian) plateau. The ridge trends NNE and lies about 50 km east of the northeasterly trending rift-valley margin. Intrusion of the dikes and buildup of the flood-lava pile, largely hawaiitic but with trachyte preponderant in the final stages, occurred during the late Pliocene-early Pleistocene and may have been contemporaneous with downwarping of the protorift trough to the west. The ensuing faulting that formed the present rift margin, however, bypassed the ridge. The peculiar situation and orientation of the Sagatu Ridge, and its temporary existence as a line of crustal extension and voluminous magmatism, are considered related to a powerful structural control by a major line of Precambrian crustal weakness, well exposed further south. Transverse rift structures of unknown type appear to have limited the development of the ridge to north and south.     

QUADRATIC PLS REGRESSION

We treat here an extension of linear PLS regression to include regression on quadratic PLS components.The quadratic regression can be viewed as a natural extension of linear PLS regression to quadratic PLSaccording to the H-principle of mathematical modelling.The numerical implementation is treated indetail.It is shown that this approach can be used for models with large numbers of variables.Somemodelling strategies are discussed depending on the purpose of the modelling.Applications of thisapproach are treated.     

Experimental modelling of shallow magma emplacement: Application to saucer-shaped intrusions

Saucer-shaped dolerite and sandstone intrusions are common in sedimentary basins world-wide. We have conducted a series of scaled experiments simulating the process of magma emplacement in sedimentary basins, with particular attention on the formation of saucer-shaped sills. The model materials were (1) cohesive fine-grained silica flour, representing brittle crust; and (2) molten low-viscosity oil, representing magma. The experiments were performed in both homogeneous and layered models. In all the experiments, oil injection resulted in doming of the surface. In the homogeneous models, the injected oil formed cone sheets and sub-vertical dykes. Cone sheets formed for shallow injection (1–3 cm), and vertical dykes formed for deeper injection (4–5 cm). In layered models, the injected oil always formed saucer-shaped intrusions. Our experimental results show that (1) sill intrusion results in the formation of a dome, with melt erupting at the rim; (2) layering controls the formation of sills and saucer-shaped sills; (3) saucer-shaped sills are fed from the bottom and the fluid flows upward and outward; and (4) the diameter of saucer-shaped sills increase with increasing emplacement depth. The systematic relation between domes and sills and the depth-dependence of sill diameters show that saucer-shaped intrusions result from the interaction between a growing flat-lying shallow sill and doming of the free surface. We conclude that saucer-shaped intrusions represent fundamental geometries formed by shallow magma intrusion in stratified basins.