A Stochastic Object Model Conditioned to High-Quality Seismic Data

We present an approach for modeling facies bodies in which a highly constrained stochastic object model is used to integrate detailed seismic interpretation of the reservoir’s sedimentological architecture directly in a three-dimensional reservoir model. The approach fills the gap between the use of seismic data in a true deterministic sense, in which the facies body top and base are resolved and mapped directly, and stochastic methods in which the relationship between seismic attributes and facies is defined by conditional probabilities. The lateral geometry of the facies bodies is controlled by seismic interpretations on horizon slices or by direct body extraction, whereas facies body thickness and cross-sectional shape are defined by a mixture of seismic data, well data, and user defined object shapes. The stochastic terms in the model are used to incorporate local geometric variability, which is used to increase the geological realism of the facies bodies and allow for correct, flexible well conditioning. The result is a set of three-dimensional facies bodies that are constrained to the seismic interpretations and well data. Each body is defined as a parametric object that includes information such as location of the body axis, depositional direction, axis-to-margin normals, and external body geometry. The parametric information is useful for defining geologically realistic intrabody petrophysical trends and for controlling connectivity between stacked facies bodies.     

Armorican provenance for the mélange deposits below the Lizard ophiolite (Cornwall,UK): evidence for Devonian obduction of Cadomian and Lower Palaeozoic crust onto the southern margin of Avalonia

Devonian sedimentary rocks of the Meneage Formation within the footwall of the Lizard ophiolite complex in SW England are thought to have been derived from erosion of the over-riding Armorican microplate during collision with Avalonia and the closure of the Rheic Ocean. We further test this hypothesis by comparison of their detrital zircon suites with those of autochthonous Armorican strata. Five samples analysed from SW England (Avalonia) and NW France (Armorica) have a bimodal U–Pb zircon age distribution dominated by late Neoproterozoic to middle Cambrian (c. 710–518 Ma) and Palaeoproterozoic (c. 1,800–2,200 Ma) groupings. Both can be linked with lithologies exposed within the Cadomian belt as well as the West African craton, which is characterized by major tectonothermal events at 2.0–2.4 Ga. The detrital zircon signature of Avalonia is distinct from that of Armorica in that there is a much larger proportion of Mesoproterozoic detritus. The common provenance of the samples is therefore consistent with: (a) derivation of the Meneage Formation mélange deposits from the Armorican plate during Rheic Ocean closure and obduction of the Lizard Complex and (b) previous correlation of quartzite blocks within the Meneage Formation with the Ordovician Grès Armoricain Formation of NW France.     

Air–Sea Interaction Features in the Baltic Sea and at a Pacific Trade-Wind Site: An Inter-comparison Study

A systematic comparison of wind profiles and momentum exchange at a trade wind site outside Oahu, Hawaii and corresponding data from the Baltic Sea is presented. The trade wind data are to a very high degree swell dominated, whereas the Baltic Sea data include a more varied assortment of wave conditions, ranging from a pure growing sea to swell. In the trade wind region swell waves travel predominantly in the wind direction, while in the Baltic, significant cross-wind swells are also present. Showing the drag coefficient as a function of the 10-m wind speed demonstrates striking differences for unstable conditions with swell for the wind-speed range 2 m s^?1 < U ₁₀ < 7 m s^?1, where the trade-wind site drag values are significantly larger than the corresponding Baltic Sea values. In striking contrast to this disagreement, other features studied are surprisingly similar between the two sites. Thus, exactly as found previously in Baltic Sea studies during unstable conditions and swell, the wind profile in light winds (3 m s^?1) shows a wind maximum at around 7–8 m above the water, with close to constant wind speed above. Also, for slightly higher wind speeds (4 m s^?1 < U ₁₀ < 7 m s^?1), the similarity between wind profiles is striking, with a strong wind-speed increase below a height of about 7–8 m followed by a layer of virtually constant wind speed above. A consequence of these wind-profile features is that Monin–Obukhov similarity is no longer valid. At the trade-wind site this was observed to be the case even for wind speeds as high as 10 m s^?1. The turbulence kinetic energy budget was evaluated for four cases of 8–16 30- min periods at the trade-wind site, giving results that agree very well with corresponding figures from the Baltic Sea.     

The ammonite fauna and genesis of a mid-Cretaceous siliceous oolite from the Alagoas Basin, Brazil

Acanthoceratid ammonites from near Maceió, in the State of Alagoas, provide evidence of a mid-Cretaceous marine incursion into the present onshore part of the Alagoas Basin. The ammonites Pseudocalycoceras sp. cf. P. harpax (Stoliczka, 1864) and Kamerunoceras sp. are assigned a late Cenomanian age. The rock is a siliceous oolite that occurs as derived nodules and fragments in late Cenozoic continental sediments. It is interpreted as an originally calcareous oolite formed in a near-shore, high-energy environment. Absence of primary cement suggests that silicification took place early in diagenesis. The silicified, and therefore more resistant material from the original Cenomanian sequence was reworked and redeposited with the Cenozoic sediments. The age, indicated by the ammonites, suggests that the original deposition was related to the global late Cenomanian—early Turonian sea-level rise.     

A high sampling-density polarization study of the Southern Coalsack

We present a densely sampled map of visual polarimetry of stars in the direction of the Southern Coalsack dark cloud. Our sample consists of new polarimetric observations of 225 stars drawn from the spectrophotometric survey of Seidensticker, and an additional 173 stars, covering the surrounding areas of the cloud, taken from the literature. Because all the target stars have at least spectroscopic parallaxes, we can reliably investigate the spatial origins of the polarization, in three dimensions. We decompose the polarization into three components, due to (i) the wall of the local hot bubble, (ii) the Coalsack cloud and (iii) material in the Carina spiral arm. The polarization due to the Coalsack varies, both in alignment efficiency  ( p / A_V )  and in the dispersion in polarization angle, across the cloud. Using a simplified radiative transfer treatment we show that the measured polarization in background gas is significantly affected by foreground polarization, and specifically that the analysis of the Coalsack polarization must take the effects of the local hot bubble wall into consideration. Correcting for this effect as well as for the internal line-of-sight averaging in the Coalsack, we find, based on a Chandrasekhar–Fermi analysis, a plane-of-the-sky magnetic field for the Coalsack cloud of  〈 B _⊥〉= 93 ± 23 μG  . A systematic error, best described by a multiplicative factor between 0.5 and 1.5, additionally arises from radiative transfer effect uncertainties. We propose that this high value for the magnetic field in the cloud envelope is due to the fact that the Coalsack cloud is embedded in the hot interior of the Upper Centaurus–Lupus superbubble.     

Gravitational waves from freely precessing neutron stars

In this paper we model the gravitational wave emission of a freely precessing neutron star. The aim is to estimate likely source strengths, as a guide for gravitational wave astronomers searching for such signals. We model the star as a partly elastic, partly fluid body with quadrupolar deformations of its moment of inertia tensor. The angular amplitude of the free precession is limited by the finite breaking strain of the star's crust. The effect of internal dissipation on the star is important, with the precession angle being rapidly damped in the case of a star with an oblate deformation. We then go on to study detailed scenarios where free precession is created and/or maintained by some astrophysical mechanism. We consider the effects of accretion torques, electromagnetic torques, glitches and stellar encounters. We find that the mechanisms considered are either too weak to lead to a signal detectable by an Advanced LIGO interferometer, or occur too infrequently to give a reasonable event rate. We therefore conclude that, using our stellar model at least, free precession is not a good candidate for detection by the forthcoming laser interferometers.