The development of astrophysics in South Africa

A brief overview is given of the history of astrophysics in South Africa up to the beginning of the modern era.     

Seismic stratigraphic framework and depositional sequences in the Santos Basin,Brazil

The Santos Basin, situated offshore southern Brazil, is one of nine marginal rift basins in the equatorial South Atlantic. It formed by the collapse of a thermal dome in the late Jurassic and by subsequent rifting and opening of the South Atlantic in the early Cretaceous. Rifting was accompanied by immense volcanic outpouring seen at the surface today throughout the onshore Paraná Basin and thought to underlie the entire Santos Basin, and the adjacent São Paulo Plateau. Vulcanism was followed by subsidence of up to 10 km from Aptian to Recent time, and a coastal hingeline coincides with the Serra do Mar uplift. The basin depocentre, which is 700 km long, is bounded to the north and south by basement and volcanic highs, respectively. A restricted water circulation in the ocean basin, which prevailed up to the Santonian stage, has important repercussions for the hydrocarbon potential of the area. The nine genetically related basins have collective reserves of ≈ 5 billion barrels of oil and associated gas. A stratigraphic framework, based largely on seismic data, has been erected for the Santos Basin. Seven regional unconformities, or ‘R’ reflections, can be traced throughout the basin and form the boundaries for seismic sequences. Isopaching the seismic sequences defines the principal depositional units in the basin and also shows how the basin depocentre shifted with time. Limited well control has enabled the seismic sequences to be correlated with litho-environmental sequences which more fully reflect the geological evolution and provide a working exploration model. Finally, an attempt has been made to recognize and map seismic facies within the seismic sequences and to predict the lithofacies in areas away from well control     

Resolution analysis for discrete systems

summary . Treatments of geophysical inverse problems have tended to polarize into approaches intended to generate models either described by piecewise continuous functions or with some prior discretization. The two approaches are here developed in parallel, and the ideas of a trade-off between the anticipated error and the attainable level of detail in the model estimate are extended to the discrete case, either with even or uneven discretization.
An alternative approach to specifying the potential resolution of a model is to establish upper and lower bounds on parameter values. Linear programming methods are extended to determine bounds which allow for subjective limits on parameter values.
For a non-linear system the possible resolution may be investigated by estimation procedures based on the full set of successful solutions obtained by Monte-Carlo inversion.     

Observations on mass media reporting and individual motivation to obtain a flood inundation map—River Torrens,Adelaide, South Australia

A four-sheet set of flood inundation maps of the River Torrens floodplain in Adelaide, prepared as part of the River Torrens Flood Mitigation Study, was made available by the government in an attempt to inform the public about the flood risk. Prior levels of awareness were low, there not having been a significant flood in the area since 1931.Announcement of the Flood Mitigation Study and the maps' availability was made by news release, ministerial press conference and paid advertisements in the local press. A content analysis of the various news media's coverage of this event shows that the media generally ignored the floodplain maps and concentrated on other aspects of the news release.The maps were available free from state and local government offices, and records were kept of all persons requesting maps. In the first three months only 277 persons requested maps. Approximately two-thirds of these collected maps for personal reasons and the other one-third for occupational reasons. There was no relationship between the numbers of each sheet collected and the number of flood-prone premises on the sheet. One of the sheets shows no flood-affected premises but has been requested as much as any other sheet.The results are compared with sales figures of floodplain maps prepared for Brisbane, Queensland, after a disastrous flood there in 1974. The effect of experience of a flood is evident on both the population and the media in Brisbane when compared to Adelaide. In addition to low prior awareness of flood risk, the low prominence of the story in the mass media, the content of the media reports and the positions of the paid advertisements in the press all contributed to the poor community response to the maps.     

CAMEL DONGA METEORITE,A NEW EUCRITE FROM THE NULLARBOR PLAIN,WESTERN AUSTRALIA

Twelve stones, ranging up to 504 g (total weight 2.92 kg), of a very fresh eucrite have been collected from a 1 km² area on the Nullarbor Plain in Western Australia. The location is approximately 75 km N6°E from Nurina Siding on the Trans-Australian Railway; coordinates 30°19′S, 126°37′E. This eucrite consists almost entirely of pyroxene (mean composition Wo 16 Fs 49) and plagioclase (mean composition An 85) in approximate proportions 3: 2, with 2% almost pure Fe metal and accessory amounts of troilite, ilmenite, and an SiO₂ phase. Gabbroic and doleritic clasts are present in a groundmass of comminuted pyroxene and plagioclase. The chemical composition (weight per cent) is: SiO₂ 49.53, TiO₂ 0.74, Al₂O₃ 12.49, Cr₂O₃ 0.33, FeO 16.07, MnO 0.56, MgO 6.31, CaO 10.41, Na₂O 0.49, K₂O 0.04, P₂O₅ < 0.01, H₂O + < 0.1, H₂O — 0.07, Fe metal 2.07, Ni < 0.01, Co < 0.01, FeS 0.19, C 0.03, sum 99.33.     

THE COMPOSITION OF THE CHASSIGNY METEORITE

Spark source mass spectrometric analysis of the Chassigny meteorite has given the following data (in ppm): Rb 0.4, Sr 7.2, Y 0.64, Zr 1.5, Nb 0.32, Ba 7.1, La 0.39, Ce 1.12, Pr 0.13, Nd 0.54, Sm 0.11, Eu 0.038, Gd 0.11, Tb 0.02, Dy 0.12, Ho 0.03, Er 0.09, Yb 0.10, Pb 1.0, Th 0.057, U 0.021. These data, in conjunction with major element composition and mineralogical and textural features, indicate that this meteorite is an olivinerich cumulate, possibly genetically related to the nakhlites.     

Charles Dickens and London: The visible and the opaque

The map is to geography what verisimilitude is to the history of the novel: the visual dominance of the one, and the omnipotent realism of the other, are powerful tools for representing a city like nineteenth century London. Dickens's of London may have relied on verisimilitude, but it did so in a way that transgressed its own terms of reference, questioning reference even as landmarks and signposts. The geographer's map may illustrate reference points, St. Paul's and the Monument, but in Dickens no objective totality is established for the reader. Instead a constellation of named places becomes representative of the reputed governance of the city as a whole. Dickens's landscape simultaneously establishes and transgresses the half-secured foundations of the relationship between individuals and the environment. Contrats and contradictions are multiplied in crowd symbols, caricatures, and historical reversions. Verisimilitude and the visible are representative of the way in which Dickens sought to penerate the opaqueness of the city of crime and cholera. The figure that best illustrates Dicken's coming to terms with the city is the diligent detective probing every obscure nook and cranny. He shows how verisimilitude acts in the service of the relationship between the visible and the opaque.     

Late Albian–Coniacian planktic foraminifera and biostratigraphy of the northeastern Caucasus

This paper presents a considerably revised biostratigraphy for Upper Albian through Coniacian pelagic limestone and shale sequences in the northeastern Caucasus region based primarily on planktic foraminiferal distributions. The use of concentrated acetic acid for the extraction of microfossils from the hard limestones has yielded a much more detailed planktic foraminiferal biostratigraphy than has been documented previously. Because of the low latitude location of the study area the high diversity assemblages contain many of the biomarkers used to identify standard Tethyan biozones ranging from the Rotalipora appenninica Zone through the Dicarinella concavata Zone. A key result of this study is the recognition of an apparently continuous Cenomanian/Turonian boundary interval within a laminated, dark marl that is enriched in organic carbon. Extinction of the single-keeled rotaliporids corresponds with the onset of deposition of the laminated marl beds.