Geophysics Competency

Bellville, South Africa

Geophysics Competency

Bellville, South Africa
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Roberts D.L.,University of the Free State | Neumann F.H.,University of Munster | Neumann F.H.,University of Witwatersrand | Neumann F.H.,Nelson Mandela Metropolitan University | And 9 more authors.
Global and Planetary Change | Year: 2017

A multi-proxy study of an offshore core in Saldanha Bay (South Africa) provides new insights into fluvial deposition, ecosystems, phytogeography and sea-level history during the late Paleogene-early Neogene. Offshore seismic data reveal bedrock topography, and provide evidence of relative sea levels as low as − 100 m during the Oligocene. 3D landscape reconstruction reveals hills, plains and an anastomosing river system. A Chattian or early Miocene age for the sediments is inferred from dinoflagellate taxa Distatodinium craterum, Chiropteridium lobospinosum, Homotryblium plectilum and Impagidinium paradoxum. The subtropical forest revealed by palynology includes lianas and vines, evergreen trees, palms and ferns, implying higher water availability than today, probably reduced seasonal drought and stronger summer rainfall. From topography, sedimentology and palynology we reconstruct Podocarpaceae-dominated forests, Proto-Fynbos, and swamp/riparian forests with palms and other angiosperms. Rhizophoraceae present the first South African evidence of Palaeogene/Neogene mangroves. Subtropical woodland-thicket with Combretaceae and Brachystegia (Peregrinipollis nigericus) probably developed on coastal plains. Some of the last remaining Gondwana elements on the sub-continent, e.g., Araucariaceae, are recorded. Charred particles signal fires prior to the onset of summer dry climate at the Cape. Marine and terrestrial palynomorphs, together with organic and inorganic geochemical proxy data, suggest a gradual glacio-eustatic transgression. The data shed light on Southern Hemisphere biogeography and regional climatic conditions at the Palaeogene-Neogene transition. The proliferation of the vegetation is partly ascribed to changes in South Atlantic oceanographic circulation, linked to the closure of the Central American Seaway and the onset of the Benguela Current ~ 14 Ma. © 2017

Hahn A.,University of Bremen | Schefuss E.,University of Bremen | Ando S.,University of Milan Bicocca | Cawthra H.C.,Geophysics Competency | And 6 more authors.
Climate of the Past | Year: 2017

Due to the high sensitivity of southern Africa to climate change, a reliable understanding of its hydrological system is crucial. Recent studies of the regional climatic system have revealed a highly complex interplay of forcing factors on precipitation regimes. This includes the influence of the tropical easterlies, the strength of the southern hemispheric westerlies as well as sea surface temperatures along the coast of the subcontinent. However, very few marine records have been available in order to study the coupling of marine and atmospheric circulation systems. Here we present results from a marine sediment core, recovered in shallow waters off the Gouritz River mouth on the south coast of South Africa. Core GeoB18308-1 allows a closer view of the last ∼4 kyr. Climate sensitive organic proxies, like the distribution and isotopic composition of plant-wax lipids as well as indicators for sea surface temperatures and soil input, give information on oceanographic and hydrologic changes during the recorded time period. Moreover, the micropaleontology, mineralogical and elemental composition of the sediments reflect the variability of the terrigenous input to the core site. The combination of down-core sediment signatures and a catchment-wide provenance study indicate that the Little Ice Age (∼300-650 calg yr BP) was characterized by climatic conditions favorable to torrential flood events. The Medieval Climate Anomaly (∼950-650 cal yr BP) is expressed by lower sea surface temperatures in the Mossel Bay area and humid conditions in the Gouritz River catchment. These new results suggest that the coincidence of humid conditions and cooler sea surface temperatures along the south coast of South Africa resulted from a strengthened and more southerly anticyclonic circulation. Most probably, the transport of moisture from the Indian Ocean by strong subtropical easterlies was coupled with Agulhas Bank upwelling pulses, which were initiated by an increase in Agulhas Current strength. © Author(s) 2017.

Copeland S.R.,Los Alamos National Laboratory | Copeland S.R.,University of Colorado at Boulder | Cawthra H.C.,Geophysics Competency | Cawthra H.C.,Nelson Mandela Metropolitan University | And 9 more authors.
Quaternary Science Reviews | Year: 2016

Middle Stone Age sites located within the Greater Cape Floristic Region on the South African southern coast have material culture with early evidence for key modern human behaviors such as projectile weaponry, large animal hunting, and symbolic behavior. In order to interpret how and why these changes evolved, it is necessary to understand their ecological context as it has direct relevance to foraging behavior. During periods of lowered sea level, a largely flat and vast expanse of land existed south of the modern coastline, but it is now submerged by higher sea levels. This exposed area, the Paleo-Agulhas Plain, likely created an ecological context unlike anything in the region today, as evidenced by fossil assemblages dominated by migratory ungulates. One hypothesis is that the Paleo-Agulhas Plain supported a migration ecosystem of large grazers driven by summer rainfall, producing palatable forage during summer in the east, and winter rainfall, producing palatable forage during winter in the west. Alternatively, ungulates may have been moving from the coastal plain in the south to the interior north of the Cape Fold Mountains, as observed for elephants in historic times.In this study, we assess ungulate movement patterns with inter- and intra-tooth enamel samples for strontium isotopes in fossil fauna from Pinnacle Point sites PP13B and PP30. To accomplish our goals we created a bioavailable 87Sr/86Sr isoscape for the region by collecting plants at 171 sampling sites and developing a geospatial model. The strontium isotope results indicate that ungulates spent most of their time on the Paleo-Agulhas Plain and avoided dissected plain, foothill, and mountain habitats located more than about 15 km north of the modern coastline. The results clearly exclude a north-south (coastal-interior) movement or migration pattern, and cannot falsify the east-west movements hypothesized in the south coast migration ecosystem hypothesis. © 2016 Elsevier Ltd.

Midzi V.,Geophysics Competency | Zulu B.,Geophysics Competency | Manzunzu B.,Geophysics Competency | Mulabisana T.,Geophysics Competency | And 3 more authors.
Journal of Seismology | Year: 2015

On 5 August 2014 at 1222 hours (local time), an earthquake of local magnitude ML = 5.5 occurred in the Orkney area in the North West Province, South Africa. The earthquake shaking was felt widely in South Africa as far as Cape Town as well as in Maputo, Mozambique, and Gaborone in Botswana. One person was killed when a wall collapsed on him, and more than 600 houses were damaged. Following the earthquake, many people submitted reports to the Council for Geoscience (CGS) through an online questionnaire which recorded their experience, whilst others reported the event and its effects on social networks like Twitter and in newspapers. The CGS also sent out a team of scientists to further assess the effects of the event in the community by interviewing members of the public and completing additional questionnaires. A total of 866 observations were collected. Analysis of the collected macroseismic data produced 170 intensity data points which showed that a maximum intensity of VII was experienced in communities located in the epicentral area. The observed attenuation of intensity values was comparable to that observed on the French stable continental region especially in the area of 600-km radius from the epicentre. Airborne geophysical data were used to try and identify the fault along which the earthquake occurred. This was necessary as there was no surface expression of the earthquake and no previously identified fault near the epicentre. The interpretation of the data showed a fault located about 500 m from the epicentre appearing to form a boundary to the east of located aftershocks. © 2015, Springer Science+Business Media Dordrecht.

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