TY - THES A1 - Löwe, Peter T1 - Methoden der Künstlichen Intelligenz in Radarmeteorologie und Bodenerosionsforschung T1 - Artificial Intelligence Methods in Radar-Meteorology and Soil Erosion Research N2 - Die Dissertation "Methoden der Künstlichen Intelligenz in Radarmeteorologie und Bodenerosionsforschung" beschäftigt sich mit der Erfassung des Parameters der potentiellen Erosivität vor dem Hintergrund der Bodenerosionsproblematik Südafrikas. Basierend auf der Betrachtung der Erosivität einzelner Niederschlagsereignisse wird demonstriert, wie durch wissensbasierte Ansätze aus Wetterradardatensätzen flächendeckende Niederschlagsinformationen gewonnen werden können. Diese dienen als Eingangsdaten für ein Erosivitätsmodell, das aus Zellulären Automaten aufgebaut wird. Die Ergebnisse des Erosivitätsmodells werden vorgestellt und diskutiert. N2 - The dissertation "Artificial Intelligence Methods in Radarmeteorology and Soil Erosion Research" discusses the assessment of potential rainfall erodibility in regard to soil erosion processes in South Africa. Knowledge-based approaches are used to derive rainfall information from weather radar data for the recording of erosivity pulses from individual rainfall events. This precipitation data is used as input for a erosivity modell consisting built out of cellular automata. The results generated by the modell are presented and discussed. KW - Südafrika KW - Bodenerosion KW - Radarmeteorologie KW - Künstliche Intelligenz KW - GRASS KW - Bodenerosion KW - Radarmeteorologie KW - Künstliche Intelligenz KW - GRASS GIS KW - Südafrika KW - Soil Erosion KW - Radar-Meteorology KW - Artificial Intelligence KW - GRASS GIS KW - South Africa Y1 - 2003 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-7594 ER - TY - JOUR A1 - Ibebuchi, Chibuike Chiedozie T1 - Revisiting the 1992 severe drought episode in South Africa: the role of El Niño in the anomalies of atmospheric circulation types in Africa south of the equator JF - Theoretical and Applied Climatology N2 - During strong El Niño events, below-average rainfall is expected in large parts of southern Africa. The 1992 El Niño season was associated with one of the worst drought episodes in large parts of South Africa. Using reanalysis data set from NCEP-NCAR, this study examined circulation types (CTs) in Africa south of the equator that are statistically related to the El Niño signal in the southwest Indian Ocean and the implication of this relationship during the 1992 drought episode in South Africa. A statistically significant correlation was found between the above-average Nino 3.4 index and a CT that features widespread cyclonic activity in the tropical southwest Indian Ocean, coupled with a weaker state of the south Indian Ocean high-pressure. During the analysis period, it was found that the El Niño signal enhanced the amplitude of the aforementioned CT. The impacts of the El Niño signal on CTs in southern Africa, which could have contributed to the 1992 severe drought episode in South Africa, were reflected in (i) robust decrease in the frequency of occurrence of the austral summer climatology pattern of atmospheric circulation that favors southeasterly moisture fluxes, advected by the South Indian Ocean high-pressure; (ii) modulation of easterly moisture fluxes, advected by the South Atlantic Ocean high-pressure, ridging south of South Africa; (iii) and enhancement of the amplitude of CTs that both enhances subsidence over South Africa, and associated with the dominance of westerlies across the Agulhas current. Under the ssp585 scenario, the analyzed climate models suggested that the impact of radiative heating on the CT significantly related to El Niño might result in an anomalous increase in surface pressure at the eastern parts of South Africa. KW - South Africa KW - drought KW - El Niño Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-268569 SN - 1434-4483 VL - 146 IS - 1-2 ER - TY - JOUR A1 - Ibebuchi, Chibuike Chiedozie T1 - Circulation pattern controls of wet days and dry days in Free State, South Africa JF - Meteorology and Atmospheric Physics N2 - Atmospheric circulation is a vital process in the transport of heat, moisture, and pollutants around the globe. The variability of rainfall depends to some extent on the atmospheric circulation. This paper investigates synoptic situations in southern Africa that can be associated with wet days and dry days in Free State, South Africa, in addition to the underlying dynamics. Principal component analysis was applied to the T-mode matrix (variable is time series and observation is grid points at which the field was observed) of daily mean sea level pressure field from 1979 to 2018 in classifying the circulation patterns in southern Africa. 18 circulation types (CTs) were classified in the study region. From the linkage of the CTs to the observed rainfall data, from 11 stations in Free State, it was found that dominant austral winter and late austral autumn CTs have a higher probability of being associated with dry days in Free State. Dominant austral summer and late austral spring CTs were found to have a higher probability of being associated with wet days in Free State. Cyclonic/anti-cyclonic activity over the southwest Indian Ocean, explained to a good extent, the inter-seasonal variability of rainfall in Free State. The synoptic state associated with a stronger anti-cyclonic circulation at the western branch of the South Indian Ocean high-pressure, during austral summer, leading to enhanced low-level moisture transport by southeast winds was found to have the highest probability of being associated with above-average rainfall in most regions in Free State. On the other hand, the synoptic state associated with enhanced transport of cold dry air, by the extratropical westerlies, was found to have the highest probability of being associated with (winter) dryness in Free State. KW - South Africa KW - atmospheric circulation KW - circulation patterns Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-268552 SN - 1436-5065 VL - 133 IS - 5 ER - TY - JOUR A1 - Höhn, Stefan A1 - Frimmel, Hartwig E. A1 - Debaille, Vinciane A1 - Price, Westley T1 - Pre‐Klondikean oxidation prepared the ground for Broken Hill‐type mineralization in South Africa JF - Terra Nova N2 - New Cu isotope data obtained on chalcopyrite from the Black Mountain and the Broken Hill deposits in the medium‐ to high‐grade metamorphic Aggeneys‐Gamsberg ore district (South Africa) require a revision of our understanding of the genesis of metamorphic Broken Hill‐type massive sulphide deposits. Chalcopyrite from both deposits revealed unusually wide ranges in δ\(^{65}\)Cu (−2.41 to 2.84‰ NIST 976 standard) in combination with distinctly positive mean values (0.27 and 0.94‰, respectively). This is interpreted to reflect derivation from various silicate and oxide precursor minerals in which Cu occurred in higher oxidation states. Together with the observation of a typical supergene base metal distribution within the deposits and their spatial association with an unconformity only meters above the ore horizon, our new data are best explained by supergene oxidation of originally possibly SEDEX deposits prior to metamorphic sulphide formation, between the Okiepian (1,210–1,180 Ma) and Klondikean (1,040–1,020 Ma) orogenic events. KW - South Africa KW - mineralization KW - Broken Hill Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218545 VL - 33 IS - 2 SP - 168 EP - 173 ER - TY - THES A1 - Bangert, Berthold T1 - Tephrostratigraphy, petrography, geochemistry, age and fossil record of the Ganigobis Shale Member and associated glaciomarine deposits of the Dwyka Group, Late Carboniferous, southern Africa T1 - Tephrostratigraphie, Petrographie, Geochemie, Alter und Fossilinhalt des "Ganigobis Shale Members" und assozierte, glaziomarine Ablagerungen der Dwyka Gruppe, Oberkarbon, südliches Afrika N2 - Thin, pyroclastic marker beds are preserved in argillaceous units of the Dwyka Group in southern Nambia and South Africa which are the earliest witnesses of volcanism in Karoo-equivalent strata of southern Africa. The aim of this study is to present the field appearance of these marker beds, to characterise their mineralogy, geochemistry and heavy mineral contents and to present new radiometric age data from their juvenile zircons. Carboniferous-Permian Karoo deposits in the Aranos Basin of southern Namibia include the glacially dominated, Carboniferous Dwyka Group and the shelf sediments of the overlying Permian Ecca Group. The Dwyka Group can be subdivided into four upward-fining deglaciation sequences, each capped by relatively fine-grained glaciolacustrine or glaciomarine deposits. The uppermost part of the second deglaciation sequence comprises a thick fossiliferous mudstone unit, referred to as the ”Ganigobis Shale Member”. An abundance of marine macro- and ichnofossils as well as extrabasinally derived ashfall tuff beds characterise the more than 40 m thick mudstones and provide the basis for an integrated high-resolution biostratigraphic and tephrostratigraphic framework. The Ganigobis Shale Member contains remains of paleoniscoid fishes, bivalves, gastropods, scyphozoa, crinoid stalks, sponges and sponge spicules, radiolaria, coprolites and permineralised wood. These mostly marine body and trace fossils record the extent of the first of a series of marine incursions into the disintegrating Gondwanan interior as early as the Carboniferous. Within the Ganigobis Shale Member 21 bentonitic tuff beds displaying a thickness of 0.1 and 2.0 cm were determined which in part can be traced laterally over tens of kilometres indicating an ashfall derivation. Further bentonitic tuff beds of the Dwyka Group were detected in cut banks of the Orange River near Zwartbas in the Karasburg Basin (southern Namibia). The 65 tuff beds vary between 0.1 and 4.0 cm in thickness. Due to a similar fossil content and age of the background deposits, the tuff beds are thought to have originated from the same source area as those from the Aranos Basin. Thin-sections reveal the derivation of the tuff beds as distal fallout ashes produced by explosive volcanic eruptions. The matrix consists of a micro- to cryptocrystalline clay mineral-quartz mixture. Rare fragments of splinter quartz, completely recrystallized ash-sized particles of former volcanic glass and few apatite and zircon grains are the only juvenile components. The tuff beds contain as non-opaque, juvenile heavy minerals mostly zircon, apatite, monazite and sphene but also biotite, garnet, hornblende and tourmaline. Geochemical analyses point to an original, intermediate to acid composition of the tuff samples. LREE enrichment and Eu-anomalies show that the parent magma of the tuff beds was a highly evolved calc-alkaline magma. Tectonomagmatic discrimination diagrams point to a volcanic arc setting. Bedding characteristics and the lack of any Carboniferous-Permian volcanic successions onshore Namibia makes an aeolian transport of the ash particles over larger distances likely. Siliceous ashes could thus have been transported by prevailing south-westerly winds from arc-related vents in South America to southern Africa. A second, more local source area could have been located in an intracontinental rift zone along the western margin of southern Africa which is indicated by north-south directed ice-flow directions in the Late Carboniferous. SHRIMP-based age determinations of juvenile magmatic zircons separated from the tuff beds allow a new time calibration of Dwyka Group deglaciation sequences II - IV and the Dwyka/Ecca boundary. Zircons of the Ganigobis Shale Member yield SHRIMP-ages of 302-300 Ma. This dates the uppermost part of the second deglaciation sequence in southern Namibia to the Late Carboniferous (Gzelian) and provides a minimum age for the onset of Karoo-equivalent marine deposition. The age of the uppermost argillaceous part of the third deglaciation sequence (297 Ma) was determined from zircons of a tuffaceous bed sampled in a roadcut in the Western Cape Province, South Africa. The deposits correlate with the Hardap Shale Member in the Aranos Basin of southern Namibia which are part of much more widespread Eurydesma transgression. The age of the Dwyka/Ecca boundary was determined by SHRIMP-measurements of juvenile zircons from two tuff beds of the basal Prince Albert Formation sampled in the Western Cape Province (South Africa). The zircons revealed ages of 289 - 288 Ma which date the Dwyka/Ecca boundary at about 290 Ma. According to these ages, deglaciation sequences II-IV lasted for 5 Ma on average. N2 - Geringmächtige, bentonitische Tuffe treten in Tonsteinabschnitten der karbonen Dwyka Gruppe im südlichen Namibia und Südafrika auf. Sie repräsentieren die ersten Hinweise auf eine vulkanische Tätigkeit innerhalb der Karoosedimente im südlichen Afrika. Die vorliegende Dissertation faßt die Geländebeschreibung der Tuffe, ihre Petrographie, Mineralogie und Geochemie zusammen. Juvenile Zirkone der Tuffe erlaubten eine radiometrisches Altersermittlung mittels SHRIMP-Analyse. Sie stellen somit die ersten radiometrisch exakt ermittelten Altersdaten innerhalb der Dwyka Gruppe dar. Permokarbone Karoosedimente des Aranos Beckens in Südnamibia setzen sich aus der glazigenen Dwyka Gruppe des Karbons und den Schelfsedimenten der folgenden Ecca Gruppe des Perms zusammen. Die Dwyka-Gruppe kann dabei in vier Entgletscherungssequenzen unterteilt werden. Der oberste Bereich jeder Entgletscherungssequenz ist meist durch glaziomarine Ablagerungen gekenn-zeichnet. Im Fall der zweiten Entgletscherungssequenz handelt es sich um einen mehr als 40 m mäch-tigen, fossilführenden Tonsteinabschnitt, der als ‘Ganigobis Shale Member’ bekannt ist. Eine Vielzahl von meist marinen Makro- und Spurenfossilien (palaeoniskoide Fischen, Bivalven, Gastropoden, Scyphozoen, Crinoideenstielglieder, Radiolarien) sowie distale Aschentuffe bilden die Grundlage für eine hochauflösende, biostratigraphische und tephrostratigraphische Gliederung des ‘Ganigobis Shale Members’. 21 bentonitische, lateral verfolgbare Aschentuffe mit einer Mächtigkeit zwischen 0.1 und 2.0 cm wurden innerhalb des ‘Ganigobis Shale Member’ bestimmt. 65 weitere, bis 4.0 cm mächtige Aschentuffe der Dwyka Gruppe wurden in Uferbänken des Orange Rivers in der Nähe von Zwartbas im Karasburg Becken Südnamibias entdeckt. Aufgrund eines ähnlichen Fossilinhaltes der Hinter-grundsedimente und eines ähnlichen Alters der Tuffe kann von dem gleichen Herkunftsgebiet der Aschen ausgegangen werden. Dünnschliffe der Tuffe zeigen, daß es sich bei den Horizonten um distale Aschenfallablagerungen handelt, die durch explosiven Vulkanismus gefördert wurden. Die Matrix besteht aus einer mikro- bis kryptokristallinem Tonmineral-Quarz- Mischung. Idiomorpher, hexagonaler Quarz, Splitterquarze und Quarzfragmente, vollständig rekristallisierte Aschenkörner und vereinzelt Schwerminerale wie Apatit und Zirkon sind weitere juvenile Komponenten. Folgende transparente, juvenile Schwerminerale treten auf: Zirkon, Apatit, Monazit, Titanit, Biotit, Granat, Hornblende und Turmalin. Geochemische Analysen weisen auf eine intermediäre bis saure Ausgangszusammensetzung der Tuffe hin. Die Anreicherung der LREE und die Eu-Anomalien zeigen, daß die Zusammensetzung des Ausgangsmagma der Tuffe kalkalkalisch und sehr differenziert war. Tektonomagmatische Diskrimi-nationsdiagramme deuten eine Subduktionszone als Herkunftsgebiet der Tuffe an. Die Korngröße der Tuffe und das Fehlen jeglicher permokarboner, vulkanischer Abfolgen in Namibia läßt auf einen Transport der Aschen über größere Distanzen schließen. Saure Aschen könnten bei vorherrschenden südwestlichen Windrichtungen von Südamerika, wo saurer Inselbogenmagmatismus im Permokarbon bekannt ist, nach Südafrika und Namibia transportiert worden sein. Ein zweites, lokaleres Herkunfts-gebiet der Aschentuffe könnte innerhalb einer kontinentalen Riftzone am Westrand des südlichen Afrikas gelegen haben. Sie ist im Oberkarbon durch allgemein nord-südgerichtete Eisstromrichtungen im Aranos und Karasburg Becken (Südnamibia) und im Perm durch die marinen Ablagerungen der Whitehill Formation (Ecca Gruppe) angedeutet. Altersbestimmungen an den juvenilen Zirkonen ermöglichten sowohl eine neue Zeiteinschätzung der Entgletscherungssequenzen II - IV innerhalb der Dwyka Gruppe als auch eine zeitliche Neukali-brierung der Dwyka-/Ecca Grenze. Datierte Zirkone aus Tuffen des Ganigobis Shale Members ergaben SHRIMP-Alter von 302 - 300 Ma. Damit fallen der oberste Bereich der zweiten Entgletscherungssequenz und die in den marinen enthaltenen Fossilien in das Oberkarbon (Gzelian). Das Alter des Topbereichs der dritten Entgletscherungssequenz (297 Ma) wurde an Zirkonen einer tuffitischen Schicht aus der Provinz Westkap in Südafrika bestimmt. Die dort aufgeschlossenen Ablagerungen korrelieren mit dem Hardap Shale Member im Aranos Becken Süd-namibias und sind Teil der weltweit bekannten Eurydesma - Transgression. Das Alter der Dwyka / Ecca-Grenze wurde an juvenilen Zirkonen von Tuffen der basalen Prince Albert Formation (Ecca Gruppe) in der Provinz Westkap (Südafrika) bestimmt. Die U-Pb - Messungen an den Zirkonen ergaben Alter von 289 - 288 Ma, die die Dwyka / Ecca-Grenze bei circa 290 Ma festlegen. KW - Südafrika KW - Namibia KW - Mariental KW - Tuff KW - Oberkarbon KW - Tephrostratigraphie KW - Gesteinskunde KW - Geochemie KW - Glaziomarines Sediment KW - Gondwana KW - Karoo KW - South Africa KW - Namibia KW - Dwyka Group KW - tuff KW - bentonite KW - glaciomarine KW - tephrostratigraphy KW - Gondwana KW - Karoo KW - Südafrika KW - Namibia KW - Dwyka Gruppe KW - Tuff KW - Bentonit KW - glaziomarin KW - Tephrostratigraphie Y1 - 2000 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-2233 ER -