@misc{Geiger2000, type = {Master Thesis}, author = {Geiger, Markus}, title = {The Geology of the southern Warmbad Basin Margin - Tephrostratigraphy, Age, Fossil Record and Sedimentary Environment of Carboniferous-Permian Glacigenic Deposits of the Dwyka Group, Zwartbas, southern Namibia}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-46251}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2000}, abstract = {At Zwartbas, about 10 km west of Vioolsdrif, southern Namibia, the Dwyka succession is composed of tillites and distal fossiliferous dropstone-bearing glacio-marine shales. The completely exposed Dwyka succession is interbedded with thin bentonites, altered distal pyroclastic deposits, which were derived from the magmatic arc at the southern rim of Gondwana. Dropstone-bearing and dropstonefree sequences intercalate with four diamictites, of which the two lowest were certainly recognised as tillites. Four events of deglaciation were proven at Zwartbas and thus consist with correlative deposits in southern Africa. Numerous fossilised fishes, trace fossils, and plant fragments appear frequently within the lower half of the Dwyka succession whereas trace fossils were principally found in the complete succession. Although the environmental determination is quite problematic, the fossil assemblage rather implies proximal, shallow water conditions with temporary restricted oxygenation. The hinterland was covered with considerable vegetation, which points to a moderate climate. Water salinity determinations based on shale geochemistry rectify contrary palaeontological results and point to rather brackish or non-marine conditions in comparison to present-day salinites. Geochemical analyses of the bentonites relate the pyroclastic deposits with acid to intermediate source magmas, as they are known from the magmatic arc in present-day Patagonia. Tectono-magmatic comparisons furthermore emphasise a syn-collision or volcanic-arc situation of the magma source. However, significant cyclicity in the production of the pyroclastic deposits was not observed. Radiometric age determinations of two tuff beds clearly date the onset of glacial activity into the Late Carboniferous.}, subject = {Namibia}, language = {en} } @misc{Geiger1999, type = {Master Thesis}, author = {Geiger, Markus}, title = {An Explanation of the Geological Map 1:10000 of the Namibian borderland along the Orange River at Zwartbas - Warmbad District - Karas Region - Namibia}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-46269}, school = {Universit{\"a}t W{\"u}rzburg}, year = {1999}, abstract = {The locality of Zwartbas is situated at the border of Namibia and South Africa about 15 km west of Noordoewer. The mapped area is confined by the Tandjieskoppe Mountains in the north and the Orange River in the south. Outcropping rocks are predominantly sediments of the Nama Group and of the Karoo Supergroup. During the compilation of this paper doubts arose about the correct classification of the Nama rocks as it is found in literature. Since no certain clues were found to revise the classification of the Nama rocks, the original classification remains still valid. Thus the Kuibis and Schwarzrand Subgroup constitute the Nama succession and date it to Vendian age. A glacial unconformity represents a hiatus for about 260 Ma. This is covered by sediments of the Karoo Supergroup. Late Carboniferous and early Permian glacial deposits of diamictitic shale of the Dwyka and shales of the Ecca Group overlie the unconformity. The shales of the Dwyka Group contain fossiliferous units and volcanic ash-layers. A sill of the Jurassic Tandjiesberg Dolerite Complex (also Karoo Supergroup) intruded rocks at the Dwyka-Ecca-boundary. Finally fluvial and aeolian deposits and calcretes of the Cretaceous to Tertiary Kalahari Group and recent depositionary events cover the older rocks occasionally.}, subject = {Namibia}, language = {en} } @phdthesis{Beyer2001, author = {Beyer, Ulrike}, title = {Regionale Niederschlags{\"a}nderungen in Namibia bei anthropogen verst{\"a}rktem Treibhauseffekt}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-1181615}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2001}, abstract = {Diese Dissertation pr{\"a}sentiert Ergebnisse regionaler Niederschlagsabsch{\"a}tzungen f{\"u}r Namibia bei anthropogen verst{\"a}rktem Treibhauseffekt, die mit der Methode des Statistischen Downscaling erzielt wurden. {\"U}ber statistische Transferfunktionen werden Beziehungen zwischen großskaliger atmosph{\"a}rischer Zirkulation und Namibischen Sommerregen aufgestellt. Dazu werden in einer 30-j{\"a}hrigen Kalibrierungsperiode Hauptkomponenten von Geopotentiellen H{\"o}hen verschiedener atmosph{\"a}rischer Niveaus (300, 500, 1000hPa) mit den Niederschlagsmonatssummen (November bis M{\"a}rz) von 84 Namibischen Stationen durch multiple Regressionsanalysen verkn{\"u}pft, die f{\"u}r jede Station oder alternativ f{\"u}r Gitternetzniederschlagsdaten berechnet werden. Nach der Verifikation der statistischen Zusammenh{\"a}nge in einem unabh{\"a}ngigen Zeitraum werden Regressionsmodelle jener Stationen bzw. Gitterpunkte selektiert, die mit signifikanten Korrelationen von r>0.4 zwischen beobachteten und modellierten Werten ausreichende Qualit{\"a}t garantieren. Diese Modelle werden eingesetzt, um unter Verwendung simulierter ECHAM3-T42 und ECHAM4tr-T42 Geopotentialdaten den lokalen Niederschlag f{\"u}r die jeweiligen Treibhauseffekt-Szenarien abzusch{\"a}tzen. Als zus{\"a}tzliche Methode, um die großskalige atmosph{\"a}rische Zirkulation mit lokalen Stationsdaten zu verkn{\"u}pfen, werden kanonische Korrelationsanalysen durchgef{\"u}hrt. Unabh{\"a}ngig von der Verfahrensweise resultieren f{\"u}r Klimabedingungen dreifacher bzw. transient ansteigender CO2-Konzentrationen im Vergleich zu einem Referenzzeitraum (1961-90) zunehmende Niederschl{\"a}ge in den n{\"o}rdlichen und {\"o}stlichen Teilen Namibias von Dezember bis Februar. In den s{\"u}dlichen und s{\"u}dwestlichen Regionen sind von November bis Januar geringe Abnahmen zu verzeichnen. Die Absch{\"a}tzungen f{\"u}r M{\"a}rz zeigen einen deutlichen R{\"u}ckgang der Niederschl{\"a}ge in ganz Namibia. Diese Ergebnisse weisen auf eine intensivierte, akzentuiertere Regenzeit hin, auch wenn die Gesamtmenge der Niederschl{\"a}ge unter Bedingungen des anthropogen verst{\"a}rkten Treibhauseffekts mehr oder weniger gleich bleibt. Daher ist es von besonderer Bedeutung, die Absch{\"a}tzungen der Niederschlags{\"a}nderungen auf monatlicher Ebene durchzuf{\"u}hren. Weitere Untersuchungen beinhalten die Trennung thermischer und dynamischer Effekte in den zur Absch{\"a}tzung herangezogenen ECHAM3 und ECHAM4 Zirkulationsdaten. Durch die globale Erw{\"a}rmung kommt es zu einer Anhebung der Geopotentiellen H{\"o}hen der Treibhauseffekt-Szenarien. Durch die Korrektur des Uplifting-Prozesses werden dynamisch induzierte Auswirkungen auf das Niederschlagsgeschehen erfasst. {\´A}us der Verwendung uplifting-korrigierter Geopotentialdaten als Pr{\"a}diktoren in der Downscaling-Prozedur resultieren sowohl im positiven als auch negativen Bereich geringere {\"A}nderungsraten in den Absch{\"a}tzungsergebnissen. Ohne Zweifel reagiert das Klimasystem auf den anthropogen verst{\"a}rkten Treibhauseffekt. In Bezug auf zuk{\"u}nftige Namibische Sommerregen ist es von besonderer Bedeutung die Auswirkungen des Treibhauseffekts regional und temporal zu differenzieren.}, subject = {Namibia}, language = {de} } @phdthesis{Brandt2003, author = {Brandt, S{\"o}nke}, title = {Metamorphic evolution of ultrahigh-temperature granulite facies and upper amphibolite facies rocks of the Epupa Complex, NW Namibia}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-10930}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2003}, abstract = {The high-grade metamorphic Epupa Complex (EC) of north-western Namibia constitutes the south-western margin of the Archean to Proterozoic Congo Craton. The north-eastern portion of the EC has been geochemically and petrologically investigated in order to reconstruct its tectono-metamorphic evolution. Two distinct metamorphic units have been recognized, which are separated by ductile shear zones: (1) Upper amphibolite facies rocks (Orue Unit) and (2) ultrahigh-temperature (UHT) granulite facies rocks (Epembe Unit). The rocks of the EC are transsected by a large anorthosite massif, the Kunene Intrusive Complex (KIC). The Orue Unit and the Epembe Unit were affected by two distinct Mesoproterozoic metamorphic events, as is evident from differences in their metamorphic grade, in the P-T paths and in the age of peak-metamorphism: (1) The Orue Unit consists of a Palaeoproterozoic volcano-sedimentary sequence, which was intruded by large masses of I-type granitoids and by rare mafic dykes. During the Mesoproterozoic (1390-1318 Ma) the Orue Unit rocks underwent upper amphibolite facies metamorphism. The volcano-sedimentary sequence is constituted by interlayered basaltic amphibolites and rhyolitic felsic gneisses, with intercalations of migmatitic metagreywackes, migmatitic metapelites, metaarkoses and calc-silicate rocks. The Orue Unit was subdivided into three parts, which record similar heating-cooling paths but represent individual crustal levels: Heating led to the partial replacement of amphibole, biotite and muscovite through dehydration melting reactions. The peak-metamorphic P-T conditions of c. 700°C, 6.5 +/- 1.0 kbar (south-eastern part), c. 820°C, 8 +/- 0.5 kbar (south-western part) and c. 800°C, 6.0 +/- 1.0 kbar (northern part) correlate well with the mineral assemblage in the metapelites, i.e. Grt-Bt-Sil gneisses and schist in the south-eastern and south-western region and (Grt-)Crd-Bt gneisses in the northern part. Peak-metamorphism was followed by retrograde cooling to middle amphibolite facies conditions. Contact metamorphism, related with the intrusion of the anorthosites, is restricted to the direct contact to the KIC and recorded by massive metapelitic Grt-Sil-Crd felses, formed under upper amphibolite facies conditions (c. 750°C, c. 6.5 kbar). (2) The Epembe Unit consists of a Palaeoproterozoic volcano-sedimentary succession, which was intruded by small bodies of S-type granitoids and by andesitic dykes. All these rocks underwent UHT granulite facies metamorphism during the early Mesoproterozoic (1520-1447 Ma). The volcano-sedimentary succession is dominated by interlayered basaltic two-pyroxene granulites and rhyolitic felsic granulites. Migmatitic metapelites and metagreywackes are intercalated in the metavolcanites. Sapphirine-bearing MgAl-rich gneisses occur as restitic schlieren in the migmatitic metagreywackes. Reconstructed anti-clockwise P-T paths are subdivided into several distinct stages: During prograde near-isobaric heating to UHT conditions at c. 7 kbar biotite- or hornblende-bearing mineral assemblages were almost completely replaced by anhydrous mineral assemblages through various dehydration melting reactions. A subsequent pressure increase of 2-3 kbar led to the formation of the peak-metamorphic mineral assemblages Grt-Opx and (Grt-)Opx-Cpx in the orthogneisses and Grt-Opx, Grt-Sil and (Grt-)(Spr-)Opx-Sil-Qtz in the paragneisses. UHT-Metamorphism is proved by conventional geothermobarometry (970 +/- 70°C; 9.5 +/- 2.5 kbar), by the very high Al content of peak-metamorphic orthopyroxene (up to 11.9 wt.\% Al2O3) in many paragneisses and by Opx-Sil-Qtz assemblages in the MgAl-rich gneisses. Post-peak decompression is recorded by several corona and symplectite textures, formed at the expense of the peak-metamorphic phases: Initial UHT decompression of about ca. 2 kbar to 940 +/- 60°C at 8 +/- 2 kbar is mainly evident from the formation of sapphirine-bearing symplectites in the Opx-Sil gneisses. Subsequent high-temperature decompression to 6 +/- 2 kbar at 800 +/- 60°C resulted in the formation of Crd-Opx-Spl, Crd-Opx and Spl-Crd symplectites. Subsequent near-isobaric cooling to upper amphibolite conditions of 660 +/- 30°C at 5 +/- 1.5 kbar led to the re-growth of biotite, hornblende, sillimanite and garnet. During continued decompression orthopyroxene and cordierite were formed at the expense of biotite in several paragneisses. In a geodynamic model UHT metamorphism of the Epembe Unit is correlated with the formation of a large magma chamber at the mantle-crust boundary, which forms the source for the anorthosites of the KIC. In contrast, amphibolite facies metamorphism of the Orue Unit is ascribed to a regional contact metamorphic event, caused by the emplacement of the anorthositic crystal mushes in the middle crust.}, subject = {Namibia }, language = {en} } @phdthesis{Kempf2000, author = {Kempf, J{\"u}rgen}, title = {Klimageomorphologische Studien in Zentral-Namibia: Ein Beitrag zur Morpho-, Pedo- und {\"O}kogenese}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-5325}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2000}, abstract = {Es werden die Ergebnisse mehrj{\"a}hriger geomorphologische, pedologischer und {\"o}kologischer Feldaufnahmen in Namibia vorgestellt. Der Schwerpunkt der Betrachtung lag auf einem West-Ost-Transekt im zentralen Drittel des Landes zwischen dem s{\"u}dlichen Wendekreis und der Etosha-Region. Das Transekt beschreibt einen klima-geomorphologischen {\"U}bergang vom namibischen Schelf, {\"u}ber das Litoral, die Namib-Rumpffl{\"a}che, das Randstufenvorland mit dem Escarpment und das Hochland mit dem Windhoek-Okahandja-Becken bis zu den ausgedehnten Kontinentalbecken der Kalahari. Schelf, Randstufenvorland, Becken und Kalahari stellen dabei potentielle Akkumulationslandschaften, dar, Hochland und Namib-Fl{\"a}che die zugeh{\"o}rigen Abtragungslandschaften. Der geomorphologische Formenschatz der Akkumulations- und Abtragungslandschaften wurde ebenso analytisch beschrieben, wie die landschafts{\"o}kologische Grundausstattung, v. a. B{\"o}den und Vegetation. Die jeweils ablaufenden Prozesse und Prozesskombinationen wurden mit klimatischen Daten in einem {\"O}kosystemmodell verkn{\"u}pft. Mit Hilfe dieses Modells wurden geomorphologische Reliktformen verschiedener Zeitalter im landschaftlichen Zusammenhang {\"o}kogenetisch interpretiert und ein historischer Ablauf der Milieugeschichte seit dem Endterti{\"a}r rekonstruiert. Unterst{\"u}tzend wurden Proxydaten, v. a. pal{\"a}o{\"o}kologische und geoarch{\"a}ologische herangezogen.}, subject = {Zentralnamibia}, language = {de} } @phdthesis{Drueppel2003, author = {Dr{\"u}ppel, Kirsten}, title = {Petrogenesis of the Mesoproterozoic anorthosite, syenite and carbonatite suites of NW Namibia and their contribution to the metasomatic formation of the Swartbooisdrif sodalite deposits}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-6987}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2003}, abstract = {During the Mesoproterozoic large volumes of magma were repeatedly emplaced within the basement of NW Namibia. Magmatic activity started with the intrusion of the anorthositic rocks of the Kunene Intrusive Complex (KIC) at 1,385-1,347 Ma. At its south-eastern margin the KIC was invaded by syenite dykes (1,380-1,340 Ma) and younger carbonatites (1,140-1,120 Ma) along ENE and SE trending faults. Older ferrocarbonatite intrusions, the 'carbonatitic breccia', frequently contain wallrock fragments, whereas subordinate ferrocarbonatite veins are almost xenolith-free. Metasomatic interaction between carbonatite-derived fluids and the neighbouring and incorporated anorthosites led to the formation of economically important sodalite deposits. Investigated anorthosite samples display the magmatic mineral assemblage of Pl (An37-75) ± Ol ± Opx ± Cpx + Ilm + Mag + Ap ± Zrn. Ilmenite and pyroxene are surrounded by narrow reaction rims of biotite and pargasite. During the subsolidus stage sporadic coronitic garnet-orthopyroxene-quartz assemblages were produced. Thermobarometry studies on amphiboles yield temperatures of 985-950°C whereas the chemical composition of coronitic garnet and orthopyroxene indicate a subsolidus re-equilibration of the KIC at conditions of 760 ± 100°C and 7.3 ± 1 kbar. In the syenites Kfs, Pl, Hbl and/or Cpx crystallized first, followed by a second generation of Kfs, Hbl, Fe-Ti oxides and Ttn. Crystallization of potassium feldspar occurred under temperatures of 890-790°C. For the crystallization of hastingsite pressures of 6.5 ± 0.6 kbar are obtained. In order to constrain the source rocks of the two suites, oxygen isotope analyses of feldspar as well as geochemical bulk rock analyses were carried out. In case of the anorthosites, the general geochemical characteristics are in excellent agreement with their derivation from fractionated basaltic liquids, with the d18O values (5.88 ± 0.19 per mille) proving their derivation from mantle-derived magmas. The results obtained for the felsic suite, provide evidence against consanguinity of the anorthosites and the syenites, i.e. (1) compositional gaps between the geochemical data of the two suites, (2) trace element data of the felsic suite points to a mixed crustal-mantle source, (3) syenites do not exhibit ubiquitous negative Eu-anomalies in their REE patterns, which would be expected from fractionation products of melts that previously formed plagioclase cumulates and (4) feldspar d18O values from the syenites fall in a range of 7.20-7.92 per mille, which, however, is about 1.6 per mille higher than the average d18O of the anorthosites. Conformably, the crustal-derived felsic and the mantle-derived anorthositic suite are suggested to be coeval but not consanguineous. Their spatial and temporal association can be accounted for, if the heat necessary for crustal melting is provided by the upwelling and emplacement of mantle-derived melts, parental to the anorthosites. In order to constrain the source of the 1,140-1,120 Ma carbonatites and to elucidate the fenitizing processes, which led to the formation of the sodalite, detailed mineralogical and geochemical investigations, stable isotope (C,O,S) analyses and fluid inclusion measurements (microthermometrical studies and synchrotron-micro-XRF analyses) have been combined. There is striking evidence that carbonatites of both generations are magmatic in origin. They occur as dykes with cross-cutting relationships and margins disturbed by fenitic aureoles, and contain abundant flow-oriented xenoliths. The mineral assemblage of both carbonatite generations of Ank + Cal + Ilm + Mag + Bt ± Ap ± pyrochlore ± sulphides in the main carbonatite body and Ank + Cal + Mag ± pyrochlore ± rutile in the ferrocarbonatite veins, their geochemical characteristics and the O and C isotope values of ankerite (8.91 to 9.73 and -6.73 to -6.98, respectively) again indicate igneous derivation, with the 18O values suggesting minor subsolidus alteration. NaCl-rich fluids, released from the carbonatite melt mainly caused the fenitization of both, the incorporated and the bordering anorthosite. This process is characterized by the progressive transformation of Ca-rich plagioclase into albite and sodalite. Applying conventional geothermobarometry combined with fluid-inclusion isochore data, it was possible to reconstruct the P-T conditions for the carbonatite emplacement and crystallization (1200-630°C, 4-5 kbar) and for several mineral-forming processes during metasomatism (e.g. formation of sodalite: 800-530°C). The composition and evolutionary trends of the fenitizing solution were estimated from both the sequence of metasomatic reactions within wallrock xenoliths in the carbonatitic breccia and fluid inclusion data. The fenitizing solutions responsible for the transformation of albite into sodalite can be characterised as of NaCl-rich aqueous brines (19-30 wt.\% NaCl eq.), that contained only minor amounts of Sr, Ba, Fe, Nb, and LREE.}, subject = {Namibia }, language = {en} } @phdthesis{Hipondoka2005, author = {Hipondoka, Martin H.T.}, title = {The development and evolution of Etosha Pan, Namibia}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-14351}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2005}, abstract = {This study explores and examines the geomorphology of a large endorheic basin, approximately twice the size of Luxemburg, situated in the Etosha National Park, Namibia. The main focus is directed on how and when this depression, known as Etosha Pan, came into being. Geomorphological investigation was complemented and guided primarily by the application and interpretation of satellite-derived information. Etosha Pan has attracted scientific investigations for nearly a century. Unfortunately, their efforts resulted into two diverging and mutually exclusive views with respect to its development. The first and oldest view dates back to the 1920s. It hypothesized Etosha Pan as a desiccated palaeolake which was abandoned following the river capture of its major fluvial system, the Kunene River. The river capture was assumed to have taken place in the Pliocene/Early Pleistocene. In spite of the absence of fluvial input that the Kunene contributed, the original lake was thought to have persisted until some 35 ka ago, long after the Kunene severed its ties with the basin. The current size of the basin and its playa status was interpreted to have resulted from deteriorating climatic conditions. The opposing view emerged in the 1980s and gained prominence in the 1990s. This view assumed that there were an innumerable number of small pans on the then surface of what later to become Etosha Pan. Since the turn of the Pliocene to Early Pleistocene, these individual pans started to experience a combined effect of fluvial erosion during the rainy season and wind deflation during the dry period. The climatic regime during that entire period was postulated to be semi-arid as today. This climatic status was used to rule out any existence of a perennial lake within the boundary of Etosha since the Quaternary. Ultimately, these denudational processes, taking place in a seasonal rhythm, caused the individual pans to deepen and widen laterally into each other and formed a super-pan that we call Etosha today. Thus the Kunene River had no role to play in the development of the Etosha Pan according to this model. However, proponents of this model acknowledged that the Kunene once fed into the Owambo Basin and assigned the end of the Tertiary to the terminal phase of that inflow. Findings of this study included field evidence endorsing the postulation that the Kunene River had once flowed into the Owambo Basin. Its infilled valley, bounding with the contemporary valley of the Kunene near Calueque, was identified and points towards the Etosha Pan. It is deliberated that a large lake, called Lake Kunene, existed in the basin during the time. Following the deflection of the Kunene River to the coast under the influence of river incision and neo-tectonic during the Late Pliocene, new dynamics were introduced over the Owambo Basin surface. After the basin was deprived of its major water and sediment budget that the Kunene River contributed, it was left with only smaller rivers, most notably the Cuvelai System, as the only remaining supplier. This resulted in the Cuvelai System concentrating and limiting its collective load deposition to a lobe of Lake Kunene basin floor. The accident of that lobe is unclear, but it is likely that it constituted the deepest part of the basin at the time or it was influenced by neo-tectonic that helped divert the Kunene River or both. Against the backdrop of fluvial action that was initiating the new lake, most parts of the rest of the basin, then denied of lacustrine activity, were intermittently riddled with a veneer of sediment, especially during phases of intensified aeolian activity. In the mean time, the area that was regularly receiving fluvial input started to shape up as a distinct lake with the depositions of sediments around the water-body, primarily via littoral action, serving as embankment. Gradually, a shoreline is formed and assisted in fixing and delineating the spatial extent of the new and much smaller lake, called Lake Etosha. That Lake Etosha is the predecessor of the modern day Etosha Pan. Indicators for a perennial lake found in this study at Etosha include fossil fragments of Clariidae species comparable to modern species measuring some 90 cm, and those of sitatunga dated to approximately 5 ka. None of these creatures exist today at Etosha because of their ecological requirements, which among others, include permanent water. The sitatunga, in addition, is known as the only truly amphibious antelope in the world. Since its inception, the new lake underwent a number of geomorphological modifications. A prominent character amongst these modifications is the orientation of the lake, which has its long-axis oriented in the ENE-WSW direction. It resulted from wave action affected by the prevailing dominant northeasterly wind, which is believed to have been in force since the Middle Pleistocene. Lake Etosha has also witnessed phases of waning and waxing under the influence of the prevailing climatic regime. Over the last 150 ka, the available data intercepted about seven phases of high lake levels. These data are generally in agreement with regional palaeoclimatic data, particularly when compared with those obtained from neighbouring Makgadikgadi Pans in Botswana. The last recorded episode of the wet phase at Etosha was some 2,400 years before the present.}, subject = {Etoschapfanne}, language = {en} } @phdthesis{Vogel2005, author = {Vogel, Melanie}, title = {Erfassung von Vegetationsver{\"a}nderungen in Namibia mit Hilfe von Fernerkundungs-Change-Detection-Verfahren und unter Ber{\"u}cksichtigung rezenter Niederschlagsereignisse}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-17176}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2005}, abstract = {Die Dornbusch-Savannen Zentralnamibias unterliegen großen Ver{\"a}nderungen. Teilweise handelt es sich dabei um Degradationsprozesse, die zu einem Verlust an Artenvielfalt und auch {\"o}konomischem Wert dieser {\"u}berwiegend als Rinderweide genutzten Systeme f{\"u}hren. Die Degradation dr{\"u}ckt sich in der Savannenlandschaft zum einen durch Verkahlung aus (Desertifikation), vor allem aber durch die massive Ausbreitung einzelner Dornbuscharten wie Acacia mellifera, die zur Umwandlung gemischter Savannenvegetation in artenarme Dominanzbest{\"a}nde f{\"u}hrt (Verbuschung). Andere Ver{\"a}nderungen erfolgen spontan und stellen eine Reaktion der Vegetation auf aktuelle Niederschlagsereignisse dar. Diese ph{\"a}nologischen {\"A}nderungen sind in der Regel reversibel. Als typische Ver{\"a}nderungsmechanismen konnten nutzungsbedingter und nat{\"u}rlicher reversibler oder irreversibler Vegetationsverlust und die Wiederbesiedelung verkahlter Fl{\"a}chen identifiziert werden. Des Weiteren gibt es moderate Schwankungen der Vegetationsdichte, zu denen die Verbuschungsprozesse und die Buschsterbe geh{\"o}ren. Die Buschsterbe ist eine Pilzerkrankung, die zum fl{\"a}chenhaften Absterben von Akazienb{\"u}schen, vor allem von Ac. mellifera f{\"u}hrt. Auch der Einfluss von Feuer kann eine Ursache f{\"u}r Ver{\"a}nderungen sein. Um insbesondere das Ausmaß der Degradationsprozesse in Zentralnamibia zu erfassen und zu quantifizieren, wurde in dieser Arbeit ein fernerkundliches Change-Detection-Verfahren auf der Basis von Landsat-TM und ETM-Daten entwickelt. Die methodische Basis hierf{\"u}r stellten das Image-Differencing und die modifizierte selektive Hauptkomponentenanalyse (sPCA) dar. Um auch Formparameter der ver{\"a}nderten Fl{\"a}chen zur Unterscheidung von Ver{\"a}nderungstypen heranziehen zu k{\"o}nnen, wurden die Ergebnisse des Differencings segmentiert und das Maß der Kompaktheit(Compactness) der Segmente extrahiert. Die Klassifikation der charakteristischen Ver{\"a}nderungen erfolgte {\"u}ber Ratios und Schwellenwerte von Einzelkan{\"a}len dieser Change-Datendatens{\"a}tze und der Compactness, die aus charakteristischen Ver{\"a}nderungssignaturen abgeleitet wurden. Diese wurden anhand von Referenzfl{\"a}chen ermittelt, die auf Felddaten basierten. Als Referenz zur Ableitung der Signaturen diente dabei der Ver{\"a}nderungsdatensatz aus dem Vergleich der Landsat- Szenen von Mai 2000 und April 2003. Diese bitemporale Change-Detection-Methode wurde f{\"u}r das Hauptuntersuchungsgebiet (A) in Zentralnamibia auf insgesamt 8 Kombinationen aus 7 Landsat-Szenen im Zeitraum von 1984 bis 2003 angewendet. Damit wurde die {\"U}bertragbarkeit der Methode auf verschiedene Zeitschnitte getestet. Zur Absch{\"a}tzung der {\"U}bertragbarkeit auf andere Naturr{\"a}ume wurde die Methode zudem auch auf jeweils ein Szenenpaar in der ariden zwergstrauchdominierten Nama-Karoo in S{\"u}dnamibia und in einem feuchteren Dornsavannen-Trockenwaldgebiet in der Kavango-Region Nordnamibias angewendet. Die Klassifikatoren zur Trennung der einzelnen Ver{\"a}nderungsklassen lieferten unterschiedlich gute Ergebnisse. Die Verkahlungs- und Wiederbesiedelungsprozesse wurden sehr zuverl{\"a}ssig detektiert, wobei allerdings die Unterscheidung von nat{\"u}rlicher und nutzungsbedingter Verkahlung anhand der Compactness-Werte den Anteil an anthropogen ver{\"a}nderten Fl{\"a}chen auff{\"a}llig untersch{\"a}tzte. Die Validierung anhand von Farmerausk{\"u}nften bzw. vergleichenden Fotos zum Aufnahmezeitpunkt lieferte dabei in allen drei Untersuchungsgebieten {\"a}hnliche Ergebnisse. Moderate Ver{\"a}nderungen der Vegetationsdichte wurden in allen drei Untersuchungsgebieten {\"u}berwiegend gut erkannt. Eine eindeutige Zuordnung auf Ver{\"a}nderungen des Busch- oder des Grasstratums war allerdings nicht immer m{\"o}glich. Die Detektion von rezenten Brandfl{\"a}chen in Zentral- und Nordnamibia verlief zufrieden stellend. Mehrere Monate alte Brandfl{\"a}chen ließen sich mit dem dazu entwickelten Klassifikator jedoch nicht von anderen ph{\"a}nologisch und nutzungsbedingten Ver{\"a}nderungen trennen. Zur Analyse der Signifikanz der Change-Detektion-Ergebnisse wurden verschiedene Niederschlagsdaten und NDVI-Zeitreihen f{\"u}r den jeweiligen Beobachtungszeitraum hinzugezogen. Es zeigte sich, dass die Change-Detection-Ergebnisse stark mit den Niederschlagssummen korrelierten, die in der jeweiligen Regenzeit bis zum Aufnahmezeitpunkt der einzelnen Landsat-Szenen gefallen waren. War die Regenzeit zum ersten Vergleichszeitpunkt ergiebiger als zum zweiten, wurde {\"u}berwiegend Vegetationsr{\"u}ckgang detektiert. War die zweite Regenzeit hingegen feuchter als die erste, wurde {\"u}berwiegend Vegetationszunahme detektiert. Die Gr{\"o}ße der Niederschlagsdifferenz zwischen beiden Zeitpunkten spiegelte sich zudem im Fl{\"a}chenanteil der einzelnen Ver{\"a}nderungsklassen wider. Durch diesen starken ph{\"a}nologischen, d.h. niederschlagsbedingten Ver{\"a}nderungsanteil wurden „echte" Ver{\"a}nderungen z.T. verschleiert oder verst{\"a}rkt. Dieses Ergebnis korrespondiert mit den Ergebnissen vieler anderer Change-Detection-Arbeiten im semiariden Raum. Als relevante Ver{\"a}nderungen wurden daher nur solche bewertet, die dem allgemeinen ph{\"a}nologischen Trend im Vergleichszeitraum entgegenstanden. So konnten z.B. Fl{\"a}chen, auf denen Vegetationszuwachs detektiert wurde, obwohl die Regenzeit zum zweiten Aufnahmezeitpunkt schw{\"a}cher war als die erste, als tats{\"a}chlich verbuscht gelten. Unter Ber{\"u}cksichtigung dieser niederschlagsbedingten Einfl{\"u}sse wurden im Untersuchungsgebiet in Zentralnamibia die Fl{\"a}chenanteile bestimmt, f{\"u}r die Degradation detektiert wurde. Demnach hat im Vergleich der Szenen von 1984 und 2003 auf etwa 681 km², entsprechend 2,8 \% der Gesamtfl{\"a}che des Untersuchungsgebietes, eine niederschlagsunabh{\"a}ngige Verdichtung der Vegetation, d.h. eine Verbuschung stattgefunden. Die Lage der betroffenen Gebiete korrespondiert mit der in der Literatur genannten Region (vgl. BESTER 1998/99). Des Weiteren wurde im Untersuchungszeitraum von 1984 bis 2003 auf ca. 0,53 km², entsprechend 0,002 \% der Gesamtfl{\"a}che des Untersuchungsgebietes irreversible Verkahlung, d.h. Desertifikation detektiert. Damit stellt in Zentralnamibia die Ver{\"a}nderung durch Verbuschung die fl{\"a}chenm{\"a}ßig gr{\"o}ßte Bedrohung f{\"u}r Artenvielfalt und landwirtschaftliche Tragkraft der Savannen dar. Aufgrund der starken ph{\"a}nologischen Einfl{\"u}sse konnten von der Buschsterbe betroffene Regionen im Untersuchungsgebiet nicht sicher erkannt und quantifiziert werden. Kleinr{\"a}umig konnten im Untersuchungsgebiet in Zentralnamibia Farmen identifiziert werden, die in einem oder mehreren Ergebnisbildern durch besondere Ver{\"a}nderungsmuster auffielen. Zumeist handelte es sich um Degradationserscheinungen wie Verbuschung und Verkahlung, f{\"u}r die bei der Besichtigung w{\"a}hrend der Feldkampagne im Jahr 2004 oft ein Zusammenhang mit ung{\"u}nstigen Landnutzungspraktiken, d.h. vor allem {\"U}berweidung hergestellt werden konnte. Des Weiteren wurden starke Ver{\"a}nderungen durch Entbuschungsmaßnahmen, kurzzeitige Weideeinfl{\"u}sse und auch einzelne wiederhergestellte Best{\"a}nde detektiert. Nutzungsbedingte Degradationserscheinungen treten im Untersuchungsgebiet in Zentralnamibia insgesamt nur kleinr{\"a}umig auf einzelnen Farmen auf. F{\"u}r das Untersuchungsgebiet in S{\"u}dnamibia lagen zwei Landsat-Szenen f{\"u}r den kurzen Vergleichszeitraum von 2001 zu 2002 vor. Anhand dieser konnten unter Zuhilfenahme von Niederschlagsdaten stark degradierte Fl{\"a}chen identifiziert werden. W{\"a}hrend auf den intakten Fl{\"a}chen aufgrund der besseren Regenzeit zum zweiten Aufnahmezeitpunkt wie erwartet Vegetationszuwachs detektiert wurde, f{\"u}hrten ebendiese reichlichen Niederschl{\"a}ge im degradierten Gebiet zu einer großfl{\"a}chigen Erosion der Vegetationsdecke. Dies ist vermutlich auf die gr{\"o}ßere Geschwindigkeit des oberfl{\"a}chlich abfließenden Regenwassers in der sp{\"a}rlichen Vegetationsdecke der degradierten Fl{\"a}che zur{\"u}ck zu f{\"u}hren. In den {\"u}brigen Gebieten reduzierte hingegen die dichtere Vegetation den Oberfl{\"a}chenabfluss, wodurch mehr Wasser versickerte und verst{\"a}rktem Pflanzenwachstum zur Verf{\"u}gung stand. Im Untersuchungsgebiet in Nordnamibia wurden zwei Landsat-Szenen von April 1991 und April 2000 verglichen. Die gravierendste Ver{\"a}nderung in diesem Zeitraum war nutzungsbedingte Verkahlung, die auf rund 4,4 \% der Gesamtfl{\"a}che, entsprechend 81 km² detektiert wurde. Ursache ist hier die Umwandlung von Dornbuschsavanne in Acker- oder Siedlungsraum. Demgegen{\"u}ber wurde aber nur f{\"u}r 1,17 \% der Gesamtfl{\"a}che, entsprechend 21,76 km², Wiederbesiedelung detektiert. Dies sind zumeist Agrarfl{\"a}chen, die (kurzzeitig) aus der Nutzung genommen wurden. Das Ergebnis dokumentiert den zunehmenden Siedlungsdruck in der Kavango-Region. Die seit den 1970er Jahren verbesserte Infrastruktur erm{\"o}glicht hier immer mehr Menschen die Landnahme, Viehhaltung und Siedlung. Die Ergebnisse dieser Arbeit zeigen, dass mit der hier entwickelten Change-Detection-Methode unter Ber{\"u}cksichtigung der Niederschlagshistorie in den semiariden und ariden Testgebieten signifikante Ver{\"a}nderungen der Vegetation in verschiedenen Landschaftsr{\"a}umen detektiert werden k{\"o}nnen. Weitere Anwendungen der Methodik auf andere Testgebiete im s{\"u}dlichen und westlichen Afrika am Rande dieser Arbeit zeigten ebenfalls gute Ergebnisse, die allerdings bislang aus Mangel an Referenzdaten nicht validiert werden konnten. Zur zuk{\"u}nftigen Operationalisierung der Methodik sollte vor allem eine verbesserte Trennbarkeit von nutzungsbedingten und nat{\"u}rlichen Verkahlungsprozessen angestrebt werden. Des Weiteren wird eine Anpassung der Klassifikatoren auf andere Sensoren wie z.B. ASTER angedacht, um auch nach dem Ausfall von Landsat 7 im Jahr 2003 aktuelle Daten vergleichen zu k{\"o}nnen. Um den ph{\"a}nologischen Einfluss von unterschiedlichen Niederschlagshistorien im Vorfeld der Eingangsdaten zu minimieren, w{\"a}re zudem die Implementierung eines Kalibrierungsfaktors denkbar, der auf Niederschlags- oder auch MODIS-NDVI-Daten der entsprechenden Zeit- und Untersuchungsr{\"a}ume basiert. Das Ergebnis w{\"a}re eine sichere Methode zur Detektion von regionalen Ver{\"a}nderungen im semiariden Raum. Die Identifizierung dieser Ver{\"a}nderungen, speziell von Degradationserscheinungen stellt die Basis dar, dort gezielt nach den Ursachen zu suchen und Handlungsempfehlungen zu entwickeln, um einer fortschreitenden Zerst{\"o}rung von Lebensraum, Artenvielfalt und {\"o}konomischem Potenzial der betroffenen Fl{\"a}chen entgegen zu wirken.}, subject = {Namibia}, language = {de} } @phdthesis{Werner2006, author = {Werner, Mario}, title = {The stratigraphy, sedimentology, and age of the Late Palaeozoic Mesosaurus Inland Sea, SW-Gondwana : new implications from studies on sediments and altered pyroclastic layers of the Dwyka and Ecca Group (lower Karoo Supergroup) in southern Namibia}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-21757}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2006}, abstract = {The Mesosaurus Inland Sea covered, in the Late Paleozoic, vast areas (~5 Mio km2) of the SW-Gondwanan continental interior. Major depocentres are represented by the Karoo basins of SW-Africa and the Paran{\´a} Basin in South America. These areas were interconnected prior to the break-up of Gondwana and the subsequent opening of the South Atlantic Ocean. In Namibia and South Africa deposits of the Mesosaurus Inland Sea are preserved in the successions of the glacial Dwyka Group and the postglacial Ecca Group (Karoo Supergroup). These deposits comprise the major part of a 60-70 Ma depositional cycle and are the main focus of this study. The large-scale transgressive part of this cycle started in the Late Carboniferous with continental glacial deposits followed by marine glacial and postglacial inland sea deposits. During the Early Permian the Mesosaurus Inland Sea reached its greatest extent, which was accompanied by widespread deposition of Corg-rich sediments. The large scale regressive part is recorded by successions ranging from deep water offshore pelites and turbidite sandstones to shallow water shoreface and deltaic sandstones, deposited in a brackish environment. Shallow water inland sea sediments are in turn overlain by fluvio-lacustrine deposits, which are assigned to the Beaufort Group and form the upper part of the cycle. This successive change in the depositional environment from marine to brackish to freshwater is also reflected in the fossil record. During Dwyka times a marine association of the Gondwana faunal province was able to colonize parts of the Mesosaurus Inland Sea. Later, during lower Ecca times, the connection to the Panthalassan Ocean became insufficient to retain normal marine conditions, leading to strong faunal endemism in an isolated and brackish inland sea environ¬ment. The most well-known and widespread representatives of this endemic fauna are mesosaurid vertebrates and megadesmid bivalves. Numerous altered tuffs occur as interlayers within argillaceous sediments of the Dwyka and Ecca Group of southern Namibia. The vast majority of these altered tuffs are represented by soft and crumbly to hard and indurated, clay-mineral-rich, bentonitic layers. Another, much rarer type is represented by very hard, chert-like tuff layers, which are predominantly albitic in composition. Furthermore, tuff layers within the Gai-As Formation of the Huab area are rich in potassium feldspar and have a porcelain-like appearance. The diagenetically modified matrix is mainly crypto- to microcrystalline. Polished tuff specimen show, in some tuffs, plane lamination or bedding with two or more subunits forming a tuff layer. Some display a weakly developed lamination. Only in very rare cases were structures reminiscent of sedimentary micro-cross lamination observed. The sedimentary textures and structures of the tuffs indicate that they have been deposited mainly as distal ash-fall layers by suspension settling in water. Some may have also been deposited or modified under the influence of weak bottom currents. The primary, pyroclastic macro-components of the tuffs are mainly represented by crystals of quartz, plagio¬clase, and biotite. In some thin sections pseudo¬morphs after pyroxene or hornblende were observed. Euhedral zircon and apatite crystals were observed in almost every tuff. Vitric or formerly vitric macro-components are very rare. The matrix of the majority of the investigated tuffs is predominantly composed of clay minerals. However, the matrix of the tuffs originally consisted most probably of fine vitric ash particles. Soon after deposition the volcanic ash was diagenetically altered to smectitic clay minerals. At a later stage smectite was progressively replaced by illite under prograde conditions. Nowadays the matrix of the bentonitic tuffs is strongly illite-dominated and only in the softer tuff layers a minor smectite content can be detected. Both the primary macrocrystic components as well as the geochemistry of the altered tuffs indicate that their source magmas were mainly of intermediate composition. The abundance of splintery quartz and feldspar crystal fragments within the tuffs hints at a highly explosive plinian or phreatoplinian eruption style of the source volcanoes, which were most probably located within a subduction-related volcanic arc region along the southern margin of Gondwana. New single zircon U-Pb SHRIMP datings of tuff layers provide a much more reliable age control of the investigated sedimentary succession. U-Pb SHRIMP ages for tuff layers from the glaciogenic Dwyka Group in southwestern Africa range from 302.0 ± 3.0 to 297.1 ± 1.8 Ma. The basal part of the early post-glacial Prince Albert Formation is dated at around 290 Ma. SHRIMP ages for tuff layers from the upper part of the Prince Albert Formation, the Whitehill Formation, and the middle part of the Collingham Formation indicate that the Mesosaurus Sea reached its greatest extent at around 280 Ma.}, subject = {Karru}, language = {en} } @phdthesis{Wanke2000, author = {Wanke, Ansgar}, title = {Karoo-Etendeka Unconformities in NW Namibia and their Tectonic Implications}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-3234}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2000}, abstract = {In north-western Namibia the fills of the Karoo-Etendeka depositories can be subdivided into (1) a Carboniferous-Permian, (2) a Triassic-Jurassic and (3) a Cretaceous megasequence, each recording extensional periods related to successive rifting phases in the evolving South Atlantic. The tectonic environment of the depositories in north-western Namibia changes successively from the coast towards the continental interior, which is reflected by the facies distribution and the position of time-stratigraphic gaps. Close to the present-day coastline synsedimentary listric faults, trending parallel to the South Atlantic rift (N-S), caused the formation of wedge shaped sediment bodies. Here, the Karoo Supergroup is only represented by the Permian succession in the Huab area. A hiatus within the Permian can be recognised by the correlation with the main Karoo Basin in South Africa and the Brazilian Paran{\´a} Basin. This stratal gap correlates with a pre-Beaufort Group unconformity in the main Karoo Basin that might be related to an orogenic pulse in the Cape Fold Belt. The Permian succession itself is unconformably overlain by the Lower Cretaceous Etendeka Group. This hiatus extending from the Upper Permian to the Lower Cretaceous has probably been induced by a combination of rift shoulder uplift and additional crustal doming associated with Etendeka flood volcanism. The enhanced tectonism during the Early Cretaceous controlled accommodation space for the alluvial-fluvial and aeolian deposits of the lower Etendeka Group. Disconformities within those deposits and the overlying lava succession attribute to distinct phases of tectonic and volcanic activity heralding the South Atlantic breakup. Towards the south-east, the Karoo succession becomes successively more complete. In the vicinity of Mt. Brandberg Early Triassic strata (Middle Omingonde Formation) follow disconformably above the Upper Permian/Lowermost Triassic Doros Formation. The sedimentation there was essentially controlled by the SW-NE trending Damaraland Uplift. South of the Damaraland Uplift the SW-NE trending Waterberg-Omaruru Fault zone is interpreted as a sinistral oblique-slip fault that compartmentalised the South Atlantic rift. This fault controlled accommodation space of the entire Triassic Omingonde Formation and the Early Jurassic Etjo Formation in its associated pull-apart and transtension structures. A locally well developed angular unconformity defines a hiatus between the two formations. Correlation with the main Karoo Basin in South Africa confirms that this gap is of a regional extent and not only a local, fault induced feature. Furthermore, it might also correlate with an orogenic pulse of the Cape Fold Belt. In general, the Mesozoic megasequences record the long-lived history of the southern Atlantic rift evolution. Rifting has been controlled by orogenic pulses derived from the Samfrau active margin throughout the Mesozoic. The associated intracratonic E-W extension caused the formation of grabens and conjugated oblique-slip zones. The generation of voluminous flood basalts marks the climax of intracratonic extension that was accompanied by enhanced uplift of the rift shoulders.}, subject = {Namibia }, language = {en} }