Dissertations / Theses on the topic 'Late Quaternary Africa'

This dissertation outlines the results of a study undertaken to describe the environmental history of Vankervelsvlei, a schwingmoor-type bog near Knysna on the south coast of South Africa. The study relies heavily on the use of fossil pollen as an indicator of vegetation change from which environmental conditions are inferred. Several additional lines of evidence including sedimentological and geochemical data are used to corroborate pollen findings. The narrative of environmental change at the site has been compared with findings from other palaeoecological studies undertaken in the area. Particular reference has been made to the expansion and contraction of afromontane forest vegetation over time to add to existing knowledge of forest history in Southern Africa.

Diese Arbeit beschäftigt sich mit der Rekonstruktion von Klima in historischen Zeiten im tropischen Ostafrika. Nach einer Übersicht über die heutigen klimatischen Bedingungen der Tropen und den Besonderheiten des ostafrikanischen Klimas, werden die Möglichkeiten der Klimarekonstruktion anhand von Seesedimenten diskutiert. Es zeigt sich, dass die hoch gelegenen Seen des Zentralen Keniarifts, als Teil des Ostafrikanischen Grabensystems, besonders geeignete Klimaarchive darstellen, da sie sensibel auf klimatische Veränderungen reagieren. Veränderungen der Seechemie, wie sie in den Sedimenten aufgezeichnet werden, eignen sich um die natürlichen Schwankungen in der Quartären Klimageschichte Ostafrikas nachzuzeichnen. Basierend auf der guten 40Ar/39Ar- und 14C-Datierbarkeit der Seesedimente wird eine Chronologie der paläoökologischen Bedingungen anhand von Diatomeenvergesellschaftungen restauriert. Dabei zeigen sich für die Seen Nakuru, Elmenteita und Naivasha kurzfristige Transgression/ Regressions-Zyklen im Intervall von ca. 11.000 Jahren während des letzten (ca. 12.000 bis 6.000 J.v.H.) und vorletzten Interglazials (ca. 140.000 bis 60.000 J.v.H.). Zusätzlich kann ein allgemeiner, langfristiger Trend der Seeentwicklung von großen Frischwasserseen hin zu stärker salinen Gewässern innerhalb der letzen 1 Mio. Jahre festgestellt werden. Mittels Transferfunktionen und einem hydro-klimatischen Modellansatz können die restaurierten limnologischen Bedingungen als klimatische Schwankungen des Einzugsgebietes interpretiert werden. Wenngleich auch der zusätzliche Einfluss von tektonischen Veränderungen auf das Seeeinzugsgebiet und das Gewicht veränderter Grundwasserströme abgewogen werden, zeigt sich, dass allein geringfügig erhöhte Niederschlagswerte von ca. 30±10 % zu dramatischen Seespiegelanstiegen im Zentralen Keniarift führen. Aufgrund der etablierten hydrrologisch-klimatischen Wechselwirkungen werden Rückschlüsse auf die natürliche Variabilität des ostafrikanischen Klimas gezogen. Zudem wird die Sensitivität der Keniarift-Seen in Bezug auf die Stärke der äquatorialen Insolation und hinsichtilch variabler Oberflächenwassertemperaturen des Indischen Ozeans bewertet.
In this work, an approach of paleoclimate reconstruction for tropical East Africa is presented. After giving a short summary of modern climate conditions in the tropics and the East African climate peculiarity, the potential of reconstructing climate from paleolake sediments is discussed. As demonstrated, the hydrologic sensitivity of high-elevated closed-basin lakes in the Central Kenya Rift yields valuable guaranties for the establishment of long-term climate records. Temporal fluctuations of the limnological characteristics saved in the lake sediments are used to define variations in the Quaternary climate history. Based on diatom analyses in radiocarbon- and 40Ar/39Ar-dated sediments, a chronology of paleoecologic fluctuations is developed for the Central Kenya Rift -lakes Nakuru, Elmenteita and Naivasha. At least during the penultimate interglacial (around 140 to 60 kyr BP) and during the last interglacial (around 12 to 4 kyr BP), these lakes experienced several transgression-regression cycles on time intervals of about 11,000 years. Additionally, a long-term trend of lake evolution is found suggesting the general succession from deep freshwater lakes towards more saline waters during the last million years. Using ecologic transfer functions and a simple lake-balance model, the observed paleohydrologic fluctuations are linked to potential precipitation-evaporation changes in the lake basins. Though also tectonic influences on the drainage pattern and the effect of varied seepage are investigated, it can be shown that already a small increase in precipitation of about 30±10 % may have affected the hydrologic budget of the intra-rift lakes within the reconstructed range. The findings of this study help to assess the natural climate variability of East Africa. They furthermore reflect the sensitivity of the Central Kenya Rift -lakes to fluctuations of large-scale climate parameters, such as solar radiation and sea-surface temperatures of the Indian Ocean.

Sand ramps are widespread but understudied landforms which have the potential to provide detailed palaeoenvironmental information in dryland regions. This thesis investigates the utility of sand ramps as late Quaternary palaeoenvironmental archives by addressing two research questions: (1) What are the main controls on sand ramp formation in southern Africa? (2) What does the sand ramp record tell us about late Quaternary palaeoenvironments in southern Africa? The distribution of sand ramps in southern Africa was surveyed using Google Earth™ and 75 features were identified in southern Namibia. Ten of these sand ramps, and an additional feature from South Africa, were studied in the field. Sediments and morphology were mapped and a total of 64 OSL dates, 96 sediment samples, 10 heavy mineral assemblages and OSL sensitivity data from 8 samples were examined. The distribution of sand ramps suggests formation is dependent on (1) sediment supply, (2) accommodation space, (3) persistent unidirectional wind and (4) a variable semi-arid to arid climate. Chronologies and sediment analyses indicate individual sand ramp accumulation is locally controlled by sediment supply modulated by the availability, and nature, of the accommodation space. Comparison between the Namibian and South African sand ramps suggests considerable regional variation in the factors controlling sediment supply. The Namibian sand ramps show an affinity to local ephemeral river channels. Periods of dated sand ramp activity in multiple features are interpreted as periods of increased regional fluvial activity. Significant activity occurred at ~21-12 ka (with peaks at 21-18.5 ka and 14.5-12 ka), ~8.5-7.5 ka and ~2 ka. Some activity is also indicated at 85-65 ka and 45-35 ka. These results correspond well to regional records. Overall, this study demonstrates that sand ramps can provide palaeoclimatic information on both the local and regional scale but only if a number of caveats are taken into consideration.

Summary in English.
Bibliography: leaves 263-292.
This thesis presents new palaeoenvironmental evidence from the semi-arid lowlands of the West Coast Sandveld, which prompts a fresh synthesis as to the nature of late Quaternary environmental changes in the southwestern Cape's fynbos biome. The study is centred on Verlorenvlei, a remote coastal lake and swamp system which is ideally situated to investigate the complex interactions between late Holocene climate change, vegetation change, sea-level fluctuation, lacustrine/estuarine/fluvial sedimentology and human activity in the Sandveld region. In addition, this region of the West Coast has provided Quaternary scientists with a rich archaeological record against which independent lines of palaeoecological evidence can be evaluated. In support of the study, a wide range of palaeoenvironmental techniques has been applied to sediments sampled from the Verlorenvlei area. Organogenic deposits have been radiocarbondated and subjected to pollen analysis and assorted sedimentological and geoarchaeological assessments. Preliminary fossil pollen data from Elands Bay Cave, assembled for the period following the Last Glacial Maximum until approximately the terminal Pleistocene, are suggestive of moister and possibly cooler conditions in the Sandveld at this time. This is in contrast to prevailing evidence from the summer rainfall region of the subcontinent. Particle size analysis and an assessment of the in situ fossil Mollusca from vibracores, derived from the estuarine reaches of Verlorenvlei, reveal substantive evidence for rapid sea-level fluctuations along the West Coast during the mid-Holocene. Further inland, several mid-Holocene higher sea-levels are reflected in the palynology of lacustrine cores derived from Grootdrift and Klaarfontein. Detailed pollen diagrams, presented from Grootdrift, Klaarfontein, Muisbosskerm and Spring Cave, reflect the regional vegetation history during several periods over the last 7 000 years. There is convincing evidence from these data that the first half of the Holocene - commensurate with the Holocene hypsithermal - was associated with reduced moisture availability, and hence arid conditions along the West Coast. By contrast, there is evidence from the latter half of the Holocene that conditions ameliorated in the Sandveld around 3 000 BP and that moisture was, at this time more freely available. Following a hiatus in sedimentation some time after 4 000 BP, marine conditions are no longer visible in Verlorenvlei, having been replaced by fresh water as the dominant hydrological regime. A high resolution palynological investigation of the Grootdrift wetland sediments has contributed to a detailed palaeolimnological reconstruction of the upper Verlorenvlei system since the time of colonial expansion into the area, some 300 years ago. The picture reveals a sequence of rapid ecological changes in the face of progressive human disturbance. Arising from these insights, a number of recommendations for the management of dryland aquatic ecosystems such as Verlorenvlei, are presented. The significance of these late Quaternary palaeoenvironmental changes, in terms of the biogeography of plants and animals and also in terms of human occupation of the region, is examined.

Pas de résumé en français
Southern African drylands are not suited for the application of climate reconstruction methods based on surface samples. Methods based on the co-existence approach, while still in their early days, are really promising, particularly those using probability density functions (pdfs) that have proven particularly valuable in certain cases as they can be applied to a wide range of plants assemblages. Most commonly applied to fossil pollen data, their performance can be limited by the taxonomic resolution of the pollen data, as many species may belong to a given pollen-type. Consequently, climate information associated with a taxon cannot always be precisely identified, resulting in less accurate reconstructions. This can become particularly problematic in regions of high biodiversity, such as southern African botanical hotspots. The first part of this PhD thesis presents the development of a novel pdf-based climate reconstruction method adapted to the southern African context. The method, which comes along with a dedicated software pack- age entitled CREST, sorts out this diversity issue by taking into account the different climatic requirements of each species constituting the broader pollen-type: pdfs are fitted in two successive steps, with parametric univariate pdfs fitted first for each species (pdfsp) followed by a combination of those individual species pdfs into a broader single pdf to represent the pollen-type as a unit (pdfpol). The curve resulting from the multiplication of the pdfpol describes the likelihood of different climate parameters based on the co-existence of a given set of taxa, each being weighted according to its normalized pollen percentage. Three majors properties were derived from this continental-scale statistical analysis: 1) the method saturates when the number of species composing a pollen type becomes larger than 30-40 species, 2) the per- formance decreases with distance to the core of the climatic space and 3) climate variables that have a direct impact of plant life cycles are better reconstructed.We revisited 13 pollen sequences (selection based on their length, continuity, chronology and pollen diversity) from southern African literature with the CREST method. To offset the limited individual potential of those sequences, we developed a Monte-Carlo framework to create interpolated curves integrating uncertainties associated with the reconstructions and age-depth models and then stack those curves together to extract regionally consistent patterns. This reanalysis allows for the quantified reconstruction of a range of distinct climatic variables from this critical region, and provides significant insight into the nature of long-term climate change. Temperature reconstructions show strong coherency among all sites considered, and parallel southwest Indian Ocean SSTs. Reconstructions of the amount of summer precipitation since mid-MIS 3 (Marine Isotope Stage 3) 45,000 years ago indicate a dichotomy in the precipitation pattern between interior and northeastern South African sites. At the glacial-interglacial timescale, precipitation in northeastern sites shows strong similarities with the Indian Ocean SST records as well as with records from the large East African lakes. Entering the Holocene, precessional forcing becomes more important and a north/south rainfall dipole appears, with a demarcation line located somewhere between Lakes Tanganyika and Malawi (3-9°S). Sites from the interior, while clearly following a similar dynamic, also appear to be sensitive to additional factors, including the position of the southern Westerlies, which may interact with tropical systems to create tropical-temperate troughs. Our results shed light on the complexity of the mechanisms driving South African rainfall, and clarify several key elements of the current debate, including limitations of models relying on direct insolation forcing to explain long-term climate dynamics

Barrier dunes represent potentially long-term, but complex, archives of coastal evolution. The examples occupying the Wilderness embayment, on the southern Cape coast of South Africa, form a regionally unique system of three shore-parallel barriers reaching up to 200 m in height and extending up to ~32 km alongshore. This research combines chronological and sediment provenance analyses to reconstruct the emplacement and evolution of the Wilderness barrier dunes through the Mid- to Late-Quaternary. Thirty-six new luminescence ages collected from ten sites across the three Wilderness barriers are presented, and are combined with a compilation of dates from the literature to produce a high-resolution chronology of barrier accumulation. The record spans at least the last two glacial-interglacial cycles, with notable phases between 245-217 ka, 155-143 ka, 128-121 ka, 91-86 ka and post-6 ka. Analysis of trace element geochemistry, heavy minerals, particle size, carbonate content and offshore topographic evidence all combine to indicate the provenance of the barrier sands has remained constant throughout their formation, and must involve marine transport pathways. The hypothesis that barrier accumulation at Wilderness during periods of low sea level was sustained by terrestrial aeolian activity is thus disproven, and evidence for a regional pre-MIS 5 marine transgression is provided. The terrestrially derived fraction of the barrier sands predominantly comprises quartzitic material derived from Table Mountain Group (TMG) rocks, most likely sourced from the Gouritz River ~75 km west of Wilderness. In addition to sediment from the TMG, the barrier sands also contain contributions of material derived from local geology, of material recycled from previous generations of aeolianite, and of authigenic marine sediment. The extensive coversand deposits inland of the Wilderness embayment, dated to >1.6 Ma using isothermal thermoluminescence, are demonstrated not to have made any significant input of sediment to the barriers. The Wilderness barriers record a complex history of erosion, as well as deposition through the Mid- to Late-Quaternary, and the preserved record clearly reflects the influence of local nearshore bathymetry on the rate of sea-level regression. The importance of previous generations of aeolianite in both fixing the position of subsequent depositional episodes, and protecting them from erosion, is also evident. The barriers exhibit similar behaviour to deposits on tectonically stable coastlines elsewhere, and contrast with the more complete and widely spaced barrier records present on uplifting coasts.

The Great Karoo spans the north-central part of South Africa at a major climatic boundary. The characteristics, spatial patterns and drivers of river channel response to Late Quaternary climate changes in the Sneeuberg, South Africa remain unclear due to the discontinuous alluvial stratigraphic record and the lack of dated palaeoclimatic archives. Dendritic channel networks in the upper Sundays River are deeply incised exposing terrace fills of varying thickness (2-6 m), extent (1 - > 10km) and pedogenic overprinting. Channels exhibit 'stepped' long profiles where resistant rock strata (dolerite, sandstone) cross valley floors, but are now partially or completely breached. DGPS surveys, sediment logging, mineral magnetic measurements and radiometric dating (OSL and 14C) were used to determine the source, age structure and depositional process of valley fills and ascribe intensity of pedogenic overprinting. A conceptual model of terrace development in relation to changing conditions of connectivity was tested. First order streams were desensitised to late Quaternary base level changes downstream due to the blocking effect of two barriers, with localised autogenic 'cut and fill'. Contrastingly, the continuity of 4 fill terraces over incised barriers in 2nd-4th order tributaries indicate relatively high sensitivity to post-LGM climatic change. However, deposition of alluvium (T2) inset within periglacial deposits (T1) was partly a complex response to re-connection of the channel network with deep upland colluvial stores resulting in the valleys becoming choked with sediment. This caused a rise in groundwater and formation of extensive (> 10 km2) rootmats on valley floors, restricting depth of subsequent channel entrenchment (T3/T4). This study presents one of the first attempts in South Africa to test and explain terrace genesis and correlation using existing conceptual models for sediment connectivity. The relative roles of periglaciation and fluvial activity are shown to be key influences on dynamics of Quaternary sedimentation, pedogenesis and erosion and help to explain how sediments can be preserved over long periods (104 years) in catchments subject to base level fall.

The relative influence of precessionally-driven changes in direct insolation and changes in boundary conditions associated with glacial-interglacial cycles on climatic conditions at low latitudes remains uncertain. This thesis presents records of late Quaternary climatic change from Tswaing crater lake in South Africa and from the Naivasha and Nakuru-Elmenteita basins in the Central Kenya Rift, with the aim of increasing our understanding of the nature and causes of climatic change at low latitudes in Africa. The sedimentary sequence from Tswaing crater lake provides some of the longest terrestrial records of palaeoclimatic change in southern Africa, but the confidence associated with these records is limited by chronological uncertainty. This thesis presents five new 230Th/234U dates from the lower, previously undated section of the sequence, which are used to construct a new age-depth model for the sediments. When viewed in light of this chronology, new sedimentological, geochemical, and diatom assemblage records from the sequence indicate that boundary conditions associated with glacial-interglacial cycles determined climatic conditions at the site over the last -150 kyr, and that the obliquity of the earth's axis may have affected conditions between -150 and -350 kyr B.P. Diatomite beds deposited in the Naivasha and Nakuru-Elmenteita basins at the time of the last interglacial document a period in which deep, dilute lakes existed in the Central Kenya Rift. 518Odiatom records from these 40Ar/39Ar-dated beds are used to reconstruct palaeohydrological conditions during this lake-level highstand. The records indicate that lake levels in both basins responded to increases in precipitation driven by peaks in March and September insolation on the equator, and by increased tropical sea-surface temperatures. It is therefore concluded that precipitation in the Central Kenya Rift was influenced by both precessionally-driven changes in insolation and global boundary conditions during this period.

Pollen analysis of organic sediments from vleis in upland areas of the Central and marginal Karoo has provided a vegetation history spanning the late Quaternary in the Winterberg, Sneeuberg, Nuweveldberg and Cederberg Mountains. Fossil pollen studies indicate moist conditions at the beginning of the Holocene, followed by a drier period. The second half of the Holocene (4 600 BP) is characterised by moister conditions, becoming drier towards the present and resulting in a decline in grasslands and an increase in Karoo-bushes. In the western Cape, the late Pleistocene (15 000 to 10 000 BP) was characterised by conditions moister than the present. This was followed by a drier period which ameliorated in the late Holocene. Although climatic fluctuations occurred, fynbos has been maintained in situ throughout the sedimentation period (14 600 BP), highlighting the dominant role of the substrate and secondary importance of climate. Climatic changes caused a shuffling of plant communities within the Fynbos Biome - this long uninterrupted history may be one reason for the high species diversity of fynbos. San hunter-gatherers, who occupied southern Africa prior to 4 000 BP, had a negligible impact on the vegetation. Khoi herders, who were first documented in the fossil record about 1 800 BP, had a slight impact on the vegetation, particularly by altering the fire regime. However, the arrival of European Trekboers some four hundred years ago had a significant effect on the environment. Although the general climatic trend in the Karoo is one of a drier phase, the decline in grasses and eastward movement of xeric Karroid elements has been accelerated due to mismanagement and sedentary farming techniques. An extensive contemporary pollen rain study has been undertaken to examine the representivity of these fossil pollen data. The investigation shows that contemporary pollen rain is a good reflection of the vegetation communities in the Karoo and Cederberg. Multiple discriminant analysis compares fossil pollen assemblages with contemporary pollen spectra and proved useful for determining whether modern analogues exist for the fossil pollen assemblages. TWISA confirmed the zones derived from discriminant analysis. Environmental changes have occurred in the Karoo during the late Quaternary, resulting in fluctuations and changes in vegetation patterns which have been accelerated in the recent past by human activity. Bibliography: pages 293-318.

The predominantly dryland climate of interior South Africa precludes the widespread preservation of organic proxy records. Various potential geoproxy records exist, but their exploitation requires accurately constrained chronologies. This study investigates the development of two luminescence chronometers, quartz OSL and K-feldspar post-IR IRSL. At four sites across the eastern interior (Moopetsi, Voordrag, St Paul's and Goedgedacht), these chronometers are used to constrain the timing of: (i) the late Quaternary initiation of deposition; (ii) intervening phases of erosion, deposition andpedogenesis; and (iii) the current deep erosional phase. The value of using paired ages (i.e. determining quartz and K-feldspar ages from the same sample) becomes apparent, particularly at Voordrag where quartz OSL reaches saturation within the limit of radiocarbon dating. Paired chronologies show good agreement for younger samples (<24 ka) but systematic underestimation of quartz ages for older samples. Investigation of the post-IR IRSL protocol showed that signal transfer between the Lx and Tx measurements caused systematic underestimation of older feldspar ages. Dose recovery tests showed that it was not possible to recover a large given dose (400 Gy) when using a small (5 Gy) test dose. Two solutions were investigated, specifically increasing the size of the test dose to ~30 % of the De value and increasing the IR stimulation time. This led to the development of a `modified' post-IR IRSL protocol. The derived quartz and K-feldspar single grain chronologies show that the initiation of deposition was not synchronous at the four study sites, and ranges from ~153 { 65 ka. Intervening phases of erosion, deposition and pedogenesis remain difficult to constrain but broad inferences regarding climatic and geomorphic drivers can be made. The current phase of deep erosion appears to be linked to two periods of abrupt climate change, the 3.8 { 4.2 ka arid event and the Little Ice Age.

Includes abstract.
Includes bibliographical references.
Despite significant advances in palaeoenvironmental research in southern Africa, the late Quaternary palaeoenvironmental history of the region remains incomplete as palaeoclimatic proxy records are temporally and spatially discontinuous. The southern Cape is a key focus area within this region as it encompasses the Fynbos Biome, a global biodiversity hotspot, as well as rare Afrotemperate forest patches and is therefore of great botanical importance. As this area includes the transition from southern Africa’s winter rainfall zone to the year-round rainfall zone, it is also important from a climatic perspective.

Includes bibliographical references (leaves 130-139).
This research project attempts to determine the relative influences of climate, sea level changes and human activities during the period of sediment accumulation in the Noordhoek basin in the southwestern Cape. South Africa. The research relies on lacustrine sedimentary deposits and their compositional changes as evidence of the dynamic depositional environments from which environmental conditions are inferred. Data on spatial changes on land surfaces have also been employed to complement the sedimentary chronology from catchments beyond historic records. Assessment of the extent of human influence on the Noordhoek basin has been achieved through comparison with the pristine conditions found on the Cape Nature Reserve. Analysis of dated sediment cores from the Noordhoek valley and the Cape Peninsula Nature reserve has facilitated the reconstruction of major environmental changes for the late Pleistocene and Holocene periods. An extended record of environmental change from the longest core (LM-Core) has enabled environmental reconstruction and the determination of the relative influences of climate, sea level change and human activities on the local! environment of the basin during the late Quaternary. Sedimentological evidence from the cores reveals the long-term evolution of the wetlands as being influenced by fluctuating sea levels and climate change until the mid-Holocene. Short-term environmental processes during the late Holocene. resulting from direct anthropogenic activities such as irrational uses of the wetlands for agriculture and urbanisation are responsible for polluting and transforming the status of the wetlands. Heavy metal concentrations in sediment cores from the two Noordhoek wetlands have allowed the elucidation of recent human impacts. The vertical distribution of these metals correlates with and complements the evidence of spatial changes in land use and land cover. Metal enrichment in the modern Noordhoek wetland sediments and increased organic matter content indicates increasing anthropogenic impacts on the valley as agriculture and urbanisation increased. In comparison. there is a much lower concentration of heavy metals at Groot Rondevlei, as its catchment has been less prone to severe local disturbance such as urban development and recent agricultural activities. The absence of a tightly resolved chronology for these cores restricts the understanding of the commencement and duration of major environmental changes, which have been accounted for elsewhere in the region. This limits the opportunity for direct comparison between this and other known sites. However, the Noordhoek valley is a potential resource for longer-term Quaternary environmental study. The application of a multi-disciplinary approach and high-resolution dating are highly recommended for future research in this area.

Bibliography: pages 171-197.
Avian remains in coastal archaeological samples from Eland's Bay Cave, Die Kelders Cave 1 and Nelson Bay Cave in the Cape Province, South Africa, cover the periods between 80 000 and 40 000 B.P. and 18 000 and 300 B.P. Results of modern comparative surveys indicate that beached birds provide a predictable food supply. Kolmogorov-Smirnov two-sample nonparametric tests confirmed the close resemblance between the relative proportions of seabirds in archaeological and beached assemblages and earlier assumptions that the composition of seabird samples in archaeological sites could not otherwise have been achieved. It is shown that this simple but effective practice has a history going well into the Middle Stone Age. Kolmogorov-Smirnov tests for differences between the relative proportions of skeletal elements of Cape cormorants preserved in archaeological and modern jackal accumulations provided a useful means of drawing attention to possible activity of jackals and/or domesticated dogs. Recognition that diagenesis in some earlier samples may mimic the characteristics of modern jackal samples has established the need to extend the comparison of skeletal elements to additional species and to study the relative durability of avian skeletal elements. Similar comparison with the proportions of modern mammalian and avian predator prey species and size (mass) categories provided no indication that black or martial eagles might have contributed to the samples. Similarly, present knowledge of Cape eagle owls argues against their being likely inhabitants of caves suitable for occupation by people. It is concluded that people were the primary accumulators of the assemblages studied and that the role of small food items in prehistoric subsistence can be addressed with greater confidence. Correspondence analysis was used to determine the existence of seasonality in the modern beached seabird samples. The profiles of the archaeological samples are plotted in relation to months in which they were most likely to have been collected. Seasonal evidence from species not subjected to the correspondence analysis supported these results. The results obtained closely supported the hypothesis for seasonal exploitation of the coast. It was also possible to indicate that visits were probably of short duration and that their timing varied. Exploitation of seabirds did not coincide with the period of maximum availability of beached birds. Comparison of the avian evidence with that from seals, Cape dune mole rats and steenbok/grysbok suggested that small food items comprised part of a seasonal strategy that made maximum use of a range of seasonal resources. Evidence for significant local environmental change in addition to, and in support of, existing information has been obtained. Fluctuations in marine, freshwater and terrestrial birds at Eland's Bay Cave have been related to evidence for changes in terminal Pleistocene and Holocene sea levels and the position of the coast, and in the morphology of Verlorenvlei. At Die Kelders Cave 1 between 80 000 and 40 000 B.P., previously drier conditions were ameliorating and mixed scrub and grass and freshwater existed on the coastal foreland in the vicinity of the cave. Fluctuations in frequencies of seabirds indicate that the sea level rose slightly and then receded during the period of deposition. At Nelson Bay Cave samples indicate the approach of the coast after the Last Glacial Maximum, the disappearance of grassland and its replacement by scrub and bush as significant elements of the vegetation. Freshwater birds did not respond as expected, however, indicating that their interpretation at Nelson Bay Cave is complex and not consistent with evidence for wetter or drier conditions. A possible link has been shown to exist between fluctuations of albatrosses, petrels and shearwaters at Nelson Bay Cave and the intensity of wind patterns which are related to oceanic and atmospheric circulation. Further investigation should establish whether seabirds would provide an index of climatic conditions without support from other sources.

Lakes Magadi (Kenya) and Manyara (Tanzania) occupy closed basins in the southern Gregory Rift valley. Water in these lakes is presently shallow and saline, testifying to the dominance of evaporation (E) over precipitation (P). Past changes in the P: E ratio, and hence in palaeoclimate, can be reconstructed from evidence of the former extent of these lakes. Lake-level fluctuations engender marked variation in water chemistry, and consequently on the composition of the limnological biota. One approach is to examine the sedimentary record of diatoms (unicellular algae), which are excellent indicators of water chemistry and relative water depth, and whose modem distribution is sufficiently well known to allow the quantitative reconstruction of chemical parameters. Diatom analysis of 116 samples from a series of radiometrically dated (14C and U/Ib) sediment cores has revealed significant changes amongst the diatom assemblages during the Late Quaternary. Conductivity and pH have been estimated from the fossil samples by transfer functions (Gasse unpublished, Gasse 1986b). However, the interpretation of fossil diatom assemblages is often problematical in hypersaline environments. Difficulties arise as a result of the operation of taphonomic and diagenetic processes which can severely alter the composition of the diatom assemblagesfr om the ambient population at the time of deposition. Probably the most important factor responsible for assemblage diagenesis in saline lakes is silica dissolution, and this is explored further by a series of laboratory experiments. Results indicate that silica dissolution acts differentially between species, by removing the smaller, more delicate taxa first, and causing the relative enrichment of large robust forms in the fossil samples. A similar dissolution gradient may be reflected in modem samples studied near hot springs at Magadi. Differential dissolution is potentially an important source of error in palaeoenvironmental reconstructions, but, with the outcome of these experiments, it has been possible to assess the extent to which the dissolution process may have shaped the diatom records from Magadi and Manyara. The bulk of the palaeolimnological evidence is focussed upon two periods, 30,000-20,000 BP and 12,700-9,500 BP. The earlier period is most clearly dated in the core from Manyara, where the diatom record suggests the development of an intermediate level lake between c. 27,500 BP and c. 26,000 BP. This is a more complete representation of the same lake phase found in earlier studies from Manyara by Holdship (1976) based on diatoms, and by Casanova (1986a) on stromatolites 20M above the present lake. This time interval may also be represented by the central portion of the Magadi cores NF1 and NF2 but here dating is more problematical. The period 12,700-9,500 BP was one of major lacustrine transgression across Africa although the fine-structure of this event is less well known. Cores NF1 and NF2 from Magadi provide a detailed register of this phase indicating a major highstand from c. 12,700-11,000 BP when the lake became deep enough to stratify and deposit laminated couplets. At c. 11,000 BP the diatoms show that salinity increased greatly from fresh-oligosaline to meso-hypersaline which was probably a consequence of lake level falling.

This thesis presents investigations on sediments from two African lakes which have been recording changes in their surrounding environmental and climate conditions since more than 200,000 years. Focus of this work is the time of the last Glacial and the Holocene (the last ~100,000 years before present [in the following 100 kyr BP]). One important precondition for this kind of research is a good understanding of the present ecosystems in and around the lakes and of the sediment formation under modern climate conditions. Both studies therefore include investigations on the modern environment (including organisms, soils, rocks, lake water and sediments). A 90 m long sediment sequence was investigated from Lake Tswaing (north-eastern South Africa) using geochemical analyses. These investigations document alternating periods of high detrital input and low (especially autochthonous) organic matter content and periods of low detrital input, carbonatic or evaporitic sedimentation and high autochthonous organic matter content. These alternations are interpreted as changes between relatively humid and arid conditions, respectively. Before c. 75 kyr BP, they seem to follow changes in local insolation whereas afterwards they appear to be acyclic and are probably caused by changes in ocean circulation and/or in the mean position of the Inter-Tropical Convergence Zone (ITCZ). Today, these factors have main influence on precipitation in this area where rainfall occurs almost exclusively during austral summer. All modern organisms were analysed for their biomarker and bulk organic and compound-specific stable carbon isotope composition. The same investigations on sediments from the modern lake floor document the mixed input of the investigated individual organisms and reveal additional influences by methanotrophic bacteria. A comparison of modern sediment characteristics with those of sediments covering the time 14 to 2 kyr BP shows changes in the productivity of the lake and the surrounding vegetation which are best explained by changes in hydrology. More humid conditions are indicated for times older than 10 kyr BP and younger than 7.5 kyr BP, whereas arid conditions prevailed in between. These observations agree with the results from sediment composition and indications from other climate archives nearby. The second lake study deals with Lake Challa, a small, deep crater lake on the foot of Mount Kilimanjaro. In this lake form mm-scale laminated sediments which were analyses with micro-XRF scanning for changes in the element composition. By comparing these results with investigations on thin sections, results from ongoing sediment trap studies, meteorological data, and investigations on the surrounding rocks and soils, I develop a model for seasonal variability in the limnology and sedimentation of Lake Challa. The lake appears to be stratified during the warm rain seasons (October – December and March – May) during which detrital material is delivered to the lake and carbonates precipitate. On the lake floor forms a dark lamina with high contents of Fe and Ti and high Ca/Al and low Mn/Fe ratios. Diatoms bloom during the cool and windy season (June – September) when mixing down to c. 60 m depth provides easily bio-available nutrients. Contemporaneously, Fe and Mn-oxides are precipitating which cause high Mn/Fe ratios in the light diatom-rich laminae of the sediments. Trends in the Mn/Fe ratio of the sediments are interpreted to reflect changes in the intensity or duration of seasonal mixing in Lake Challa. This interpretation is supported by parallel changes in the organic matter and biogenic silica content observed in the 22 m long profile recovered from Lake Challa. This covers the time of the last 25 kyr BP. It documents a transition around 16 kyr BP from relatively well-mixed conditions with high detrital input during glacial times to stronger stratified conditions which are probably related to increasing lake levels in Challa and generally more humid conditions in East Africa. Intensified mixing is recorded for the time of the Younger Dryas and the period between 11.4 and 10.7 kyr BP. For these periods, reduced intensity of the SW monsoon and intensified NE monsoon are reported from archives of the Indian-Asian Monsoon region, arguing for the latter as a probable source for wind mixing in Lake Challa. This connection is probably also responsible for contemporaneous events in the Mn/Fe ratios of the Lake Challa sediments and in other records of northern hemisphere monsoon intensity during the Holocene and underlines the close interaction of global low latitude atmospheric circulation.
In dieser Arbeit werden Ergebnisse von Untersuchungen an den Sedimenten zweier afrikanischer Seen vorgestellt, die ein Archiv für Klimaveränderungen über einen Zeitraum von mehr als 200.000 Jahren darstellen. Der Schwerpunkt liegt in dieser Arbeit auf dem letzten Glazial und dem Holozän (ca. 100.000 Jahre vor heute [nachfolgend als 100 kyr BP bezeichnet] bis heute). Grundlegende Voraussetzung für solche Studien ist ein gutes Verständnis der Ökosysteme in und um den See, sowie des gegenwärtigen Sedimentationsgeschehens. Deswegen beinhalten beide Seestudien Untersuchungen der heutigen Organismen, Böden, Gesteine, Wasserchemie und Sedimentablagerungen. Im Tswaing-See im nordöstlichen Südafrika wurden anhand eines 90 m langen Sedimentprofils Studien zur Sedimentzusammensetzung und Untersuchungen der Zusammensetzung und Qualität des organischen Materials durchgeführt. Sie zeigen einen Wechsel zwischen Phasen hohen detritischen Eintrags, während derer v.a. kaum autochthones organisches Material im See erhalten blieb, mit Phasen geringen Eintrags und dafür karbonatischer oder evaporitischer Sedimentation, die hohe Gehalte v.a. autochthonen organischen Materials aufweisen. Diese Phasen werden als relativ feuchte bzw. trockene Perioden interpretiert und folgen bis vor ca. 75 kyr BP Schwankungen der lokalen solaren Einstrahlung. Dieser Einfluss nimmt nach 75 kyr BP ab und azyklische feuchte Phasen werden beobachtet. Mögliche Ursachen sind Veränderungen in der ozeanischen Zirkulation und Verschiebungen in der Lage der Innertropischen Konvergenzzone (ITCZ); beides sind auch heute Haupteinflussfaktoren auf die Niederschläge in der Region. Die heute lebenden Organismen des Tswaing-Kraters wurden mittels Analysen der Biomarkerzusammensetzung und der Kohlenstoffisotopie charakterisiert und ihr Einfluss auf die heutigen Seeablagerungen untersucht. Dabei konnten zusätzlich Indikatoren für die Aktivität methanotropher Bakterien nachgewiesen werden. Der Vergleich heutiger Sedimente mit denen des Zeitraumes 14 bis 2 kyr BP zeigt deutliche Veränderungen sowohl in der Zusammensetzung, als auch in der Kohlenstoffisotopie der Biomarker, die mit Veränderungen in der Hydrologie erklärt werden können. Die gefundenen Hinweise auf feuchtere Bedingungen im Zeitraum älter als 10 kyr BP, für trockenere Verhältnissen zwischen 10 und 7.5 kyr BP und für die nachfolgende Wiederzunahme an Feuchtigkeit werden durch die sedimentologischen Ergebnisse unterstützt. Objekt der zweiten Seestudie ist der Challa-See am Fuß des Kilimanjaro. Hier werden heute im mm-Maßstab laminierte Sedimente gebildet, die mit Mikro-XRF-scanning auf Veränderungen in der Elementzusammensetzung untersucht wurden. Zusammen mit Untersuchungen der Mikrofazies und im Vergleich mit ersten Ergebnissen noch laufender Sedimentfallenstudien, mit meteorologischen Daten und Analysen des Umgebungsgesteins werden die saisonalen Veränderungen in der Temperaturverteilung, der Durchmischungstiefe, dem detritischen Eintrag und der Bioproduktivität des Sees in den Sedimenten nachvollziehbar. Der See ist in den feucht-warmen Perioden von Oktober bis Dezember und von März bis Mai stratifiziert. Während dieser Zeit erfolgt der Eintrag detritischen Materials und Kalziumkarbonat fällt aus; eine dunkle Lage mit hohen Gehalten an Fe und Ti und mit hohen Ca/Al- und niedrigen Mn/Fe-Verhältnissen bildet sich am Boden des Sees. Diatomeen blühen während der kühlen, windigen Periode von Juni bis September, wenn die Durchmischung bis auf etwa 60 m Tiefe Nährstoffe verfügbar macht. Die Ausfällung von Fe- und Mn-oxiden sorgt für hohe Mn/Fe-Verhältnisse; es bildet sich eine helle Lage auf dem Sediment. Trends im Mn/Fe-Verhältnis werden als Signal für Veränderungen in der Intensität oder Dauer der saisonalen Durchmischung interpretiert. Dies wird unterstützt durch parallele Trends im Gehalt an organischem Material und an biogenem Silizium, wie durch Analysen an einem 22 m langen Bohrkern gezeigt werden kann. Nach gut durchmischten und von erhöhtem Eintrag von außen geprägten Verhältnissen während des letzten Glazials erfolgt gegen 16 kyr BP ein Übergang zu stärker stratifizierten Bedingungen. Diese korrespondieren mit einem steigenden Seespiegel und verbreiteten Hinweisen auf feuchte Bedingungen im tropischen Ostafrika. Stärkere Durchmischung herrschte während der Jüngeren Dryas und von 11.4 bis 10.7 kyr BP. Diese Perioden entsprechen Zeiten verringerter Südwest- und vermutlich verstärkter Nordostmonsunintensität im Bereich des Indisch-Asiatischen Monsuns und spiegeln eine global beobachtete südliche Verschiebung der ITCZ wider. Nach einer kurzen stabilen, feuchten Phase im frühen Holozän nimmt die Durchmischung des Sees im Verlauf des Holozän wieder zu. Abrupte Ereignisse während des Holozän scheinen im Challa-See zeitgleich mit Veränderungen der Monsunintensität der Nordhemisphäre aufzutreten und bezeugen die starke klimatische Kopplung der niederen Breiten in globalem Maßstab.

Includes abstract.
Includes bibliographical references (leaves 123-146).
Rock hyrax (Procavia capensis) middens have been identified as excellent sources ofpalaeoenvironmental information in arid and semi-arid areas, and have been successfully used in various parts of southern Africa. Hyrax middens from the De Rif site in theCederberg Mountains of the south-western Cape have been collected and sampled. Through the application of pollen analysis to the midden material, local plant communities were inferred and a palaeoenvironmental reconstruction of prevailing conditions over the period of accumulation was produced. An assessment of the overall pollen assemblages indicates that typical mountain fynbos were present at De Rif throughout the last 28 ka and that generally there were no major changes in vegetation communities throughout this period.

Bibliography: leaves 124-144.
The southwestern Cape of South Africa is a floristically diverse region experiencing winter rainfall, and is important as it represents a significant southern hemisphere example of a Mediterranean climate regime. Acquiring palaeoenvironmental data from this region is imperative in understanding the climatic changes that have occurred during the Late Quaternary, with a view to improved palaeclimatic modelling. The spatial distribution of studies for the Late Quternary in the southwestern Cape is uneven and palaeoenvironmental reconstructions have been largely restricted to sites, which are easilty accessible, and appropriate only for the methods being used (e.g. palynology for wetlands). Moreover, many of the palaeoenvironmental reconstructions implemented thus far fall outside the winter rainfall region sensu stricto. Hence spatial differentiation in climatic response may have remained obscured due to the 'selection' of sites used.

Includes abstract.
Includes bibliographical references (leaves 215-241).
The study is focused on four study sites, two in the Western Cape, namely the Bruno section and Lake Michelle and two in southwestern Australia, namely Wambellup Swamp and Devil's Pool. These sites were chosen as they are well situated to investigate the complex interaction between Late Quaternary climate change, the influence of fluctuating sea levels and the impact of human interaction with the environments in question and provide a regional picture of these interactions.

A primary goal of paleoclimatology is to extend the instrumental record to capture a wider range of natural variability, documenting the climate system's response to past changes that have no analog in the historical record. Sediment archives of the recent geologic past, both marine and lacustrine, offer the opportunity to study how climate responds to a range of forcings and changing boundary conditions on timescales ranging from years to millennia. In this dissertation I use lacustrine and marine sediment to investigate changes late Quaternary climate, with particular focus on the Last Interglacial period (LIG). First, I use multiple approaches to reconstruct long-term changes in the West African Monsoon by investigating centennial-scale hydrologic variability recorded in Lake Bosumtwi sediments over the past 530,000 years. Over this interval, hydrology in the region is driven by a complex interplay of orbital forcing and glacial-interglacial boundary conditions. Lake level was generally much lower between 50 and 300 ka, likely due to the redistribution of rainfall from the tropics to the subtropics, driven by eccentricity's amplification of precession. Consequently, the Holocene highstand at the lake was both larger and longer lived than the maximum highstand during the LIG.Annual layers were continuously deposited through the LIG in Lake Bosumtwi, and I also present a new, 12,100 year-long, varve record spanning the interval from 128.6 to 116.5 ka. Over the course of the LIG, lake level generally tracks sea surface temperatures (SST) in Gulf of Guinea, including an abrupt drop in lake level that lasted about 500 years ca. 118 ka, coincident with cool SSTs in the North Atlantic and severe aridity in Europe. I find that the despite the generally drier conditions, hydrology varied on similar timescales as the late Holocene, with pronounced multidecadal to centennial-scale variability with non-stationary periodicities. I also investigate the contribution of ocean thermal expansion to sea level rise during the LIG, using a synthesis of paleoceanographic data and a climate model simulation. Globally, LIG SSTs were similar to, or slightly cooler than late Holocene SSTs, with the exception of the North Atlantic, which was several degrees warmer. Consequently, thermal expansion was likely a minor component of sea level rise during the interval, explaining between -0.3 and 0.4 m. of the 6 to 8 m highstand. Lastly, I tested the potential of Raman spectroscopy as a new, non-destructive technique to rapidly measure oxygen isotopic ratios in carbonates at extremely high resolution. Analyses on a suite a synthetic calcites indicate that ¹⁸O/¹⁶O ratios can be measured directly from the Raman spectra and have a 1:1 correspondence with traditional mass-spectrometry measurements. At present, the technique does not have the precision necessary to record natural variability, although there is considerable potential for improving the precision of the technique.

Includes bibliographical references.
Changes in circulation and productivity in the southeastern South Atlantic Ocean over the last 850 kyr are investigated through the multiproxy study of two giant piston cores, MD962080 and MD962084, retrieved from the Agulhas Bank and Olifants River continental slopes of South Africa. The stable oxygen isotope record of the benthic foraminifer, Cibicidoides wuellerstorfi, and the planktonic taxon, Globorotalia inflata, provide the stratigraphic framework from which the age models were created. The results indicate that biotic responses to surface hydrological changes in the study area are complex and involve both high- and low-frequency variations.

Bibliography: leaves 105-121.
This thesis is comprised of sedimentological and geochemical studies of seven 7m core sediments retrieved from the Namaqualand Mudbelt, South Africa. The purpose of this research is to contribute to the evidence for environmental change during the late Quaternary in the southern Africa from the analyses of continental shelf sediments and more specifically, to examine feasibility of using Namaqualand mudbelts as a key to understanding late environmental dynamics of both terrestrial and marine environment. Namaqualand mudbelts seem to have been deposited during the last 10 000 years. Chrono- and lithostratigraphy, coarse-fraction and geochemical analyses suggest the following sedimentary development on the Namaqualand offshore. An early period of deposition dominated by marine conditions off the coast, but with significant input in the north (Orange Delta) and south (off KIeinsee). There is a fining upcore sequence from the Orange Prodelta southward to the inner shelf (off Kleinsee). This fining-upward sequence is generally indicative of shoreward transgression of the sea (rising sea-level). As sea-level rises (shoreward transgression), finer-grained deeper water deposits migrate landward and are deposited over shallower water deposits. While the Orange River might be a major source of sediments on the Orange River Delta, marine contribution is increasingly important far south of the Orange Delta (off KIeinsee). ln addition, berg winds and local ephemeral Namaqualand rivers are also increasingly important.

Lake Tanganyika is a complex, tropical ecosystem in East Africa, harboring an estimated 2,100 species. Extensive watershed deforestation threatens the biodiversity and ecological integrity of the lake. In this dissertation, ecological and paleoecological methods were employed to study the distribution of invertebrate biodiversity through space and time, with particular emphasis on linkages between biodiversity and land –use patterns. Ecological surveys of fish, mollusc, and ostracod crustacean diversity at sites in northern Lake Tanganyika representing different levels of watershed disturbance revealed a negative correlation between biodiversity and intensity of watershed disturbance. To elucidate the long -term relationship between disturbance and biodiversity, paleoecological records of invertebrates offshore from watersheds experiencing different degrees of anthropogenic disturbance were examined. Life, death, and fossil assemblages of ostracod valves were compared to assess the reliability and natural variability inherent to the paleoecological record. These comparisons indicated that paleoecological (i.e. death and fossil) assemblages reliably preserve information on species richness, abundance, and occurrence frequency at comparable -to- annual resolution. Unlike life assemblages, species composition of paleoecological assemblages reflects input of species from multiple habitat types. Ostracod paleoecological assemblages are characterized by spatiotemporal averaging that renders them representative of larger areas and longer time spans than life assemblages. Thus, paleoecological assemblages provide an efficient means of characterizing longer -term, site -average conditions. Natural variability in ostracod fossil assemblages from a sediment core representing the Late Glacial to the present indicates that abundance of individual ostracod species is highly variable. Ostracod assemblages were preserved in only the most recent 2,500 years of sediment. Species composition of ostracod assemblages reflects lake water depth. Core geochemical data indicate that the coring site may have been below the oxycline for ~2,000 years, inhibiting ostracod survival and preservation. Paleoecological, sedimentological, and stable isotope data revealed differences in biodiversity and watershed disturbance through time offshore from a pair of sites. The protected site is offshore from Gombe Stream National Park (Tanzania), the other offshore from a deforested watershed outside the park. Offshore from the deforested watershed, sedimentation rates increased, and turnover in ostracod species composition occurred during the past 50 years. Comparable changes were not observed offshore from the park.

Ce travail présente une analyse des systèmes turbiditiques actuels du Golfe d’Oman et de la marge est-africaine (océan Indien occidental), auparavant méconnus. Il se base sur une base de données acoustique (bathymétrie, imagerie multifaisceaux, sismique THR et multitraces) et sédimentologique (carottes küllenberg et calypso) issues de campagnes successives réalisées par le SHOM et l’IFP. L’architecture des systèmes de dépôts profonds et les processus associés ont révélé une grande diversité selon le contexte géodynamique et physiographique des marges étudiées (marge passive, marge transformante, marge active). Les différents systèmes étudiés illustrent notamment le rôle du contexte tectonique régional sur la répartition et la morphologie des dépocentres à plusieurs échelles d’observation. L'analyse détaillée des faciès et séquences sédimentaires a permis de mettre en évidence le fonctionnement sédimentaire des différents systèmes en lien avec les conditions physiographiques et environnementales régionales (influence des crues liées à la mousson sur le transfert sédimentaire). A travers la reconstruction des transferts sédimentaires dans ces systèmes turbiditiques, nous discutons de l’impact relatif des différents facteurs forçant la sédimentation gravitaire sous-marine à haute-fréquence (eustatisme, climat, et tectonique). Pour cela, une étude stratigraphique détaillée a été réalisée sur la base de différents outils (datation radiocarbone, géochimie élémentaire, biostratigraphie) permettant de contraindre dans le temps les séries sédimentaires gravitaires. L’évolution des apports sédimentaires et des processus de dépôt au cours du Quaternaire terminal, en relation avec les modifications paléo-environnementales continentales, a permis d’identifier l’impact, l’importance relative et les interactions entre les forçages externes sur le développement à haute-fréquence (103-104ans) de systèmes de dépôt gravitaires, dans divers contextes géodynamiques. Les connaissances acquises sur la sédimentation du Golfe d’Oman ont finalement permis d’alimenter une base de données sédimentologique conséquente. L’intégration de cette base dans un modèle numérique géoacoustique (« simulateur ») développé par le SHOM a permis d’évaluer quantitativement l’impact des variations sédimentaires à différentes échelles (distribution spatiale, lithologie, stratification, processus de dépôt) sur la propagation du signal acoustique pour différentes gammes de fréquence (de 300 Hz jusqu’à 3 kHz) et angles d’émission (de 0 à 90°). Ces travaux constituent une base pour la réalisation d’un modèle géoacoustique régional robuste
This study focuses on the Late Quaternary turbidite systems of the Gulf of Oman and the East-African margin (western Indian Ocean), previously poorly studied. It is based upon a compilation of acoustic data (bathymetry, multibeam imagery, 3.5 kHz and multi-channel seismic) and sedimentological data (küllenberg and calypso piston cores) recovered during several cruises leaded by the SHOM and IFP institutes. Turbidite system architecture and sedimentary processes revealed a strong variability primarily related to the physiographic, hydro-climatic and geodynamic context of each margin. High-resolution stratigraphy has been achieved using a combination of radiocarbon dating, XRF geochemistry, biostratigraphy). This allowed to investigate the impact, the interaction and the relative importance of the external forcings on deep water sedimentation (i.e. tectonics, climate and eustasy) at high- frequency (103 -104 yrs) in different tectonic setting (active & passive margins). Finally, integration of the sedimentological data set in a geoacoustic numerical modelling leaded to a first quantitative estimation of the regional relationship between sea-floor properties (lithology, depositional environment, stratification) and propagation of acoustic signal at 300 Hz- 3kHz frequencies and 0-90°. This work constitutes a basis for future geoacoustic modelling in the area

A total of 193 dates are listed from the Eastern Cape. Middle Stone Age hunter-gatherers existed in the Drakensberg prior to the rigours of cold climatic conditions after ca. 22,000 BP. These uplands were reoccupied under more favourable climatic conditions after ca. 12,600 BP but were apparently abandoned between ca. 6000 BP and 3000 BP. Hunter-gatherer occupation throughout the Holocene is indicated at lower altitudes, with in-migration of pastoralists ca. 1800 BP in the Fish River area, and with Iron Age farmers entering coastal districts and adjacent river valleys from ca. 1400 BP. Sand dunes accumulated in the Holocene adjacent to the Indian Ocean. Flood plain development in the early Holocene was succeeded by incision of rivers in the later Holocene. Flood plain deposition began again in the Southern Drakensberg ca. 1000 BP. Palynological studies evidence marked climatic oscillations around the Late Glacial/Holocene boundary, with apparent stability at high altitude subsequent to 2700 BP.

A total of 193 dates are listed from the Eastern Cape. Middle Stone Age hunter-gatherers existed in the Drakensberg prior to the rigours of cold climatic conditions after ca. 22,000 BP. These uplands were reoccupied under more favourable climatic conditions after ca. 12,600 BP but were apparently abandoned between ca. 6000 BP and 3000 BP. Hunter-gatherer occupation throughout the Holocene is indicated at lower altitudes, with in-migration of pastoralists ca. 1800 BP in the Fish River area, and with Iron Age farmers entering coastal districts and adjacent river valleys from ca. 1400 BP. Sand dunes accumulated in the Holocene adjacent to the Indian Ocean. Flood plain development in the early Holocene was succeeded by incision of rivers in the later Holocene. Flood plain deposition began again in the Southern Drakensberg ca. 1000 BP. Palynological studies evidence marked climatic oscillations around the Late Glacial/Holocene boundary, with apparent stability at high altitude subsequent to 2700 BP.

Conflicting reports from geomorphic studies appear in the literature describing the environment of the southern African Main Escarpment region adjacent to the Lesotho Highlands during the cold phases of the Late Quaternary. Evidence cites limited glaciation and/or periglacial conditions with or without permafrost. The thesis emphasises debates and presents arguments for alternative interpretation of landforms previously described in the literature as indicative of specific cold environments. Field investigations into the distribution and characteristics of openwork accumulations in southern Africa show that blocky accumulations are found within a range of climatic conditions, including arid and semi-arid environments. Mode of emplacement is highlighted as the critical factor in association with a periglacial environment. Relict openwork block accumulations in the Lesotho highlands area around Thabana Ntlenyana, the highest summit in the escarpment range, supports the contention for a relatively arid periglacial environment during the Late Pleistocene. Findings militate against either deep snow cover or localised glaciation of insolation-protected south-facing slopes. The evidence for periglacial conditions is supported by the presence of relict sorted patterns that indicate deep seasonal freeze. Contemporary soil temperature monitoring indicates a near-surface current seasonal freeze of two and a half months which would have been prolonged and deepened under depressed temperature. No specific evidence for periglacial conditions is found for the escarpment region in the Amatola mountains.
Thesis (DPhil)--University of Pretoria, 2003.
Geography, Geoinformatics and Meteorology
unrestricted

Four major climato-environmental phases have been identified in the Eastern Cape, Plettenberg Bay-Knysna region and Little Karoo between somewhat before ~ 40 000 cal. a BP and the present: the Birnam Interstadial from before 40 000 cal. a BP until ~ 24 000 cal. a BP; the Bottelnek Stadial (apparently equating with the Last Glacial Maximum) from ~24 000 cal. a BP until before ~ 18 350 cal. a BP; the Aliwal North (apparently equating with the Late Glacial) from before ~ 18 350 cal. a BP until ~ 11 000 cal. a BP; the Dinorben (apparently equating with the Holocene) from ~ 11 000 cal. a BP until the present. The evidence for, and the characteristics of, these phases is briefly described.

Zur Rekonstruktion der jungquartären Landschaftsentwicklung am Kilimanjaro werden Sedimente aus Paläoböden am Mt Kilimanjaro untersucht, um die lokale und regionale Ökosystem-, Klima-, Feuerdynamik in einem größeren Rahmen zu verstehen. Desweiteren soll die Reaktion der Ökosysteme auf Umweltveränderungen erforscht werden, um die Beziehungen verschiedener Ökosysteme und ihre Rolle hinsichtlich der Entwicklung von „Biodiversity Hot Spots“ in Ostafrika aufzudecken. Die Ergebnisse tragen zu einem besseren Verständnis der heutigen und zukünftigen Dynamik von Ökosystemen bei. Sie sind außerdem eine wichtige Grundlage im Naturschutz, da sie bedeutende Informationen für die Aufrechterhaltung und das Management der hohen Biodiversität in den ostafrikanischen Hochländern liefern. Die Durchführung von paläoökologischen Untersuchungen ist unerlässlich, da die Prozesse der Vergangenheit eine wichtige Rolle bei der Entwicklung der Ökosysteme und Biodiversität spielen. Die vorliegende Arbeit erforscht die spätquartäre Vegetation-, Klima- und Feuerdynamik am Kilimanjaro, um das Verständnis der dortigen Ökosystem zu vertiefen. Sowohl Pollen als auch weitere Klima-Proxies von zwei Sedimentkernen werden analysiert, um die Vegetationsdynamik vom frühen Spätglazial bis heute zu rekonstruieren und die jeweiligen Einflußfaktoren aufzudecken. Die Ergebnisse vom Maundi Krater, welcher auf 2780 m Höhe am südostlichen Hang des Kilimanjaros gelegen ist, stellen eines der längsten, terrestrischen Klimaarchive im tropischen Ostafrika dar, und ermöglichen den Einblick in fast 100 000 Jahre Vegetations- und Klimageschichte. Das WeruWeru Paläobodenprofil aus dem montanen Waldgürtel am Kilimanjaro ermöglicht die detaillierte Rekonstruktion der Reaktionsdynamik der Vegetation auf Veränderungen in der Umwelt. Die Ergebnisse beider Untersuchungen zeigen, dass Klimaveränderungen zu einer Verschiebung der montanen Vegetationsgürtel entlang des Höhengradienten des Mt Kilimanjaro geführt haben. Das Pollenarchiv des WeruWeru Profils dokumentiert starke Veränderungen in den höchsten Vegetationgürteln, dem Erikagürtel und dem oberen montanen Wald. Trotz markanter Klimaveränderungen scheint Mt Kilimanjaro aber auch als eiszeitliches Refugium für Waldarten gedient zu haben. Feuerereignissen spielten hinsichtlich der Ausbildung des Erikagürtels eine entscheidende Rolle. Hinweise auf verstärkte menschliche Aktivitäten können an keinem der beiden Untersuchungsstandorte festgestellt werden. Die Pollenregen-Studie entlang des Höhengradienten am Kilimanjaro zeigt, dass es sehr entscheidend ist, die quantitative Beziehung zwischen Pollen-Niederschlag und moderner Vegetation zu untersuchen, um die Rekonstruktionen der Vergangenheit zu kalibrieren. Die Ergebnisse ermöglichen eine weitaus präzisere Interpretation der Vegetations- und Klimarekonstruktionen im tropischen Ostafrika.

Palaeoenvironmental evidence indicative of former climatic conditions in the Eastern and adjoining Western Cape during the last ~ 45 000 yr is presented and summarised. Interstadial conditions began before 43 000 BP but were succeeded by stadial conditions at ~ 24 000 BP. These climatic phases are designated the Birnam Interstadial and the Bottelnek Stadial after the type sites at which they were identified in the Eastern Cape. The Bottelnek Stadial apparently equates with the Last Glacial Maximum. Late Glacial warming was apparent by 18/17 000 BP. Sea level rose markedly by ~ 14 000 BP. Climatic oscillations marked the end of the Late Glacial. The Early Holocene was drier than the Late Holocene and, at least in the Drakensberg, there was marked aridity in the mid-Holocene. Human responses to these climatic events are briefly described.