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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The late quaternary palaeoenvironments of a subalpine wetland in Cathedral Peak, KwaZulu-Natal Drakensberg.

Lodder, Jared. January 2011 (has links)
In contrast to the wealth of palaeoenvironmental research stemming from the eastern Afromontane archipelago, the southern Afromontane component, which comprises largely of the Drakensberg, remains understudied. The Drakensberg constitute an area of significant biodiversity, cultural and economic importance. Suitable sites for palaeoenvironmental research are rare in South Africa due to general arid climatic conditions over much of the country. The KwaZulu-Natal Drakensberg offers a unique opportunity for palaeoenvironmental research through its increased rainfall and higher altitudes, which enable the development of wetlands that have the potential for polliniferous accumulation to occur. Catchment Six in Cathedral Peak is one such wetland that has provided an opportunity to research palaeoenvironmental conditions of the southern Afromontane archipelago component. A 371 cm sediment core was extracted from a subalpine wetland in Catchment Six and analysed using multiple proxies including; pollen, charcoal and geochemistry (carbon and nitrogen stable isotopes). A chronological framework for the core was established based on accelerated mass spectrometry radiocarbon dating of eight bulk sediment samples. A basal date of 15,100 ± 445 cal yr BP was determined at a depth of 298 cm. Poor pollen preservation of the basal portion of the core limited palaeoenvironmental inference for the late Pleistocene section of the record. The multiproxy record provides high chronological resolution for the early to late Holocene. Multi-proxy data indicate that the Holocene period in the Drakensberg was characterised by variable climatic conditions. Charcoal data indicate periods of increased regional fires in the last ca. 400 cal yr BP. Palaeoenvironmental inferences from the Catchment Six record are broadly in agreement with regional climatic indications based on existing literature. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
2

The biostratigraphy, palaeoecology and geochemistry of a long lacustrine sequence from NW Greece

Frogley, Michael Reginald January 1998 (has links)
Examination of an important new 319m core of lake sediment recovered from Ioannina in NW Greece has attempted to relate changes in the lake to variations in the regional climate of south-central Europe over the last 600,000 years. The site is known to have been extremely sensitive to past climatic change for three reasons: (i) temperate vegetation persisted throughout glacial stages (albeit at low frequencies), so the vegetational response to climatic change would therefore have been almost immediate; (ii) the extreme thickness of the sediments suggests that accumulation rates were high (at times, > 1m per thousand years), which has enabled high-resolution palaeoclimatic reconstructions; and (iii) precipitation of authigenic carbonate has preserved a remarkably sensitive proxy record of productivity variations for most of the lake's history. Well-defined shifts from glacial - interglacial mode have been correlated with vegetational changes identified in a core previously analysed from the same basin (using magnetic susceptibility profiles), enabling tentative correlations to be suggested with other European terrestrial sequences and with the marine oxygen isotope record, back to marine isotope stage 16. Twelve AMS radiocarbon determinations from the upper part of the core, together with the identification of a series of reversed palaeomagnetic events within the Brunhes chron, support the proposed age model for the sequence. The sediments at Ioannina, unlike most of the other long terrestrial European sequences, are calcareous and contain mollusc and ostracod assemblages. Part of this project has involved a comprehensive review of Quaternary and modem aquatic faunas from the lake, as well as the description, illustration and critical assessment of several poorly-known endemic taxa. Faunal assemblage data have been used to provide valuable information concerning the variable response of lake-level to climatic change over time. Convincing new mollusc an evidence indicates low lake-levels at the Last Glacial Maximum, agreeing with regional pollen data, but conflicting with geomorphological evidence derived from Kastritsa, a well-documented nearby Palaeolithic cave site. It is suggested that this discrepancy may be a result of subsequent tectonic uplift of the rockshelter. In addition, stable isotopic analyses of both the ostracods and the bulk carbonate within the sediments have contributed towards deriving a comprehensive palaeoenvironmental history for the site. Although the study analysed physical, biological and geochemical aspects of the entire core, two distinct parts of the record were selected for more detailed investigation. High-resolution analysis over the last interglacial (the Eemian) has revealed evidence for a clear, two-step deglaciation at the beginning of the period, known from elsewhere as the Zeifen-Kattegat Oscillation. Climatic instability has also been detected within the full interglacial. Comparisons are drawn with a range of other Eemian records from across Europe, as well as the Greenland ice cores. High-resolution analysis of the period from the end of the last glacial to the present day has also revealed evidence for climatic instability. A cool and arid oscillation is demonstrated by several climatic proxies that may constitute the first recognition of the Younger Dryas stadial from Greece. A shorter, but more subdued cooling event has also been detected during the first half of the Holocene, which may correspond with a widespread climatic oscillation from high-resolution terrestrial, marine and ice core records that has been dated to between 7,500 and 8,000 years BP.
3

Late quaternary palaeoenvironments of the Mfabeni Peatland, Northern KwaZulu-Natal.

Finch, Jemma M. January 2005 (has links)
To assist in developing a more precise understanding of past climatic changes in southern Africa, further pollen analytical research is required. In the past, pollen sites in the subregion have been restricted to swampy areas such as permanent springs and peat deposits. While such sites are often rare as a consequence of the aridity of the country, rich polliniferous deposits can be found in the peatlands surrounding coastal lakes in the Maputaland Coastal Plain. The Mfabeni peatland, situated on the eastern shores of St. Lucia, contains relatively old sediments dating back to >45000 years bp at a depth of 7.80m. A multi-proxy approach, comprising radiocarbon, stable carbon isotope (513C) and palynological analysis, was applied in the investigation of Late Quaternary climatic conditions and vegetation changes along the Maputaland Coastal Plain. A single 10 m sediment core, dating back to >45000 years bp, was extracted from the Mfabeni Peatland. A detailed fossil pollen analysis of Mfabeni sediments indicated the existence of extensive Podocarpus-abundant coastal forests before ca. 44500 years bp. The onset of wetter local conditions after this time is inferred from forest retreat and the development of swampy conditions, which prevailed until ca. 25000 Cal years BP. Conditions during the Last Glacial Maximum (LGM; 18000 years BP) are inferred to have been generally colder and drier, as evidenced by forest retreat and replacement of swampy reed/sedge communities by dry grassland. A significant depletion in 813C values at ca. 18200 Cal years BP indicates the dominance of C3 vegetation during the LGM, reflecting considerably colder conditions. This is in agreement with palaeoenvironmental indications from elsewhere in the Transvaalian Ecozone, although conditions at Mfabeni were more moderated in their manifestation, which can be attributed to the proximity of this site to the ocean. Cool, relatively moist conditions are inferred for the Holocene Altithermal (ca. 8000-6000 years BP), as evidenced by forest growth and expansion during this time. Warm, dry conditions are inferred for the Late Holocene, with the establishment of grassland/savanna type vegetation in the area after ca. 2000 Cal years BP. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

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