ETD Collection

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Subject: search.filters.subject.Paleoclimatology

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Now showing 1 - 4 of 4
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    Analyzing lithic raw material qualities and hominid selectivity in the Early Palaeolithic
    (2020) Sherwood, Nicole
    Numerous studies have been employed to analyse early hominid lithic raw material selection using a variety of different methods, but have not been done for the large majority of sites throughout the world, with the main focus being on East African Oldowan sites. Thus, our knowledge of early hominid behaviour across the world and across time is not nearly as extensive and complete. In addition, a universal methodology to gauge raw material selection has not yet been presented. This is because each archaeological site is unique, making it difficult to do so. Some researchers have made use of rigorous engineering and geochemical testing methods to determine the quality of rock types selected and utilised, while others have applied more qualitative methods or included an experimental aspect to their research. The research presented in this thesis incorporates raw material studies from China and South Africa for both the Oldowan and Acheulean technological time periods. Most importantly it shows the significance of developing a methodology to gauge raw material selection that is unique for each particular site with the aid of experimental knapping. The inclusion of experimental knapping is not only important for determining quality characteristics of rocks for analyses, but it can also help in discovering behavioural aspects of early hominids by isolating specific reasons for their selection choices. Such knapping experiments were performed for the Cradle of Humankind sites Sterkfontein and Swartkrans, as well as for sites in the Danjiangkou Reservoir Region (DRR), central China. In the Cradle, experimental creation and use of tools made from the twelve different available rock types determined which of these rock types were best for tool creation. The experimentally created lithics also provided a basis for comparison with the artefacts from Oldowan and Acheulean assemblages at both sites showing that selection was present, and to what extent. The two time periods were compared to each other and differences between the two sites assessed. The results indicated that there was more selection during the Acheulean and that more selection was practiced at the Sterkfontein site. This is likely due to the larger distance from Sterkfontein to the main source of gravels in the area. Experimental knapping of materials in the DRR revealed that hominid selection for raw material is also present in Asia during the Middle Pleistocene and is just as complex as selection in Africa. Variables for analyses had to be adjusted to suit the uniqueness of the geology of the area as the rock types available in this region are different from the materials in East and South Africa. The rock type most often selected for large cutting tools (LCTs) at the DRR sites (terrace three)is one that frequently exhibits a multitude of visible flaws (quartz phyllite) and is the most common material available from the local gravels. This might leave one to conclude that raw material selection was absent or highly expedient for the creation of LCTs at this Middle Pleistocene site. Experimental knapping of this material, and the others available, revealed that quartz phyllite was the most optimal for the creation of LCTs. The unique nature of the flaws allowed for cobbles to be easily split in half with little effort. The halves could then easily be shaped into functional LCTs with minimal further shaping, despite the flaws in the material. Furthermore, these flaws could be circumvented or further exploited with knapping skill. Another factor that contributed to this material’s usefulness was the ease with which large flakes could be dislodged. Less force was needed to flake this material (much like glassy material) than the quartzites and igneous cobbles, which rarely exhibited flaws. Quartz phyllite is also durable and allowed for exceptionally sharp edges to be created. Experimentation with various knapping techniques indicated that bipolar flaking of quartz phyllite cobbles was the most successful method for blank creation for LCTs. The bipolar knapping of this material made it possible to determine a feature often unique to this technique, namely compression fractures, which could be used to identify which of the Acheulean LCTs were created from bipolar flakes. This technique was present in the assemblages, and shows flexible technological solutions among the Middle Pleistocene hominids living in the DRR. These experiments demonstrated the importance of experimental knapping being included within lithic raw material studies, as it helped show the intricacies of raw material reduction and its associated selection at the sites in this project. This thesis also presents information with regards to the complexities of raw material selection during the Acheulean and the Palaeolithic in Asia
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    Tree-growth rings as a palaeoclimate proxy for the Karoo basin
    (2018) Kock, Simone
    The almost complete stratigraphic and fossil records of the Karoo Basin have made it one of the main focal points for Gondwanan palaeoenvironmental studies. The majority of Karoo palaeoenvironmental studies use vertebrate, invertebrate, macroflora and microflora fossils as proxies. Very few studies have been done on the Karoo fossil woods and their significance as palaeoenvironmental, and more specifically palaeoclimate, proxies. In this preliminary study, thirty-one Agathoxylon wood samples from the Ecca-Beaufort contact and five of the Beaufort Group’s (Karoo Basin) formations have been analysed to reconstruct the palaeoclimate for the Karoo Basin during the Beaufort times. The growth rings of each sample underwent a detailed growth ring analysis where six palaeoclimate significant anatomical features were chosen and used to obtain palaeoclimate information. The growth rings are generally wide and reflect a seasonal climate with warm/moderate temperatures and sufficient rainfall. The presence of false rings in some of the growth rings suggests that some years experienced water-stressed/semi-arid conditions. The intra-ring variation and CSDM curves of the growth rings indicate that the fossil wood samples generally reflect ‘complacent’ trees with deciduous habits. The majority of growth rings contain shear zones (i.e. S-type growth rings), which indicate a seasonal climate but can also be seen as indicators of zones with weakened wood cells (due to disease or post-depositional compression). Although this study only represents a small sample size (thirty-one specimens with very few growth rings each), the growth ring analysis illustrates the palaeoclimate potential of the Karoo fossil woods and how they could aid in improving Karoo Basin palaeoenvironmental interpretations. However, a wider geographic range and more fossil woods from other stratigraphic positions/time periods are required for the basin-wide palaeoclimate reconstruction that would make these improved palaeoenvironmental interpretations possible.
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    Phytolith analysed to compare changes in vegetation structure of Koobi Fora and Olorgesailie basins through the mid-pleistocene-holocene periods
    (2018) Kinyanjui, Rehab Njuhi
    The Koobi Fora and Olorgesailie Basins are renowned Hominin sites in the Rift Valley of northern and central Kenya, respectively with fluvial, lacustrine and tuffaceous sediments spanning the Pleistocene and Holocene. Much research has been done on the fossil fauna, hominins and flora with the aim of trying to understand when and how the hominins evolved, and how the environment impacted on their behaviour, land-use and distribution over time. One of the most important factors in trying to understand the hominin-environment relationship is firstly to reconstruct the environment. Important environmental factors are the climate, rate or degree of climate change, vegetation structure and resources, floral and faunal resources. Vegetation structure/composition is a key component of the environments and, it has been hypothesized the openness and/or closeness of vegetation structure played a key role in shaping the evolutionary history not only of man but also other mammals. Various proxies have been studied to determine and reconstruct vegetation history. They include: fossil pollen, stable isotopes, fossilised wood and phytoliths. This study applied phytolith analyses to reconstruct the vegetation history of the Koobi Fora and Olorgesailie Basins during the Pleistocene to Holocene periods respectively. Firstly, modern phytolith analogues from plants and surface soils were used to interpret the past vegetation from fossil phytolith assemblages. Four vegetation structures were clearly recognisable: grasslands, wetlands/riparian, woodlands/forests and mixture of woody and herbaceous dicotyledons. Although the proposed goal of this study was to compare temporal changes in phytolith assemblage, hence vegetation structure for the two basins, this was not achieved due difference in the sampling strategies available for the two basins. A continuous sediment core was drilled from the Olorgesailie Basin representing ~970kyr to ~77kyr, while in Koobi Fora sampling was done from well dated archaeological and geological exposures representing the early Pleistocene period (2.525-2.51Ma) and the Holocene period (9.6kyr to 0.93kyr), lacking mid-late Pleistocene deposits Determining the vegetation structure from both basins was possible. Two approaches were applied, a general approach for vegetation reconstruction (phytolith abundance) and phytolith indices (aridity and tree cover indices). Phytolith assemblages from paleosols deposited between 1.525Ma and 1.52Ma suggest a general vegetation cover dominated by woodlands which shifted to woody mixed grasslands that resemble present savanna habitats and a moister grassland habitat is also reflected. From ~970kyr to ~77kyr the vegetation structure comprised open grasslands, wooded grasslands, woodland/forest, and wetland/riparian/riverine habitats. These habitats fluctuated and the environments were unstable. The rate of fluctuations changed from high to low throughout the Olorgesailie sequence. From the Koobi Fora samples the Early Holocene (~9.6kyr to ~4.2kyr) was to the Early Pleistocene with woodlands remaining dominant, mixed grassland always present and a mosaic vegetation. A clear vegetation shift is noted during the late Holocene period (~1.34kyr to 0.93kyr), where woodlands declined while Chloridoideae grasses increased significantly indicating arid habitats similar to present-day savanna grasslands For future research directions it will be a valuable opportunity to have a long sediment core drilled from either the current Lake Turkana basin or a paleolake basin from which phytolith data can be analysed and studied to give a continuous vegetation reconstruction history. Key words: Phytoliths, Pleistocene, Holocene, Paleoenvironments, Koobi Fora, Olorgesailie
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    The Quaternary pollen of Ntsikeni Wetland, KwaZulu-Natal, South Africa
    (2017) Combrink, Maria
    Ntsikeni wetland, one of the highest altitude wetlands (~1795 m.asl) in South Africa, is a Ramsar site. Data from Ntsikeni Wetland will add to the spatial and temporal palaeoclimate data for southern Africa. The CONISS analysis separates the sequence into four primary zones of statistically significant similarity: WNT4: 25,000-13,000 cal. yr BP; WNT3: 13,100-10,800 cal. yr BP; WNT2: 9,000-4,300 cal. yr BP; WNT1: 4,200-650 cal. yr BP. From 22,000-21,000 cal. yr BP an increase in temperature and moisture is observed, followed by an increase in temperature and a decrease in moisture from 21,000-18,750 cal. yr BP. At 17,000 cal. yr BP a short but sudden drop in temperature and moisture is recorded. The final two changes in Zone WNT1 are short and definitive shifts to colder temperatures; the first at 15,000-14,800 cal.yr BP, the second 14,000-13,200 cal. yr BP; at 13500 cal. yr BP it is possibly the coldest period. The entire Zone WNT1 points to an increase in precipitation during colder periods. The wetland continued to contract until 11,000 cal. yr BP. A hiatus in pollen 9,000-10,700 cal. yr BP is observed, followed by an increase in moisture 8,800-8,200 cal. yr BP, and a warm period, with a contraction of the wetland from 7,000-5,050 cal. yr BP. A very brief wet and warmer period from 4,300-4,100 cal. yr BP is recorded, as the wetland starts to expand. Temperatures continue to increase, with a short localised drying period (100 years) and evaporation.