An investigation of the movement of sediment through the Noordhoek headland bypass dunefield system at Cape Recife, South Africa
- Authors: Goosen, Gerrit Pieter
- Date: 2018
- Subjects: Sedimentation and deposition , Fluvial geomorphology Geomorphology Sand dunes -- Environmental aspects
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22101 , vital:29840
- Description: A detailed study of the movement of sediment across the Cape Recife headland via the Noordhoek headland bypass dunefield was conducted. The Noordhoek HBD is important because of the environmental impacts anticipated on the sewerage works, settling ponds, and road to the Cape Recife lighthouse situated in the migration path of the dunefield to the ENE of its active boundary. The primary objective of the study was to investigate the movement of sediment in and through the Noordhoek HBD system. This study has provided sand transportation and dune migration rates by making use of various dune monitoring techniques. In doing so, useful predictions have been made as to when the settling ponds and the road to the lighthouse will be inundated. An indication has also been given as to how much sand moves through the system. Some key findings from this research included: the net migration direction of the Noordhoek HBD was found to be towards the east-north-east; the wind environment at the study area was classified as a high energy wind environment; this study has highlighted that various climatic factors such as rainfall and temperature influence the movement of sediment through dune systems; sediment transport was found to be directly related to the source area and topography; the central zone of the dunefield proved to be a groundwater recharge zone for the western and eastern zones; and the leading lobes of the migrating Noordhoek dunefield are gradually covering stabilising vegetation by pulses of dunes moving through. In this study, it was calculated that presently a total volume of about 26 000 m3 of sand is migrating into the vegetation at the leading lobes annually. If the Noordhoek HBD is left to run its natural course and migrate across the Cape Recife headland to the downwind beach, an approximate volume of 26 000 m3 of sand could be supplied to the downwind beach by this system. In doing so, it has the potential to play a role in replenishing some of the sand to Port Elizabeth’s eroded southern beaches via a natural process.
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- Date Issued: 2018
An erosion and sediment delivery model for semi-arid catchments
- Authors: Bryson, Louise Kay
- Date: 2016
- Subjects: Sedimentation and deposition , Erosion , Watershed management -- South Africa , Water-supply -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:6056 , http://hdl.handle.net/10962/d1020331
- Description: Sedimentation has become a significant environmental threat in South Africa as it intensifies water management problems in the water-scarce semi-arid regions of the country. As South Africa already allocates 98% of available water, the loss of storage capacity in reservoirs and degraded water quality has meant that a reliable water supply is compromised. The overall aim of this thesis was to develop a catchment scale model that represents the sediment dynamics of semi-arid regions of South Africa as a simple and practically applicable tool for water resource managers. Development of a conceptual framework for the model relied on an understanding of both the sediment dynamics of South African catchments and applicable modelling techniques. Scale was an issue in both cases as most of our understanding of the physical processes of runoff generation and sediment transport has been derived from plot scale studies. By identifying defining properties of semi-arid catchments it was possible to consider how temporal and spatial properties at higher levels emerged from properties at lower levels. These properties were effectively represented by using the Pitman rainfall-runoff model disaggregated to a daily timescale, the Modified Universal Soil Loss Equation (MUSLE) model incorporating probability function theory and through the representation of sediment storages across a semi-distributed catchment. The model was tested on two small and one large study catchment in the Karoo, South Africa, with limited observed data. Limitations to the model were found to be the large parameter data set and the dominance of structural constraints with an increase in catchment size. The next steps in model development will require a reduction of the parameter data set and an inclusion of an in-stream component for sub-catchments at a larger spatial scale. The model is applicable in areas such as South Africa where water resource managers need a simple model at the catchment scale in order to make decisions. This type of model provides a simple representation of the stochastic nature of erosion and sediment delivery over large spatial and temporal scales.
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- Date Issued: 2016
Analysis of the tectonic and basin evolution of the seychelles microcontinent during the mesozoic to cenozoic, based on seismic and well data
- Authors: Mondon, Jean-Luc Andre
- Date: 2014
- Subjects: Sedimentation and deposition , Gondwana (Continent) , Sedimentary basins
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/4386 , vital:20593
- Description: The Seychelles Microcontinent (SMc) is a fragment of continental lithosphere that experienced multiple phases of rifting and thermal subsidence during its isolation and submergence within the Indian Ocean. Originally part of central Gondwana, along with India and Madagascar, the SMc first emerged during Mesozoic fragmentation of Gondwana (ca. 220 – 180 Ma) along a complex rifted margin. Fragmentation involved three major rift phases, viz.: 1) Middle Triassic – Middle Jurassic (Rift I), associated with the “Karoo rifts” and break-up between [India-Madagascar-Seychelles] and East Africa; 2) Middle Jurassic – Early Cretaceous (Rift II), associated with the rifting and break-up of Madagascar from [India-Seychelles]; 3) Late Cretaceous (Rift III), associated with the rifting and final break-away of the SMc from India. In this study, the tectonic and sedimentary history of the SMc is analysed using 2D seismic reflection datasets and three exploration wells. Seismic to well-log correlations provide a chrono-stratigraphic framework that identifies seven sequences from the Middle Triassic to the Paleogene. This also identified horst and graben structures related to the extensional tectonics and thermal subsidence of this continental fragment. The latter is reflected also in changes of its litho-facies preserved on the SMc, from terrestrial to marine. The oldest sedimentary rocks identified on the SMc are Middle Triassic organic rich claystones (Sequence 7, Rift I), which grade upwards into alternating Upper Triassic sandstones and mudstones (Sequence 6, Rift I) followed by upward coarsening Lower Jurassic mudstones to sandstone units (Sequence 5, Rift I). These sequences are interpreted as lacustrine facies that evolved into fluvial channel migration facies and finally into progradational delta front facies. Sequence 5 is overlain by Middle Jurassic oolitic limestones that grade upwards into organic rich mudstones (Sequence 4, thermal subsidence after Rift I); the latter are interpreted as restricted-marginal marine deposits. Following Sequence 4, separated by a major break-up unconformity (BU), are the Upper Cretaceous open marine deposits comprising limestones, claystones and sandstones, and terminated with basaltic volcanics (ca. 66 Ma) prior to the separation of the SMc from India (Sequence 3, Rift III). This is overlain by the post-rift – thermal subsidence sequences comprising open marine claystones and shelf limestones (Sequence 2) followed by a sequence of shelf limestones (Sequence 1) that form the present carbonate platform, the Seychelles Plateau that lies approximately 200 m below the present sea-level. Backstripping and subsidence analysis quantifies 3 stages of subsidence; Phase A: Slow subsidence (ca. 5-20 m/Ma), from the Middle Jurassic to the Upper Cretaceous that terminated during a major marine transgression during ingression of the Tethys Sea between East Africa and [Madagascar-Seychelles-India]. This created marine conditions and the subsequent deposition of Sequences 4 and 3; Phase B: Accelerated subsidence (ca. 35-60 m/Ma) recorded throughout the Paleocene to the middle Eocene leading to deeper marine conditions and the subsequent deposition of Sequence 2; and Phase C: Reduced subsidence (ca. 10-30 m/Ma) following the interaction between the Carlsberg Ridge and the Reunion hotspot (ca. 55 Ma) that possibly introduced a reduction in subsidence and the subsequent deposition of Sequence 1 as the SMc drifted and thermally subsided to its submerged present location, and is now dominated mainly by marine carbonates. The effects of the Madagascar and Seychelles/India separation (ca. 84 Ma) are not observed in the subsidence analysis, possibly because it involved transcurrent-rotational movement between the two plates over a short period of time.
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- Date Issued: 2014
A review of sediment-hosted gold deposits of the world with special emphasis on recent discoveries outside the U.S.A
- Authors: Daglioglu, Yasar Mehmet
- Date: 1996
- Subjects: Gold ores , Sedimentation and deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4997 , http://hdl.handle.net/10962/d1005609 , Gold ores , Sedimentation and deposition
- Description: Most of the Great Basin sediment-hosted gold deposits are located along well defined, northwest-striking trends. Trends coincide with faults, intrusive rocks and magnetic anomalies. Sedimentary host rocks are siltstone, sandstone, conglomerate, argillic, interbedded chert and shales. Silty bedded silty dolomites, limestone and carbonaceous shales are the most favourable hosts. High, and locally, low-angle faults are very important structural features related to the formation of the ore bodies. High-angle faults are conduits of hydrothermal fluids which react, shatter and prepare the favourable host rock. Decalcification, silicification, and argillization are the most common hydrothermal alteration types. Jasperoid (intense silica replacement) is a significant characteristic; not all of these deposits are gold-bearing. Most deposits contain both oxidized and unoxidized ore. Fine grained disseminated pyrite, arsenian pyrite, and carbonaceous material are the most common hosts for gold in many deposits. These deposits are also characterized by high Au/Ag ratios, notable absence of base metal and geochemical associations of Au, As, Sb, Hg, Ba and TI. Recently numerous sediment-hosted gold deposits have been recognized in different regions of the world. They vary in their size, grades, textwe, host rock lithology, degrees of structural control and chemical characteristics. However, they have many common features which are very similar to the general characteristics of sediment-hosted gold deposits in the Great Basin, U.S.A. Besides these similarities, several unusual features are recorded in some newly discovered deposits elsewhere, such as predominant fault controlled paleokarst related mineralization and the lack of two very common trace elements (Hg, TI) in Lobongan/Alason, Indonesia; and Early Proterozoic age metamorphosed host rocks and lack of Sb in Maoling, China. The discovery of the deep ores in the Post-Betze and Rabbit Canyon, Nevada, proposed sediment-hosted Au emplacement at deeper level (4 ± 2 km; Kuehn & Rose, 1995) combined with a lack of field evidence for paleowater table and paleosurface features has ruled out a shallow epithermal origin. Recent discoveries in other parts of the world throw important new light on the ongoing genetic problems. Intrusive rocks are present in nearly all sediment-hosted gold deposits. Numerous intrusion-centred districts worldwide are characterized by tWo or more different mineralization types and consequently by metal zoning. Sediment-hosted gold deposits are proposed as a distal part of intrusion-centred magmatic hydrothermal systems (Sillitoe &Bonham, 1990).
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- Date Issued: 1996
Review of carbonate hosted lead-zinc (copper) deposits and the geological factors affecting their shape, size and grade
- Authors: McDonald, B
- Date: 1981
- Subjects: Lead ores , Zinc ores , Copper ores , Sedimentology , Sedimentation and deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5028 , http://hdl.handle.net/10962/d1006903
- Description: From Introduction: For at least two centuries and a corresponding number of generations of geologists and miners there has been active argument concerning the origin of certain types of carbonate hosted mineral deposit. The characterization of the type itself was and still is debatable. Objections have been raised to grouping several examples under one heading because each has its individually distinctive features. ·This is especially applicable to the carbonate hosted lead-zinc "sedimentary" deposits. The type that will be discussed in the text to follow is composed chiefly of galena, sphalerite, barite and fluorite, with pyrite , marcasite and chalcopyrite as conspicuous accessory ore minerals. Exceptions to this general copper deficient characteristic displayed by the sedimentary carbonate-hosted lead-zinc deposits are the deposits at Tsumeb and Kombat, Namibia. These deposits are hosted by the carbonate sequence of the Otavi Shelf sediments, and copper, in the form of tennantite, chalcopyrite and bornite, is the major ore constituent. Calcite, aragonite, dolomite and quartz are the commonest nonmetallic gangue minerals but siderite and silica may also be present. In contrast with other lead and zinc sulphide (volcanogenic) deposits, those to be considered here seldom carry noteworthy amounts of silver or any other precious metals. Commonly the country rock is a carbonate; limestone or dolomite, but deposits in. sandstone, shale and conglomerate are not unknown. Characteristic features are ore bodies that extend parallel or nearly so with the bedding although many such deposits are partly, or completely developed along crosscutting fissures and breccias. Some observers regard these fissure fillings as evidence for a magmatic source of the metals, whereas others regard them as an indication of remobilization of ions, metals or minerals orginally present in low-grade stratiform deposits elsewhere in the stratigraphic succession.
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- Date Issued: 1981
An examination of the spatial variation of surficial sediment characteristics in the Howison's Poort Reservoir
- Authors: Weaver, Alex van Breda
- Date: 1979
- Subjects: Howison's Poort Reservoir , South Africa , Sedimentation and deposition
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: vital:4790 , http://hdl.handle.net/10962/d1001890
- Description: From Introduction: Lakes, estuaries and man-made water impoundments can be considered as intervening basins which provide for the temporary storage both of sediment and of water. Because of the potential energy of soil in elevated positions and because of the kinetic energy of water flowing under the influence of gravity, eroded material is eventually transported to the lowest possible level, i.e. the ocean deeps, or some intervening basin. This denudation process may be compared with Newton’s second law of thermodynamics which states that each system tends to move in the direction of lowest energy. Sedimentation in intervening basins may be seen as part of the natural process of landscape evolution. The rates at which sedimentation occurs may be strongly influenced by the activities of man.
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- Date Issued: 1979