OpenUCT :: Browsing by Author "Compton, John"

Browsing by Author "Compton, John"

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Open Access
Foraminiferal species distributions and sedimentological dynamics of the Knysna Estuary, South Africa
(2003) Simpson, Keryn; Compton, John
Although the status of the Knysna Estuary is considered to be in an acceptable environmental condition, pressures of development and tourism in the area are likely to cause substantial deterioration. Investigating the microfossil assemblages in the Knysna Estuary is imperative, since foraminifera serve as essential ecological indicators, and can be used to monitor the health of the ecosystem during development, as they are extremely sensitive to any environmental changes. The Knysna Estuary is well suited for investigating microfossil assemblages, since it has the richest fauna of the larger benthic invertebrates of any of the South African estuaries and it is open to the sea throughout the year.
Open Access
The formation and origin of carbonate minerals in the Darling and Yzerfontein hypersaline pans, Western Cape, South Africa
(2009) Mauger, Carla; Compton, John; Roychoudhury, Alakendra N
The Darling and Yzerfontein hypersaline pans are located on the western coastal plain of South Africa. The area has an arid, Mediterranean type climate. The carbonate minerals calcite and dolomite have precipitated in the pans through the evaporation and concentration of ions derived from weathering of bedrock, marine aerosols and coastal rainfall. Five pans were studied, the brine-type pans Rooipan South, Zwartwater North and Zwartwater South, the brackish saline pan Rooipan North, and the coastal Yzerfontein pan. Directly below the surficial halite crust of the three brine-type pans is a black organic-matter rich layer in which bacterial sulphate reduction is occurring (hydrogen-sulphide smell). All of the pans contain disseminated calcite, with only the Zwartwater North and Zwartwater South pans containing a mixture of dolomite and calcite. Yzerfontein and Zwartwater North pans contain small aragonitic gastropod shells (Tomichia ventricosa) which are no longer active in the pans due to the high present-day salinities of the pan waters. Low-magnesian calcite is likely the first evaporite mineral to precipitate in the pans because of its low solubility.
Open Access
A geochemical investigation into the occurrence and fate of nitrogen and phosphorus in the lower Oliphants River, Western Cape
(2004) Germs, Wijnand J; Compton, John; Roychoudhury, Alakendra
Knowledge of nutrient dynamics within aquatic ecosystems are of fundamental importance for water quality management, especially in cultivated areas where irrigation farming pose a salinization and eutrophication risk to water bodies. A range of water quality problems is associated with eutrophication, which is generally controlled by the nutrients nitrogen and phosphorus. The lower Olifants River is situated in an arid region with intensive irrigation agriculture. This study set out to investigate the loading and fate of nitrogen and phosphorus in the lower Olifants River.
Open Access
A geochemical investigation of the Darling and Ysterfontein saline pans, Western Cape, South Africa
(2000) Smith, Meris; Compton, John
Saline pans are an important component of the hydrologic cycle in arid areas, and are common in South Africa. Natural saline pans on the coastal lowlands of the Western Cape Province, South Africa, were studied to determine the origin and evolution of salts within the pans. Samples of surface, stream and spring water as well as pan sediments were collected from two large coastal pans near Ysterfontein, and eight smaller pans 10-20 km from the sea, on the inland side of the granitic Darling hills.
Open Access
Geochemistry of a pristine fynbos ecosystem in the Harold Porter National Botanical Gardens and Kogelberg Biosphere Reserve
(2002) Smit, A K; Compton, John; Roychoudhury, Alakendra
Water, soil and rock samples were taken from the Harold Porter National Botanical Gardens and the Kogelberg Biosphere Reserve in order to investigate interactions between the various nutrient pools in a pristine fynbos ecosystem. Physical variables (pH, EC, temperature, DO, alkalinity) were measured in the field, and water samples were collected and analysed for chemical composition. Chemical composition and mineralogy of soil and rock samples from the Peninsula, Cedarberg and Goudini formations were determined to assess the influence of parent geology on soil chemistry. The surface water chemistry in the study area was remarkably homogeneous, with only major ions Na, CI, Mg, Ca, Si and S04 exceeding concentrations of 1 ppm at any of the sample sites. Concentrations of other major ions AI, K, NH4, N03 and Fe ranged between 0.1 and 0.7 ppm. The minor and trace elements B, Sb, Sr, Zn and Mn were present in concentrations greater than 1 ppb. Compared to the seawater chloride ratio, Na, Mg, K and S04 were depleted in the streams relative to CI, showing that these elements are preferentially accumulated and are conserved within the fynbos ecosystem. In contrast, CalCI ratio is elevated in streams, indicating an external source of Ca other than the seawater. This source may be windblown dust. The Fe content of soils appears to be lower than that of the parent bedrock, especially in the case of the iron-rich Goudini Formation. This indicates an as yet undetermined pathway for iron to leave the system, which may be through deeper anoxic groundwaters in the area. Only one site from the Oudebosch River headwaters showed significant deviation from other sites in several of the elemental trends, and also had no measurable DOC content, compared to the other sites which ranged from 10 to 16 mg/L DOC. These differences are probably the result of the different vegetation (afromontane forest as opposed to fynbos) and geological setting (clay rich, Cedarberg Formation soils). Soils contained higher concentrations of water-soluble ions than the streams, and organic carbon content ranges from 6 to 34 wt%. Organic 0 horizons and Melanic/Humic A horizons constituted the major soil types. Cation exchange capacities of the soil samples ranges between 31.3-93 mmolJkg, and about half of the soil samples were determined to be acid saturated and fairly leached of ions, probably due to the high rainfall. The soil composition and mineralogy correlate well with that of the underlying bedrock, and was dominated by quartz, with some clays, micas, feldspars and hematite. The study was similar to one in the Cedarberg, which has the same geological setting and equal fynbos species richness. This is the first integrated geochemical study to characterise the pristine fynbos biome of the Harold Porter National Botanical Gardens and the Leopards Gorge River Catchment, and will allow rapid assessment of any future changes.
Open Access
The geological evolution and sedimentary dynamics of Hout Bay, South Africa
(2012) MacHutcheon, Michael R; Compton, John
Hout Bay is situated on the Atlantic seaboard of the Cape Peninsula, in the Western Cape Province of South Africa approximately 17 km southwest of Cape Town. Hout Bay is a southward opening bay that hosts a fishing harbour and coastal residential town. This study was initiated to map the marine geology of Hout Bay and to quantify and explain the sediment dynamics of the area. This is important as Hout Bay has the only substantial accumulation of Quaternary sediments on the Atlantic Seaboard of the Cape Peninsula. The Hout Bay study area was saturated with the latest in cutting-edge geophysical techniques to collect detailed and comprehensive bathymetric, sidescan sonar, magnetic, seismic and beach profiling data. Collectively these data can be used to map offshore geological units as well as infer how Hout Bay has responded to the varying changes in sea-level throughout the Quaternary and allow for the reconstruction of the geological evolution of the Hout Bay seafloor.
Open Access
Geological mapping of the inner shelf off Cape Town's Atlantic Seaboard, South Africa
(2018) Van Zyl, Frederik Wilhelm; Compton, John
The Atlantic Seaboard is an 18 km stretch of coastline located on the Cape Peninsula, South Africa, roughly between the Cape Town suburbs of Mouille Point in the north and Hout Bay in the south. It borders heavy shipping traffic and contains a mix of urban and natural environments including up-market seaside neighbourhoods and is part of the Table Mountain National Park. The predominantly rocky coastline has a northeast–southwest orientation with interspersed sandy pocket beaches. A narrow, low-lying coastal plain (marine terrace) in the north merges with coastal cliffs further south. The geomorphology and sedimentology of the coast are closely linked to the underlying geology, influencing the shape of coastal embayments and promontories, as well as the composition and distribution of sediment. Hydrographic, geophysical and sedimentological techniques were used to collect high-resolution bathymetry, seafloor geology and sediment distribution data to better understand modern coastal processes. The results indicate a low-relief seafloor consisting of Malmesbury Group rocks in the north. To the south the seafloor consists of high-relief Cape Granite reefs interspersed with fine to medium grain sand and bioclastic (shelly) gravel. Sediment transport is generally northward by longshore drift. In the south, the high-relief granite reef and headlands form sediment traps resulting in several large pocket beaches and offshore sediment deposits. In the north, the low-relief Malmesbury bedrock is largely free of sediment, except within narrow erosional gullies. Most sediment rapidly passes through to the north resulting in a sediment-starved rocky seafloor. The three principal sources of beach sand are aeolian fine sand transported by the Karbonkelberg headlands bypass dune entering the sea at Sandy Bay, biogenic carbonate production along the coast, and weathering of Table Mountain Group sandstone and granite bedrock. A fourth source is sediment entering the system via longshore drift from the south of Duiker Point. The water depth around the Duiker Point headland is presently too deep for sediment to be transported easily through longshore drift, other than during large storm events, but during past sea-level low stands this would have played an important part in supplying sediment to the coast. Changes in sea level play an important part in shaping the geomorphology of the coastline. Beach deposits, both sandy and boulder beaches have been left at various elevations along the coast, both offshore and onshore. Although today the Sea Point area is protected by sea walls and man-made structures, a higher sea level was responsible for shaping the narrow coastal plain. Increasing rates of global sea-level change are becoming an important issue all over the world and the Atlantic Seaboard coast is not immune to the effects of sea-level rise. The frequency and magnitude of storm events that breach the sea defences erode beaches and sea cliffs and cause damage to private and public property are likely to increase in the future
Open Access
Geology of Aeolian and marine deposits in the Saldanha Bay region, Western Cape, South Africa
(2003) Franceschini, Giuliana; Compton, John; McMillan, Ian K; Rogers, John
The west coast of South Africa has been exploited for diamonds for most of the last century. Although some literature has accumulated over this period, the evolution of the coastal plain since the Cainozoic remains poorly understood. The aim of this thesis is to offer a multidisciplinary study of the evolution of coastal deposits in the Saldanha Bay area, along the southern part of the west coast. The environments investigated comprise lagoons, coastal dunes and shorelines. The ages of the deposits were obtained with radiocarbon dating, strontium isotope stratigraphy and biostratigraphy.
Open Access
Impact on soil chemistry of atmospheric sulfur fallout near Arnot coal-fired power station, in the Eastern Transvaal highveld region, South Africa
(2000) Abanda, Peter Azah; Compton, John; Fey, Martin V
The objective of the study was to evaluate the potential impact of atmospheric sulfur deposition on the soils surrounding Arnot power station. In particular, the study focused on the relationship between sulfur and organic carbon (OC) and on the various pools of sulfur in the soil. A representative selection of collected soil samples was characterized both physically and chemically in the laboratory. In addition to the representative soils sampled in 2000, archived soils sampled in 1996 and 1999 from the same area were included in some of the chemical analyses.
Open Access
Late cenozoic shallow marine diamond placers off the northern Sperrgebiet, Namibia
(2008) Oelofsen, André; Compton, John
Small scale diver-assisted diamond mining has taken place since 1990 in the shallow marin (<30 m water depth) portions of Mining Licence 45 (Elizabeth Bay) between Halifax Island and Elizabeth Bay along the southwestern coast of Namibia. These operations in the northern part off the coast of the Sperrgebiet have produced almost 400,000 carats over a period of 17 years. Although sparse records remain from the early days, sufficient data from various sources were collected, collated and summarised to make meaningful observations. From historic and current diamond diving records, 4 submarine areas which have yielded high returns were described in terms of their geomorphology, sedimentology and diamond occurrence. Using detailed geophysical survey data (Sidescan Sonar and Multi-beam Bathymetry), the deposition of diamonds at these sites were modelled in GIS-based reconstructions. The diamond size frequency distribution (SFO) of the Shallow Marine (0 to -30 m) deposits in the study area is similar to the proximal aeolian deposit mined on land at Elizabeth Bay and the deeper Midwater (-30 to -70 m depth) deposits situated southwest of the study area.
Open Access
Life after extinction: palaeoenvironments of the earliest Triassic lower Katberg formation, including the origin of Lystrosaurus Bonebeds from the Karoo Basin, South Africa
(2012) Viglietti, Pia A; Smith, Roger; Compton, John
This study argues for the formation of bonebeds by aggregation of sub-adult Lystrosaurus during extended episodic periods of extreme climatic conditions, such as cold or drought, in the earliest Triassic Karoo Basin.
Open Access
Manganese deposits of the Cape Peninsula, South Africa
(2013) MacGregor, Duncan Graeme; Compton, John
The outcrops, petrography and geochemistry of manganese deposits were studied at several sites on the Cape Peninsula (Skeleton Gorge, Kasteelpoort Path, Kommetjie and Hout Bay) as well as at Rooi Els on the opposite side of False Bay. The purpose of this study was to understand the origin and depositional history of these manganese deposits. Manganese ore samples contain between 16 and 86 wt% MnO, 0.3 to 29 wt% Fe2O3 , 1.2 and 5.6 wt% K2O and a P2O5 content of 0.3 to 1.8 wt%. The primary manganese oxide mineral present is cryptomelane (KMn8O16). The iron and quartz content of bulk rock samples have a positive correlation, and a negative correlation to manganese. From the field data, petrography and chemistry by electron microprobe analysis, it was established that the method of deposition was lateral secretion and the deposits fit into Harrison’s (1998) manganese classification as a Type 1 deposit. Lateral secretion involves the reduction of manganese and iron oxides within the soil profile by acidified rain water, further leaching of oxides as reducing groundwaters flow through regolith and bedrock, and the eventual precipitation as oxides at groundwater seeps and springs. Field observations and the chemistry of water and rock samples support the lateral secret ion model in which the manganese and iron are chemically leached from the Peninsula Format ion quartzarenite sandstone bedrock and transported along fractures and faults to be deposited as oxides upon emergence at the surface. Minor surface coatings of iron and manganese oxides are ubiquitous in the study area but can become concentrated in locally historic economic deposits where the groundwater f low is focused by topography, aquitards and faults. Trace element composition of the manganese-rich deposits indicates that they are low-temperature, hydrogenous freshwater deposits. The proposed Eh - pH evolution of surface and ground water flow paths is consistent with the reduction of manganese and iron within the soil profile, and the precipitation of first iron and then manganese at springs and seeps. The Rare Earth Element (REE) pat terns suggest variable sources and transport of the manganese and iron. The manganese deposits of the Cape Peninsula are no longer economic but do provide insights into the remobilisation of metals by low temperature groundwaters during the process of lateral secretion.
Open Access
The marine geology of Mossel Bay, South Africa
(2014) Cawthra, Hayley Candice; Compton, John
This thesis presents work undertaken to better understand the complex evolution of the terrestrial landscape now submerged by high sea levels offshore of Mossel Bay along the South Coast of South Africa. Three marine geophysical surveys and scuba diving were used to examine evidence of past sea-level fluctuations and interpret geological deposits on the seafloor. Additional geological mapping of coastal outcrops was carried out to link land and sea features and rock samples were dated using Optically Stimulated Luminescence (OSL). Geophysical investigations include a regional seismic survey extending from Still Bay in the west to Buffels Bay in the east out to a maximum water depth of 110 m; a high-resolution investigation of the Mossel Bay shelf using multibeam bathymetry, side-scan sonar and sub-bottom profiling; and a shallow seismic pinger survey of Swartvlei, the most prominent coastal lake in the Wilderness Embayment. This study presents 9 discrete seismic sequences, and describes major offshore geomorphic features such as submerged sea cliffs, palaeo-coastal zones and fluvial systems. Oscillation in sea level between ca. 2.7 and 0.9 Ma likely resulted in the formation of the prominent -45 m terrace, which separates a relatively steep inner from a low-gradient mid shelf. Beach and dune deposits span from Marine Isotope Stage 15 (MIS 15) (582 ka) to Recent based on an age model that integrates OSL ages and the established eustatic sea-level record. The most prominent deposits date from the MIS 6 glacial to MIS 5 interglacial periods and include incised lowstand river channels and regressive aeolianites that extended at least 10 km inland from their associated palaeoshorelines. The MIS 5 deposits include transgressive beachrock, an extensive foreshore unit which prograded on the MIS 5e highstand, and regressive beach and dune deposits on the shelf associated with the subsequent fall in sea level. MIS 4 lowstand incised river channels were infilled with sediment truncated during rapid landward shoreface migration at the MIS 4 termination. Lowenergy, back-barrier MIS 4/3 sediments are preserved as a result of overstepping associated with meltwater pulses of the MIS 2 termination. The MIS 1 sediment wedge comprises reworked sediment and is best developed on the inner shelf. Holocene highstand sedimentation continues to prograde. Accommodation space for coastal deposits is controlled by antecedent drainage pathways and the gradient of the adjacent inner continental shelf. The geological deposits on the emergent shelf indicate a greatly expanded glacial coastal plain that potentially received more rain feeding low-gradient meandering rivers and wetland lakes. These extensive wetland environments provided a rich source of diverse food types which along with abundant marine resources on the shoreline made the Southern Coastal Plain an ideal habitat for our ancestors.
Open Access
Nutritional contribution of atmospheric deposition to the Strandveld vegetation of West Coast South Africa Justine Muhoro Nyaga.
(2013) Nyaga, Justine Muhoro; Cramer, Michael D; Neff, Jason C; Compton, John
Ecosystem nutrient availability depends on the balance between rates of nutrient inputs and losses. Nutrients may be lost through fire and displacement of ash, herbivory, leaching and volatilization. The main pathways through which nutrients may be acquired are weathering of rock and atmospheric deposition. Symbiotic and free-living diazotrophic bacteria and blue green algae also contribute N. In ecosystems with limited occurrence of N₂-fixation and occurring on low-nutrient bedrock, atmospheric deposition is the most significant source of nutrients. Nutrients from atmospheric deposition may be of natural or anthropogenic origin, and can be “wet-deposited” dissolved in precipitation and “dry-deposited” when aerosols settle out of the atmosphere onto plant and soil surfaces. Studies on nutrient cycling around the world suggest that nutrient deposition can provide substantial amounts of nutrients to coastal ecosystems, although mineral weathering of rocks can also a significant source. Limited prior work on deposition in coastal areas of South Africa suggests that nutrient deposition could be an important component of nutrient budgets in the Cape Floristic Region. The west coast of South Africa borders a section of the Atlantic Ocean that is highly productive and characterized by strong seasonal winds, rough waters and strong wave action. This area is home to the Strandveld vegetation, which grows on marine-derived soils. Based on this, I hypothesized that marine aerosol deposition is a significant source of nutrients for the vegetation in west coast South Africa. To test this hypothesis, I examined the spatial and temporal characteristics of atmospheric deposition as well as the climatic and ecological characteristics of the area.
Open Access
A one-year, postfire record of element deposition and cycling in the Kogelberg sandstone fynbos mountain ecosystem of the Western Cape, South Africa by Eugene W. Bergh.
(2012) Bergh, Eugene W; Compton, John
Fire is a critical component of the fynbos ecosystem and this study documents the macronutrient (C1, Na, So4, Mg, Ca and K) dynamics of the fynbos for one year following a major fire event on 3 June 2010. Chloride and sodium in rainwater and stream water were found to be primarily derived from a marine aerosol source.
Open Access
Petrographic and geochemical evidence for the origin of phosphorites and phosphate rocks from the West Coast of South Africa
(2003) Middleton, Xavier N; Compton, John
The onshore marine phosphorite and aluminium phosphate deposits of Varswater Quarry (near Langebaanweg), Bomgat (near Hoedjiespunt), Kreefte Bay and Konstabelkop were studied to determine the origin of the various deposits.
Open Access
Sedimentary facies from the Head of the Cape Canyon : insights into the Cenozoic evolution of the western margin of South Africa
(2004) Wigley, Rochelle Anne; Compton, John; Rogers, John
Cenozoic sedimentary successions have a restricted distribution and are largely incomplete due to erosion and non-deposition on the western margin of southern Africa. For this reason, much controversy and uncertainty remains on the geological evolution of the western margin. The wide western margin is largely devoid of bathymetric features, except for the deeply incised Cape Canyon that crosscuts the continental slope and shelf ~150 km to the northwest of Cape Town. The Head of the Cape Canyon forms a well-developeed trough landwards of the Western Ridge, which separates the middle and outer shelf. More than 50 cores, up to 6 m in length, at water depths between 190 and 450 m were recovered from the Head of the Cape Canyon region. Siliclastic, authigenic and biogenic sediments, varying in age from Cretaceous to Holocene provide the basis of a detailed sedimentary analysis. The diversity of lithostratigraphic units recovered from the condensed sedimentary record provides a unique opportunity to define in detail, for the first time, a late Cenozoic stratigraphic record for the western outer continental shelf.
Open Access
Sources of suspended load in the upper Orange River, South Africa
(2012) Maake, Livhuwani; Compton, John
A lot of work has been done on the upper Orange River but little attention has been given to the source of its suspended sediment load. The source of the suspended load is important because it can provide insight into soil erosion, a major problem in South Africa and globally. In this study the composition of the suspended sediment load of upper Orange River tributaries is related to bed rock geology, topography, soils and land use. Orange River catchment bed rock includes sedimentary rocks of the Karoo Supergroup and flood basalts of the Drakensberg Group each with distinct geochemical signatures.
Open Access
A trace element study of sediments from the Olifants River estuary, the Berg River estuary, and the off-shore Mud Belt
(2004) Taylor, Arthur; Compton, John; Roychoudhury, Alakendra N
Trace elements have received increased attention since the mid-1900's. Although some studies have investigated trace element accumulation as a result of urban expansion in the Western Cape, South Africa, few have catalogued the accumulation and behavior of trace elements resulting from agricultural practices. This study investigates the distribution and behavior of trace elements for the Olifants and Berg river catchments by focusing on the sediments of the estuaries. The dominant industry in both catchments is agriculture and there exists relatively little urban sprawl. Two sediment samples taken from the offshore mud belt in the vicinity of the two river mouths were also analyzed. The sediments were analyzed for trace elements using inductively coupled plasma mass spectrometry (ICP-MS), major elements using X-ray ﬂuorescent spectroscopy (XRF), total sulfur using XRF, total and organic carbon using a C:H:N analyzer, and grain size analysis was performed (>62 μm, 38-63 μm, 2-38 μm, <2μm). The mud belt cores were dated using 14C dating. Estuarine surface waters were analyzed for trace elements, pH, dissolved oxygen (DO), electrical conductivity (EC), and temperature. The trace elements arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) were focused on. The trace element concentrations in the sediments were compared with those of soils that occur in the study area, as well as their parent materials, to determine background concentrations. The concentration proﬁles of elements with respect to depth are compared with natural deposition rates to recognize signs of recent enrichment of individual trace elements. Inter-element comparisons are made in an attempt to determine speciation. Comparison between the estuarine and mud belt sediments were made to assess the estuaries ability to ﬁlter ﬂuvial trace elements, as well as to determine the sediment contributions of the Olifants and Berg rivers to the mud belt. Statistical analysis was performed to"group sediment populations Trace element and organic matter concentrations showed strong positive correlations with ﬁne-sized particles. The mud belt sediments displayed considerably more OC than the estuarine sediments. The trace elements appear to associate predominantly with clay minerals (alumino-silicates), Fe/Mn oxides, and organic matter. Trace element correlations with S and carbonate carbon were also observed. Comparison with estimates of natural deposition rates and compositions of soils occurring in the catchments did not suggest an anthropogenic pollution input. From the data available the estuarine and Mud Belt sediments appear enriched in Cd, Cu and Zn in comparison to the background soils. The estuaries seem to effectively trap Zn and Pb, but do not capture As well. Statistical analysis suggest that, of the rock types considered, the sediments of the Olifants and Berg river estuaries and those of the off shore mud belt are most similar to sediments derived from the Malmesbury and Ecca Groups. The Olifants and Berg rivers are important sources of water for the farming community, as well as for municipal use in the Western Cape. Based on this investigation of the estuarine waters and sediments the rivers appear to be in good health in regards to trace element concentrations.
Open Access
Trace metal accumulation in urban sediments, Black River, Western Cape, South Africa
(2003) Haniff, Naadira; Roychoudhury, Alakendra N; Compton, John
The increase in urbanisation and the use of metal compounds and products domestically and in industry has resulted in the production of by-products and wastes, which needs to be evaluated in the urban environment. The discharge of some of these wastes into urban rivers should be evaluated to determine the potential effects, for example, toxicity and mobility. The effects may, in part, be determined by the chemical states in which these wastes manifest themselves, and by the chemical associations they have.