Browsing by Author "Coetzee, Andre"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Geometry and emplacement controls of dolerite sill complexes in the Karoo basin
    (Stellenbosch : Stellenbosch University, 2020-04) Coetzee, Andre; Kisters, Alexander F. M.; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: This dissertation is a compilation of three case studies that integrates drilling, field and geophysical data on dolerite sill complexes across the Karoo basin to constrain the emplacement processes, feeder systems and regional controls during the formation of the Karoo Large Igneous Province (KLIP) at ca. 183 Ma. Chapter 4 describes the relationships between several saucer-shaped sills in the sedimentary strata of the northern Karoo basin and underlying Archaean to Neoproterozoic basement strata of the Kalahari craton. The three-dimensional geometry of numerous individual sills across an area of 7400 km² were reconstructed using extensive drill hole and mining data up to a depth of 2.5 km. Saucer-shaped sills, largely confined to the Karoo Supergroup and representing various geometries, dip towards distinct narrow, funnel-like dolerite structures seated exclusively within the basement layers that likely represent a connection to deep-seated feeders. Importantly, many of these funnel-shape structures are localised near or rooted in older, dykes and normal faults in the basement strata. This highlights the significance of preexisting basement structures in facilitating magma transport through the upper crust and into the Karoo basin. Furthermore, the wide spatial distribution of magma feeders across the Kalahari craton is more aligned with thermal incubation of the sub-lithospheric mantle than the development of mantle plumes beneath Gondwana. Chapter 5 constrains the emplacement controls of sills in the central Karoo basin through field and drill hole data from the Victoria West sill complex. The sill complex consists of five successively emplaced saucers-shaped sills across an area of 2000 km2 that formed though magmatic underaccretion beneath earlier sills. Rigid and fully crystallised earlier sills served as stress barriers to the upwards propagation of later sill feeders which resulted in a nested sill structure marked by a sill-in-sill configuration. The close spatial overlap between the individual saucer-shaped sills and NW-SE trend of the sill complex suggest the reutilization of the same feeder system, most likely the rim of a large underlying sill. Emplacement controls of the Victoria West sill complex indicates sill formation occurred under a mild compressional stress regime at the onset of Karoo magmatism. The changeover from sill complexes at 184-180 Ma to later dyke swarms at 182-174 Ma suggest a switch in the prevailing stress field prior to Gondwana break-up. Thermal loading followed by lithospheric subsidence due to the rapid emplacement of >350 000 km3 of sills and outpouring of >106 km3 of lavas across southern Africa and Antarctica may have triggered extension and the subsequent intrusion of dyke swarms along cratonic margins. Therefore, inherited basin and lithospheric architecture was crucial in the later development of Karoo magmatism. Chapter 6 represents a study of the distinct variations of sill geometries and associated intrusive structures across the Karoo basin in relation to the basal elevation of the Drakensberg Group lavas. These spatial variations in the mode of emplacement of sills are attributed to emplacement depth in addition to changes in sedimentary facies and driving magma pressures. The northern Karoo basin is characterised by shallow (<500m) emplacement depths with sills typically showing small (<10 km) diameters and thicknesses up to 40 m. The central Karoo basin represent intermediate emplacement depths of up to 700 m with sill diameters over 30 km and thicknesses below 100 m. Advanced emplacement depths of <2 km is found in the southern Karoo basin where sills reach sizes of 50-80 km and thicknesses of 35 m. Local dyke networks show similar depth dependent relationships across the Karoo basin. Dense systematic and non-systematic dyke networks are associated with respective shallow (<500 m) and intermediate (<700 m) emplacement depths whereas greater depths (<2 km) are largely devoid of dykes. Additionally, the asymmetric distribution of different sedimentary rock types and southward thickening of layers in addition to differential magma pressures across the Karoo basin further influenced sill emplacement processes and associated structural features. Generally, the wide spatial and stratigraphic occurrence of sills throughout the Karoo basin is more consistent with many distributed feeders emplaced in the underlying basement rocks than a single plume-related source along the rift margins of southern Africa.
  • Thumbnail Image
    Item
    The geometry of Karoo dolerite dykes and saucers in the Highveld Coalfield : constraints on emplacement processes of mafic magmas in the shallow crust
    (Stellenbosch : Stellenbosch University, 2016-12) Coetzee, Andre; Kisters, Alexander F. M.; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences
    ENGLISH ABSTRACT: This dissertation is a compilation of two case studies that integrates an extensive underground mining and drilling data set on Karoo dolerite intrusions in the Highveld Coalfield to constrain the emplacement processes of the upper-crustal plumbing system of the Karoo large igneous province. Chapter 3 describes by means of a three-dimensional strata model the geometry of a regional-scale Karoo-age (ca. 180Ma) saucer complex locally referred to as the number 8 sill. The saucer complex consists of three saucers largely confined to the Karoo Supergroup underlain by a shallow dipping basement feeder. The model demonstrates the lateral emplacement of magma where a single basement feeder gives rise to several split level saucers that subsequently coalesces into one vast saucer complex. Furthermore, these relationships show a strong spatial and geometric dependency of saucers to their underlying feeders. Lithological interfaces and weak layers control and facilitate the lateral emplacement of magma during the development of saucers in the Karoo Supergroup. The common occurrence of localised dome- and ridge-shaped structures along the flat inner sill of the saucers are likely generated from lobate magma flow processes. Inflation of individual magma lobes induce overlying strata failure along multiple curved faults that facilitates the formation of circular inclined sheets feeding a flat lying roof seated at a higher stratigraphic level. Chapter 4 examines the spatial and temporal relationships between dolerite dykes and the saucers that make up the larger number 8 sill complex. These dykes have distinct short strike lengths, curved geometries and form interconnected and cross-cutting patterns. Moreover, the dykes are often rooted along the upper surface of underlying saucers and cannot be seen to extend below the base (inner sill) of the saucers. Contact relationships show a mainly coeval or contemporaneous emplacement of dykes to the inner sill and inclined sheets of the underlying saucer. The dykes can be described as two diverse sets, namely systematic and non-systematic dykes. Systematic dykes form a well-organised interconnected boxwork or ladder-like pattern of two near-orthogonal dyke sets confined to the inner sill of the underlying saucer. The formation of these dykes is related to the uplift and stretch of the strata directly overlying propagating magma lobes along the inner sill of the underlying saucer. Conversely, non-systematic dykes display a more irregular array of structures that not only overlie the inner sill but often cross-cut or extend outwards from the inclined sheets of the saucer. These dykes are likely the product of multi-directional stretch induced during the emplacement of coeval and adjacent saucers forming a so called “cracked lid” similar to field descriptions of stacked saucers in Antarctica. Dyke-saucer relationships of the Highveld Coalfield highlight the influence of magma emplacement processes and the deformation of host strata rather than far-field tectonic stresses.
  • Thumbnail Image
    Item
    Severe acute respiratory infection with influenza A (H1N1) during pregnancy
    (Health and Medical Publishing Group (HMPG), 2009-10) Langenegger, Eduard; Coetzee, Andre; Jacobs, Samier; Le Roux, Alrisah; Theron, Gerhard
    ABSTRACT FROM JOURNAL: Pregnant women are at high risk of severe acute respiratory infection if infected with the influenza A (H1N1) virus. On 14 August 2009 the first complicated H1N1 obstetric patient was admitted to the obstetric critical care unit (OCCU) at Tygerberg Hospital with respiratory distress. The clinical picture was that of bronchopneumonia, and she tested positive for H1N1. Subsequent pregnant patients admitted to the OCCU with respiratory compromise or flu symptoms were screened for the virus. Eleven days later 13 cases were confirmed. Five patients had acute lung injury and required ventilation and inotropic support. Three of the patients with acute lung injury subsequently died. Three patients required continuous positive airway pressure (CPAP) support only, with no inotropics needed. The remaining 5 patients presented early, received oseltamivir within 48 hours and did not require critical care admission. All the patients admitted to the OCCU and the medical intensive care unit (ICU) initially presented with flu symptoms, respiratory distress and changes on the chest radiograph indicating an active diffuse pulmonary parenchymal process. Six patients underwent uncomplicated caesarean sections for fetal distress after they were stabilised. Maternal and neonatal outcomes varied. The key factor appears to be early clinical diagnosis and oseltamivir within 48 hours of the onset of symptoms. The demographic data and maternal and fetal outcomes are set out in Table I.
  • Thumbnail Image
    Item
    The way in which a physiotherapy service is structured can improve patient outcome from a surgical intensive care : a controlled clinical trial
    (BioMed Central, 2012-12) Hanekom, Susan D.; Louw, Quinette; Coetzee, Andre
    Introduction: The physiological basis of physiotherapeutic interventions used in intensive care has been established. We must determine the optimal service approach that will result in improved patient outcome. The aim of this article is to report on the estimated effect of providing a physiotherapy service consisting of an exclusively allocated physiotherapist providing evidence-based/protocol care, compared with usual care on patient outcomes. Methods: An exploratory, controlled, pragmatic, sequential-time-block clinical trial was conducted in the surgical unit of a tertiary hospital in South Africa. Protocol care (3 weeks) and usual care (3 weeks) was provided consecutively for two 6-week intervention periods. Each intervention period was followed by a washout period. The physiotherapy care provided was based on the unit admission date. Data were analyzed with Statistica in consultation with a statistician. Where indicated, relative risks with 95% confidence intervals (CIs) are reported. Significant differences between groups or across time are reported at the alpha level of 0.05. All reported P values are two-sided. Results: Data of 193 admissions were analyzed. No difference was noted between the two patient groups at baseline. Patients admitted to the unit during protocol care were less likely to be intubated after unit admission (RR, 0.16; 95% CI, 0.07 to 0.71; RRR, 0.84; NNT, 5.02; P = 0.005) or to fail an extubation (RR, 0.23; 95% CI, 0.05 to 0.98; RRR, 0.77; NNT, 6.95; P = 0.04). The mean difference in the cumulative daily unit TISS-28 score during the two intervention periods was 1.99 (95% CI, 0.65 to 3.35) TISS-28 units (P = 0.04). Protocol-care patients were discharged from the hospital 4 days earlier than usual-care patients (P = 0.05). A tendency noted for more patients to reach independence in the transfers (P = 0.07) and mobility (P = 0.09) categories of the Barthel Index. Conclusions A physiotherapy service approach that includes an exclusively allocated physiotherapist providing evidence-based/protocol care that addresses pulmonary dysfunction and promotes early mobility improves patient outcome. This could be a more cost-effective service approach to care than is usual care. This information can now be considered by administrators in the management of scarce physiotherapy resources and by researchers in the planning of a multicenter randomized controlled trial. Trial registration PACTR201206000389290