Doctoral Degrees (Geology)

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The geological evolution of a part of the Pongola basin, southeastern Kaapvaal Craton.
(1993) Gold, Digby James Comrie.; Strydom, Dawie.; Von Veh, Mark.; Hunter, Donald Raymond.
A stratigraphic and structural study of the Archaean Pongola Sequence on the southeastern Kaapvaal Craton centred on the area around the Klipwal Gold Mine is described. The lower predominantly volcanic Nsuze Group is overlain with a gradational transition by the upper clastic Mozaan Group in which six formations are recognized. The Sinqeni, Ntombe, Thalu, Hlashana, Odwaleni and the Kulphiso Formations. The Sinqeni and Hlashana Formations are predominantly arenaceous while the Ntombe and Kulphiso Formations are mainly argillaceous. The Odwaleni Formation contains a diamictite which is interpreted as a tillite, and is therefore the oldest glacial rock on record. The stratigraphic position of the Kulphiso Formation is problematic. The Mozaan Group was deposited in a deepening epeiric sea which was invaded periodically by storm generated deposits. Dolerite and ultramafic dykes and sills of various ages are represented. Three phases of deformation are recognized in the Klipwal area. Early compression from the south-southeast initiated a major zone of bedding-parallel shear, the Izermijn shear zone, along the Nsuze-Mozaan contact and an oblique ramp, the Klipwal shear zone, at a higher stratigraphic level. An extensional phase caused reactivation of the Klipwal shear zone and the development of a major low-angle normal fault, the Gu'nsteling fault, above the Sinqeni Formation. The main phase of deformation, related to northeast-southwest compression is the most complex and most widely developed. Early northwest-trending subhorizontal upright folds were disrupted by contemporaneous north-striking dextral or dextral reverse shearing and northwest-striking sinistral or sinistral normal shearing. The obtuse relationship of these shear zones to the compression direction is probably the result of reactivation of basement structures with similar orientations. Northwest-trending folding continued during and after the shearing. The structural styles and orientations observed in the Klipwal area are recognized regionally in the main Pongola basin, highlighting the need for further detailed studies before basin-wide correlations are made.
On the engineering geology of granite saprolite and its significance to the construction of Injaka Dam, South Africa.
(2004) Haskins, David Rodney.; Bell, Frederic Gladstone.
The intention of this work is to provide a deeper understanding of the engineering geological behaviour of granite saprolite and how this affects the engineering of such material, with specific reference to the construction of Injaka Dam in the north eastern portion of South Africa Whilst extensive investigation of weathered granites has been carried out internationally, very little detailed research on the nature of this material is documented locally. The construction of Injaka Dam afforded the opportunity to investigate the saprolite in detail. This study was initially submitted to the Department of Geology and Applied Geology at the University of Natal, Durban (renamed the University of KwaZulu-Natal in 2004) to fulfill the requirement of a Master of Science degree in 200 I. Following this submission, and supported by recommendations made by the external examiners and the project supervisor, it was agreed to upgrade the work and submit this thesis for the degree of Doctor of Philosophy. Intensive chemical weathering of granite at Injaka Dam site has resulted in the formation of thick saprolitic deposits overlying the weathered bedrock. The granite forms part of the 3 075 Ma Nelspruit Suite which has been intersected by the African erosion surface. The extensive, multicyclic period of weathering and erosion that formed this surface has resulted in deep (up to 35 m) chemical weathering of the underlying bedrock in this area. The construction of Injaka Dam on this material necessitated a thorough engineering geological investigation to understand the nature of the weathering and the possible influences it exerts on the engineering behaviour of the saprolite. This was accomplished by analysing the weathering of the granite and relating the effects of these weathering processes and changes to the engineering behaviour of the material. By applying various chemical and mineralogical indices to the weathered granite, the intensity of weathering and related changes could be quantified and compared with the engineering behaviour of the material. This was achieved by applying a series of engineering indices to the material and relating these to the quantified weathering changes. In this way tentative extrapolation of the engineering behaviour of the material could be gained and used to predict engineering performance. The resultant effects of the engineering behaviour of the material on the design and construction of the dam are also discussed.
The Ahlmannryggen group, western Dronning Maud Land, Antarctica.
(2001) Perritt, Samantha.; Watkeys, Michael Keith.
The Mesoproterozoic Ritscherflya Supergroup forms an extensive volcano-sedimentary cover succession on the Archaean Grunehogna Province of western Dromring Maud Land, Antarctica. The oldest:, predominantly sedimentary deposits of this cover succession are exposed across the Borgmassivet and southern Ahlmannryggen mountain ranges, and are collectively assigned to the Ahlmannryggen Group. A revised lithostratigraphy places exposures from these two regions in separate subdivisions, with three formations being recognised in the Ahlmannryggen (Pyramiden, Schumacherfjellet and Grunehogna Formations) and four formations being defined for the Borgmassivet (Veten, Framryggen, HogfOlma and Brapiggen Formations). Deposition of these successions occurred in a combination of fluvial braid-plain and braid-delta plain environments, with exposures in the Ahlmannryggen and Borgmassivet regions representing contemporaneous sedimentation in different portions of the same basin, under similar conditions. The development of the Ahlmannryggen Group basin is attributed to flexing associated with continental collision during the assembly of Rodinia. Collision and accretion of a continental island arc terrain (the Maudheim Province) along the southern margin of the Grunehogna Province is considered responsible for flexural snbsidence and the development of a peripheral foreland basin. The Ahlmannryggen Group represents 'molasse' stage infilling of this basin, with sedimentation being dominated by a combination of transverse and longitudinal drainage systems entering a depo-centre located to the east/southeast of the presently exposed succession. SAMANTIIA PERRlTT Detritus entering the basin was sourced either directly or indirectly from at least seven different terrains, aged ca. 1135Ma, ca. 1335Ma, ca. 1600-1700Ma, ca. 2000-2100, ca. 2645Ma, ca. 2400-2900Ma and ca 2900-3300Ma, according to UlPb detrital zircon SHRIMP analysis. The source terrains included the Maudheim Province, basement granites of the Grunehogna Province, an older sedimentary terrain dominated by a banded ironstone association, at least two further magmatic provinces and two metamorphic terrains. Of these source terrains, only the Maudheim Province and Grunehogna Province basement granites are presently exposed in western Dromring Maud Land The subsequent development of large-scale buckle folds and extensive brittle deformation within the Grunehogna Province cover rocks is attributed to the formation of a regionally extensive sinistral strike-slip system during NNW-SSE Pan-African compression, and can be correlated to structures exposed in the Maudheim Province and northern Mozambique. It is proposed that this strike-slip system developed in response to escape tectonics operating during a late stage of Gondwana amalgamation, as a result of the Ross Orogeny, and the suturing of East and West Antarctica
The development and application of a 3D geotechnical model for mining optimisation Sandsloot open pit platinum mine South Africa.
(2003) Bye, Alan Russell.; Jermy, Colin A.; Bell, Frederic Gladstone.; Stacey, Thomas Richard.
Detailed geological knowledge is often a major unknown factor in open pit mining and design, and therefore poses a significant risk in the mining venture. As the knowledge of the geology improves so the risk of unforeseen conditions reduces and therefore safety and productivity can be increased. Historically, geotechnical methods and information have predominantly been used exclusively for pit slope optimisation. This research documents the procedures and developments undertaken to compile a comprehensive geotechnical database, and the application of the geotechnical data to open pit mining, beneficiation and planning. The utilisation of the geotechnical information has been enhanced through the novel development and application of a computerised, 3D geotechnical model. Sandsloot open pit was developed to extract the Platreef pyroxenite orebody, which is hosted within the Northern Limb of the Bushveld Complex. Sandsloot is currently the world's largest open pit exploiting Platinum Group Metals. Interaction of the basic magma with the footwall sediments of the Transvaal Supergroup and varying degrees of assimilation has resulted in a unique suite of hybrid rock types. These various rock types provide significant engineering geological challenges. Geology and the detailed understanding of its properties are fundamental to the optimal design and successful operation of any mine. Extensive fieldwork was conducted to collect geotechnical information, both from exploration boreholes and in-pit mining faces. Over a 5-year period, geotechnical data were collected from 29,213 m of exploration core and 6,873 m of exposed mining faces. Extensive field and laboratory testing was undertaken in order to define the complete set of geotechnical properties for each rock type in the Sandsloot mining area. The geotechnical information relating to each borehole and facemap was stored in the Datamine® software package. The information was collected in the form of rock mass rating (RMR), uniaxial compressive strength (DCS), fracture frequency (FF/m) and rock quality designation (RQD). The architecture of the database was developed along the principals used for generating an ore reserve model. One of the novel applications was the development of a computerized 3D, geotechnical model in Datamine®. The geotechnical parameters, namely RMR, DCS, FF/m and RQD, were modelled for each rock type, using geostatistics, to generate a 3D model. The data were interpolated between exploration boreholes and exposed mining faces and the modelling was constrained using wireframes separated by rock type. The result is a 3D model containing 15 m3 model blocks populated with interpolated geotechnical information. The dimensions of the model blocks are linked to the mining bench height of 15 m. The model can be queried to give predictions on rock mass conditions for any planned mining area, as is the case with the ore reserve model, which provides predictions on platinum grades. The crux of the innovative research is the practical application of the 3D geotechnical model. This was achieved through the development of both a fragmentation and a slope design model, which read the interpolated geotechnical information. These models provided an engineering tool to optimise mining and milling perfonnance. Rather than viewing the drill and blast department as an isolated cost centre and focussing on minimising drill and blast costs, the application of the model concentrated on the fragmentation requirements of the milling and mining business areas. Two hundred and thirty-eight blasts were assessed to detennine the optimum fragmentation requirements for ore and waste. Based on the study a mean fragmentation target of 150 mm was set for delivery to the crushing circuit and a mean fragmentation of 230 mm was set for waste loading from the pit. The mine operates autogenous mills, which are sensitive to the fragmentation profile delivered. The harder zones occurring in the ore zone have a major impact on the plant's perfonnance. The geotechnical parameters in the model were related to Lilly's Blastability Index, and in turn to required explosive volumes and the associated drill and blast costs. Having defmed the fragmentation targets, the Kuz-Ram equation was used in the fragmentation model to predict the explosive volumes required to ensure consistent mining and milling perfonnance. The geotechnical model is used to predict changes in geotechnical conditions and therefore the blasting parameters can be adjusted in advance to ensure the milling and mining fragmentation requirements are met. Through the application of the fragmentation model over an eighteen-month period the loading and milling efficiencies improved by 8.5% and 8.8% respectively, resulting in additional revenue ofR29 million for PPL. Based on the mining rock mass rating (MRMR) values within the geotechnical model a stable slope design model was created in order to calculate optimum inter-ramp angles. From a slope design perspective the model was used to target data-deficient zones and highlight potentially weak rock mass areas. As this can be viewed in 3D, the open pit slopes were designed to accommodate the poor quality areas before they are excavated. It also follows that competent geotechnical zones can be readily identified and the slope optimised accordingly. Due to the detailed geotechnical infonnation being available in three dimensions, the open pit slopes were designed based on a risk versus reward profile. As a significant geotechnical database was available, more accurate and reliable designs were generated resulting in the overall slope angle increasing by 3 degrees. This optimisation process will result in a revenue gain of R900 million over the life of the mine. The revenue and safety benefits associated with this design methodology are substantial and have potential application to all open pit mining operations. The research has enabled detailed geotechnical infonnation to be available in three dimensions. This information can be readily accessed and interpreted, thus providing a powerful planning and financial tool from which production optimisations, feasibility studies and planning initiatives can be implemented. The development and application of a 3D geotechnical model has added a new dimension to the constant strive for business improvement and reflects a novel and successful approach towards the application of engineering geology at the Sandsloot mining operation.
The structural, metamorphic and tectonic context of selected sub-economic veining in the Natal thrust front and Natal Nappe zone, Northern KwaZulu-Natal.
(2000) Basson, Ian James.
The eastern portion of the Namaqua-Natal Mobile Belt, the Natal Metamorphic Province is divided into four main tectonostratigraphic units. These units comprise two accreted island arcs: the Mzumbe and Margate Terranes; an imbricately thrust nappe zone consisting of four ophiolitic nappes in a hinterland-dipping duplex; and the highly deformed metavolcaniclastic/metagreywacke Mfongosi Group directly adjacent to the stable northern foreland of the Kaapvaal Craton. Theories of late-tectonic left-lateral movement in the southern island arcs are extrapolated northwards of the southern margin of the Kaapvaal Craton coincident with the Lilani-Matigulu Shear Zone. The relative timing and structural context of vein-hosted mineralization with respect to major recognized tectonic events is resolved in five separate areas, two in the Natal Nappe Zone and three in the Natal Thrust Front. The Madidima Nappe of the Natal Nappe Zone contains several north-northeast- to northeast-trending and northeast- to east-northeast trending quartzofeldspathic veined reefs considered to have formed in a late-tectonic left-lateral shear system (main shear and synthetic shear orientations, respectively). The northeast- to east-northeast-trending reef is duplicated due to infilling of normally-faulted steep structures in the semi-brittle, incremental normal faulting of the banded amphibolite component of the nappe. Later left-lateral movement has reactivated one of these steep structures along the southern margin of a regional F2-folded band of granite-gneiss in that a southwest extension of this structure may be responsible for sub-economic veining for a length of up to 9 km. The extensive flat-lying topography of the Mbongolwane Flats area, in which the reefs are situated, is accounted for by the accelerated weathering of rocks which underwent sustained late-tectonic metamorphism in the epidoteactinolite facies, accompanied by pervasive shearing and block rotation to the south of the southern limb of the regional F2 fold in the granite-gneiss. A large, kilometer-scale, open advective fluid system which provided fluid-mediated exchange between co-existing rocks existed at the time of vein formation. The fluid system was driven by early-tectonic intrusion of a granite gneiss and amphibole-rich granite. Two areas in the Mfongosi River valley, the northern and southern Mfongosi Valley areas, contain typical evidence of deformation at the leading edge of collision in a mobile belt. The southern Mfongosi Valley area, at the confluence of the Mfongosi and Tugela Rivers, contains veining which resulted from pressure solution of the host metavolcaniclastic/metagreywacke. Veining occupies predictable shear and tension fractures formed during the initial deformation of a foreland margin sequence, in addition to occupying those fractures formed by buckling on the layer-scale. The structural context of the northern Mfongosi Valley veining is defined by subsequent deformation and vein fragmentation such that the metavolcaniclastic/metagreywacke was reduced to a melange in which vein segments acted as competent clasts; a large-scale porphyroblast/matrix system. Formation of the Manyane Thrust to the south of the Mfongosi Group interrupted the normal retrograde metamorphism of the remainder of the Tugela Nappe and initiated a "hot iron effect" whereby a short-lived thermal pulse acted at the thrust plane, producing a reversed geothermal gradient in the underlying Mfongosi group. This reversed gradient would have been counteracted by a steepened normal geothermal gradient in the Mfongosi Group caused by overloading of the Natal Thrust Front by the Natal Nappe Zone. These geothermal gradients partly account for the concentration of veining in the areas of the Mfongosi Group which are directly adjacent to the Manyane Thrust, and directly adjacent to the Kaapvaal Craton, in the lower portions of the thrust front Stable isotope studies indicate fractionation between vein and wall rock under a short-lived, mainly rock-buffered, layer-scale fluid-movement system. Also forming part of the Mfongosi Group of the Natal Thrust Front, the Ngubevu area contains an apparently enigmatic distribution of veining accompanied by gold and base metal mineralization. The structural evolution of the Ngubevu area occurred during consistent left-lateral transpression into which has intruded early-tectonic veins, formed by pressure solution and having the same structural format as the early-tectonic veining in the southern Mfongosi Valley area. Subsequent deformation of the system was accompanied by 1900 -trending tension gashes which were continually ptygmatically-folded, sheared and offset to form occasionally mineralized quartzofeldspathic "blows" and along-strike stringers in the epidote- actinolite schist. Where veining cross-cuts narrow calcite - graphite - sericite - quartz - albite - tourmaline ± chlorite schist layers, gold mineralization occurred. The late-tectonic tension gashes, antitaxially filled by quartz and amorphous calcite, cross-cut the entire range of lithologies. The fluid system during vein deposition varied: during infilling of early-tectonic fractures a short-lived fluid-flow system dominated, with the emplacement of re crystallized wallrock occurring in a closed, non-advective regime under the influence of diffusion caused by pressure solution. The fluid system changed to a more open, advective, greater than layer-scale rock-buffered one with a decreasing contribution of material from immediate host rocks. An internal fluid source is implied for the entire period of vein emplacement, derived from structural analyses which indicates negative dilation across the Mfongosi Group in this area and by comparison of vein:wallrock δ180 values which indicate a lack of igneous-derived fluids. The Phoenix Mine, in the central portion of the Tugela Nappe, and the Ayres Reef, hosted in Manyane amphibolite adjacent to the Manyane Thrust, are grouped together on the basis of their cross-cutting nature and timing with respect to metamorphism and deformation of the host rock, and also due to their similarity in isotopic plots. Both vein sets occur in approximately east-west to east-northeast-trending zones which show evidence of late-tectonic left-lateral movement. Phoenix Mine veining occurs in weakly-metamorphosed meta-gabbro/meta-norite of the Tugela Rand Complex. The Manyane amphibolite demonstrates the amphibolite facies of metamorphism due to the short-lived thermal pulse at the Manyane Thrust. Both sets of veining display slickenlines which are indicative of their emplacement prior to the late-tectonic left-lateral movement. The unusually thick quartz veins of both deposits are the results of late- to post-Tugela Rand Complex fluids or the tapping of late-tectonic metamorphic fluid reservoirs. This caused silica metasomatism and redeposition of material in post-thrusting collapse features. A highly channelized, single-pass fluid system is proposed in the absence of intrusion-derived fluids. Whole rock geochemical data allow a distinction to be made between the Natal Thrust Front and the Natal Nappe Zone: the Foremost nappe of the nappe zone consists primarily of N-type mid-ocean ridge basalts/ocean-floor to within-plate basalts which were intruded prior to nappe emplacement by metaluminous orogenic volcanic arc granitiods. The thrust front displays a lateral variation in metabasite/metasediment ratio, with the ratio increasing from east to west in this inlier. In the east, in the Nkandlha area, melanged metagreywackes dominate and there is a marked paucity of associated metabasites. In the central portions of the thrust front, in the vicinity of the Mfongosi area, active continental margin/continental arc magmatogenic greywackes and arkoses are interlayered with calk-alkaline volcanic arc basalts (volcaniclastics). The greywacke geochemistry indicates little to no mafic/ultramafic influences in sediment contribution and the source of sediment is inferred to be the southern portions of the Kaapvaal Craton. The Nkandlha and Mfongosi area Mfongosi Group segments are considered to be in-situ or para-autochthonous. The western-most Ngubevu area predominantly hosts metabasites. The geochemistry of the metabasites indicates that they are N-type mid-ocean ridge basalts/ocean floor basalts from a destructive plate margin setting. The metabasites are interbanded with metapelitic/metacalcsilicate layers produced in a shallow water oxic environment, here inferred as a spatially-restricted shallow, marginal basin. The metabasites in the Ngubevu area are notably similar to those of the Madidima Nappe, indicating a similar provenance and pre-collisional mode of formation. It is proposed that the variation in the Natal Thrust Front was due to a north-east/south-west distribution of lithological proportions or mixing, with greywackes dominating in the northeast (in proximity to the Kaapvaal Craton) and metabasites dominating in the southwest. Left-lateral transpressional movement within the Mfongosi Group of the Natal Thrust Front, and the Natal Nappe Zone, was continuous throughout plate collision and obduction.
Aspects of the geology and geochemistry of the proterozoic rocks of the Valley of a Thousand Hills, KwaZulu-Natal.
(1999) Milne, George Charles.; Kerr, Alan.; Watkeys, Michael Keith.
A regional field and geochemical study has allowed the identification of three primary units within the Proterozoic basement of the Valley of a Thousand Hills. The Nagle Dam Formation incorporates several chemically distinct orthogneiss series, characterised by limited intragroup fractionation, and derived from discrete sources. Intrusive into the gneisses are the megacrystic A-type granites of the Mgeni batholith, comprising the biotite granites of the Ximba Suite; the hornblende granites and charnockite of the Mlahlanja Suite; and the medium grained leucogranite of the Nqwadolo Suite. Petrogenetic modelling indicates that these are predominately cumulates. A general model for the A-type granites suggests that they were derived through variable MASH processes on an original within plate type basalt. Enclaves within the Mgeni batholith form a distinct series, the Valley Trust Formation, comprising a nongenetic orthogneiss association of amphibolite and crustal sourced quartzo-feldspathic gneiss and locally derived paragneisses. Interaction between the biotite granite and the pelitic enclaves generated a biotite garnet granite. Geothermobarometry suggests temperatures of metamorphism to a maximum of 770°c for the Nagle Dam Formation and c.850°C at a pressure of 6 kb for the Valley Trust Formation. Potential magmatic temperatures of c.760°C at 5 kb are derived for the Mgeni batholith. High Mn garnets within late veins indicate subsequent intrusion at higher levels. Derivation of a tectonic model for the Valley of a Thousand Hills is assisted by a revaluation of the chemical tectonic discrimination plots as source or initiator discriminators. These indicate an origin for the Nagle Dam Formation in an arc environment, while the bimodal orthogneiss association of the Valley Trust Formation and the A-type character of the Mgeni batholith suggests their evolution during extensional events. Geothermobarometry defines an isothermal decompression path, possibly generated during a collision event, superimposed on which is a potential midcrustal heating event, resultant on the intrusion of the Mgeni batholith. These data can be integrated with revised lithotectonic data from the southern portion of the Natal Province to derive a regional model. This comprises: the collision of a number of arcs with associated splitting to form backarcs, sedimentation, and failed rift systems; syn-collisional S-type magmatism, contemporaneous with isothermal decompression of the region; and a series of pulses of post-orogenic granites.
The geology and structure of the Bushveld Complex metamorphic aureole in the Olifants River area.
(1998) Uken, Ronald.; Watkeys, Michael Keith.
The contact metamorphic aureole of the Rustenburg Layered Suite of the Bushveld Complex extends to a depth of over 5 km into the underlying mainly argillaceous Pretoria Group. When compared to other parts of the metamorphic aureole, the Olifants River area is unique in that it is characterised by a high degree of syn-Bushveld Complex deformation and very coarse grained pelitic assemblages. This is believed to have resulted from a combination of greater magma thickness, a deeper emplacement depth and a high degree of subsidence related deformation that was focused along the Thabazimbi-Murchison Lineament. This area also contains a laterally extensive and deformed quartz-feldspar porphyry sill, the Roodekrans Complex that is shown to represent a hypabyssal equivalent of the volcanic Rooiberg Group. There are three main metamorphic zones. A wide andalusite zone dominated by staurolite, garnet and cordierite assemblages. This is followed by a narrow fibrolite zone without staurolite, and a wide inner aureole of migmatite. The migmatite zone is characterised by garnet-cordierite-aluminosilicate assemblages with corundum, spinel and orthopyroxene assemblages at the highest grades. Metamorphic pressure and temperature estimates indicate pressures of between 3 kb and 4 kb in the lower part of the andalusite zone at temperatures of approximately 550°C. Porphyroblast-matrix relationships reveal a close link between deformation and metamorphism resulting in a spectrum of textural relationships developed as a result of inhomogeneous strain. Porphyroblasts in low strain domains preserve textures of “static type" growth whereas syntectonic textures are found in foliated rocks. Pre-tectonic porphyroblasts in many foliated domains indicate that deformation outlasted porphyroblast growth and increased in intensity and extent with time. Retrograde porphyroblasts are post-tectonic. Evidence is presented for both rotation and non-rotation of porphyroblasts in relation to geographical coordinates during extensional top-to-south, down-dip shear in the floor. The unique structural setting in this area triggered the growth of large diapiric structures in the floor of the Rustenburg Layered Suite that are preserved as periclinal folds on the margin and within the northeastern Bushveld Complex. Extreme gravitational loading and heating of the floor by a thickness of up to 8 km of mafic magma resulted in the generation of evenly spaced, up to 7 km diameter wall-rock diapirs that penetrated the overlying magma chamber. Diapiric deformation is restricted to rocks above a decollement zone that is developed along competency contrasts and corresponds approximately with the 550 °C peak metamorphic isotherm. Strongly lineated, boudinaged and foliated rocks are developed in the interpericlinal domains between adjacent periclines. Migmatites in these domains are characterised by conjugate extensional ductile shears and associated asymmetrical boudinage suggesting bulk deformation by pure shear processes. The extension lineation was produced by lateral extension along flow lines directed toward dome culminations. Each of the four diapiric periclines is cut by a different erosional section enabling reconstruction of a typical diapir geometry. At the highest structural levels, periclines have bulbous shapes with overturned limb geometries forming overhangs. The surrounding layered igneous rocks are locally deformed into a series of outward verging folds that define a broad rim syncline. Deformation within the pericline cores is represented by constrictional deformation that produced radial curtain-type folds with steeply plunging lineations and concentrically orientated folds in the outer shell. Diapirism is closely linked to magma emplacement mechanisms. Floor folds in the country rocks were initiated in the interfinger areas of a fingered intrusion. With further magma additions and the coalescence of intrusion fingers into a single sheet, interfinger folds matured into large diapiric periclines which rose to the upper levels of the magma chamber. Strain rates estimated from strain analyses, pericline geometry and model cooling calculations are in the order of 10-14 S-1, corresponding to diapiric uplift rates of 0.6 cm/yr. Diapirism is broadly compatible with a N-S extension in the Olifants River area during emplacement of the Rustenburg Layered Suite. On a regional scale, this is indicated by existence of a major EW dyke swarm that coincides with the long axis of the Bushveld Complex. The accommodation of the Bushveld Complex into the Kaapvaal Craton was facilitated by a combination of craton-wide extension that accompanied plume related magmatic underplating, and loading of the Bushveld Complex. Isostatic adjustment in response to Bushveld Complex subsidence resulted in further development of large basement domes around the perimeter of the Bushveld Complex.
Tectonostratigraphy, structure and metamorphism of the Archaean Ilangwe granite - greenstone belt south of Melmoth, Kwazulu-Natal.
(1997) Mathe, Humphrey Lawrence Mbendeni.; Matthews, P. E.; Watkeys, Michael Keith.
The mapped area, measuring about 400m2, is situated along the southern margin of the Archaean Kaapvaal Craton south of Melmoth in KwaZulu-Natal and comprises greenstones and metasediments forming a narrow, linear E-W trending and dominantly northerly inclined belt flanked to the north and south by various granitoids and granitoid gneisses which have been differentiated for the first time in this study. This belt is here referred to as the ILANGWE GREENSTONE BELT. The lIangwe Belt rocks are grouped into the Umhlathuze Subgroup (a lower metavolcanic suite) and the Nkandla Subgroup (an upper metasedimentary suite). The former consists of: (a) the Sabiza Formation: a lower amphibolite association occurring along the southern margin of the greenstone belt; (b) the Matshansundu Formation: an eastern amphibolite-BIF association; (c) the Olwenjini Formation: an upper or northern amphibolite-banded chert-BIF association. whereas the latter is sub-divided into: (a) the Entembeni Formation: a distinctive phyllite-banded chert-BIF association occurring in the central and the eastern parts of the belt; (b) the Simbagwezi Formation: a phyllite-banded chert-amphibolite association occurring in the western part of the belt, south-east of Nkandla; (c) the Nomangci Formation: a dominantly quartzite and quartz schist formation occurring in the western part of the belt, south-east of Nkandla. The contacts between the six major tectonostratigraphic formations are tectonic. In the eastern sector of the lIangwe Belt, the lowermost metasedimentary formation, the Entembeni Formation, cuts across both the Sabiza and Matshansundu Formations (the lower formations of the Umhlathuze Subgroup) in a major deformed angular unconformity referred to as the Ndloziyana angular unconformity. In the central parts of the belt, the Entembeni Formation structurally overlies the Olwenjini Formation in what seems to be a major local unconformity (disconformity). In the western sector of the belt, the Simbagwezi Formation occurs as a structural wedge between the lower and upper formations of the Umhlathuze Subgroup. That is, it structurally overlies the Sabiza Formation and structurally underlies the Olwenjini Formation. The uppermost metasedimentary unit, the Nomangci Formation occurs as a complex series of finger-like wedges cutting and extending into the Simbagwezi Formation and in each case showing that the Nomangci Formation structurally underlies the Simbagwezi Formation. This structural repetition of lithological units is suggestive of normal dip-slip duplex structures. Palimpsest volcanic features, such as pillow structures and minor ocelli, indicate that many of the amphibolitic rocks represent metavolcanics, possibly transformed oceanic crust. This is also supported by limited major element geochemistry which suggests that the original rocks were ocean tholeiites. Evidence suggests that the talc-tremolite schists and the serpentinitic talc schists represent altered komatiites. The nature of the metasediments (represented by banded metacherts, quartzites and banded iron formations) and their similarity to those of the Barberton, Pietersburg and Nondweni greenstone complexes suggests that they were formed in relatively shallow water environments. The lIangwe magmatism is represented by different types of granitoids and granitoid gneisses and basic-ultrabasic intrusive bodies. Based on similar geochemical and mineralogical characteristics and on regional distribution, mutual associations and contact relationships, these granitoids and granitoid gneisses can be divided into three broad associations, viz: (a) The Amazula Gneiss - Nkwa/ini Mylonitic Gneiss - Nkwalini Quartzofeldspathic Flaser Gneiss Association: a migmatitic paragneiss and mylonitic to flaser gneiss association of older gneisses of Nondweni age occurring in several widely separated areas and intruded by younger granitoids. (b) The early post-Nondweni Granitoids comprising the Nkwalinye Tonalitic Gneiss (a distinctive grey gneiss intrusive into the greenstones and older gneisses) and the Nsengeni Granitoid Suite (an association of three granitoid units of batholithic proportions flanking the greenstone belt and intrusive into the greenstones, older gneisses and Nkwalinye Tonalitic Gneiss). (c) The late post-Nondweni Granitoids comprising the Impisi-Umgabhi Granitoid Suite, a batholithic microcrystic to megacrystic association of five granitoid phases/units occurring to the north and south of the greenstone belt and intrusive into the greenstones, older gneisses and early post-Nondweni granitoids. Limited major element geochemistry suggests that the granitoids and granitoid gneisses are of calc-alkaline origin and are of tonalitic, granodioritic, adamellitic and granitic composition. An igneous derivation from material located possibly at the lower crust or upper mantle is suggested. At least three major episodes of deformation (01, O2 and 03) have been recognized in the greenstones. During 01, a strong penetrative S1 tectonic foliation developed parallel to the So primary layering and bedding. This period was characterized by intense transpositional layering, recumbent and isoclinal intrafolial folding with associated shearing,thrusting and structural repetition of greenstone lithologies. These processes took place in an essentially horizontal, high strain tectonic regime. The first phase of deformation (OG1) in the migmatitic and mylonitic gneisses was also characterized by recumbent and isoclinal intrafolial folding and is remarkably similar to the 01deformational phase in the lIangwe greenstones. Structural features of the first phase of deformation suggest that it was dominated by formation of fold nappes and thrusts and was accompanied by prograde M1 medium-grade middle to upper amphibolite facies metamorphism. During D2 deformation, the subhorizontal D1 structures were refolded by new structures with steeply inclined axial planes. This resulted in the formation of superimposed Type 3 interference folding in the amphibolitic rocks and large-scale, E-W trending, doublyplunging periclinal folds in the metasediments. These periclinal folds have steeply inclined and overturned limbs and are characterized by narrow, closed elliptical outcrop patterns well-defined by extensive banded ironstones and metacherts. The second phase of deformation in the granitoids (DG 2) was characterized by steeply plunging and steeply inclined small-scale tight to isoclinal similar folds. Large-scale folds are not present in the granitoids. Evidence suggests that the second phase of deformation was a major compressional event which resulted in the large-scale upright, flattened flexural folds. It was accompanied by widespread regional greenschist metamorphism and the intrusion of the early postNondweni granitoids. The third phase of deformation produced steeply plunging small-scale folds on the limbs and axial planes of the pre-existing large-scale F2 folds and upright open folds in the granitoid terrain. This episode was characterized by the emplacement of the late postNondweni granitoids (along the D2 greenstone boundary faults) and is associated with two significant events of prograde M3 upper greenschist facies metamorphism and retrograde M3 lower greenschist facies metamorphism. Post-D3 deformation is characterized by late cross-cutting faults and the emplacement of younger basic - ultrabasic bodies.
Geological evolution of western H.U. Sverdrupfjella, Dronning Maud land, Antarctica.
(1992) Grantham, Geoffrey Hugo.; Hunter, Donald Raymond.
The oldest rocks of western H.U. Sverdrupfjella, the Jutulrora Formation, consist of interlayered mafic to felsic ortho- and paragneisses thought to represent calc-alkaline volcanic and clastic sedimentary rocks. These rocks are structurally overlain by the largely paragneissic, carbonate- dominated Fuglefjellet Formation which may represent a miogeosynclinal shelf facies. This sequence is structurally overlain by the dominantly para-gneissic Sveabreen Formation which may comprise a eugeosynclinal facies. Three granitic bodies, the Roerkulten, Jutulrora and Brekkerista Granites intrude the Jutulrora Formation. The trace element chemistry of these granites suggest that accessory minerals played significant roles during their generation and crystallization. Various mafic intrusions, now discordant amphibolites, and a phase of diorite veining are present. The Dalmatian Granite was emplaced syntectonically with the 470Ma Pan-African (or Ross) orogeny during D3. This granite was generated by crustal anatexis at >5kb. Jurassic age intrusions include alkaline complexes at Straumsvola and Tvora and numerous dolerite dykes, some of which postdate the alkali intrusions. Five episodes of deformation are recognised. The first two resulted in folds (F1 and F2) which are co-planar and coaxial resulting in type 3 interference structures. Low angle thrust faulting occurred during D2. Fold vergence and associated lineations suggest tectonic transport from the southeast during D1 and D2, D3 involved folding and reverse faulting. The orientations of the fault and axial planes of these structures suggest transport from the west and north-west. D4 involved open dome and basin folding. D6 involved normal faulting and jointing, adjacent and parallel to the Jutulstraumen Glacier in the west. The joints affect the Tvora Alkaline Complex. Three phases of metamorphism, related to the deformation, are recognised. The dominant mineral assemblages are typical of medium to high grade metamorphism and define S1 and S2 planar fabrics. Discordant mafic intrusions provide evidence of a long history of metamorphism. M3 mineral development, commonly represented by biotite, is oriented axial planar to D3 folds. Comparison of the geology of the area with that of southern Mozambique reveals many similarities. These support reconstructions based on geophysical data which juxtapose Dronning Maud Land and southern Africa prior to the break up of Gondwanaland.
A study of titanium-bearing oxides in heavy mineral deposits along the East Coast of South Africa.
(1993) Hugo, Victor Emmanuel.; Cornell, David H.
Heavy mineral deposits along the east coast of South Africa represent the world's largest demonstrated resource of beach placer ilmenite. This mineral occurs as homogeneous, subrounded grains, with chemical compositions close to pure FeTi03• Concentrates contain between 48 and 52 per cent Ti02, with minor impurities of MnO, MgO, and Cr203. Most coastal ilmenites are unaltered or display only incipient alteration, but the entire spectrum of alteration products from ilmenite to rutile or anatase, is observed. Transmission electron microscopy of weathered ilmenites reveals that ilmenite commonly alters to pseudorutile and then to rutile or anatase, as described by Teufer and Temple (1966) and Grey and Reid (1975). Ilmenite may also alter directly to rutile (or anatase) in a single-stage process. In addition, ilmenite altered by high temperature oxidation and hydrothermal processes is found in the deposits. There is good mineralogical evidence that the alteration of ilmenites found in the coastal sediments is best described by a multi stage model, in which some ilmenite grains were altered prior to final deposition. Other common iron-titanium oxides in the deposits include magnetite, rutile and hematite, which may occur as discrete grains or as composite grains of two or more oxides. Ilmenite and magnetite in the coastal sediments are derived from rocks of both the Karoo Igneous Province and the Natal Basement, while rutile is derived solely from the latter. Ilmenites from certain rock groups may be distinguished on the basis of their chemical composition. However, magnetite chemistry is a better indicator of provenance, and magnetites from the above two sources can be clearly distinguished. The petrography of the iron-titanium oxides may be used as a provenance indicator, but may be misleading, as the proportions of the oxide intergrowths change with transport and weathering. Variations in the proportions and chemical compositions of iron-titanium oxides and other heavy minerals within the coastal sediments are caused by provenance, selective sorting during deposition, age of the deposit, weathering, and the recent geological history of the area. A model is proposed in this study which describes the formation of the heavy mineral deposits in relationship to the above influences.
The marine geology of the Northern KwaZulu-Natal continental shelf, South Africa.
(2009) Green, Andrew Noel.; Uken, Ronald.
This study proposes that the submarine canyons of the northern Kwazulu-Natal continental margin formed contemporaneously with hinterland uplift, rapid sediment supply and shelf margin progradation during the forced regression of upper Miocene times. These forced regressive systems tract deposits volumetrically dominate the shelf sediments, and comprise part of an incompletely preserved sequence, amongst which six other partially preserved sequences occur. The oldest unit of the shelf corresponds to forced regression systems tract deposits of Late Cretaceous age (seismic unit A), into which a prominent erosive surface, recognized as a sequence boundary, has incised. Fossil submarine canyons are formed within this surface, and underlie at least one large shelf-indenting canyon in the upper continental slope. Smaller shelf indenting canyons exhibit similar morphological arrangements. Late Pliocene deposits are separated from Late Cretaceous lowstand deposits (seismic unit B) by thin veneers of Late Palaeocene (seismic unit C) and mid to early Miocene (seismic unit D) transgressive systems tract deposits. These are often removed by erosive hiatuses of early Oligocene and early to mid Pliocene age. These typically form a combined hiatus surface, except in isolated pockets ofthe upper slope where late Miocene forced regressive systems tract units are preserved (anomalous progradational seismic unit). These sediments correspond to the regional outbuilding of the bordering Tukhela and Limpopo cones during relative sea level fall. Either dominant late Pliocene sediments (seismic unit E), or transgressive systems tract sediments which formed prior to the mid Pliocene hiatus, overlie these sediments. Widespread growth faulting, slump structures and prograding clinoforms towards canyon axes indicate that these sediments initiated upper slope failure which served to create proto-canyon rills from which these canyons could evolve. The association of buried fossil canyons with modern day canyons suggests that the rilling and canyon inception process were influenced by palaeotopographic inheritance, where partially infilled fossil canyons captured downslope eroding flow from an unstable upper slope. Where no underlying canyons occur, modern canyons evolved from a downslope to upslope eroding system as they widened and steepened relative to the surrounding slope. Statistical quantification of canyon forms shows a dominance of upslope erosion. Landslide geomorphology and morphometric analysis indicate that this occurred after downslope erosion, where the canyon axis was catastrophically cleared and incised, leading to headward retreat and lateral excavation of the canyon form. Trigger mechanisms for canyon growth and inception point to an overburdening ofthe upper slope causing failure, though processes such as freshwater sapping may emulate this pattern of erosion. It appears that in one instance, Leven Canyon, freshwater exchange with the neighbouring coastal waterbodies has caused canyon growth. The canyons evolved rapidly to their present day forms, and have been subject to increasingly sediment starved conditions, thus limiting their evolution to true shelf breaching canyon systems. Sedimentological and geomorphological studies show that the shelf has had minor fluvial influences, with only limited shelf-drainage interaction having occurred. This is shown by isolated incised valleys of both Late Cretaceous and Late PleistocenelHolocene age. These show classic transgressive valley fills of wave dominated estuaries, indicating that the wave climate was similar to that of today. The narrowness of the shelf and the inheritance of antecedent topography may have been a factor in increasing the preservation potential of these fills. Canyons thus appear to have been "headless" since their inception, apart from Leven Canyon, which had a connection to the Last Glacial Maximum (LGM) St Lucia estuary, and Wright Canyon, which had an ephemeral, shallow LGM channel linking it to the Lake Sibaya estuarine complex. Coastline morphology has been dominated by zeta bays since at least 84 000 BP, thus littoral drift has been limited in the study area since these times. The formation of beachrock and aeolianite sinks during regression from the last interstadial has further reduced sediment supply to the shelf. The prevalence of sea-level notching in canyon heads, associated with sea levels of the LGM indicates that canyon growth via slumping has been limited since that time. Where these are obscured by slumping in the canyon heads (Diepgat Canyon), these slumps have been caused by recent seismic activity. The quiescence of these canyons has resulted in the preservation of the steep upper continental slope as canyon erosion has been insufficient to plane the upper slope to a uniform linear gradient such as that of the heavily incised New Jersey continental margin. Progressive sediment starvation of the area during the Flandrian transgression has resulted in a small shore attached wedge of unconsolidated sediment (seismic unit H) being preserved. This is underlain by a mid-Holocene ravinement surface. This crops out on the outer shelf as a semi-indurated, bioclastic pavement. Thinly mantling this surface are Holocene sediments which have been reworked by the Agulhas Current into bedforms corresponding to the flow regime and sediment availability to the area. Bedforms are in a state of dis-equilibrium with the contemporary hydrodynamic conditions, and are presently being re-ordered. It appears that sediment is not being entrained into the canyons to the extent that active thalweg downcutting is occurring. Off-slope sediment loss occurs only in localized areas, supported by the dominance of finer grained Early Pleistocene sediments of the outer slope. A sand ridge from the mid shelf between Wright and White Sands Canyons appears to have been a palaeo-sediment source to White Sands Canyon, but is currently being reworked southwards towards Wright Canyon. The prevalence of bedform fields south of regularly spaced canyon heads is considered a function of hydrodynamic forcing of the Agulhas Current by canyon topography. These bedforms are orientated in a northerly direction into the canyon heads, a result ofnortherly return eddying at the heads of these canyons.
Sedimentology, coral reef zonation, and late Pleistocene coastline models of the Sodwana Bay continental shelf, Northern Zululand
(1991) Ramsay, Peter John.; Mason, Tom R.
This geostrophic current-controlled Zululand/Natal shelf displays a unique assemblage of interesting physical, sedimentological and biological phenomena. The shelf in this area is extremely narrow compared to the global average of 75km, and is characterised by submarine canyons, coral reefs, and steep gradients on the continental slope. A shelf break occurs 2.1km to 4.1km offshore and the shelf can be divided into a northern region and a southern region based on the presence or absence of a defined shelf break. The southern shelf has a poorly-defined shelf break whilst the northern shelf has a well-defined break at -65m. The poor definition of the shelf break on the southern shelf can possibly be attributed to the presence of giant, climbing sand dunes offshore of Jesser Point at depths of -37m to -60m. The northern shelf has a series of coast-parallel oriented patch coral reefs which have colonised carbonate-cemented, coastal-facies sequences. The northern shelf can be divided into three distinct zones: inner-, mid-, and outer-shelf zones. The inner-shelf is defined as the area landward of the general coral reef trend, with depths varying from 0m to -I5m and having an average gradient of 1.1. The mid-shelf is defined by the general coral reef trend, varying from -9m over the shallow central axis of the reefs to -35m along the deep reef-front environments. The outer-shelf is seaward of the coral reefs and occurs at a depth range of -35m to - 65m. Gradients vary from 1° in the south to 2.5° in the northern part of the study area, and are steep compared to world average shelf gradient of 0.116°. Four submarine canyons occur in the study area and are classified as mature- or youthful-phase canyons depending on the degree to which they breach the shelf. The origin of these canyons is not related to the position of modern river mouths but can probably be linked to palaeo-outlets of the Pongola and Mkuze River systems. It is suggested that the canyons are mass-wasting features which were exploited by palaeo-drainage during regressions. The youthful-phase canyons appear to be mass-wasting features associated with an unstable, rapidly-deposited, progradational late Pliocene sequence and a steep upper continental slope. The mature-phase canyons were probably initiated by mass-wasting but have advanced shoreward, breaching the shelf, due to their link with the palaeo-outlets of the Pongola and Mkuze Rivers during late Pleistocene regressions. Evidence of modem canyon growth has been noted on numerous SCUBA diving surveys carried out on the canyon heads. These take the form of minor wall slumps and small-scale debris flows. The canyons are also supplied with large quantities of sand in the form of large-scale shelf subaqueous dunes generated and transported by the Agulhas Current. As these bedforms meet the canyons the sediment cascades down the canyon thalweg and causes erosion and downcutting of the canyon walls and floor thereby increasing the canyon dimensions. Late Pleistocene beachrock and aeolianite outcrops with or without an Indo-Pacific coral reef veneer are the dominant consolidated lithology on the shelf. These submerged, coast-parallel, carbonate cemented, coastal facies extend semi-continuously from -5m to -95m, and delineate late Pleistocene palaeocoastline events. The rock fabric of these high primary porosity lithologies shows grains floating in a carbonate cement with occasional point-contacts. Grains are mostly quartz (80-90%), minor K-feldspar and plagioclase (5-10%), and various lithic fragments. The rocks contain conspicuous organic grains including foraminifera, bivalve, echinoid, bryozoan, red algal, and occasional sponge spicule fragments; these commonly display replacement fabrics or iron-stained rims. The dominant sedimentary structures found in these sandstone outcrops include high-angle planar cross-bedding and primary depositional dip bedding. Palaeocurrent directions sngest a palaeoenvironment dominated by a combination of longitudinal and transverse dunes with wind directions similar to those observed forming the modem dune systems. Erosional features evident on the submerged beachrocks and aeolianites include gullies trending in two different directions and sea-level planation surfaces with or without the presence of potholes. The unconsolidated sediment on the shelf is either shelf sand, composed mainly of terrigenous quartz grains; or bioclastic sediment which is partially derived from biogenic sources. The quartzose sand from the inner-shelf is generally fine-grained, moderately- to well-sorted, and coarsely- to near symmetrically-skewed. Carbonate content is low, and varies between 4-13%. Quartzose sand from the outer-shelf is fine-grained, moderately- to well-sorted, and coarsely- to very coarsely-skewed. The inner-shelf quartzose sand is better sorted than the outer-shelf sand due to increased reworking of this sediment by the high-energy swell regime. Sediment from the shallower areas of the outer-shelf (< -50m) is better sorted than sediment from depths of greater than -50m. Generally wave-reworking of quartzose shelf sand from the Sodwana Bay shelf results in greater sediment maturity than that observed from geostrophic current effects or a combination of geostrophic and wave-reworking. This sediment was derived by reworking of aeolian and beach sediments, deposited on the shelf during the period leading up to the Last Glacial Maximum (15 000 - 18 000 years B.P.) when sea-level was -130m, during the Holocene (Flandrian) transgression. Bioclastic sediment on the Sodwana Bay shelf is defined as having a CaC03 content of greater than 20% and is a mixture of biogeoically-derived debris and quartzose sand. The distribution of bioclastic sediment in the study area is widespread, with reef-derived and outer-shelf-derived populations being evident. This sediment consists of skeletal detritus originating from the mechanical and biological destruction of carbonate-secreting organisms such as molluscs, foraminifera, alcyonaria, scleractinia, cirripedia, echinodermata, bryozoa, porifera. The reef-derived bioclastic population is confined to depths less than -40m in close proximity to reef areas, whereas the shelf-derived bioclastic population occurs at depths greater than -40m and is derived from carbonate-producing organisms on deep water reefs and soft-substrate environments on the shelf. Large-scale subaqueous dunes form in the unconsolidated sediment on the outer-shelf due to the Agulhas flow acting as a sediment conveyor. These dunes are a common feature on the Sodwana Bay shelf occurring as two distinct fields at depths of -35m to -70m, the major sediment transport direction being towards the south. The two dune fields, the inner- and outer subaqueous dune fields, are physically divided by Late Pleistocene beachrock and aeolianites ledges. A bedform hierarchy has been recognised. The larger, outer dune field appears to have originated as a system of climbing bedforms with three generations of bedforms being superimposed to form a giant bedform, while the inner dune field has a less complex construction. The largest bedforms are those of the outer dune field off Jesser Point, being up to 12 m high, 4 km long and 1.2 km wide. A major slip face, with a slope of 8° is present. Bedload parting zones exist where the bedform migration direction changes from south to north. Three bedload parting zones occur in the study area at depths of -60m, -47m and -45m; two in the inner dune field and one in the outer dune field. These zones are invariably located at the southern limits of large clockwise eddy systems. Such eddies appear to be the result of topographically induced vorticity changes in the geostrophic flow and/or the response to atmospheric forcing caused by coastal low-pressure system moving up the coastline. It has been demonstrated that the inner subaqueous dune sediment conveyor is not active all the time but only during periods . of increased current strength when the Agulhas Current meanders inshore. The smaller bedforms in the outer dune field undergo continuous transport due to the current velocity on the shelf edge outer dune field being higher than the velocity experienced on the inner dune field. The very large 2·D dune which forms the outer dune field is probably not active at present: this is inferred due to the shallow angle of the mega-crest lee slope (8°). The very large Sodwana Bay subaqueous dune fields may be compared with the very large, reconstructed, subaqueous dunes which occur in Lower Permian sediments of the Vryheid Formation, northern Natal. These Permian dunes are represented, in section, as a fine- to medium-grained distal facies sandstone with giant crossbeds. These large-scale bedforms are unidirectional, but rare directionally-reversed, climbing bedforms do occur, this directional reversal may be related to bedload parting zones. On the evidence presented in this thesis, it is proposed that these Permian subaqueous dunes may be ancient analogues of the modem subaqueous dune field on the Sodwana Bay shelf. Positive-relief hummocks and negative-relief swale structures are fairly common in the fine-grained, quartzose shelf sand at depths of -30m to -60m. These appear to be transitional bedforms related to the reworking by storms of medium 2-D subaqueous dunes. These hummocky structures may be the modem equivalent of hummocky cross-stratification noted in the geological record, and if so, they are probably the first to have ever been observed underwater. The occurrences of ladderback ripples on the Sodwana Bay shelf at depths of -4m to -17m, suggest that subtidal ladderback ripples may be more common than previously thought. Ladderback ripples are common features of tidal flats and beaches where they form by late-stage emergence run-off during the ebb tide. They are generally considered diagnostic of clastic intertidal environments. The mode of formation on the Sodwana Bay shelf is different from the classic late-stage emergence run-off model of intertidal occurrences, being a subtidal setting. Subaqueous observations indicate that ladderback ripples are not environment-specific, and that additional evidence of emergence is therefore necessary to support an intertidal setting in the rock record: ladderback ripples alone are insufficient to prove an intertidal environment. The coral patch reefs of the northern Natal coast are unique, being the most southerly reefs in Africa, and totally unspoilt. The Zululand reefs are formed by a thin veneer of Indo-Pacific type corals which have colonised submerged, late Pleistocene beachrocks and aeolianites. Two-Mile Reef at Sodwana Bay has been used to develop a physiograpbic and biological zoning model for Zululand coral reefs, which has been applied to other reefs in the region. Eight distinct zones can be recognised and differentiated on the basis of physiographic and biological characteristics. The reef fauna is dominated by an abundance of alcyonarian (soft) corals, which constitute 60-70% of the total coral fauna. The Two-Mile Reef zoning model has been successfully applied to larger reefs such as Red Sands Reef, and smaller patch reefs (Four-Mile and Seven-Mile Reefs) in the same general area. In this thesis extensive use has been made of Hutton's uniformitarian principles. Hutton's doctrine is particularly relevant to the study of depositional processes and relict shorelines. Coastal processes and weather patterns during the late Pleistocene were broadly similar to modem conditions enabling direct comparisons to be made. A computer-aided facies analysis model has been developed based on textural statistics and compositional features of carbonate-cemented coastal sandstones. Many attempts have been made to distinguish different ancient sedimentary depositional environments, most workers in this field having little success. The new method of facies reconstruction is based on: (1) underwater observations of sedimentary structures and general reef morphology; (2) a petrographic study of the reef-base enabling flve facies: aeolianite, backbeach, forebeach, swash, and welded bar facies to be recognised, which control the geomorphology of Two-Mile Reef; (3) cluster and discriminant analysis comparing graphic settling statistics of acid-leached reef-base samples with those of modem unconsolidated dune/beach environments. The results of this analysis demonstrated that the beachrocks and aeolianites on the shelf formed during a regression and that late Pleistocene coastal facies are similar to modem northern Zululand coastal environments, which have been differentiated into aeolian, backbeach, forebeach, swash, & welded bar. A late Pleistocene and Holocene history of the shelf shows that during the late Pleistocene, post Eemian regressions resulted in deposition and cementation of coast-parallel beachrocks and aeolianites, which define a series of four distinct palaeocoastline episodes with possible ages between 117 000 and 22 000 years B.P. The beachrock/aeolianites formed on the shelf during stillstands and slow regressions, and the gaps between these strandline episodes represent periods of accelerated sealevel regression or a minor transgressive phase which hindered deposition and cementation. The formation of these lithologies generated a considerable sediment sink in the nearshore zone. This reduced sediment supply and grain transport in the littoral zone during the Holocene, and probably enhanced landward movement of the shoreline during the Flandrian transgression. Prior to the Last Glacial Maximum, the beachrock/aeolianite sedimentary sequence was emergent and blanketed by shifting aeolian sands. The Pongola River, which flowed into Lake Sibaya, reworked the unconsolidated sediments on the shelf, and exploited the route of least resistance: along White Sands and Wright Canyon axes. The erosion resulting from fluvial denudation in Wright Canyon has caused this canyon to erode some of the beachrock/aeolianite outcrops which form palaeocoastline episode 2 and entrench the canyon to a deeper level; this eroded the shelf to a distance of 2km offshore. During the Flandrian transgression the unconsolidated sediment cover was eroded, exposing and submerging the beachrock/aeolianite sequence. Flandrian stillstands caused erosional features such as wave-planed terraces, potholes, and gullies to be incised into beachrock and aeolianite outcrops; these are seen at present depths of -47m, -32m, .26m, -22m, -17m to -15m, and -12m. High energy sediment transfers, in an onshore direction, resulted in the deposition of sand bars across the outlet of Lake Slbaya's estuary and the development of a 130m + coastal dune barrier on a pre-existlng, remnant Plelstocene dune stub. Sea-level stabilised at its present level 7 000-6 000 years B.P. and coral reef growth on the beachrock/aeolianite outcrops probably started at 5 000 years B.P. A minimum age for the formation of the northern Zululand coral reefs has been established at 3780 ± 60 years B.P. A mid Holocene transgression relating to the Climatic Optimum deposited a + 2m raised beach rock sequence. This transgression eroded the coastal dune barrier and caused a landward shoreline translation of approximately 40m. A minor transgression such as this can be used as a model for coastal erosion which will result from the predicted 1.5m rise in sea-level over the next century. This rise in sea-level could result in a 30m landward coastline translation of the present coastline, ignoring the influence that storms and cyclones will have on the coastline configuration.
Aspects of the engineering geology of Maputo City, Mozambique.
(2011) Vicente, Enoque Mendes.; Schreiner, Hilson Deneys.; Jermy, Colin A.; Richards, Nicholas.
The geological formations of Maputo City, which are mainly unconsolidated materials with soil like properties, are described in terms of their engineering geological and geotechnical characteristics with relevance to their distribution patterns and spatial trends. Problematic conditions such as collapse potential characteristics, loose aeolian sand dune deposits and loose sand plains characterize many of the materials. The geological characteristics combined with anthropogenic interference such as intensive urbanization with inappropriate land use, construction in sensitive areas like steep sandy slopes has led to many problems including slope stability. Foundation problems with building settlement and gully erosion also occur. The aim of this research was to study the engineering geological characteristics and the geotechnical properties of the geological formations of Maputo City and various related problems. Special relevance has been given to the understanding of three specific problems: building damage, gully erosion and slope instability. The geological formations are predominantly sandy (coarse to very fine sand) with very low clay content, are non-plastic and are classified as from the group SP-SM which are poorlygraded sand with silt. The majority of the materials are loose and normally consolidated with a high level of residual strength. Assessment of collapse settlement through double consolidation technique indicated soil compressibility and significant sensibility to collapse upon wetting. Truly collapsible soils that show full collapse of the soil structure were identified in 33% of the tested materials where the highest collapse behaviour reached values above 5%, predicted to cause moderate trouble in foundation design. Some of the bonded materials are bonded (evident in 67% of samples tested). Bonding was confirmed by comparing the compressibility of the undisturbed and remoulded samples. The remoulded samples showed a significantly higher compression than that of the bonded materials as part of the stress applied is carried by the bonds themselves, as the bonded material is stiffer than the same without bonds. The curves of the remoulded samples were used to establish the limit between the stable and meta-stable states of the material. A qualitative evaluation of the erosion susceptibility was investigated by physical tests such as the crumb test, shear strength and chemical indicators while a quantitative evaluation of the erodibility characteristics was obtained using a flume test. Some correlations were found between the results of various methods. Almost all samples that were found to be dispersive with ESP were also dispersive with TDS vs. %Na and SAR. Results of the flume erodibility test have very little correlation with the chemical properties related to dispersion revealing that the erosion susceptibility and gullying in Maputo City have more relation to the physical processes than to the dispersion related chemical properties of the soils. The positive identification of dispersive and erodible soils can only be carried out using a combination of various techniques. Therefore, a new rating system for erosion susceptibility of sandy soils combining the physical and chemical factors of dispersion is proposed including the flume test, crumb test, TDS/%Na, SAR and ESP. The proposed rating system was applied to the tested soils of Maputo City. Fifteen samples (83% of the rated samples) were classified with intermediate susceptibility to erosion while 3 samples (17%) were classified as having a low susceptibility to erosion. The highest rating scores were obtained by the same samples that showed dispersive behaviour with SAR, ESP and TDS/%Na. This group of samples was of intermediate erodibility in the flume test. The slope instability mechanisms observed in Maputo City are predominantly rotational failures with a mass of soil sliding along a curved surface of rupture followed by sand flow at the toe as failure occurs in the presence of excess water. Four groups of factors account for the slope instability problems in Maputo City: geomorphological causes, physical and meteorological causes, geological and geotechnical properties of soils, and anthropogenic causes. The mechanism of failure is mostly due to the loss of matric suction of soils in the presence of rainwater and possibly from destruction of bonding agents. Factors of safety values indicate that the slopes are generally unstable with the control being the slope angle. The slopes in the Polana-Caniço and Ferroviário Quarters show high factor of safety values but is the area most affected by slope instability. Slope failure in these areas is intrinsically caused by anthropogenic factors related to inappropriate land use planning. The gully sidewalls are unstable as the slope created is very steep. The slope at Friedrich Engels Avenue causes most concern due not only to the slope height and angle but also to the size and number of buildings constructed at the crest, mainly high rise buildings along the Julius Nyerere Avenue, the integrity of which could be threatened by a landslide event (this slope has recently been affected by active landslides).
Sedimentary models for coal formation in the Klip River coalfield.
(1988) Christie, Angus David Mackay.; Tavener-Smith, Ronald.
The primary objective of this study was to establish sedimentary models for peat formation in the southern part of the Klip River coalfield during Ecca (Permian) times and to assess palaeoenvironmental controls on coal seam behaviour and distribution. In order to achieve this approximately 2 400 borehole logs and 25 field sections were collected. The coal-bearing Vryheid Formation records early to late Permian fluvio-deltaic sedimentation within the northeastern main Karoo basin. Three informal lithostratigraphic subdivisions, based on the investigations of Blignaut and Furter (1940, 1952), are proposed: the Lower zone, Coal zone and Upper zone. An examination of the structural framework and history of the northeastern Karoo basin reveals that the southern and western boundaries of the Klip River coalfield are defined by zones of rapid basement subsidence : the Tugela and Oannhauser Troughs respectively. There is some doubt as to the locality of the source area to the rivers emptying into the Ecca sea. Ryan (1967) postulated the "Eastern Highlands" situated off the present southeast African coast, but it is contended that the Swaziland area, situated no more than 200 to 300 km to the northeast of the Klip River coalfield, constituted a more plausible source area. The Lower zone represents sedimentation along a westerly to southeasterly prograding coastline dominated by high-constructive lobate or braid deltas, but also showing significant influence by wave processes. The Coal zone, which varies in thickness from 35 to 60 m, represents a major phase of coastal progradation and braided-river deposition on extensive alluvial plains. Significant coal seams formed only during periods of fluvial inactivity, the duration of which was dependent on source-area processes. Coal seam geometry and behaviour in the Klip River coalfield were not influenced by the depositional environments of associated clastic sediments. The following factors were found to have of profound influence in determining the extent, distribution and rate of peat accumulation: 1. Platform stability and temporal and spatial variations therein. 2. The absence or presence of penecontemporaneous clastic sedimentation. 3. Duration of periods of peat formation. 4. Lithology and topographic expression of clastic sediments underlying peat-forming swamps. The peat-forming phase of the Vryheid Formation was terminated by an extensive transgression brought about by an eustatic rise in basin water-level and/or an increased rate of platform subsidence.
The hydrogeology of Botswana.
(1974) Jennings, Christopher Mark Hubert.
Botswana covers an area of 570 000 km and has a population of about 600 000. It is estimated that three-quarters of the human and livestock populations are dependent on ground water, with an estimated 26 x 10 m of water from this source being used annually. Details of the physiography, climate, denudational and depositional surfaces and geology are given: Ground water occurs in both primary and secondary aquifers under both water-table and artesian conditions at varying depths from less than 1m to over 300m. The water-bearing properties of the various aquifers are described with the basalt/Cave sandstone contact providing the greatest number of successful boreholes and the sedimentary rocks of the Pretoria Group providing the highest yields (208,45 litres/minute). The shallowest water is found in the Kalahari Beds and the deepest in the Ecca Group. Detailed descriptions are given of the hydrogeology of the Central Kalahari, Lobatse, Orapa and Serowe. In the Lobatse area, estimates of the average monthly recharge rate have been made as well as estimates of the total storage capacity of the various ground-water basins. The percentage of annual rainfall contributing to ground water has also been calculated. An annual recharge rate has also been calculated for Serowe while the total amount of water in storage in the important Cave sandstone aquifer has been estimated. Hydrogeological details of the Kalahari Beds, basalt/Cave sandstone aquifer and Middle Ecca aquifers are given following core drilling programmes. ERTS photography was used to assist in obtaining a figure of 56 x 10 m of extractable water present in storage in the "sand rivers" of eastern Botswana. Detailed aquifer tests on a variety of aquifers are described and show that the secondary aquifers generally present often behave in a similar fashion to primary aquifer. Approximately 5 000 boreholes are presumed to be present in Botswana. It is estimated that 17% of the successful boreholes have yields in excess of 150 1/min. The siting of boreholes using geological/geophysical aids has resulted in an increase in the success rate of nearly 25%. New geophysical techniques for the location of ground water have been investigated and ground geophysical methods used include electrical resistivity, inductive and conductive electromagnetic, Afmag, self-potential and seismic reflection and refraction methods. The well-tried resistivity method remains the most successful technique but self-potential, Afmag and seismic methods have given encouraging results. Extremely detailed studies using environmental isotopes are described. These have enabled quantitative estimates of ground-water storage and turnover times to be made; have given round-water flow rates; have outlined areas of recharge; have enabled permeabilities to be calculated; have enabled a clearer picture of recharge mechanisms through the unsaturated zone to be built-up; and have provided important evidence of areas in which recent recharge has contributed to ground-water supplies. The studies have shown that measurable amounts of tritium are present over far wider areas than originally anticipated and thus more recharge is taking place than thought earlier from laboratory tests and hydrogeological considerations. In Lobatse a water balance model is proposed and calculations based on this model indicate that some leakage, hitherto unsuspected, between several of the ground-water basins, take place. The carbon-14 method has, in addition, helped outline areas of recharge (Central Basin, Lobatse) which tritium had failed to do and has shown by using combined 3H and l4C data that mixing of young and old waters takes place. In the Kalahari, radiocarbon has been used to calculate ground-water flow rates, permeability and transmissivity. The oldest ground water in Botswana has an age of 33 700 years. Isotopic studies in the unsaturated zone have shown that water moves given rates downward at a rate of between 31 and 41 cm per year. Studies of water levels in boreholes have shown that nearly all boreholes show responses which can be directly correlated with seasonal recharge and hence the nature and frequency of recharge can be estimated. In addition, storage capacity and safe yield have been estimated using long term water level changes and knowing the amount abstracted from the basin. The rapid responses shown in some boreholes indicates surprisingly rapid recharge. Two boreholes in Botswana showed effects of the Tulbagh earthquake on 29th September 1969. The disturbance of semi-diurnal fluctuations in boreholes could possibly be used as an early warning device to predict catastrophic earthquakes. A prelimlinary annual safe yield for ground-water supplies in Botswana is estimated to be 4 x 10 9 m3 per annum. Tree roots have been found in boreholes at depths greater than 68m. This emphasises the role vegetation can have in causing transpirational losses from ground-water supplies. Irrigation from boreholes is unlikely to be profitable unless exceptionally large supplies are obtained or water be present at very shallow depth. Underutilised boreholes, e.g. boreholes drilled specifically for cattle ranching, could also be profitably used for irrigation. Details of ground-water chemistry and examples of fresh water overlying saline, saline water overlying fresh, chemical stratification with depth and changes in quality with time are given. The distribution of fluoride rich waters in Botswana is also given. This thesis has therefore attempted to outline the current status of hydrogeological research in Botswana and it is hoped that this will lay the foundation for later, more detailed and quantitative, studies. These will become even more vital than at present, as it is estimated that all readily available surface water resources in eastern Botswana will be fully utilised by the late 1980's and the country will rely even more heavily on ground water than at present.
Rock fabric study of the Northern Lebombo and Rooi Rand dyke swarms : regional and local implications.
(2012) Hastie, Warwick William.; Aubourg, Charles.; Watkeys, Michael Keith.
No abstract available.
The marine geology of the Aliwal Shoal, Scottburgh, South Africa.
(2012) Bosman, Charl.; Uken, Ronald.
This study represents the first detailed geological, geophysical and geochronological investigation of the continental shelf surrounding the Aliwal Shoal, ~5 km offshore of Scottburgh, in southern KwaZulu-Natal. Mapping of the seafloor geology using geophysics and direct observations from SCUBA diving transects were integrated with the seismic stratigraphy and constrained by new geochronological data. Four seismic stratigraphic units (A to D) were identified and interpreted with the subsequent sequence stratigraphic model consisting of four incompletely preserved stratigraphic sequences separated by three sequence boundaries (SB1 - SB3) comprising complex reworked subaerial unconformity surfaces. Sequence 1 is the deepest, subdivided by a basin-wide marine flooding surface (MFS1) into a lower Campanian (and possible Santonian) TST and an upper Maastrichtian combined regressive systems tract comprising HST/FRST deposits. SB1 follows Sequence 1 and spans most of the Tertiary representing multiple erosional events. Shelf sedimentation resumed during the Late Pliocene to early Pleistocene with deposition of Sequence 2, the shelf-edge wedge, which again was followed by erosion and non-deposition during the high frequency and amplitude Early to Middle Pleistocene sea-level fluctuations resulting in the formation of SB2. Sequence 3 consists of coast-parallel, carbonate cemented aeolianite palaeo-shoreline ridges of various ages overlying Sequence 1 and 2. Sequence 4 unconformably overlies all the earlier sequences and comprises a lower TST component displaying characteristic retrogradational stacking patterns and an upper local HST clinoform component showing progradation and downlapping. Inner and middle shelf TST units constrained between Sequence 3 ridges form thick sediment deposits showing a progression from lagoonal and lower fluvial-estuarine deposits, overlain by foreshore and shoreface sands, documenting the changing depositional environments in response to a sea-level transgression. Laterally, in the absence if Sequence 3 ridges, TST sediments comprise only a thin transgressive sand sheet. The upper HST component comprises a prograding shore-attached subaqueous-delta clinoform sediment deposit, the Mkomazi Subaqueous-Delta Clinoform (MSDC) which evolved in four stages. An initialization and progradation stage (Stage 1) (9.5 to 8.4 ka cal. B.P.) was interrupted by retrogradation (Stage 2) and backstepping of the system due to rapid sea-level rise between 8.4 to 8.2 ka cal B.P. Stage 2 backstepping of the clinoform controlled the subsequent overlying topset morphologies resulting in later stages inheriting a stepped appearance upon which shoreface-connected ridges (SCR’s) are developed. Stages 3 (8.2 to 7.5 ka cal. B.P.) and 4 (7.5 to 0 ka cal. B.P) show a change from ‘proximal’ topset aggradation to ‘distal’ foreset progradational downlap, linked to a change in the dominant sedimentary transport mechanism from aggradational alongshore to progradational cross-shore related to variations in accommodation space and the rate of sediment supply. Morphologically the MSDC is characteristic of sediment input onto a high energy storm-dominated continental shelf where oceanographic processes are responsible for its northward directed asymmetry in plan-view, for the lack of a well defined bottomset and for the re-organisation of its topset into very large SCR’s. The SCR’s are 1 - 6 m in height, spaced 500 to >1350 m apart and vary from 3 km to >8 km in length, attached on their shoreward portions to the shoreface between depths of -10 m to -15 m (average at -13 m) and traceable to depths exceeding -50 m, although the majority occur on the inner shelf between -20 m to -30 m. Several individual crests can be identified forming a giant shoreface-connected sand ridge field with a sigmoidal pattern in plan-view postulated to be a surficial expression of the subjacent retrogradational phase (MSDC Stage 2). SCR’s development occurred in two stages. Stage 1 involved deposition of sediment on the shoreface and ridge initiation during the MSDC Stage 2 retrogradational event. Sediment was reworked during sea-level rise generating clinoforms with proximal along-shore aggradation and distal across-shore progradation. This occurred during the last post-glacial sea-level rise from ca. 8.4 ka cal. B.P. SCR Stage 2 represents modern maintenance of the SCR system which is continually modified and maintained by shelf processes and consists of two physical states. State 1 considers SCR maintenance during fair-weather conditions when transverse ridge migration is dominant and driven by the north-easterly flowing counter current shelf circulation. State 2 considers SCR development during storm conditions when longitudinal ridge growth is suggested to occur as a result of storm return flows. Following the storm, the regional coast-parallel current system is restored and the fair-weather state then moulds the SCRs into a transverse bedform. Deposition on the MSDC is ongoing on a continental shelf that is still in a transgressive regime. The exposed seafloor geology comprises late Pleistocene to Holocene aeolianite and beachrock lithologies, deposited as coastal barrier and transgressive shoreface depositional systems. Extensive seafloor sampling was combined with a multi-method geochronological programme, involving the U-series, C14 and optically stimulated luminescence (OSL) to constrain the evolution of the aeolianite and beachrock complex. The Aliwal Shoal Sequence 3 ridge comprises three distinct aeolianite units (A1 to A3) which represent different types of dune morphologies deposited during the climatic and associated sea-level fluctuations of MIS 5. Units A1 and A2 deposited during the MIS 6/5e (~134 to ~127 ka cal. B.P.) transgression represent contemporaneous evolution of a coastal barrier system which consisted of two different dune forms associated with a back-barrier estuarine or lagoonal system. Unit A1 most likely originated as a longitudinal coastal dune whilst Unit A2 comprised a compound parabolic dune system that migrated into the back-barrier area across an estuary mouth/tidal inlet of the back-barrier system. The coastal barrier-dune configuration established by Unit A1 and A2 was most likely re-established during similar subsequent MIS 5 sea-level stands which during MIS 5c/b resulting in the formation of the back-barrier dune system of Unit A3. Palaeoclimatic inferences from Units A1 and A2 aeolianite wind vectors indicate a change from cooler post-glacial climates (lower Unit A1) to warmer interglacial-like conditions more similar to the present (upper Unit A1 and Unit A2). Unit A3 palaeowind vector data show variability interpreted to be related to global MIS 5c climatic instability and fluctuations. For Units A1, A2 and A3 pervasive early meteoric low-magnesium calcite (LMC) cementation followed shortly after deposition protecting the dune cores from erosion during subsequent sea-level fluctuations. Sea-spray induced vadose cementation in Units A1 and A2 may have been a key factor in stabilising dune sediment before later phreatic meteoric cementation. The final preserved Late Pleistocene depositional event in the study area was that of the storm deposit of beachrock Unit B5. Induration followed shortly after deposition by marine vadose high-magnesium calcite (HMC) cementation. Following deposition and lithification, Units A1, A2, A3 and B5 underwent a period of cement erosion associated with decementation and increased porosity due to either 1) groundwater table fluctuations related to the high frequency MIS 5 sea-level fluctuations and/or 2) carbonate solution due to complete subaerial exposure related to the overall MIS 4 - 2 sea-level depression towards the LGM lowstand. In addition to the decementation and porosity development Unit B5 also experienced inversion of the original unstable HMC cement to LMC. During MIS 4 to 2 the Aliwal shelf comprised an interfluve area which was characterised by subaerial exposure, fluvial incision of coast-parallel tributary river systems and general sediment starvation. Beachrock Units B1 to B4 were deposited in the intertidal to back-beach environments and subsequently rapidly cemented by marine phreatic carbonate cements comprising either aragonite or HMC. Unit B1 was most likely deposited at 10.8 ka cal. B.P., B2 at 10.2 ka cal. B.P, B3 at 9.8 ka cal. B.P and B4 <9.8 ka cal. B.P. thereby indicating sequential formation during the meltwater pulse 1b (MWP-1b) interval of the last deglacial sea-level rise. Unit B3 marks the change from a log-spiral bay coastal configuration established by Units B1 and B2 to a linear coastline orientation controlled by the trend of the pre-existing aeolianite units. This change in the morphology of the coastline is also documented by the shape of the underlying transgressive ravinement surface (reflector TRS, Sequence 4) which again was controlled by the subjacent sedimentary basin fill architecture and subsequent transgressive shoreline trajectory (Sequence 4). Sea-level rose at an average rate of 67 cm/100 years from B1 to B2 and 86 cm/100 years from B2 to B2 indicating an acceleration in the rate of sea-level rise supporting enhanced rates of sea-level rise during the MWP-1b interval which also seemed to have altered the coastal configuration and resulted in the closure of the southern outlet of the back-barrier estuarine system. Two cycles of initial aragonite followed by later HMC cement are tentatively linked to two marine flooding events related to different pulses of enhanced rates of sea-level rise during MWP-1b which are considered responsible for significant changes in the marine carbon reservoir ages. Comparisons of the U-series, C14 and optically stimulated luminescence (OSL) methods have shown OSL to be the most reliable method applied to dating submerged aeolianites and beachrocks. OSL not only provides the depositional age of the sediment but also does not suffer from open system behaviour, such as marine reservoir changes and contamination. Acoustic classification of the unconsolidated sediment samples resulted in the demarcation of 3 major acoustic facies, C to E, interpreted with sample analyses as quartzose shelf sand (C), reef-associated bioclastic-rich sand (D) and an unconsolidated lag and debris deposit (E). Grain size distribution patterns of the unconsolidated seafloor sediments indicate that the SCR system delivers fine and medium sand to the inner and middle shelf and imparts a general N-S trending pattern to the gravel and sand fractions. In addition grain size distributions support selective erosion of the seaward flank of the Sandridge with the remobilised sediment deposited in the Basin as low amplitude bedforms over the Facies E lag and debris pavement. The mud fraction is interpreted to be deposited by gravity settling from buoyant mud-rich plumes generated by river discharge. Integration of acoustic mapping, field observations and sample analyses indicate that the present distribution of the unconsolidated sediment is the result of a highly variable distribution of modern and palimpsest sediments which are continually redistributed and reworked by a complex pattern of bottom currents generated by the interaction of opposing oceanographic and swell driven circulation patterns.
Structural evolution and tectonostratigraphy of the Kheis Orogen and its relationship to the south western margin of the Kaapvaal Craton.
(1999) Hilliard, Paul.; McCourt, Stephen.
Alkaline intrusives from the Tugela terrane, Natal metamorphic province.
(1991) Scogings, Andrew John.; Cooper, Mike.; Dunlevey, John N.
Three gneissose alkaline granitoid intrusives at Ngoye, Bulls Run and Wangu are described. They are located within the Nkomo Nappe of the Tugela Terrane, near the northern margin of the Natal Metamorphic Province. The Ngoye Complex comprises alkaline granites, with minor syenite and monzodiorite phases. According to modal am geochemical criteria the Ngoye granites range from peraluminous (muscovite-bearing), through metaluminous (biotite- and/or hornblende-bearing), to peralkaline (riebeckite-, aegirine- and magnetite-bearing). The granites are A-types according to their modal and geochemical characteristics. Rb-Sr isotopic data for the hornblende granites indicate an age of 1063 ± 17 Ma and the initial ratio (R๐ = 0.7025) provides evidence for derivation from a mantle source. Plotting of the Ngoye geochemistry on tectonic-discrimination diagrams suggests intrusion into rifted continental crust. It is concluded that the gneissose Ngoye granites constitute a deformed central complex, similar to anorogenic complexes in Nigeria and the Sudan. The Bulls Run Complex is situated 30 km west of the Ngoye Complex. A concentric outcrop pattern has been mapped, according to which an envelope of silica-saturated biotite-muscovite syenite surrounds a core of nepheline-bearing syenites. Minor intrusive phases include biotite-rich dykes, sovite carbonatite sheets, silica-oversaturated microsyenite dykes and feldspathic ijolite. The outer envelope of muscovite-rich syenite is interpreted as fenitised pelitic country rock. An alkali-lamprophyre origin is suggested for the biotite-rich dykes. Geochemically the syenites are predominantly miaskitic, apart from the microsyenite dykes which are mildly peralkaline. Rb-Sr isotopic data for the nepheline syenites indicate an age of 1138 ± 45 Ma (Ro = 0.70322). Carbonate separates from the carbonatites provide a similar low initial ratio (Ra = 0.70319) which supports a comagmatic mantle origin. A comparison is drawn between the Bulls Run Complex and miaskitic nepheline syenite gneisses in the mid-Proterozoic Grenville Province of canada. From this, it is suggested that the Bulls Run Complex is pretectonic and was intruded into the rifted passive margin of a continent. The Wangu Granite Gneiss is situated 3 km southwest of the Bulls Run Complex. The granites are fine grained and contain aegirine-augite and/or magnetite, and classify as alkali-feldspar granite. Peralkaline chemistry is characteristic of the Wangu granites, with trace-elenent contents indicating a distinct A-type signature. Biotite-rich mafic dykes intrude the southern part of the Wangu outcrop and, on the basis of major- and trace-element signatures, are suggested to be metamorphosed volatile-rich alkaline lamprophyres similar to those at Bulls Run. Geochemical similarities between the Wangu granites and certain comendites from the Kenya Rift are noted. It is suggested that the Wangu granites were emplaced as high-level dykes, within rifted continental crust. It is proposed that the Ngoye, Bulls Run and Wangu intrusives be united as the Nkwaleni Suite. Comparison of the Tugela Terrane with the Grenville Province reveals many similarities, particularly their mid- to late-Proterozoic age and the occurrence of pre-tectonic anorogenic continental magmatism. It is concluded that, unlike the current model which would have the Tugela Terrane as obducted ophiolite, these new data indicate that the Tugela Terrane is a metamorphosed continental rift system.
Geochemistry and structure of the archaean granitoid-supracrustal terrane, southeastern Transvaal and northern Natal.
(1987) Smith, Roric Gerard.; Wilson, Allan H.; Hunter, Donald Raymond.

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