Thesis (MSc)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: The Barremian to Albian siliciclastic deep-water deposits of the central Bredasdorp Basin were investigated primarily in terms of their stratigraphic evolution, depositional characteristics and facies distribution. Cores from the deep-water deposits reveal that the facies successions are composed of massive, ripple cross- to parallel-laminated sandstones, conglomerate, massive claystone, alternating laminated to interbedded sandstone/siltstone and claystone, laminated and clay-rich siltstone. These facies are grouped into channel-fill, sheet-lobe, overbank and basin plain deposits, by inference. The application of sequence stratigraphy, based on gamma ray and resistivity log patterns, reveals that all 3rd-order depositional sequences comprise 4thorder cycles. The latter are subdivided into three components (lowstand, transgressive and highstand systems tracts), based on vertical facies changes and internal stratigraphic key surfaces. Taking the 13Amfs as the stratigraphic datum for each well, correlation was possible on a regional basis. Lowstand deposits, comprising thick amalgamated massive sandstones, were interpreted to represent channelfills. Their vertical and horizontal stacking forms channel-fill complexes above Type 1 unconformities. Adjacent thin-bedded intervals, comprising parallel- to ripple cross-laminated sandstones, were interpreted as levee/overbank deposits, whereas clay-rich intervals were interpreted to represent basin plain deposits of hemipelagic origin. Facies associations and their distribution have revealed that channel-fills are associated with overflow deposits and sheet sand units. These deposits, as well as downdip sheet sands associated with small channel-fills within the 9A, 11A/12A, 13A Sequences and the 14A Sequence were interpreted to have been deposited in a middle fan to upper fan setting. A similar association occurs in the 10A Sequence, except that thick conglomerate units are present at the base of proximal channel-fills. This led to interpret the 10A Sequence as being deposited in a base-of-slope to upper fan setting. The thickness of each sequence, as revealed by isochore maps, shows sinuous axial flow path which corresponds to channel-fill conduit. The continuous decrease of this sinuosity upward in the succession was interpreted as being related to basin floor control along the main sand fairways. Successive flows result in erosion-fill-spill processes, which locally favour connectivity of reservoirs over large areas. Recognition of higher-order sequences and key stratigraphic surfaces helps to understand internal stratigraphic relationships and reveals a complex and dynamic depositional history for 3rd-order sequences. However, sparse well control and uneven distribution of boreholes, as well as lack of seismic and other data, limited the models derived for this study. / AFRIKAANSE OPSOMMING: Die Barremiaanse tot Albiaanse silisiklastiese diepwater afsettings van die sentrale Bredasdorp Kom is hoofsaaklik in terme van stratigrafiese evolusie, afsettingskarakteristieke en fasies distribusie ondersoek. Kerne van die diepwater afsettings toon dat die fasies opeenvolgings uit massiewe, riffelkruis- tot parallel-gelamineerde sandstene, konglomerate, massiewe kleistene, afwisselende gelamineerde tot intergelaagde sandstene/slikstene en kleistene, sowel as gelamineerde en klei-ryke slikstene bestaan. Hierdie fasies word onderverdeel in kanaalopvulsel, plaatlob, oewerwal en komvlakte afsettings. Die toepassing van opeenvolgingsstratigrafie gebaseer op gammastraal en resistiwiteit log patrone toon dat alle 3de-orde afsettingsopeenvolgings uit 4deorde siklusse bestaan. Laasgenoemde word onderverdeel in drie komponente (lae-stand, transgressie en hoë-stand sisteemgedeeltes), gebaseer op vertikale fasies veranderinge en interne stratigrafiese sleutel vlakke. Korrelasie op ‘n regionale basis is moontlik gemaak deur die 13Amfs as die stratigrafiese verwysing vir elke boorgat te neem. Lae-stand afsettings, wat uit dik saamgevoegde massiewe sandstene bestaan, word geïnterpreteer as kanaalopvulsels. Die vertikale en horisontale stapeling van die sandstene vorm kanaalopvulsel komplekse bo Tipe 1 diskordansies. Naasliggende dungelaagde intervalle, wat uit parallel- tot kruisgelaagde sandstene bestaan, word geïnterpreteer as oewerwal afsettings, terwyl klei-ryke intervalle geïnterpreteer word as verteenwoordigend van komvlakte afsettings van hemipelagiese oorsprong. Fasies assosiasies en hul verspreiding toon dat kanaalvul geassosieër word met oorvloei afsettings en plaatsand eenhede. Hierdie afsettings, sowel as distale plaatsande geassosieër met klein kanaalopvulsels binne die 9A, 11A/12A, 13A en die 14A Opeenvolgings, word geïnterpreteer as afgeset in ‘n middelwaaier tot bo-waaier omgewing. ‘n Soortgelyke assosiasie bestaan in die 10A Opeenvolging, behalwe dat dik konglomeraat eenhede teenwoordig is by die basis van proksimale kanaalopvullings. Dit het gelei tot die interpretasie van die 10A Opeenvolging as afgeset in ‘n basis-van-helling tot bo-waaier omgewing. Die dikte van elke opeenvolging, soos verkry vanaf isochoor kaarte, toon ‘n kronkelende aksiale vloeipad wat ooreenkom met ‘n kanaalopvulling toevoerkanaal. Die aaneenlopende afname van hierdie kronkeling na bo in die opeenvolging word geïnterpreteer as verwant aan komvloer-beheer langs die hoof sand roetes. Opeenvolgende vloeie veroorsaak erosie-opvul-oorspoel prosesse, wat lokaal die konnektiwiteit van reservoirs oor groot areas bevoordeel. Herkenning van hoër-orde opeenvolgings en sleutel stratigrafiese vlakke dra by tot ‘n goeie begrip van die interne stratigrafiese verhoudings en ontbloot ‘n komplekse en dinamiese afsettingsgeskiedenis vir 3de-orde opeenvolgings. Beperkte boorgatbeheer en ‘n tekort aan seismiese en ander data het egter ‘n beperkende rol gespeel in die daarstel van modelle vir hierdie studie.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Basin subsidence analysis, employing the backstripping method, indicates that fundamentally two different basin-generating mechanisms controlled Tanqua depocentre development in SW Karoo Basin. The subsidence curves display initial dominantly decelerating subsidence, suggesting an extensional and thermal control possibly in a strikeslip setting during the depocentre formation; on the other hand, subsequent accelerating subsidence with time suggests that the dominant control on the depocentre formation in SW Karoo was flexure of the lithosphere. Based on these observations on the subsidence curves, it is possible to infer that the first stage of positive inflexion (~ 290 Ma) is therefore recognised as the first stage of Tanqua depocentre formation. Petrographic study show that most of the studied sandstones of the Tanqua depocentre at depth of ~ 7.5 Km were subjected to high pressure due to the overlying sediments. They are tightly-packed as a result of grains adjustment made under such pressure which led also to the development of sutured contacts. It is clear the high compaction i.e. grain deformation and pressure solution occurred on the sediments; leading to total intergranular porosity reduction of the quartz-rich sediments and dissolution of the mineral grains at intergranular contacts under non-hydrostatic stress and subsequent re-precipitation in pore spaces. Furthermore, siliciclastic cover in the Tanqua depocentre expanded from minimal values in the early Triassic (Early to Late Anisian) and to a maximum in the middle Permian (Wordian -Roadian); thereby accompanying a global falling trend in eustatic sea-level and favoured by a compressional phase involving a regional shortening due to orogenic thrusting and positive inflexions (denoting foreland basin formation). The estimate of sediment volume obtained in this study for the Permian Period to a maximum in the middle Permian is therefore consistent with published eustatic sea-level and stress regime data. In addition, this new data are consistent with a diachronous cessation of marine incursion and closure of Tanqua depocentre, related to a compressional stress regime in Gondwana interior during the late Palaeozoic. / AFRIKAANSE OPSOMMING: Die ontleding van komversakking met behulp van die terugstropingsmetode bring aan die lig dat die ontwikkeling van die Tankwa-afsettingsentrum in die Suidwes-Karoo-kom hoofsaaklik deur twee verskillende komvormende meganismes bepaal is. Die versakkingskurwes toon aanvanklike, hoofsaaklik verlangsaamde versakking, wat daarop dui dat ekstensie- en termiese beheer gedurende die vorming van die afsettingsentrum plaasgevind het, waarskynlik in strekkingwaartse opset. Aan die ander kant toon daaropvolgende versnellende versakking wat mettertyd plaasgevind het dat die vorming van die afsettingsentrum in die Suidwes-Karoo eerder oorwegend deur kromming van die litosfeer beheer is. Op grond van hierdie waarnemings met betrekking tot die versakkingskurwes, kan mens aflei dat die eerste stadium van positiewe infleksie (~ 290 Ma) dus as die eerste stadium van die vorming van die Tankwa-afsettingsentrum beskou kan word. Petrografiese studie toon dat die meeste van die sandsteen wat van die Tankwaafsettingsentrum bestudeer is, op diepte van ~ 7,5 Km aan hoë druk onderwerp was weens die oorliggende sedimente. Die sandsteen is dig opmekaar as gevolg van die korrelaanpassing wat onder sulke hoë druk plaasvind, wat op sy beurt ook tot die ontwikkeling van kartelnaatkontakte aanleiding gegee het. Dit is duidelik dat die sediment aan hoë verdigting, dit wil sê korrelvervorming en drukoplossing, onderwerp was, wat gelei het tot algehele afname in interkorrelporeusheid by die kwartsryke sedimente; die ontbinding van die mineraalkorrels in interkorrelkontaksones onder niehidrostatiese spanning, en daaropvolgende herpresipitasie in poreuse ruimtes. Voorts het silisiklastiese dekking in die Tankwa-afsettingsentrum toegeneem van minimale waardes in die vroeë Triassiese tydperk (vroeë tot laat Anisiaanse tydperk) tot hoogtepunt in die mid-Permiaanse tydperk (Wordiaans–Roadiaans). Dié ontwikkeling het gepaardgegaan met algemene dalingstendens in die eustatiese seevlak, en is verder aangehelp deur saamdrukkingsfase wat gekenmerk is deur regionale verkorting weens orogeniese druk en positiewe infleksies (wat met voorlandkomvorming saamhang). Die geraamde sedimentvolume wat in hierdie studie vir die Permiaanse tydperk bepaal is, met die hoogtepunt in die middel van dié tydperk, is dus in pas met gepubliseerde data oor die eustatiese seevlak en spanningstoestand. Daarbenewens strook hierdie nuwe data met diachroniese staking van mariene instroming en die afsluiting van die Tankwaafsettingsentrum wat met spanningstoestand in die Gondwana-binneland gedurende die laat Paleosoïkum verband hou.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The close spatial and temporal relationship of shear-zones and magmas is commonly interpreted to indicate positive feedback between magma migration, granitic emplacement and shear-zone-associated deformation. Emplacement geometries and structural fabrics are however rarely preserved, hampering the study of shear-zones and granitic magmas interactions. This study focuses on an area around the Pofadder Shear Zone (PSZ) in Namibia and South Africa as a case study for granitic bodies, mainly as pegmatite sills and dykes, and their spatial and temporal relationships to a crustal-scale shear-zone. The PSZ is a NW-SE trending, dextral, Mesoproterozoic-Neoproterozoic transpressional shear-zone in Namaqualand, interpreted to have accommodated late-stage lateral escape of the Namaqua Metamorphic Complex in response to southward indentation of the Kaapvaal Craton around 1030 – 1080 Ma. In this study it is shown that the shear-core records an asymmetrical strain variation across the PSZ. This is indicated by pervasively banded ultramylonites, mylonites and the significant development of pervasive phyllonites at the southern margin, defining the internal ductile to brittle-ductile fabrics of the shear, during a progressive deformational evolution. Mapping of the PSZ fabrics and associated pegmatites documents how pegmatites are emplaced in structurally distinctive sites within, and adjacent to the PSZ. New U-Pb monazite ages derived from this study, show how pegmatite emplacement has occurred at different times of shear-zone development. The pegmatites are emplaced into earlier ductile to later brittle-retrograde fabrics that accompanied the ca. 45 Ma shear-zone exhumation. Pegmatites concentrated along the northern PSZ-margin are interpreted to be controlled by anisotropies developed axial planar to large km-scale and parasitic folds during the initial, predominately strike-slip stages of shearzone deformation that occurred as early as 1005 ± 5 Ma. Within the PSZ core, pegmatite emplacement is controlled by the syn-kinematic development of (a) subvertical, mylonitic and phyllonitic foliations and (b) fracture permeabilities created by synthetic Riedel shears and dextral dilatant jogs. The most significant pegmatite development around the PSZ is the Skimmelberg Pegmatite Stockwork (SPS) which forms an extensive interconnecting network of concurrent, foliation-parallel sills and thick (> 50 m) discordant dykes within the southern footwall of the PSZ. The dykes intrude as late as 958 ± 5 Ma into feather-shaped N-S extensional fractures (mode I) that developed due to episodic stick-slip at the boundary between the PSZ core and footwall rocks during periods of late-stage transpression. The SPS forms a steeply dipping fracture network that not only creates space needed for emplacement but effectively acts as a conduit for magma transport along the margin of the PSZ. The large extensional fractures of SPS create the necessary hydraulic gradients to tap the magma source of a regional trending pegmatite belt and form a sheeted complex adjacent to the PSZ. Therefore, this study documents how, during the progressive exhumation of a largescale transcurrent shear-zone, magma emplacement is not only concentrated within the highly permeable, high-strain domains (cores) of shear-zones but may be concentrated in diachronous, structurally controlled sites along the shear-zone margins. / AFRIKAANSE OPSOMMING: Die noue ruimte-tydsverband tussen skuifskeure en magmas word algemeen geïnterpreteer as ‘n aanduiding van positiewe terugkoppeling tussen magma migrasie, graniet-inplasing en skuifskeurgeassosieerde vervorming. Geometrie en struktuurmaaksels van inplasings word egter selde bewaar en belemmer die studie van interaksies tussen skuifskeure en graniet-magmas. Die studie fokus op ‘n area rondom die Pofadder Skuifskeur (PSS) in Namibië en Suid-Afrika as ‘n gevallestudie vir graniet-liggame, hoofsaaklik as pegmatiet plate en gange, asook voorafgenoemde se ruimte-tydsverband met ‘n grootskaalse skuifskeur. Die PSS is ‘n NW-SO-waarts strekkende, regs-laterale, Mesoproterosoïse-Neoproterosoïse transpressieskuifskeur in Namakwaland, wat geïnterpreteer word om die latere-stadium laterale ontsnapping van die Namakwa Metamorfiese Kompleks te akkomodeer in reaksie op die suidwaartse indrukking van die Kaapvaal Kraton omstreeks 1030-1080 Ma. In hierdie studie word getoon dat asimmetriese vervormingsvariasie deur die skuifskeurkern aangeteken word. Hierdie word aangetoon deur gebande ultramilioniete, milioniete en die noemenswaardige ontwikkeling van filoniete wat die suidelike rand deurtrek en definiëer die interne plastiese- tot bros-plastiese maaksels van die skuifskeur gedurende ‘n progressiewe vervormingsevolusie. Kartering van die PSS maaksels en geassosieerde pegmatiete dokumenteer hoe pegmatiete, aangrensend en binne die PSS, in eiesoortige strukturele terreine binnedring. Nuwe U-Pb monasiet ouderdomme, afgelei vanuit hierdie studie, toon aan hoe inplasing plaasgevind het gedurende verskillende tye van skuifskeurontwikkeling. Pegmatiete het vroeëre plastiesetot latere bros-retrogressiewe maaksels binnegedring wat die herontbloting van die ca. 45 Ma skuifskeur meegaan. Pegmatiete, gekonsentreerd langs die noordelike rand van die PSS, word geïnterpreteer as beheer deur anisotrope wat parallel aan die asvlak van groot km-skaalse en ondergeskikte plooie ontwikkel gedurende die aanvanklike, hoofsaaklik strekkingwaarste, stadiums van skuifskeurontwikkeling wat so vroeg as 1005 ±5 Ma plaasgevind het. Binne die kern van die PSS word die inplasing van pegmatiete beheer deur die sinkenimatiese ontwikkeling van (a) subvertikale, milionitiese- en filonitiese foliasies en (b) breukdeurdringbaarheid wat gevorm is deur sintetiese riedelskuifskeure en regslaterale uitsettende “jogs”. Die mees noemenswaardige pegmatiet ontwikkeling rondom die PSS is die Skimmelberg Pegmatiet Stokwerk (SPS) wat ‘n intensiewe netwerk vorm van intergekonnekteerde konkurrente plate, parallel aan die foliasie, en dik (>50m) diskordante gange binne die suidelike vloer van die PSS. Die gange dring in so laat as 958 ± 5 Ma binne-in veervormige N-S uitbreidende breuke (modus1) wat ontwikkel het as gevolg van die episodiese hak-en-glip op die grens tussen die PSS kern- en vloergesteentes gedurende periodes van laat-stadium transpressie. Die SPS vorm ‘n styl hellende breuk-netwerk wat nie net spasie maak vir indringing nie, maar dien ook effektief as ‘n geleidingsweg vir die vervoer van magma langs die rand van die PSS. Die groot uitbreidende breuke van die SPS skep die nodige hidroliese gradiënt om die magma bron van ‘n regionale pegmatiet gordel te tap en vorm ‘n bladvormige kompleks aangrensend tot die PSS. Gevolglik dokumenteer die studie hoe, gedurende die progressiewe ontbloting van ‘n grootskaalse torsieskuifskeur, magma inplasing nie net gekonsentreer is binne die hoogs deurdringbare, hoogsvervormde areas (kerne) van skuifskeure nie, maar ook hoe magma kan konsentreer in diachroniese, struktuur beheerde gebiede teen die rande van skuifskeure.