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Call number: LD2668 .T4 1986 C52 / Master of Science / Geology

published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy

M.Sc. (Geology) / Please refer to full text to view abstract

Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Foreland basins commonly fill with sediment derived from the adjacent fold/thrust belt, providing a relatively simple source-to-basin configuration. However, that is not true for the early southwestern Karoo Basin, since the composition of the Ecca Group sedimentary rocks do not match the composition of the adjacent fold/thrust belt. The southwestern Karoo Basin is bordered to the west and south by the Cape Fold Belt (CFB) and provides the opportunity to study the linkage between its early structural evolution and deposition in the two spatially and temporally distinct Tanqua and Laingsburg depocentres. The CFB was formed when the early Palaeozoic passive continental margin, which formed a large section of the southern edge of Gondwana, evolved into an active convergent margin during the late Palaeozoic. Orogenesis resulted in a northwest-trending Cedarberg branch and an eastwest-trending Swartberg branch. The oroclinal bend between the two branches includes large-scale northeast-trending syntaxis structures, such as the Hex River and Baviaanshoek anticlinoria, which influenced the sedimentation path into the basin. Spectral gamma ray (SGR), mineralogical and geochemical studies of exposed rocks from the Tanqua and Laingsburg depocentres indicate a near uniform provenance for both, dominated by granitic and metamorphic material derived from a provenance seemingly far beyond the CFB. SGR data, combined with lithology, show that regional stratigraphic correlation is possible in the Skoorsteenberg, Kookfontein and Waterford Formations in the Tanqua depocentre. The same is true for the Laingsburg and Fort Brown Formations in the Laingsburg depocentre. There are no major changes in the SGR data set between the successive sandstone or shale units that could imply different origin, and no distinct signals in the SGR pattern of the shale intervals that could potentially correspond to maximum flooding surfaces. The Tanqua and Laingsburg depocentre sandstones are very fine- to lower mediumgrained, tightly packed, poorly to well sorted, and have undergone mechanical compaction and pressure solution. The mineralogical composition and texture of these sandstones suggest that they have undergone high-grade diagenesis to low-grade regional burial metamorphism to the lower greenschist facies (250 ± 50ºC; ~2 kbars). They are mineralogically and geochemically classified as lithic arenites and greywackes, and the Tanqua depocentre sandstones are slightly more mature than the Laingsburg depocentresandstones. REE patterns for the Tanqua and Laingsburg depocentre sandstones are similar, suggesting that both form part of the same evolutionary pattern and that the sediments have one common origin, i.e. a provenance predominantly composed of granitic material. Homogenous εNd-values for all sandstone samples of around –5 at the time of deposition indicate that there is little or no variation in provenance between the Tanqua and Laingsburg depocentre sediments. TCHUR model ages of 0.70 to 0.95 Ga, and TDM model ages of 1.19 to 1.49 Ga, resulted from a mixture of Archaean and Proterozoic material in unknown proportions. The most likely source terrane is thought to be the North Patagonian Massif. The latter show Nd isotopic compositions corresponding to an average εNd-value of -5 at 265 Ma. / AFRIKAANSE OPSOMMING: Voorlandkomme word oor die algemeen gevul met sediment afkomstig van die aanliggende plooigordel, wat lei tot ‘n redelik eenvoudige brongebied-tot-afsettingskom konfigurasie. Dit is egter nie van toepassing vir die vroeë suidwestelike Karookom nie, aangesien die samestelling van die Ecca Groep sedimentêre gesteentes nie ooreenstem met die samestelling van die aanliggende plooigordel nie. Die suidwestelike Karookom word aan die weste en suide begrens deur die Kaapse Plooigordel en bied die geleentheid om die verwantskap tussen die vroeë strukturele evolusie en afsetting in die twee ruimtelik en temporeel afsonderlike Tankwa en Laingsburg subkomme te bestudeer. Die Kaapse Plooigordel het gevorm toe die vroeë Palaeosoïkum kontinentale grens, wat ‘n groot deel van die suidelike grens van Gondwana was, ontwikkel het tot ‘n aktiewe konvergerende grens gedurende die laat Palaeosoïkum. Orogenese het gelei tot die vorming van ‘n noordwes-strekkende Sederberg tak en ‘n ooswes-strekkende Swartberg tak. Die oroklinale buig tussen die twee takke sluit grootskaalse noordoosstrekkende sintaksis strukture in, soos die Hex Rivier en Baviaanshoek antiklinoria, wat die sedimentasie rigtings na die kom beïnvloed het. Spektrale gammastraal (SGR), mineralogiese en geochemiese studies op die dagsome van die Tankwa en Laingsburg subkomme dui ‘n byna identiese brongebied aan vir beide, oorheers deur granitiese en metamorfe materiaal vanaf ‘n brongebied oënskynlik vêr vanaf die Kaapse Plooigordel. SGR data, gekombineer met litologie, dui aan dat dit moontlik is om regionale stratigrafiese korrelasies in the Skoorsteenberg, Kookfontein en Waterford Formasies in die Tankwa subkom te maak. Dieselfde geld vir die Laingsburg en Fort Brown Formasies in die Laingsburg subkom. Daar is geen groot veranderinge, wat ‘n verskil in oorsprong kan aandui, in the SGR datastel tussen die opeenvolgende sandsteen of skalie eenhede nie, en ook geenuitstaande tekens in the SGR patroon van die skalie-intervalle wat moontlik kan ooreenstem met ‘n maksimum vloedingsvlak nie. Die Tankwa en Laingsburg subkom sandsteenlae is baie fyn- tot laervlak mediumkorrelrig, dig gekompakteer, swak tot goed gesorteer, en het meganiese kompaksie en drukoplossing ondergaan. Die mineralogiese samestelling en tekstuur van hierdie sandsteenlae dui daarop dat hulle hoë-graadse diagenese tot lae-graadse regionale begrawingsmetamorfose tot laervlak groenskis fasies (250 ± 50ºC; ~2 kbars) ondergaan het. Hulle word mineralogies en geochemies geklassifiseer as litiese areniete en grouwakke. Die Tankwa subkom sandsteenlae is effens meer volwasse as die Laingsburg subkom sandsteenlae. Die lantanietgroep patroon vir die Tanqua en Laingsburg sandsteenlae is eenders, wat aandui dat beide deel gevorm het van dieselfde evolusionêre ontwikkeling en dat die sedimente een gesamentlike oorsprong gehad het, naamlik ‘n brongebied bestaande hoofsaaklik uit granitiese materiaal. Homogene εNd-waardes van ongeveer –5 by tye van afsetting vir al die sandsteen monsters dui daarop dat daar min of geen verandering in brongebied vir die Tankwa en Laingsburg subkom sedimente was nie. TCHUR model ouderdomme van 0.70 tot 0.95 Ga, en TDM model ouderdomme van 1.19 tot 1.49 Ga, is afkomstig van ‘n mengsel van Argeïese en Proterosoïese materiaal in onbekende hoeveelhede. Die mees waarskynlike brongebied is die Noord Patagoniese Gebergtes. Dit wys Nd isotopiese samestellings wat ooreenstem met ‘n gemiddelde εNd-waarde van –5 by 265 Ma.

Thesis (MSc)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: Fan System 5 forms the uppermost submarine fan system of the Permian-age Tanqua Fan Complex (Ecca Group) of the southwestern Karoo Basin. It is the most widespread system and represents the final phase of fan deposition in the Tanqua sub-basin. Depositional characteristics differ markedly from the rest of the fan systems, mainly because it lacks sedimentary features indicative of a single point source basin floor fan. The entire system consists of six different stages of fan growth and development in the lower slope settings. A hypothetical model was composed for Fan System 5 to understand the spatial/temporal distribution of reservoir and seal facies in slope turbidite settings. The facies vary from massive amalgamated sandstone beds to thin-bedded, ripple cross-laminated sand and siltstone beds. A thick shale unit identified as a regional marker layer overlies Fan System 5. lts base is defined by the presence of a regionally developed 20 cm thick hemipelagic shale unit. Six sand-rich units with channel-complexes are present in the Klein Hangklip, Groot Hangklip, Kalkgat, Tongberg, Skoorsteenberg and Blauwkop localities. The facies characteristics in the southernmost outcrops of Fan System 5 (Groot Hangklip, Tongberg and Kalkgat) reflect deposition in a lower slope setting where local structural control seems to have played a major role in the distribution and regional development of channel-fill and overbank depositional elements. The channel-fills are arranged in vertical to off-set stacking patterns and are comprised of massive, amalgamated [me to very fine-grained sandstone units up to 30 m in thickness. They are separated by thinner sandstone/siltstone units of varying thickness. The channelization displayed by the more proximal outcrops are interpreted to represent an upper fan, deposited in a lower- to mid-slope setting. In contrast to the channel-fill deposits at Skoorsteenberg, Klein Hangklip and Groot Hangklip, ripple cross-laminated overbank deposits, associated with smaller channel-fill units, predominate in the northeastern and eastern parts of the outcrop area. Massive- and thinbedded frontal sheet sandstones constitute the down-dip extensions to the most northern outcrops of Fan System 5. Highly erosive, stacked base-of-slope channel complexes, seemingly controlled by subtle early structural features, were able to construct significant thicknesses of regionally well-developed overbank deposits, marginal to the channel complexes. These facies changes occur over relatively short distances, which hold significant implications for the prediction of and the heterogeneity of reservoir facies in slope settings. Gradients are much steeper in the lower slope to mid-slope area than on the proximal basin floor. The occurrence of soft-sediment deformation in the overbank and upper parts of the channel-fill deposits supports a slope origin. Weakly developed wave-ripple marks in the uppermost layers of Fan System 5 further indicate that water depths approached wave base prior to deposition of the upper markerbed shales. Paleotransport for Fan System 5 was towards the north, northeast and east. The palaeocurrent directions of the channel-fill complexes in Klein- and Groot Hangklip seem to roughly correspond to the structural trend of synclinal depressions in this area. However, the effect and influences of basin floor topography and structural features on deposition were determined to be minimal on the regional development and local facies control of the fan. / AFRIKAANSE OPSOMMING: Waaiersisteem 5 vorm die laaste submarine waaiersisteem van die Perm-ouderdom Tankwa Waaierkompleks (Ecca Groep) in die suidwestelike Karoo-kom. Dit vorm die mees wydverspreide sisteem en verteenwoordig ook die fmale fase van waaierafsetting in die Tankwa sub-kom. Afsettingseienskappe verskil aansienlik van die onderliggende waaiersisteme, omdat kenmerkende sedimentêre eienskappe van 'n enkele toevoer bron ontbreek. Die hele sisteem bestaan uit ses verskillende periodes van waaiergroei en ontwikkeling in die laer kornhelling omgewmgs. 'n Voorspellingsmodel is opgestel vir Waaiersisteem 5 om die ruimtelike/temporele verspreiding van die reservoir en seël fasies in kornhelling turbidiet omgewings te kan verstaan. Hierdie fasies varieer van massiewe, geamalgameerde sandsteen tot dun gelaagde riffel- lamineerde sand- en sliksteenlae. 'n Dik regionale skalie eenheid oorlê Waaiersisteem 5 en vorm die boonste merkerlaag. Die basis word onderlê deur 'n 20 cm dik regionaalontwikkelde hemipelagiese skalie laag wat die onderste merkerlaag vorm. Ses sandige eenhede met geassosieerde kanaalkomplekse is onderskeidelik teenwoordig in: Klein Hangklip, Groot Hangklip, Kalkgat, Tongberg, Skoorsteenberg en Blauwkop omgewings. Die fasies-eienskappe van die mees suidelike dagsome van Waaiersisteem 5 (Tongberg, Groot Hangklip en Kalkgat) toon afsetting in 'n laer kornhelling omgewing, waar plaaslike tektoniese effekte moontlik 'n groot rol gespeel het in die verspreiding en regionale ontwikkeling van die kanaalvulsels en geassosieerde oewerwal-afsettings. Die gestapelde, wegstand kanaalvulsels-afsettings bestaan uit massiewe, geamalgameerde fyn tot baie fynkorrelrige sandsteen eenhede, wat diktes tot ongeveer 30 m kan bereik. Dit word van mekaar geskei deur dun sandsteenlsliksteen eenhede van afwisselende diktes. Die kanaal komplekse in die mees proksimale dagsome word interpreteer as 'n bo-waaier, wat afgeset is in 'n laer- tot middel kornhelling omgewmg. In teenstelling met die kanaalvulsels in die Skoorsteenberg, Klein Hangklip en Groot Hangklip omgewings, domineer riffel kruisgelamineerde oewerwal-afsettings, geassoseer met klein kanaalvulsels, die noordoostelike en oostelike dagsome van Waaiersisteem 5. Massiewe en dungelaagde frontale plaat sandstene, kom voor in die distale helling-omgewings in die mees noordelike dagsome van Waaiersisteem 5. Hoogs eroderende, gestapelde kanaalkomplekse, aan die basis van die komhelling wat moontlik beheer is deur vroeë komvloer topografie, was die oorsaak vir regionaal goed-ontwikkelde oewerwalafsettings. Hierdie fasies-verandering vind plaas oor 'n baie kort afstand wat betekenisvolle gevolge inhou vir die voorspelling van heterogeniteit van petroleum reservoir fasies in komhelling afsetting-omgewings. Die gradiënt vir die laer komhelling tot mid-komhelling omgewings is baie steiler as die distale komvloer omgewings. Die voorkoms van sagte-sediment deformasies in die oewerwal en boliggende dele van die kanaalvulsels weerspeël 'n moontlike komhelling omgewing. Swakontwikkelde golfriffelmerke in die boonste lae van Waaiersisteem 5 dui 'n waterdiepte aan wat nabyaan golf-basis is, voordat dit deur diepmariene skalies oorlê word. Paleovloeirigtings vir Waaiersisteem 5 was in 'n noord, noordoostelike en oostelike rigting. Die paleovloeirigting vir die Klein- en Groot Hangklip kanaalkomplekse stem min of meer ooreen met die strukturele grein van die sinklinale laagtes in die omgewing. Die effek en beheer van komvloer topografie en ander strukturele faktore op afsetting was minimaalop die regionale ontwikkeling en plaaslike fasies verspreiding van die waaier.

The Permo-Carboniferous Dwyka Group and Vryheid Formation of the Karoo. Sequence in the Highveld Coalfield are analysed to determine the depositional systems operative during sedimentation. The investigation involves the processing of "629" borehole cores and logs in an area of 860km2.[Abbreviated Abstract. Open document to view full version] / AC2017

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