Piroklastiese afsettings van perm-ouderdom in die Hoof-Karookom met spesiale verwysing na die Collingham Formasie, Ecca Groep
| dc.contributor.advisor | Verwoerd, W. J. | en_ZA |
| dc.contributor.author | Viljoen, J. H. A | |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. | |
| dc.date.accessioned | 2012-08-27T11:39:06Z | |
| dc.date.available | 2012-08-27T11:39:06Z | |
| dc.date.issued | 1995 | |
| dc.description | Proefskrif (Ph. D) -- Universiteit van Stellenbosch, 1995. | |
| dc.description.abstract | ENGLISH ABSTRACT: This study comprises a geological and geochemical investigation of the K-bentonites (potassium-rich, illitic clay beds interpreted as altered volcanic ash) of Permian age in the Karoo Supergroup of the Main Karoo Basin. It also includes a sedimentological and stratigraphical study of the Collingham Formation (Ecca Group), which is the unit with the h.ighest concentration of K-bentonite layers. The 30 co 70 m thick Collingham Formation is conformably underlain by the white-weathering, carbonaceous Whitehill Formation and is overlain by the Ripon Formation in the southeast, the Vischkuil Formation in the southwest and the Tierberg Formation in the west and northwest. The formation consists essentially of alternating thin beds of hard, dark grey, siliceous mudrock and very thin beds of relatively softer yellow weathering K-bentonite beds. These sediments are sporadically interrupted by chert beds, and in the upper part of the formation by siltstone and very fine-grained sandstone beds. In the southern and southwestern part of its outcrop area the formation can be divided into three members, namely the Zoute KJoof, Buffels River and Wilgehout River. The basal two members are separated by the Matjiesfontein Chert Bed. Deposition of the Collingham Formation occurred as basin floor muds which settled out of suspension from under and upper flows and as pelagic and hemipelagic material. These deposits were sporadically interrupted by short-lived volcanic ash-falls. The upper part of the formation in the west consists of basin floor and outer fan deposits of a submarine fan. K-bentonite layers are distributed throughout the Karoo Basin, ranging stratigraphcally from the Dwyka Group through the Ecca Group up to and including the basal Beaufort Group. Three zones of relatively higher concentrations of K-bentonite occur, namely in the Prince Albert, Collingham and Abrahamskraal Formations. By using the K-bentonites as marker beds it was confirmed that the Dwyka/Prince Albert contact is younging southwards, that the Whitehill Formation is correlatable with the upper part of the Vryheid Formation and that the Wilgehout River Member is older that the Ripon Formation. Transport of the volcanic ash was from the south and southwest as aerially transported tephra originating from terrestrial Plinian eruptions. The K-bentonite consists mainly of illite, feldspar and quartz (except where it is silicified or enriched in iron oxides and/or carbonates). The maximum opserved grain size of the largest feldspar and quartz grains is 0.5 mm. Diageneticstructures indicate that a large percentage of the minerals that are recognised are diagenetic of origin. The diagenesis and very low grade metamorphism which the K-bentonite has undergone can be represented by the following reactions: Siliceous volcanic ash + H₂0 -> montmorillonite + silica (opal-A) + ions in solution -> montmorillonite + zeolite + silica (opal - CT) -> mixed-layer montmorillonite/illite + zeolite + silica (chert) - > illite + albite + quartz. Chemically the K-bentonite is depleted in Si0₂ and enriched in Al₂ (20-30%} and O (5-10%) in comparison with normal mudstones. Most of the movement of the components occurcd during the first phase i.e. when the volcanic glass was altered to montroorillonite. Only the following analysed components were apparently to a large extent immobile; A1₂0₃, Ti0₂, Zr, Nb, Y and Ga. The geochemistry indicates that the K-bentonites and silicified K-bentonites were originally acid (felsic) volcanic ash. The K-bentonite beds in the lower half of the Collingham Formation as well as the older ones show a within-plate granite geochemical signature, whereas the younger ones correspond better to a volcanic-arc granite association. All the K-bentonites seem to originate from a magma which was generated by the melting of crust that had already undergone a cycle of subduction-zone or continent-continent collision magmatism. The dacitic to rhyolitic volcanism was probably related to the broad Permian magmatic belt which at present crops out in southern South America and/or its eastward extension. This magmatism can probably be linked to tension and graben formation in Patagonia and was followed by southward-directed, and later northward directed subduction-related magmatism to the south of the African Plate. A counter-clockwise rotation of Patagonia can probably explain the tension in the west and the compression in the east to form the Cape Fold Belt. Although still tentative, the possiblity exists that the three K-bentonite-rich zones in the Karoo Supergroup can be correlated with the deformation events of the Cape Fold Belt. A preliminary single zircon age of 262 ± 4 Ma was obtained by R. Armstrong for the basal part of the Collingham Formation. Due to their mineralogical composition (illite instead of montmorillonite) the K-bentonites no longer possess the physical properties necessary for use as an industrial material (eg. drilling mud). There is, however, the possibility that the K-bentonites could be exploited as a source for potassium and aluminium, but at present this is not economically viable. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Hierdie studie omvat 'n geologiese en geochemiese ondersoek van die K-bentoniete (kaliumryke, illitiese kleilae wat as veranderde vulkaniese aslagies beskou word) van Perm-ouderdom in die Karoo Supergroep van die Hoof-Karookom. Dit behels ook 'n sedimentologiese en stratigrafiese ondersoek van die Collingham Formasie (Ecca Groep) wat die eenheid is met die hoogste konsentrasie K-bentonietlae. Die 30 tot 70 i:n dik Collingham Formasie word konkordant deur die witverwerende, koolstofryke Whitehill Formasie onderle en deur die Ripon Formasie in die suidooste, die Vischkuil Formasie in die suidweste en die Tierberg Formasie in die weste en noordweste oorle. Die formasie bestaan hoofsaaklik uit afwisselende dun lae harde, donkergrys, silikahoudende modderklip en baie dun relatief sagter geelverwerende K bentonietlagies. Hierdie opeenvolging word sporadies onderbreek deur chertlae, en in die boonste gedeelte van die formasie deur sliksteen en baie fynkorrelrige sandsteenlae. Ysterryke moddersteen en fosfatiese kleisteen kom ook sporadies voor. Die formasie kan in die suidelike en suidwestelike gedeelte van sy dagsoomgebied in drie lede onderverdeel word naamlik die Zoute Kloof, Buffelsrivier en Wilgehoutrivier. Die basale twee lede word geskei deur die Matjiesfonteinchert Laag. Afsetting van die Collingham Formasie het plaasgevind as komvloermodders wat uit suspensie uitgesak het van onder- en bovloeie en as pelagiese en hemipelagiese materiaal. Hierdie afsettings is periodiek onderbreek deur kortstondige vulkaniese asvalle. Die boonste gedeelte van die formasie bestaan in die weste uit komvloer- en buitewaaier-afsettings van 'n fynkorrelrige onderwaterwaaier. K-bentonietlagies kom verspreid oor die hele Karookom voor, stratigrafies vanaf die Dwyka Groep regdeur die Ecca Groep tot en met die basale Beaufort Groep. Drie sones wat relatief hoer konsentrasies K bentoniet bevat is teenwoordig, naamlik in die Prins Albert, Collingham en Abrahamskraal Formasies. Deur die K-bentoniete te gebruik as merkerlae is bevestiging verkry dat die Dwyka/Prins Albert-kontak suidwaarts jonger word, dat die Whitehill Formasie met die boonste gedeelte van die Vryheid Formasie gekorreleer kan word en dat die Wilgeboutrivier Lid ouer is as die Ripon Formasie. Aanvoer van die vulkaniese as was vanuit die suide en suidweste as lugvervoerde tefra afkomstig van oplandige Pliniese erupsies. Die K-bentoniet bestaan hoofsaaklik uit illiet, veldspaat en kwarts (buiten waar dit gesilisifiseer of verryk is aan ysteroksiede en/of karbonate). Die maksimum waargenome korrelgrootte vir die grootste veldspaat- en kwartskorrels is 0,5 mm. Diagenetiese teksture dui daarop dat 'n groot persentasie van die minerale wat tans waarneembaar is diageneties van oorsprong is. Die diagenese en baie laegraadse metamorfose wat die K bentoniet ondergaan het kan deur die volgende reaksies weergegee word: Silikaryke vulkaniese as + H₂0 -> montmoriJloniet + silika (opaal-A) + ione in oplossing-> montmorilloniet + zeoliet + silika (opaal-CT) -> montmorilloniet/illiet menglaagklei + zeoliet + silika (chert) -> illiet + albiet + kwarts. Cbemies is die K-benloniet verarm aan SiO₂ en verryk in Al₂O₃ (20-30%) en KP (5-10%) in vergelyking met normale moddcrstenc. Die mccste beweging van komponente bet gedurende die eerste stadium van diagenese plaasgevind, dit wil se gedurende die verandering van vulkaniese glas na montmorilloniet. Dit is slegs die volgende geanaliseerde komponenlc wat skynbaar tot 'n groot mate immobiel gebly het: Al₂O₃, TiO2i Zr, Nb, Y en Ga. Die geochemie dui daarop dat die K-bentoniet en gesilisifiseerde K-bentoniet oorspronklik suu.r (felsiese) vulkaniese as was. Die K-bentonietlagies in die onderste helfte van die Collingham Formasie en die wat ouer is vertoon geochemies 'n inlraplaatgraniet-verwantskap terwyl die wat jonger is meer 'n vulkaniese eilandbooggraniet-neiging toon. Al die K-bentoniete skyn afkomstig te wees van 'n magma wat gevorm bet deur die smelting van kors wat reeds deur 'n siklus van subduksie- of kontinent kontinent-botsingsmagmatisme was. Die dasitiese tot riolitiese vulkane was waarskynlik verwant aan die bree magmatiese gordel van Perm ouderdom wat tans in suidelike Suid-Amerika dagsoom, en/ of sy ooswaartse voortsetting. Hierdie magmatisme kan waarskynlik gekoppel word aan tensie en graben-vorming in Patagonie gevolg deur suidwaarts- en nog later noordwaartsgerigte subduksie-verwante magmatisme ten suide van die Afrilcaplaat. 'n Linksomdraaiing van Patagonie kan moontlik die tensie in die weste en die kompressie tydens dievormiog van die Kaapse Plooigordel in die ooste verklaar. Hoewel baie tentatief bestaan die moontli.kheid dat diedrie K-bentonietryke sones in die Karoo Supergroep met die vervormingsfases van die Kaapse Plooigordel gekorreleer kan word. 'n Voorlopige enkelsirkoon-ouderdom van 262 :!: 4 mj is vir die basale gedeelce van die Collingham Formasie deur R. Armstrong verkry. As gevolg van sy mineralogiese samestelling (illiet i.p.v. montmorilloniet) besit die K-bentoniel nie meer die gewensLe fisiese eienskappe vir gebruik as indusLriele maleriaal (bv. boormodder) nie. Daar bescaan egter 'n moontlikheid dal die K-bentoniet as 'n bron van kalium en aluminium benut kan word, maar dit is tans nie ekonomies rue. | af_ZA |
| dc.format.extent | 299 pages : illustrations, maps | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/58705 | |
| dc.language.iso | af_ZA | |
| dc.publisher | Stellenbosch : Stellenbosch University | |
| dc.rights.holder | Stellenbosch University | |
| dc.subject | Bentonite -- South Africa -- Karoo | en_ZA |
| dc.subject | Sedimentology | en_ZA |
| dc.subject | Geology, Stratigraphic | en_ZA |
| dc.subject | Dissertations -- Geology | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | Piroklastiese afsettings van perm-ouderdom in die Hoof-Karookom met spesiale verwysing na die Collingham Formasie, Ecca Groep | af_ZA |
| dc.type | Thesis |
Files
Original bundle
1 - 1 of 1
Loading...
- Name:
- viljoen_prioklastiese_1995.pdf
- Size:
- 66.81 MB
- Format:
- Adobe Portable Document Format
- Description:
- Download thesis