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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50454 |
| Date | 12 1900 |
| Creators | Van der Merwe, Willem C |
| Contributors | De V. Wickens, H., Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 202 p. : ill. |
| Rights | Stellenbosch University |
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