Thesis (MSc)--Stellenbosch University, 1989. / ENGLISH ABSTRACT: The Ceres Syntaxis comprises that part of the Cape Fold Belt
Syntaxis that lies north of the Worcester Fault. Most of the
area consists of folded Cape Supergroup (primarily Witteberg
Group) rocks. Fold styles of all fold trends are essentially
the same. However, different multilayer rheologies led to the
development of either sinusoidal or kink-like fold geometries
in different parts of the cover sequence. The character of
Witteberg sediments led to the development of large megakink
folds and peculiar fold zones in this part of the sequence.
Fold trends in the Ceres Syntaxis vary between NW-SE, NE-SW
and E-W. The southern part of the area is dominated by the
NE-SW trend, with the NW-SE trend being only important in the
west. Interference between these two trends only exists in
the Witteberg Group, where it occurs as crossing linear fold
zones and conjugate, intersecting kink folds . Cross-folding
relationships in the north-eastern part of the Ceres Syntaxis
indicate that the area had been affected by two
contemporaneous, orthogonally opposed compressions that worked
simultaneously in different parts of the multilayer.
Differences in the magnitude of strain, or in the local timing
of fold initiation, produced local refolding or transecting
relationships. The microfabric of Witteberg sandstones
suggests deformation under conditions of low temperature and
pressure, as well as low strain rates. Some microfabrics also
indicate that substantial buckle shortening occurred while the
Middle and Upper Witteberg beds were still unlithified.
Isotopic dating of Cedarberg shale from both main trends did
not yield unequivocal results, mainly due to the
deformatio~al intensity. The positioning of the Cape
low
Fold
Belt Syntaxis was strongly influenced by basement tectonic
grain and basin floor relief. The NW and NE fold trends
formed on a heterogeneous basement that resolved the
stress configuration into components which
external .
acted
simultaneously towards the north-west and north-east. Ecca
and Beaufort Group sedimentation patterns in the western Karoo
corroborate the above findings. / AFRIKAANSE OPSOMMING: Die Ceres-sintaks beslaan daardie deel van die sintaks van die
Kaapse Plooigordel wat noord van die Worcesterverskuiwing Ie.
Die gebied bestaan grotendeels uit geplooide gesteentes van
die Supergroep Kaap (hoofsaaklik Groep Witteberg). AIle
plooirigtings openbaar dieselfde plooistyl. Reologiese
verskille in'die rnultilaehet egter gelei tot die ontwikkeling
van of sinusoidale ~f knikvorrnigeplooie in verskillende dele
van die dekgesteentes. Die Wittebergsedirnente se aard het
veroorsaak dat rnegaknikkeen eienaardige plooisones in hierdie
deel van die opeenvolging ontstaan het. Plooirigtings in die
Ceres-sintaks wissel tussen NW-SO, NO-SW en O-W. Die NO-SW
plooirigting oorheers in die suidelike deel van die gebied,
terwyl die NW-SO plooirigting eintlik net in. die weste
belangrik is. Interferensie van hierdie twee.hoofrigtings korn
slegs voor in die Groep Witteberg, waar dit as dwarssnydende
lineere plooisones en snydende, konjugerende knikke aanwesig
is. Onderlinge verhoudings tussen kruisplooie in die
noordoostelike Ceres-sintaks, toon dat die gebied beinvloed is
deur twee gelyktydige drukspannings wat reghoekig op rnekaar
ingewerk het, sorntyds in effens verskillende dele van die
rnultilaag.Verskille in die spanningsbedrag en tydsberekening
het lokale herplooiing of dwarssnydende strukture veroorsaak.
Die mikrornaaksel van die Wittebergsandsteen toon dat die
vervorming onder lae temperatuur- en druktoestande, tesame met
'n lae vervorrningsternpo, plaasgevind het. Die rnaaksel toon
ook aan dat heelwat buigplooiing plaasgevind het terwyl die
Middel- en Bo-Witteberglae nog ongekonsolideer was. Isotopiese
datering van Sederbergskalie afkornstigvan die twee hoofplooirigtings,
het weens die lae vervormingsintensiteit swak
resultate gelewer. Die posisie van die sintaks van die Kaapse
Plooigordel, insluitende die van die Ceres-sintaks, is sterk'
belnvioed deur die tektoniese grein en re~i~f van die
vloergesteentes. Die heterogene vloer waarop die NW en NO
plooie gevorrn het, het daartoe gelei dat die eksterne
spanningsopset verdeel is in kornponentewat gelyktydig na die
noordweste en noordooste gewerk het. Sedirnentasiepatrone in
die Groepe Ecca en Beaufort ondersteun bostaande afleidings.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/67079 |
| Date | 12 1900 |
| Creators | De Beer, C. H |
| Contributors | Hälbich, I. W., 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 | 124 p., [27] p. of plates : ill. |
| Rights | Stellenbosch University |
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