Structure of the Cape Fold Belt in the Ceres Syntaxis

[摘要] ENGLISH ABSTRACT:The Ceres Syntaxis comprises that part of the Cape Fold BeltSyntaxis that lies north of the Worcester Fault. Most of thearea consists of folded Cape Supergroup (primarily WittebergGroup) rocks. Fold styles of all fold trends are essentiallythe same. However, different multilayer rheologies led to thedevelopment of either sinusoidal or kink-like fold geometriesin different parts of the cover sequence. The character ofWitteberg sediments led to the development of large megakinkfolds and peculiar fold zones in this part of the sequence.Fold trends in the Ceres Syntaxis vary between NW-SE, NE-SWand E-W. The southern part of the area is dominated by theNE-SW trend, with the NW-SE trend being only important in thewest. Interference between these two trends only exists inthe Witteberg Group, where it occurs as crossing linear foldzones and conjugate, intersecting kink folds . Cross-foldingrelationships in the north-eastern part of the Ceres Syntaxisindicate that the area had been affected by twocontemporaneous, orthogonally opposed compressions that workedsimultaneously in different parts of the multilayer.Differences in the magnitude of strain, or in the local timingof fold initiation, produced local refolding or transectingrelationships. The microfabric of Witteberg sandstonessuggests deformation under conditions of low temperature andpressure, as well as low strain rates. Some microfabrics alsoindicate that substantial buckle shortening occurred while theMiddle and Upper Witteberg beds were still unlithified.Isotopic dating of Cedarberg shale from both main trends didnot yield unequivocal results, mainly due to thedeformatio~al intensity. The positioning of the CapelowFoldBelt Syntaxis was strongly influenced by basement tectonicgrain and basin floor relief. The NW and NE fold trendsformed on a heterogeneous basement that resolved thestress configuration into components whichexternal .actedsimultaneously towards the north-west and north-east. Eccaand Beaufort Group sedimentation patterns in the western Karoocorroborate the above findings.

[发布机构] Stellenbosch University