A stratigraphic-structural profile through parts of the Beaufort Group: fold genesis and relationship to U-distribution
Date
1994
Authors
Halbich I.W.
Grobler L.
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Abstract
A technique for constructing a composite profile of a very gently folded sedimentary multilayer sequence, some 1200 m thick, is introduced and applied. Accuracy checks and balances are discussed. Real changes in layer thickness are found to be related to the position, attitude and intensity of folds. Upright as well as verging, open sinusoidal megafolds formed during diagenesis and compaction. Monoclines (macrokinks) formed late during the deformation history, and are antithetic with respect to the regional couple force. Most macrokinks eventually became locked. In some cases thrusting of the steep limb seems to have accompanied shortening inside the kinkband immediately before the locking occurred. Other monoclines have developed sets of short listric normal faults on the steep limb that merge with the beds on their downthrow side. The association of all structures is readily explained by a theory of visco-elastic folding of multilayers with varying competency. Some 50% of the stratiform uranium mineralization that is associated with the thicker, more permeable sandstone units occurs in monoclines. The positioning of monoclines relative to the axial planes of the early megafolds seems to be controlled by thickness variations in sequences of macrocycles. These variations can be linked to changes in transport direction across syndepositional early folds. Macrokinks can therefore be considered a valuable additional indicator for exploration targets. © 1994.
Description
Keywords
Beaufort Group, compaction, diagenesis, fold genesis, monocline, sedimentary rock, uranium, South Africa, Cape Province
Citation
Journal of African Earth Sciences
18
3
18
3