A STRATIGRAPHIC-STRUCTURAL PROFILE THROUGH PARTS OF THE BEAUFORT GROUP - FOLD GENESIS AND RELATIONSHIP TO U-DISTRIBUTION

A technique for constructing a composite profile of a very gently fold ed sedimentary multilayer sequence, some 1200 m thick, is introduced a nd applied. Accuracy checks and balances are discussed. Real changes i n layer thickness are found to be related to the position, attitude an d intensity of folds. Upright as well as verging, open sinusoidal mega folds formed during diagenesis and compaction. Monoclines (macrokinks) formed late during the deformation history, and are antithetic with r espect to the regional couple force. Most macrokinks eventually became locked. In some cases thrusting of the steep limb seems to have accom panied shortening inside the kinkband immediately before the locking o ccurred. Other monoclines have developed sets of short listric normal faults on the steep limb that merge with the beds on their downthrow s ide. The association of all structures is readily explained by a theor y of visco-elastic folding of multilayers with varying competency. Som e 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 m egafolds seems to be controlled by thickness variations in sequences o f 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 .