Christopher Aiden-Lee Jackson1, Robert L Gawthorpe2
(1) The University of Manchester, Manchester, England
(2) University of Manchester, Manchester
ABSTRACT: Tectono-stratigraphic evolution of a half-graben; the importance of fault propagation and segmentation, the Tanka fault zone, Suez Rift, Egypt
The temporal and spatial evolution of normal fault zones may exert a first-order control on the stratigraphic development of extensional basins. It may be expected, therefore, that the syn-tectonic strata contains "signals" of the tectonic events that controlled their deposition, in particular, periods of fault-propagation and segment linkage. Well exposed syn-rift strata from the Tanka half-graben, Oligo-Miocene Suez rift system, gives an insight into the evolution of a ~ 3km long, segmented normal fault zone.
Initial syn-rift facies distributions suggest the existence of two isolated fault segments. Coarse-clastic material was focused through a relay ramp which "soft-linked" the faults, resulting in the localised deposition of fanglomerates within the hanging wall. Subsequent deposits form two isopach thicks, indicating that during this interval the faults were physically isolated and probably had individual displacement to length profiles.
The overlying syn-rift deposits indicate a modification of sediment supply pathways, and a distinct change in stratal architecture. Continued fault growth and relay ramp breaching (hard-linkage) led to uplift/backtilting of the footwall, diversion of drainage away from the basin, and the cessation of coarse-clastic deposition. The new composite fault zone was "under-displaced" with respect to its new length thus displacement was concentrated within the zone of linkage. Coeval syn-rift sediments thicken into this region and showing pronounced thinning towards the tips of the new composite fault zone.
This study illustrates the importance of integrating structural and stratigraphic data when attempting to reconstruct the temporal and spatial evolution of normal fault zones.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado