Underhill, John R.
University of Edinburgh,
Scotland
Abstract: Role of Propagating Normal Faults in Controlling Sequence Variability and Sediment Dispersal in Rift Systems
Fieldwork in Oligo-Miocene clastic deposits of the Gulf of Suez rift, Sinai, Egypt, demonstrates the important role that fault growth has on the variability of synsedimentary sequence architecture. As fault segments propagate vertically and laterally they affect stratal geometries, basin physiography, the location of sedimentary entry points, and sediment dispersal patterns. As such, their growth not only influences sequence stratigraphic development of the basin fill but also controls the external form and internal character of subtle hanging-wall traps. Vertical propagation of buried (blind) structures leads initially to the development of monoclinal flexures marked by the progressive rotation of strata, occurrence of synsedimentary unconformities and creation of traps adjacent to the controlling faults. Subsequent surface break by faults leads to a major change in cross- section geometry with the formation of a conventional half-graben wedge. Further complexity occurs due to the lateral propagation of fault segments since it leads to overlap, interference, and linkage, all of which have the potential to influence basin gradients and sediment transport pathways. In Sinai, relay ramps initially act as the main conduits through which sediment reaches hanging-wall depocenters. Although lateral propagation leads to their modification, sediment supply is not always terminated and supply may persist even after complete fault linkage has been achieved. Findings in other rift systems like the North Sea Jurassic replicate the Sinai studies. As such, the results may have far-reaching consequences for sequence stratigraphic predictions and understanding the site, development, and nature of hanging-wall stratigraphic plays.
AAPG Search and Discovery Article #90929©1998-1999 AAPG Distinguished Lecturers