4-D Evolution of a Normal Fault Array During Rift Initiation: From Integrated Digital Outcrop Study of the Nukhul Half-Graben, Suez Rift, Egypt

Paul Wilson, Franklin Rarity, David Hodgetts, and Rob L. Gawthorpe
School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, United Kingdom

We use a half-graben scale terrestrial LiDAR dataset integrated with ‘conventional’ field data to create a close-to-deterministic geological model of the Nukhul half-graben, Suez rift. The resulting model allows us to constrain the structural evolution of the half-graben. Rift-initiation deposition within the half-graben was controlled by the northwest-striking Nukhul fault. The Nukhul fault is composed of at least four segments that initiated in pre-rift strata. The fault propagated upward into syn-rift strata, forming a fault-propagation monocline ahead of the propagating fault tip. The fault segments became geometrically linked and broke the surface within the first 2.5 m.y. of rifting. Fault-perpendicular anticlines in the hangingwall opposite the segment linkage points persist for a further 1.8 m.y., suggesting that the fault remained kinematically segmented following geometric linkage. We suggest this occurs because earthquake rupture propagation is inhibited where there are sudden changes in fault strike at fault segment linkage points. The initiation of the fault within lithified pre-rift strata followed by vertical propagation into unlithified syn-rift strata leads to vertical changes in fault geometry and architecture along the Nukhul fault. Throw distribution patterns (generated using Badley Geoscience Ltd’s Trap Tester software) show that antithetic faults in the hangingwall of the Nukhul fault display increasing throw with depth, while antithetic faults to the east-striking Baba-Markha fault have throw maxima within the upper syn-rift succession. This suggests that some faults in the array developed as upward-propagating structures initiated in pre-rift lithologies, while others initiated within the syn-rift succession. Late east-striking structures may be related to the development of late transfer faults that link the major fault-block bounding faults.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas