Ian R. Sharp1,
Rob L. Gawthorpe2,
John R. Underhill3
(1) Norsk Hydro Research Centre, Bergen, Norway
(2) University of Manchester, Manchester, United Kingdom
(3) Edinburgh University, Edinburgh, United Kingdom
Field data from onshore exposures of the Oligo-Miocene Gulf of Suez Rift in the Sinai document the passive rotation of early formed meso-scale syn- and antithetic faults and associated half-graben due to long-lived activity on large displacement (2-5 km) block-bounding faults. Early-formed small displacement (< 250 m) meso-scale antithetic faults and half graben in the footwall of regional sale fault blocks underwent progressive steepening due to footwall uplift and rotation. In contrast, meso-scale synthetic faults were progressively rotated to shallower angles.
Analysis of palaeohorizontal surfaces within syn-rift sediments deposited in half-graben adjacent to the meso-scale faults indicate passive rotations of up to 25° since deposition. These data allow some constraints to be put on the activity and throw of regional scale block bounding faults during eh early stages of rifting. Passive burial and in-filling of early formed meso-scale faults and half graben by syn-rift sediments indicates that extension was transferred from numerous meso-scale faults to few block-bounding macro-scale faults as extension preceded, resulting in a marked change in basin configuration and syn-rift sedimentation. Identification of passively rotated normal faults and half graben is important both for correctly reconstructing the early stages of basin palaeogeography and sediment dispersal, differentiating phases of compression (inversion) from ongoing extension and rotation, and for models of rift basin evolution.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana