James S. Jackson¹
(1) Consultant, Portland, OR

Abstract: Transform Faults Revisited: Implications for Deep Water Exploration

Transform faults occur between ocean ridges. They are divided into seismic segments, located between the active ocean ridges, and aseismic segments, located ‘outboard’ of the active ridges. The aseismic segments can be traced toward the continental shelf, but their location is often obscured by overlying shelf sediments. Transform faults bound several continetal margins, and separate deep water basins from adjacent shallow water basins. If sea floor spreading reorganizes, then strike-slip faulting will occur along the seismic segments of nearby transform faults. It has been assumed that coeval movement does not occur on the aseismic segments of these faults. However, examination of seismic data from mid-Norway, west of Britain, and Brazil indicates that the aseismic segments are effected by the reorganization of sea floor spreading. The effected segments show inverse and strike slip fault movement occuring on a range of scales. Faults located near these segments also show reactivation. Movement on aseismic segments of transform faults is likely to be more pronounced in deep water settings. Local effects may include both disruption of existing traps and creation of traps which post-date hydrocarbon migration. Regional effects may include changes in deep marine sedimentation patterns and changes in hydrocarbon migration pathways. The risk associated with deep water exploration may be better quantified by (1) identifying transform faults in the adjoining ocean basins, (2) identifying changes of sea-floor spreading geometry that may effect those faults, and (3) examining the trace of the transform fault's seismic and aseismic segments in the deep water play area.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana