Abstract: Seismic Analysis of Glide-Plane Fault Structures: Styles, Mechanisms, and Relations to Sedimentation
H. J. Yorston, G. H. Weisser
Major oil and gas traps along the U.S. Gulf Coast are produced by the general gulfward creep of the sedimentary section. Gravity, an incompetent layer of shale or salt, and an elevation change are the essential ingredients for glide-plane faulting. Seismic data across varied glide-plane faults reveal that the structural and depositional environments control the mechanism of fault development and the style of the associated structure. Three structural styles are recognized.
1. Breakaway structures form after local or regional tilting by the rupture and basinward sliding of a sediment layer above a shale or salt bed. Collapse and downbending along the plane of rupture produce a residual anticline at the updip margin of the basinward block. These structures form along the basin margin and are characterized by simple normal faults or grabens and low-relief anticlines.
2. Local-slope-transport structures develop by the successive detachment and creep of deltaic lobes deposited on a slope. Loading of the shales underlying the lower reaches of the slope produces a basinward mound referred to as a toe structure. The basinward flank of the toe structure provides the slope needed to start a new series of structures. This structural style is characterized by a series of troughs and mounds separated by glide-plane faults.
3. Migrating-load-transport structures form by the sediment load displacing underlying shales or salt into basinward mounds or ridges. Structures of extensive relief and complexity, including diapirs, may result.
All glide-plane fault styles can produce structural traps by downbending and mobility of the underlying plastic layer. The breakaway style tends to have little influence on sedimentation. The local-slope-transport and migrating-load-transport styles create local depocenters that concentrate potential reservoir sands. However, these sands are frequently of poor reservoir quality. Hydrocarbon accumulations associated with the structures are generally in shallower sediments that postdate the major structural activity.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC