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Abstract: Exploration Opportunities in Inverted Rift Basins Defined by Syntectonic Strata and Axial Surface Mapping

John H. Shaw, Stephen C. Hook, Edward P. Sitohang

Structural highs and syntectonic depositional sites in Central Sumatra rift basins are controlled by three-dimensional normal fault geometries and lateral fault slip distributions. The rift basins formed due to crustal extension accommodated by normal faults that flatten with depth, causing collapse of the hanging wall and formation of inclined rollover panels. We model this deformation by coulomb shear of the hanging wall localized along active fold hinges (axial surfaces) that are pinned at depth to fault bends. Three-dimensional fault geometries are predicted and mapped based on the shapes of rollover panels and fault segments imaged in seismic reflection (depth) profiles. Rollover panels widen during progressive fault slip and are bound by anticlinal and synclinal axial surfaces. ollover panels also narrow upward into syntectonic strata, which record the kinematics and timing of basin formation. We map axial surfaces to define the positions of fault bends and widths of rollover panels, which are related to slip on underlying fault segments. Structural highs form where fault segments decrease in dip along strike and/or in regions of minimum fault slip. These areas are defined on fault maps by shallow slopes of fault segments and on axial surface maps by narrow rollover limb widths. Structural highs formed during rifting and later tectonic inversion can be defined on these maps prior to detailed contouring, which is often difficult in frontier areas and in lacustrine sequences. We present examples of producing hydrocarbon fields defined by axial surface maps from t e Central Sumatra basin.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994