ABSTRACT: The 3D geometry of inversion structures
Coward, Michael Peter , Ries-Coward Associates Limited, Reading, United Kingdom
Variations in i) original basin geometry along strike, ii) original fault dip and strike and iii) footwall and hangingwall lithologies cause lateral variations in the geometries of inversion-related structures. This is especially the case where there has been a change in displacement direction during inversion, rather than simple reversal in movement. The complexities affect apparently straight faults as well faults offset by lateral ramps and transfer zones. Along original "straight" faults, during the original extensional fault growth, small faults coalesce together to form an irregular cuspate surface with the ridges of the cusps pointing down the normal fault displacement direction. Where the cusps are large and inversion involves displacement of the hangingwall obliquely over these cusps, several interfering orientations of folds, thrusts and normal faults may develop, the footwall may break into varied fault orientations, or locally the displacement may jam, causing irregularly orientated zones of shortening and buckle folding. Small hangingwall basins may develop both parallel and perpendicular to the trend of the original normal fault, controlling the distribution of syn-inversion sediments.
The processes will be examined using 3D/4D restorations and forward models from examples principally from the North Sea, but also worldwide.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia