New Approaches to 3D Structural Restoration in Fold-And-Thrust Belts Using Growth Strata

Joachim P. Mueller¹, Chris Guzofski¹, Carlos Rivero², Andreas Plesch¹, John H. Shaw¹, Pierre Muron³, Frank Bilotti², and Don Medwedeff^4
1 Harvard University, Cambridge, MA
² Unocal Corporation, Sugar Land, TX
³ Nancy School of Geology, Nancy, France
⁴ ChevronTexaco E&P Technology Company, San Ramon, CA

Sequential, three-dimensional restorations of geologic structures provide important constraints on their kinematic evolution, helping to validate structural interpretations and to define the temporal evolution of prospective hydrocarbon traps. We apply and evaluate two new 3D restoration approaches implemented in Gocad, using a series of contractional detachment and fault-propagation folds in the Caspian Sea, Los Angeles basin, CA, and Niger Delta. The first of these restoration approaches is based on a new parametric method applied to tetrahedral volumes, in which conservation of volume and strain minimization constraints govern the restoration kinematics. The second approach employs variable inclined shear, with restoration kinematics specified by the user, to restore geologic surfaces. Using both methods we demonstrate how sequential restorations can be guided by patterns of syntectonic (growth) strata. These restorations define the relative components of kink-band migration and limb rotation involved in the folding. On the folds that we studied, detachment folding occurred predominantly by limb rotation, whereas fault-propagation folding reflects both kink-band migration and limb rotation. These derived fold kinematics, in turn, distinguish the fault-related folding theories, such as constant-thickness, or trishear fault-propagation folding that are most appropriate for modeling the structures. To summarize, these restoration methods are qualified to guide structural interpretations, and to derive the timing and history of trap formation, for structures in both passive margin and orogenic fold-and-thrust belts.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005