--> Abstract: Shale Tectonics from Rifted Continental Margins: Insights from Margin Scale Numerical Models That Couple Deformation to Fluid Flow, by Steven J. Ings, Christopher Beaumont, Christina Morency, and Markus Albertz; #90078 (2008)

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Shale Tectonics from Rifted Continental Margins: Insights from Margin Scale Numerical Models That Couple Deformation to Fluid Flow

Steven J. Ings1, Christopher Beaumont1, Christina Morency2, and Markus Albertz1
1Department of Oceanography, Dalhousie University, Halifax, NS, Canada
2Seismological Laboratory, California Institute of Technology, Pasadena, CA

Rifted continental margin shale tectonics is investigated using newly developed 2D numerical models that couple fully-saturated porous compaction to sediment deformation. Mechanical and viscous (pressure solution) compaction is coupled to deformation of the skeleton through the pore fluid pressure. This new approach allows an examination of the relationship between overpressure generation, sediment failure, and the resulting margin scale structural style.

The numerical models comprise two mechanical and hydraulic layers; both with similar fluid filled frictional-plastic materials. The lower layer represents potentially mobile shale deposited in an early post-rift setting and the upper layer represents sediments deposited during subsequent delta progradation. The lower layer is weak (dry frictional angle of 10°) and has hydraulic properties that allow it to become highly overpressured during the model evolution. This layer is modeled as a visco-plastic Bingham fluid that is frictional-plastic below yield; the velocity of the post-yield flow is limited by the viscosity of the Bingham fluid. The upper layer is frictional-plastic (dry frictional angle of 30°) and remains approximately hydrostatically pressured.

The numerical models are used to investigate how the following factors influence the behavior of an idealized large scale rifted continental margin shale tectonic system: (1) syn-rift tectonic subsidence and early post-rift thermal subsidence; (2) hydraulic properties and sedimentation rate of the lower shale layer; (3) post-yield shale viscosity, and; (4) progradation rate and geometry of the upper deltaic layer. We will present model results that illustrate the relative importance of these factors and preliminary results of models designed to match the approximate spatial and temporal scale of the Niger Delta shale tectonic system.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas