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Houston Geological Society Bulletin

Abstract


Houston Geological Society Bulletin, Volume 50, No.03, November 2007. Pages 11 and 13.

Abstract: Salty Tales: Numerical Investigations of Continental Margin Salt Tectonics

Christopher Beaumont1, Markus Albertz1, Steven Ings1, Sofie Gradmann2, and John Shimeld3
1Department of Oceanography, Dalhousie University
2Department of Earth Science, Dalhousie University
3Geological Survey of Canada

The study of continental margin salt tectonics has a long and illustrious history. Major advances in our understanding have come from the direct interpretation of data supported by analogue laboratory models. Numerical modeling of salt tectonics has to some degree lagged behind. We will show applications in which 2D finite element numerical modeling of salt tectonics, driven by gravitational spreading and gliding, can test mechanisms proposed from data interpretation and provide insight beyond that of analogue models. The models are not designed to simulate or mimic particular geological examples. Instead we are using simplified examples to understand the underlying mechanical controls. Armed with this understanding we can predict the styles of salt tectonics that will develop under differing sedimentation regimes and explain the variations among natural salt tectonic provinces. The models also act as “intuition enhancers” and can help explorationists visualize just how dynamic salt tectonic systems can be.

Starting from the basic problem of the large-scale failure of frictional-plastic overburden above viscous salt and the seaward translation of the failed margin sediments, we investigate the requirements

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for failure, the ensuing flow velocity and the way in which structural components of this system evolve. We will consider a set of archetypal problems:
1) A dynamic model for initiation and early evolution of minibasins (when the basin sediments are less dense than the salt);
2) An explanation of the basic styles of salt tectonics of the Scotian Basin, eastern Canada; and
3) The conditions required for the development of toe-of-salt fold belts, such as the Perdido Fold Belt of the Gulf of Mexico, by gravitational spreading.

We use the finite element models to calculate the large-scale deformation of the system during progradation and aggradation of frictional sediments above salt. Additional factors included in the models are the syn-rift geometry of a rifted continental margin with the associated thermal subsidence and tilting, the loading of the margin by seawater, and finally the isostatic response to the water and sediment loads which then modifies the margin geometry. Within the sediments the effects of pore-fluid pressure, which reduces their strength, and compaction, which modifies density and accommodation, are also shown to be important.

The lecture addresses the critical controlling factors for each of the problems listed above and includes some neat animations of the models.

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