Numerical experiments on the formation of extensional sedimentary basins

Observations show that extension of the Earth's lithosphere typically leads to localisation of deformation in the crust in the form of extensional sedimentary basins. The geometry of these basins is variable and can in a simple manner be classified as ranging from more or less symmetric to asymmetric. Symmetric basins have approximately equal displacements on the normal faults bounding the basin, while for asymmetric half-graben displacements are focussed on one main planar or listric basin-bounding fault. Our aim is to provide an improved understanding of the dynamic development of sedimentary basins and their geometries. To this purpose, we view the formation of extensional sedimentary basins as a surface expression of mode selection occurring on a crustal scale. We predict modes of deformation by using an analytical analysis of the rate of internal dissipation of energy and the gravitational rate of work. Results of finite-element calculations of equivalent simple models agree with the analytical mode predictions.

basin formation

The figure shows an example of the formation of a sedimentary basin by extension. The centre 200 km out of the 400 km modelling domain are shown. The frictional strength of the model materials softens with increasing strain. The basin is always kept completely filled with sediments (the different shades of yellow indicate different times of deposition), which also undergo strain softening. The grid in the figure is used to track material properties and visualises deformation; it is not the calculation grid (which is more dense). Calculations used sopale, developed by the Geodynamics Group at Dalhousie University.


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