Structural
Consequences of Seepage Forces in Overpressured Thin-skinned Thrust Belts
Cobbold, Peter R.1, Benjamin
J. Clarke2, Helge Loseth3 (1) Geosciences-Rennes, Rennes,
France (2) Statoil ASA, Stavanger, Norway (3) Statoil Research Centre, 7005
Trondheim, Norway
In thin-skinned thrust belts, fluid
overpressure can facilitate detachment. If the overpressure has a gradient, it
causes fluid flow, according to Darcy's Law. Where fluid migrates upward,
through a sealing layer of small permeability, the pressure profile has a ramp.
Where fluid generates within a source layer, the profile has a parabolic peak.
The migrating fluid imparts seepage forces to all elements of the solid
framework and these forces have structural consequences.
We discuss experiments on thrusting in
multilayered granular models, where permeability is a function of grain size.
At the base of a sealing layer, if the pressure reaches lithostatic values, it
facilitates detachment. Fore-thrusts and back-thrusts form in alternation and the
resulting prism acquires a small apical angle. The faults
curve up, from the detachment, through the sealing layer, becoming straighter
in the overburden.
Similar structural styles are common in
overpressured deltas and accretionary prisms. For example the outer thrust belt
of the
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California