Faultbend folding

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Introduction Fault-bend folding Fault-propagation
folding Detachment folding Buckles Fold-thrust
complexes in multilayers Trishear
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Problem imaging the forelimb critical for
evaluating the structural style
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Problem imaging fore-limb from seismic
interpretations are commonly strongly model-driven
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First-pass interp - steep faults..not in vogue
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Low-angle thrust (detachment at depth??)
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Introduction Fault-bend folding Fault-propagation
folding Detachment folding Buckles Fold-thrust
complexes in multilayers Trishear
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Simple fault-bend fold
Suppe model
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Suppe fault bend folding..
But is this too simplistic a style?
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Introduction Fault-bend folding Fault-propagation
folding Detachment folding Buckles Fold-thrust
complexes in multilayers Trishear
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Panels of constant-dip strata, folds grow by
hinge migration
Fault-propagation folding
Fault-bend folding
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Test kinematic models using growth strata
Growth triangles
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growth fans rather than growth triangles are
the usual style.
So are the fault-bend models applicable?
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Introduction Fault-bend folding Fault-propagation
folding Detachment folding Buckles Fold-thrust
complexes in multilayers Trishear
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Detachment fold
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From Sherkati et al. 2004 (Mar. Pet. Geol. )
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McQuarrie 2004 J. Struct. Geol.
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Structural styles in the Zagros.. Geomorphologic
evolution suggests buckle sheet detached on
Hormuz salt minor internal detachments
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Geomorphological studies of developing folds
using Landsat images from the Zagros Mountains,
Iran. (Henry Lickorish)
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Fold collision
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• Fold interactions
• Long cylindrical
• Abrupt plunges
• Collided folds
• Merged folds

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Introduction Fault-bend folding Fault-propagation
folding Detachment folding Buckles Fold-thrust
complexes in multilayers Trishear
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Fold train initiates If one fold amplifies
slightly fasterit will weaken So strain
transferred onto that fold - other folds slow
down/stop. System experiences stress drop.
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• CONTROLS ON BUCKLE FOLD EVOLUTION?

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Quantify through modelling
by Martin Casey.
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Buckle fold development
Finite element modelling by Martin Casey
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Viscosity ratio 101
Differential stress
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Stress concentrated in hinge area
Stress drop on limbs
Differential stress
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Example.
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• Chevron fold
• (Hartland Quay)
• Bed-parallel slip
• Strain in hinge

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Structures on limbsshear fibres on
beddingfractures in beds
More models..
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Contrast with higher viscosity ratio...
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Stress drop throughout
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Viscosity ratio 101
Viscosity ratio 401
Longer wavelength (and lower diff stress) for
higher viscosity contrast
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Stress history is complex
Unloading limbs - can promote fracture here
But can be modelled..
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Modelling fracture potential and
evolution Timing might be crucial. Diagenetic
events Fluid migration events
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Buckling is important
Stress history is complex
Model in 3D and. Fold-thrust complexes
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Introduction Fault-bend folding Fault-propagation
folding Detachment folding Buckles Fold-thrust
complexes in multilayers Trishear
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Multilayers?
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Examples from Champsaur
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WNW
ESE
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WNW
ESE
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• Thrust cuts through
• Ramp area folds
• Thrust breaks back

? continuum - localised slip plus distributed
deformation
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ESE
WNW
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Different predictions for sand connectivity
Precursor buckling important.
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Introduction Fault-bend folding Fault-propagation
folding Detachment folding Buckles Fold-thrust
complexes in multilayers Trishear
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• Strat YES

• Complex localisation

orogenic interiors?
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Introduction Fault-bend folding Fault-propagation
folding Detachment folding Buckles Fold-thrust
complexes in multilayers Trishear