Flexural flow folding: Does it occur in nature?

Hudleston, Peter J.; Treagus, Susan H.; Lan, Labao

doi:10.1130/0091-7613(1996)024<0203:fffdio>2.3.co;2

Cited by 59 publications

(11 citation statements)

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“…While simple shear is discontinuous from layer to layer, the amount of shear between limestone layers is not nearly as large as would be the case for¯exural-slip folds with thin shale interlayers. Our model resembles the view of Hudleston et al (1996) that a¯exural-¯ow fold consists of alternating layers that have a large viscosity contrast.…”

Section: Stress Con®guration In Limestone Beds During the Developmentmentioning

confidence: 93%

Joint development normal to regional compression during flexural-flow folding: the Lilstock buttress anticline, Somerset, England

Engelder

Peacock

2001

Journal of Structural Geology

102

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Alpine inversion in the Bristol Channel Basin includes reverse-reactivated normal faults with hanging wall buttress anticlines. At Lilstock Beach, joint sets in Lower Jurassic limestone beds cluster about the trend of the hinge of the Lilstock buttress anticline. In horizontal and gently north-dipping beds, J 3 joints ( 295±2858 strike) are rare, while other joint sets indicate an anticlockwise sequence of development. In the steeper south-dipping beds, J 3 joints are the most frequent in the vicinity of the reverse-reactivated normal fault responsible for the anticline. The J 3 joints strike parallel to the fold hinge, and their poles tilt to the south when bedding is restored to horizontal. This southward tilt aims at the direction of s 1 for Alpine inversion.Finite-element analysis is used to explain the southward tilt of J 3 joints that propagate under a local s 3 in the direction of s 1 for Alpine inversion. Tilted principal stresses are characteristic of limestone±shale sequences that are sheared during parallel (¯exural-¯ow) folding. Shear tractions on the dipping beds generate a tensile stress in the stiffer limestone beds even when remote principal stresses are compressive. This situation favors the paradoxical opening of joints in the direction of the regional maximum horizontal stress. We conclude that J 3 joints propagated during the Alpine compression caused the growth of the Lilstock buttress anticline. q 2001 Published by Elsevier Science Ltd. IntroductionAn old paradigm is that outer-arc stretching leads to foldrelated jointing (Van Hise, 1896). Outer-arc stretching is associated with tangential longitudinal strain folds that develop when a homogeneous, isotropic layer is buckled (Price and Cosgrove, 1990). The tangential longitudinal strain fold is divided by a neutral surface beyond which the inner arc of the fold is compressed. Joints that initiate in the outer arc of anticlines propagate down to but do not cross the neutral surface. When fold-related jointing penetrates the entire thickness of a bed, the tangential longitudinal strain model is less useful as a mechanism to explain the strain that may have caused jointing. This is also true when jointing is well developed in the limbs of folds or at in¯ection points where strain goes to zero in a tangential longitudinal strain fold. To understand the development of jointing in the limbs of folds, we must look to another model. Flexural¯ow folds have maximum strains at the in¯ection points and zero strain at the hinges (Price and Cosgrove, 1990).We consider the possibility that one or more sets of un®lled joints of the Bristol Channel were contemporaneous with¯exural-¯ow folding during Alpine shortening. Here, we describe ®eld data gathered to test this hypothesis. We presume that the joint geometries interpreted to date from the Alpine inversion re¯ect the superposition of local and remote (i.e. regional) stress conditions. We also use the orientation of systematic joints in carbonate beds to constrain a mechanical model for stress dis...

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Section: Stress Con®guration In Limestone Beds During the Developmentmentioning

confidence: 93%

Joint development normal to regional compression during flexural-flow folding: the Lilstock buttress anticline, Somerset, England

Engelder

Peacock

2001

Journal of Structural Geology

102

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“…The last authors note that the numerical modelling of flexural flow folding by Hudleston et al (1996) also revealed such increase in flexural-flow intensity towards the centre of competent layers. From the microstructural evidence in our study (Fig.…”

Section: Variation Of Strain Between Fold Limbsmentioning

confidence: 92%

“…Using numerical modelling, Hudleston et al (1996) demonstrated that only the aggregate response of a highly anisotropic medium may approximate that of pure flexural flow. However, extremely high anisotropy parallel to the shear plane is normally only seen in incompetent layers, such as slates or phyllites with a pervasive slaty cleavage fabric.…”

Section: Introductionmentioning

confidence: 98%

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Mechanisms of flexural flow folding of competent single-layers as evidenced by folded fibrous dolomite veins

Torremans

Muchez

Sintubin

2014

Journal of Structural Geology

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a b s t r a c tFlexural flow is thought unlikely to occur in naturally deformed, competent isotropic single-layers. In this study we discuss a particular case of folded bedding-parallel fibrous dolomite veins in shale, in which the internal strain pattern and microstructural deformation features provide new insights in the mechanisms enabling flexural flow folding. Strain in the pre-folding veins is accommodated by two main mechanisms: intracrystalline deformation by bending and intergranular deformation with bookshelf rotation of dolomite fibres. The initially orthogonal dolomite fibres allowed a reconstruction of the strain distribution across the folded veins. This analysis shows that the planar mechanical anisotropy created by the fibres causes the veins to approximate flexural flow. During folding, synkinematic veins overgrow the pre-folding fibrous dolomite veins. Microstructures and dolomite growth morphologies reflect growth during progressive fold evolution, with evidence for flexural slip at fold lock-up. Homogeneous flattening, as evidenced by disjunctive axial-planar cleavage, subsequently modified these folds from class 1B to 1C folds. Our study shows that the internal vein fabric has a first-order influence on folding kinematics. Moreover, the fibrous dolomite veins show high viscosity contrasts with the shale matrix, essential in creating transient permeability for subsequent mineralising stages in the later synkinematic veins during progressive folding.

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“…Whilst such analyses can help the interpretation of folding mechanisms in ductile conditions, they are not really adapted to solving the problem of fracture distribution within buckled folds. Fracture patterns have all been estimated from, or related to, those predicted from theoretical or experimental models (Hudleston 1986;Hudleston & Lan 1993;Hudleston et al 1996;Fisher & Jackson 1999).…”

mentioning

confidence: 99%

Fold amplification and style transition involving fractured dip-domain boundaries: buckling experiments in brittle paraffin wax multilayers and comparison with natural examples

Bazalgette

Petit

2007

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Experiments aiming to study the conditions of fracture localization during buckle folding in brittle sedimentary layers of the upper crust were conducted using brittle paraffin wax multilayers submitted to axial and vertical load. The particular aim was to understand the mechanisms of development of subtle features often observed in apparently rounded natural folds. These consist of scarcely visible discontinuous fractured zones, more or less parallel to the fold axis, that separate domains of constant dip. These zones are of great interest for fluid dynamics in folded fractured reservoirs. It is shown that such axial kink boundaries referred to as dip-domain boundaries (DDBs) play a major role in the development of curvature in fractured buckle folds. DDBs observed in experiments consist of the localization and coalescence of tensile fractures along axial planes after the elastic instability stage. The tested physical parameters were (1) the intensity of the vertical load, (2) the bed thickness within a mechanical unit of constant thickness, (3) the stiff (multilayer)-soft (embedding material) thickness ratio and (4) the interlayer friction. In low interlayer friction conditions DDBs remain relatively localized during shortening, leading to chevron-style folds. With high interlayer friction conditions, DDBs tend to multiply laterally from an initial chevron fold. The latter phenomenon leads towards a more rounded fold, but one that still shows discontinuous curvature comparable to that observed in natural conditions. Fold models of flexural slip and tangential longitudinal strain (orthogonal flexure) are discussed under the influence of tensile failure in multilayer materials.

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Flexural flow folding: Does it occur in nature?

Cited by 59 publications

References 0 publications

Joint development normal to regional compression during flexural-flow folding: the Lilstock buttress anticline, Somerset, England

Joint development normal to regional compression during flexural-flow folding: the Lilstock buttress anticline, Somerset, England

Mechanisms of flexural flow folding of competent single-layers as evidenced by folded fibrous dolomite veins

Fold amplification and style transition involving fractured dip-domain boundaries: buckling experiments in brittle paraffin wax multilayers and comparison with natural examples

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