Folding Of Rocks Research Articles

Joint Studies In The Western Part Of Ikom-Mamfe Basin, Lower Benue Trough, Nigeria

The Ikom-Mamfe basin, also called the Mamfe embayment, is a bifurcation of the Benue trough in southeastern Nigeria and southwestern Cameroun. The basin is about 130km long, 60km wide basin and is filled with about 4km thick sedimentary rocks. Deformational events led to gentle folding of rocks in the basin and emplacement of magmatic rocks. Systematic and detailed field studies were carried out in eight (8) locations within the study area, in which the orientations of 1437 joints and 102 veins were acquired. Two sets of orthogonal joints observed in the study exhibited symmetry with respect to the directions of the fold axes and were dominated by high-angle dips averaging about 80o. This implies a syntectonic origin of these structures also during their propagation, the maximum principal stress directions (σ1) were orientated in two different directions NW- SE and NNE-SSW for DI and D2 respectively. The relative strength of deformation during DI was greater than D2 and it was also unfolded that the ‘ac’ extension joints trending NW- SE and NNE-SSW hosted relatively thicker veins in both DI and D2. These joints served as better conduits for mineralizing fluids and also most suitable directions for future prospecting.

Growth of a salt diapir in an anticline - A record from the Cenozoic halokinetic sequences in the Zagros Fold and Thrust Belt, Iran

Salt diapirs in southern Iran provide excellent exposures of the host rock sedimentary sequences that record salt diapiric growth in compressional settings. This study addresses the reactivation of one particular diapir in the core of an anticline of the Zagros Fold and Thrust Belt (ZFTB) using the classical concept of halokinetic sequences. These sequences reflect the relative rise of the salt diapirs with respect to the depositional rate of the sediments in their surroundings. The resulting reconstruction indicates irregular deposition of the total eight sets of host rock sedimentary packages around the diapir during the Oligocene-Miocene that developed in response to the progressive rise of the host anticline. Folding of host rocks was associated with vertical movement of blocks bounded by cross-faults radiating from the boundary of the diapir, specifically around the triangular indenter on the north, deflecting the anticline to a southward advancing salient. The halokinetic sequences record an early stage of diapiric rise in the rhythmic alternation of gypsum and fossiliferous carbonate with siliciclastic material followed by fossiliferous limestone typical for lagoonal to slope environment in a limestone reef setting. The last stage is associated with thin-skinned tectonics of the uppermost halokinetic sequences thrust towards the diapir. Rapid thickness change of the halokinetic strata along the periphery of the diapir in the southern sector that includes also the crestal region of the anticline indicates compressional reactivation of the structure as early as 11 Ma (Gachsaran Formation), likely associated with salt overflow in the anticline crestal region, where the adjacent halokinetic sequences are completely overturned.

Architecture of ophiolitic mélanges in the Junggar region, NW China

Ophiolitic mélanges, units that contain components of an ophiolite suite, provide crucial information on earth history and orogenic evolution. In this paper, four ophiolitic mélanges are characterized, including the Baijiantan-Yeyagou, Hebukesair, Zhaheba and Hongguleleng mélanges in the Junggar region (NW China), southern Altaids. Detailed geological mapping, structural, geochronological, and geochemical analyses constrain ages, geochemical affinities and relationships of magmatic with clastic rocks. MORB-/OIB-type (meta)gabbros and plagiogranite are the oldest mélange components, slightly older or coeval with associated chert and MORB-/OIB-type basalt; these rocks collectively constitute an ophiolite suite. Ophiolitic rocks predate associated clastic sedimentary rocks (conglomerate and turbidite) by ∼90-25 My, and associated SSZ-type hornblende gabbro, basaltic andesite, diabase, diorite and rhyolite by ∼78-37 My, except in the Hongguleleng mélange, where ophiolitic rocks predate latter units by ∼9-25 My. The ophiolitics are repeated by imbricate thrusts and duplexes, and folded. Ophiolitic blocks in mélanges locally preserve similar structures. Such blocks commonly have MORB and/or OIB geochemical affinities. Significantly older ages of MORB/OIB igneous rocks compared to ages of associated clastic sedimentary/SSZ-type igneous rocks shows that the former rocks formed as part of the crust of a large ocean, far from a convergent margin. The far-traveled oceanic crustal slices were imbricated and disrupted into block-in-matrix structures during accretion and incorporation into a subduction complex. SSZ-type magmatic rocks locally intrude into and extrude onto clastic rocks, demonstrating that a mélange contains multi-stage magmatic rocks. Folds, tilted structures and shear band cleavages are locally cross-cut by dikes, and these rocks are themselves have been dismembered into blocks. An intruded conglomerate in the Hongguleleng mélange contains pebbles of gabbro and basaltic andesite, the latter of which overlies sandstone. Superimposed folds in clastic rocks and chert record the polydeformation of the mélanges. Determination of the complex relationships of multi-stage magmatism and deformation illuminates the tectonic history of ophiolitic mélanges in the Junggar region. This history includes formation and subduction-accretion of the crust of a large ocean and post-subduction intracontinental deformation.

Complex shape of the Palaeoproterozoic Serpovidny refolded mega-sheath fold in northern Fennoscandia revealed by magnetic and structural data

The Serpovidny large-scale synform located in the Arctic zone of the north-eastern Fennoscandian Shield was studied with geological mapping and structural analysis, and its core with a ground detailed magnetic survey. This is a tight to isoclinal mega-sheath fold with the strongly thinned lower limb, almost undeformed upper limb, and the ՙcat's eye՚ core. The innermost rift-related sequence of the fold core is a synformal anticline, whilst limbs are composed of Palaeoproterozoic Keivy Group (metamorphosed redeposited products of mainly deep chemical weathering) and form a syncline. The Serpovidny mega-sheath fold formed during progressive non-coaxial, high strain deformation in simple shear/general shear regimes and a northward thrusting under mid-crustal conditions. This mega-sheath fold evolved from a NNE-verging anticline originated at the base of a nappe transported north-northeastwards from the Palaeoproterozoic Imandra-Varzuga Rift-Belt during the 1.9 Ga Lapland-Kola collisional orogeny. After a thrusting of this nappe onto the Keivy Group, one anticline plunged into these rocks and was transformed into the NNE-closing Serpovidny mega-sheath fold. Its geometric parameters and/or kinematic evolution are close to those of mega-sheath folds in Cretaceous rocks in the Oman Mountains, large-scale synformal anticlines in the Helvetic nappes in the Alps, and a Caledonian nappe in northwest Ireland.

Drag folds in sedimentary rocks hosting kimberlites, West Yakutia

Drag folds were revealed in Lower Paleozoic sedimentary strata of Mirny, Nakyn and Syuldyukar diamondiferous fields, West Yakutia. They consist of minor anticlinal forms (3-5 to 15-20 cm thick) and cut marl, clayey limestone and dolomite bands located between monolith seams of carbonate rocks. Some folds as monocline, flexures and S- or Z-shaped folds reflect the degree of shearrelated interlayer offset. Drag folds are among shear zone occurrences including microfaults, slickensides with slip groove horizontal planes, and schistosity zones. Drag folds reflect local extension points while schistosity zones indicate compression points. For Syuldyukar field, detailed mapping results for drag folds and schistosity zones are provided at 3 scales: across 20 × 20 m observation grid within a local 2 km2 site; across 200 × 200 m grid within 20 km2 area; across 500 × 500 m grid within ~100 km2 territory. For all scales, drag fold halos are restricted to schistosity zones. Within a local site adjacent to kimberlites, drag folds mark ore-hosting fault controlling long axes of kimberlite areal projections. Within large areas, drag fold halos are 1,2-2 km, which compares with kimberlite group areal parameters. Drag fold halos reflect shear junctions, with some of them hosting kimberlites. Local occurrences of drag folds mark a major shear hosting a kimberlite body. Drag fold analysis combined with other evidence should be used as an indirect prospecting indicator of concealed shears and local extension areas controlling kimberlites.

Thermodynamically consistent model for poroelastic rocks towards tectonic and volcanic processes and earthquakes

Summary A general-purpose model combining concepts from rational continuum mechanics, fracture and damage mechanics, plasticity, and poromechanics is devised in Eulerian coordinates, involving objective time derivatives. The model complies with mass, momentum, and energy conservation as well as entropy inequality and objectivity. It is devised to cover many diverse phenomena, specifically rupture of existing lithospheric faults, tectonic earthquakes, generation and propagation of seismic waves, birth of new tectonic faults, or volcanic activity, aseismic creep, folding of rocks, aging of rocks, long-distance saturated water transport and flow in poroelastic rocks, melting of rocks and formation of magma chambers, or solidification of magma.

Laramide structure of southeastern Arizona: Role of basement-cored uplifts in shallow-angle subduction

AbstractLaramide reverse faults in southeastern Arizona commonly are obscured by mid- to late Cenozoic extension and subsequent cover, resulting in debate about their configuration and origin. A new mid-Cenozoic paleogeologic map depicts the structural configuration before extension, and new structural reconstructions characterize Laramide shortening in terms of structural style, magnitude, evolution, and timing.Reverse faults restore to moderate to high angles, are associated with fault-propagation folds, and involve significant basement and thus constitute thick-skinned deformation. The paleogeologic map suggests several major basement-cored block uplifts, many of which are newly identified. The largest uplifts may measure 150 km along strike, similar to those in the classic Laramide province of Wyoming and Colorado. Estimated shortening across the central study area is 14% or 23 km, whereas it is only 5% (9 km) to the north and 11% (12 km) to the south. Shortening by this mechanism is inadequate to explain previous estimates of crustal thickening in the region (∼50–60 km). Therefore, magmatic underplating, lower-crustal flow, or underplating of trench sediments and lithospheric material also may have contributed to thickening. Shortening largely occurred from 86 Ma to 64 Ma and possibly as late as 53 Ma, with initiation being younger to the northeast or north. Integration with data from southwestern New Mexico implies complex geometry for the subducting flat slab. Finally, reverse faults generally do not appear to have reactivated older faults, as previously suggested, primarily because reverse faults have associated fault-propagation folds in rocks that predate supposed reactivated structures.

Spatial variations of ductile strain in fold-and-thrust belts: From model to nature

Fold and thrust belts (FTBs) accommodate tectonic convergence through folding and faulting of crustal rocks during a collisional event between two continental plates. Although evidence of distributed deformation is common in FTBs that usually leads to continuous foliations and regionally occurring ductile structures of multiple orders, it has rarely been given much attention assuming that zones of localized deformation, like shear zones and brittle faults, accommodate the entire amount of tectonic convergence. This study presents 3D laboratory-scale models, using viscous thin sheet as crustal layers, to understand the evolution of ductile strain in a tectonic wedge. We varied the degree of mechanical coupling at the basal decollement (i.e., weak versus strong) to investigate this issue at constant convergence velocity in all experiments to avoid the influence of rate-dependence on viscous rheology. Our results reveal that the strength of basal decollement controls the mode of wedge growth and hence, the strain pattern particularly towards the hinterland. The weak decollement models yield a zone of constriction towards the central part of hinterland, explaining the occurrence of isolated patches of L-tectonites and cross-folds in FTBs; while the strong decollement condition allows gravity driven flow to be active in the hinterland, leading to orogen-parallel recumbent folds. In contrast, both weak and strong decollement models produce deformation that characterises the commonness of pervasive, hinterland dipping ductile fabrics towards the mountain front. We correlate our findings to show that spatio-temporal variations in basal coupling are responsible for varying occurrence of ductile structures in FTBs.

About this title - Folding and Fracturing of Rocks: 50 Years of Research since the Seminal Text Book of J. G. Ramsay

This Special Publication is a celebration of research into the Folding and Fracturing of Rocks to mark the 50th anniversary of the publication of the seminal textbook by J. G. Ramsay. Folding and Fracturing of Rocks summarised the key structural geology concepts of the time. Through his numerical and geometric focus John pioneered and provided solutions to understanding the processes leading to the folding and fracturing of rocks. His strong belief that numerical and geometric solutions, to understanding crustal processes, should be tested against field examples added weight and clarity to his work. The basic ideas and solutions presented in the text are as relevant now as they were 50 years ago, and this collection of papers celebrates John's contribution to structural geology. The papers explore the lasting impact of John and his work, they present case studies and a modern understanding of the process documented in the Folding and Fracturing of Rocks .

Celebrating 50 years since the publication of Folding and Fracturing of Rocks by J. G. Ramsay

Abstract John G. Ramsay's book Folding and Fracturing of Rocks was first published in 1967. It set the research agenda for, and the approaches to, modern structural geology. It is recognized as one of the most influential texts in the subject area and was underpinned by significant research publications by the author; its weight added to by later texts and articles. John was also an enthusiastic teacher of structural geology, and many of his tutees have gone on to forge their own careers in structural geology, inspired to do so by John, his teaching and approaches. This Special Publication serves as a golden 50 year celebration of the book, and also of John's life-long work and career as an innovative scientist, inspiring mentor, excellent teacher, and great field structural geologist.

Stress and strain evolution during single-layer folding under pure and simple shear

Folds in rocks are commonly used in geology for strain analysis. They contain information about rock rheology, and the kinematics and mechanics of deformation. The systematic analysis of the evolution of stress and strain during rock folding can provide key information on the mechanical behaviour of rocks and the efficiency of the folding process. In order to investigate the evolution of rock rheology during fold development, a series of two-dimensional simulations of single-layer folding are presented here. They are run using the finite element method BASIL, integrated within the software platform ELLE, to simulate linear and non-linear viscous deformation. The kinematics of deformation, the competence ratio between the folding layer and surrounding matrix as well as the stress exponent of the power-law viscous material are systematically varied. The results allow comparing the stages of folding under different deformation kinematic conditions. For all simulations the folding amplification process starts when the second invariant of the strain rate tensor in the competent layer deviates from the theoretical strain rate curve for a homogeneous material, which corresponds to a viscosity ratio between layer and matrix of m = 1. The relative time when the fold amplification starts is determined by the viscosity ratio between the competent layer and its surrounding matrix, the initial layer orientation with respect to the shear plane, the kinematics of deformation and the stress exponent. The folding process is more effective in cases with high viscosity ratio, non-linear rheology and layers initially oriented at a low angle with respect to the shear plane, because the second invariant of the strain rate tensor at the layer deviates earlier from the theoretical curve. The results also show differences depending on the boundary conditions, where (1) folding a competent layer requires less work in simple shear than in pure shear, and (2) the geometrical softening experienced by the competent layer due to fold development is followed by a hardening stage in pure shear and by a major softening phase in simple shear. The simulation results suggest that the decrease of stress of a competent layer without decreasing the mechanical strength has a direct influence on the behaviour of a lithospheric layer around the crust-mantle boundary, which may experience geometrical softening depending on the tectonic settings rather than material softening due metamorphic reactions or grain size reduction.

Determining finite strain: how far have we progressed?

Abstract One of the main aims in the field of structural geology is the identification and quantification of deformation or strain. This pursuit has occupied geologists since the 1800s, but has evolved dramatically since those early studies. The quantification of strain in sedimentary lithologies was initially restricted to lithologies of known initial shape, such as fossils or reduction spots. In 1967, Ramsay presented a series of methods and calculations, which allowed populations of clasts to be used as strain markers. These methods acted as a foundation for modern strain analysis, and have influenced thousands of studies. This review highlights the significance of Ramsay's contribution to modern strain analysis. We outline the advances in the field over the 50 years since publication of Folding and Fracturing of Rocks , review the existing limitations of strain analysis methods and look to future developments.

Folding during soft-sediment deformation

Abstract The detailed analysis of folding in rocks was in part pioneered by John Ramsay, and resulted in a range of techniques and criteria to define folds. Although folding of unlithified or ‘soft’ sediments is typically assumed to produce similar geometries to those in ‘hard rocks’, there has to date been little detailed analysis of such folds. The aim of this paper is therefore to investigate folds developed during soft-sediment deformation (SSD) by applying techniques established for the analysis of tectonic folds during hard-rock deformation (HRD). We use the Late Pleistocene Lisan Formation exposed around the Dead Sea as our case study, as the laminated lake sediments record intricacies of fold detail generated during seismically triggered slumping of mass transport deposits (MTDs) towards the depocentre of the basin. While it is frequently assumed that folds created during SSD are chaotic and form disharmonic structures, we provide analyses that show harmonic fold trains may form during slumping, although larger upright folds cannot be traced for significant distances and are more typically disharmonic. Our analysis also reveals a range of fold styles, with more competent detrital-rich layers displaying buckles (Class 1B), as well as upright Class 1A folds marked by thickened limbs. Class 1A buckle folds are generally considered to be created by flattening that overprints folds with an original Class 1B geometry. As thickened fold limbs are truncated by overlying erosive surfaces, the vertical flattening is considered to have occurred during the slump event. Different fold shapes may partially reflect variable flattening, depending on the original orientation of upright or recumbent folds, together with continued downslope-directed simple-shear deformation that modifies the fold geometry. Analysis of fold wavelength, amplitude and bed thickness allows us to plot strain contour maps, and indicates that beds defining slump folds display viscosity contrasts in the range of 50–250, which are similar to values estimated from folds created during HRD in metamorphic rocks. A range of refold patterns, similar to those established by John Ramsay in metamorphic rocks, are observed within slumps, and are truncated by the overlying sediments, indicating that they formed during a single progressive slump event rather than distinct ‘episodes’ of superimposed deformation. This study confirms that techniques developed for the analysis of folds created during HRD are equally applicable to those formed during SSD, and that resulting folds are generally indistinguishable from one another. Extreme caution should therefore be exercised when interpreting the origin of folds in the rock record where the palaeogeographical and tectonic contexts become increasingly uncertain, thereby leading to potential misidentification of folds created during SSD.

Measuring the research impact of the book Folding and Fracturing of Rocks by John G. Ramsay

Abstract On the 50th anniversary of the publication of the book Folding and Fracturing of Rocks by John G. Ramsay we use an analysis of citations to assess the book's impact on research in the field of structural geology. Five topics dealt with in the book have had special success in terms of the number of citations: (1) superimposed folding; (2) fold classification based on layer thickness variation; (3) simple shear deformation; (4) the R f / φ method; and (5) the flexural-slip mechanism of folding. The great impact of this book can be seen in several examples where the book has inspired new lines of research, such as: progressive deformation, strain analysis, shear zones and folding analysis. Ramsay's great merit in writing his book was to have wisely known to apply the quantitative methodology of continuum mechanics to the analysis of the geological structures. We conclude that Folding and Fracturing of Rocks is the most influential textbook in the field of structural geology research.

Folding and Fracturing of Rocks : the birth of modern structural geology

Abstract In 1967, the publication of John Ramsay's book, Folding and Fracturing of Rocks , was a landmark event that affected both of us, inspiring us into careers in structural geology. At that time, one of us was a postgraduate student at Imperial College, London, the other a second-year undergraduate at Manchester University. It is hard to convey, 50 years on, how precious this book was then. The true and lasting value is how this book has changed individuals, and influenced the teaching and research in structural geology, in Britain and around the world. In our view, Folding and Fracturing of Rocks marks the birth of modern structural geology.

Right-Angle Pattern of Minor Fluvial Networks from the Ionian Terraced Belt, Southern Italy: Passive Structural Control or Foreland Bending?

Morphometric analyses of both the topography and drainage network have been carried out in a large sector of the Ionian coastal belt of southern Italy in order to unravel the possible control of Late Quaternary thrust front activity on the evolution of the fluvial net. The study area extends in the southernmost sector of the Bradano Foredeep and is featured by several orders of uplifted marine terraces, ranging in age from Middle Pleistocene to Late Quaternary. The flight of the marine terraces is deeply cut by a trellis-type and regularly spaced minor fluvial network. Morphotectonic investigations based on field survey, photo-aerial interpretation, topographic attributes, morphometric indices, and analysis of longitudinal river profiles suggest a strong control on the drainage network arrangement by a pervasive orthogonal fracture system, produced and preserved into the brittle caprock of the terraces, made by conglomerate. Since a similar pervasive and orthogonal fracture pattern is typically generated by gentle folding of rocks, the development of the Ionian hydrographic networks could be attributed to a general—maybe still active—bending of the foredeep area due to the eastward propagation of blind thrusting of the Apennines orogenic chain.

The structure of the northern Agrio fold and thrust belt (37°30’ S), Neuquén Basin, Argentina

The Agrio fold and thrust belt is a thick-skinned orogenic belt developed since Late Cretaceous in response to the convergence between the Nazca and South American plates. The integration of new structural field data and seismic line interpretation allowed us to create two balanced cross-sections, which help to analyse the geometry of both thick and thin-skinned structures, to calculate the tectonic shortenings and finally to discuss the main mechanisms that produced this fold and thrust belt. The predominantly NNW-SSE structures show varying wavelengths, and can be classified into kilometer-scale first order basement involved structures and smaller second, third and fourth order fault-related folds in cover rocks with shallower detachments. Thick-skinned structures comprise fault-bend folds moving into the sedimentary cover, mainly along Late Jurassic evaporites, which form basement wedges that transfer the deformation to the foreland. Thus, shortenings in both basement and cover rocks must be similar and consequently, by measuring the contraction accounted for thin-skinned structures, is possible to propose a suitable model for the thick skinned deformation. The balanced cross-sections indicate shortenings of 11.2 km (18%) for the northern section and 10.9 km (17.3%) for the southern section. These values are different from the shortenings established by previous works in the region, reflecting differences in the assumed model to explain the basement-involved structures. According to our interpretation, the structural evolution of this fold and thrust belt was controlled by major basement-involved thrust systems with subordinate influence of inversion along pre-existing normal faults during the Andean compression.

Structural evolution of Mesozoic complexes in Western Chukotka

Detailed structural investigations were carried out in the Pevek area in order to verify the tectonic evolution of the Mesozoic thrust and fold belt in Chukotka. South-vergent F1 folds in Triassic rocks were proved to be the earliest structures formed during the first deformation stage DI. These structures were deformed by north-vergent folds F2 that were formed during the second deformation stage DII. North-vergent folds are the main structures of the Jurassic–Lower Cretaceous complex. The fold structures of the first two stages are deformed by shear folds F3 finishing the stage DII. All these structures are deformed by submeridionally trending normal faults referred to the deformation stage DIII.

Heterozoan carbonate deposition on a steep basement escarpment (Late Miocene, Almería, south‐east Spain)

AbstractHeterozoan temperate‐water carbonates mixed with varying amounts of terrigenous grains and muddy matrix (Azagador limestone) accumulated on and at the toe of an inherited escarpment during the late Tortonian–early Messinian (late Miocene) at the western margin of the Almería–Níjar Basin in south‐east Spain. The escarpment was the eastern end of an uplifting antiform created by compressive folding of Triassic rocks of the Betic basement. Channelized coralline‐algal/bryozoan rudstone to coarse‐grained packstone, together with matrix‐supported conglomerate, are the dominant lithofacies in the higher outcrops, comprising the deposits on the slope. These sediments mainly fill small canyon‐shaped, half‐graben depressions formed by normal faults active before, during and after carbonate sedimentation. Roughly bedded and roughly laminated coralline‐algal/bryozoan rudstone to coarse‐grained packstone are the main lithofacies forming an apron of four small (kilometre‐scale) lobes at the toe of the south‐eastern side of the escarpment (Almería area). Channelized and roughly bedded coralline‐algal/bryozoan rudstone to coarse‐grained packstone, conglomerates, packstone and sandy silt accumulated in a small channel‐lobe system at the toe of the north‐eastern side of the escarpment (Las Balsas area). Carbonate particles and terrigenous grains were sourced from shallow‐water settings and displaced downslope by sediment density flows that preferentially followed the canyon‐shaped depressions. Roughly laminated rudstone to packstone formed by grain flows on the initially very steep slope, whereas the rest of the carbonate lithofacies were deposited by high‐density turbidite currents. The steep escarpment and related break‐in‐slope at the toe favoured hydraulic jumps and the subsequent deposition of coarse‐grained, low‐transport efficiency skeletal‐dominated sediment in the apron lobes. Accelerated uplift of the basement caused a relative sea‐level fall resulting in the formation of outer‐ramp carbonates on the apron lobes, which were in turn overlain by lower Messinian coral reefs. The Almería example is the first known ‘base of slope’ apron within temperate‐water carbonate systems.

Formation of dome and basin structures: Results from scaled experiments using non-linear rock analogues

Dome and basin folds are structures with circular or slightly elongate outcrop patterns, which can form during single- and polyphase deformation in various tectonic settings. We used power-law viscous rock analogues to simulate single-phase dome-and-basin folding of rocks undergoing dislocation creep. The viscosity ratio between a single competent layer and incompetent matrix was 5, and the stress exponent of both materials was 7. The samples underwent layer-parallel shortening under bulk pure constriction.Increasing initial layer thickness resulted in a decrease in the number of domes and basins and an increase in amplitude, A, arc-length, L, wavelength, λ, and layer thickness, Hf. Samples deformed incrementally show progressive development of domes and basins until a strain of eY=Z = −30% is attained. During the dome-and-basin formation the layer thickened permanently, while A, L, and λ increased. A dominant wavelength was not attained. The normalized amplitude (A/λ) increased almost linearly reaching a maximum of 0.12 at eY=Z = −30%. During the last increment of shortening (eY=Z = −30 to −40%) the domes and basins did not further grow, but were overprinted by a second generation of non-cylindrical folds. Most of the geometrical parameters of the previously formed domes and basins behaved stable or decreased during this phase. The normalized arc-length (L/Hf) of domes and basins is significantly higher than that of 2D cylindrical folds. For this reason, the normalized arc length can probably be used to identify domes and basins in the field, even if these structures are not fully exposed in 3D.