Chaotic Bodies Research Articles

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Geology of the High Sillaro Valley (Northern Apennines of Italy)

ABSTRACT We map the High Sillaro Valley, in the Northern Apennines of Italy. Here the Ligurian wedge overthrust the foredeep deposits of the Marnoso Arenacea formation – MA. The overthrusting occurred through a shear zone with components derived from the frontal part of the Ligurian wedge and interpreted as a tectonic mélange (Sestola-Vidiciatico Tectonic unit - SVU) here subdivided into two different subunits structurally independent one from the other. In the area, the Visignano chaotic body (VIS) constitutes an intercalation within the Serravallian-Tortonian MA and derives, as the SVU, from the frontal part of the Ligurian wedge. We performed a detailed investigation of the components of the VIS that helps to better define the architecture of the frontal part of the Ligurian wedge and to constrain the timing of the deformation phases affecting this portion of the Northern Apennines during the middle-late Miocene.

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Geophysical Characterization of Disturbances in the Phosphate Series of the OuladAbdoun, Morocco: Relationship with Atlasictectonics

The sedimentary phosphates series from the Upper Maastricht to the Lutetion of the OuladAbdoun sedimentary basin is almost identical at the basin-scale. It is made up by alternation of either phosphate or non-phosphate sub-horizontal levels. The series was characterized by rhythmic sedimentation under the form of successive elementary sequences. On the other hand, the series of SidiChennaneis distinguished by the presence of local disturbances defined by the miners under the term derangements. These derangements, which are less frequent at other mining sites (MEA Lahrech, El Hlassa, Point A), are a notable problem during extraction and remain a real obstacle at phosphate mining sites. The morphology of these derangements is almost subcircular to subconical sinkholes and chaotic bodies of anarchical materials. They are fontis type paleokarsts, it is an amalgam of highly altered yellowish brecciated rusty material whose lithological nature reflects that of the surrounding series. They also reflect endokarst siliceous and ferruginous neoformedfacies in the empty spaces of the palaeokarst. The origin of the palaeokarstshasbeen linked to the presence of NE-SW trend faults that have favoured the alteration and dissolution of the gypsum and chalk facies of the Senonian. The regular spatial distribution of these fontisis well related to the regionalAtlasictectonics. This study aims to investigate these problems in its geological aspect, in order to characterize and understand their origin. The purpose of this work isto compare the results obtained by electric tomography, gravimetry and lineament mapping and match them with geological data to draw a meaningful conclusion on the existence of these disturbances and their spatial distribution in relation to tectonic.

Sedimentary and diapiric mélanges in the Skrzydlna area (Outer Carpathians of Poland) as indicators of basinal and structural evolution

The Dukla Nappe in the Skrzydlna area exposes two types of mélange reflecting two different phases of basinal and tectonic evolution of the Outer West Carpathian orogen in its Polish sector. The Oligocene-age sedimentary mélange (olistostrome) is related to growth of the accretionary wedge, whereas the Miocene-age diapiric mélange postdates the orogenic thrusting. Textural and structural features of the very coarse-grained sedimentary mélange suggest non-cohesive debris flows and high-density turbidity currents as predominant emplacement mechanisms. Growth strata, associated with progressive unconformities, and facies contrast between the underlying fine-grained unit and the overlying olistostrome reflect a considerable uplift of the source area and rotation of the adjacent part of the basin floor. The olistostrome and the overlying turbidite succession form a retrogressive sequence interpreted as a submarine canyon infill grading to a small submarine fan. The diapiric mélange, injected into the Oligocene-age succession of the Dukla Nappe, contains the Early and Late Cretaceous-age blocks and matrix derived from the underlying Silesian Nappe. The features reflecting diapiric emplacement include matrix proportion increase and block content decrease towards the mélange margins, scaly fabric and shear zones. Both mélanges, interpreted in the past as chaotic bodies, upon detailed examination reveal genesis-related subtle internal organization.

Structure of the wedge-top and foredeep of the Magallanes-Malvinas basins between 62° W and 67° W (SW Atlantic Ocean)

This work analyzes the geometry and geodynamic development of the offshore sector (between 62° W and 67° W) of the south Magallanes and Malvinas basins wedge-top and foredeep, and associated orogenic wedge. It is based on the interpretation of more than 20,000 km of multichannel seismic profiles, along with bathymetric data. The fold-and-thrust belt front was mapped, and three structural domains were distinguished: western, transitional and eastern. A stepped foredeep characterizes the western domain with flower-structures that affect the basement, and by an intense erosion in the Miocene deposits. Towards the transitional domain, the erosion is less evident, and the wedge-top is more developed. This configuration is associated with the syn-deformational deposition and the generation of thrusts within an acoustically chaotic body in the transitional and eastern domains, deposited by processes of mass removal in the Oligocene. During the Oligocene/Miocene, the area was affected by compression/transpression, which generated an incipient tectonic inversion of the basement extensional faults, with the formation of anticlines associated with piggy-back basins in the wedge-top. The differences observed between the western and eastern domains would be related to the differential movement between the crustal blocks of Tierra del Fuego and Burdwood Bank, respectively, against the South American shelf since the Oligocene.

Signe du miroir et adolescence : entre normal et pathologique

ObjectivesDuring adolescence, girls and boys undergo profound bodily and psychic changes, which upset their relationship with themselves as well as with others. Even though chaotic body changes promise many advantages, they also cause anxieties because of the fragile nature of body image and identity. Due to narcissistic and object-relation transformations, adolescents may seek comfort in contemplating themselves in the mirror. The aim of this article is to explore the (psychic?) functions of the mirror sign, considered a normal and transitional symptom in adolescents except when bearing witness to a psychotic condition. MethodThe method is the clinical case study between two adolescent girls presenting an important mirror sign. The comparison leads to admit the idea of a continuum between normal and pathological mirror sign. ResultIf mirror sign can be a psychotic symptom, it also can be a normal narcissistic aid during this period of vulnerability. DiscussionMirror sign does not have to automatically be considered a schizophrenic symptom. One symptom can hide many psychic meanings and functions depending on the quality of narcissistic resources. ConclusionDepersonalization and inquiring admiration of ones own mirror image can too quickly be assigned to schizophrenia. Two case studies of adolescent girls with mirror sign underline its dynamic sense. In Isis's case, the mirror sign helps her to cope with the transformation of narcissism during adolescence, while in Flore's it characterizes a psychotic disorganization.

Mélanges and broken formations at the boundary zone of the Magura and Silesian nappes (Gorlice area, Polish Outer Carpathians) - a result of sedimentary and tectonic processes

Based on geological field mapping, analyses of cores from explanatory wells, and foraminiferal age control data, we have differentiated a few types of mélanges and broken formations at the bordering zone between the Magura and Silesian nappes (Gorlice area in the Polish Outer Carpathians). These mélanges and broken formations differ in composition and structure due to different settings and processes of their formation. Several levels of broken formation within the uppermost part of the Krosno Beds were formed as mass-transport deposits at the southern slope of the Silesian Basin. They may record tectonic pulses related to advancing accretionary wedge within Magura area and directly predate the stage of the larger-scale sedimentary mélange formation at the front of the wedge. This mélange is composed mainly of the material representing the Magura succession (Siary Subunit) and the Krosno type sediments of the Silesian succession. It was emplaced within the Silesian basin in the Early Miocene time. The so-called “Harklowa peninsula”, whose geological structure has been the subject of discussions and various interpretations in the past years, is built of this type of mélange. The other recognized type of broken formation and mélange represents the chaotic bodies formed at the base of the Magura Nappe.The results of our studies contribute to better understanding of the structural evolution of this part of the Outer Carpathians.

High resolution seismic data coupled to Multibeam bathymetry of Stromboli island collected in the frame of the Stromboli geophysical experiment: implications with the marine geophysics and volcanology of the Aeolian Arc volcanic complex (Sicily, Southern Tyrrhenian sea, Italy).

New high resolution seismic data (Subbottom Chirp) coupled to high resolution Multibeam bathymetry collected in the frame of the Stromboli geophysical experiment aimed at recording active seismic data and tomography of the Stromboli Island are here presented. The Stromboli geophysical experiment has been already carried out based on onshore and offshore data acquisition in order to investigate the deep structure and the location of the magma chambers of the Stromboli volcano. A new detailed swath bathymetry of Stromboli Island is here shown and discussed to reconstruct an up-to-date morpho-bathymetry and marine geology of the area compared to the volcanologic setting of the Aeolian Arc volcanic complex. Due to its high resolution the new Digital Terrain Model of the Stromboli Island gives interesting information about the submerged structure of the volcano, particularly about the volcano-tectonic and gravitational processes involving the submarine flanks of the edifice. Several seismic units have been identified based on the geologic interpretation of Subbottom Chirp profiles recorded around the volcanic edifice and interpreted as volcanic acoustic basement pertaining to the volcano and overlying slide chaotic bodies emplaced during its complex volcano-tectonic evolution. They are related to the eruptive activity of Stromboli, mainly poliphasic and to regional geological processes involving the intriguing geology of the Aeolian Arc, a volcanic area still in activity and needing improved research interest.

Characterizing a Landslide Hazard along the Wasatch Mountain Front (Utah)

Construction in mountainous areas of northern Utah is a concern due to landslide potential. As a result of dense vegetation and poor outcrops (from advanced weathering), the study of landslides along the Wasatch Mountain “Front” benefits from integrating geological and geophysical methods. We present a study of a Paleogene volcanic landslide along a portion of the Traverse Mountains. An integrated approach distinguishes an actual landslide from the weathered in situ volcanic rocks that mantle the area. We incorporate surface mapping, seismic methods, trenching, boreholes, and Light Detection And Ranging (LiDAR) to characterize the landslide. Our study reveals a faulted, chaotic body of variably altered block-and-ash flow tuffs. Multiple clay-lined shear planes and open fissures, now filled with soil, show that prehistoric landslides were focused within the altered block-and-ash flows. A major reflector lies at a depth of 80–100 m (262–328 ft) in seismic profiles, has an apparent dip of 4° to the south, and is approximately parallel to surface topography. The depth and character of this boundary indicate a contact between Paleogene volcanic rocks and underlying Paleozoic mixed siliciclastic and minor carbonate rocks. This unconformity may have acted as the slip surface for subsequent landsliding. The combination of weak block-and-ash flow tuffs and abundant clay alteration produced a body highly susceptible to multiple landslides. Using LiDAR and surface geology, discrete margins of the mapped landslide have been inferred in several areas. An integrated interpretation provides the range and resolution needed to assess the complex geology of such landslides.

Sense Violence

688 Feminist Studies 40, no. 3. © 2014 by Helena Boberg Helena Boberg Translated by Johannes Göransson Sense Violence The men in the city with stiff snakes in their hands Want to make the earth clean and beautiful again With desire fluttering around them they search for hidden rich milk-veins among maimed bodies whose raw fumes excite them in ever widening circles Where have they learned this destructivity so deep and disguised? The chaotic bodies that still live —do they hide something in their organs’ inner chaos? Children crush their eyes with living stones The women’s bellies swelling algae sacs in the tracks of these dynamic rites The images stiffen and the game slows down Elastic time compresses these moments into meaningless rhymes Erupts again into split tongues Helena Boberg 689 Here starts the disenchantment of the world and the moon falters The poppy has taken off its red dress The throat soft and open for life Away from this place Let me open like an egg Dark summer closes its eyes Drools its water against clinking ground Water pearls That man is so beautiful The flowers hunger as after breast milk Late summer nothing at all sails parallel with the sun’s cranium The neck almost comes loose 690 Helena Boberg The throat soft and open for life lily-red cleft-lip The heavy flour-breast that powders I want to return to everything rain simple things hatred opened to the marvelous Dream about the sanitarium its set boundaries White cube where we moved freely Appeared insane Then the men gather (because of her dress) in clusters Call on her with their shuddering snakes How funny they look from here : Same kinds of hands on the same kinds of breasts And the egg runs from her mouth The fertile darkness’s raw fumes fools Helena Boberg 691 the mouth into begging like a sick person for the electroshocks’ releasing spasm the muffled cigarette smoke or the sweet that fixes one’s own palate in the middle of the world Isn’t it true that tongues have never collapsed as in the hall for ruined bitches lords geniuses Our games seemed like ballets of poorly handled marionettes An inverted social order with narcotic aftertaste where balance is reached in a sleeping state Rage a foreboding side effect We slept and slept Promiscuous fallen fruit with an ache that fell asleep at the same time as us 692 Helena Boberg But started over as soon as we again opened our eyes In the same moment as the temporal bone was anaesthetized for the electricity’s symmetrical branching-out which would fill me with a fantastic happiness I was taken to this sorrow chasm of all things’ inner time (It’s long ago, the shout was another) There is only this violent human society that resembles a wronged mind ...

Le Brecce argillose di Musigliano (Appennino Vogherese – Tortonese): dati stratigrafici preliminari

The Musigliano argillaceous Breccias (Voghera and Tortona Apennines): preliminary stratigraphic data.An integrated biostratigraphic study based on foraminifers and calcareous nannofossils has been performed on two chaotic bodies involved within the Epiligurian pelitic sequence outcropping in the Alessandria and Pavia Apennines (M. Penola & M. Vallassa area), allowing to define the age of their emplacement. The investigated deposits mainly consist of strongly tectonized sediments ensuing from the Ligurian substratum mainly through submarine cohesive mud flows and lithic debris. These chaotic bodies have been previously considered (Gelati et al., 1974; Gelati & Vercesi, 1994) as involved within the Antognola Formation and correlated with similar Lower Miocene deposits widespread in Northern Apennines (Canossa Olistostrome, Val Tiepido-Canossa argillaceous Breccias). Dissenting from previous interpretations, our study shows that these chaotic bodies, named here as “Musigliano argillaceous Breccias” were displaced in an interval between Late Eocene and Early Oligocene. In fact, the biostratigraphic analyses of the marlstones under the chaotic bodies indicate they are attributable to the P15 and P16 planktonic foraminifer biozones of Berggren et al., (1995) corresponding to the G. semiinvoluta and T. cerroazulensis biozones of Mancin et al. (2003). The same pelitic rocks are relatable to the MNP19/20 nannofossil biozone of Catanzariti et al. (1997), corresponding to the NP19/20 of Martini (1971). The Epiligurian marlstones and turbiditic mudstones upon the Musigliano argillaceous Breccias fall in the P19 p.p. / P20 (corresponding to the G. ampliapertura biozone, Mancin et al., 2003) corresponding to the MNP23 biozone (Catanzariti et al., 1997) and to the NP23 biozone of Martini(1971). We correlate the pelitic rocks under the Musigliano argillaceous Breccias to the uppermost part of the Monte Piano Marls (“grey lithofacies” according to Mancin & Cobianchi, 2000 and Panini et al., 2002), and the marlstones and turbiditic mudstones upon the sedimentary chaotic bodies to the Ranzano Formation, on the basis of lithologic features and age. The displacement of the Musigliano chaotic breccias marks a strong stratigraphic break in the Epiligurian sequence; it could be related to events (probably of tectonic nature) previously reported as affecting the lower part of the Epiligurian succession and the coeval sequence of the Tertiary Piedmont Basin (Mutti et al., 1995; Catanzariti et al.,1997; Martelli et al., 1998; Ottria et al., 2001). As in the Emilia south-easternmost Apennines, the Oligocene-Lower Miocene Epiligurian sedimentary record seems to be devoid of typical resedimented arenaceous bodies generally characterizing the Ranzano Formation also in the studied area.

Mechanisms and processes of stratal disruption and mixing in the development of mélanges and broken formations: Redefining and classifying mélanges

The terms mélange and broken formation have been used in different ways in the literature. The lack of agreement on their definition often leads to confusion and misinterpretations. An evaluation of the various uses of these terms allows us to consider several types of chaotic rock bodies originated by tectonic, sedimentary and diapiric processes in different tectonic settings. Our review of stratal disruption and mixing processes shows that there exists a continuum of deformation structures and processes in the generation of mélanges and broken formations. This continuum is directly controlled by the increase of the degree of consolidation with burial. In tectonically active environments, at the shallow structural levels, the occurrence of poorly consolidated sediments favors gravitational deformation. At deeper structural levels, the deformation related to tectonic forces becomes gradually more significant with depth. Sedimentary (and diapiric) mélanges and broken formations represent the products of punctuated stratal disruption mechanisms recording the instantaneous physical conditions in the geological environment at the time of their formation. The different kinematics, the composition and lithification degree of sediments, the geometry and morphology of the basins, and the mode of failure propagation control the transition between different types of mass-transported chaotic bodies, the style of stratal disruption, and the amount of rock mixing. Tectonically broken formations and mélanges record a continuum of deformation that occurs through time and different degrees of lithification during a progressive increase of the degree of consolidation and of the diagenetic and metamorphic mineral transformation. Systematic documentation of the mechanisms and processes of the formation of different broken formations and mélanges and their interplay in time and space are highly important to increase the understanding of the evolutionary history of accretionary wedges and orogenic belts.

Small-scale polygenetic mélanges in the Ligurian accretionary complex, Northern Apennines, Italy, and the role of shale diapirism in superposed mélange evolution in orogenic belts

The Argille varicolori (Varicolored scaly clays) of the External Ligurian Units of the Northern Apennines have been widely described as a typical unmetamorphosed broken formation (i.e., a chaotic unit without exotic blocks), produced by offscraping and tectonic imbrication during the evolution of the Ligurian accretionary wedge. Geological mapping and integrated structural and stratigraphic observations show that the Argille varicolori consist of diverse types of small-scale mélanges (non-mappable at a 1:25,000 scale) forming a composite chaotic unit, in which the superposition of tectonic, sedimentary and diapiric processes resulted in the occurrence of polygenetic chaotic bodies at different scales. These mélange units record the evolution of the Ligurian accretionary wedge from subduction to collision and intracontinental deformation. Tectonically Disrupted Body 1 (TDB1) comprises boudinage and pinch-and-swell structures formed by layer-parallel extension/contraction at the wedge front of the Ligurian accretionary complex during the late Cretaceous–middle Eocene. It is interleaved with non-mappable Gravity-driven Chaotic Bodies (GCB) developed during alternating episodes of accretion and removal of material at the wedge front. The late Oligocene–early Miocene out-of-sequence thrusting related to the collisional episodes in the Apennines overprinted the previously formed chaotic bodies and formed a polygenetic tectonic mélange (Tectonically Disrupted Body 2, TDB2). This unit is characterized by a structurally ordered block-in-matrix fabric and by the gradual decrease of stratal disruption away from the regional thrust. Overpressurized fluids concentrated along the shear surfaces, and the scaly cleavage planes facilitated the diapiric upward movement of unconsolidated sediments in the early Miocene. This process produced non-mappable shale dike injections (DDB1) and mappable Diapirically Disrupted Bodies (DDB2), which show an internal zonation of deformation. This deformation reworked the previously formed chaotic bodies. Although some of these polygenetic mélanges cannot be mapped at a 1:25,000 scale, their careful documentation provides a better understanding of time-progressive, scale-independent mélange-forming processes.

Mélanges and mélange-forming processes: a historical overview and new concepts

Mélanges represent a significant component of collisional and accretionary orogenic belts and occur widely around the world. Since its first introduction and use, the term has evolved to cover both processes (tectonic, sedimentary, and diapiric) and tectonic settings of mélange formation. The meaning and significance of various terms referring to the origin of ‘block-in-matrix chaotic rocks’ are still subject to debate. This study presents a historical overview of the evolving mélange concept and investigates the relationships between mélange types and their tectonic settings of formation. We investigate the contribution of mass-transport versus contractional deformation processes at the onset of mélange formation and throughout the evolution of different mélange types, and the nature of the continuum and transition from broken formations to true tectonic mélanges. A mélange is a mappable chaotic body of mixed rocks with a block-in-matrix fabric whose internal structure and evolution are intimately linked to the structural, sedimentary, magmatic, and metamorphic processes attending its origin. On the basis of a comparative analysis of exhumed, ancient on-land mélanges and modern tectonic environments, where mélange-forming processes are at work, such units are classified into those related to extensional tectonics, passive margin evolution, strike-slip tectonics, subduction zones, collisional tectonics, and intracontinental deformation. Sedimentation and contractional deformation contribute significantly to mélange formation in all these tectonic environments, although the internal structure of deposits is strongly controlled and overprinted by processes that prevail during the last stages of mélange formation in a single tectonic setting. Tectonic mélanges are commonly subordinate to broken formations and are restricted to narrow, elongated-to-coalescent fault zones, large-scale fault zones, and plate boundaries.

Perched lobe formation in the Gulf of Cadiz: Interactions between gravity processes and contour currents (Algarve Margin, Southern Portugal)

The Gulf of Cadiz is swept by the strong saline Mediterranean Outflow Water (MOW). On the Algarve Margin (South Portugal), this current has constructed fine-grained contourite drifts. This margin is dissected by the Portimao Canyon and three short channels that only incise the upper slope, and are absent on a terrace located at mid-slope depths along the Algarve Margin. High-resolution seismic profiles and sediment cores highlight the original architecture of the sedimentary deposits on this terrace. Coarse-grained lenticular chaotic bodies formed during major relative sea-level lowstands are intercalated within the drift. The lobate shape and sandy nature of the lenticular chaotic bodies and their location at the mouths of the three short channels suggest they are gravity-generated deposits that are perched on the middle continental slope. In the Gulf of Cadiz, the interaction between contour current and gravity processes is strongly controlled by climatic variations and relative sea-level changes during the late Quaternary. During cold periods when sea-level was low, erosion intensified on the continental shelf and the deepest part of MOW was active. Sediment was transported downslope through the channels and deposited on sedimentary lobes perched on the mid-slope terrace. During warm periods when relative sea-level was high, the supply of sediment from the shelf was shut off and the shallowest part of MOW was more active. Contourite drifts fill the channels and bury the sandy lobes.

Mud volcanoes, olistostromes and Argille scagliose in the Mediterranean region

AbstractTectonic and sedimentary mélanges, rocks with block‐in‐matrix fabric often referred to as ‘chaotic’, are widespread in the circum‐Mediterranean collisional orogenic belts as well as in submerged Mediterranean Arcs. These rock types have been defined originally as ‘Argille scagliose’ (Bianconi, 1840) and ‘olistostromes’ (Flores, 1955, 1959) in the outcrops of the Apennine chain (Italy). Both terminology and concepts have undergone a rather complex evolution through time owing to the gradual recognition of similar chaotic bodies in all the circum‐Mediterranean orogenic belts. Submarine mud volcanoes of the Mediterranean region, also composed by block‐in‐matrix, more commonly referred to as mud breccias, have a much younger history. These mud breccias were discovered in 1981 and, since then, a growing number of sea‐going geophysical and geological expeditions have allowed the recognition of a major mud volcano belt in the Eastern Mediterranean and of a number of mud diapirs and mud volcano fields from the Black Sea to the Gulf of Cadiz. Structural, textural and genetic similarities between the mud breccias of the Mediterranean mud volcanoes and the olistostromes and Argille scagliose of the Apennines were noted from the very beginning, but the matter has not been the focus of any detailed study. In this paper, the use of the terms in the geological literature is analysed, the distribution of these rock units in the Mediterranean region explored and the assumed genetic processes are identified in order to formulate a common genetic model that can be applied to the evolution of the circum‐Mediterranean sedimentary basins.

DISABLED BODIES AND STORIED SELVES: AN EXAMPLE OF QUALITATIVE RESEARCH AND NARRATIVE INQUIRY

Based on life history data, this qualitative article explores the self-perceptions of a small group of men who, due to a spinal cord injury (SCI) through playing rugby union football, have made a transition from the world of the able-bodied into the world of disability where they remain to this day. The most common kinds of perceptions of self used by the men through telling their stories as they live post-SCI is focused upon in detail. The narrative analyses reveal that three types of narratives help structure and shape the ways in which these men storied their embodied perceptions of self. For the majority of the participants, the restitution narrative was drawn on, and this helped structure a restored self and entrenched self, and was linked to a disciplined body. In contrast, two people told quest narratives that constitute a perception of a self that is developing and affirmative, and a body that is communicative. For one person, the chaos narrative was foregrounded that resulted in a fragmented self-perception and a chaotic body in action. The implications of all this for disabled people's body-self relationships are critically considered.

Adaptive synchronization of chaotic systems via linear balanced feedback control

Synchronization of a chaotic rigid body system via adaptive linear balanced feedback control is investigated in this paper. Firstly, we obtain feedback gains by linear feedback control scheme based on Lyapunov stability theory and constrained extreme strategy. Next, using the result of the analysis, an adaptive linear balanced feedback controller is designed for chaos synchronization. The proposed scheme can be implemented without requiring the upper bound of the trajectory of a chaotic system in advance. Numerical simulations are provided to verify the effectiveness and feasibility of the designed synchronization schemes.

The structure of the Atlantic–Mediterranean transition zone from the Alboran Sea to the Horseshoe Abyssal Plain (Iberia–Africa plate boundary)

The diffusive plate boundary between Iberia and Africa has been analyzed by means of already published and new 28 multichannel seismic profiles covering most of the Atlantic margins of SW Spain and NW Morocco. This region includes the prolongation of the Betic–Rifean tectonic units along the Gibraltar Arc. One of the most characteristic units in the study area is the Miocene seismically chaotic unit that has been divided in a tectonic and a gravitational domains in accordance to previous interpretation by Torelli et al. [Torelli, L., Sartori, R., Zitellini, N., 1997. The giant chaotic body in the Atlantic Ocean off Gibraltar: new results from a deep seismic reflection survey. Marine and Petroleum Geology 14, 125–138.]. In this work we redefine the limits of both domains and rename them as the Gulf of Cadiz Imbricate Wedge and the Horseshoe Gravitational Unit. We interpret the Gulf of Cadiz Imbricate Wedge as a west-migrating thick thrust system that build up in a relatively short period of time. This unit constitutes the continuation of the Miocene chaotic units observed onshore to the front of the External Units in the Betics and the Rif (the Guadalquivir Allochthonous Unit and the Rides Prerifaines). The Horseshoe Gravitational Unit, covering an approximate area of 18 000 km 2 with a volume of around 23 000 km 3, is interpreted as giant submarine debris flows sourced from the up-building of the Gulf of Cadiz Imbricate Wedge, surrounding basement highs and the continental Iberian Slope. The fast westward migration of the Flysch units, the External Units and the Gulf of Cadiz Imbricate Wedge, from the Early Miocene to the Late Tortonian corresponds to a different tectonic process than the protracted but slow NNW to NW convergence of Africa. Our interpretation favours the westward slab retreat theory to form the arcuate shape of the Atlantic side of the Iberia–Africa plate boundary. The subduction mechanism as well as potential roll-over was only active from late Early Miocene to Late Miocene spanning about 12 Myr.