Main Detachment Research Articles

Footwall refrigeration versus footwall hydration: Reassessing steep thermal gradients below detachment faults with in situ SIMS oxygen isotope analysis

The extensional detachment systems of metamorphic core complexes (MCC) have the potential to facilitate significant fluid movement between Earth's surface and the warm, ductile middle crust. One long-standing and influential detachment fault-fluid interaction model called the “footwall refrigeration hypothesis” (Morrison and Anderson, 1998) postulates that cool meteoric fluids circulating downward along a detachment can facilitate large-scale heat loss at depth before rocks are exhumed by faulting. Stable isotopes of oxygen and hydrogen have long been recognized as potentially useful tracers of surface-to-depth fluid flow in core complexes; however, typical sampling methods and the competing effects between temperature and fluid composition have made oxygen isotope signatures of meteoric fluid infiltration difficult to detect and/or interpret in the rock record.Here, we use in situ δ18O measurements by secondary ion mass spectrometry (SIMS) to address the rock record of meteoric fluid interactions and temperature variation within the Whipple Mountains MCC footwall beneath the Whipple detachment fault (WDF). The micro-scale sampling of SIMS (10 µm diameter x 1–2 µm deep pits) allows investigation of isotope variability as a function of mineral geochemistry and microstructure and enables more accurate interpretation of the causes of isotope variability. In the Whipple footwall mylonites, quartz and epidote show grain-to-grain oxygen-isotope variability within samples and as a function of distance from the main detachment. Approaching the WDF, both quartz and epidote show increasing spread toward low δ18O values. The lowest SIMS-measured δ18O epidote values require exchange with a low δ18O, meteoric fluid at high temperature. However, SIMS data also reveal that meteoric fluid-rock interactions were spatially heterogeneous at the scale of individual grains, resulting in local preservation of metamorphic quartz-epidote oxygen isotope equilibrium unaffected by infiltrating meteoric fluid. Within preserved metamorphic domains at all investigated structural levels of the WDF footwall, quartz and epidote δ18O values are tightly clustered and yield similar fractionations (∆18Oqz-ep). For samples from the longest footwall traverse, these ∆18Oqz-ep values are 4.0 ± 0.4‰, consistent with δ18O equilibrium at 521+43/-37 °C. We conclude that there is no evidence of a large paleo-thermal gradient associated with the Whipple Detachment Fault (i.e., no evidence for footwall refrigeration).

Effect of humidity on atmospheric pressure humid air discharge—interpretation from the perspective of detachment reactions

Detachment reactions have an important influence on the decreasing trend of electron density after high-field excitation, yet existing studies on humidity’s impact on discharge have failed to address this issue. To bridge this gap, we utilize a validated global model to explore how species density changes during humid air discharge corona inception. Our results indicate that humidity influences the detachment reaction rate by altering the negative ion composition. In dry conditions, the primary species involved in detachment reactions is O− ions. However, in environments with higher water vapor density, O− ions primarily react with water molecules, depleting O− ions. This change results in H− ions becoming the main detachment negative ions during the pulse. The greater the rate of the Detachment reaction the slower the decrease in electron density, and a rise in humidity causes the Detachment reaction to peak at a higher value and have a shorter duration, thus causing the electron density to decrease more rapidly. This discovery offers fresh insights into humidity’s effect on discharges. Additionally, we introduce the concept of the average negative ion detachment reaction rate constant, denoted as k d, to quantify the impact of detachment reactions within the three-element model.

Interaction between shallow and deep structures: Forward-modeling kinematics sequence of a fold-and-thrust belt with double detachment

It is crucial to determine the sequence of deformation and the interaction between shallow and deep structures within the multiple detachment systems to comprehend geological processes fully in fold-and-thrust belts (FTBs). Here, we implement forward modeling to investigate the geometric, kinematic, and syntectonic sedimentary characteristics of shallow and deep structural interactions. We design four combinative patterns of geometric structures, three kinematic sequence scenarios, and two settings with different ratios of the sedimentation rate to the uplift rate to examine the influence of such settings on growth strata geometry. The most effective results of 24 groups of shallow and deep structural interactions were obtained for various combinations of fault-bend fold, detachment fold, and tectonic wedge. This study provides a sequential kinematic image of FTBs, illustrating the interaction of two sets of detachments and demonstrating how different styles of pre- and growth strata can be utilized to identify shallow and deep structure deformation processes. The geometry of pre- and growth strata observed in the models is similar to that observed in natural structures. These forward models facilitate a better understanding of the complex geometry and kinematics of the interaction between shallow and deep fault-related folds.

Thrust tectonics in the Fuegian Andes central belt: A detailed geometric-kinematic analysis and new thermochronological constraints

New structural data from the central belt of the Fuegian Andes (Argentina), allowed us to constrain the geometry of a previously interpreted Cenozoic duplex thrust system that connects forelandwards with the frontal thrust-fold belt. This duplex developed between two main detachment horizons: a basal detachment between Jurassic rocks and pre-Jurassic basement, and a roof detachment between Jurassic rocks and the Lower Cretaceous sedimentary fill of the Rocas Verdes back-arc basin. The duplex constitutes an intermediate structural level within a multiple detachment thrust belt and covers deeper structures that accommodated crustal deformation during the Cenozoic evolution of the Fuegian Andes. New zircon and apatite fission track and (UTh)/He cooling ages from rocks within the duplex were modelled together with previously published data, finding time-temperature trajectories that indicate acceleration in cooling rates during the middle Eocene to earliest Miocene, but with more moderate rates than previously reported. This is interpreted as exhumation associated with rock uplift due to duplex thrusting in the hinterland and shortening transference to the foreland, where known contractional stages are as young as early Miocene, and Oligocene-Miocene increased supply of detritus from the eroded central belt is widely reported.

Several types of triangle zones from the Subandean ranges of Peru: Fish-tails, tectonic wedges and passive-roof duplexes

Surface geology, well data and 2D seismic interpretations reveal the presence of triangle zone structures at the contact of the Subandean Ranges and the Amazonian foreland in Peru. From north to south the Santiago, Marañon, Ucayali and Madre de Dios basins have been studied. Interpretations presented in this study show a great variety of structural styles at this contact area. Simple triangle zones with one back thrust, composite ones with several back thrusts, more complex double vergent ones with pop-up structures, best described as fish-tails, tectonic wedges and passive-roof duplexes are present in the study area. The role of pre-Andean tectonics and paleogeography is key to understanding the Andean evolution, due to the control on the location and geometry of the main detachment levels. The Santiago Basin is characterized by the presence of fish-tail structures with a Permian-Triassic evaporitic basal detachment located at the base of the Pucara Gr. At the Ucayali Basin, several detachment levels interact, the basal ones located within the Ordovician, Devonian, and Carboniferous defining triangle zones or tectonic wedges. At the Madre de Dios Basin, two detachment levels define the base of the triangle zone, Permian shales in the northwest at the Inambari Imbricates area, and Lower Devonian (Cabanillas Gr.) in the southeast at the Candamo area. A roof thrust is located within the Paleogene section at both the Madre de Dios and Ucayali basins, defining passive-roof duplex structures.Several detachment levels are rooted into the Lower Paleozoic; others within the Permian-Triassic section, being locally evaporitic, and finally others are located at the base of the Cretaceous. Paleozoic shales represent the main basal detachment level of the southern Subandean ranges. The role of these detachments and the role of the sedimentation rate are discussed as factors that control the development and geometry of the triangle zones described in the study area.Except for the San Martin-Sagari area of the Ucayali Basin, the triangle zones of the Santiago and Madre de Dios basins remain unexplored even though active petroleum systems are present. Sub-thrust structures at the Azulmayo area of the Madre de Dios Basin remain promising undrilled structures.

Tectono-stratigraphic evolution, regional structure and fracture patterns of the Zagros fold-thrust belt in the Duhok region, Kurdistan, northern Iraq

This study is the first detailed investigation of the tectono-stratigraphy, regional structure and mesoscopic fractures of the Zagros fold-thrust belt in the Duhok region, Kurdistan, Northern Iraq, and is based on field studies, remote sensing-GIS analyses, cross-section restorations, and tectonic analysis of key structures. The Duhok fold belt is a frontal zone of the north-western part of the Zagros fold and thrust belt in the Kurdistan region near the north-eastern margin of the Arabian Plate. It is characterized by WNW-ESE striking, doubly-plunging, upright symmetric to asymmetric detachment folds that involve ~8.2–10.9 km of Paleozoic to Quaternary strata. These folds vary from 5 to 75 km long, 4–20 km wide and have a surface relief (caused by basement uplift) up to 3.2 km. Five regional and twelve local structural cross-sections were constructed parallel to the regional SSW tectonic transport and perpendicular to the fold axial trends. Section lengths vary between 4.94 km and 101.55 km. Two main detachment levels have been inferred for the Duhok fold belt. A deep basal detachment was placed at the base of the Paleozoic successions within the Ordovician shales of the Khabour Formation at depths from 8 km to 10 km. Shallower, intermediate detachment levels occur within the shales and evaporites of the Mid-Upper Permian and Upper Jurassic strata at depths 1.7 km in the frontal sectors to around 5.5 km in the hinterland. The thickness of the Paleozoic succession in the Duhok fold belt is ~2 km. Deformation by thin-skinned detachment folding together with thick-skinned thrusting is inferred to have occurred in the Duhok region from the Mid Miocene through to the Present-Day. The maximum NNE-SSW-directed shortening produced by detachment folding was about 18.62 km (19.71%) over a section length of 94.45 km. The maximum shortening along thrust faults was around 1.98 km (1.95%) over a section length of 101.55 km. The mesoscopic fracture patterns in the study area were grouped into two major extension sets, four major shear-hybrid sets and eight minor shear-hybrid sets. Field characteristics and relative chronology indicate that most of the fractures are tectonic in origin, and they developed before (i.e., pre-folding fractures) and during (i.e., early- and late-folding fractures) the Mid Miocene folding in the Duhok fold belt.

Potential seismic precursors and surficial dynamics of a deadly Himalayan disaster: an early warning approach

On 7 February 2021, Chamoli district (Uttarakhand, India) was devastated by a deadly rock-ice avalanche that led to a large causality of more than 200 people and a huge economic loss. We found noteworthy sequence of precursory signals of main failure/detachment preceded by a dynamic nucleation phase. The rock-ice avalanche appears to have been initiated by seismic precursors which were continuously active for 2:30 h prior to main detachment. The seismic amplitude, frequency characteristics and signal-to-noise ratio variation of detected tremors indicate static to dynamic changes in nucleation phase located at the source of detached wedge. The characteristics of seismic data distinguished debris flow and hitting obstacles from other seismic sources and allowed the estimations of debris flow speed. We analyzed and verified the seismic signals with field evidences to estimate the associated impacts and velocity of dynamic flow. The proximal high-quality seismic data allowed us to reconstruct the complete chronological sequence and evaluate impacts since the initiation of nucleation phase to its advancement. Furthermore, we suggest that real-time seismic monitoring with existing network and future deployment of integrated dense network can be used for forecasting of flow events and hazard mitigation in the downstream.

Triassic evaporites and the structural architecture of the External Hellenides and Albanides (SE Europe): controls on the petroleum and geoenergy systems of Greece and Albania

A combination of well data, seismic information on thrusting and tectonic shortening, plus analyses of the nature and depth of the Mesozoic units related to main detachment horizons (Triassic evaporites, flysch), are used to review, and further update the complex structural styles of the External Hellenides and Albanides Orogenic Belts, SE Europe. In the study area, the late Alpine orogenic evolution resulted in a structural architecture characterised by the successive westward thrusting of tectonic nappes (Gavrovo/Kruja, Ionian), with an imbricate tectonic style prevailing in all external zones. In the internal and central Ionian zone, imbricate thrusts and duplex structures are recorded, especially where about 24 km of stacked Mesozoic–Tertiary successions have been formed in Albania. Triassic evaporites, up to 3.5 km thick, acted as a detachment horizon for the internal deformation of the Ionian and Pre-Apulia zones (1.7–1.8 km thick in Greece), whereas the flysch unit of Upper Eocene–Oligocene (External Hellenides) and Oligocene–Aquitanian (Albanides) contributed to the deformation of the Ionian zone. In the Ionian zone, Triassic evaporites are laterally continuous and act as an effective seal unit when thrusted above Mesozoic carbonate/Tertiary units. Most of the oil and gas fields, oil shows and surface seeps have been developed in association with the relative more complex structure styles in the internal and the central Ionian zone of Albania and Greece. The Triassic evaporite detachment is detected at depths of 8–22 km in Albania, and about 5 km to 12–13 km in Greece. Thin and probably combination of thin- and thick-skinned deformation (SW Greece) of the Meso-Cenozoic succession above the Triassic evaporite and Permian sequences better depicts the complex structural architecture of the External Hellenides and Albanides, later affected by strike-slip tectonics and extensional deformation active since the Early Pliocene times. The main source rock levels, Lower Cretaceous shale/carbonate, Toarcian Posidonia and Triassic shales, are common in the Albanides and the Hellenides forelands. The thickness and Total Organic Carbon of these levels significantly increase in Albania, whereas trapping mechanism is almost the same and the Triassic evaporites play a significant role in both forelands. The hydrocarbon migration primarily followed developed thrust faults and important halokinesis, to charge fractured Cretaceous–Eocene carbonate reservoirs in the overthrust unit (Ionian zone), likely beneath the thrusted anticlinal belts. These sub-thrust structural models are related to the evaporites. Sub-thrust plays, referred to the autochthonous units (Apulia, Pre-Apulia/Paxos, Sazani zones), may also present reservoir potential in Albania and Western Greece. Upper Miocene and Pliocene deposits (sands) record reservoir potential in stratigraphic traps and good caprock characteristics in the Peri-Adriatic depression (Albania), whereas Messinian evaporites and clays may document seal potential for Upper Miocene sands in the southern areas of the Ionian Sea (Kyparissiakos Gulf, SW Kythira).

Theoretical Limits in Detachment Strength for Axisymmetric Bi-Material Adhesives

AbstractReversible dry adhesives rely on short-ranged intermolecular bonds, hence requiring a low elastic modulus to conform to the surface roughness of the adhered material. Under external loads, however, soft adhesives accumulate strain energy, which release drives the propagation of interfacial flaws prompting detachment. The trade-off between the required compliance, for surface conformity, and the desire for a reduced energy release rate, for better strength, can be achieved with a bi-material adhesive having a soft tip and a rigid backing (RB). This design strategy is widely observed in nature across multiple species. However, the detachment mechanisms of these adhesives are not completely understood and quantitative analysis of their adhesive strength is still missing. Based on linear elastic fracture mechanics (LEFM), we analyze the strength of axisymmetric bi-material adhesives. We observed two main detachment mechanisms, namely (i) center crack propagation and (ii) edge crack propagation. If the soft tip is sufficiently thin, mechanism (i) dominates and provides stable crack propagation, thereby toughening the interface. We ultimately provide the maximum theoretical strength of these adhesives obtaining closed-form estimation for an incompressible tip. In some cases, the maximum adhesive strength is independent of the crack size, rendering the interface flaw tolerant. We finally compare our prediction with experiments in the literature and observe good agreement.

Contractional salt tectonics and role of pre-existing diapiric structures in the Southern Pyrenean foreland fold–thrust belt (Montsec and Serres Marginals)

Triassic Keuper evaporites have long been recognized as the main detachment level for thrusting in the Pyrenean fold–thrust belts. The deformed Late Cretaceous–Eocene foreland basin of the Southern Pyrenees has structures and stratal geometries that can be interpreted as related to salt tectonics (e.g. unconformities, rapid thickness variations, long-lived growth fans and overturned flaps), although they have been overprinted by shortening and thrusting. Based on field observations and published maps, we build new structural cross-sections reinterpreting two classic transects of the Southern Pyrenees (Noguera Ribagorçana and Noguera Pallaresa river transects). The sequential restoration of the sections explores the variations in structural style, addressing the role of halokinesis in the tectonic and sedimentary development. In the Serres Marginals area, we propose that salt pillows and diapirs started developing locally during the Mesozoic pre-orogenic episode, evolving into a system of salt ridges and intervening synclines filled with early synorogenic sediments. Rapid amplification of folds recorded by widespread latest Cretaceous–Paleocene growth strata is taken as marking the onset of contractional folding in the area. During Pyrenean compression, folding mechanisms transitioned from dominantly halokinetic to a combination of buckling and differential sedimentary loading. Squeezing of salt diapirs and thrust welding occurred as salt ridges were unroofed. We provide new field observations that lead to a reinterpretation of the regional structural development and contribute to the debate about the role of salt tectonics in the Pyrenees. Supplementary material: Table S1, giving the thickness of the main stratigraphic units, is available at https://doi.org/10.6084/m9.figshare.c.5287737

A structural analysis of the Washita Valley Fault in the southeast Anadarko Basin

We propose that the Washita Valley Fault in the southeast Anadarko Basin originated when Precambrian-Cambrian preexisting rift-related faults became reactivated as a rotational stress field reached a favorable orientation for strike-slip displacement. During the Early to Middle Pennsylvanian, contractional deformation dominated as a Precambrian-Cambrian failed rift underwent structural inversion along a northeast-directed stress field. Structures that developed in the basin consisted primarily of thin-skinned fold-thrust structures resulting from slip along two main detachment levels. By the Late Pennsylvanian, stress rotated toward the east–northeast causing left-lateral strike-slip displacement along east–west-oriented structures. During this time, the Washita Valley Fault originated from an east–west-oriented preexisting basement fault. The Washita Valley Fault formed as a near-vertical segment cutting through the earlier fold-thrust structures. Movement was accompanied by oblique normal slip allowing grabens to develop that were subsequently filled with Virgilian-age sediment. A left step of the Washita Valley Fault allowed for a significant graben to develop near the east end of the study area resulting in a thick Virgilian-age growth section validating the timing of the fault movement. The Wichita Mountain Fault also underwent a component of left-lateral strike-slip displacement during the Late Pennsylvanian highlighting its continuous movement and deformation history in a rotating stress field. Although much of the published literature on the Washita Valley Fault is limited to the Arbuckle Uplift, our study documents its subsurface architecture, timing, and structural history in the southeast Anadarko Basin using a modern 3D seismic data set in relation to evolving Pennsylvanian tectonics.

«Исламское государство провинции Хорасан» – угроза Центрально-азиатскому региону

Over the past several years, there has been an influx of immigrants from Central Asian states into the ranks of “Islamic State” (IS) militants in Syria and Iraq. Those who survived after the defeat of the main detachments of terrorists on their return cannot escape the territory of Afghanistan, the northern regions of which are inhabited by related ethnic groups. It is easy to find supporters of radical Islam in Central Asian countries. The weakness of state and public institutions contributes to the politicization of Islam, especially in the periphery. Islamist preachers, skillfully using the mistakes of local authorities, call for the creation of alternative state structures. Most of the former IS fighters do not hide their intentions to return home. They can gain support in the border provinces of Afghanistan, among their comrades-in-arms in the war, and also join some of the Taliban groups. The planned withdrawal of American troops and their allies from Afghanistan does not yet imply the coming of peace in the region. Therefore, among the main threats to the security of the region are the activities of transnational terrorist groups such as “The Islamic State of Khorasan Province”, “The Islamic Movement of Uzbekistan” and “The Islamic Movement of Eastern Turkestan”.

Geomorphological and geophysical surveys with InSAR analysis applied to the Picerno earth flow (southern Apennines, Italy)

Landslides represent a major geomorphological feature influencing the evolution of the southern Apennine slopes with earth flows being one of the most representative types of landslide. The development of earth flows in the southern Apennines is facilitated by the widespread occurrence of clayey lithologies. Earth flows can either produce marked scars along the slopes, when their activity is high, or give rise to bumpy areas that are frequently covered by vegetation, when their activity is low. In this latter case, although the risk is significantly reduced, the earth flow can still represent a problem for buildings and infrastructure. The Picerno earth flow in the Basilicata region is an example of a low-activity earth flow. This NW-SE–oriented landslide extends for a length of ~ 5.5 km, has an average width of ~ 680 m, and affects the village of Picerno. Our investigations mainly focused on the terminal portion of the landslide and revealed that some significant linear infrastructures (e.g., the Potenza–Naples railway) and important provincial and municipal roads are affected by the earth flow. In order to better define the amount of displacement characterizing the Picerno earth flow and gain insights into the lateral extension and the depth of the main detachment surface, we undertook a detailed geological and geomorphological survey. Interferometry synthetic aperture radar data provided by the processing of SAR images, with the aim of highlighting the regions of the landslide that are currently active, together with electrical resistivity tomography data which have been utilized to define the geometry of the landslide body. Our results provide useful suggestions for planning appropriate actions aimed at stabilizing the landslide body.

Four-dimensional analog and geometrical modeling of the Hides anticline, Papua New Guinea: Structure of a giant gas field

The Hides anticline in the Papua New Guinea fold belt is the core part of the Papua New Guinea liquified natural gas project that commenced production in 2014, yet little is known about its internal structure, particularly at depth. The structure of the upper 3 km (9843 ft) is relatively well constrained from surface data, recent development wells, and poor-quality two-dimensional seismic data, but the deep structure has been obscure. Seismic data and gravity modeling suggest an underlying large normal fault in basement. Forward geometrical modeling using MoveTM and four-dimensional analog sandbox modeling under an x-ray tomography scanner have greatly constrained the structural interpretation. The modeling confirms the presence of the underlying basement normal fault and suggests that it was mildly inverted prior to the onset of pure compression deformation in the sedimentary section. The main detachment level was just above basement approximately 8–10 km (∼5–6 mi) beneath the surface, but this ramped up at the basement fault creating an array of triangle-zone faults through the overlying sedimentary section, building the Hides anticline. The early inversion was instrumental in initiating a back thrust and hinterland-verging tight fold in the Mesozoic section, including the source, reservoir, and seal. Deformation in the thick Miocene carbonates at the surface was detached from that in the underlying reservoir along an Upper Cretaceous mudstone horizon that varies strongly in thickness such that the 2–4-km (6562–13,123-ft)-high Mesozoic structure verges northeast and the overlying Miocene structure verges southwest. Analog modeling shows that a ductile stratigraphy is required with slow strain rates of approximately 1–3 km/m.y. (∼3281–9843 ft/m.y.).

The influence of a weak upper ductile detachment on the Longmen Shan fold-and-thrust belt (eastern margin of the Tibetan Plateau): Insights from sandbox experiments

The topic of the Longmen Shan fold-and-thrust belt has been vigorously debated due to the steep topography in contrast with the low convergence rate and earthquake hazards. The Longmen Shan fold-and-thrust belt is characterized by two main detachments: a strong lower detachment at 15–17 km depth in the hinterland and a weak upper detachment at ~7 km depth in the Sichuan Basin. Nevertheless, how the two detachments control deformation in the Longmen Shan remains unclear. In this study, we focus on the mechanical strengths of the two detachments in the study area and design three analog models to investigate the kinematics and mechanisms of the Longmen Shan fold-and-thrust belt. All three model experiments have the same strong lower detachments at the basement, but different upper detachments. The results indicate that for Model 1 with no upper detachment and Model 2 with a strong frictional upper detachment, the strain and deformation only concentrate near the mobile backwall, and particle image velocimetry analysis reveals that both models deform in the forward in-sequence style. However, for Model 3 with a weak ductile upper detachment, the strain and deformation propagate into the foreland, and the model deforms in the out-of-sequence style consistent with the Longmen Shan fold-and-thrust belt. The model results indicate that the spatial relation of strong lower detachment and weak upper detachment may be one of the important factors producing the current structural pattern and the out-of-sequence style of the Longmen Shan fold-and-thrust belt.

Mesozoic – Cenozoic evolution of the Southern Patagonian Andes fold and thrust belt (47°–48°S): Influence of the Rocas Verdes basin inversion and onset of Patagonian glaciations

The Southern Patagonian Andes (SPA) between 47°–48°S are characterized by relatively high elevations (1500–4000 m) and a 200-km-wide, largely exhumed, basement domain along the backbone of the Cordillera, bounded by a narrow 30-km-wide fold and thrust-belt to the east. The tectonic evolution of the SPA includes widespread Jurassic extension during the opening of the Austral-Magallanes basin and the Rocas Verdes back-arc oceanic basin (RVB), followed by Cretaceous to Cenozoic shortening. Although the main phases of deformation that affected this Andean segment have been the focus of previous studies, its finite geometry and step by step structural and kinematic evolution have not been quantitatively determined. In this work, we present kinematically restored cross sections, showing the variable geometry, trough time, of the eastern basement domain and the fold and thrust-belt. A regional westward-dipping listric decollement, interpreted as formed during the Jurassic extensional event, was reactivated during the Andean deformation constituting the main detachment surface of basement structures and the fold and thrust belt. West verging faults systems are considered a consequence of inversion of north-south trending extensional features as passive roof high-angle west-vergent faults. Using regional data such as field relations, unconformities, and existing ages to differentiate deformational stages, three main phases of contractional deformation are proposed for the area, starting with an Aptian - Cenomanian? phase related to inversion of the extensional depocenter in inmediate response to the closure of northernmost RVB. A second, Miocene phase responsible for most of the shortening occurred between 18 Ma and 10 Ma. Finally, the onset of glaciations and glacial erosion might have triggered out-of-sequence thrusting in the interior of the orogen after 7 Ma.

The sedimentary and tectonic features of the Niger Delta

The Niger Delta, one of the largest delta in the world, is located on the eastern passive continental margin of the Atlantic Ocean. It was formed during the Niger River entering the Atlantic Ocean. The main part of the delta lies on the Atlantic oceanic crust, and the minor part on the African pre-Cambrian basement. The Central and West African Rift Systems indirectly control the formation of the Niger Delta through controlling the distribution and development of the Benue-Niger river system. It is a prograded delta with typical prograding sequence, i.e., regressive sequence. The prograding sequence is constituted with the marine shale (Akata Formation), paralic sand and shale (Agbada Formation) and continental alluvial sands (Benin Formation) from the bottom to the top. These three lithostratigraphic units are diachronous. All of them are younger seaward. There is a large scale gravity gliding tectonics. The main detachment fault lies in the Akata marine shale. The gravity tectonics can be divided into the front compressional deformation province and the trail extensional deformation province. The front compressional deformation formed a fold-thrust belt. The trail extensional deformation formed horst-graben structures. The detachment folds are well developed in the transitional zone between these two deformation provinces. Accompanied with the gravity-gliding tectonics, shale tectonics are widely developed in the Niger Delta. There is possibly some formation-relation between the gravity-gliding tectonics and the Cenozoic volcanic activities of the Cameroon volcanic line.

The extent of penetrative Pyrenean deformation in the Ebro foreland Basin: Magnetic fabric data from the eastern sector

We studied Cenozoic sedimentary rocks in the NE Ebro foreland Basin using the Anisotropy of Magnetic Susceptibility (AMS) as a proxy for grain preferred orientation. Our new data, in combination with existing results, reveal that penetrative strain by layer-parallel shortening extends well beyond the Pyrenean thrust-wedge front into the Ebro foreland Basin, challenging the concept of the location of “deformation front” in the Southern Pyrenees. Penetrative strain, as revealed by the magnetic fabrics, seems to reach larger distances into the Ebro foreland Basin where stiffer layers constitute the main detachment level, whereas to the East strain dissipates closer to the deformation front when the detachment is mostly due to salt deposits.

Mechanical stratigraphy influence on fault-related folds development: Insights from the Cantabrian Zone (NW Iberian Peninsula)

An excellently exposed outcrop of Carboniferous rocks in the Cantabrian Zone (Variscan foreland fold-thrust belt in NW Iberia) displays fault-bend, fault-propagation and detachment folds. To unravel the parameters that controlled their development, we constructed detailed cross-sections and analysed them. Detachment folds exhibit the greatest amounts of layer-parallel/bulk strain, forelimb dip and forelimb/hinge thickening and the lowest interlimb angle, whereas fault-bend folds have the lowest values except for the interlimb angle, with fault-propagation folds exhibiting intermediate values. The forelimbs of all these folds show some strain and thickening, and the detachment folds also show thickening and strain in the hinge area. Mechanical stratigraphy was determined to be the main controlling factor on the fold/thrust style; ramp folds developed in thick-bedded, isotropic, relatively strong and brittle rocks, whereas detachment folds developed in a thin-bedded, anisotropic, relatively weak and ductile unit. Competent rocks and smooth bedding surfaces induced fault-bend folding, whereas less competent and rough bedding surfaces favoured fault-propagation folding. The main detachments are located at the boundaries between mechanical units with substantial changes in their mechanical properties. The size of the structures depends on the occurrence of a basal detachment, variety of lithologies with different competences and smoothness of bedding surfaces.

An automatic trunk-detection system for intensive olive harvesting with trunk shaker

Trunk shakers are widely used for olive harvesting, being the main detachment system for fruit harvesting. In recent decades, the components of trunk shakers have evolved at mechanical, hydraulic and control levels. However, machine accuracy depends on the operator, whose expertise is a key factor for issues such as trunk debarking caused by grabbing systems, shaking parameters, or on-foot operator safety. The objective of this work was to develop an automatic trunk-detection system to reduce operator influence on the process. Thus, the automatic system via infrared sensor was implemented on a trunk shaker head hitched to a tractor. A control algorithm, control logic and display for trunk grabbing automation were developed. The automatic system was tested under laboratory and field conditions to assess the influence of some variables on trunk detection. The evaluated variables were colour, material, diameter, and target location within the sensor field of vision. The success rate of the automatic system was 91% for trunk grabbing. In the field phase, the efficacy of the automatic system was compared to an operator performing the tasks manually, obtaining times of 16.05 ± 2.8 s tree−1 and 21.54 ± 5.29 s tree−1 respectively, and a percentage of success in trunk grabbing of 92.9%. Automatic mode improved manual mode by saving 27.3% of time, improving effective field capacity. The automatic mode developed here provided a high ratio of success and it showed highly reliable and efficient performance compared with manual mode.