Morphostructural Analysis Research Articles

Recent sedimentary processes along the Makran trench (Makran active margin, off Pakistan)

A geophysical and geological survey (CHAMAK) has been carried out on the Makran accretionary wedge off Pakistan in order to understand the structure of the margin and the recent sedimentary processes in this self-maintaining prism disconnected from the modern Indus inputs (Qayyum et al., 1997; Gaedicke et al., 2002a; Schluter et al., 2002). Morphostructural analysis, based on the interpretation of bathymetric data and backscatter imagery, as well as a 3.5 kHz echo-character mapping, allow us to distinguish three structural domains, from north to south, where sedimentary processes differ: (1) the accretionary wedge to the north, (2) the trench and (3) the northern Murray Ridge at the seaward edge of the trench. The accretionary wedge is cut by canyons responsible for an important erosion of the prism especially in the eastern part of the wedge. Within the trench, sediments transported by the canyons generate sediment waves and are transported westward, parallel to the E–W axis of the trench. The eastern part of the abyssal plain is eroded by strong turbidity currents whereas important sediment deposition occurs in the western part of the abyssal plain, as a consequence of a decrease in the current energy. Nearly no mass transport deposits are recognized in the study area except near the ridges forming the accretionary wedge. Small-scale slope failure scars are described. The prevalence of turbiditic processes and the existence of a morphological barrier formed by the Murray Ridge allow the confinement of turbidites within the trench. Migrating sediment waves seem to be common sedimentary structures in this setting. These features might be produced by important velocity decrease of turbidity currents when reaching the trench.

Clinical Applications of Positron Emission Tomography (PET) Imaging in Medicine: Oncology, Brain Diseases and Cardiology

Positron Emission Tomography (PET) is a diagnostic imaging procedure used regularly to acquire essential clinical information. The PET – CT hybrid, which consists of two scanning machines: PET scanner and an x-ray Computed Tomography (CT). At present these represent the technological hierarchy of Nuclear Medicine, occupying an important position in diagnostics. In fact, PET – CT has the capability to evaluate diseases through a simultaneous functional and morphostructural analysis. This allows for an earlier diagnosis of the disease state which is crucial for obtaining the required information to provide a more reliable prognosis and therapy. Presently, the most frequently used PET radiotracer [18F]fluorodeoxyglucose (FDG) has a major role in oncology. Useful information is being regularly obtained by using both FDG and a selection of radiotracer compounds to evaluate some of the most important biological processes. Thus, creating an opening for ‘Molecular Imaging’ and providing a platform for a potential revolution in the clinical diagnostic field. In this review, we hope to present the most interesting technicalogical and methodological advances in clinical diagnostics for oncology, neurology, and cardiology. A particular attention is dedicated to the applications of PET in neuropsychiatric diseases and its connections with receptor imaging.

Morphostructural analysis of Jamaica

To Jamaica, macroblock in differential ascent in the plate boundary zone of the Caribbean—North America, a set of morphostructural and geological methods and procedures was applied that permitted its neostructure to be explained. It is composed of two mesoblocks, 11 blocks, 29 microblocks, and 65 nanoblocks. This group configures a heterogeneous network of morphoalignments and knots; knot N1 (Montego) and N11 (Kingston) being the most active. The main watershed was delimited, with an E-W strike, that reflects in its inflections the influence of a shear tectonic, mainly ancient, and that watershed divides the insular territory into two sectors (of rectangular figures) to the north and to the south. The river network is conditioned, in sectors and fundamentally, by tectonic factors. From a morphometric point of view the greater levels of uplifting (>1000 m) are located in the eastern part, in the Blue Mountains, though the estimated raising sectors denote that on its edges the recent intensity reaches values of ∼500 m. The contemporary faulting is more important in the marine parts of the north and of the south zones where the strongest earthquakes are located; however, this element is linked differently with the disruptive structures inherited, modified and active of the emerged part, those which determined that they are neither vast nor homogeneous. The seismic activity is justified by its space—time location in a transpression area of the plate boundary zone and where six relevant seismogenetic zones exist. In these elements the larger geological hazard is framed.

A multidisciplinary approach to the study of the fault networkin the internal Cottian Alps (Western Alps)

The architecture of the fault network and the late- to post-metamorphic structural evolution in the internal Cottian Alps have been studied by an integrated approach combining morphostructural analysis, field mapping and detailed mesostructural analysis between the Susa and Pellice Valleys. Available apatite fission track data indicate that this sector of the Western Alps reached shallow crustal levels, where brittle deformation mechanisms prevail, by Late Oligocene times. The analysed area comprises two main N-S striking regional, polyphasic semi-brittle to brittle deformation zones: the Colle delle Finestre Fault Zone (CFFZ) and the Col del Lis-Trana Deformation Zone (LTZ). The activity of those long-lived structures evolved, respectively, from dextral and dextral-reverse to extensional. In the block bounded by these two regional structures, the late- to post-metamorphic tectonic evolution is characterized by two faulting stages: (a) the development of an E-W left-lateral fault zone with a minor normal component of movement; at the regional scale, this fault zone may be considered as an antithetical shear of the major LTZ and the CFFZ; (b) the extensional reactivation and development of N-S normal faults, coeval with those recorded both by the LTZ and the CFFZ. The geometry of the fault and fracture systems has been compared with the remote sensed lineaments pattern, characterized by four main systems: Ln1 (N0°-30°E), Ln2 (N45°-70°E), Ln3 (N80°-100°E) and Ln4 (N100°-120°E). The lineament systems display similarities in terms of orientation, geometry and length with the fault systems observed at different scales. These similarities allowed us to extrapolate the structural model outlined in the mapped area to the adjoining sectors. Comparison between the different data suggests that the pattern of the lineaments detected between the LTZ and the CFFZ agrees with the architecture of a strike-slip fault network, which accommodated the internal deformation of the block bounded by these two major N-S transcurrent deformation zones. The transcurrent activity of these faults is here interpreted as coeval with the late dextral movements along the Canavese Line and with the propagation, in the Late Oligocene-Early Miocene, of the roughly E-vergent South-Alpine Thrusts beneath the Tertiary Piemonte Basin. The extensional event that followed may be related to the uplift with the subsequent isostatic readjustment of the chain which may have also induced the normal reactivation of the Penninic Frontal Thrust. This extensional regime is also in agreement with focal mechanisms of recent earthquakes.

DEM generation using ASAR (ENVISAT) for addressing the lack of freshwater ecosystems management, Santa Cruz Island, Galapagos

Low relief oceanic islands often suffer from scarcity of freshwater resources. Remote sensing has proved to be an effective tool to generate valuable data for hydrological analysis and has improved the management of ecosystems and water. However, remotely sensed data are often tested over areas with existing validation databases and not always where the need is greatest. In this paper we address the need for topographical data to understand the hydrological system of Santa Cruz Island (Galapagos archipelago) so that management of freshwater ecosystems and resources can take place. No high resolution, high accuracy topographical data exist for Santa Cruz Island, and its growing population has created an urgent need for water resource management and protection of unique and pristine ecosystems. Inaccessible National Park land covers more than 97% of Galapagos territory, which makes the use of remote sensing methods indispensable. SRTM data was insufficient in terms of grid size (90 m) to carry out the needed data analysis. We used ASAR data (ENVISAT) in VV polarization image mode for Digital Elevation Model (DEM) generation, in order to extract drainage network, watersheds, and flow characteristics from a morpho-structural analysis. Results show the high potential of these data for both interferometric and radargrammetric generation methods. Although interferometry suffered from low coherence over highly vegetated areas, it showed high precision over the rest of the island. Radargrammetry gave consistent results over the entire island, and details were enhanced by integrating the 90 m SRTM data as an external DEM. Accuracy of the SRTM and the combined radargrammetric/SRTM DEM was similar, with the radargrammetric having a finer pixel-based resolution (20 m). Validation of the extracted drainage networks and watersheds was carried out using ground-based field observations and comparison to mapped river networks visually extracted from aerial photographs and high resolution (1 m) satellite imagery available on GoogleEarth ©. For the first time, watershed characteristics and flow paths were made available for an island of the Galapagos archipelago. Furthermore, the drainage network is shown to be strongly influenced by observed and extracted structural discontinuities. Having characterized freshwater flow, water balance calculations were carried out for Pelican Bay watershed, where urban areas, agricultural land and Galapagos National Park land are concomitant.

Consequences of continental subduction on forearc basin and accretionary wedge deformation in SE Taiwan: Insights from analogue modeling

In southeastern Taiwan a slice of forearc basement belonging to the Philippine Sea Plate upper-plate is suspected to subduct under the Luzon arc as a consequence of the transition from oceanic to incipient continental subduction. Effects on the morphology, deformation, geometry of structures and tectonic evolution of the orogenic wedge in the collision area are numerous. This study examines the impact of forearc lithosphere subduction on forearc basin and accretionary wedge deformation. A morpho-structural analysis of the geological features observed onland and offshore allows describing in detail the complex deformation suffered by the area. A combined approach by analogue modeling is applied to better understand the phenomenon. Comparison between nature and experimental results shows that subduction of a forearc basement slice induces intense shortening and concomitant deformation in the forearc domain. Such process involves deformation of the forearc basin previously developed in a setting of oceanic subduction. Sediments of the forearc basin are involved in the growth of a new thrust ridge backthrusted against the basement slope of the volcanic arc edifice. Sediments coming from the growing orogenic wedge are trapped in the trough developed between its backpart and the topographic high of the new rising ridge. A syn-collisional orogenic basin develops which structural evolution characterizes the progressive shortening of the forearc domain. Most of the deformation and tectonic events recorded offshore or onland in the complex area south of Taiwan can be explained using results of our specific modeling which well describe the tectonic processes associated with continental subduction under a volcanic arc.

Morphostructural Analysis of Human Follicular Stem Cells on Highly Porous Bone Hydroxyapatite Scaffold

In this study we investigated the in vitro behaviour, morphostructure and extracellular matrix synthesis of human dental follicular stem cells (hDFSCs) isolated from human dental bud, which resulted to be positive for mesenchymal markers (CD29, CD90, CD146 and CD166) by FACS analysis. Cells were analysed by light and electronic microscopy to evaluate their biological response either at week 1, that is before differentiation, or at weeks 3-6, when they had been cultured in osteogenic medium onto a highly porous natural scaffold material (Bio-Oss). Microscopy analysis of primary culture cells showed they had a mesenchymal stem cell-like morphostructure, spindle shaped, similar to the culture of mesenchymal stem cells derived from adult bone marrow. Also, after osteogenic differentiation, these analyses indicate typical osteoblast morphostructure and reveale a tri-dimensional organization of the cells and deposition of extracellular matrix (ECM) in close contact with biomaterial. This approach would allow to personalize the scaffold for bone tissue engineering in order to accelerate the process of osteogenesis.

Two scales of inflation at Lastarria-Cordon del Azufre volcanic complex, central Andes, revealed from ASAR-ENVISAT interferometric data

ASAR-ENVISAT Interferometric Synthetic Aperture Radar (InSAR) data collected over the Lastarria-Cordon del Azufre complex (Chile–Argentina) between March 2003 and May 2005 show the persistence of the large wavelength ground inflation revealed by Pritchard and Simons in 2002 from the analysis of ERS InSAR data [Nature 418 (2002) 167–170]. After reducing the tropospheric contribution in the interferograms using a combination of data network adjustment and analysis of MODIS images, we produced an accurate interferometric time series showing a 2 yr long temporal evolution of the ground displacements patterns. Two distinct inflating signals are detected. The main signal covers an elliptical area with a 45 km NNE–SSW major axis and a 37 km minor axis. It is correlated with a regional topographic dome. We estimated its maximum inflation rate to ∼ 2.5 cm yr − 1 . We inverted the InSAR data for a range of source geometries (spherical, prolate ellipsoids, penny-shaped cracks). The inferred source parameters for 2003–2005 period are consistent with an over-pressured reservoir at shallow to intermediate crustal depths (7–15 km), with an average volumetric rate of inflation of about 14 × 10 6 m 3 yr − 1 . In addition to this main signal a new feature highlighted by the ASAR data is short wavelength inflation (6 km wide) at the location of Lastarria volcano on the northern margin of the large wavelength signal. We explain this short wavelength signal by a spherical over-pressured source lying 1000 m below the summit of Lastarria volcano. We estimate the average volumetric rate of inflation during the observation period to be ∼ 35 × 10 3 m 3 yr − 1 . It is remarkable that both volumetric variations for the large and small inflations exhibit the same evolution during the 2003–2005 period, suggesting that both processes could be related. On the basis of the inversion results and of arguments provided by field evidences and a morpho-structural analysis of the Digital Elevation Model of the area, we propose that the deep source have a magmatic origin while the shallow source is most likely related to hydrothermal fluids. In our interpretation, the on-going deformation processes observed at Lastarria-Cordon del Azufre volcanic complex could represent an evolving pre-caldera silicic system. Further field geological and geophysical investigations will be required to confirm these hypotheses and refine the proposed model, mostly based on satellite observations.

Spatial and temporal relationships between compression, strike-slip and extension in the Central Venezuelan Andes: Clues for Plio-Quaternary tectonic escape

The geometry of tectonic structures, attributed to the Neogene–Quaternary time interval, is described in the active setting of the Venezuelan Andes. Our methodology is based on the analysis of radar satellite and Digital Elevation Model imagery, complemented by structural fieldwork and the compilation of seismotectonic data to make a structural analysis on a regional scale. Radar images provide first class data for morphostructural analysis in areas of dense vegetation and frequent cloud covering, like the Venezuelan Andes. We focused our analysis in the Burbusay–Río Momboy and Boconó faults corner located in the central part of the belt. We have described three stages of deformation during the Neogene–Quaternary. The first one, Mio-Pliocene in age, is a NW–SE compression responsible for the uplift of the Venezuelan Andes. The second tectonic stage corresponds to a strike-slip regime of deformation marked by shearing along the Boconó, Burbusay and Valera faults, which separates two triangular wedges in the larger Trujillo block. This strike-slip faulting-dominated compressional-extensional tectonic regime allowed the Trujillo crustal block to move towards the NE. Wrenching has therefore started at some point between the Pliocene and the Quaternary. These two tectonic events are consistent with ongoing strain partitioning in the Venezuelan Andes. The third stage corresponds to extensional deformation limited to the Trujillo block and is still active today. Extension is associated with the motion of crustal blocks moving relative to each other, probably above the upper-lower crust boundary. Such extensional deformation can be understood considering that the crust extends and stretches at the same time as it moves towards the NE. The combination of both horizontal lateral motion and extension is characteristic of a tectonic escape process. The northeastward escape of the Trujillo block, which belongs to the larger North Andes block, occurs as a result of the combination of the NW–SE intracontinental convergence between the South-American plate and the Maracaibo block, and the presence to the north of the Caribbean oceanic plate considered as a free boundary. We have showed that the kinematics of the Caribbean plate offers not only a favorable environment, but may also be considered as the driving force of the tectonic escape of the North Andes block.

Tectonic evolution of the central-eastern sector of Trans Mexican Volcanic Belt and its influence on the eruptive history of the Nevado de Toluca volcano (Mexico)

The Nevado de Toluca is an andesitic to dacitic stratovolcano of Late Pliocene–Holocene age located within the central and eastern sectors of the Trans Mexican Volcanic Belt. Morphostructural analysis, aerial photograph and satellite image interpretation, structural analysis and geological fieldwork were methods used to investigate the relationship between the evolution of the volcano and the tectonic framework of its basement. The study revealed that the area of Nevado de Toluca is affected by three main fault systems that intersect close to the volcanic edifice. These are from oldest to youngest, the Taxco–Querétaro, San Antonio and Tenango fault systems. The NNW–SSE Taxco–Querétaro fault system was active in the area since Early Miocene, and is characterized by right-lateral transtensive movement. Its reactivation during Early to Middle Pleistocene was responsible for the emplacement of andesitic to dacitic lava flows and domes of La Cieneguilla Supersynthem. The NE–SW San Antonio fault system was active during Late Pliocene, before the reactivation of the Taxco–Querétaro fault system, and is characterized by extensional left-lateral oblique-slip kinematics. The youngest is the E–W Tenango fault system that has been active since Late Pleistocene. This fault system is characterized by transtensive left-lateral strike-slip movement, and partly coeval with the youngest eruptive phase, the Nevado Supersynthem, which formed the present summit cone of the Nevado de Toluca volcano. The stress re-orientation from the Taxco–Querétaro to the Tenango fault system during Late Pleistocene is responsible for the ∼ 1 Ma hiatus in the magmatic activity between 1.15 Ma and 42 ka. After this period of repose, the eruptive style drastically changed from effusive to explosive with the emission of dacitic products. The methodology presented here furnish new data that can be used to better assess the complex structural evolution of this sector of the Trans Mexican Volcanic Belt and to understand the influence of changes in the tectonic setting on the growth of volcanic edifices.

Submarine geology of Hana Ridge and Haleakala Volcano's northeast flank, Maui

We present a morphostructural analysis of the submarine portions of Haleakala Volcano and environs, based upon a 4-year program of geophysical surveys and submersible explorations of the underwater flanks of Hawaiian volcanoes that was conducted by numerous academic and governmental research organizations in Japan and the U.S. and funded primarily by the Japan Agency for Marine–Earth Science and Technology. A resulting reconnaissance geologic map features the 135-km-long Hana Ridge, the 3000 km 2 Hana slump on the volcano's northeast flank, and island-surrounding terraces that are the submerged parts of volcanic shields. Hana Ridge below 2000 m water depth exhibits the lobate morphology typical of the subaqueously erupted parts of Hawaiian rift zones, with some important distinctions: namely, subparallel crestlines, which we propose result from the down-rift migration of offsets in the dike intrusion zone, and an amphitheater at its distal toe, where a submarine landslide has embayed the ridge tip. Deformation of Haleakala's northeast flank is limited to that part identified as the Hana slump, which lies downslope from the volcano's submerged shield, indicating that flank mobility is also limited in plan, inconsistent with hypothesized volcanic spreading driven by rift-zone dilation. The leading edge of the slump has transverse basins and ridges that resemble the thrust ramps of accretionary prisms, and we present a model to describe the slump's development that emphasizes the role of coastally generated fragmental basalt on gravitational instability of Haleakala's northeast flank and that may be broadly applicable to other ocean-island slumps.

Geomorphological information system: Physical model and options of geomorphological analysis

The paper has two main aims. Firstly, to postulate a physical geodatabase model of a geomorphological information system based on the already existing logical geodatabase model. Secondly, to define processes of geomorphological analysis based on the physical geodatabase model. The structure of the physical model follows the logical model and is divided into three parts: adopted layers (hydrology, geology, topography and others), basic layers (elementary forms, digital elevation model and derivatives, documentation materials, genetic groups of landforms, morphodynamic phenomena, basin based features and geomorphic network) and special layers (morphostructural analysis, comprehensive geomorphological analysis and so on). The geodatabase modelling methodology was used for developing the physical geodatabase model. The geomorphological analysis is based mainly on the layer of elementary forms (defined according to their morphology and morphometry) and the derived layer of morphogenetical forms (determined by genesis of landforms). The traditional methods of geomorphological mapping and also more recent concepts of geomorphological analysis were used. The concept is presented in the context of research in the surroundings of Prášilské jezero (lake) in the Šumava (Mts.). ESRI products were used to carry out the project.

Analysis of the Mw 4.3 Lorient earthquake sequence: a multidisciplinary approach to the geodynamics of the Armorican Massif, westernmost France

A Mw 4.3 earthquake occurred on 2002 September 30, in the Armorican Massif, NW France. Since it was one of the largest events ever recorded in this region, this was the opportunity to improve our seismotectonic knowledge of the Armorican Massif. We performed a post-seismic survey (SISBREIZH), which allowed us to locate accurately 62 aftershocks within 14 days. An analysis of the main shock using broadband records provided a normal fault mechanism with a dextral strike-slip component located at 12-km depth. The aftershock sequence exhibits: (1) a combination of almost pure right-lateral strike-slip and dominant normal faulting similar to the main shock; (2) magnitudes ranging from 0.4 to 1.9 and (3) depths ranging from 11.5 to 13.5 km, that is, close to the main shock hypocenter. The distribution of the aftershocks defines a rupture plane dipping 60° to the south with a fault length of ≈2 km consistent with the source parameters of the main shock. Beside the SISBREIZH survey, a morpho-structural analysis has been conducted: we found fault plane solutions with southward-dipping N120–150 normal fault planes. The stress tensor computed after the aftershock focal mechanisms is a strike-slip regime with a NE–SW extensional direction. The Lorient earthquake appears to reactivate Late Hercynian structures and the whole sequence is reflecting the regional-scale tectonic stress field expressed by a combination of strike-slip and normal faulting.

Tectonic evolution of the Tehuantepec Ridge

The Tehuantepec Ridge is one of the most prominent lithospheric structures of the Cocos Plate, yet its tectonic evolution has remained poorly constrained until now. Calculated ocean floor ages and spreading rates, morphostructural analysis of the ridge and the surrounding ocean floor are used to infer the tectonic evolution and pattern of the Tehuantepec Ridge and associated structures. The ocean floor age estimates south of the Tehuantepec Ridge suggest an age of ∼26 Ma at the Middle America trench. A mean age difference across the Tehuantepec Ridge of ∼7 Ma suggests that the Tehuantepec Ridge would be formed as a long transform fault on the Guadalupe plate, prior to 15 Ma. The full-spreading rate estimates show that there might be a differential full-spreading rate across the transform fault between 15 and 5 Ma, when the oceanic plate just south of Clipperton Fracture Zone was decelerating between 15 and 10 Ma, then accelerating for the next 5 Ma. We propose a model in which between 13 and 8 Ma temporarily transpressional intratransform-spreading centers would have been existing as a consequence of the East Pacific Rise onset with an angle of ∼10° clockwise with respect to the ceased Mathematician ridge. Our model estimates indicate that between 21 and 15 Ma a prominent pseudofault was formed south of the Tehuantepec Ridge due to an unstable offset on the Mathematician ridge that migrated northward. The Tehuantepec Ridge and the pseudofault trace bound a deeper oceanic basin than the surrounding area, with no corresponding anomalous depth on the western side of the East Pacific Rise. The complete absence of a pseudofault trace and a deeper oceanic basin on the western side of the East Pacific Rise, as well as the spreading rate changes, suggest the existence of a microplate embedded into the Cocos Plate just south of the Tehuantepec Ridge. Also, the asymmetric and sharp morphology of the Tehuantepec Ridge suggests that it may be the expression of a major transpressional structure along the former transform fault on the Guadalupe plate 15–20 Ma ago.

Neotectonics and channel evolution of the Lower Ivinhema River: A right-bank tributary of the upper Paraná River, Brazil

The Ivinhema River, an important right-bank tributary of the upper Paraná River, cuts a series of terraces, geomorphic surfaces, floodplains and associate features. Through terrace mapping, sediment composition, absolute ( 14C, TL) dating and morphostructural analysis, this paper presents the composed longitudinal profile and the structural analysis of the lower course of the Ivinhema River. The tectonic model of the study area constitutes a sequence of NW tilting fault-blocks formed from antithetic faults that control channel sinuosity, longitudinal profile, floodplain distribution and valley asymmetry. The area began to be structured during the Paleocene with formation of the oligomict conglomerate, probably under an arid climate. Another tectonic reactivation in the Mio-Pliocene boundary defined the divides of the Upper Paraná and Paraguay River basins, with formation of the polymict conglomerate. An active depositional phase taken place at the Tertiary–Quaternary limit produced the massive reddish clayey sand sediments very common in the area. During the Late Pelistocene (42.5 ± 1.7 and 31.1 ± 1.7 ka BP), the Paraná and Ivinhema rivers constructed a sedimentary sequence of gravelly sand deposits in a braided channel environment. At the beginning of the Holocene a new tectonic pulse, lifted up a group of blocks parallel to the Paraná River valley, developed a series of antithetic faults. Tectonic intensity associated with the pluvial stage (Hypsithermal phase between 8 and 6 ka) changed the channel pattern of the river from braided to meandering. Channel evolution during the Late Pleistocene and Holocene was also influenced by climatic changes.

Tar sandstones in the Paraná Basin of Brazil: structural and magmatic controls of hydrocarbon charge

There are tar accumulations in Lower Triassic sandstones along the eastern margin of the Paraná Basin. The tar was derived from Permian source rocks that matured along the basic sills of the Serra Geral continental flood basalt cover. This paper exams the habitat of tar accumulation, integrating fieldwork with morphostructural data, digital elevation modelling, gravity and airborne magnetic data, remote sensing, and radiometric dates that constrain the timing of maturation and migration. The focus of this work is the Jacu structural complex, a large annular drainage anomaly, 20 km in diameter, that owes its origin to reactivation of pre-existing faults. Interpretation of the structural framework is based primarily on morphostructural analysis and the distribution of gravity anomalies. The Jacu structure consists of a central low-lying fault block that is surrounded by several structural highs, and is attributed to the interaction of NE- and NW-striking fault zones. The principal basement faults that encapsulate this structure were invaded by the dolerite dykes that fed the widespread flood basalt cover during the Early Cretaceous. An 40Ar/ 39Ar analysis directly dates this episode of magmatism to 134±2 Ma. Tar sandstones are restricted to the lower Pirambóia Formation and are present around the Jacu structure, especially near the structural highs or close to basic dikes. Morphostructural interpretation suggests the occurrence of tar sandstones at intermediate positions too, between the structural highs and lows. The most likely explanation for these tar accumulations relates oil maturation and migration to the intrusion of Lower Cretaceous Serra Geral sills into the Upper Permian black shales of the Irati Formation, and subsequent migration along faults and dyke walls into eolian sandstone reservoirs of the Triassic Pirambóia Formation. Not only did the basic dykes locally facilitate migration, but there were also places where they were barriers to lateral migration. Furthermore, the interdune and fluvial facies of the Pirambóia Formation formed local seals and barriers to vertical migration.

Morphological and microtectonic analysis of Quaternary deformation from Puná and Santa Clara Islands, Gulf of Guayaquil, Ecuador (South America)

This paper presents the neotectonic study of Santa Clara and Puná Islands sited in the Gulf of Guayaquil eastern part. Both islands are located on the south-western segment of the fault zone bounding to the east the North Andean Block. Fault motion and morphostructural analysis were carried out from Pleistocene age terrain. A two step deformation characterises the South Puná tectonics. The first step involves the Zambapala Cordillera uplift that post-dates Pleistocene sediments and pre-dates a marine terrace correlated with the M.I.S. 11 or 13 (440–550 ka). The second step is the formation of a pull-apart that shows evidence of 2.9 km dextral offset since the M.I.S. 11 or 13, giving an offset mean rate of 5.3 to 6.6 mm/yr. This rate is higher than the one calculated on the Pallatanga Fault northeast of the study area, in the Western Andean Cordillera, suggesting that deformation is split in different fault segments from the Gulf of Guayaquil to the continent. The Zambapala Cordillera uplift and transpression deformation requires a compressive event that may have been induced by the subduction process during the early Pleistocene.

Approach to the Morphostructural Analysis of the Relief in Publications of Czech and Slovak Geomorphologists

The article presents approaches Czech and Slovak geomorphologists use while working on morphostructural analysis. The analysis consists of partial analyses (methods) that contribute to description of the relief and its parts. The article shows which of these methods are mostly used. The aim is to point out that the geomorphologists' approach to the morphostructural analysis is very different and varies from author to author.

Análise morfoestrutural em área de ocorrência de arenito asfáltico, Bacia do Paraná, São Paulo

Arenitos asfálticos ocorrem na borda leste da Bacia do Paraná, Estado de São Paulo. As ocorrências estão relacionadas a condicionantes estratigráficos, estruturais e geomorfológicos. Desse modo, uma análise morfoestrutural foi feita para estabelecer quais elementos geomorfológicos refletem os controles geológicos relacionados à gênese dos arenitos asfálticos. A análise morfoestrutural foi baseada no mapa da rede de drenagem e em imagens de sensoriamento remoto. A interpretação considerou os lineamentos de relevo e a delineação das principais flexuras do terreno. O método de interpretação foi baseado na identificação de anomalias de drenagem, que correspondem a modificações geométricas em relação ao padrão de drenagem regional, como anomalias anelares, radiais e padrões assimétricos. Além disso, foram interpretadas feições retilíneas de drenagem, de mesmo comprimento; estas feições representariam zonas de juntas. Foram detectadas várias anomalias de drenagem na área de ocorrência de arenito asfáltico, várias delas relacionadas a estruturas geológicas mapeadas. Desse modo, o mapa morfoestrutural com a delineação de altos e baixos e os lineamentos são os principais elementos geomorfológicos que refletem os fatores geológicos relacionados à ocorrência de arenito asfáltico. As ocorrências encontram-se em áreas de alta e média densidade de zonas de juntas. Terrenos fraturados são favoráveis à migração dos hidrocarbonetos mas também, à erosão do depósito, agindo de forma antagônica em tempos diferentes. As principais estruturas geológicas da área, estrutura do Jacu e Alto Estrutural de Anhembi, são exemplos da relação entre substrato geológico e relevo, o que ajuda no entendimento da gênese das ocorrências.

Use of morphostructural analysis to show halokinesis during Mio-Plio-Quaternary in the South-West part of Aquitain Basin

In the South Aquitain sector, salt bodies of varying sizes present two geographical gradients. The first gradient, south to north, associated with the proximity of the Pyrenees shows a decreasing deformation of the structures towards the north. The second gradient explains their increasing depth of burial from the west (extrusive structures) to the east (intrusive structures). This organization has been studied from the western sector (Tercis-Benesse and Bastennes-Louer) to the eastern sector (Viella-Labarthete and Nogaro-Lussagnet). Other more modest structures, revealed by hydrographical anomalies, illustrate halokinetic events during the Quaternary. Then the detailed study of the Geaune dome shows a neotectonic phenomenon dating from the Mio-Pliocene. The radial annular drainage pattern of this structure is guided by recurrent faulting during the Quaternary. Thus the halokinetic dynamics consist in three phases: deformation of the diapirs (overthrusts) during the Oligocene, resuming of halokinesis during the middle of the Miocene and recurrent faulting during the Riss. A model of geomorphological evolution of the domes is then proposed. The first phase (stages of positive relief) is characterized by the centrifugal drainage pattern of the dome. The second phase (stages of inverted relief) is distinguished by the erosion of the center of the structure, by an inversion of the drainage pattern and by the sedimentary accretion in the central depression.