ENE-WSW Trending Research Articles

South China Sea crustal thickness and oceanic lithosphere distribution from satellite gravity inversion

Inversion of satellite-derived free-air gravity-anomaly data has been used to map crustal thickness and continental lithosphere thinning in the South China Sea. Using this, we determine the ocean–continent transition zone structure, the distal extent of continental crust, and the distribution of oceanic lithosphere and continental fragments in the South China Sea. We construct a set of regional crustal cross-sections, with Moho depth from gravity inversion, spanning the South China Sea from offshore China and Vietnam to offshore Malaysia, Brunei and the Philippines to examine variations in ocean–continent transition structure and ocean-basin width. Our analysis shows a highly asymmetrical conjugate margin structure. The Palawan margin shows a narrow transition from continental to oceanic crust. In contrast, the conjugate northern margin of the South China Sea shows a wide region of thinned continental crust and an isolated block of continental crust (the Macclesfield Bank) separated from the Chinese margin by a failed oceanic rift. The Dangerous Grounds are predicted to be underlain by fragmented blocks of thinned continental crust. We use maps of crustal thickness and continental lithosphere thinning from gravity inversion together with free-air gravity- and magnetic-anomaly data to identify structural trends and to show that rifting and the early seafloor-spreading axis had an ENE–WSW trend while the later seafloor-spreading axis had a NE–SW trend.

Deformation history and characteristics of the Ilgwang Fault in Southeast Korea

The NNE-SSW trending Ilgwang Fault is one of the major structural features in Southeast Korea. It is a high angle, right-lateral strike-slip fault with a displacement of about 1.2 km. The basement around the fault consists of Cretaceous sedimentary and volcanic rocks with younger igneous intrusions, forms part of the Gyeongsang Basin. The fault has not been studied thoroughly due to poor exposures along the fault; however, it is important to understand the characteristics of the Ilgwang Fault, as it is located near nuclear facilities and large cities with tall buildings. In this study, we investigated exposures in new road-cut sections along the Busan–Ulsan Highway. The structural patterns analyzed show wide deformation zones and may indicate various multi-deformation events including reactivation of pre-existing faults. Based on kinematic analysis of faults, joints, and dykes, the deformation history of the study area includes the following phenomena: 1) E-W trend reverse faulting with the intrusion of N-S trending acidic dykes; 2) NNE-SSW trend reverse faulting and folding; 3) ENE-WSW trend left-lateral faulting and NNESSW trend right-lateral faulting with the intrusion of NE-SW trending intermediate dykes; 4) E-W trend normal faulting; 5) N-S or NNE-SSW trend reverse faulting; and 6) NNW-SSE trend reverse faulting and reactivation of pre-existing normal faults. The angular change of the structural elements (e.g., beddings) is used here as an indicator of deformation intensity across the fault. The analysis shows that the deformation zone across the Ilgwang Fault spans about 200 m in volcanic rocks and 1 km in sedimentary rocks, indicating that the deformation is strongly localized in volcanic rocks and more diffused in sedimentary rocks. Numerical modeling supports the conclusion that sedimentary substrate has a wider deformation zone than do massive granitic or volcanic rocks, suggesting that material properties are one of the main factors controlling concentration of stress and possible resultant damage.

Geology of the Río de la Plata and the surrounding areas of Argentina and Uruguay related to the evolution of the Atlantic margin

An integrated study of geological and geophysical data of the Río de la Plata region and its relation to the evolution of the Atlantic passive margin is herein described. This characterization is based on the available geological and geophysical information and on the correlation of the southern end of the best-known Santa Lucía Basin in Uruguay to the Salado Basin in Argentina, and their connection through the Quilmes Trough. Furthermore, a new Meso-Cenozoic depocenter is characterized and identified as Recalada Trough, subparallely aligned to the Quilmes Trough and separated from it by the Magdalena-Montevideo High. Both sedimentary fillings present ENE-WSW trending main axes and reach an average thickness of almost 2000 m. This suggests an evolution from a triple junction where interconnected extensional arms developed, which have had common Mesozoic tectosedimentary histories related to the early opening of the Atlantic Ocean. Based on the geophysical and geological evidence, the previously accepted existence in the Río de la Plata of a first-order structural feature along the international border between Argentina and Uruguay, associated to an ENE-WSW trending tectonic high, identified as Martín García, is unjustified. The tectonic evolution of the Atlantic margin in front of the Río de la Plata estuary is the consequence of a long deformation history starting in the Precambrian up to recent times. Each Precambrian, Paleozoic, Mesozoic and Cenozoic tectonic scenario adds different weak trends on the continental crust, which control the evolution of the sedimentary depocenters. The presence of these tectosedimentary records influence the bathymetric control of the Río de la Plata and the dynamics of the recent estuarine deposits. The Meso-Cenozoic sedimentary infill is estimated to comprise considerable ranges of sandstones and conglomerates associated with faulted blocks of the crystalline basement, with expected petrophysical conditions oscillating in the order of 12%–15% of effective porosity and with expected traps of the stratigraphic and combined (closing against faulting) type, and overlapped by fine sediments with excellent quality as seals. The economic significance of these sedimentary volumes lies in their yet unexplored potential as natural fluid reservoirs (hydrocarbons and groundwater), of great importance due to their strategic position near the large urban areas of Buenos Aires and Montevideo.

Combined high-resolution aeromagnetic and radiometric mapping of uranium mineralization and tectonic settings in Northeastern Nigeria

Geological lineaments, depths to the basement, uranium concentrations, and remobilization in parts of the Upper Benue Trough, covering about 55 × 55 km2 (longitudes 11°30′–12°00′E and 10°30′–10°30′N), Northeastern Nigeria were investigated using integrated High-Resolution Aeromagnetic Data (HRAD) and radiometric data. This was with a view to identifying the potential zones of uranium occurrence in the area. The HRAD was processed to accentuate anomalies of interest and depths estimate of 150–1941 m were obtained from source parameter imaging technique. The results from the superposition of the horizontal gradient magnitude, analytical signal amplitude, first vertical derivative, and 3D Euler solutions of the HRAD revealed that the study area was dissected by linear structures that trend ENE–WSW, NE–SW, E–W, NNE–SSW, WNW–ESE, and NW–SE; among which the ENE–WSW and NE–SW trends dominated. Analyses of radiometric data showed that uranium ores in the study area were possibly remobilized epigenetically from the granitic rocks, and were later deposited into sedimentary rocks (Bima formation). Burashika group (Bongna hills) and Wawa area of the study area showed vein-type deposits, while the anatectic migmatite in the northeastern region and the uranium rich Bima formation showed both fault/fracture and contact types of deposition. It was also observed the northwesterly and southeasterly, dominant dip direction, dipping faults dip in the same direction as the paleocurrent direction (direction of depositions of sediments), and trend in a direction perpendicular to the hypothetical direction of uranium deposition. The study concluded that the studied area is dissected by several linear structures and the studied area possibly contains deposits of uranium ore, which are likely to be found in: the Bima Sandstones of Wade, Shinga, Bima hill, Wuyo, Teli, Bryel, Dali, Barkan, Gasi, Kunkun, Boragara, Deba, and Gberundi localities; the anatectic migmatite at Kubuku, Whada, and Hyama; and the Bongna hills and agglomerates around Burashika, Kawaba, and Galu.

Structural mapping based on potential field and remote sensing data, South Rewa Gondwana Basin, India

Intracratonic South Rewa Gondwana Basin occupies the northern part of NW–SE trending Son–Mahanadi rift basin of India. The new gravity data acquired over the northern part of the basin depicts WNW–ESE and ENE–WSW anomaly trends in the southern and northern part of the study area respectively. 3D inversion of residual gravity anomalies has brought out undulations in the basement delineating two major depressions (i) near Tihki in the north and (ii) near Shahdol in the south, which divided into two sub-basins by an ENE–WSW trending basement ridge near Sidi. Maximum depth to the basement is about 5.5 km within the northern depression. The new magnetic data acquired over the basin has brought out ENE–WSW to E–W trending short wavelength magnetic anomalies which are attributed to volcanic dykes and intrusive having remanent magnetization corresponding to upper normal and reverse polarity (29N and 29R) of the Deccan basalt magnetostratigrahy. Analysis of remote sensing and geological data also reveals the predominance of ENE–WSW structural faults. Integration of remote sensing, geological and potential field data suggest reactivation of ENE–WSW trending basement faults during Deccan volcanism through emplacement of mafic dykes and sills. Therefore, it is suggested that South Rewa Gondwana basin has witnessed post rift tectonic event due to Deccan volcanism.

Regional crustal architecture of Ellesmere Island, Arctic Canada

Abstract New deep seismological data from Ellesmere Island and the adjacent Arctic continental margin provide new information about the crustal structure of the region. These data were not available for previous regional crustal models. This paper combines and redisplays previously published results – a gravity-derived Moho map and seismological results –to produce new maps of the Moho depth, the depth to basement and the crystalline crustal thickness of Ellesmere Island and contiguous parts of the Arctic Ocean, Greenland and Axel Heiberg Island. Northern Ellesmere Island is underlain by a thick crustal block (Moho at 41 km, c. 35 km crust). This block is separated from the Canada–Greenland craton in the south by a WSW–ENE-trending channel of thinned crystalline crust (Moho at 30–35 km, <20 km thick crust), which is overlain by a thick succession of metasedimentary and younger sedimentary rocks (15–20 km). The Sverdrup Basin in the west and the Lincoln Sea in the east interrupt the crustal architecture of central Ellesmere Island, which is interpreted to be more representative of its initial post-Ellesmerian Orogen structure, but with a later Sverdrup Basin and Eurekan overprint.

Granite emplacement at the termination of a major Variscan transcurrent shear zone: The late collisional Viseu batholith

A major event of plutonic activity occurred all across the Central Iberian Zone of the Iberian Variscan Belt at the end of Late Paleozoic Variscan collisional tectonism. The present study focuses on the western sector of the Viseu late-post-tectonic batholith (central Portugal), a large composite intrusion comprising three main plutonic units: (a) small bodies of mafic to intermediate composition preferentially concentrated along the northern border, (b) a wide ring of coarse porphyritic biotite monzogranite (Cota-Viseu granite) and (c) a more evolved medium porphyritic, biotite-muscovite monzogranite occupying the central part of the intrusion (Alcafache granite).The compositional zonation pattern of the whole batholith and the complex mixing/mingling relationships between the voluminous Cota-Viseu porphyritic granite and the mafic/intermediate rocks suggest that these melts were withdrawn from a lower crustal source region undergoing partial melting, invasion by mantle-derived mafic magmas, mixing and fractional crystallization. New CA-ID-TIMS U-Pb zircon ages indicate that pluton assembly via multipulse injection of successive magma batches took place between 299.4 ± 0.4 Ma and 296.0 ± 0.6 Ma.A detailed anisotropy of magnetic susceptibility (AMS) survey suggests that pluton emplacement occurred at the extensional termination of a regional-scale, ENE-WSW trending, sinistral D3 shear zone - the Juzbado-Penalva Shear Zone (JPSZ). A dilational opening model involving the development of “en-échelon” tensional gashes at the extensional termination of the fault, followed by progressive opening and widening of north-south trending fractures, provided the space into which the successive magma batches arriving from below were emplaced. Vertical inflation was accommodated by depression of the pluton floor. The proposed model is consistent with the asymmetric wedge-shaped geometry of the intrusion (steep root zone on the northern side, discordant subvertical walls and a shallowing pluton floor towards the south).

Ore minerals and geochemical characterization of the Dungash gold deposit, South Eastern Desert, Egypt

The Dungash historic gold mine is located in the South Eastern Desert of Egypt. The gold-bearing quartz veins are hosted by the metavolcanic and metavolcaniclastic rocks along an ENE–WSW trending shear zone. Alteration types recorded in the wall rocks are sericitization, silicification, carbonatization, chloritization, sulfidization, ferruginization, and listwanitization. The ore mineral assemblage comprises arsenopyrite, pyrite, native gold, pyrrhotite, sphalerite, chalcopyrite, and galena. The primary sulfide mineral assemblage formed during a hypogene hydrothermal stage whereas anglesite and goethite occur as secondary supergene phases. Microthermometric fluid inclusion analysis revealed that the auriferous quartz precipitated from a moderately saline (5 to 11.22 wt% NaClequiv) solution at temperatures above the recorded homogenization temperatures (Th), which range from 380 to 177 °C. The minimum pressures of trapping are between 350 and 400 bars. The fluid evolution during mineralization is explained by mixing of a magmatic fluid with meteoric waters. Initially, the high temperature and moderately saline magmatic fluid dominated and progressively became diluted with meteoric waters. Highest gold content is recorded in the carbonatized zone and the quartz veins. However, gold content in the carbonatized zone of the footwall exceeds several times its content in the quartz veins and the carbonatized zone of the hanging wall.

Geochemistry of two contrasting deep fluids in the Sardinia microplate (western Mediterranean): Relationships with tectonics and heat sources

The Sardinia microplate in the western Mediterranean represents an ideal example for examining the relationship between fluid geochemistry, tectonic and heat sources in hydrothermal circuits. It consists of a portion of Variscan basement partly covered by sedimentary (mainly carbonate) and volcanic successions that record significant Permian to Pliocene geodynamic events within the southern European margin. The regional structure of the northern Sardinia is dominated by Tertiary ENE–WSW trending strike-slip and NNW–SSE trending normal faults, both capable of controlling deep and shallow fluid circulation. In this paper, results of a detailed geochemical investigation of waters and gases coming from a W-E trending section of central-north Sardinia are presented in order to explain the contrasting thermal and geochemical features of two - already known groups - of fluids. The Volcanic Logudoro Waters (VLW) is a group of cold to hypothermal Na–HCO3 waters characterised by high CO2 contents and mantle-derived He, that are localized in the volcanic-dominated Tertiary grabens. The He mantle signature within the VLW waters is associated with Plio-Pleistocene Quaternary volcanism where the outgassing of mantle-derived fluids is reasonably due recently active magma sources at depth. The currently active emission of mantle-derived gas linked to cold and hypothermal waters, provides evidence that the heat diffusion associated with the Plio-Pleistocene volcanism has already ended. In contrast, the Granite Variscan Basement Waters (GBW) group is characterised by hot-NaCl-rich waters, containing high concentrations of both dissolved N2 and radiogenic 4He. The high contribution of 4He produced by radiogenic decay of U and Th in the crust indicates a supply of radiogenic heat to the hydrothermal system localized within the granitic basement or in the tectonic contact between granite and Tertiary covers.

Geophysical investigation of the possible extension of Ifewara fault zone beyond Ilesa area, southwestern Nigeria

High-resolution aeromagnetic data (HRAD) of parts of the southwestern and north-central Nigeria between 7° 30′ N – 8° 30′ N and 4° 30′ E – 5° 30′ E have been analyzed with a view to investigate the possible extension of Ifewara fault zone beyond Ilesa area. Analyses of the filtered HRAD by analytic signal amplitude (ASA), horizontal gradient magnitude (HGM), first vertical derivative (FVD), and Euler deconvolution (ED) methods were combined to delineate the locations, strikes, and dip directions of the subsurface structures in the area. The inferred structural map and the associated rose diagram indicate that the area is bisected by a number of major and minor faults that trend NE-SW, ENE-WSW, E-W, NW-SE, WNW-ESE, NNE-SSW, and NNW-SSE, among which the NE-SW trending faults predominate. The Ifewara and other major fault zones were clearly delineated. The mapped Ifewara faults trend between NNE-SSW and NE-SW directions and extend from the southwestern part (Ilesa area) to the extreme of north-eastern part of the study area. The study concluded that the Ifewara fault zones exist and do not terminate in the southwestern part of Nigeria but further extends to the northern part, possibly to Nupe basin and Zungeru area.

A new tectonic model for Abu-Dabbab seismogenic zone (Eastern Desert, Egypt): evidence from field-structural, EMR and seismic data

Abu-Dabbab area is the most active seismic zone in the central Eastern Desert of Egypt, where seismic activities are daily recorded. The reported earthquakes are microearthquakes of local magnitudes (ML < 2.0). A spatial distribution of these microearthquakes shows that the earthquakes of the area follow an ENE–WSW trending pattern, which is nearly perpendicular to the Red Sea Rift. Focal mechanisms of different fault styles were recognized with dominant normal faulting (with a strike-slip component) events characterized by focal depths greater than 7 km and reverse ones of shallower focal depths. Several lines of evidence indicating that the brittle-ductile transition zone underlies the Abu-Dabbab area occurs at a relatively shallow depth (10–12 km) and it is acting as a low-angle normal shear zone (LANF). Field-structural, EMR and seismic data (this study) reveal that the maximum compressive stress (σ1) in the area is perturbed from the regional NW–SE direction to ENE–WSW orientation. This stress rotation is evidently akin to the reactivation of the crustal scale Najd Fault System (NFS), where such reactivation is attributed to the ongoing activity/opening of the Red Sea. Our tectonic model proposes that the continuous activity on the brittle-ductile transition zone including the LANF led to stress localization, which triggering a brittle deformation in the upper crustal-levels and associated shallow dipping thrusts. Such bimodal tectonic model suggests that the deep earthquakes are owing to the tectonic movement on the LANF (transtension), whereas the shallow earthquakes are related to a brittle deformation inside the fault blocks of the upper crust (transpression). Deformation creep along this zone didn’t permit continuous accumulation of strain and hence reduce the possible occurrence of large earthquakes.

Basement influences on structural styles in the Bremer and Eyre Sub-Basins, southern Australia

The Bight Basin on the southern margin of Australia is nearly 2000 km wide from west to east and overlies a number of different basement terranes (Figure 1). Major basement terrane divisions occur between the basement of the Ceduna delta and the Eyre and Bremer sub-basins, resulting in changes in structural styles in the overlying basin successions. The Eyre Sub-Basin overlies the boundaries of the Proterozoic Madura and Coompana basement provinces, which are separated by the Mundrabilla shear zone. The shear zone is a N-S trending, continent-wide structure visible in magnetic data which appears to extend offshore in the Eyre Sub-Basin and is also visible as a north-trending present-day fault scarp in the onshore Eucla Basin. Seismic data interpretation suggests that the shear zone steps to the east in the region of the Jerboa-1 well. Differential movement across the shear zone during Jurassic-Cretaceous rifting may have influenced the location of depocentres within the Eyre Sub-Basin. Overlying the Albany Fraser Orogen’s northern foreland, the Bremer Sub-Basin is dominated by WSW-ENE trending half graben structures and large rollover anticlines associated with Jurassic-Cretaceous rifting. The basin is divided by a N-S trending basement structure, visible in gravity data, and in the overlying sedimentary succession as a broad zone of subsidence with several periods of reactivation. Similarities between this structure and the shear zone in the Eyre Sub-Basin suggest they may have a similar origin.

Late Saalian and Weichselian glaciations in the German Baltic Sea documented by Pleistocene successions at the southeastern margin of the Arkona Basin

Seismic profiles and numerous sediment cores of a planned offshore wind farm area northeast of Rügen Island provide a unique insight into the distribution and thickness of glacial deposits in the southern Baltic Sea. Fine gravel analysis enabled recognition of five tills that correspond to different ice advances. On the basis of a 3D structural model, the main Pleistocene events could be reconstructed and correlated with stratigraphical records in the circum‐Baltic area comprising Marine Isotope Stages (MIS) 6 to 2. The oldest till was deposited during the Late Saalian Warthe advance (qs2; c. 150–130 ka). It is only preserved in ENE–WSW trending subglacial channels incised into Upper Cretaceous soft chalk. Isolated rafts and remnants of two Middle Weichselian tills occur locally, whereas Eemian interglacial sediments are missing. The older till (qw*) has an unusual fine gravel composition and might have formed during ice advances known only from northern Denmark and northern Poland (c. 65–60 ka). The younger till represents the Warnow advance (qw0) in NE Germany that can be correlated with the Danish Ristinge advance (c. 55–50 ka). Furthermore, two tills deposited during the Late Weichselian Last Glacial Maximum (c. 24–16 ka) occur. One can be correlated with the Pomeranian advance (qw2), while the other has characteristics typical for the Mecklenburg advance (qw3). These advances eroded older Pleistocene deposits, thus probably also removing the till of the Brandenburg/Frankfurt advance (qw1) – in contrast to the onshore areas. The Pomeranian till is limited to the southeast, close to the shallow Adlergrund, but the Mecklenburg till covers the whole study area. This first detailed lithostratigraphical classification of till units from the Arkona Basin allows for the identification and correlation of Pleistocene successions in other parts of the southern Baltic Sea.

Geomorphology and structural development of the nested summit crater of Láscar Volcano studied with Terrestrial Laser Scanner data and analogue modelling

Many volcano summits host craters that are partially overlapping. The formation of such nested craters has been commonly interpreted as vent migration. Here, we present an additional mechanism that may explain the geometry of nested craters at volcanoes. Láscar Volcano, the most active volcano of the Central Volcanic Zone in the Chilean Andes, hosts ENE-WSW trending summit craters that are partially overlapping (nested). Details on the evolution and interaction between the different craters remain unclear.To create a robust dataset, Terrestrial Laser Scanner (TLS) data were collected at the summit of Láscar in 2013. The resulting topographic data set, consisting of more than 15 million data points with centimetre sampling, allows visualising almost the complete eastern edifice of the volcano's summit. From the TLS data, a Digital Elevation Model (DEM) and a slope map were generated allowing us to create a lineament map and quantify the observed morphological and structural features. To further improve our understanding of the processes responsible for the formation of the craters and geomorphology, we designed sandbox analogue models. Results suggest that one of the craters is a ‘parasite’ crater, formed as a consequence of ongoing activity in the adjacent crater. Our data suggest that the nested craters have all been modified since the last major eruption in 1993, by near surface effects associated with cooling, compaction and gravitational sliding of the crater floor infill. As the active crater deepens, the adjacent inactive crater extends and partially slumps towards the active one. Understanding the structural development of these nested craters is relevant for assessing potential future eruption sites, thus making Láscar a dynamic target for a detailed morphology study. These findings may similarly be applied to other volcanoes, where nested craters have developed.

Active tectonic trends and crustal modeling of the eastern Mediterranean Sea deduced from geophysical data

The eastern Mediterranean Sea is considered as a highly tectonic region evolving from the progressive African-Eurasian collision. The current research is an attempt to resolve the problems related to the geodynamic evolution of this region to delineate the main tectonic trends, the nature and thickness of the crust. These tectonic trends have played a very significant role in the most recent discovery of large gas fields in the mapped region. This has drawn the attention to the needs to investigate this region more thoroughly. Published gravity and magnetic data are utilized and analyzed using the most recent proposed techniques. The integration of the implemented methods revealed more new tectonic trends. The NW–SE trend is the major trend that is associated with Temsah and Misfaq-Bardwil trend while the NE–SW trend that is associated with Rosetta and Eratosthenes Seamount trends. The N–S trend that is associated with Baltim fault trend and another E–W trend is associated with the Neogene hinge zone and the Cyprian Arc. Moreover, a NNE–SSW related to the Tartus thrust trend and the Gulf of Aqaba was observed, in addition to an ENE–WSW trend relates to the Kyrenia-Missi trend. The observed WNW–ESE direction relates to the Animaxander Seamount trend and finally the NNW–SSW trend. Based on the delineated tectonic trends, the mapped region was classified into four main basins namely the Shelf basins, the Margin-dominated basins, the Deep basins, and the Levantine basin to the east. The depth to the basement is an irregular surface and gradually changes from more than 13 km in the northern part and decreases to less than 6 km in the southeastern Mediterranean Sea.

Geomorphic evidences and chronology of multiple neotectonic events in a cratonic area: Results from the Gavilgarh Fault Zone, central India

The ENE–WSW trending Gavilgarh Fault Zone (GFZ) is an important tectonic lineament within the Central Indian shield. Geomorphological mapping and spatial analyses of rivers were carried out to elucidate the imprints of active tectonics on the fluvial systems of this region. The sinuosity index, width–depth ratio of river valleys, longitudinal profile, S–L index and hypsometric index of the rivers flowing from north to south across the GFZ lineament suggest that the northern side of GFZ was tectonically uplifted. Luminescence dating of sediments from river terraces and calculation of knickpoint migration rates in the rivers indicate occurrence of multiple neotectonic events in GFZ at ca. 65–80ka, ca. 50ka, ca. 30–40ka, and ca. 14ka. Evidences of neotectonic activity, presence of active geothermal springs, and occurrence of recent earthquakes along GFZ suggest that this lineament is tectonically active and there is a need for proper seismic monitoring of this fault zone.

Reorganisation of the Triassic stratigraphic nomenclature of northern Switzerland: overview and the new Dinkelberg, Kaiseraugst and Zeglingen formations

In the context of the harmonisation of the Swiss stratigraphic scheme (HARMOS project), the stratigraphic nomenclature of the Triassic sedimentary succession of northern Switzerland has been reorganised to six formations (from base to top): Dinkelberg, Kaiseraugst, Zeglingen, Schinznach, Bankerjoch, and Klettgau Formation. The first three are formally introduced in this paper. The Dinkelberg Formation (formerly «Buntsandstein») encompasses the siliciclastic, mainly fluvial to coastal marine sediments of Olenekian to early Anisian age. The formation is some 100 m thick in the Basel area and wedges out towards southeast. The Kaiseraugst Formation (formerly «Wellengebirge») comprises fossiliferous siliciclastic and carbonate sediments documenting a marine transgressive—regressive episode in early Anisian time. It starts with sandstone, dolomite, continues with subtidal limestone and marl and ends with bituminous shale and supratidal dolomite. Thickness decreases from approximately 50 m in the High Rhine area to 10 m in the south and east. In the Lake Constance area, a transition to the siliciclastic marginal facies of the Vindelician High (Eschenbach Formation in Germany) is documented by borehole evidence. The Zeglingen Formation (formerly «Anhydritgruppe») documents a regressive marine evaporitic megacycle during the Illyrian (late Anisian). At most places, except in far eastern Switzerland, it starts with massive halite deposits. It continues with sulfate and marl sequences and ends with littoral stromatolitic dolomite. In the WSW–ENE trending depot centre total formation thickness is 150 m and more, and thickness of salt layers reaches up to 100 m. In the High Rhine area, the thickness is reduced due to subrecent subrosion. At some places evidence points to syn- to early-post-diagenetic erosion. For practical reasons, the six formations are organised in three lithostratigraphic groups: Buntsandstein Group (with the Dinkelberg Formation), Muschelkalk Group (combining the Kaiseraugst, Zeglingen and Schinznach Formations) and Keuper Group (combining the Bankerjoch and Klettgau Formations).

Neotectonic Activities in Northern Saurashtra Peninsula Bordering Gulf of Kachchh

This study points out the evidences of neotectonics and possible existence of active fault in northern part of Saurashtra Peninsula. The methodology used for the detection of neotectonism are: a) analysis of numerical data obtained from Digital Elevation Model (DEM) and its derivatives (morphometric indices), b) study of geomorphic markers and c) correlation of seismic & palaeoseismic data and geomorphology with structural lineaments. Morphometric indices such as drainage density, stream frequency, bifurcation ratio, basin length, basin relief, relief ratio, elongation ratio, stream gradient index, hypsometric index and sinuosity ratio have been used to assess the tectonic signatures. Morphometric indices suggest that Aji river basin is tectonically active, whereas Und and Sasoi river basins show some of the parameters in active tectonic range. Regional study using remotely sensed data (Landsat OLI multispectral) has helped to show a) about 100° dextral rotation of Aji river trunk channel near the Gulf coast and b) dextral deflection of both Aji and Und river about 25 km from the coast. Study of a segment of Aji river basin near Ranjitpura- Balamba proved upliftment and tilting of land resulting a) narrowing of trunk channel towards sea, b) development of new sets of channels over tilted river terrace, c) development of beheaded channels, d) presence of palaeo-channels and palaeo-delta in different directions with the present ones and e) formation of estuary with definite geometric shape. Occurrence of earthquake epicentres, in conformity with predicted lineaments in addition to paleoseismic records supports the existence of the fault. On the basis of integrated evidences it has been established that the Saurashtra coast along the Gulf of Kachchh is tectonically active with the existence of a dextral strike slip fault (ENE-WSW trending) with a rotational component manifesting tilting of the northern block towards east.

Structure of the Crust Beneath the South Western Cameroon, from Gravity Data Analysis

The study area is located in the south western Cameroon and includes part of the Cameroon Volcanic Line (CVL). Volcanic activity has been recorded in this area, precisely on the Mount Cameroon which recently erupted in 2002. In addition, deadly carbonic gas was emitted by crater lakes (Monoun and Nyos) in 1984 and 1986 respectively. Potential field model EGM2008 has been used to investigate the structure of the crust. A regional/residual separation is performed using upward continuation and polynomial separation methods. The results from this operation show a similarity between the regional anomalies resulting from both methods. The regional anomaly maps present an increasing gradient trending ENE-WSW above and below latitude 5?N. Moreover, six nearly parallel profiles were drawn on the CVL in addition to two other profiles at the northern edge of Congo craton. These profiles were used to estimate the depths of the Moho discontinuity and some shallow sources by the means of the Bouguer and the residual anomalies respectively. The results show that the Moho discontinuity depths vary from 19 - 25 km (under Mount Cameroon) to 28 - 34 km (in Kumbo), while the southern neighbouring zone presents a Moho discontinuity depth ranging between 23 - 31 km (in Ngambe) and 22 - 32 km (in Eseka). These findings agree with the previous seismic and gravity researches lead in the area. EGM2008 is therefore a reliable tool to investigate the subsurface structures.

The integration of gravity, magnetic and seismic data in delineating the sedimentary basins of northern Sinai and deducing their structural controls

The Sinai Peninsula is a part of the Sinai sub-plate that located between the southeast Nubian–Arabian shield and the southeastern Mediterranean northward. The main objectives of this investigation are to deduce the main sedimentary basin and its subdivisions, identify the subsurface structural framework that affects the study area and determine the thickness of sedimentary cover of the basement surface. The total intensity magnetic map, Bouguer gravity map and seismic data were used to achieve the study aims. Structural interpretation of the gravity and magnetic data were done by applying advanced processing techniques. These techniques include; Reduce to the pole (RTP), Power spectrum, Tile derivative and Analytical Signal techniques were applied on gravity and magnetic data. Two dimensional gravity and magnetic modeling and interpretation of seismic sections were done to determine the thickness of sedimentary cover of the study area. The integration of our interpretation suggests that, the northern Sinai area consists of elongated troughs that contain many high structural trends. Four major structural trends have been identified, that, reflecting the influence of district regional tectonic movements. These trends are: (1) NE–SW trend; (2) NNW–SSE trend; (3) ENE–WSW trend and (4) WNW–ESE trend. There are also many minor trends, E–W, NW–SE and N–S structural trends. The main sedimentary basin of North Sinai is divided into four sub-basins; (1) Northern Maghara; (2) Northeastern Sinai; (3) Northwestern Sinai and (4) Central Sinai basin. The sedimentary cover ranges between 2km and 7km in the northern part of the study area.