Structural Lineations Research Articles

Failure mechanism by wrench faulting in Central Anatolia

The study area, where volcanism and tectonism are active at the same time, consists of the Cappadocia Volcanic Complex (CVC) in the middle, Tuzgölü on the west side, and Ecemiş fault systems on the east side. Remote sensing image processing method and derivation to aeromagnetic data were applied to identify the structural lineations that tectonically control the study area within the scope of the study. As a result of the lineation analysis performed in the west of the study area, 167 lineaments in the west, most of which are NW oriented, and 316 lineaments, most of which are NE oriented, were determined in the east. These findings are in agreement with the known fault orientations in the area. It is known that earthquakes greater than M > 4 occurred in these known faults during the neotectonics period, and they also have the potential to produce M > 6 earthquakes. In addition, the Tuzgölü and Ecemiş Faults' shearing effect relative to each other is an indication that a wrench tectonics mechanism has developed in the study area. With the remote sensing study and following the existing surface traces, two fault systems in opposite directions, the Tuzgölü Fault (−30°) dipping counterclockwise and the Ecemiş Fault, clockwise (60°) dipping, were determined. The orientation and locations of the faults could be determined by tilt transformation applied to the magnetic anomaly map of the study area. In particular, the effects of wrenching in the study area can be clearly observed in magnetic anomalies.

Geomorphic characterization of a seasonal river network in semi-arid western India using the River Styles Framework

The imprint of geologic, climatic and anthropogenic memory as controls on geomorphic river diversity is assessed for twelve River Styles in the Sabarmati Catchment. Geologic controls are the primary determinant of river character and behavior in the hinterland and pediment landscape units, where headwater streams transition to partly confined valleys and gorges with distinct structural lineations in a rectangular drainage network. Climate memory imprints entrenched rivers that make up alluvial fan and alluvial plain landscape units of the mid-lower catchment, shaped by phases of sediment aggradation and subsequent incision in response to enhanced monsoonal rains around 10 ka. Terraces constrain channels within confined and partly confined valleys with occasional and discontinuous floodplains respectively. Laterally unconfined channels are only found in the lower parts of the catchment, immediately upstream of the estuary/delta. Limited space for adjustment, impacts of flow regulation and ephemeral conditions restrict the range of contemporary river morphodynamics, but ridges and swales and abandoned channels on floodplains indicate more dynamic conditions in the past. Impacts of anthropogenic memory are most pronounced in the stopbank-controlled, barrage- and dam-impacted reaches, especially in the cities of Gandhinagar and Ahmedabad. An explanation of controls upon geomorphic river diversity, including an assessment of the role of stream power, presents a coherent platform to develop geomorphologically-informed approaches to river management.

The Significance of the Banda Sea: Tectonic Deformation Review in Eastern Sulawesi

DOI:10.17014/ijog.7.3.291-303The geology of eastern Sulawesi is widely known for its complexity due to multiple deformation stages.The geology on land has been studied excessively, but little assessment has been made on the offshore geology, thus the geological evolution of the area remains a subject of controversy. A thorough observation of high multibeam bathymetry dataset offshore and SRTM dataset onshore provides an understanding on the geological features relating to the tectonic deformation. Exquisite morphological features include carbonate buildups and gravitational collapse dominating the shelf areas whereas distinct form of ridges and seamount exists in the offshore. Structural features in this area including the major Tolo Thrust and South Sula Fault varied structural lineations on land with several polygonal extensional faulting and accretionary wedge on the west of the North Banda Sea. The existence of these features may indicate that the area was majorly deformed during Neogene, specifically relating to the opening of the Banda Sea due to the subduction rollback of Banda.

Neotectonics of the Eastern Korean Margin Inferred from Back-arc Rifting Structure

Earthquakes occur frequently in the continental shelf and slope area of the Korean Peninsula in the East Sea (Japan Sea) although they are mostly not large in magnitude. This area constitutes the eastern Korean margin, marking a transitional structure from rifted continental crust to oceanic crust that resulted from lithospheric extension into breakup in a back-arc. We reviewed how the crustal structure of the eastern Korean margin was emplaced to understand its correlation with the present seismicity. Back-arc extension that caused rifting and breakup at the Korean margin took place sequentially from the northern to southern parts in the Late Oligocene through the Early Miocene. The stress regime of the Korean margin switched from extension to compression in the Middle Miocene, resulting from the collision of the Philippine Sea Plate with the Japan Arc. The structural lineations at the Korean margin inherited from backarc rifting and breakup are interpreted to be prone to earthquakes by showing a close spatial correlation with ongoing seismicity. The changing geometry of the estimated locus of breakup at the Korean margin that follows a curvilinear path appears to induce diverse focal mechanisms of the earthquakes under the present compressive stress field.

53–43 Ma Deformation of Eastern Tibet Revealed by Three Stages of Tectonic Rotation in the Gongjue Basin

AbstractThe Gongjue basin from the eastern Qiangtang terrane is located in the transition region where the regional structural lineation curves from east‐west‐oriented in Tibet to north‐south‐oriented in Yunnan. In this study, we sampled the red beds in the basin from the lower Gongjue to upper Ranmugou formations for the first time covering the entire stratigraphic profile. The stratigraphic ages are bracketed within 53–43 Ma by new detrital zircon U‐Pb ages constraining the maximum deposition age to 52.5 ± 1.5 Ma. Rock magnetic and petrographic studies indicate that detrital magnetite and hematite are the magnetic carriers. Positive reversals and fold tests demonstrate that the characteristic remanent magnetization has a primary origin. The Gongjue and Ranmugou formations yield mean characteristic remanent magnetization directions of Ds/Is = 31.0°/21.3° and Ds/Is = 15.9°/22.0°, respectively. The magnetic inclination of these characteristic remanent magnetizations is significantly shallowed compared to the expected inclination for the locality. However, the elongation/inclination correction method does not provide a meaningful correction, likely because of syn‐depositional rotation. Rotations relative to the Eurasian apparent polar wander path occurred in three stages: Stage I, 33.3 ± 3.4° clockwise rotation during the deposition of the Gongjue and lower Ranmugou formations; Stage II, 26.9 ± 3.7° counterclockwise rotation during deposition of the lower and middle Ranmugou formation; and Stage III, 17.7 ± 3.3° clockwise rotation after 43 Ma. The complex rotation history recorded in the basin is possibly linked to sinistral shear along the Qiangtang block during India indentation into Asia and the early stage of the extrusion of the northwestern Indochina blocks away from eastern Tibet.

Discussion on ‘The structural interpretation of domainal trace lineation: an example from the Mona Complex, Anglesey’

In a recent short note, Lisle (2013) uses an example from the New Harbour Group of Anglesey, UK, to illustrate a type of structural lineation he terms ‘domainal trace lineation’. This is a form of intersection lineation manifested in fine banding, considered to be the intersection of one domainal foliation (e.g. crenulation cleavage) on another domainal foliation. If Lisle’s interpretation is correct, it implies that the New Harbour Group has at least four phases of deformation, compared with the two that are recognized in the underlying South Stack Group at Rhoscolyn (e.g. Shackleton 1969; Treagus et al . 2003). Furthermore, if the pervasive lineation in the New Harbour Group is considered to be an intersection lineation, this has significant consequences for the regional tectonics. As noted by Lisle, the much-described lineation in the New Harbour Group has been described as a ‘stretching lineation’ by Shackleton (1969), Powell (1979) and Roper (1992), and a ‘quartz stretching lineation’ by Phillips (1991). In a paper overlapping Lisle’s, we describe it as a ‘quartz elongation lineation’ (L1) that is folded with the S1 foliation (Treagus et al . 2013). Lisle notes that only Hudson & Stowell (1997) considered the prominent lineation in the New Harbour Group to be an ‘intersection lineation’. Nevertheless, on the basis of one locality, …

Seismic volcanostratigraphy of the western Indian rifted margin: The pre-Deccan igneous province

[1] The Indian Plate has been the focus of intensive research concerning the flood basalts of the Deccan Traps. Here we document a volcanostratigraphic analysis of the offshore segment of the western Indian volcanic large igneous province, between the shoreline and the first magnetic anomaly (An 28 ∼63 Ma). We have mapped the different crustal domains of the NW Indian Ocean from stretched continental crust through to oceanic crust, using seismic reflection and potential field data. Two volcanic structures, the Somnath Ridge and the Saurashtra High, are identified, extending ∼305 km NE–SW in length and 155 km NW–SE in width. These show the internal structures of buried shield volcanoes and hyaloclastic mounds, surrounded by mass-wasting deposits and volcanic sediments. The structures observed resemble seismic images from the North Atlantic and northwest Australia, as well as volcanic geometries described for Réunion and Hawaii. The geometry and internal seismic facies within the volcanic basement suggest a tholeiitic composition and subaerial to shallow marine emplacement. At the scale of the western Indian Plate, the emplacement of this volcanic platform is constrained by structural lineations associated with rifting. By reviewing the volcanism in the Indian Ocean and plate reconstruction of the area, the timing of the volcanism can be associated with eruption of a pre-Deccan continental flood basalt (∼75–65.5 Ma). The volcanic platform in this study represents an addition of 19–26.5% to the known volume of the West Indian Volcanic Province.

Methodology for the computation of volcanic susceptibility: An example for mafic and felsic eruptions on Tenerife (Canary Islands)

A new method to calculate volcanic susceptibility, i.e. the spatial probability of vent opening, is presented. Determination of volcanic susceptibility should constitute the first step in the elaboration of volcanic hazard maps of active volcanic fields. Our method considers different criteria as possible indicators for the location of future vents, based on the assumption that these locations should correspond to the surface expressions of the most likely pathways for magma ascent. Thus, two groups of criteria have been considered depending on the time scale (short or long term) of our approach. The first one accounts for long-term hazard assessment and corresponds to structural criteria that provide direct information on the internal structure of the volcanic field, including its past and present stress field, location of structural lineations (fractures and dikes), and location of past eruptions. The second group of criteria concerns to the computation of susceptibility for short term analyses (from days to a few months) during unrest episodes, and includes those structural and dynamical aspects that can be inferred from volcano monitoring. Thus, a specific layer of information is obtained for each of the criteria used. The specific weight of each criterion on the overall analysis depends on its relative significance to indicate pathways for magma ascent, on the quality of data and on their degree of confidence. The combination of the different data layers allows to create a map of the spatial probability of future eruptions based on objective criteria, thus constituting the first step to obtain the corresponding volcanic hazards map. The method has been used to calculate long-term volcanic susceptibility on Tenerife (Canary Islands), and the results obtained are also presented.

ESTUDO DA RELAÇÃO ENTRE LINEAMENTOS ESTRUTURAIS E A EXPLORAÇÃO DE ÁGUA SUBTERRÂNEA POR MEIO DA ANÁLISE DE FAVORABILIDADE

Favorability analysis has been applied as a method to evaluate the correlation between the structural lineament and flow behavior in aquifers. The analysis was carried out in the outcropping areas of Tubarão Group, between the cities of Campinas and Sorocaba (São Paulo State, Brazil). The study area was chosen because of its geological complexity and the consequent lower predictability of well performance before drilling. To apply this method, we considered as “mineralized” areas those regions with highest specific capacity values, taking also into account six types of variables interpreted from radar images Landsat 7-ETM, Shuttle Radar Topography Mission (SRTM) and structural geological maps. The results reveal that the region encompassing between the cities of Elias Fausto and Monte Mor presents the best correlation with structural lineation which can be a factor in the high potential for groundwater exploration in this area.

Paleotectonic structures and their influence on recent seismo‐tectonics in the south Kuril subduction zone

Abstract Bathymetric data from south of Hokkaido obtained during a cruise of R/V Hakuho‐Maru are summarized, and their correlation with earthquake occurrence is discussed. There are structural lineations on the seaward slope of the Kuril Trench, oblique to the Kuril Trench axis and parallel to the magnetic lineations in the Pacific plate. The structural lineations comprise horst‐grabens generated by normal faulting. This suggests that Cretaceous tectonic structures originating at the spreading centre affect present seismotectonics around the trench axis. The structural‐magnetic relation is compared to the case of the Japan Trench. North‐east of the surveyed area, there are two major fracture zones (Nosappu Fracture Zone and Iturup Fracture Zone) that divide the oceanic plate into three segments. If the fracture zones (FZ) and the zone of paleo‐mechanical weakness, represented by magnetic lineations, can control the direction of normal faults at a trench, the extent of the resulting topographic roughness on the seaward slope of the trench would be different across an FZ because of the differences in ages. By studying recent large earthquakes occurring in the south Kuril region, it is shown that several main‐aftershock distributions for large earthquakes in this region are bounded by the Nosappu FZ and the Iturup FZ. Two models (Barrier model and Rebound model) are presented to interpret earthquake occurrence near the south Kuril Islands. The Barrier model explains seismic boundaries seen in several examples for earthquake occurrence in the south Kuril regions. The fracture zone forming the boundary of two segments with different magnetic lineations is also the boundary of two different normal fault systems on their ocean bottom, and the difference in sea‐bottom roughness between two normal fault systems should affect the seismic coupling at a plate interface. Due to the difference of seismic coupling, earthquake occurrence is controlled by an FZ and then the FZ acts as a seismic boundary (Barrier model). Existing normal faults created by plate bending of subducting oceanic plate should rebound after its subduction (Rebound model). This rebound of normal faults may cause intraplate earthquakes with a high‐angle reverse‐fault mechanism such as the 1994 Shikotan Earthquake. The energy released by an intraplate earthquake generated by normal‐fault rebounding is not directly related to that of interplate earthquakes such as low‐angle thrust earthquakes. It is a reason why large earthquakes occurred in the same region during a relatively short period.

The Pitcairn Islands, South Pacific Ocean: plate tectonic and climatic contexts

Abstract The remote Pitcairn Group in the South Pacific Ocean comprises a volcanic island (Pitcairn Island), two low coral atolls (Oeno, Ducie) and a raised coralline island (Henderson Island). The geological history of these islands, on anomalously thin oceanic lithosphere, is related to the development of two subparallel island chains (Oeno-Henderson-Ducie; Pitcairn) associated with intra-Pacific plate `hotspot' activity; the surface manifestation of this activity has been partly determined by structural lineations in the plate inherited from past plate history. The climate of the Pitcairn Islands is determined by the position of the subtropical high pressure system and the South Pacific Convergence Zone. Variations in the strength of this atmospheric circulation system, measured by changes in the Southern Oscillation index of pressure difference, provide a partial explanation of the long-term variability of mean annual rainfall at Pitcairn Island. Knowledge of past climates in the Pitcairn Group remains speculative. Maps of the Pitcairn Islands and a report of climate at Henderson Island (2/91–1/92) are included in the paper.

Magnetic susceptibility, magnetic mineralogy and magnetic fabrics in a late Archean granitoid-gneiss belt

The Opatica belt is a late Archean granitoid-gneiss terrane situated within the northern Abitibi Subprovince, along the northern margin of the Abitibi greenstone belt, Quebec. This belt is composed of several suites of tonalite-granodiorite-granite composition, variably deformed under epidote-amphibolite to upper-amphibolite grade conditions. Specimens from 87 sampling sites within the Opatica belt show a wide range in variation of magnetic susceptibility ( K ); the large variations are due essentially to varying proportions of ferromagnetic trace minerals. Detailed study of the opaque mineralogy by reflected light petrography, electron microprobe analysis and SEM observations, as well as alternating field and thermal demagnetization experiments confirm that multi-domain, very pure magnetite is the dominant ferromagnetic phase which, along with ferrosilicates, contribute to the magnetic susceptibility. In some cases, hematite may also make a significant contribution to K . In rocks with low K , the susceptibility may be dominated by the ferrosilicates hornblende and biotite. Intensity of anisotropy of magnetic susceptibility (AMS) is also highly variable, and appears to be controlled by the mineralogy of the rock rather than by strain intensity or deformation state. The shapes of AMS ellipsoids are also controlled by mineralogy. Detailed comparisons are made of AMS fabrics with field measurements of magmatic and metamorphic foliations and mineral and stretching lineations, and with mineral lineations determined by image analysis of polished slabs. There is very good agreement between the average orientations of poles to structural foliations, and the average orientation of the K 3 principal axes of the susceptibility ellipsoids in all outcrops. In most cases, there is also good agreement between average structural lineations and the average K 1 axis. In quartz-monzodiorites, disagreement between the average lineation and average K 1 may be due to complex textural occurrences of magnetite, and the presence of abundant hematite. In gneisses, broad scatter of the orientations of K 1 for individual samples from an outcrop (quantified by statistical confidence regions about the principal axes) locally occurs within the foliation plane, and may be attributed to the partial overprinting of earlier fabrics by subsequent deformation.

Morphological and structural studies of the Society and Austral hotspot regions in the South Pacific

The southeastern extension of the Society (Teahitia hotspot) and Austral (Macdonald hotspot) volcanic chains were extensively studied (1986–1989) using multi-channel echo-sounding (Seabeam), bottom imaging systems and submersible dives. Sea floor within these hotspot regions consists of recently constructed submarine highs built on crust that shows morphological and structural discontinuities with the surrounding, ancient abyssal hill regions (> 4200 m in depth). Recent volcanic and hydrothermal activity is present on several volcanoes within the Society hotspot and on the Macdonald volcano. Previous studies carried out in the Society hotspot region showed several geological provinces: 1. (1) Eight major highs (> 1000 m in height) which extend from above sea level down to a depth of 3750 m. These features have been formed by lateral eruptive events along rift zones which are aligned along four main structural directions—N150°–180°, N80°, N30°–40° and N110°—which correspond to the orientations of ancient ridge axes, transform faults and Riedel-type shear zones, respectively. 2. (2) The sea floor, which slopes away from the base of each major volcano (3750–4200 m depth), has an average slope of 0.5°, and is characterized by smooth topography and volcanic cones less than 500 m high. 3. (3) The surrounding abyssal hill region, which has an average slope of 0.1° near the Society hotspot, consists of faulted terrane with a N170° orientation, and ancient elongated structural highs. From the structural lineations observed in the Society hotspot volcanoes, a reconstruction of volcanic features has been made. It is proposed that the formation of the seamounts occurs in an organized fashion along pre-existing preferential structural orientations that are associated with zones of crustal weakness.

Relationship Between Structural Development, Carbonate Reservoir Development, and Basement Faulting in Southern Scott and Northwestern Finney Counties, Kansas: ABSTRACT

Hydrocarbon production from carbonate reservoirs in the Hugoton embayment, southwest Kansas, is mainly from structurally positive features with well-developed porosity and permeability. In the study area, these reservoirs tend to be associated with oolite development on shallow shelflike areas and accumulations of oolites along relatively rapid changes in paleorelief. However, not all positive structures of similar depositional environments displayed productive reservoir characteristics. In an attempt to understand reservoir development and the timing of the apparent tectonic events in this area, structural and magnetic lineation data (defined by airborne magnetic data) were correlated.

Seismotectonics around the Mariana trough

Strike-slip type mechanism solutions, with approximately east-west striking tension axes, were obtained for large shallow earthquakes under the central topographic high of the northern Mariana Trough. These solutions are consistent with the model that spreading is in progress in the direction perpendicular to the structural lineations trending N-S in most of the trough and NNW-SSE in the northern part. Weak coupling at the subduction zone between the Pacific plate and the landward plate (Mariana platelet) is suggested by the occurrence of few thrust type and many normal fault type earthquakes near the Mariana Trench. Spreading striking nearly E-W with an approximate total rate of 6 cm/yr in the widest section of the trough is speculatively inferred from the plate motion model of the Philippine Sea plate with respect to the surrounding plates and from the anchored slab model and the collision effect of the Caroline Ridge with the Philippine Sea plate.

Isotopic dating and structural relationships of granitoids and greenstones in the East Pilbara, Western Australia

A structural RbSr isotopic study has been made on two small areas in the eastern Pilbara block, Western Australia. The sites were chosen because they showed good interrelationships of granitoid and greenstone units. At Warrery Gap, on the western side of the Corunna granitic dome, the acid volcanics of the Duffer Formation (at the top of the lower Talga-Talga Subgroup of the Warrawoona Group) show some updating, but a good 3506 ± 62 Ma isochron, with initial ratio (IR) of 0.7006 ± 0.0011, was recognized, consistent with the 3452 ± 16 Ma zircon measurement of Pidgeon (1978b). Both a penetrative D 1 deformation, and the doming of D 2 preceded intrusion of late tectonic granitoids, dated at 3270 ± 22 Ma (IR = 0.7015 ± 0.0003), into both the Duffer Formation and the overlying pillow lavas of the Salgash Subgroup. Thus, the Salgash Subgroup is much older than suggested by Glikson (1979) and the stratigraphic succession cannot contain a hiatus between the apparently conformable Talga-Talga and Salgash Subgroups of the magnitude he proposed. The granitic domes clearly owe their form to the D 2 deformation rather than to batholitic intrusion, but near horizontal structural lineations suggest that they were not formed by diapiric movements. A granodiorite and pink feldspar granite from just within the Corunna granitic dome are slightly deformed: pooled isochrons indicate an age of 3232 ± 27 Ma but different IRs of 0.7032 and 0.7009, respectively. At Tambourah, in the eastern Shaw granitic dome, local D 2 also deforms an intrusive microadamellite of age 3087 ± 34 Ma and IR = 0.7103 ± 0.0057. There is therefore a real spread in ages of D 2 granitoids and D 2 deformation between about 3300 and 3100 Ma. Layered megacrystic gneiss, at Tambourah, also intruded by the microadamellite, contains a nebulous foliation argued to be local S 1 . Layered and homogeneous megacrystic gneiss produce updated RbSr total rock isochrons of 2995 ± 95 and 2779 ± 38 Ma, respectively. The primary age of these D 1 gneisses is clearly greater than that of the D 2 granitoids and is probably indicated by Pidgeon's (1978c) zircon age of 3417 ± 40 Ma from the Shaw granitic dome. If so, Hickman's (1975) “Migmatite Suite” contains both D 1 gneisses and D 2 granitoids separated in age at Tambourah by ca. 300 Ma, although neither appears to be older than the lower part of the preserved layered sequence. The protocrust on which that sequence was deposited has yet to be directly identified.

Crustal studies in the La Malbaie Region, Quebec

The results of three seismological investigations of the crust in the seismically active La Malbaie Region are reported. First arrivals from a reversed reflection–refraction profile within the Charlevoix structure indicate a uniform Pg velocity of 6.08 ± 0.04 km/s. Secondary arrivals forming discontinuous, sometimes arcuate segments on the record sections are interpreted as subcritical reflections from structural contortions related to impact of the Charlevoix meteorite. A coherent event at 14 s may signal reflection from the M-discontinuity near 45 km depth.Analysis of travel times from calibration shots recorded by a network of stations spanning the St. Lawrence River in terms of time–distance profiles, travel time residuals, and numerical models provides excellent support for a model of the Precambrian–Paleozoic contact striking along the north shore and dipping to the southeast about 20° beneath the wedge of 5.5 km/s sediments.Unreversed profiles obtained by recording timed Thetford Mines blasts across a similar network suggests a comparable deep structure beneath the north and south shores, with average crustal velocities of 6.8 and 6.7 km/s, respectively. A minor mid-crustal discontinuity is suggested, and Moho depth is estimated at 42–43 km.The 6.2 km/s upper crustal velocity found for the crater and immediately surrounding area is anomalously low compared to the 6.4–6.5 km/s reported for the eastern shield region. Structural lineations gleaned from satellite imagery suggest an elongated area of impact-related disruption much larger than previously recognized. This expanded area of crustal weakening encompasses and may partially explain the zone of continuing microseismic activity, as well as the low upper crustal velocity of the La Malbaie Region.

Landsat satellite imagery of the Qattara Depression area, Egypt

The Qattara Depression lies in the northern part of the Western Desert of Egypt at a distance of some tens of kilometers to the south of the Mediterranean Sea Coast. The depression in question is the largest one in the great Sahara extending across North Africa. It covers an area of some 19,000 km 2 at − 60 m level and the absolute level of its lowest point is about − 134 m. The depression extends for about 300 km in a roughly ENE-WSW direction, while its width is variable reaching to a maximum of about 145 km. Feasibility studies are currently carried out for the Qattara solar-hydro-electric project which aims at generating hydro-electric power by the drop of the Mediterranean Sea water into the depression after passing through a canal/tunnel system. Peak load electric power may be also generated by raising the water to the small hollow of Deir Kirayim, situated at a higher level near the depression, and allowing it to drop to a low level. For the purpose of assessing the regional criteria involved in the implementation of the project and the environmental impact of such implementation, the Qattara Depression and the surrounding area has been studied on a regional scale by the utilization of LANDSAT satellite imagery. The maps produced by the interpretation of the images in question include those of the geological and environmental units, structural lineations, drainage and vegetation cover. Lineation density and drainage density maps are derived by the computation of the structural lineation and drainage maps respectively. A map of groundwater conditions is worked out on the basis of the image interpretation, and the observations previously carried out on the groundwater aquifers in the Qattara Depression and the surrounding area. LANDSAT satellite image interpretation and computation are supported by intensive observations carried out in the field as well as chemical, petrological and mineralogical analyses of the samples collected. The LANDSAT satellite images proved to be of great importance in mapping the Qattara Depression floor which is hardly accessible to classical mapping, and especially in view of the large area which could be covered by imagery mapping in a reasonably short time compatible with the duration of the feasibility study. The special characters of the spaceborne multispectral imagery have been paramount in deciphering the major regional features of the investigated area. The overall synoptic picture of the regional setting of the geological and environmental units, faults, fractures and folds, drainage lines and plant cover in the large area studied has been clarified for the first time. It has been demonstrated that the Qattara Depression is actually constituted of several small depressions. The environmental impact of the project implementation has been visualized especially regarding the possible influence of the saline water on the fresh groundwater sources. The thick salt accumulation in the depression has been found to be of such extension as to increase the salinity of the Mediterranean Sea water stored in the depression following the implementation of the project. The lineation density map has been particularly of great help in the localization of sites subjected to intense crustal deformation, greater slope instability and run off surface water flooding.

Structural lineations in the Canary basin, eastern central North Atlantic

A corridor 315 km wide centered along the southeast projection of the Atlantis fracture zone between 21°W and 29°W was investigated with seismic reflection, bathymetric, gravity, and magnetic profiles. Six sub-parallel, sediment-filled troughs in acoustic basement trend about 106° across the abyssal hills and lower continental rise off northwest Africa. Where the southernmost structural lineations cross the abyssal plain, they are interrupted by a ridge trending 080° surmounted by volcanic peaks. The structural lineations become less distinct landward of the western margin of the abyssal plain coincident with a decrease in topographic relief on acoustic basement and increasing sediment thickness. This transition is coincident with a reduction in the amplitude of gravity and magnetic anomalies.

Stratigraphy and Tectonic Features of Paradox Basin, Four Corners Area

The Permian-Pennsylvanian Paradox basin of the Colorado Plateau contains an elongate wedge of sedimentary rocks which is more than 20,000 feet thick near the Uncompahgre front. Cambrian shelf-carbonate and detrital sediments were deposited over the general area as the sea transgressed eastward from central Utah onto the southwestern extension of the Transcontinental arch. Ordovician and Silurian strata are absent, but a carbonate unit of questionable age may prove to be Ordovician. Upper Devonian shelf deposits and Mississippian carbonates were deposited over the area, again along the eastern flank of a western sea. Regional uplift and exposure of the Mississippian carbonate resulted in the formation of a karst topography, on which the regolithic Molas Formation of Atokan age was developed. Tectonic activity associated with the growth of the Ancestral Rockies then broke up the old shelf area in Early Pennsylvanian time and formed the Paradox basin with its p esent northwest-southeast structural grain. The Hermosa Group, Des Moines-Virgil in age, is a heterogeneous rock unit composed of: marine sandstone and carbonate with plate-algal mud-mounds and bioherms; restricted marine sapropelic dolomite, anhydrite, and salt; conglomeratic marine and continental arkose, red sandstone, and shale. The Hermosa Group is divided into three formations where the anhydrite facies is present: lower Hermosa or Pinkerton Trail Formation, dolomite and black shale; Paradox Formation, evaporites; and upper Hermosa or Honaker Trail Formation, carbonate, sandstone, and red, green, and gray shale. The rock units are cyclic and the black shales are used as time-markers for a finite time-rock zonation; these cycles have been named the Alkali Gulch, Barker Creek, Akah, Desert Creek, and Ismay. Hy rocarbons are produced from the sediments of each of these cycles, but this paper is concerned only with the Desert Creek and Ismay cycles. During Pennsylvanian time the Paradox basin was almost encircled by highlands (Uncompahgre and San Luis uplifts) on the northeast and east, and by lowlands (Defiance, Kaibab, and Emery uplifts) on the south and west. The sea entered the basin from the southeast through what is now the San Juan basin. The detritus for approximately 15,000 feet of conglomerate, arkose, and red shale (Permian-Pennsylvanian Cutler Group) was shed southwestward from the highlands and was deposited in a narrow frontal belt. In the southwestern part of the basin, the Permian is only 2,000 feet thick and is represented by four formations: Halgaito, red siltstone, sandstone, and shale; Cedar Mesa, sandstone; Organ Rock, red siltstone and shale; and DeChelly, eolian sandstone. Approximately 3,000 feet of Jurass c-Triassic continental shale and fluvial and eolian sandstone blanketed the Permian-Pennsylvanian basin and highlands, and these sedimentary rocks now crop out in the western two-thirds of the basin. Upper Cretaceous marine detritus, remnants of which are present only on the eastern basin edge, were derived from a distal southern and western source. Major tectonic phases in the Paradox basin area were: (1) Ordovician-Silurian, regional uplift; (2) latest Mississippian, regional uplift; (3) Early Pennsylvanian, Paradox basin formed; (4) Late Pennsylvanian-Cretaceous, salt flowage producing salt anticlines; (5) Late Cretaceous, Laramide orogeny developed new structural lineations and rejuvenated the Pennsylvanian trend; and (6) Tertiary, regional uplift and igneous intrusion and extrusion. Major hydrocarbon production is from reservoirs developed in Mississippian and Pennsylvanian carbonates with only minor production from Devonian and Permian sandstones. The important Cretaceous reservoirs are essentially a northwestern continuation of the bar-sandstone trend of production of the San Juan basin. Traps in the Mississippian are structural whereas those in the Pennsylvanian are mostly stratigraphic. Approximately 90 per cent of the current ultimate recovery estimate, 425-450 million barrels of oil, will be from Pennsylvanian reservoirs, with the Aneth field ultimate recovery from Desert Creek-Ismay plate-algal mud-mounds estimated to be 350 million barrels.