Top Of Salt Research Articles

Table Top Salt Triage In Improving Pre Hospital Triage Capacity And Disaster Victim Handling Preparedness

Disasters have broad and complex impacts, both on humans and the surrounding environment. One of the challenges often faced in health management efforts in disaster areas is the lack of skills of nurses and other health workers in disaster victim preparedness and the ability to carry out pre hospital triage which will ultimately hamper health services. The knowledge and skills of nurses in handling disaster victims including conducting triage on victims are still in the sufficient category at 60%. In pre hospital situations, the correctness of officers in making triage decisions in handling victims has a very important role. The research objective was to determine the effect of the SALT triage table top in improving pre hospital triage capabilities and disaster victim handling preparedness. The research design used was a quasi experiment with a pre-post test with a control group. Sampling using purposive sampling technique. The number of respondents obtained was 78 people. The results of the Wilcoxon test showed a value of p = 0.000, which means that there is an influence of the SALT triage table top in increasing the ability of pre hospital triage and preparedness for handling disaster victims. Keywords: disaster; preparedness; pre hospital; table tops; triageTable Top Salt Triage Dalam Meningkatkan Kemampuan Triage Pre Hospital Dan Kesiapsiagaan Penanganan Korban BencanaABSTRAK Bencana memiliki dampak yang luas dan kompleks, baik terhadap manusia maupun lingkungan sekitarnya. Salah satu tantangan yang sering dihadapi dalam upaya penanggulangan kesehatan di daerah bencana adalah kekurangan ketrampilan perawat dan tenaga kesehatan lainnya dalam kesiapsiagaan penanganan korban bencana maupun kemampuan melakukan triage pre hospital yang akhirnya akan menghambat pelayanan kesehatan. Pengetahuan dan ketrampilan perawat dalam penanganan korban bencana termasuk melakukan triage terhadap korban masih berada pada kategori cukup sebesar 60%. Pada situasi pre hospital, kebenaran petugas dalam membuat keputusan triage dalam penanganan korban memiliki peran yang sangat penting. Tujuan penelitian untuk mengetahui pengaruh table top SALT triage dalam meningkatkan kemampuan triage pre hospital dan kesiapsiagaan penanganan korban bencana. Desain penelitian yang digunakan adalah quasi eksperiment dengan pre-post test with control group. Pengambilan sampel dengan menggunakan tehnik purposive sampling. Responden yang didapatkan berjumlah 78 orang. Hasil uji Wilcoxon menunjukkan nilai p = 0,000 yang artinya ada pengaruh table top SALT triage dalam meningkatkan kemampuan triage pre hospital dan kesiapsiagaan penanganan korban bencana. Kata Kunci : bencana; kesiapsiagaan; pre hospital; table top; triage

Thin-skinned extensional salt tectonics, counterregional faults, and the Albian Gap of Brazil

Thin-skinned extension detached on salt is mostly well understood. Faults may dip basinward or landward (counterregional) and intersect the top salt or equivalent weld at cusps/rollers. The polarity of faulting may switch over time, and with sufficient extension, the oldest suprasalt strata separate into rafts with intervening younger depocenters. Salt may break through extensionally thinned overburden to grow as passive diapirs, which can widen during ongoing extension but collapse if the salt supply cannot keep pace with extension. Counterregional normal faults are the most debated structures as they may form by: extension, with the footwall moving basinward relative to the hanging wall; or progressive basinward salt expulsion but only vertical movement of the overburden. Extensional counterregional structures are characterized by: (i) strata that predominantly thicken into the bounding structures, but with areas of basinward thinning due to fault/salt geometry and displacement transfer; (ii) highly elongate plan-view geometries; and (iii) the presence of coeval distal translation and contraction. The most controversial counterregional system is the Albian Gap of the Santos Basin, Brazil. We use the criteria above to argue that it formed by post-Albian thin-skinned extension, with little/no extension during the Albian. This contrasts with the Campos Basin along strike to the NE, where Albian and later extension were accommodated on basinward-dipping faults, and is explained by the rift architecture and consequent base-salt dip. The Aptian salt dipped basinward in the Campos Basin and extension was therefore triggered by Albian gravity gliding. However, the base salt dipped landward over a large area of the northern and central Santos Basin, so that Albian gravity gliding was minimal and Late Cretaceous progradational loading drove gravity spreading and the development of the counterregional system. Accommodation for sediment within the Albian Gap was provided in part by stretching and consequent thinning of the underlying salt.

Mud volcanoes and dissolution structures as kinematic markers during salt tectonic deformation

AbstractThe recognition of linear trails of fluid escape pipes that have been deformed by salt flow have recently been suggested to offer a novel approach to reconstructing the internal kinematics of thick salt sequences deforming under gravity. These deformed pipes constrain a number of key parameters for salt tectonic analysis including the salt flow direction, translation distance of the top salt and overburden, the internal flow profile and from the flow velocity, the bulk viscosity of the salt. Here we interpret and characterise two previously unrecognised large‐scale strain markers within a salt sequence that may be equally as valuable as the deformed pipes for constraining salt flow. This study is based on the interpretation of a ca. 4,600 km2 3D seismic survey from the outer slope of the Nile Cone, offshore Egypt, located at the boundary between the extensional and translational domains of the deformed marginal region of the Messinian salt basin. We mapped five deformed pipe trails that allow us to constrain the average flow velocity of the top salt, at ca. 2 mm/yr over the past 2–3 Myrs. The salt flowed in a basinward NW/NNW direction away from the basin margin. In addition, we mapped two large (ca. 2 km diameter) salt dissolution depressions formed by subjacent dissolution of the evaporites. These are presently located down the salt flow direction of a large remnant erosional high at the base of the salt, and in the general alignment of one of the pipe trails. We therefore argue that this dissolution structure most likely formed by fluid venting from the base salt high, and as such can be used to measure translation direction, distance and average velocity. The second of the two novel kinematic indicators requires mapping of genetically connected mud volcanoes and their depletion zones. The study area contains over 400 individual mud volcanoes that are sourced from beneath the salt and erupted from the Early Pliocene to Recent. A subset of these, extruded at or near to the present day seafloor, have well imaged pre‐salt depletion zones vertically beneath the erupted volcanic cones. A smaller subset, typically buried Early Pliocene extrusions, is found to have volcanic cones that are systematically offset laterally from their corresponding depletion zones, with an offset direction and distances closely matched with other kinematic markers. Hence we suggest that mud volcanic plumbing systems can provide another independent kinematic marker from which to infer salt flow regime.

Subsalt imaging in northern Germany using multiphysics (magnetotellurics, gravity, and seismic)

Imaging subsalt is still a challenging task in oil and gas exploration. We have used magnetotellurics (MT) to improve the integration of seismic and gravity data to image the Wedehof salt dome, located in the Northern German Basin. High-density natural field source broadband MT data were acquired and enhanced the definition of the top and overhanging salt structures in addition to imaging the salt dome root. Salt boundaries show strong resistivity contrasts with the surrounding sediments and thus represent a good target for electromagnetic measurements, especially for top salt and salt flanks imaging. With integrated 3D gravity modeling focusing on the salt dome’s flanks at intermediate depths, an improved model was achieved. The new model provided sound input to a follow-up seismic depth migration that led to an improved imaging of the subsalt target proven by subsequent exploration drilling. The integrated interpretation of MT, gravity, and seismic combines the strengths of the different physics, thus increasing imaging reliability and reducing exploration drilling risks. Using a conservative workflow that included a feasibility study with field noise evaluation and careful acquisition parameter testing prior to survey start, a broadband array data acquisition, and advanced processing, the survey area's severe cultural noise issues could be overcome.

Reconstructing salt geometry using 3D CSEM data

Abstract In this paper we demonstrate the imaging capabilities of a newly developed 3D Gauss-Newton inversion algorithm for marine controlled source electromagnetic (CSEM) data by inverting synthetic data generated from a known salt resistivity model. We show that the high resistivity contrast between salt and background sediments can be utilized to reconstruct reliable images of the salt structure without the use of any a-priori information which could bias the outcome. Further, we re-invert a CSEM data set acquired in 2012 in the Salina basin in the Gulf of Mexico, using the same 3D Gauss-Newton inversion algorithm. The resulting resistivity model is compared to the initial salt interpretation based on seismic data. The top salt boundary in the inverted resistivity model correlates well with the initial interpretation. However, the base salt geometry, which is often difficult to map with seismic data alone, is imaged very differently. The CSEM inversion result is robust and independent of other geophysical data and therefore very valuable in a salt imaging workflow to support seismic interpretation and velocity model building.

3D shallow water seismic survey planning to deliver sub-salt imaging in South Gabon

The shallow offshore in south Gabon has been explored for more than 50 years, highlighting the potential for oil discoveries.However, exploration of the sub-salt syn-rift section requires an advanced support that only modern, regionally consistent 3D seismic data can provide. Such support was the objective of a large-scale multi-client 3D seismic programme, representing a collaboration between Spectrum Geo Ltd and the Gabonese Hydrocarbon Authorities (Direction Generale des Hydrocarbures (DHG)), which commenced in December 2016. This survey acquired 11,500 km2 of 3D seismic data in the ‘Gryphon Area’ – the shallow offshore of Mayumba and Sette Cama, west of the Olowi Field, in a range of water depths from 20 to 1000 m (Figure 1). Advanced and accurate modelling allowed for the survey specifications to be tailored to the geological setting and the exploration targets. The previous geological and geophysical exploration was taken as background information to develop the new subsurface imaging. For many years the accepted exploration target in South Gabon has been the high-quality transgressive Gamba Sand-stone of Lower Aptian age, located just below the Ezanga Salt Fm. As the base of the salt is separated from the near ubiquitous Gamba Sandstone Fm. by thin shale (Vembo shale member) the main challenge for seismic acquisition therefore has been the accurate imaging of the base salt, and more importantly the accurate depth imaging of this unit. The overburden is complicated by heterogeneous and highly variable velocities in the post-salt carbonate of Madiela Fm., complex geometries of top salt and variable compositions and velocities within the salt. In south-west Congo (Brazzaville), a number of discoveries have been made over the past 4-5 years, in a new intra syn-rift play. This play targets the Djeno Fm., equivalent in age to the lower syn-rift Kissenda Fm. of South Gabon. This play has rarely been targeted in Gabon owing to the poor imaging of the pre-salt section on legacy 2D and 3D data. This article describes the methodology applied to the pre-acquisition study, which guided the acquisition operation and gave a preliminary insight of the challenges to be faced during the processing.

Intra-salt deformation: Implications for the evolution of the Messinian evaporites in the Levant Basin, eastern Mediterranean

We present new evidence of deformation features supporting a multiple deformation phase mechanism of the Messinian evaporites, through the interpretation of Pre-Stack Depth Migration (PSDM) seismic data including all intra-salt, base of salt (BS) and top of salt (TS) reflectors. The mechanism presented here involves a syn-depositional deformation event caused by a NW basin tilting during the last stage of the Messinian Salinity Crisis (MSC). This was followed by post-depositional differential sediment loading through radial spreading of the Nile Cone after the MSC. Inside the evaporite sequence, the upper intra-salt units may reside in a brittle domain with predominant thrust faults while the lower units in a ductile deformation domain with folds instead. A NW-flowing channel system is for the first time observed on the TS horizon, suggesting a northwestward basin depocenter during the TS formation. The observed NNW-NNE flow of the water bottom (WB) channels indicates the direction of the current basin depocenter, which suggests a dramatic clockwise shift during post-Messinian. A model of the Messinian evaporite evolution in the Levant Basin during the MSC has been established. The model is based on our observations and the detailed intra-salt interpretation, and is divided into four stages: a) the horizontal deposition of all the intra-salt units excluding the uppermost unit, b) the deposition of the uppermost unit and basin NW tilting occurred coevally or sequentially, c) the TS erosion and the development of NW trending TS channels and d) the deposition of post-Messinian sediments over the evaporite sequence.

Structural setting and evolution of the Mensa and Thunder Horse intraslope basins, northern deep-water Gulf of Mexico: A case study

The Mensa and Thunder Horse intraslope minibasins in southcentralMississippi Canyon, northern deep-water Gulf ofMexico, had a linked structural evolution from the Early Cretaceous through the late Miocene. Analysis of the two minibasins illustrates the complexities of deep-water sedimentation and salt tectonics in intraslope minibasins. This study is based on the integration of a 378-mi2 (979-km2) three-dimensional seismic data set,wire-line logs, and biostratigraphic data. These two minibasins comprise several structural features that affected their geologic evolution: basement faults, autochthonous salt, three allochthonous salt systems (top Barremian, top Cretaceous, and Neogene), a growth fault and raft system, three major turtle structures with associated extensive crestal faults, and strike-slip faults. Remnant allochthonous salt pillows are present above the 125 Ma horizon (approximate top Barremian system) and on the 66 Ma horizon (top Cretaceous system) throughout the Mensa minibasin, whereas the top Cretaceous allochthonous salt system is identified regionally by a salt weld in the Thunder Horse area. These allochthonous salt systems formed weld surfaces beneath the Mensa and Thunder Horse turtle structures. Structural features and associated minibasins evolved during several discrete intervals. From the Early Cretaceous through the latest Oligocene (125 to 24 Ma), an extensive allochthonous salt canopy was present within the Mensa and Thunder Horse minibasins. During this interval, sediments loaded the salt, forming thinwedge-and sheet-formdeposits in theMensa area and a thick, northwest-Trending trough in the ThunderHorse area. A secondary allochthonous salt system extruded at the Top Cretaceous level, as seen by remnant salt bodies. Salt withdrawal from these allochthonous salt systems provided accommodation for bowl-and trough-shaped external stratigraphic forms to develop during the Miocene. High sedimentation rates produced salt evacuation from these allochthonous salt systems and initiated diapirism that formed the Neogene allochthonous salt level. The prominent turtle structures in the two minibasins, critical to the formation of traps to the two major fields, developed at slightly different times: Thunder Horse at 14.35 and Mensa at 11.4 Ma. Copyright © 2017 The American Association of Petroleum Geologists. All rights reserved.

Numerical modeling of the deformation of embedded brittle rock bodies in compressive environment during salt tectonics – A case study from SOSB

Large rock inclusions (called stringers) such as carbonate or anhydrite blocks are embedded in many salt bodies. The observation from seismic data shows different ways of movement and deformation of the inclusions, including displacement, folding and fracturing. There remains much unknown about the deformation process of embedded inclusions in a compressive environment during salt tectonics. In this research, we investigate how the differential displacement of the top salt surfaced caused by downbuilding process leads to the deformation of brittle stringers located in-between two sediment pods in a compressive environment by an interative procedure with adaptive remeshing technique to detect and simulate fracture, overtrusting, folding deformation in a finite element model which is established as the generic model from the observations from South Oman Salt Basin (SOSB). The model shows that the compressive environment induces different deformation ways such as shear failure, folding and thrusting of stringers and the stringers can break soon after the onset of salt tectonics. The orientation of the possible shear failure plane (first break) determines the final complex deformation pattern. The initial depth and position of stringer (parallel or horizontal location) strongly influences the time and frequency of breaks.

Megaflaps adjacent to salt diapirs

Megaflaps are steep stratal panels that extend far up the sides of diapirs or their equivalent welds. They have multiple-kilometer fold widths and structural relief and are thus distinct from smaller-scale composite halokinetic sequences. Maximum dips range from near-vertical to completely overturned. Although overturned megaflaps are associated with flaring salt, there is no direct link between megaflap formation and the initiation of salt sheets. Strata within a megaflap are usually convergent, and the lower boundary is typically concordant with the top salt. The upper boundary ranges between a prominent onlap surface and a more diffuse zone of gradual rotation and thinning, and growth strata likewise display both onlap and stacked wedge geometries. We use quantitative cross-section restoration to elucidate the origin and development of megaflaps. Megaflaps typically represent the relatively thin roofs of early salt structures that include single-flap active diapirs, passive diapirs, salt pillows, and salt sheets. They develop during halokinetic drape folding as the minibasin sinks, during contractional squeezing of the diapir and its roof, or during some combination of the two. The kinematics are dominated by either limb rotation or kink-band migration, in which roof strata move through a fold hinge into a lengthening steep megaflap. Both restoration results and direct field evidence suggest that internal strain is minor, with little bed lengthening and thinning. Recognition and understanding of megaflaps are critical to successful petroleum exploration of three-way truncation traps against salt. Megaflaps also have implications for the lateral seal of stratigraphic traps and fluid pressures in minibasins.

Lithology and characteristics of the Messinian evaporite sequence of the deep Levant Basin, eastern Mediterranean

As the lithological composition of the Messinian salt sequence of the Levant Basin is still controversial and unconstrained, we reveal for the first time the lithology of the entire evaporite sequence from deep basin depth migrated seismic and borehole data. The data presented here shows that the seismic transparent layers are composed of pure and uniform halite while the reflective layers are bundles of thin clay layers interbedded in the halite background. The thin clay layers inside the deep basin evaporites have a cumulative thickness of 25–40m. High amplitude fan structures are observed on the deepest internal reflector which may suggest clay transportation. Among all the internal reflectors, the upper units are more deformed while the deeper units are more coherent and flat. Two sets of folds/faults are shown on the shallower intra-units: folds with NNE–SSW trending axes and thrust faults strike NW–SE. On a regional scale, the top salt reflector is generally horizontal while the other internal reflectors dip toward the NW. The shallowest intra-unit is the only one that has a wedge shape thickening to the NW, while the other intra-units generally have uniform thicknesses.

Allochthonous salt initiation and advance in the northern Flinders and eastern Willouran ranges, South Australia: Using outcrops to test subsurface-based models from the northern Gulf of Mexico

The northern Flinders Ranges and eastern Willouran Ranges, South Australia, expose Neoproterozoic salt diapirs, salt sheets, and associated growth strata that provide a natural laboratory for testing and refining models of allochthonous salt initiation and emplacement. The diapiric Callanna Group (∼850–800 Ma) comprises a lithologically diverse assemblage of brecciated rocks that were originally interbedded with evaporites that are now absent. Using stereonet analysis to derive three-dimensional information from two-dimensional outcrops of stratal geometries flanking salt diapirs and beneath salt sheets, we evaluate 10 examples of the transition from steep diapirs to salt sheets, 3 of ramp-to-flat geometries, and 2 of flat-to-ramp transitions. Stratal geometries adjacent to feeder diapirs range from a minibasin-scale megaflap to halokinetic drape folds to high-angle truncations and appear to have no relationship to subsequent allochthonous salt development. In all cases, the transition from steep diapirs to salt sheets is abrupt and involved piston-like breakthrough of thin roof strata, which permitted salt to flow laterally. We suggest two models to explain the transition from steep diapirs to subhorizontal salt: (1) salt-top breakout, where salt rise occurs inboard of the salt flank, thereby preserving part of the roof strata beneath the sheet; and (2) salt-edge breakout, where rise occurs at the edge of the diapir with no roof preservation. Lateral emplacement of salt sheets is dependent on the interplay between the rate of salt supply to the front of the sheet and the sediment-accumulation rate. When the ratio of salt-supply rate to sediment-accumulation rate is high to moderate, thrust advance produces base-salt flats and truncation ramps, respectively. Halokinetic folds are absent because the thrust emerges at the base of the sea-floor scarp and mass-transport complexes are rare as a result of relatively low scarp relief. If the ratio is low, pinned inflation leads to drape folding of the top salt and cover into a fold ramp, with occasional slumping of the sheet and its roof and further breakout on thrust or reverse faults. In the shallow-water depositional environments of South Australia, lateral emplacement of salt sheets occurred through some combination of thrust advance, extrusive advance, and open-toed advance, with no evidence for subsalt thrust imbricates, shear zones, or continuous rubble zones. In deep-water environments, such as the northern Gulf of Mexico, thrust imbricates and rubble zones, which represent slumped carapace, are more common. The presence of slumped carapace is caused primarily by higher topographic relief related to thicker hemipelagic roofs, a lack of dissolution, and gravity-driven transport of overburden strata to the toes of large canopies.

Новые данные по геохимии газов калийных месторождений

Рассмотрен состав газовой фазы соляных пород из ряда европейских (Верхнекамское, Старобинское, польский цехштейн) и азиатских (Тюбегатанское, Жилянское, Сатимолинское) месторождений, что позволило разделить их на две группы. В азиатских объектах происходило формирование только аутигенных сухих газов за счет диагенетического разложения органики. Структурная открытость этих залежей привела к окислению метана и водорода и обогащению углекислым газом. Верхнекамское и Старобинское месторождения в структурном отношении были закрыты для процессов окисления, но открыты во время соленакопления, когда в бассейн седиментации происходил подток тяжелых углеводородов с нижних горизонтов. В истории формирования газового режима Верхнекамского месторождения могут быть выделены три этапа: 1) сингенетичный захват глубинных газов и аутигенной органики, преобразованной при диагенезе до метана, доля которого постепенно возрастает за счет увеличения мощности флюидоупорной соляной залежи; 2) «прорыв» глубинных газов в бассейн при накоплении верхов карналлитовой зоны и покровной каменной соли; 3) соскладчатая мобилизация флюидов, рассеянных в газово-жидких включениях и, вероятно, подток тяжелых углеводородов с углекислым газом, способствующий формированию зон вторичных солей. «Замещение» карналлитовых пластов приводит к высвобождению изоморфного иона аммония и образованию водорода.

An iterative approach to updating velocities beneath postsalt anomalies and its impact on presalt imaging

Complex geology and deepwater presalt targets offshore Brazil lend themselves to seismic imaging challenges. The postsalt sections of the Santos and Campos Basins also featured thin-bed, high-impedance layers of volcanic material and other shallow velocity anomalies. These features were often near the top of salt (TOS) and produced areas of poor presalt focusing. Because accurately modeling the postsalt was imperative for imaging the presalt, we developed a new workflow for velocity model updating. Where previous top-down methods have failed, our method embraced the challenges of imaging beneath the volcanics by incorporating additional presalt information into the updates. Our method is interpretation-dependent but provides a robust and reliable workflow for updating the postsalt velocity model in the presence of complex geology. Using a narrow azimuth data set acquired with variable-depth streamers, we evaluated the effectiveness of our iterative workflow. The result was improved presalt imaging.

The Szamotuły salt diapir and Mid-Polish Trough: Decoupling during both Triassic-Jurassic rifting and Alpine inversion

The Szamotuły diapir is located on the southwestern shoulder of the Mid-Polish Trough in west-central Poland. The area underwent crustal-scale extension during the Triassic-Jurassic and Alpine-related inversion during the Late Cretaceous to Paleogene. The diapir is sourced entirely from the Permian Zechstein salt, but there are also thin evaporites within the Triassic. A regional 2D depth-migrated seismic profile, an array of 2D time-migrated data, and quantitative structural restorations are used to illustrate that extensional and contractional deformation were almost completely decoupled by the Zechstein salt. Beneath the salt, interpreted Carboniferous half-grabens were reactivated during the Triassic, offsetting the base salt but not the top salt and causing regional thickening of the Triassic-Jurassic overburden. Inversion was accommodated by reverse movements on the deep faults and uplift of the Triassic-Jurassic strata to form the broad anticlinorium of the Mid-Polish Swell. Cover extension and contraction were concentrated around the Szamotuły Diapir. A linear reactive diapir formed during the Early to Middle Triassic and broke through to become a passive diapir during the Late Triassic that subsequently widened into the Jurassic. Along strike, coeval extension was recorded by ongoing reactive diapirism. Alpine contraction caused squeezing of the passive diapir and the correlative reactive diapir, folding of flanking and overlying strata, and inversion of some of the reactive normal faults. However, shortening was accommodated differently above and below the Upper Triassic Keuper salt. Lower and Middle Triassic strata moved laterally into salt, whether into the passive diapir or into the reactive diapir along strike. Younger strata were folded and thrusted, with delamination at the Keuper evaporites that were depositionally thicker adjacent to the reactive diapir. Zechstein salt squeezed from deeper levels flowed passively into the space created by delamination, producing an allochthonous salt wing in the subsurface.

Numerical modelling of the displacement and deformation of embedded rock bodies during salt tectonics: A case study from the South Oman Salt Basin

Abstract Large rock inclusions are embedded in many salt bodies and these respond to the movements of the salt in a variety of ways including displacement, folding and fracturing. One mode of salt tectonics is downbuilding, whereby the top of a developing diapir remains in the same vertical position while the surrounding overburden sediments subside. We investigate how the differential displacement of the top salt surface caused by downbuilding induces ductile salt flow and the associated deformation of brittle stringers by an iterative procedure to detect and simulate conditions for the onset of localization of deformation in a finite element model, in combination with adaptive remeshing. The model set-up is constrained by observations from the South Oman Salt Basin, where large carbonate bodies encased in salt form substantial hydrocarbon plays. The model shows that, depending on the displacement of the top salt, the stringers can break very soon after the onset of salt tectonics and can deform in different ways. If extension along the inclusion dominates, stringers are broken by tensile fractures and boudinage at relatively shallow depth. Spacing of the boudin–bounding faults can be as close as 3–4 times the thickness of the stringer. In contrast, salt shortening along the inclusion may lead to folding or thrusting of stringers.

3D seismic study of complex intra-salt deformation: An example from the Upper Permian Zechstein 3 stringer, western Dutch offshore

Abstract Most of the information on subsurface evaporitic structures comes from 3D seismic data. However, this data only provide limited information about the internal structure of the evaporites, which is known from salt mines and salt diapir outcrops. Brittle intra-salt layers (carbonate, anhydrite, clay) of at least 10 m thickness form good reflectors in evaporites, but the structure and dynamics of such ‘stringers’ in the salt movement are poorly understood. In this study, we investigate the intra-salt Zechstein 3 (Z3) stringer from 3D seismic data in an area offshore the Netherlands. Observations show complex deformation including boudinage, folding and stacking. Reflections from thin and steep stringer parts are strongly reduced, and we present different structural models and tests of these. We compare our observations to structural models from salt mines and analogue/numerical models of intra-salt deformation. A smoothed representation of the upper surface of the stringer fragments follows the shape of Top Salt, but smaller-scale stringer geometries strongly differ from this and imply boudinage. The imaged disharmonic patterns of constrictional folds provide evidence for the complexity of the intra-salt, in agreement with observations in salt mines. This may be explained by interaction of the layered salt rheology, complex three-dimensional salt flow, different phases and styles of basement tectonics and movement of the overburden.

Geology and tectonics of the South Atlantic Brazilian salt basins

Abstract This paper first reviews the salt basins and depositional ages in the South Atlantic salt province. This comprises a series of salt basins separated by basement highs, deep graben (that never dried up), later volcanic highs and subaerial ocean spreading ridges. Initial halite and anhydrite deposition occurred first in the Sergipe-Alagoas Basin of NE Brazil at c. 124.8 Ma, and was closely followed by deposition in the Kwanza Basin, Angola between 124.5 and 121 Ma. The later potassium-magnesium-rich salts were deposited in the Sergipe-Alagoas and Gabon-Congo basins before 114.5 Ma. The age of the main Santos-Campos salt is not known precisely, but the latest anhydrites deposited on the southern margin of the Santos Basin post-date volcanic rocks dated at 113.2 Ma. The paper then compares the salt tectonics of the wide Campos-Santos Basin segment with the narrow South Bahia basins segment. Sediment loading in the Santos Basin produced a landward-dipping base salt, which led to the development of counter-regional faults, and inhibited downslope sliding, and enhanced later contractional effects caused by either gravity spreading or regional tectonic compression. Folding occurred in simultaneous pulses across the Santos Basin, suggesting that regional tectonic compression occurred. The narrow salt basins of South Bahia have a steeply dipping base salt horizon (4°) and pronounced folding, which initiates at the oceanward pinch-out of the salt and propagates back up the slope. The topographic highs, above fold anticlines, are rapidly eroded on narrow margin slopes, which allows the folds to grow more easily to large amplitudes at the top salt horizon.

The Geophysics Department of Humble Oil and Refining Company (1924–1945)

Editor's note: Historical Perspective is a new feature to accommodate unsolicited articles that deal with historical records and personal perspectives of early geophysics. These invaluable documents are usually written in styles of their own that would often require extensive editing, reorganization, and/or fact verification to suit TLE standards—a process which could, in turn, rob them of their patina and even historical value. To differentiate them from Profiles, Mentoring, and other regular TLE human interest articles, and acknowledge their unique status as historical documents is the reason the Editorial Board has created this new feature. Here, these unsolicited and sometimes unorthodox contributions can be published with only the most essential of microedits and abridgements. This column is based on a document authored by D. P. Carlton in February 1946 and submitted to TLE by Thomas Barrow. L. F. Garrett made the first proposal to use refraction seismograph surveys for finding structures in the Gulf Coast of Texas, according to E. DeGolyer, in 1905 or 1906. He and Robert Welch tried to obtain seismograph equipment but gave up the idea because of the expense and the fact that no suitable instruments were available. The first trail of any geophysical method was made in 1922 when the Rycade Oil Co., using a torsion balance, completed a gravity survey of the Spindle Top salt dome in Jefferson County, Texas. The first seismograph crew with German equipment and personnel came to Texas in 1924 from Seismos, Ludger Mintrop's company. They were under contract to the Marland Oil Co. Shortly a similar Seismos crew went to work for the Gulf Production Co. Early in 1924, Wallace Pratt, chief geologist of the Humble Oil and Refining Co., was convinced that geophysical methods were based on real scientific principles; that in order to keep pace with the industry, …

Wave equation GSP prestack depth migration and illumination

A heterogeneous medium with strong velocity contrast and complex subsurface structures presents a great challenge to seismic imaging. Prestack depth migrations based on the wave equation are accurate but very expensive, thereby limiting their use. However, recent advances in efficient 3D wavefield extrapolators and the continued increase in computing performance are making application of full 3D prestack wave equation depth imaging more affordable. In addition, since PreSDM was first employed for subsalt and carbonate imaging, there have been major advances in efficient and accurate 3D wavefield extrapolation technologies. The generalized screen propagator (GSP) is a one-way wave-equation-based wide-angle propagator that can provide high-resolution and high-fidelity subsurface images. GSP neglects up/down reverberations between heterogeneities and correctly handles forward multiple-scattering phenomena including focusing/defocusing, diffraction, and wave-interference effects. The algorithm alternates between the space-domain and wavenumber-domain via the fast Fourier transform (FFT). The operations within each domain are self-adaptive to the complexity of the medium, making this method robust in the presence of strong velocity contrasts. GSP can be directly applied for prestack shot-record depth migration. The forward downgoing wave from the source side and backward extrapolation of the upgoing wave from the receiver side independently use the same propagator. At each depth step, application of a correlation or deconvolution imaging condition determines a depth image. Figure 1 shows a prestack shot-record migration on the Sigsbee2 data set provided by the Smaart JV Project. Figure 1b shows that the top of salt is well imaged by the GSP migration even for the very steep-sided synclinal feature in the top salt surface. The amplitude and phase of the base salt are imaged well and have good continuity, and the diffractors beneath the salt are clearly reconstructed. The image quality in the finite-difference migration (Figure 1c) is generally comparable to the GSP result, but the …