Elisional processes and salt tectonics: Communication 1. Catagenetic transformations in saliferous sequences

The work is dedicated to catagenetic transformations in sedimentary rocks with consideration of defluidization in clayey and evaporite sediments and analysis of salt tectonics and hydrogeology in the North Caspian depression.     

Distribution and formation conditions of salt diapirs and mud volcanoes

Analysis of the distribution of salt diapirs and mud volcanoes in the Earth’s continental block reveals their frequent spatial coincidence. These structures are also characterized by similar morphological and geological structures indicating their elisional origin. The appearance of zones with anomalously high formation pressures (AHFP) is the main factor responsible for the development of mud volcanoes and salt diapirs. The anomalously high formation pressure reflects transformation of the phase composition of salts, clay minerals, and dispersed organic matter under the influence of thermolysis and thermocatalysis in closed physicochemical systems.     

Geological and geophysical study of salt diapirs for hazardous waste disposal

Solving the problem of waste is one of the central tasks of environmental protection. It is becoming increasingly difficult to find suitable sites that are acceptable to the public. Salt and salt formations have relevant properties to be utilizing as a repository for each kind of waste. The favourable properties of salt make rock salt highly suitable as a host rock, in particular for non-radioactive and radioactive wastes. Tehran and suburb as an industrial state require a waste reservoir. The Great Kavir (the largest salt desert in Iran) with more than 50 diapirs has surrounded the eastern and southern part of Tehran Province. The Qom and Garmsar basins are the nearest salt diapirs to Tehran province, and there are suitable repository for waste disposal. Great Kavir diapirs have been investigated as a case study based on surface and subsurface studies for its suitability to host a repository for various types of waste. The procedure should be based on field work for surface investigation and also include geophysical studies for subsurface investigations. This research work is presented in regard to site selection in the Central Iran Salt Basins for deposition of only certain types of waste. Results of this study will indicate if the Central Iran Salt Basins are appropriate place to deposit industrial wastes in the deep bedded salt.     

Multiple fluid components of salt diapirs and salt dome cap rocks, Gulf Coast, U.S.A.

Salt diapirs contain a few percent of anhydrite that accumulated as residue to form anhydrite cap rocks during salt dissolutions. Reported ⁸⁷Sr/⁸⁶Sr ratios of these salt-hosted and cap rock anhydrites in the Gulf Coast, U.S.A., indicate their derivation from Middle Jurassic seawater. However, a much wider range of ⁸⁷Sr/⁸⁶Sr ratios, incorporating a highly radiogenic component in addition to the Middle Jurassic component, has been found in several Gulf Coast salt domes. This wide range of ⁸⁷Sr/⁸⁶Sr ratios of anhydrite within the salt stocks records Sr contributions from both marine water and formation water that has equilibrated with siliciclastics. During cap rock formation this anhydrite either recrystallized in the presence of, or was cemented by, a low-Sr fluid with a Late Cretaceous seawter-type Sr isotope ratio or simply lost Sr during recrystallization. Later, the cap rock was invaded by warm saline brines with high Sr isotope ratios from which barite and metal sulfides were precipitated. Subsequently, low-salinity water hydrated part of the anhydrite bringing to six the total number of fluids that interacted througout the history of salt dome and cap rock growth. The progenitor of these salt diapirs, the Louann Formation, is generally thought to have formed from marine water evaporated to halite and, rarely, higher evaporite facies. Salt domes in the East Texas, North Louisiana, and Mississippi Salt Basins have ⁸⁷Sr/⁸⁶Sr and δ³⁴S values that corroborate a Mid-Jurassic age for the mother salt. However, salt domes in the Houston and Rio Grande Embayments of the Gulf Coast Basin have ⁸⁷Sr/⁸⁶Sr ration ranging to values higher than both Middle Jurassic seawater and all Rb-free marine Phanerozoic rocks. These anomalous ⁸⁷Sr/⁸⁶Sr ratios are probably derived from radiogenic Sr-bearing fluids that equilibrated with siliciclastic rocks and invaded the salt either prior to, or during, diapirism. Potential sources of the radiogenic ⁸⁷Sr component include clay and/or feldspar (located either in older units beneath the Louann Formation or younger units flanking the salt diapirs) and K-salts within the Louann evaporites. Because partial Sr exchange in anhydrite had to take place in a fluid medium, admittance of radiogenic ⁸⁷Sr-bearing fluids into the salt may have led to diapirism by lowering the shear strength of the crystalline salt. The slight number of anomalous ⁸⁷Sr/⁸⁶Sr values in the interior basins indicates that anomalous values are related to areally discrete structural or stratigraphic controls that affected only the Gulf Coast Basin.     

Formation mechanism of diapirs of relict lagoonal sediments on the underwater slope of the Curonian Spit

Geological-geophysical methods were applied to provide deeper insight into the nature of unique relict lagoonal sediments exposed on the underwater slope of the Curonian Spit. The study of textural features and morphology of the deformed lagoonal sediments indicates a similarity of their formation mechanism with clay diapirism. Analysis of seismoacoustic data and side scan sonar survey allowed us to establish the configuration of paleolagoon and to determine the direction of dune migration in the past.     

Evaporate deposits and salt diapirs of the Urvantsev trough on the North Kara Sea

The Evaporate Urvantsev Trough was recognized on the basis of new geophysical seismic data. The trough is filled with Lower Paleozoic deposits, with a regional unconformity located at the Devonian-Carboniferous boundary. Salt diapirs of various shapes are a typical peculiarity of the trough. By analogous wtih the sections of Severnaya Zemlya and the Timan-Pechora basin, the age of the salts is defined as Early Ordovician.     

Formation and upwelling of mantle diapirs through the cratonic lithosphere: Numerical thermomechanical modeling

This paper reports the results of the numerical modeling of gravitationally instable processes in the lithospheric mantle of ancient cratons. The gravitational instability is considered as a result of melting at the lithosphere base owing to its local heating by anomalous mantle. Modeling was based on a finite element method in 2D formulation and took into account the geological structure and thermomechanical parameters of the lithosphere of the Siberian platform. Numerical results revealed the main tendencies in the mantle diapirisim of the mafic and ultramafic magma ascending through the “cold” high-viscosity lithosphere. It was shown that the shape of diapiric magmatic bodies is controlled by realistic visco-elastic-plastic rheology of lithosphere. The ascent of diapir in lithosphere was modeled for diverse regimes differing in duration, temperature field, and upwelling depth. It was concluded that the ascent of melt through lithosphere to the crust-mantle boundary is mainly controlled by rheology, and conditions of oscillatory diapirism with recurrent magma replenishments were modeled. Modeling results may shed light on some features related to the trap magmatism of the Siberian igneous province. The duration and rate of magma upwelling as well as the parameters of periodical magma upwelling were estimated and attempt was made to explain the high-velocity seismic anomalies that were recorded in the subcrustal regions of the Siberian platform.     

The origin of dolomite associated with salt diapirs in central Tunisia: Preliminary investigations of field relationships and geochemistry

Black and white dolomite crystals (mm to cm width) of different isotopic composition are associated with Triassic diapirism in central Tunisia, as well as with evaporite minerals and clays. The white dolomites occur mostly in the Jabal Hadifa diapir near the contact with Cretaceous limestones, whereas the smaller black dolomites occur in the Jabal Hamra diapir. The former dolomite has a narrow range of δ¹⁸O and δ¹³C values (− 3.83‰ to − 6.60‰ VPDB for δ¹⁸O; − 2.11‰ to − 2.83‰ VPDB for δ¹³C), whereas the latter dolomite has a wider range and more depleted values (− 4.92‰ to − 9.97‰ for δ¹⁸O; − 0.55‰ to − 6.08‰ for δ¹³C). However, the ⁸⁷Sr / ⁸⁶Sr ratios of most of the samples are near Triassic seawater values. Dolomite formation is due to at least two different fluids. The main fluid originated from deeper hydrothermal or basinal sources related to the Triassic saliferous rocks and ascended through faults during the diapiric intrusion. The second, less important fluid source is related to meteoric water originating from Cretaceous rocks.     

被动大陆边缘盐构造研究进展

内容提要:被动大陆边缘的含盐盆地多在重力作用下发育薄皮盐构造.这些构造不但记录了盆地的演化过程,而且往往富含大量的油气资源.因此,被动陆缘盐构造是学术界与工业界共同关注的热点.在传统的被动陆缘含盐盆地模型中,盆地主要在重力作用下形成上坡的拉张区,下坡的挤压区和两者之间的转移区.近年来,国际学术界围绕重力变形在盆地中的作...     

Characteristic features of salt tectonics offshore North Sinai, Egypt

Salt tectonic along offshore North Sinai was studied using seismic reflection data. The study revealed and identified various types of salt tectonics and structures in the study area. The triggering mechanism of salt tectonics was attributed to the pressure regime initiated from overloading sediments on the Messinian evaporites. The sediment load of 3,000?m exceeds the critical load (more than 1,000?m) and hence creates a pressure zone. The salt-generated structures resulted from thin-skinned extension that is driven by gravity gliding of the overloading sediments above the Messinian evaporite boundary, which acts as a detachment layer. These structures comprise normal growth faults and keystone grabens, trending roughly perpendicular to the slope of the continental margin. Salt tectonics in the study area were also triggered by the deformation of the movement of evaporite layer that causes stretching and fragmentation of the evaporite layer. Moving salt layer took place laterally and vertically, causing lateral and vertical pressures inside the Pliocene sediments. These movements of sediments led to the formation of salt rollers, salt weld, salt diapirs, rollover structures, and fault blocks. The interpretation of seismic data illustrates that the evaporite layer was switched off between the famous reflector M at its top and another reflector N at its base. M reflector is present and can be traced across the whole study area, while the N reflector pinched out in some parts of the study area.     

3D gravity modeling of the Triassic salt diapirs of the Cubeta Alavesa (northern Spain)

Up to now subsurface information permitted the delineation of the top of the Triassic salt, all throughout the Cantabro–Navarro domain, although little was known on the location and geometry of its base and thus on the estimation of the total salt thickness. A 3D-gravity inversion scheme combined with a 3D analytic method has been conducted to map out the geometry of the main salt structures of the basin. The gravity modeling results have been constrained by well log information and available geological and reflection seismic data. The combined 3D scheme integrated with available geological and geophysical data has allowed us to obtain the geometry of the main diapirs that characterize the central and marginal regions of the basin.From our interpretation, the Salinas de Añana diapir has almost vertical flanks and can be divided into two different parts, one of them forming a lateral overhang of the main body.The Salinas de Oro diapir has near vertical flanks and a main axis in the N–S direction. Also, the anomaly is rather more extensive than the outcrop of the diapir, which implies an important expansion of non-outcropping salt in this area. Like the Hoz-Sobrón diapir, the Salinas de Ollo diapir is long and narrow. stretching in the NW–SE direction, which includes three important highs, plus an intense zone of salt migration.The Estella and Alloz diapirs crop out individually in spite of being connected at depth. Also two non-outcropping salt domes have been detected to the south of Atauri that, like the Estella diapir, are related to the thrust front. We point out the gravity signature of the Murguia diapir, which shows an intense gravity high probably due to the presence of high-density rocks in the cap rock or more probably due to the existence of Triassic volcanites of ophitic texture pinched-off into the diapir.     

含油气盆地盐构造研究进展

简要讨论了近年来含油气盆地盐构造研究的主要进展,这些进展主要表现在盐构造地质建模、三维可视化、物理模拟和数值模拟、平衡剖面分析和构造复原以及盐构造形成机制等方面。盐构造是一类与油气聚集关系极为密切的构造类型,在波斯湾、北海、墨西哥湾、北欧和非洲大陆边缘等油气资源丰富的地区有大量分布。中国在塔里木、渤海湾、江汉、四川等盆地广泛发育多期盐岩层和多种类型的盐构造,但国内盐构造研究相对较少,对盐及其相关构造的变形组合样式、三维地质建模和三维可视化、盐构造形成机理和动力学演化的研究是薄弱环节。对于塔里木、渤海湾盆地以及中国南方海相碳酸盐岩层系来说,区域性盐岩盖层的存在和分布将是油气藏得以保存的关键。深入探讨盐构造特征将有助于深化对中国含油气盆地构造演化、构造样式和油气成藏过程的认识。     

The impact of salt diapirs on the quality of carbonate karst waters,Bastak, Iran

The Gavbast karstic aquifer located in southern Iran is in direct contact with an exposed salt diapir. To assess the influence of the diapir on the quality of groundwater in the karstic aquifer, electrical conductivity, total dissolved solids, flow rate, temperature and major ion concentrations were measured at 57 sampling sites, including springs, surface waters and wells. A conceptual model of groundwater flow is proposed for the Gavbast karstic aquifer based on the geological setting, water budget, local base of erosion, and hydrochemistry of the sampling sites. The model suggests two subbasins in the Gavbast Anticline draining into two distinct discharging alluvial sections. Unexpectedly, groundwater discharging from the carbonate Gavbast aquifer is saline or brackish and water is of chloride type. The study indicates that the source of salinity of the Gavbast aquifers is infiltration of surface diapir-derived brine into the aquifer. The contribution of the diapir brine in the Gavbast karst aquifer is calculated about 4 L/s, using chloride mass balance. Construction of salt basins to evaporate brine discharging from the diapir springs is proposed to reduce the salinity of karst water. A row of strategically placed wells in the Gavbast karst aquifer would potentially exploit large volumes of fresh groundwater before it is contaminated by the salt. Such low-cost remediation should allow the agricultural exploitation of 40 km² of currently barren land.     

Holocene marine terraces on two salt diapirs in the Persian Gulf,Iran: age,depositional history and uplift rates

Slightly inclined Holocene marine terraces cover parts of two circular salt diapirs (Hormoz and Namakdan) in the Persian Gulf. Their relative altitude above present sea level results from a combination of general marine transgression/regression affecting the whole area, and of local uplift related to salt diapirism. Differential uplift rate of the studied diapirs in centre‐to‐rim profiles was calculated from results based on: (i) radiocarbon ages of skeletal remains of benthic faunas (19 samples), which originally grew close to sea level; (ii) original altitude of samples, estimated from general sea‐level oscillation curves for the last 10 kyr, and (iii) present sample altitude measured in the field. Calculated uplift rates increase from rim to centre on both diapirs in the range from: 2 mm yr^?1 at the rim to 5–6 mm yr^?1 at the interior of Hormoz, and 1–3 mm yr^?1 at the rim to 3–5 mm yr^?1 at the interior of Namakdan. Such uplift rate distributions fit into the parabolic profile of Newtonian fluid rather than to profiles typical for pseudoplastic fluids. The increase in uplift rate with distance from rim to centre of diapirs is gradual as demonstrated also by generally smooth surface of marine terraces. No tectonic dissections were found. The depositional history on both salt diapirs is similar although they are situated more than 100 km apart. Marine sedimentation started at about 9.6k cal. yr BP on Hormoz and at 8.6k cal. yr BP on Namakdan. Owing to rapid transgression, the sea partially truncated both salt diapirs and rapidly deepened, and carbonate mud was deposited on the peripheries of both salt diapirs. Between 7 and 5k cal. yr BP beach deposition replaced carbonate mud. Soon after 5k cal. yr BP, the sea retreated from most of the marine terraces on both salt diapirs. Copyright © 2006 John Wiley & Sons, Ltd.     

Hydroextrusion as a possible mechanism for the ascent of diapirs,domes, and mantle plumes

A possible mechanism of the ascent of material within the Earth’s crust and mantle is the mechanism of hydroextrusion, i.e., the effect of squeezing of material under excess pressure. The major factors that predetermine the high plasticity of the material and its ability to produce hydroextrusions are high lithostatic pressures and temperatures. The phenomenon of hydroextrusion can be most clearly illustrated by the example of the origin of salt diapirs. The driving force of hydroextrusions of material in the crust and mantle is excess pressure, which can result from lateral differences between the densities of rocks (as is the case during the development of salt diapirs) and phase transitions associated with a volume increase. When the material of the upper mantle undergoes partial melting with the derivation of basaltic melts at depths of 60–100 km, excess pressures reach 80 MPa, whereas the plasticity limit of 20% melted rocks is no higher than 5 MPa. As a result, the partially molten material is forced from the melting region toward zones with lower lithostatic pressures. A local temperature increase in the transitional zones in the Earth’s mantle at positive dP/dT values of the phase transitions also gives rise to excess pressures, whose values can range from 100 to 800 MPa at a 0.5–3.0% volume change and which can be the driving force during the origin of mantle plumes. Original Russian Text ? V.N. Anfilogov, Yu.V. Khachai, 2006, published in Geokhimiya, 2006, No. 8, pp. 873–878.     

Structural evolution of the southern Rif Cordillera (Morocco): tectonics and synsedimentary fault processes

This paper attempts to investigate the tectonics of the southern Rif Cordillera. Hydrogeological and oil well data, together with interpretation of seismic reflection lines help to characterize the architecture of the Rharb–Mamora Basin located in the frontal region of the Gibraltar Arc. The facies map constructed from the drilling data exhibits four main types of Pliocene facies: (i) conglomerates; (ii) limestones; (iii) sandstones and sands more or less rich with shelly remains; (iv) clays. The lateral variation of deposits is accompanied by thickening, which can reach a few tens of metres. Thickening of layers and lithofacies variation indicate synsedimentary faulting processes. Two major fault zones have been identified: Kenitra–Sidi Slimane Fault Zone (K2SFZ) and Rabat–Kenitra Fault Zone (RKFZ). In the western coastal area, the geometrical configuration suggests a partition into horsts and grabens in the southern part, and a system of three geological units in the northern part. The analysis and interpretation of the gravity data reveal an important gravity anomaly, referred to as the Kenitra Gravity Anomaly. It corresponds to the Hercynian faults deduced by the seismic reflection line interpretation: K2SFZ and RKFZ. From Larache to El Jadida cities, the Kenitra area represents the hinge between the positive and negative gravity values, with a major negative anomaly in the eastern part of Kenitra. Copyright © 2004 John Wiley & Sons, Ltd.     

Mud Volcanoes: Distribution Regularities and Genesis (Communication 2. Geological–Geochemical Peculiarities and Formation Model)

The work discusses relationships between mud volcanoes, tectonic faults, folds, and oil-and-gas deposits. The location of roots and centers of mud volcanic activity is analyzed. It proposes a new model of mud volcano formation, according to which these structures result from the development of elision systems of sedimentary basins.     

库车前陆盆地与波斯湾盆地盐构造对比研究

通过对库车前陆盆地和波斯湾盆地的盐层发育状况、盐构造特征以及盐构造与油气关系的对比研究,认为盐底辟构造与油气密切相关。库车前陆盆地勘探程度较低,应注重寻找盐底辟构造,以及与其相关的圈闭。库车前陆盆地盐构造的形成机制与波斯湾盆地下法尔斯组/加奇萨兰组相似,与霍尔姆兹组不同。根据波斯湾盆地下法尔斯组/加奇萨兰组盐构造在油气成藏中的作用,认为库车前陆盆地南部盐层较厚的地区应加强盐下勘探的力度,寻找盐下圈闭。北部山前盐层欠发育地区应注重寻找盐上圈闭,同时兼顾盐下圈闭。库车前陆盆地具有良好的三叠系和侏罗系烃源岩,应该有很广阔的勘探前景。     

Problems of Siderite Formation and Iron Ore Epochs: Communication 2. General Issues of the Precambrian and Phanerozoic Ore Accumulation

It is shown that peat bogs, which accumulate coal- and siderite-bearing sediments, serve as a generator of ferruginous solutions with the significant part of Fe migrating from them in the form of metalloorganic compounds. The stability of organic Fe-bearing complexes provides favorable conditions for the late diagenetic–catagenetic siderite formation in adjacent sea basins. It has been established that the formation of Phanerozoic coals, oil shales, and black shales was nearly coeval with the formation of goethite–chlorite–siderite ores. The paper discusses the influence of volcanic activity on the formation of Precambrian–Phanerozoic iron ore deposits and emphasizes the significance of siderite formation in the general evolution of the sedimentary iron ore formation.