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Hemin Koyi - One of the best experts on this subject based on the ideXlab platform.
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Geometry and structural evolution of Lorbeus Diapir, northwestern Tunisia: polyphase Diapirism of the North African inverted passive margin
International Journal of Earth Sciences, 2014Co-Authors: Amara Masrouhi, Olivier Bellier, Hemin KoyiAbstract:Detailed geologic mapping, structural analysis, field cross-sections, new dating based on planktonic foraminifera, in addition to gravity signature of Lorbeus Diapir, are used to characterize polyphase salt Diapirism. This study highlights the role of inherited faulting, which controls and influences the piercement efficiency and the style and geometry of the Diapir; and also the localization of evaporite early ascent displaying Diapiric growth during extension. Salt was extruded along the graben axis developed within extensional regional early Cretaceous tectonic associated with the North African passive margin evolution. Geologic data highlight reactive Diapirism during Albian time (most extreme extension period) and passive Diapirism during the late Cretaceous post-rift stage. Northeastern Maghreb salt province gives evidences that contractional deformations are not associated with significant Diapirism. During shortening, the initial major graben deforms as complex anticlines where Diapirs are squeezed and pinched from their feeding.
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Sheets within Diapirs – Results of a centrifuge experiment
Journal of Structural Geology, 2011Co-Authors: Carlo Dietl, Hemin KoyiAbstract:We carried out a centrifuge experiment to model the Diapiric rise of a stratified PDMS layer from three perturbations through a non-Newtonian, ductile overburden. The experiment carried out at 700 g resulted in three composite Diapirs fed by different PDMS layers. The three resulting Diapirs represent two different stages of Diapirism. One of the Diapirs (Diapir 1), which reached its level of neutral buoyancy and extruded at the surface of the model, was tabular in profile and copied by an internal intrusive body. The other two Diapirs (Diapirs 2 and 3) were still in the ascending stage when centrifuging was stopped and thus did not extrude at the surface. They displayed a typical balloon-on-string geometry, which develops at a high viscosity contrast between a highly viscous overburden and a less viscous buoyant material. The internal geometry of these last two Diapirs, fed by the lower impure PDMS, however, did not copy the shape of their precursors. Instead, they had a finger-like shape. The finger geometry of the internal part of the Diapirs might be the result of the higher viscosity of the impure lower PDMS intruding a less viscous clean PDMS. Compared to nature, Diapir 1 represents a fully developed concentrically expanded pluton or nested Diapir, while Diapirs 2 and 3 resemble composite plutons which host magma batches of dyke-like geometry. Based on the results of our experiment we suggest that truly concentrically expanded plutons develop from the latter.
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Viscosity estimates of salt in the Hormuz and Namakdan salt Diapirs, Persian Gulf
Geological Magazine, 2010Co-Authors: Soumyajit Mukherjee, Christopher J Talbot, Hemin KoyiAbstract:The parabolic surface profiles of the Hormuz and Namakdan salt Diapirs in the Persian Gulf suggest that they have been extruding with Newtonian viscous rheologies for the last 10 4 years. We derive velocity profiles for these Diapirs, neglecting gravitational spreading and erosion/dissolution while assuming incompressible Newtonian rheology of the salt. Fitting known rates of extrusion at specific points in its elliptical cross-section, the dynamic viscosity of the salt of the Hormuz Diapir is found to range between 10 18 and 10 21 Pa s. Approximating its sub-circular cross-section to a perfect circle, the range of viscosity of the salt of the Namakdan Diapir is obtained as 10 17 –10 21 Pa s. These calculated viscosities fall within the range for naturally flowing salts elsewhere and for other salt Diapirs but are broader than those for salts with Newtonian rheology deforming at room temperatures. The salts of the Hormuz and Namakdan Diapirs are expected to exhibit a broader range of grain size, which matches the limited existing data.
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The control of salt supply on entrainment of an anhydrite layer within a salt Diapir
Journal of Structural Geology, 2008Co-Authors: Zurab Chemia, Hemin KoyiAbstract:The influence of four parameters (sedimentation rate, viscosity of salt, stratigraphic location of the anhydrite layer within the salt layer, and the perturbation width) on salt supply to down-built Diapirs and its entrainment capacity are studied systematically in numerical models. Model results show that these four parameters affect salt supply, and the evolution history of a salt Diapir. As such, these parameters strongly influence the style and the amount of entrainment of dense inclusions into a Diapir. In active Diapirs (i.e. unburied Diapirs), salt supply increases with increasing sedimentation rate whereas it decreases with an increase in salt viscosity. Diapirs initiating from wide perturbation provide more salt supply to feed the Diapir. Presence and initial stratigraphic location of any denser layer (e.g. an anhydrite layer) within a salt layer also affects salt supply. When lateral forces are negligible, salt supply into a Diapir depends on these four parameters, which directly control the entrainment of any embedded anhydrite layer into the Diapir.
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Numerical modelling of rise and fall of a dense layer in salt Diapirs
Geophysical Journal International, 2008Co-Authors: Zurab Chemia, Hemin Koyi, Harro SchmelingAbstract:This thesis uses results of systematic numerical models to argue that externally inactive salt structures, which are potential targets for radioactive waste disposal, might be internally active due to the presence of dense layers or blocks within a salt layer.The three papers that support this thesis use the Gorleben salt Diapir (NW Germany), which was targeted as a future final repository for high-grade radioactive waste, as a general guideline.The first two papers present systematic studies of the parameters that control the development of a salt Diapir and how it entrains a dense anhydrite layer. Results from these numerical models show that the entrainment of a dense anhydrite layer within a salt Diapir depends on four parameters: sedimentation rate, viscosity of salt, perturbation width and the stratigraphic location of the dense layer. The combined effect of these four parameters, which has a direct impact on the rate of salt supply (volume/area of the salt that is supplied to the Diapir with time), shape a Diapir and the mode of entrainment. Salt Diapirs down-built with sedimentary units of high viscosity can potentially grow with an embedded anhydrite layer and deplete their source layer (salt supply ceases). However, when salt supply decreases dramatically or ceases entirely, the entrained anhydrite layer/segments start to sink within the Diapir. In inactive Diapirs, sinking of the entrained anhydrite layer is inevitable and strongly depends on the rheology of the salt, which is in direct contact with the anhydrite layer. During the post-depositional stage, if the effective viscosity of salt falls below the threshold value of around 1018-1019 Pa s, the mobility of anhydrite blocks might influence any repository within the Diapir. However, the internal deformation of the salt Diapir by the descending blocks decreases with increase in effective viscosity of salt.The results presented in this thesis suggest that it is highly likely that salt structures where dense and viscous layer/blocks are present undergo an internal deformation processes when these dense blocks start sinking within the Diapir. Depending on size and orientation of these blocks, deformation pattern is significantly different within the Diapir. Furthermore, model results applied to the Gorleben Diapir show that the rate of descent of the entrained anhydrite blocks differs on different sides of the Diapir. This suggests that if the anhydrite blocks descent within the Gorleben Diapir, they initiate an asymmetric internal flow within it.
Bahman Soleimany - One of the best experts on this subject based on the ideXlab platform.
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characterizing halokinesis and timing of salt movement in the abu musa salt Diapir persian gulf offshore iran
Marine and Petroleum Geology, 2019Co-Authors: Ali Faghih, Soumyajit Mukherjee, Mohammad Ezatiasl, Bahman SoleimanyAbstract:Abstract Geometric and stratigraphic characteristics of halokinetic sequences adjacent to the salt Diapirs highlight the sedimentation response to variation in the rate of salt rise. The style of salt movement-sedimentation interaction and episodes of salt movement can be reconstructed by mapping these halokinetic sequences adjacent to the Diapirs. Detailed interpretation of 2D seismic profiles adjacent to the Abu Musa salt Diapir within the Persian Gulf Basin, offshore Iran, indicates that this Diapir originated from the Miocene Fars salt, which created a central- and several ring-like peripheral-salt structures. Our results show that the evolution of the salt structures take place in three stages-mound, dome and post-dome- associated with sedimentation cycles periodically by passive and active rising to present. The pattern of these halokinetic sequences reveals that the Fars salt rose since Mid-Miocene coeval sedimentation of the Gachsaran Formation. The main mechanism of driving salt body has been the differential loading caused by down-building processes.
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style and timing of salt movement in the persian gulf basin offshore iran insights from halokinetic sequences adjacent to the tonb e bozorg salt Diapir
Journal of Structural Geology, 2019Co-Authors: Mohammad Ezati Asl, Soumyajit Mukherjee, Ali Faghih, Bahman SoleimanyAbstract:Abstract The variations in the rate of salt rise is reflected in the sedimentary sequences adjacent to salt Diapirs and provides insights into the style of salt movement-sedimentation interaction and the timing of halokinetic phases. Episodic movement of salt Diapir is defined by wedge- and tabular-shaped salt-related sedimentary strata (halokinetic sequences) adjacent to the Diapir. Detailed mapping of depositional strata on 2D seismic sections adjacent to salt Diapirs on the Tonb-e-Bozorg Island (Persian Gulf, SW Iran) reveals the presence of a series of sedimentary sequences related to the halokinetic activity of two salt source layers, the Hormuz and Fars salts, respectively. The Hormuz salt deposited in the uppermost Proterozoic, mobilized in the Lower Paleozoic and then continued to move periodically to present and to create the deep salt structures in the Tonb-e-Bozorg region. The Fars salt deposited in the Lower Miocene and then started rising, and created the central salt structure, the Tonb-e-Bozorg Island, and several peripheral ring-like salt structures around the island. Our results reveal that both the salt layers within the Tonb-e-Bozorg region grew by downbuilding and continued to move periodically by passive and active Diapirism to the present. Salt movement-sedimentation interaction during salt Diapirism influences petroleum play and therefore is of interest in petroleum geoscience.
Soumyajit Mukherjee - One of the best experts on this subject based on the ideXlab platform.
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characterizing halokinesis and timing of salt movement in the abu musa salt Diapir persian gulf offshore iran
Marine and Petroleum Geology, 2019Co-Authors: Ali Faghih, Soumyajit Mukherjee, Mohammad Ezatiasl, Bahman SoleimanyAbstract:Abstract Geometric and stratigraphic characteristics of halokinetic sequences adjacent to the salt Diapirs highlight the sedimentation response to variation in the rate of salt rise. The style of salt movement-sedimentation interaction and episodes of salt movement can be reconstructed by mapping these halokinetic sequences adjacent to the Diapirs. Detailed interpretation of 2D seismic profiles adjacent to the Abu Musa salt Diapir within the Persian Gulf Basin, offshore Iran, indicates that this Diapir originated from the Miocene Fars salt, which created a central- and several ring-like peripheral-salt structures. Our results show that the evolution of the salt structures take place in three stages-mound, dome and post-dome- associated with sedimentation cycles periodically by passive and active rising to present. The pattern of these halokinetic sequences reveals that the Fars salt rose since Mid-Miocene coeval sedimentation of the Gachsaran Formation. The main mechanism of driving salt body has been the differential loading caused by down-building processes.
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style and timing of salt movement in the persian gulf basin offshore iran insights from halokinetic sequences adjacent to the tonb e bozorg salt Diapir
Journal of Structural Geology, 2019Co-Authors: Mohammad Ezati Asl, Soumyajit Mukherjee, Ali Faghih, Bahman SoleimanyAbstract:Abstract The variations in the rate of salt rise is reflected in the sedimentary sequences adjacent to salt Diapirs and provides insights into the style of salt movement-sedimentation interaction and the timing of halokinetic phases. Episodic movement of salt Diapir is defined by wedge- and tabular-shaped salt-related sedimentary strata (halokinetic sequences) adjacent to the Diapir. Detailed mapping of depositional strata on 2D seismic sections adjacent to salt Diapirs on the Tonb-e-Bozorg Island (Persian Gulf, SW Iran) reveals the presence of a series of sedimentary sequences related to the halokinetic activity of two salt source layers, the Hormuz and Fars salts, respectively. The Hormuz salt deposited in the uppermost Proterozoic, mobilized in the Lower Paleozoic and then continued to move periodically to present and to create the deep salt structures in the Tonb-e-Bozorg region. The Fars salt deposited in the Lower Miocene and then started rising, and created the central salt structure, the Tonb-e-Bozorg Island, and several peripheral ring-like salt structures around the island. Our results reveal that both the salt layers within the Tonb-e-Bozorg region grew by downbuilding and continued to move periodically by passive and active Diapirism to the present. Salt movement-sedimentation interaction during salt Diapirism influences petroleum play and therefore is of interest in petroleum geoscience.
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Viscosity estimates of salt in the Hormuz and Namakdan salt Diapirs, Persian Gulf
Geological Magazine, 2010Co-Authors: Soumyajit Mukherjee, Christopher J Talbot, Hemin KoyiAbstract:The parabolic surface profiles of the Hormuz and Namakdan salt Diapirs in the Persian Gulf suggest that they have been extruding with Newtonian viscous rheologies for the last 10 4 years. We derive velocity profiles for these Diapirs, neglecting gravitational spreading and erosion/dissolution while assuming incompressible Newtonian rheology of the salt. Fitting known rates of extrusion at specific points in its elliptical cross-section, the dynamic viscosity of the salt of the Hormuz Diapir is found to range between 10 18 and 10 21 Pa s. Approximating its sub-circular cross-section to a perfect circle, the range of viscosity of the salt of the Namakdan Diapir is obtained as 10 17 –10 21 Pa s. These calculated viscosities fall within the range for naturally flowing salts elsewhere and for other salt Diapirs but are broader than those for salts with Newtonian rheology deforming at room temperatures. The salts of the Hormuz and Namakdan Diapirs are expected to exhibit a broader range of grain size, which matches the limited existing data.
Martin P. A. Jackson - One of the best experts on this subject based on the ideXlab platform.
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enigmatic structures within salt walls of the santos basin part 1 geometry and kinematics from 3d seismic reflection and well data
Journal of Structural Geology, 2015Co-Authors: Christopher A L Jackson, Martin P. A. Jackson, Michael R Hudec, Clara RodriguezAbstract:Abstract Understanding intrasalt structure may elucidate the fundamental kinematics and, ultimately, the mechanics of Diapir growth. However, there have been relatively few studies of the internal structure of salt Diapirs outside the mining industry because their cores are only partly exposed in the field and poorly imaged on seismic reflection data. This study uses 3D seismic reflection and borehole data from the Sao Paulo Plateau, Santos Basin, offshore Brazil to document the variability in intrasalt structural style in natural salt Diapirs. We document a range of intrasalt structures that record: (i) initial Diapir rise; (ii) rise of lower mobile halite through an arched and thinned roof of denser, layered evaporites, and emplacement of an intrasalt sheet or canopy; (iii) formation of synclinal flaps kinematically linked to emplacement of the intrasalt allochthonous bodies; and (iv) Diapir squeezing. Most salt walls contain simple internal anticlines. Only a few salt walls contain allochthonous bodies and breakout-related flaps. The latter occur in an area having a density inversion within the autochthonous salt layer, such that upper, anhydrite-rich, layered evaporites are denser than lower, more halite-rich evaporites. We thus interpret that most Diapirs rose through simple fold amplification of internal salt stratigraphy but that locally, where a density inversion existed in the autochthonous salt, Rayleigh–Taylor overturn within the growing Diapir resulted in the ascent of less dense evaporites into the Diapir crest by breaching of the internal anticline. This resulted in the formation of steep salt-ascension zones or feeders and the emplacement of high-level intrasalt allocthonous sheets underlain by breakout-related flaps. Although regional shortening undoubtedly occurred on the Sao Paulo Plateau during the Late Cretaceous, we suggest this was only partly responsible for the complex intrasalt deformation. We suggest that, although based on the Santos Basin, our kinematic model may be more generally applicable to other salt-bearing sedimentary basins.
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Isochores and 3-D visualization of rising and falling slat Diapirs
Marine and Petroleum Geology, 1999Co-Authors: Giovanni Guglielmo, Bruno C. Vendeville, Martin P. A. JacksonAbstract:Abstract Diapir fall, which was predicted by physical models, has been identified in salt provinces, such as the South Atlantic margins, the North Sea, and the Paradox Basin (Colorado–Utah). However the 3-D geometry of falling Diapirs and their country rock is still poorly understood. 3-D visualization and isochore patterns from a physical model help elucidate this geometry. The model initially comprised a unit of viscous silicone overlain by a prekinematic sand unit. Sand units representing brittle sediments were deposited episodically during gravity gliding and spreading. Regional extension triggered and eventually widened salt walls, causing them to sag. The 3-D visualization shows that regional hydrocarbon migration, which tends to be seaward during Diapir rise and landward during Diapir fall, can potentially be orthogonal to local migration along grabens at soft-linked zones of relay ramps. Furthermore, anticlinal culminations may form (1) in horsts that bend along strike and (2) adjoining the fork of Y-shaped salt walls. Sequential isochore maps of the overburden show how patterns of sedimentation, deformation, and underlying salt thickness changed through time. Isochores of prekinematic units record only strain: thinned belts record early extension. In contrast, isochores of synkinematic units record mostly thickness variations due to deposition on actively deforming topography. Isochores above sagging Diapirs identify the thickest part of crestal depocenters, where the most rapid sagging occurred in regions of maximum extension near the unbuttressed downdip part of the gravity-spreading system. Additionally, asymmetric isochore patterns may reveal underlying half-grabens or tilted symmetric grabens. In relay systems, overlying isochores may indicate which part of a salt wall rose to compensate for sagging elsewhere in the relay.
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Rejuvenation and Subsidence of Salt Diapirs by Regional Extension
1995Co-Authors: Martin P. A. Jackson, Bruno C. VendevilleAbstract:ABSTRACT Because salt is much weaker than its surrounding sedimentary rocks, buried salt Diapirs are sensitive to regional extension. To investigate extensional reactivation of salt walls and stocks, we conducted physical experiments using dry quartz sand to simulate brittle sedimentary rocks and a silicone polymer to simulate viscous salt. Initially, salt walls had triangular profiles and their height decreased along strike. Salt stocks had circular planforms. In experiments, Diapiric walls widened by extension. The Diapiric roof first extended where it was thinnest, forming a graben over the crest of the walls. The crestal graben then propagated along strike to the lower parts of the wall, where the roof was thicker. Along strike off the Diapirs, the graben broadened in an array of widely spaced faults. Where the Diapir was initially oblique to the regional extension, crestal faults formed en echelon arrays above the Diapir, and their traces deflected sharply above the ends of the walls. Where the source layer was thick and extension was slow, walls were rejuvenated to form reactive and even emergent, passive Diapirs. Conversely, where the source layer was depleted or where extension was rapid, the walls subsided. Salt stocks were even more modified than were salt walls. Regional grabens formed above the stocks and propagated laterally but were not significantly deflected beyond the salt stocks. Salt eventually pierced the thinned roofs of the Diapirs and extruded to form salt sheets above foundered roof blocks surrounded by salt. Grabens above the stocks were connected by an oblique transtensional zone. We apply the model results to the Paradox Basin, Utah and Colorado, where salt structures were affected by regional extension during Cenozoic time.
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Regional extension as a geologic trigger for Diapirism
Geological Society of America Bulletin, 1994Co-Authors: Martin P. A. Jackson, Bruno C. VendevilleAbstract:Initiation of Diapirs is one of the least understood aspects of salt tectonics. Differential sedimentary loading or erosion are both effective but not universal. A survey of 18 major salt-Diapir provinces shows that salt upwelling is closely linked in time and space to regional extension. Extended salt basins typically develop salt structures, whereas nonextended basins typically do not. Even in salt basins overprinted by inversion or orogenic contraction, the Diapirs were initiated during extension on divergent continental margins or in intracontinental rifts. Regional extension thins brittle overburden by forming grabens and half grabens above flowing salt. These fault structures (1) differentially load the salt by their surface relief and (2) weaken the overburden by fracturing and thinning it. Diapiric walls of pressurized salt rise in reaction to the shitting positions of fault blocks in extending overburdens, regardless of thickness, density, or lithology. If regional extension stops, these reactive Diapirs stop rising. Eventually the roof of the reactive Diapir can be thinned by extension below a critical thickness. Only then can the Diapir break through actively as an independent intrusion. Diapiric alignments have been ascribed to basement faulting, even where such faults were conjectural or had trivial displacements. Physical modeling shows that extension of the basement has only indirect influence on Diapirism by creating space for extension of the overburden, which is the direct cause of Diapirism, whether extension is thick-skinned or thin-skinned and whether the salt was deposited before, duing, or after rifting.
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The fall of Diapirs during thin-skinned extension
Marine and Petroleum Geology, 1992Co-Authors: Bruno C. Vendeville, Martin P. A. JacksonAbstract:Abstract Grabens above Diapirs are generally attributed to the intrusion, withdrawal, or dissolution of salt. In contrast, this paper proposes that many grabens or half-grabens above Diapirs form by regional thin-skinned extension. These conclusions are supported by dynamically scaled physical modelling, theoretical reasoning and observations from seismic sections. A Diapir pierces a thick, brittle overburden in three evolutionary stages: reactive, active and passive. Regardless of overburden density, Diapirs initially pierce a thick overburden reactively in response to faulting during slow regional extension. The hanging wall of an initial fault sinks into the source layer until resisted by increasing pressure forces and bending resistance. New faults form repeatedly nearer the axis of the graben. The dwindling central fault block sinks while the Diapir rises below it. Progressively smaller fault blocks are supported by the fluid pressure at progressively higher levels flanking a triangular Diapir. Sedimentation keeps Diapirs in the reactive stage longer by filling the graben. Reactive Diapirism is controlled by the slow rate of regional extension: whenever regional extension ceases, reactive Diapirs stop growing. If the Diapir becomes tall enough, its roof sufficiently thinned, and the graben trough deep enough, a Diapir can pierce actively by lifting and shouldering aside its roof to emerge rapidly at the surface. During subsequent passive piercement, a Diapir widens by regional extension and increases in relief by downbuilding concurrent sedimentation. Diapirs can also bypass the reactive and active modes of growth if the overburden is thin and uneven. Faulting, folding and thickness changes are negligible around passive Diapirs. Rounded stocks can evolve passively from walls initiated by grabens.
Christopher J Talbot - One of the best experts on this subject based on the ideXlab platform.
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Viscosity estimates of salt in the Hormuz and Namakdan salt Diapirs, Persian Gulf
Geological Magazine, 2010Co-Authors: Soumyajit Mukherjee, Christopher J Talbot, Hemin KoyiAbstract:The parabolic surface profiles of the Hormuz and Namakdan salt Diapirs in the Persian Gulf suggest that they have been extruding with Newtonian viscous rheologies for the last 10 4 years. We derive velocity profiles for these Diapirs, neglecting gravitational spreading and erosion/dissolution while assuming incompressible Newtonian rheology of the salt. Fitting known rates of extrusion at specific points in its elliptical cross-section, the dynamic viscosity of the salt of the Hormuz Diapir is found to range between 10 18 and 10 21 Pa s. Approximating its sub-circular cross-section to a perfect circle, the range of viscosity of the salt of the Namakdan Diapir is obtained as 10 17 –10 21 Pa s. These calculated viscosities fall within the range for naturally flowing salts elsewhere and for other salt Diapirs but are broader than those for salts with Newtonian rheology deforming at room temperatures. The salts of the Hormuz and Namakdan Diapirs are expected to exhibit a broader range of grain size, which matches the limited existing data.
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potash in a salt mushroom at hormoz island hormoz strait iran
Ore Geology Reviews, 2009Co-Authors: Christopher J Talbot, Pedram Aftabi, Zurab ChemiaAbstract:Abstract Increasing volumes of potash are currently being discovered in a cluster of Diapirs of Hormoz (formerly Hormuz) salt near Bandar Abbas, Iran. Most of the potash beds studied so far occur in complex recumbent folds in a salt mountain that would be difficult to exploit safely. However, Holocene marine erosion removed any salt mountains from a sub-group of near-shore Zagros Diapirs and exposed their deeper structural levels. Even though these Diapirs are still active, their potash deposits are likely more tractable to safe exploitation than in a salt mountain — as we make clear here for Hormoz Island. Geochemical surveys on Hormoz Island reveal two separate potash anomalies that are valuable pseudo-stratigraphic markers. Integrating field measurements of the attitudes of bedding with lineaments on air photos suggests that Hormoz Island consists of a mature bell- or plume-shaped mushroom Diapir with potash beds wound around a toroidal axis of rotation near current exposure levels. 2D numerical models simulate the salt mushroom on Hormoz Island and its internal circulation. They also suggest that the Diapir has a wide overhand above a narrow stem in this gas-rich region. We use the mushroom Diapir model to outline a regional exploration strategy that has the potential of influencing the world potash market thereafter.
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Numerical analysis of how sedimentation and redistribution of surficial sediments affects salt Diapirism
Tectonophysics, 1993Co-Authors: A.n.b. Poliakov, Yuri Y. Podladchikov, R.t. Van Balen, Betrand Daudre, Sierd Cloetingh, Christopher J TalbotAbstract:Abstract Two-dimensional finite-element models are used to study how sedimentation and redistribution of sediments on the upper surface affects the development of subsurface salt Diapirs. A rising Diapir creates a bulge flanked by topographic lows in a generally accumulating sedimentary pile. We find that the rate at which this topography is flattened by erosion and redeposition controls the style of Diapirism. This is because the redistribution of material from topographic highs to flanking lows is equivalent to changing the effective forces acting on the salt. Redistributing a potential topography modulates Diapiric growth rate. The main effects of including surficial sediment redistribution in numerical models of Diapirism are: 1. (1) Diapirs grow 10–100 times faster; 2. (2) Diapirs may rise above their level of neutral buoyancy and extrude; 3. (3) Diapirs assume “finger” or “stock” like shapes rather than “mushroom” or balloon-on-string shapes; 4. (4) layers in the surrounding sediments remain nearly horizontal and only steepen sharply near the Diapir. In effect, the rate of redistribution of surficial overburden strongly controls the mode of Diapirism. Sediment redistribution (referred to as erosion for brevity) is modeled using a one dimensional diffusion equation. We show the results of two different erosion rates: infinitely slow (no erosion) and extremely fast (which redistributes surficial sediments but does not remove them from the system). We show that the shapes of model Diapirs rising beneath surfaces subjected to rapid erosion simulate salt Diapirs in the Gulf of Mexico. Columnar Diapirs indicate rapid deposition on the shelf and plug-like Diapirs slow sedimentation on the abyssal plane. Diapirs rising beneath surfaces with negligible erosion have the “mushroom” shapes interpreted for salt Diapirs in central Iran.
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Numerical models of complex Diapirs
Tectonophysics, 1993Co-Authors: Yu. Podladchikov, Christopher J Talbot, A.n.b. PoliakovAbstract:Abstract Numerically modelled Diapirs that rise into overburdens with viscous rheology produce a large variety of shapes. This work uses the finite-element method to study the development of Diapirs that rise towards a surface on which a Diapir-induced topography creeps flat or disperses (“erodes”) at different rates. Slow erosion leads to Diapirs with “mushroom” shapes, moderate erosion rate to “wine glass” Diapirs and fast erosion to “beer glass”- and “column”-shaped Diapirs. The introduction of a low-viscosity layer at the top of the overburden causes Diapirs to develop into structures resembling a “Napoleon hat”. These spread lateral sheets.