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1.
Landscape evolution of the Five Islands of south Louisiana: scientific policy and salt dome utilization and management 总被引：2，自引：0，他引：2
The Five Islands of south central Louisiana are piercement-type salt domes uplifted from several kilometers depth as the surrounding strata experiences regional subsidence. In general, the domes are nearly circular in plan with maximum land surface elevations 23–52 m asl. Geomorphic evidence of salt-induced uplift includes surface lineations, aligned gullies, excessively steep land surface topography, and shear fractures in surficial sediments. Evidence of subsidence includes sinkhole ponds a few hectares in area, broad topographic saddles over tens of hectares in size, and kilometer-scale collapse structures.On each of the Five Islands, Peoria Loess and silty colluvium bury a paleosol developed in the Late Pleistocene Prairie Complex of the Lower Mississippi Valley. The loess represents a single genetic unit of eolian origin, is typically thickest on lower side slopes, and is thin or absent on ridge crests. The silty colluvium around the perimeter of the islands is a reworked loess derived from higher elevations. Shear fractures with high-angle average dips occur in both Peoria Loess and the Prairie Complex. Conjugate shear pairs probably develop from extensional stress associated with vertical uplift of the underlying salt.Prairie Complex deposition and initial soil development in a low-relief alluvial plain of the Mississippi River predates the latest emergence of the Five Islands. Loess and colluvial stratigraphy indicate that the domes were emergent during loess deposition. Gully incision, shearing of Quaternary sediments, and the distribution of colluvium indicate continued uplift after loess deposition. Sinkholes and collapse structures are influenced by salt dissolution and corrasion, whereas broad subsidence areas and topographic saddles form over areas of structural weakness within the salt.Five Islands landscape evolution is controlled by the interaction of driving and resisting forces that operate over various time scales. Diapiric uplift is a driving force of net upwards motion, and the external and internal salt dome hydrology are driving forces of solution and corrasion. The structure and lithology of the internal salt stocks and the surrounding sediments are heterogeneous and have variable strength. Collectively, this interaction produces both uplift and subsidence features across the salt dome landscape.Resource use at the Five Islands correlate with instability of both underground facilities and the surface landscape. Uplift of the Five Islands has continued since at least the Late Pleistocene, is probably still active at present, and periods of tectonic and geomorphic instability are possible in the future. Sediments overlying salt domes record discrete periods of surface uplift and periods of episodic and incremental subsidence that is common where salt domes pierce surficial sediment. The rate, magnitude, and pattern of landscape modification by salt domes have implications for the safe utilization of mineral extraction and geostorage facilities. Geomorphic evaluation of salt dome landscapes can help to develop policies that ensure safe salt dome utilization. Salt dome resource planning should include detailed characterization of internal and external stratigraphy and structure; modeling of geomorphic, soil and rock mechanic, and hydrologic processes; routine and emergency planning at operating facilities; and closure and post-closure plans. 相似文献
2.
Dynamic modelling of passive margin salt tectonics: effects of water loading, sediment properties and sedimentation patterns 总被引：1，自引：0，他引：1
We investigate the evolution of passive continental margin sedimentary basins that contain salt through two‐dimensional (2D) analytical failure analysis and plane‐strain finite‐element modelling. We expand an earlier analytical failure analysis of a sedimentary basin/salt system at a passive continental margin to include the effects of submarine water loading and pore fluid pressure. Seaward thinning sediments above a weak salt layer produce a pressure gradient that induces Poiseuille flow in the viscous salt. We determine the circumstances under which failure at the head and toe of the frictional–plastic sediment wedge occurs, resulting in translation of the wedge, landward extension and seaward contraction, accompanied by Couette flow in the underlying salt. The effects of water: (i) increase solid and fluid pressures in the sediments; (ii) reduce the head to toe differential pressure in the salt and (iii) act as a buttress to oppose failure and translation of the sediment wedge. The magnitude of the translation velocity upon failure is reduced by the effects of water. The subsequent deformation is investigated using a 2D finite‐element model that includes the effects of the submarine setting and hydrostatic pore pressures. The model quantitatively simulates a 2D approximation of the evolution of natural sedimentary basins on continental margins that are formed above salt. Sediment progradation above a viscous salt layer results in formation of landward extensional basins and listric normal growth faults as well as seaward contraction. At a later stage, an allochthonous salt nappe overthrusts the autochthonous limit of the salt. The nature and distribution of major structures depends on the sediment properties and the sedimentation pattern. Strain weakening of sediment favours landward listric growth faults with formation of asymmetric extensional depocentres. Episodes of low sediment influx, with partial infill of depocentres, produce local pressure gradients in the salt that result in diapirism. Diapirs grow passively during sediment aggradation. 相似文献
3.
The Permo‐Carboniferous to Eocene Sverdrup Basin in Canada's Arctic Archipelago is strongly influenced by evaporite diapirism. However, salt structures within the basin have not been extensively investigated recently due to their remote location. This study includes the interpretation of legacy seismic reflection and borehole data to characterize the geometry of selected evaporite domes, and 1D backstripping of wells to investigate tectonic and sedimentary influences on diapirism. Extensional rift‐structures appear to have played a significant role in the formation of evaporite domes by triggering and directing salt movement. Diapirism was initiated by at least the Middle Triassic and continued to develop during the Mesozoic. Differential loading of salt on opposing east–west dome margins led to their present day asymmetric geometries. Diapir growth rates in the Mesozoic were closely linked to the rate of sedimentation and influenced by regional tectonism. 相似文献
4.
5.
Modelling of pore pressure evolution associated with sedimentation and uplift in sedimentary basins 总被引：5，自引：0，他引：5
Unconformities, which represent either periods of interruption of sedimentation or, in most cases events characterized by deposition and subsequent erosion, are commonplace geological phenomena in sedimentary basins, and will affect the pore pressure evolution of the basin fill. The effect of unconformities on pore pressure, as well as on sediment compaction and on burial processes is studied using a numerical basin model. For coarse sediments, which are permeable so that their pore pressure always remains nearly hydrostatic, the effects of both pure deposition interruption (hiatus) and deposition-erosion events are negligible for pore pressure evolution. However, for fine-grained sediments, unconformities can modify the pore pressure and the stress state to varying degrees. The results show that the rate of removal of overlying sediments, the permeability of sediments and time play important roles in the pore pressure evolution. In the East Slope of the Ordos Basin (China), in which overpressure has not been detected in deep wells, the modelling results suggest that the large-scale erosion occurring in the Late Cretaceous and in the Tertiary may have removed high overpressure existing in the basin before the erosion. 相似文献
6.
B. D. Trudgill 《Basin Research》2011,23(2):208-238
The northern Paradox Basin evolved during the Late Pennsylvanian–Permian as an immobile foreland basin, the result of flexural subsidence in the footwall of the growing Uncompahgre Ancestral Rocky Mountain thick‐skinned uplift. During the Atokan‐Desmoinesian (～313–306 Ma) fluctuating glacio‐eustatic sea levels deposited an ～2500 m thick sequence of evaporites (Paradox Formation) in the foreland basin, interfingering with coarse clastics in the foredeep and carbonates around the basin margins. The cyclic deposition of the evaporites produced a repetitive sequence of primarily halite, with minor clastics, organic shales and anhydrite. Sediment loading of the evaporites subsequently produced a series of salt walls and minibasins, through the process of passive diapirism or downbuilding. Faults at the top Mississippian level localised the development of linear salt walls (up to 4500 m high) along a NW–SE trend. A crosscutting NE–SW structural trend was also important in controlling the evaporite facies and the abrupt termination of the salt walls. Seismic, well and field data define the proximal Cutler Group (Permian) as a basinward prograding sequence derived from the growing Uncompahgre uplift that drove salt basinwards (towards the southwest), triggering the growth of the salt walls. Sequential structural restorations indicate that the most proximal salt walls evolved earlier than the more distal ones. The successive development of salt‐withdrawal minibasins associated with each growing salt wall implies that parts of the Cutler Group in one minibasin may have no chronostratigraphic equivalent in other minibasins. Localised changes in along‐strike salt wall growth and evolution were critical in the development of facies and thickness variations in the late Pennsylvanian to Triassic stratigraphic sequences in the flanking minibasins. Salt was probably at or very close to the surface during the downbuilding process leading to localised thinning, deposition of diapir‐derived detritus and rapid facies changes in sequences adjacent to the salt wall structures. 相似文献
7.
Numerical models are used to study the entrainment of a dense anhydrite layer by a diapir. The anhydrite layer is initially horizontally embedded within a viscous salt layer. The diapir is down-built by aggradation of non-Newtonian sediments ( n = 4, constant temperature) placed on the top of the salt layer. Several parameters (sedimentation rate, salt viscosity, perturbation width and stratigraphic position of the anhydrite layer) are studied systematically to understand their role in governing the entrainment of the anhydrite layer. High sedimentation rates during the early stages of the diapir evolution bury the initial perturbation and, thus, no diapir forms. The anhydrite layer sinks within the buried salt layer. For the same sedimentation rate, increasing viscosity of the salt layer decreases the rise rate of the diapir and reduces the amount (volume) of the anhydrite layer transported into the diapir. Model results show that viscous salt is capable of carrying separate blocks of the anhydrite layer to relatively higher stratigraphic levels. Varying the width of the initial perturbation (in our calculations 400–800 m), from which a diapir triggers, shows that wider diapirs can more easily entrain an embedded anhydrite layer than the narrower diapirs. The anhydrite layer is entrained as long as rise rate of the diapir exceeds the descent rate of the denser anhydrite layer. We conclude that the four parameters mentioned above govern the ability of a salt diapir to entrain an embedded dense layer. However, the model results show that the entrained blocks inevitably sink back if the rise rate of the diapir is less than the rate of descent of the anhydrite layer or the diapir is permanently covered by a stiff overburden in case of high sedimentation rates. 相似文献
8.
Breakout of squeezed stocks: dispersal of roof fragments,source of extrusive salt and interaction with regional thrust faults 
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下载免费PDF全文 We used seven scaled physical models to explore the near‐surface structural evolution of shallowly buried, actively rising salt stocks. The models consisted of dry sand, ceramic microspheres and silicone. Previously dormant stocks rose because of lateral squeezing or pumping of salt from below. The pressure of rising salt created a dynamic bulge in the crest of the diapir, which arched the overlying roof sediments. Eventually this dynamic bulge collapsed and its overlying roof broke into rafts along subradial grabens. The rafts were dispersed outwards by shear traction of spreading salt, surmounting an upturned collar of country rock and eventually grounding at the front of the extrusive flow. Flow of salt around these stranded fragments created a lobate extrusion front, common in submarine salt sheets in the Gulf of Mexico and subaerial salt glaciers in Iran. Stock geometry, regional dip and roof density affected extrusion rates and spreading directions. Stocks leaning seaward extruded salt faster and farther than did upright stocks. Dense roofs foundered and plugged the vent, limiting surface extrusion. In tilted models, broad salt sheets spread asymmetrically downslope. Stock contents were inverted within the extruded salt sheet: successively deeper parts of the stock's core rose to the surface and overran salt extruded from the shallower parts of the diapir. As shortening continued, salt from the source layer reached the surface after being driven out by thrusting. A central thrust block, or primary indenter, moved ahead of surrounding thrust blocks, impinging against and squeezing the stock into an elliptical planform. After high shortening, secondary indenters converged obliquely into the salt stock, expelling salt from the periphery of the diapir. The models shed light on (1) the origin and fate of large rafts or carapace blocks atop allochthonous salt, (2) cuspate margins of salt sheets and (3) interaction of thrusting, diapir pinch‐off and emplacement of allochthonous salt sheets. 相似文献
9.
Widespread bimodal-calcalkaline magmatism and contemporaneously active faulting reflect the combined effects of late-orogenic collapse and strike-slip faulting during syn-rift development of the late-Variscan Saar-Nahe Basin. The intrabasinal drainage systems experienced major but differing influences from three prominent styles of volcanic extrusives: extensive basic lava flows; localized acidic domes; and widespread pyroclastic units. Sedimentary sections including basic to intermediate lavas show the transformation of pre-eruptive meandering fluvial systems into lacustrine systems following lava eruptions. These relationships are interpreted in terms of damming of the drainage systems by the topographic barriers represented by the basic lavas themselves. Siliciclastic sediments re-entered and ultimately filled the lakes through prograding, small-scale crevasse channel/mouth bar complexes. Uplift associated with the intrusive/extrusive emplacement of acidic domes affected both the accommodation space and the internal topography of the basin. Following an extrusive pulse, each dome collapse caused the progradation of voluminous volcaniclastic aprons onto the surrounding alluvial plain. Locally, the overload by large volumes of unconsolidated detritus converted the regional meandering drainage system into a braided one. The overall duration of acidic dome activity could have been longer than 106 years, but was interrupted by repose periods varying probably between a few hundred years to several thousand years. Pyroclastic activity accompanied dome emplacement and registers their episodic activity in the stratigraphic record. Fine-grained ashes of phreatoplinian eruptions were spread widely within the basin and overloaded streams in the area of fallout. Rapid reworking of huge amounts of unconsolidated material supplied an abundance of volcanic detritus, which tended to fill topographic lows that were usually fault-controlled. The relationships between basin evolution, intrabasinal volcanism and contemporaneously active faulting, identified in the Saar-Nahe Basin, are important. They emphasize and further the understanding of how similar volcanic products in sedimentary basins worldwide impacted on the depositional system. 相似文献
10.
Wooil Moon 《Geophysical Journal International》1981,67(3):735-746
Summary. A new method is proposed for the geopotential field computation and gravitational attraction modelling. The usual method is to use a uniform density discrete numerical integration to represent either the gravitational potential or the gravitational attraction from a given density configuration. In this paper, an interpolation scheme is explained, using a piecewise continuous basis function to represent the arbitrarily varying density configuration in one, two and three dimensions. This new approach greatly simplifies the potential integrations and, in certain cases where symmetry exists, analytical evaluation of the integrals is also possible. Numerical tests and examples are given for a hypothetical salt dome, a vertical dyke with varying density structure and the hydrostatic ellipticity of earth model 1066B. The numerical error in this method is limited to the analytical approximation and interpolation errors in each case. This new approach can also be used as efficiently for other potential field studies. 相似文献
11.
M. Mart&#;´n-Mart&#;´n J. Rey † F. J. Alcala-Garcia ‡ J. Tosquella § J. Deramond † E. Lara-Corona † F. Duranthon¶ P.-O. Antoine¶ 《Basin Research》2001,13(4):419-433
ABSTRACT During the Eocene in the Corbières–Minervois foreland basin, southern France, there was a transition from marine carbonate to fluvial–lacustrine sedimentation. This evolution took place in six depositional sequences, the first controlled by a eustatic rise or flexural downwarping, then following under compressive tectonic conditions. The second to the fourth sequences show marine to marshy, mainly carbonate sediments with a transgressive–regressive evolution, while the last two comprise terrigenous and carbonate continental sediments. The tectonic evolution is marked by blind fault-propagation folds which deformed the basin during the Ilerdian–Cuisian. A paroxysmal compressive tectonic phase occurred at the Bartonian when the ancient blind thrusts started to emerge. A model for the evolution of the basin is presented, involving the northward propagation of structural culminations, which focused shallow water or emergent conditions, and structural lows in which deeper water sedimentation took place. The diachronous migration of these structural zones can be constrained from the high biostratigraphic resolution of the foreland basin fill. 相似文献
12.
Salt tectonics driven by differential sediment loading: stability analysis and finite-element experiments 总被引：11，自引：0，他引：11
Lykke Gemmer Steven J. Ings† Sergei Medvedev Christopher Beaumont 《Basin Research》2004,16(2):199-218
At many continental margins, differential sediment loading on an underlying salt layer drives salt deformation and has a significant impact on the structural evolution of the basin. We use 2‐D finite‐element modelling to investigate systems in which a linear viscous salt layer underlies a frictional‐plastic overburden of laterally varying thickness. In these systems, differential pressure induces the flow of viscous salt, and the overburden experiences updip deviatoric tension and downdip compression. A thin‐sheet analytical stability criterion for the system is derived and is used to predict conditions under which the sedimentary overburden will be unstable and fail, and to estimate the initial velocities of the system. The analytical predictions are in acceptable agreement with initial velocity patterns of the numerical models. In addition to initial stability analyses, the numerical model is used to investigate the subsequent finite deformation. As the systems evolve, overburden extension and salt diapirism occur in the landward section and contractional structures develop in the seaward section. The system evolution depends on the relative widths of the salt basin and the length scale of the overburden thickness variation. In narrow salt basins, overburden deformation is localised and characterised by high strain rates, which cause the system to reach a gravitational equilibrium and salt movement to cease earlier than for wide salt basins. Sedimentation enhances salt evacuation by maintaining a differential pressure in the salt. Continued sedimentary filling of landward extensional basins suppresses landward salt diapirism. Sediment progradation leads to seaward propagation of the landward extensional structures and depocentres. At slow sediment progradation rates, the viscous flow can be faster than the sediment progradation, leading to efficient salt evacuation and salt weld formation beneath the landward section. Fast sediment progradation suppresses the viscous flow, leaving salt pillows beneath the prograding wedge. 相似文献
13.
Quantifying the contribution of tectonics vs. differential compaction in the development of domes along the Mid-Norwegian Atlantic margin 总被引：1，自引：0，他引：1
A sequential restoration based on combined backstripping and unfolding methods affords the opportunity to study the Cenozoic evolution of two low amplitude domes in the Mid‐Norwegian extensional margin, the Helland Hansen Arch and the Vema Dome. The integration of growth strata geometries observed in both flanks of the domes demonstrate that the structures grew by a variable combination of tectonics and differential compaction mechanisms. Sequential restoration shows that the Helland Hansen Arch grew between Early Oligocene and earliest Late Pliocene times (33–1.9 Ma). During the first phase of growth (33–9 Ma), the tectonic compression accounted for a minimum of 27% of the total dome amplitude. During Late Miocene to Pliocene times (9–1.9 Ma), differential compaction was the mechanism for dome growth. During Late Pliocene times, the Helland Hansen Arch grew with the highest rates coinciding with initial deposition of prograding wedges (3.6–1.9 Ma). In contrast, the Vema Dome started to develop in Early Eocene times and grew at a fairly constant rate up to Early Pliocene times at 3.6 Ma. The amplification of the Vema Dome took place through both differential compaction and tectonics between Early Eocene and Late Miocene times (54.8–7 Ma). The tectonic contribution accounted for a minimum of a 37% of the total dome amplitude. During Pleistocene times, the progradation of clastic wedges led to a decrease of the amplitudes of both the Helland Hansen Arch and the Vema Dome. The different timing of tectonic growth for analysed domes and arches suggest that a small and protracted phase of compression affected the Mid‐Norwegian Margin. This agrees with well‐known widespread contractional deformation affecting the Atlantic Margin of the European Plate during the Tertiary. 相似文献
14.
The Molasse Basin of Switzerland evolved through a distinct late Neogene history with initial development as a classic foredeep or foreland basin in response to loading of the lithosphere by the Alpine orogen. In the central and western foreland, the foredeep behaviour was terminated by deformation and uplift of the Jura Mountains in the distal regions of the foredeep. Following the Jura deformation the Plateau Molasse remained largely undeformed as it rode ‘piggy‐back’ style above the decollement feeding displacement into the Jura. Sediment accumulation data for the Molasse suggests that sedimentation in the Plateau Molasse region continued until the basin was inverted at about 5 Ma. We present a mechanical model for this sequence of events in which deformation jumps across much of the basin to the distal Jura because of the dip on the weak evaporitic decollement and the wedge‐shape of the foredeep basin. Subsequently, the Plateau Molasse remained largely undeformed as a result of continued sedimentation in a wedgetop basin, where the physical properties and geometry of the orogenic wedge combine to produce a critical wedge whose critical surface slope would be less than zero and thus should dip towards the Alpine interior. Accommodation space is created over this negative surface–slope segment of the wedge and sedimentation maintains this slope near zero, stabilizing the wedge. We present a simple analytical theory for the necessary conditions for such a ‘negative‐alpha basin’ to develop and be maintained. We compare this theory to the late Neogene evolution of the Alps, Molasse Basin and Jura Mountains and infer physical properties for the decollement. 相似文献
15.
A reconstruction of the hydrological and environmental evolution of the crater lake at Malha (Northern Darfur, Sudan) resulted from the mineralogical and biological study of a 9.21 m section of lake sediments, representing an uninterrupted sequence of lacustrine deposition since 8 290 14C years BP.Important changes in water supply and conditions of sedimentation are reflected in the nature of the sediments and the morphology and stratigraphical distribution of various salt minerals. Additional information on lake circulation patterns and salinity conditions are obtained from associated benthic paleocommunities, represented by ostracods and dipterid larvae. Combining both lines of evidence, the studied sequence can be divided in six distinct sections, which correspond to six successive periods in the lake's Holocene history. The first three periods, generally characterized by high lake levels, represent three generations of a meromictic lake, two of which have ended with a complete desiccation of the lake basin. Meromixis was stable during Period I, due to wind shelter and pronounced density stratification. In the course of Periods II and III stratification was repeatedly interrupted. During Period II, the disruptions were accompanied by important water budget fluctuations; a superimposed gradual decrease in net water supply eventually resulted in holomictic conditions terminating this period. Evidence of turbulence periodically affecting profundal waters is recorded in the sediments of Period III, suggesting that disruptions of stratification were now initiated by very strong winds. Between Period I and Period III, the littoral mixolimnion gradually evolved from near fresh to mesosaline. In Periods IV to VI, lake level was intermediate to low. The lake was holomictic for most of the time and meso- to hypersaline; during Period V, it repeatedly shrunk to a shallow brine pool.The Holocene evolution of Malha Crater Lake illustrates the progressive increase in aridity over most of North Africa following a well-established, early- to mid-Holocene major humid episode. The uninterrupted sedimentary sequence lends itself for detailed reconstruction of Holocene climatic evolution in arid Northeast Africa, a region where records of continuous lacustrine deposition are extremely scarce. As the chronology of critical events in the lake's history remains as yet unsupported by radiocarbon dates, correlation with other Holocene sequences in the eastern Sahara is highly tentative at this point. 相似文献
16.
A model for temperature variations in sedimentary basins due to random radiogenic heat sources 总被引：1，自引：0，他引：1
The thermal structure of a sedimentary basin is controlled by its thermal conductivity, its boundary conditions, water flow, rate of sedimentation and erosion and radiogenic heat sources. The radiogenic heat production in the sediments is known to vary over several orders of magnitude, with the lowest values in evaporites and carbonates and the highest values in black shales. Due to a paucity of information available on the existing heat sources, this parameter can be represented with a known mean value and a Gaussian correlation structure rather than a deterministic function. In this paper, the 1-D steady-state thermal structure in a sedimentary basin has been modelled in a stochastic framework with a random radiogenic heat source, and analytical expressions for the first two moments of the temperature field have been obtained. A synthetic example has been examined to quantify the error bounds on the temperature field due to uncertainties in the radiogenic heat sources. 相似文献
17.
利用TM影像分析潮河与密云水库入库口处泥沙的空间分布 总被引：2，自引：2，他引：2
河流携带的泥沙进入水库后 ,由于河流水体与水库水体的共同作用而在河口区产生沉降。理论上水体中的泥沙含量是与距入库口处的空间距离相关的。并且 ,根据实验与模拟的结果 ,在可见光的任一波段内 ,水体中的含沙量与水面反射率具有一定的相关关系。TM影像的第二、三波段刚好位于含沙水体反射光谱的肩部和峰值部分 ,可以准确地反映水体的含沙情况。以潮河与密云水库的交接处为例 ,在泥沙含量与反射率负指数关系式的基础上 ,利用两个时相的TM影像 ,通过泥沙沉降过程的主轴作用线 ,采用回归模拟和经验公式相结合的办法 ,建立了泥沙沉降过程的遥感空间分布模型 ,讨论了模型中各参数的具体含义 ,描述水体中泥沙含量与沉降的情况。最后 ,采用多个作用轴线进行拟和与空间插值分析 ,建立了水体中泥沙含量的空间分布模拟图 ,经过检测 ,该图较好地反映了河流入库处水体中的泥沙含量情况 ,为遥感技术在监测水体含沙量方面的应用提供了技术基础。 相似文献
18.
近期长江北支口门圆陀角附近潮滩地貌动态变化 总被引：2，自引：0，他引：2
圆陀角位于长江北支岸线与江苏海岸线的交会处,独特的互花米草潮滩、淤泥质光滩环境和复杂的河海沉积动力,决定了潮滩地貌对海洋环境变化的响应具有敏感性。由于大规模的围垦,圆陀角附近过去40年来海岸线向东推进了6km。根据2006年以来多次的野外调查和室内粒度与钻孔岩芯的137Cs分析, 2006年以来圆陀角附近潮滩淤积明显加强,由137Cs时标估算的互花米草滩多年平均沉积速率为2.3cm/a, 2006~2008年观测到的互花米草滩淤积速率>4cm/a,粉砂淤泥质光滩的淤积速率更高;圆陀角风景区内互花米草滩前缘陡坎在风暴潮影响下侵蚀后退,并因粉砂淤泥质光滩的快速淤长而消亡,圆陀角附近潮滩地貌动态是对人类围垦活动、风暴潮与潮汐海洋动力的综合响应,互花米草与光滩快速淤积是近期圆陀角附近潮滩地貌演化的主要特点。 相似文献
19.
This paper examines interactions among syn‐rift continental margin extension, evaporites, particularly rocksalt (halite), deposited in the overlying sedimentary basins, and clastic sediment loading. We present dynamically evolving 2D numerical models that combine syn‐rift lithospheric extension, with salt (viscous halite, 1018–1019 Pa s) and clastic (frictional‐plastic) sediment deposition to investigate how salt is distributed and subsequently mobilized during syn‐rift extension. Example results are shown, contrasting salt deposition in the early, mid and late syn‐rift phases of a single lithospheric extension model. The lithospheric model is chosen to give depth‐dependent extension and intermediate width margins with proximal grabens and a hyperextended distal region. The models exhibit diachronous migration of extension towards the rift axis and this is reflected in the faulting of overlying sediments. The models illustrate the roles of timing of salt deposition, relative to rifting and subsequent sedimentation, in defining the location and deformation of syn‐rift salt, with post‐salt sediment progradation in some models. Late deposition of salt leads to increased lateral extent of the original salt body and decreased variation in salt thickness. Seaward flow of salt increases with later deposition; early syn‐rift salt is deposited and trapped in the grabens, whereas mid and late syn‐rift salt tends to flow towards the distal margin or even over the oceanic crust. Prograding clastic post‐salt sediments drive more substantial seaward movement of mid and late syn‐rift salt. A numerical model of the Red Sea with evaporite deposition during the mid to late syn‐rift period, preceded and followed by aggrading and prograding clastic sediment, shows reasonable agreement with observations from the central Red Sea. 相似文献
20.
Integrated acoustic and coring investigation of glacigenic deposits in Spitsbergen fjords 总被引：2，自引：0，他引：2
In many areas of Svalbard, the Neoglacial terminal deposits represent the Holocene glacial maximum. The glaciers began the retreat from their Neoglacial maximum positions around 1900 AD. Based on high resolution acoustic data and sediment cores, sedimentation patterns in four tidewater glacier-influenced inlets of the fjord Isfjorden (Tempelfjorden, Billefjorden, Yoldiabukta and Borebukta), Spitsbergen, were investigated. A model for sedimentation of tidewater glaciers in these High Arctic environments is proposed. Glacigenic deposits occur in proximal and distal basins. The proximal basins comprise morainal ridges and hummocky moraines, bounded by terminal moraines marking the maximum Neoglacial ice extent. The distal basins are characterized by debris lobes and draping stratified glacimarine sediments beyond, and to some extent beneath and above, the lobes. The debris lobe in Tempelfjorden is composed of massive clayey silt with scattered clasts. Distal glacimarine sediments comprise stratified clayey silt with low ice-rafted debris (IRD) content. The average sedimentation rate for the glacimarine sediments in Tempelfjorden is 17 mm/yr for the last ca. 130 years. It is suggested that the stratified sediments in Tempelfjorden are glacimarine varves. The high sedimentation rate and low IRD content are explained by input from rivers, in addition to sedimentation from suspension of glacial meltwater. The debris lobes in Borebukta are composed of massive clayey silt with high clast content. Distal glacimarine sediments in Yoldiabukta comprise clayey silt with high IRD content. The average sedimentation rate for these sediments is 0.6 mm/yr for the last 2300 years. 相似文献