潮滩盐沼物理过程的研究进展综述   总被引：9，自引：2，他引：9  

时钟 Pye  K 《地球科学进展》1995,10(1):19-30

综述了本世纪国外潮滩盐沼堆积、侵蚀机制的研究进展，主要包括潮滩盐沼的粘性泥沙沉积动力机制的分析、对潮滩盐沼的物理过程的详细观测研究、沉积模式研究，以及潮滩盐沼物理过程的知识在海岸防护和其它方面的应用。  相似文献   

Numerical simulation of vertical marsh growth and adjustment to accelerated sea-level rise,North Norfolk,U.K.     

Jonathan R. French 《地球表面变化过程与地形》1993,18(1):63-81

In parts of North America and Europe, present and future sedimentary deficits translate into major areal losses of coastal salt marsh. Physically based simulations of medium- to long-term adjustment to accelerated sea-level rise are few, partly due to the difficulty in extrapolating imperfectly understood sedimentation parameters. This paper outlines the implementation and application of a simple one-dimensional mass balance model designed to simulate the vertical adjustment of predominantly minerogenic marsh surfaces to various combinations of sediment supply, tidal levels and regional subsidence. Two aspects of marsh growth are examined, with reference to sites on the macro-tidal north Norfolk coast, U.K.: (i) historical marsh growth under a scenario of effective (long-term) eustatic stability but slow regional subsidence; and (ii) marsh response to various non-linear eustatic rise scenarios for the next century. In contrast to more organogenic North American marshes, sedimentation rates in Norfolk are strongly time-dependent. Where the overall sediment budget is so closely linked to marsh age and relative elevation, some form of numerical simulation offers a preferred means of predicting the impact of accelerated sea-level rise. Simulations performed here show that only the most dramatic eustatic scenarios result in ecological ‘drowning’ and reversion to tidal flat within the conventional 2100 prediction interval. Currently favoured scenarios give rise to accretionary deficits which are clearly sustainable in the short-term, albeit at the expense of increased inundation frequency and consequent changes in the distribution of marsh flora and fauna.  相似文献   

Subsidence-sinkhole development in light of mud infiltrate structures within interstratal karst of the Coastal Plain,southeast United States     

M. Jancin  D. D. Clark 《Environmental Geology》1993,22(4):330-336

Mud infiltrate structures (MIS) are a class of clastic sedimentary structures that have formed by high-angle gravitational sedimentation in vadose cavernous limestones beneath the Miocene Hawthorn Group. Observations of MIS in caves beneath the Pelham Escarpment, southwest Georgia, suggest three main types occurring either beneath, within, or contiguous to subvertical feeder pipes in the ceiling: (1) rubbly, conical masses; (2) polished, striated, cylindrical masses; and, (3) mud-flow, -drape, and-splash forms. MIS abundance suggests gravitative deposits are a major component to the total volume of cave mud. The muds apparently do not include soil-mantle materials; rather, their sources are poorly cemented clay-rich layers within the overlying Hawthorn Group. In cases where an individual MIS volume is large in proportion to the clastic-cover thickness, but no surface depression is found, the MIS location hypothetically predicts a directly overlying site of potential cover-collapse sinkhole development. Smaller-volume and/or shallower MIS predict the location of potential cover-subsidence sinkholes. The MIS forms suggest plastic and fluid behavior of the sediments occurs during displacements. The capacity for subsurface voids to accept mobile sediments depends on several factors that influence sinkhole development: (1) void size and interconnectedness; (2) spacing and size of subvertical solution pipes which can act as MIS feeders; (3) depth beneath the sediment source of any main horizontal cave development; (4) thickness of the cover sediments; and (5) the presence and depth of any breakout domes. The Hawthorn is present over more than 50 percent of the area underlain by the Floridan Aquifer system and is the system's major upper confining unit. MIS-forming processes are likely to be widely distributed within this stratigraphic setting, promoting ground subsidence and subsurface porosity obliteration. Given the existence of feeder pipes, MIS also are expected to form within the phreatic zone.  相似文献   

Geomorphological effects of catastrophic flooding on a small subtropical Estuary     

J. A. G. Cooper  T. R. Mason  J. S. V. Reddering  W. K. Illenberger 《地球表面变化过程与地形》1990,15(1):25-41

The Mgeni Estuary is situated on the east coast of South Africa. Tidal salinity changes commonly extend 2.5 km upstream from the mouth. The subtropical climatic regime causes seasonal flooding, the geomorphological effects of which are increased by a steep river gradient. A 120-150 year flood event during September 1987, with an estimated peak discharge of 10800 cumecs, resulted in the erosion of 1.86 × 10⁶ m³ of sediment from the estuary. The normal high tide volume of the estuary (0.35 × 10⁶ m³) increased to 1.85 × 10⁶ m³ after the flood. The post-flood intertidal volume (tidal prism) of the estuary was 0.43 × 10⁶ m³ compared to 0.19 × 10⁶ m³ before the event. The nature and extent of erosion in the estuary was controlled by the composition of the estuary banks and bed material. Gravel and sand substrates were preferentially eroded from the estuary bed before the cohesive bank materials were undercut in sections of the estuary. Mud and fine sand were deposited on overbank areas when the flood waned and a lag of coarse sand and gravel was produced on the estuary bed. Approximately 46 per cent of the bedload sediment supplied to the estuary since 1917 was retained in the estuary until the 1987 flood. The remainder was transported through the system and into the Indian Ocean. Results show that catastrophic floods play an important role in sedimentation in small estuaries.  相似文献   

Strong Magnetic Levels in Lake Chapala Sediments (western Mexico): Their Mineralogy and Stratigraphic Significance     

François Michaud  Hermes U. Ramírez-Sánchez  Claude Parron  Pedro F. Zárate-del Valle  François Fernex  Geneviève Barci-Funel 《Journal of Paleolimnology》2006,35(4):819-836

Lake Chapala, located 120 km northeast of Colima Volcano, lies at the north and northeast of the Citala rift in the Trans-Mexican Volcanic Belt. It belongs to the watershed of the Lerma River, which originates from the Mexico City area, 450 km to the east. Sediment cores, 0.5–2 m long, were collected from the lake. Magnetic susceptibility of the lake sediments generally ranges from 400 to 800 × 10⁻⁹ m³ kg⁻¹; but in some layers it exceeds 1000 or 1500 × 10⁻⁹ m³ kg⁻¹. The magnetic susceptibility vertical profiles display a thin peak (2–5 cm) or a double peak with magnetic susceptibility > 2000 × 10⁻⁹ m³ kg⁻¹. Scanning electron microscope analysis shows that the main mineral responsible for the magnetic susceptibility is titano-magnetite, which is relatively abundant in the magnetic layers. In most of the cores, the layer with magnetic susceptibility > 2000 × 10⁻⁹ m³ kg⁻¹ is coarser grained than the directly under and overlying sediments, which are composed of fine silt. But not all coarser levels are magnetic nor are all magnetic levels bound to coarser layers. The high titano-magnetic concentration probably originates from volcanic ash falls. Sedimentation rates, evaluated for several sites by means of the ²¹⁰Pb and ¹³⁷Cs methods, allow a date approximation (between 1535 and 1670) for the strong magnetic layer deposition. Since important eruptions of Colima Volcano, with ash fall, were reported from 1576 to 1623, the main peak of magnetic susceptibility in the sediment profiles is assumed to be related to these events. The main magnetic layer extends to greater depth in the profiles of the eastern part of the lake plain than at the west. It can, therefore, be suggested that a relative subsidence occurs in the eastern part of the lake; the axis of the eastern plain overlaps the area displaying the maximum subsidence rate and seems therefore to correspond to the prolongation of Citala rift.  相似文献   

潮间带盐沼植物对海岸沉积动力过程影响的研究进展   总被引：11，自引：1，他引：11  

李华  杨世伦 《地球科学进展》2007,22(6):583-591

根据已有文献归纳出盐沼植物对水动力、悬沙运动、沉积、地貌影响研究已取得的进展，包括：①单位距离盐沼中波能的损失可为相邻光滩的数倍至数十倍；波浪传入互花米草盐沼20~30 m后，波能可全部损失；②盐沼植物可使潮流流速降低一个数量级；当植冠被淹没后，垂向流速剖面在植冠附近出现转折；③当植冠被淹没后，垂向上植冠层内的紊动强度趋于一致且明显低于植冠层以上；互花米草盐沼中的紊动强度可比相邻光滩低1~2个数量级；④盐沼植物通过2种机制影响悬沙的运动：其一是降低水体紊动，从而促进悬沙的沉降并遏制滩面沉积物再悬浮；其二是茎叶对悬沙的直接黏附。这两种机制可使盐沼中的悬沙浓度比相邻光滩低一半以上；⑤植物对细颗粒悬沙的促淤作用导致盐沼中的底床滩面沉积物细化；⑥盐沼中的垂向沉积速率可比光滩高7~8倍；盐沼中波痕和侵蚀坑等微地貌不易发育，滩面平整化；与光滩上频繁发生的冲淤交替相比，盐沼中通常只淤不冲，滩面稳定性较高；⑦植物对上述沉积动力过程的影响程度与植物的高度、密度、盖度等生态参数密切相关，因此，不同的植物种类对沉积动力过程的影响往往存在显著差异。在此基础上，展望了今后该领域研究进一步加强的几个方面。 [HT5H]关〓键〓词：[HT5K] [HT5H]中图分类号:〓〓〓文献标识码：A[HT5SS][HK]  相似文献   

Sedimentation–consolidation of a double porosity material     

Henry Wong  Chin J. Leo  J.M. Pereira  Ph. Dubujet 《Computers and Geotechnics》2007,34(6):532-538

This paper studies the sedimentation–consolidation of a double porosity material, such as lumpy clay. Large displacements and finite strains are accounted for in a multidimensional setting. Fundamental equations are derived using a phenomenological approach and non-equilibrium thermodynamics, as set out by Coussy [Coussy, Poromechanics, Wiley, Chichester, 2004]. These equations particularise to three non-linear partial differential equations in one dimensional context. Numerical implementation in a finite element code is currently being undertaken.  相似文献   

Nature and rates of fine-sedimentation on a mid-shelf: “La Grande Vasière” (Bay of Biscay,France)     

C. Dubrulle  J.M. Jouanneau  P. Lesueur  J.F. Bourillet  O. Weber 《Continental Shelf Research》2007

The study area, “La Grande Vasière” (LGV), stretches out on the French Atlantic continental shelf (at ca. 100 m water depth), along 250 km from the Glénan Islands at the north to the southwest of Rochebonne at the south. Box-cores were sampled in this mid-shelf area during four cruises in June 1995, and in April, June and September 2002. They were investigated using sedimentological approaches (X-radiographs and grain-size analyses) and radionuclide studies (²¹⁰Pb geochronology and excess ²³⁴Th). The main results are: (1) the surficial sediments are generally organized into a decimetre-scale fining up sequence which can be the result of extreme storms; (2) an upper mixing layer of 7–20 cm reflects an important biological benthic activity and/or the impact of fishing (i.e. trawlers); (3) a thin (i.e. a few mm) surficial mud-rich layer is the result of the present-day sedimentation; (4) an apparent annual sedimentation rate of 1–3 mm is recorded in several loci of the study area. Some seasonal variations appear, corresponding to the deposition of fine material from April to September, and to the reworking and the re-suspension during the winter. This fine material is the result of the decantation of estuarine plumes, mainly the Loire and the Vilaine rivers, over the study area. LGV lies (1) under the influence of a winter-to-spring thermo-haline wedge that acts as a filter for the transfer of fine river-borne material to the slope and the open sea, and (2) below water depths where the mean swell action permits sedimentation, mainly in summer.  相似文献   

Characteristics of Milankovitch cycles recorded in Eocene strata in the eastern depression of North Yellow Sea Basin,North China     

《China Geology》2021,4(2):274-287

As cyclical orbital movements of Earth, Milankovitch cycles can be recorded in sedimentary strata. The time they reflect can be used to accurately divide and compare strata. Milankovitch cycles recorded in strata enrich the stratigraphic theory, especially the theories of cycle stratigraphy, and thus they are widely used in geological survey engineering nowadays. This study explored the characteristics of the Milankovitch cycles recorded in the eastern depression of the North Yellow Sea Basin, highlighting their control over high-frequency stratigraphic sequences. The Eocene Milankovitch cycles in the depression were calculated based on the method proposed by J. Laskar, and their parameters primarily include eccentricity cycles of 125 ka and 99 ka, obliquity cycles of 51 ka and 39 ka, and precession cycles of 23 ka and 19 ka. Spectral analysis of gamma-ray (GR) and spontaneous potential (SP) log curves of the Eocene strata was carried out to divide and compare stratigraphic sequences, revealing that the spectral peaks correspond well to astronomical cycles. This indicates that the strata in the depression fully record Milankovitch cycles. Furthermore, there are long-, medium-, and short-term stratigraphic cycles in the eastern depression, with a thickness of 13.03–15.89 m, 3.70–5.21 m, and 2.17–2.94 m, respectively. The sedimentation rates of the Eocene strata were calculated to be 121.2–127.12 m/Ma accordingly. From the uplift to the center of the lacustrine basin along the slope in the eastern depression, both the sedimentation duration and the sediment thickness increase, while the sedimentation rate remains relatively stable. The Eocene strata can be divided into six stages of high-frequency sequences by continuous wavelet transformation, namely E₆–E₁ from bottom to top. The sedimentation duration and sedimentation rates of the sequences were calculated using spectral analysis with each of the sequences as a separate window. Moreover, the impacts of climate change on the sedimentary environment in the eastern depression were analyzed. It can be concluded that E₆ was a lowstand system tract, E₅ and E₄ were lacustrine expansion system tracts, E₃ was a highstand system tract, and E₂ and E₁ were lacustrine contraction system tracts. All these verify that Milankovitch cycles serve as an effective approach for the analysis of sedimentary cycles.  相似文献   

Entropy model to assess sediment resuspension probability and trap efficiency of small dams     

《国际泥沙研究》2022,37(5):675-686

In the Brazilian drylands, there are tens of thousands of small dams. Despite their paramount importance to the rural population, they are rarely monitored. Water demand increases with time while, simultaneously, siltation reduces reservoir water capacity and availability. Reservoir siltation models are, therefore, mandatory to manage the numerous ungauged small dams in these drylands. The objective of the current study is to improve sediment trap efficiency (TE) modeling by including resuspension as a key probabilistic process. The Shannon entropy was used to estimate the sediment resuspension probability, which was merged with the Camp model and generated the RETSED entropy model. To validate the RETSED model, an experimental check dam (ECD, 300 m³), located in the Gilbués desertification site, Brazil, was monitored hourly during one hydrological year (July 2018–July 2019). Measurements show that the annual volumetric decline of the check dam was 12%; and that the average trap efficiency equaled 86%. Only 9.5% of the hourly sediment concentration outflow exceeded the average plus one standard deviation, showing that the reservoir is well mixed; a fact which highlights the relevance of the resuspension process. Three empirical models failed to mimic the experimental results: Churchill (TE = 99%), Brune (TE = 75%), and Maryland (TE = 94%). According to the RETSED entropy model, the resuspension probability during the experiment was 10% and TE = 81%, a value only 6% below the measured one. The Camp model simulated TE = 89%, only 3% higher than the measured value, but confirmed the Camp model's tendency to overestimate TE due to a disregard of resuspension. The deterministic model showed low sensitivity concerning the hydrodynamic effects, whereas the entropy formulation proved to be more consistent with physical behavior: the resuspension probability clearly increased and trap efficiency decreased with rising reservoir discharge.  相似文献