The last interglacial sea-level high stand on the southern Cape coastline of South Africa     

Andrew S. Carr  Mark D. Bateman  Colin V. Murray-Wallace  Peter J. Holmes 《Quaternary Research》2010,73(2):351-363

The continental margin of southern South Africa exhibits an array of emergent marginal marine sediments permitting the reconstruction of long-term eustatic sea-level changes. We report a suite of optical luminescence ages and supplementary amino acid racemization data, which provide paleosea-level index points for three sites on this coastline. Deposits in the Swartvlei and Groot Brak estuaries display tidal inlet facies overlain by shoreface or eolian facies. Contemporary facies relations suggest a probable high stand 6.0-8.5 m above modern sea level (amsl). At Cape Agulhas, evidence of a past sea-level high stand comprises a gravel beach (ca. 3.8 m amsl) and an overlying sandy shoreface facies (up to 7.5 m amsl). OSL ages between 138 ± 7 ka and 118 ± 7 ka confirm a last interglacial age for all marginal marine facies. The high stand was followed by a sea-level regression that was associated with the accumulation of eolian dunes dating to between 122 ± 7 ka and 113 ± 6 ka. These data provide the first rigorous numerical age constraints for last interglacial sea-level fluctuations in this region, revealing the timing and elevation of the last interglacial high stand to broadly mirror a number of other far-field locations.  相似文献   

东南沿海末次盛冰期古海平面标志与地震的关系──-100m以下最低海平面问题质疑   总被引：1，自引：0，他引：1  

徐起浩  黄镇国 《地震地质》1995,17(2):149

东南沿海末次盛冰期（２１～１４ｋａＢ．Ｐ，）滨海相沉积垂相分布多在海拔３８～－５０．８ｍ的范围内，以正向分布（海平面附近及以上）、正负向混合分布及负向（海平面以下）分布在断块交界区或其附近，是强震的主要发生地。在滨海相沉积垂向分布愈离散的区段，其地震活动性也愈强，本研究地区不存在末次盛冰期－１００ｍ以下的最低海平面，那些局部在外陆架海底发现的－１００ｍ以下的滨海相沉积，可能与地壳呈长趋势下沉作用有关  相似文献   

The response of coastal marshes to sea-level rise: Survival or submergence?     

Denise J. Reed 《地球表面变化过程与地形》1995,20(1):39-48

In order to maintain an elevation in the intertidal zone at which marsh vegetation can survive, vertical accretion of the marsh surface must take place at a rate at least equal to the rate of relative sea-level rise. Net vertical accretion of coastal marshes is a result of interactions between tidal imports, vegetation and depositional processes. All of these factors are affected, directly or indirectly, by alterations in marsh hydrology which might occur as a result of sea-level rise. The overall response of coastal marshes to relative sea-level rise depends upon the relative importance of the inorganic and organic components of the marsh soil and the impact of increased hydroperiod on net accumulation. The varied combination of factors contributing to sediment supply, and their complexity at the scale of individual marshes, means that predicting the response of suspended sediment concentration in marsh floodwater to any changes which may occur as a result of sea-level rise, at anything other than the local scale is unlikely to be accurate. The impact of sea-level rise on net below-ground production is also complex. The sensitivity of certain species to waterlogging and soil chemical changes could result in a change in species composition or the migration of vegetation zones. Consequently, predicting the net impact of sea-level rise on organic matter accumulation is fraught with difficulties and requires improved understanding of interactions between vegetation, soil and hydrologic processes.  相似文献   

Continental deposits and archaeological data in the Trieste Karst area (north-east Italy: evidence of sea-level changes and possible tectonic activity in the Late Pleistocene and Early Holocene     

G. Boschian 《International Journal of Earth Sciences》1993,82(2):227-233

The relationships between the land and sea in the northern Adriatic at the Pleistocene—Holocene boundary are examined by considering sea-level curves and archaeological data. Changes in the Mesolithic (Early Holocene) economy of the inhabitants can be interpreted as a result of palaeoecological variations due to glacioecustatic sea-level changes and recent tectonics. This hypothesis is also supported by evidence of older tectonic movements which may have continued until the end of the Pleistocene.  相似文献   

Geodynamic significance of localized spasmodic rapid-subsidence rates within the Cretaceous of central North America     

E.H.T. Whitten 《Cretaceous Research》1982,3(3):261-271

On the basis of spatial-time analyses, rates of subsidence within 5 Ma intervals in Montana, Wyoming, and adjacent areas, are mapped on the basis of thicknesses of the dominantly shallow-water sedimentary rocks; this is possible by using (a) existing detailed radiometric (mainly for abundant bentonites) and biostratigraphic chronology, and (b) published details of several hundred well logs and measured outcrop sections. Nine 5 Ma-interval maps for Montana and Wyoming show that, in general, as in eastern U.S.A. and eastern Brazil, subsidence rates tend to be low (< 50 m/Ma and commonly < 25 m/Ma) and monotonous in space and time. However, a few localized domains are characterized by significantly higher sedimentation and subsidence rates (> 100 m/Ma and very locally > 200 m/Ma or even > 300 m/Ma); these domains are sharply defined in both space and time. Domains of very high rates sometimes partially overlap areally in successive 5 Ma intervals, but they do not do so in all cases.The well-documented Cretaceous global marine transgressions are complicated by these differential-downwarp events of the “basement”. The broadly analogous patterns documented in the Western Interior Basin, eastern U.S.A., and eastern Brazil militate against special localized explanations (e.g. a shallowly subducted plate). Analogies with major cratonic basins and geodynamic implications are reviewed briefly.  相似文献   

Modelling tidally induced sediment-transport paths over the northwest European shelf: the influence of sea-level reduction     

Philip?Hall  Alan M.?DaviesEmail author 《Ocean Dynamics》2004,54(2):126-141

A three-dimensional model covering the northwest European Shelf and part of the adjacent Atlantic Ocean is used to examine the influence of water depth change upon the distribution of maximum tidal bed stress. The direction of bed stress is an indicator of sediment movement as bed load and various regions of convergence and divergence in good agreement with observations are identified. Calculations are performed with water depths reduced by 35 m, corresponding to 10 000 years before present (B.P.). Initially, the model is forced by only the M₂ tide, although subsequently five constituents, namely M₂, S₂, N₂, K₁ and O_1, are used for tidal forcing. Although the distribution of extreme bed stresses computed with only M₂ tidal forcing is comparable to that computed with five tides, the additional tidal constituents modify the magnitude of the bed stress. In particular the diurnal tides show regions of local enhanced current amplitude in the shelf-edge region with corresponding changes in bed stress. When water depths are reduced such that the North Sea and English Channel are separated, then there is a significant change in the tidal distribution in the shallow Southern Bight which influences bed-stress distributions and hence bed-load sediment transport in the area. Besides changes in shallow regions, the distribution of tides at the shelf edge is affected. A discussion of the limitations of the present coarse-grid model in shelf-edge regions and how it can be used to provide boundary conditions for limited-area three-dimensional models that can include stratification is presented. Also the importance of stratification for sediment movement at the shelf edge is briefly discussed.Responsible Editor: Phil Dyke  相似文献   

On the sensitivity of the sedimentary system in the East Frisian Wadden Sea to sea-level rise and wave-induced bed shear stress     

Emil Vassilev Stanev  Jörg-Olaf Wolff  Gerold Brink-Spalink 《Ocean Dynamics》2006,56(3-4):266-283

The paper addresses the individual and collective contribution of different forcing factors (tides, wind waves, and sea-level rise) to the dynamics of sediment in coastal areas. The results are obtained from simulations with the General Estuarine Transport Model coupled with a sediment transport model. The wave-induced bed shear stress is formulated using a simple model based on the concept that the turbulent kinetic energy (TKE) associated with wind waves is a function of orbital velocity, the latter depending on the wave height and water depth. A theory is presented explaining the controls of sediment dynamics by the TKE produced by tides and wind waves. Several scenarios were developed aiming at revealing possible trends resulting from realistic (observed or expected) changes in sea level and wave magnitude. The simulations demonstrate that these changes not only influence the concentration of sediment, which is very sensitive to the magnitude of the external forcing, but also the temporal variability patterns. The joint effect of tides and wave-induced bed shear stress revealed by the comparison between theoretical results and simulations is well pronounced. The intercomparison between different scenarios demonstrates that the spatial patterns of erosion and deposition are very sensitive to the magnitude of wind waves and sea-level rise. Under a changing climate, forcing the horizontal distribution of sediments adjusts mainly through a change in the balance of export and import of sediment from the intertidal basins. The strongest signal associated with this adjustment is simulated North of the barrier islands where the evolution of sedimentation gives an integrated picture of the processes in tidal basins.  相似文献   

Long-term changes in salt marsh extent affected by channel deepening in a modified estuary   总被引：2，自引：0，他引：2  

Ruth Cox  R. A. Wadsworth  A. G. Thomson 《Continental Shelf Research》2003,23(17-19):1833

The aim of this study is to quantify the long-term (54 years) rates of marsh extension and retreat at two sites in the Westerschelde Estuary, SW Netherlands. Nine sets of aerial photographs were obtained for each of the two salt marsh sites, Zuidgors and Waarde, taken at various times between 1944 and 1998. The seaward edges of the marshes were digitised from rectified images after the photographs had been scanned and georegistered to the Dutch National Grid. Comparison of the extents of the marshes at these nine time points revealed that the areas of both marshes had fluctuated during these 54 years with periods of both extension and retreat of the seaward marsh edges. These periods of extension and retreat appeared to be approximately synchronised until the 1990s, with mean changes in position of marsh front ranging from −7.92 to 6.04 m a⁻¹.The rate of landward retreat and seaward extension of the marsh front is shown to be related to an increase in the tidal prism brought about by dredging operations to maintain or increase the depth of the main navigable channel of the estuary. The consequent greater frequency with which the high tides reach the edge of the fringing marshes increases the risk of erosion. Strong westerly winds may also be a factor in increasing erosion. No relationship between the volume of shipping traffic using the estuary and marsh erosion was found.  相似文献   

Sedimentary response of Pagham Harbour, southern England to barrier breaching in AD 1910     

A. B. Cundy  A. J. Long  C. T. Hill  C. Spencer  I. W. Croudace 《Geomorphology》2002,46(3-4)

This paper examines the evolution of Pagham Harbour, southern England following storm-induced breaching of a protective barrier in AD 1910. Stratigraphic studies of sediments collected from intertidal areas show the presence of a distinct stratigraphic horizon in the northeast of Pagham Harbour at ca. 0 to +1.0 m ordnance datum (OD). Radiometric data indicate that this horizon is a ‘reclamation surface’ formed after land claim in AD 1846. Following marine flooding in AD 1910, sediment has accreted relatively rapidly (at a broadly constant rate of between 4 and 8 mm a⁻¹), wave and/or tidal energy have decreased and extensive marshes have developed. An asymptotic reduction in sediment accretion rate through time, as predicted in various theoretical models of salt marsh accretion, is not observed. Over the entire Pagham Harbour area, the period between AD 1948 and AD 1986 has seen an average marsh loss of 0.0087 km² a⁻¹, which is relatively small in comparison with other more exposed sites in the local area. Historically breached sites such as Pagham Harbour are common around European coasts, and these provide important natural laboratories within which the medium-term (decadal to centennial) coastal response to barrier breaching, and to managed-realignment coastal protection schemes, can be assessed.  相似文献   

厦门海洋垃圾防治与管理实践及启示          下载免费PDF全文

高宇  黄海萍  吴侃侃  李青生  王炳坤  陈克亮 《海洋开发与管理》2021,38(11):91-96

海洋垃圾污染问题已经成为国际社会重点关注的环境问题,也是我国海洋环境治理的重要组成部分。文章从协调机制、日常监测、预测预报、风险评估、国际合作、宣传教育方面总结和分析了厦门市海洋垃圾污染防治与管理实践和经验,针对国内当前在海洋垃圾防治与管理实践中存在的问题,在厦门模式的基础上,提出了加强立法建设、关注源头控制、开展日常监测和预报、建立评价体系、拓展合作交流、强化宣传教育等方面的措施建议,为我国其他沿海地方海洋垃圾污染防治与管理提供参考。  相似文献