Management and sediment dynamics of the St. Lucia Estuary mouth,Zululand, South Africa

St. Lucia Estuary is on the subtropical, predominantly microtidal Zululand coast of South Africa. Lake St. Lucia's surface area fluctuates between 420 and 215 km² and has a mean depth of less than 1 m. The 21-km-long narrows connects Lake St. Lucia with the Indian Ocean. Tidal effects penetrate 14 km up the narrows. The St. Lucia system has changed substantially since the 1930s due to bad farming techniques within its catchment. Large amounts of sediment were deposited in the estuary mouth, resulting in relocation of the Mfolozi River mouth to the south at Mapelane. The St. Lucia catchment was subjected to two devastating floods in the last ten years: Cyclone Domoina during February 1984 and the September 1987 cutoff low flood. After floods scoured out the estuary, marine sand advanced up the estuary at a rate of 1200 m/y as a series of flood-tidal deltas. Over 600,000 m³ of sediment accumulated in the St. Lucia Estuary mouth from February 1988 to November 1989. Of this amount, 466,000 m³ of sediment was removed by dredging, although this has not stopped the shoaling. During high rainfall years, the estuary mouth is able to maintain an open outlet to the sea, but as lake levels drop, shoaling causes the mouth to constrict and eventually close. Without the dredging program the mouth would ultimately close during low rainfall years, causing management problems.     

Spatial variations in heavy metals on tidal flats in the Yangtze Estuary,China

Surface samples are used to determine onshore-offshore variations in heavy metal concentrations on tidal flats on Chongming and Hengsha Islands in the Yangtze Estuary, China. The Mann-Whitney U-Test suggests that proximity to the estuarine turbidity maximum does not result in significantly higher metal concentrations on tidal flats. Principal Components Analysis shows that grain-size is the primary control on metal concentrations, reflecting the occurrence of salt marsh and mud and sand flats. Sediment quality is comparable to that of pristine estuaries because of dilution by high river sediment loads.     

Distribution and assessment of sediment toxicity in Tamaki Estuary,Auckland, New Zealand

Heavy metal levels in surface sediments from Tamaki Estuary demonstrate significant up estuary increases in Cu, Pb, Zn, Cd and mud concentrations. Increased metal levels towards the head of the estuary are linked to local catchment sources reflecting the historical development, industrialisation and urbanisation of catchment areas surrounding the upper estuary. The relatively narrow constriction in the middle estuary (Panmure area), makes it susceptible to accumulation of upper estuary pollutants, since the constriction reduces circulation and extends the time required for fine waterborne sediments in the upper estuary to exchange with fresh coastal water. As a result fine fraction sediments trapped in the upper estuary facilitate capture and retention of pollutants at the head of the estuary. The increase in sandy mud poor sediments towards the mouth of the estuary is associated with generally low metal concentrations. The estuary’s geomorphic shape with a mid estuary constriction, sediment texture and mineralogy and catchment history are significant factors in understanding the overall spatial distribution of contaminants in the estuary. Bulk concentration values for Cu, Pb, Zn, and Cd in all the studied surface samples occur below ANZECC ISQG-H toxicity values. Cd and Cu concentrations are also below the ISQG-L toxicity levels for these elements. However, Pb and Zn concentrations do exceed the ISQG-L values in some of the surface bulk samples in the upper estuary proximal to long established sources of catchment pollution.     

Tidal propagation in the Gulf of Khambhat, Bombay High, and surrounding areas

The continental shelf on the west coast of India is widest off Bombay and leads into a strongly converging channel, the Gulf of Khambhat. Tides in the Gulf are among the largest on the coast. We use data on amplitude and phase of major semi-diurnal and diurnal constituents at forty-two ports in the Gulf and surrounding areas to define characteristics of the tides. We then use a barotropic numerical model based on shallow water wave equations to simulate the sea level and circulation in the region. The model is forced by prescribing the tide along the open boundaries of the model domain. Observed sea level at Bombay and currents from the Bombay High region at the centre of the model domain and from a shallow station off the port of Dahanu compare favourably with the fields simulated by the model. The simulated amplitudes and phases of the four most prominent tidal constituents also compare favourably with those observed along the coast, except at a few locations where the model spatial resolution (6.37 km × 6.37 km) appears to be inadequate to resolve the local geometry. Though this encourages us to conclude that the circulation in the region is dominated by barotropic tides, a concern is that the observational database on hydrography and directly measured currents in the region is weak.     

几内亚共和国Firawaya一带铁矿床地质特征及找矿标志

几内亚拥有丰富的矿产资源,目前宁巴山铁矿和西芒杜铁矿均为世界级铁矿,位于几内亚东南部,品位均达到66%~68%。本文通过对矿区地质特征的研究,确立磁铁矿的找矿标志,对指导本区域BIF型铁矿的地质找矿具有实际意义。     

长江河口崇明东滩周期性淹水区域水流的基本特征

潮间带周期性淹水区域水深、流速的变化过程是潮滩水动力过程的基本组成部分,也是潮流与泥沙相互作用的基础。通过2002年4月至2003年1月4个季节的野外实测,获得了平静天气条件下,崇明东滩滩面潮流水深、流速与流向的变化过程数据。结果表明,崇明东滩盐沼和邻近光滩处涨潮历时均小于落潮历时,水深过程变化呈现出“陡涨缓落”的特点。光滩与盐沼交界处光滩一侧流速过程呈“双峰型”特征,涨落潮均出现流速峰值;盐沼（植物生长期）流速过程具有“单峰型”特点,仅在涨潮初出现峰值。研究区潮流不对称性明显,主要表现为涨潮优势,且由光滩向盐沼上部不断增强,潮沼植物和地形变化是加强盐沼区涨潮优势的主要原因。流速变化过程的差异和潮流不对称性使盐沼区域发生稳定的泥沙淤积,盐沼前缘光滩则会出现较频繁的冲淤变化,平静天气条件下,它们是控制崇明东滩泥沙输移和潮滩动力地貌过程的动力基础。     

Scale effects of eroded sediment transport in Wujiang River Basin,Guizhou Province,China

In recent years, research on spatial scale and scale transformation of eroded sediment transport has become a forefront field in current soil erosion research, but there are very few studies on the scale effect problem in Karst regions of China. Here we quantitatively extracted five main factors influencing soil erosion, namely rainfall erosivity, soil erodibility, vegetative cover and management, soil and water conservation, and slope length and steepness. Regression relations were built between these factors and also the sediment transport modulus and drainage area, so as to initially analyze and discuss scale effects on sediment transport in the Wujiang River Basin (WRB). The size and extent of soil erosion influencing factors in the WRB were gauged from: Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM), precipitation data, land use, soil type and Normalized Difference Vegetation Index (NDVI) data from Global Inventory Modeling and Mapping Studies (GIMMS) or Advanced Very High Resolution Radiometer (AVHRR), and observed data from hydrometric stations. We find that scaling effects exist between the sediment transport modulus and the drainage area. Scaling effects are expressed after logarithmic transformation by a quadratic function regression relationship where the sediment transport modulus increases before decreasing, alongside changes in the drainage area. Among the five factors influencing soil erosion, slope length and steepness increases first and then decreases, alongside changes in the drainage area, and are the main factors determining the relationship between sediment transport modulus and drainage area. To eliminate the influence of scale effects on our results, we mapped the sediment yield modulus of the entire WRB, adopting a 1 000 km2 standard area with a smaller fitting error for all sub-basins, and using the common Kriging interpolation method.     

Deducing sediment transport direction and the relative importance of rivers on a tropical microtidal beach using the "McLaren model"

 Analyses of the sedimentological trend from 90 samples collected at 1-km intervals along a tropical microtidal coastline of northern Terengganu indicate that the preferred sediment transport direction was northwards, following the McLaren model. The extent of disruption to and reestablishment of the sedimentological trend on beaches north of two river mouths within the study area was used to determine their relative importance in supplying sediment to the beaches. The extent of disruption to the sedimentological trend was 18 and 14 km for the beaches north of the Terengganu and Setiu River mouths, respectively. This suggests that the Terengganu River is more important in supplying sediments to the beach than the Setiu River. To a limited extent this study showed that the McLaren model can be applied to deduce sediment transport direction on a microtidal coastline, while disruption to the sedimentological trend adjacent to river mouths can be used to compare the relative importance of rivers in supplying sediments, provided that the disruption to the sedimentological trend is small enough so as to allow for the trend to be discernible again further along the transport path. Received: 8 May 1997 · Accepted: 12 August 1997     

Tidal effects of groundwater levels in the coastal aquifers near Beihai, China

Four times of observation of the ocean tide and groundwater levels in the coastal aquifers near Beihai, China show that fluctuation in the tide-induced groundwater levels follows the tide, with the highest and lowest water levels corresponding to the high water level syzygy tide and the low water level neap tide. The tidal coefficient is less than 0.5, decreasing approximately exponentially with the distance from the coast. The tide can affect the groundwater levels at observation wells as far as about 4,200 and 3,300 m in the southern and northern coasts in Beihai. Observations and spectrum analyses of the time series of the tide and water levels suggest that the tide and water levels have similar changes with complex fluctuations of a long period of 14.37 days and two short periods of 24.7 and 12.5 h. Time lags of water levels to the tide at observation wells last several hours and increases roughly linearly with the distance from the coast. Mathematic models consisting of a periodic term plus a linear term are established to describe the changes in the tide and the groundwater levels. The periodic terms for the tide and water levels are constructed using finite Fourier’s series consisting of 7 to 11 terms other than a single term of a sine function in earlier work. Computed water levels with the models can fit the observed water levels with reasonable accuracy and satisfactory prediction of the changes in the water levels is also obtained.     

Tidal triggering of earthquakes in the subducting Philippine Sea plate beneath the locked zone of the plate interface in the Tokai region, Japan

We found a characteristic space–time pattern of the tidal triggering effect on earthquake occurrence in the subducting Philippine Sea plate beneath the locked zone of the plate interface in the Tokai region, central Japan, where a large interplate earthquake may be impending. We measured the correlation between the Earth tide and earthquake occurrence using microearthquakes that took place in the Philippine Sea plate for about two decades. For each event, we assigned the tidal phase angle at the origin time by theoretically calculating the tidal shear stress on the fault plane. Based on the distribution of the tidal phase angles, we statistically tested whether they concentrate near some particular angle or not by using Schuster's test. In this test, the result is evaluated by p-value, which represents the significance level to reject the null hypothesis that earthquakes occur randomly irrespective of the tidal phase angle. As a result of analysis, no correlation was found for the data set including all the earthquakes. However, we found a systematic pattern in the temporal variation of the tidal effect; the p-value significantly decreased preceding the occurrence of M ≥ 4.5 earthquakes, and it recovered a high level afterwards. We note that those M ≥ 4.5 earthquakes were considerably larger than the normal background seismicity in the study area. The frequency distribution of tidal phase angles in the pre-event period exhibited a peak at the phase angle where the tidal shear stress is at its maximum to accelerate the fault slip. This indicates that the observed small p-value is a physical consequence of the tidal effect. We also found a distinctive feature in the spatial distribution of p-values. The small p-values appeared just beneath the strongly coupled portion of the plate interface, as inferred from the seismicity rate change in the past few years.     

Modeling the influence of settling velocity on cohesive sediment transport in Tanshui River estuary

Settling velocities of suspended cohesive sediment in estuaries vary over a range of several orders in magnitude. Variations in the suspended sediment concentration are often considered as the principal cause. Turbulence and the suspended sediment concentration, as well as other factors such as salinity, dissolved organic substances, flocculation ability, and the rate of floc growth affect setting velocities. A laterally–averaged finite difference model for hydrodynamics and cohesive sediment transport is developed and applied in the Tanshui River estuary, Taiwan. The model has been calibrated and verified with water surface elevation, longitudinal velocity, salinity, and cohesive sediment measured. The overall performance of the model is in qualitative agreement with the available data. The model is used to investigate the influence of settling velocity on cohesive sediment transport dynamics. The simulation indicates that the turbidity maximum zone is near Kuan–Du. When settling velocities increase the surface cohesive sediment concentration at Kuan–Du station trends to decrease and bottom cohesive sediment concentration increases. Both surface and bottom cohesive sediment concentrations decrease at Taipei Bridge and Pa–Ling Bridge. This implies that suspended sediment advected seaward and deposited. There is consequently a net seaward flux of suspended sediment near surface, and a net landward flux near the bed.     

Prograde metamorphism and decompression of the Gföhl gneiss, Czech Republic

Quartzofeldspathic rocks of the Gföhl gneiss from the Moldanubian of the Czech Republic span amphibolite-to granulite-facies, and are associated with eclogite. Protomylonitic fabrics related to terminal tectonic emplacement and reworking of the gneiss are common. Some non-mylonitic rocks, however, preserve early, prograde features (e.g., Opx-rimmed Hbl in metabasites), whereas others have characteristics generally associated with near-isothermal decompression (e.g., Pl-Opx moats separating Grt and Qtz in metabasites; Crd ± Spl coronas on Grt and aluminosilicates in metapelites); the unequivocal distinction between prograde and decompressional features in these rocks, however, may not be possible or even justified. For example, some metapelites contain growth-zoned (i.e., rimward increase in X_Mg) garnets that also record evidence (i.e., rimward decrease in X_Ca, compensated by the presence of reversely-zoned plagioclase in the same rock) of decompression. In rare instances, eclogitic rocks (P > 11 kbar) interpreted as tectonic enclaves within the gneiss also record mineralogic evidence of decompression (e.g., Crd-Opx-Spr coronas on pyrope). In metapelites, plagioclase-cored coronal garnets with high Prp/Grs ratios (˜ 2.5) record near-isobaric cooling from near the thermal maximum at a relatively shallow but undetermined crustal level.

Unlike Gföhl gneisses elsewhere (e.g., in Austria), the rocks described here do not preserve evidence of extreme metamorphic conditions. Texturally stable Grt-Bt pairs in non-mylonitic samples give T_max < 750 °C. P_max is not known, but prograde metamorphism apparently progressed from the kyanite to sillimanite fields, implying P ˜ 8 kbar at the maximum Grt-Bt temperature. At these conditions, dehydration of mafic gneiss occurred in the presence of a CO₂-rich (X_CO2 ˜ 0.85) pore fluid     

民国时期的地质矿产类博物馆

综述民国时期各种类别的地质矿产博物馆,并对其进行简要评说。地质科研机构附设的地质馆、大学的地质标本陈列室、专类地质陈列馆、综合性博物馆中的地质馆以及临时性的地质展览会。在各类地质矿产陈列馆中,由科研机构附设的地质馆占有极其重要的地位和分量。各种类别地质馆共同构成的民国时期地质矿产类博物馆体系,为博物馆史研究者提供了较为详实的参考资料。     

长江口崇明岛滩地重金属元素分布探讨

该文通过对长江口崇明岛滩地柱状样进行^210Pb和^137Cs以及11个重金属元素的测试，以探讨重金属元素在河口滩地中的沉积与迁移过程，剖析其分布规律，从而为崇明岛滩涂资源的合理规划、利用提供科学依据。研究发现70年代以来的沉积物中重金属元素含量普遍高于70年代以前。在空间上，堡镇附近重金属元素含量比崇明岛其它地方明显要高，在岛上的另一个主要城镇城桥附近，重金属元素没有显示高值，反映重金属含量与径、潮流的淘洗作用有关。     

Distribution of foraminifera and ostracods in the Onkaparinga Estuary,South Australia

Analysis of sediment and aquatic vegetation samples collected along the Onkaparinga estuary, South Australia, revealed the distribution patterns of benthic and epi-benthic micro-organisms, specifically foraminifera and ostracods. The total assemblage provided an assemblage ‘snap shot,’ contemporaneous with the environmental conditions at the time of sampling, as well as seasonally and time-averaged distribution information. Species richness is low in the upper reaches of the estuary and favours species with a wide salinity tolerance. Observed species richness increases seawards. Species richness and abundance within species is greater where there is conspicuous aquatic vegetation. Thus, species richness and distribution appear to be related to the proximity to the sea and the provision of diverse habitable substrate. Foraminiferal species, Ammonia beccarii and Elphidium excavatum, and ostracods belonging to the genera Paracypria, Xestolebris and Leptocythere dominate the total assemblage. These species are characteristic of euryhaline conditions. The mutual maximum occurrences of Reophax barwonensis, Ammobaculites barwonensis and Trochammina inflata signify mid-estuarine conditions. In the lower regions of the estuary, the appearance of shallow marine species of foraminifera such as Elphidium crispum and Quinqueloculina poeyana, and ostracods Bairdoppilata sp., Hemicytherura spp. and Paranesidea spp. signifies interactions with the adjacent inner shelf coastal waters. Throughout the entire length of the estuary, the presence of vegetal substrate created a strong numerical bias towards live occurrences of the ostracods Paracypria sp. and Xestolebris cedunaensis. These species are potentially useful as proxies for paleoenvironmental interpretations of estuarine sediments.     

嘉陵江不同区域场次洪水输沙规律

对于雨洪河流,河流年输沙量主要来源于1场或几场高强度暴雨洪水过程,开展流域次洪输沙规律研究对认识流域水沙变化特性、提升流域产输沙的预测能力具有重要意义。利用嘉陵江流域小河坝站、罗渡溪站、武胜站及北碚站的历年场次洪量与输沙量资料,基于径流侵蚀功率理论和M-K分析等方法,系统分析了嘉陵江不同区域的次洪输沙特性。结果表明：嘉陵江流域汛期洪量和输沙量主要来自于嘉陵江干流;嘉陵江不同区域场次洪量均呈不显著减少趋势,次洪输沙模数(输沙量)总体呈显著减少趋势,但小河坝站2013—2020年次洪输沙模数(输沙量)呈显著增加趋势;随着径流侵蚀功率的逐渐增加,各区域不同时段的次洪输沙模数(输沙量)的变幅逐渐减小;嘉陵江干流区武胜站场次洪水输沙过程受人类活动影响最大、渠江罗渡溪站次之、涪江小河坝站最小;受汶川地震及强降雨等影响,小河坝站和北碚站2013—2020年次洪输沙量较1999—2012年有一定程度增加,但北碚站增幅小于小河坝站。     

Neoproterozoic diamictites from the Itombwe Synclinorium, Kivu Province, Democratic Republic of Congo: Palaeoclimatic significance and regional correlations

The Itombwe Synclinorium in the Kivu Province of the Democratic Republic of Congo contains a Neoproterozoic succession of greenschist facies metasedimentary rocks defined as the Itombwe Supergroup, dated between 1020 ± 50 and 575 ± 83 Ma. The Itombwe Supergroup unconformably overlies the Mesoproterozoic Kibaran belt and is subdivided into the Upper and Lower Kadubu Groups which are separated by a faulted tectonic contact. Graded, rhythmically repeated sequences of sandstones, greywackes, phyllites and shales indicate deposition as turbiditic sediment-gravity flows. Periods of basin anoxia are indicated by the presence of graphitic black shales. The Lower and Upper Kadubu Groups contain three stratigraphic levels of diamictites and lonestone-bearing iron-rich sedimentary rocks interpreted as glaciogenic strata, which broadly correlate with other Neoproterozoic glacial sequences in the Central African region and elsewhere around the world. Current stratigraphic and geochronological knowledge of these beds is insufficient to provide more accurate correlations.     

几内亚西南部莫拉铁矿区地质特征及找矿方向

莫拉(Mola)铁矿区位于几内亚金迪亚省,西非克拉通莱奥(Leo)地盾西部边缘的太古代Kenema-Man Domain地盾与西侧罗克列德褶皱带(Rokelide Fold Belts)的接壤地带。区内发育铁角砾岩型、似条带状赤铁矿型2类矿体。研究认为,铁角砾岩型铁矿主要由后期风化淋滤作用对原生赤铁矿改造并富集形成,赋存于地表;似条带状赤铁矿矿体是经初始海底热液喷溢沉积和后期构造作用改造而富集形成。     

Millennial‐scale precipitation changes over Central Africa during the late Quaternary and Holocene: evidence in sediments from the Gulf of Guinea

We combine environmental magnetism, geochemical measurements and colour reflectance to study two late Quaternary sediment cores: GeoB 4905‐4 at 2° 30′ N off Cameroon and GeoB 4906‐3 at 0° 44′ N off Gabon. This area is suitable for investigating precipitation changes over Central and West Africa because of its potential to record input of aeolian and fluvial sediments. Three magnetozones representing low and high degree of alteration of the primary rock magnetic signals were identified. The magnetic signature is dominated by fine‐grained magnetite, while residual haematite prevails in the reduced intervals, showing increase in concentration and fine grain size at wet intervals. Our records also show millennial‐scale changes in climate during the last glacial and interglacial cycles. At the northern location, the past 5.5 ka are marked by high‐frequency oscillations of Ti and colour reflectance, which suggests aeolian input and hence aridity. The southern location remains under the influence of the Intertropical Convergence Zone and thus did not register aeolian signals. The millennial‐scale climatic signals indicate that drier and/or colder conditions persisted during the late Holocene and are synchronous with the 900 a climatic cycles observed in Northern Hemisphere ice core records. Copyright © 2009 John Wiley & Sons, Ltd.     

巴布亚新几内亚奥克泰迪铜金矿床成矿特征和控制因素

巴布亚新几内亚西部Fubilan山奥克泰迪矿床是一个世界级铜金矿床,在大地构造上位于新几内亚造山带的巴布亚褶皱带。该矿床的铜金矿化赋存于Fubilan二长斑岩及其周边的磁铁矿夕卡岩和硫化物夕卡岩中。矿石类型以原生硫化物矿石为主,金属矿物包括磁铁矿、黄铁矿、磁黄铁矿、白铁矿、黄铜矿、斑铜矿等。蚀变类型包括夕卡岩化、钾化、泥化和青盘岩化。矿床氧化次生富集带发育,表生矿石矿物为蓝辉铜矿、辉铜矿、自然铜、铜蓝和银金矿。成矿作用主要受区域构造、侵入杂岩体、Darai组灰岩地层、断裂等因素的控制。根据矿床的主岩、矿石特征、蚀变特征和控矿因素,认为该矿床成因类型属于较为典型的夕卡岩—斑岩型矿床。