Grain size analysis and sedimentology of beach sediments in Lagos, southwestern Nigeria have been studied. Ten fresh beach sediment samples were randomly collected at a depth of 25 cm - 40 cm along Lagos and Badagry a...Grain size analysis and sedimentology of beach sediments in Lagos, southwestern Nigeria have been studied. Ten fresh beach sediment samples were randomly collected at a depth of 25 cm - 40 cm along Lagos and Badagry axis. The sediments were analyzed by wet sieving method. Ternary diagrams indicate that the beach sediment is silty. The graphic mean ranges from 1.02ф (medium grained) to 2.21ф (fine grained) with an average of 1.61ф (medium grained). The preponderance of medium grained sediments and lack of coarse sands suggest moderate to high energy conditions of deposition. Graphic standard deviation ranges from 0.01ф - 0.81ф (very well sorted to moderately well sorted), with an average of 0.52ф (moderately well sorted). This is probably due to rapid back and forth flow of the depositing medium. Inclusive graphic skewness ranges from -0.38 to 1.41 (strongly coarse skewed to strongly fine skewed), with an average of 0.41 (strongly fine skewed). The graphic kurtosis values are between 0.44 and 1.37, which indicates very platykurtic to leptokurtic;with an average of 0.78 (platykurtic). This variation suggests that part of the sediment achieved its sorting elsewhere in high-energy environment. Histograms of the sediments exhibit both unimodal and bimodal trends. The arrangement is dominantly asymmetrical with varying modal class, which could be attributed to variation in the energy of the transporting medium. Bivariate plots (simple skewness vs. standard deviation and mean size vs. standard deviation) show the samples plotting mainly in the river sand zone, which suggests that the sediments were initially river sediments before reworking to the present site;other parameters that discriminate between river channel deposits, overbank deposits and overbank-pool deposits show the beach sediments plotting in the river channel zone. Linear discriminant functions analysis indicates a shallow marine beach environment in agitated water, with inputs from aeolian source. The Passega C-M diagram suggests suspension and rolling as the mode of deposition.展开更多
Geochemical and mineralogical studies were performed in the La Pesca(LP)and Tesoro Altamira(TA)beach sediments,located in the Tamaulipas state,northern Gulf of Mexico.The main aim of this study is to infer the weather...Geochemical and mineralogical studies were performed in the La Pesca(LP)and Tesoro Altamira(TA)beach sediments,located in the Tamaulipas state,northern Gulf of Mexico.The main aim of this study is to infer the weathering history and provenance and to discriminate the tectonic environment of the beach sediments.The sediments are composed of quartz with small amounts of accessory minerals such as plagioclase,calcite,orthoclase,microcline,and zircon.Both beach sediments are classified as fine-grained and very well sorted,however LP has coarse skewed and leptokurtic sediments,whereas TA has fine-skewed and very leptokurtic sediments.The chemical index of weathering(CIW’)indicates intense weathering in the source area.The quartz grain microtextures in the LP and TA are classified into mechanical,chemical,and mechanical/chemical origin.Mechanical features such as fractures,pits,percussion marks,abrasion fatigue,and V-shaped marks favor high-energy littoral,fluvial,subaqueous-marine,and aeolian environments.The chemical features indicate solution pits and crystalline overgrowth,which suggests a silica saturated marine environment.The mechanical/chemical features display adhering particles and elongated depressions suggest formation in a sub-aqueous nearshore marine environment.Major and trace elements-based provenance discrimination diagrams indicate a felsic source derived from the Mesa Central(MC),Sierra Madre Oriental(SMOr)and Oaxaquia terranes.The major and trace element concentrations imply a passive margin setting for the northern Gulf of Mexico,which is consistent with the general geology.展开更多
Zircons are abundant in the beach sediments.In this study,surface microtexture,mineralogy,bulk sediment geochemistry,trace element composition and U−Pb isotopic geochronology of detrital zircons collected from the Ria...Zircons are abundant in the beach sediments.In this study,surface microtexture,mineralogy,bulk sediment geochemistry,trace element composition and U−Pb isotopic geochronology of detrital zircons collected from the Riachuelos and Palma Sola beach areas,southwestern Gulf of Mexico were performed to infer the sediment provenance and palaeoenvironment.The zircon microtexture was categorized as mechanically-and/or chemically-induced features.The weathering index values for the Riachuelos(~72−77)and Palma Sola(~71−74)beach sediments indicated moderate weathering of both of the two source areas.The major and trace element data of bulk sediments suggested passive margin settings for the two areas.The trace elemental ratios and chondrite-normalized rare earth element(REE)patterns of bulk sediments revealed that the sediments were likely sourced by felsic and intermediate igneous rocks.And the zircon Th/U ratios(mostly more than 0.2)and zircon REE patterns(with negative Eu and positive Ce anomalies)suggested a magmatic origin for both of the beach sediments from these two areas.Two distinct zircon age peaks respectively belonging to the Paleozoic and the Cenozoic were identified both in the Riachuelos and Palma Sola beach sediments.Zircon geochronology comparison research between the Riachuelos−Palma Sola beach sediments and potential source areas in SW Gulf of Mexico revealed that the source terrane supplied the Paleozoic zircons of this study was identified as the Mesa Central Province(MCP),and the Cenozoic zircons were transported from the nearby Eastern Alkaline Province(EAP).Moreover,although the Precambrian zircons were very few in the studied sediments,their geochronology and geochemistry results still could infer that they were contributed by the source terranes of Grenvillian igneous suites in the Oaxaca and the Chiapas Massif Complexes.展开更多
Between April 2002 and April 2003,in situ measurements of water depth,current velocity and suspended sediment content were carried out in edge region of East Chongming salt marsh and neighboring bald flat in the Chang...Between April 2002 and April 2003,in situ measurements of water depth,current velocity and suspended sediment content were carried out in edge region of East Chongming salt marsh and neighboring bald flat in the Changjiang （Yangtze） Estuary under different weather conditions.Cross-shore suspended sediment flux was calculated and analyzed.The results show that under calm weather conditions,the current velocity process in bald field and salt marsh area varied differently during semidiurnal tidal cycles.Owing to current velocity asymmetry,mean SSC during flood tide phase was 1.8 times higher than that of ebb tide phase.As a result,net onshore sediment flux controlled cross-shore suspended sediment transport process and salt marsh pioneer zone was generally accreting.There was significant positive correlation between total sediment flux and quartic power of maximum water depth.It indicates that tidal ranges dominate suspended sediment transport and sedimentation process in the salt marsh pioneer zone under the calm weather condition.The sedimentation rate on the adjacent mudflat was higher than the salt marsh,which induced stable accreting of salt marsh towards the sea.The wind events enhanced SSC and current velocity during the semidiurnal tides.And the remarkable onshore net sediment flux could occur on the high marsh and mudflat close to the marsh fringe during the short period under the rough weather condition.展开更多
This paper deals with the recovery of zircon minerals from beach sand and red sediments of bad land topography and flow sheets with material balance are suggested. The experimental data reveal that the total heavy min...This paper deals with the recovery of zircon minerals from beach sand and red sediments of bad land topography and flow sheets with material balance are suggested. The experimental data reveal that the total heavy mineral content of red sediment sample is 43.9% in which zircon mineral concentrate is 2.75% by weight, where as for beach-dune sand sample the THM content is 16.7% in which zircon mineral concentrate is 0.16% by weight. It is found that U and Th and REE elements contents are much higher in red sediment zircon sample than beach sand zircon. Zircon concentrates recovered from beach-dune sand and red sediments contain 98 to 98.1% zircon with 79.6 to 80% recovery respectively. These zircon minerals from both the sources are suitable for industrial applications.展开更多
This paper, after briefly reviewing the experimental research on sediment transport on muddy beach since the 1950s, improves and perfects the method for forecasting siltation in navigation channels and harbour basins ...This paper, after briefly reviewing the experimental research on sediment transport on muddy beach since the 1950s, improves and perfects the method for forecasting siltation in navigation channels and harbour basins which was first put forward in China by the authors. In consideration of silty sediment and sand, some factors in forecasting methods have been changed and modified. Consequently, the modified methods can be used either to compute siltation in navigation channels and harbour basins on muddy beach or to compute siltation and scouring in navigation channels and harbour basins on both silty beach and sandy beach. The verification of field data from eleven large, medium and small natural harbours shows a good agreement between the forecasting by the modified method and the natural conditions. Finally, the paper deals with the rational utilization of water area after the construction of the West Dyke in Lianyungang, the maintenance of water depth of the navigation channel at the entrance, siltation distribution, siltation in the navigation channel and harbour basin for ships of 100 thousand tonnnage. Results once again prove that the prospect of constructing Lianyungang Harbour into a deepwater harbour is bright.展开更多
To analyze the grain size and depositional environment of the foreshore sediments, a study was undertaken on wave refraction along the wide sandy beaches of central Tamil Nadu coast. The nearshore waves approach the c...To analyze the grain size and depositional environment of the foreshore sediments, a study was undertaken on wave refraction along the wide sandy beaches of central Tamil Nadu coast. The nearshore waves approach the coast at 45° during the northeast(NE) monsoon, at 135° during the southwest(SW) monsoon and at 90° during the non-monsoon or fair-weather period with a predominant wave period of 8 and 10 s. A computer based wave refraction pattern is constructed to evaluate the trajectories of shoreward propagating waves along the coast in different seasons. The convergent wave rays during NE monsoon, leads to high energy wave condition which conveys a continuous erosion at foreshore region while divergent and inept condition of rays during the SW and non-monsoon, leads to moderate and less energy waves that clearly demarcates the rebuilt beach sediments through littoral sediment transport. The role of wave refraction in foreshore deposits was understood by grain size and depositional environment analysis. The presence of fine grains with the mixed population, during the NE monsoon reveals that the high energy wave condition and sediments were derived from beach and river environment. Conversely, the presence of medium grains with uniform population, during SW and non-monsoon attested less turbulence and sediments were derived from prolong propagation of onshore-offshore wave process.These upshots are apparently correlated with the in situ beach condition. On the whole, from this study it is understood that beaches underwent erosion during the NE monsoon and restored its original condition during the SW and non-monsoon seasons that exposed the stability of the beach and nearshore condition.展开更多
The Ouladine lagoon has an irregular bottom lined with different substrates. The lithological characteristics make it possible to observe sediments ranging from silts to sands and mixed sediments of variable color. Th...The Ouladine lagoon has an irregular bottom lined with different substrates. The lithological characteristics make it possible to observe sediments ranging from silts to sands and mixed sediments of variable color. These different fractions have varying proportions. The coarse fraction (>63 μm) has percentages ranging from 0 to 77% and the fine fraction ( μm) from 22.46 to 100% in the different sediments collected. The minority fraction of fine sands occupies the northern banks where the greatest depths of the section parallel to the coastal strip are observed. On the other hand, the sandy fractions occupy the southern shore up to the vicinity of the Azuretti mangrove island. This sandy fraction is also present on almost the entire section from the Comoé-Ebrié lagoon confluence to the closed mouth. The grain size characters of the sediments, such as the diagram of the classification coefficient So and the mean Mz, show well-classified sands. These sediments are deposited in a slightly agitated environment coming mainly from dunes and rivers. The sands of the estuarine complex were emplaced by saltation for most samples and by rotation.展开更多
文摘Grain size analysis and sedimentology of beach sediments in Lagos, southwestern Nigeria have been studied. Ten fresh beach sediment samples were randomly collected at a depth of 25 cm - 40 cm along Lagos and Badagry axis. The sediments were analyzed by wet sieving method. Ternary diagrams indicate that the beach sediment is silty. The graphic mean ranges from 1.02ф (medium grained) to 2.21ф (fine grained) with an average of 1.61ф (medium grained). The preponderance of medium grained sediments and lack of coarse sands suggest moderate to high energy conditions of deposition. Graphic standard deviation ranges from 0.01ф - 0.81ф (very well sorted to moderately well sorted), with an average of 0.52ф (moderately well sorted). This is probably due to rapid back and forth flow of the depositing medium. Inclusive graphic skewness ranges from -0.38 to 1.41 (strongly coarse skewed to strongly fine skewed), with an average of 0.41 (strongly fine skewed). The graphic kurtosis values are between 0.44 and 1.37, which indicates very platykurtic to leptokurtic;with an average of 0.78 (platykurtic). This variation suggests that part of the sediment achieved its sorting elsewhere in high-energy environment. Histograms of the sediments exhibit both unimodal and bimodal trends. The arrangement is dominantly asymmetrical with varying modal class, which could be attributed to variation in the energy of the transporting medium. Bivariate plots (simple skewness vs. standard deviation and mean size vs. standard deviation) show the samples plotting mainly in the river sand zone, which suggests that the sediments were initially river sediments before reworking to the present site;other parameters that discriminate between river channel deposits, overbank deposits and overbank-pool deposits show the beach sediments plotting in the river channel zone. Linear discriminant functions analysis indicates a shallow marine beach environment in agitated water, with inputs from aeolian source. The Passega C-M diagram suggests suspension and rolling as the mode of deposition.
基金Newton Advanced Fellowship award-The Royal Society,UK[grant#NA160116]National Council of Humanities Science and Technology(CONAHCYT),Mexico[grant#1101236].
文摘Geochemical and mineralogical studies were performed in the La Pesca(LP)and Tesoro Altamira(TA)beach sediments,located in the Tamaulipas state,northern Gulf of Mexico.The main aim of this study is to infer the weathering history and provenance and to discriminate the tectonic environment of the beach sediments.The sediments are composed of quartz with small amounts of accessory minerals such as plagioclase,calcite,orthoclase,microcline,and zircon.Both beach sediments are classified as fine-grained and very well sorted,however LP has coarse skewed and leptokurtic sediments,whereas TA has fine-skewed and very leptokurtic sediments.The chemical index of weathering(CIW’)indicates intense weathering in the source area.The quartz grain microtextures in the LP and TA are classified into mechanical,chemical,and mechanical/chemical origin.Mechanical features such as fractures,pits,percussion marks,abrasion fatigue,and V-shaped marks favor high-energy littoral,fluvial,subaqueous-marine,and aeolian environments.The chemical features indicate solution pits and crystalline overgrowth,which suggests a silica saturated marine environment.The mechanical/chemical features display adhering particles and elongated depressions suggest formation in a sub-aqueous nearshore marine environment.Major and trace elements-based provenance discrimination diagrams indicate a felsic source derived from the Mesa Central(MC),Sierra Madre Oriental(SMOr)and Oaxaquia terranes.The major and trace element concentrations imply a passive margin setting for the northern Gulf of Mexico,which is consistent with the general geology.
基金This study was supported by the Consejo Nacional de Ciencia y Tecnologfa(CONACyT)(Project No.Al-S-21287)Direcci6n General de Asuntos del Personal Academico(DGAPA)—Programa de Apoyoa Proyectos de Investigacione Innovacion Tecnologia(PAPIIT)(Project No.IN 107020)Instituto de Ciencias del Mary Limnologia Institutional Fund(Project No.616).
文摘Zircons are abundant in the beach sediments.In this study,surface microtexture,mineralogy,bulk sediment geochemistry,trace element composition and U−Pb isotopic geochronology of detrital zircons collected from the Riachuelos and Palma Sola beach areas,southwestern Gulf of Mexico were performed to infer the sediment provenance and palaeoenvironment.The zircon microtexture was categorized as mechanically-and/or chemically-induced features.The weathering index values for the Riachuelos(~72−77)and Palma Sola(~71−74)beach sediments indicated moderate weathering of both of the two source areas.The major and trace element data of bulk sediments suggested passive margin settings for the two areas.The trace elemental ratios and chondrite-normalized rare earth element(REE)patterns of bulk sediments revealed that the sediments were likely sourced by felsic and intermediate igneous rocks.And the zircon Th/U ratios(mostly more than 0.2)and zircon REE patterns(with negative Eu and positive Ce anomalies)suggested a magmatic origin for both of the beach sediments from these two areas.Two distinct zircon age peaks respectively belonging to the Paleozoic and the Cenozoic were identified both in the Riachuelos and Palma Sola beach sediments.Zircon geochronology comparison research between the Riachuelos−Palma Sola beach sediments and potential source areas in SW Gulf of Mexico revealed that the source terrane supplied the Paleozoic zircons of this study was identified as the Mesa Central Province(MCP),and the Cenozoic zircons were transported from the nearby Eastern Alkaline Province(EAP).Moreover,although the Precambrian zircons were very few in the studied sediments,their geochronology and geochemistry results still could infer that they were contributed by the source terranes of Grenvillian igneous suites in the Oaxaca and the Chiapas Massif Complexes.
基金The National Natural Science Foundation of China under contract Nos 40901010 and 40730526Leading Academic Discipline Project of Shanghai Normal University under contract No.DZL809
文摘Between April 2002 and April 2003,in situ measurements of water depth,current velocity and suspended sediment content were carried out in edge region of East Chongming salt marsh and neighboring bald flat in the Changjiang （Yangtze） Estuary under different weather conditions.Cross-shore suspended sediment flux was calculated and analyzed.The results show that under calm weather conditions,the current velocity process in bald field and salt marsh area varied differently during semidiurnal tidal cycles.Owing to current velocity asymmetry,mean SSC during flood tide phase was 1.8 times higher than that of ebb tide phase.As a result,net onshore sediment flux controlled cross-shore suspended sediment transport process and salt marsh pioneer zone was generally accreting.There was significant positive correlation between total sediment flux and quartic power of maximum water depth.It indicates that tidal ranges dominate suspended sediment transport and sedimentation process in the salt marsh pioneer zone under the calm weather condition.The sedimentation rate on the adjacent mudflat was higher than the salt marsh,which induced stable accreting of salt marsh towards the sea.The wind events enhanced SSC and current velocity during the semidiurnal tides.And the remarkable onshore net sediment flux could occur on the high marsh and mudflat close to the marsh fringe during the short period under the rough weather condition.
文摘This paper deals with the recovery of zircon minerals from beach sand and red sediments of bad land topography and flow sheets with material balance are suggested. The experimental data reveal that the total heavy mineral content of red sediment sample is 43.9% in which zircon mineral concentrate is 2.75% by weight, where as for beach-dune sand sample the THM content is 16.7% in which zircon mineral concentrate is 0.16% by weight. It is found that U and Th and REE elements contents are much higher in red sediment zircon sample than beach sand zircon. Zircon concentrates recovered from beach-dune sand and red sediments contain 98 to 98.1% zircon with 79.6 to 80% recovery respectively. These zircon minerals from both the sources are suitable for industrial applications.
文摘This paper, after briefly reviewing the experimental research on sediment transport on muddy beach since the 1950s, improves and perfects the method for forecasting siltation in navigation channels and harbour basins which was first put forward in China by the authors. In consideration of silty sediment and sand, some factors in forecasting methods have been changed and modified. Consequently, the modified methods can be used either to compute siltation in navigation channels and harbour basins on muddy beach or to compute siltation and scouring in navigation channels and harbour basins on both silty beach and sandy beach. The verification of field data from eleven large, medium and small natural harbours shows a good agreement between the forecasting by the modified method and the natural conditions. Finally, the paper deals with the rational utilization of water area after the construction of the West Dyke in Lianyungang, the maintenance of water depth of the navigation channel at the entrance, siltation distribution, siltation in the navigation channel and harbour basin for ships of 100 thousand tonnnage. Results once again prove that the prospect of constructing Lianyungang Harbour into a deepwater harbour is bright.
文摘To analyze the grain size and depositional environment of the foreshore sediments, a study was undertaken on wave refraction along the wide sandy beaches of central Tamil Nadu coast. The nearshore waves approach the coast at 45° during the northeast(NE) monsoon, at 135° during the southwest(SW) monsoon and at 90° during the non-monsoon or fair-weather period with a predominant wave period of 8 and 10 s. A computer based wave refraction pattern is constructed to evaluate the trajectories of shoreward propagating waves along the coast in different seasons. The convergent wave rays during NE monsoon, leads to high energy wave condition which conveys a continuous erosion at foreshore region while divergent and inept condition of rays during the SW and non-monsoon, leads to moderate and less energy waves that clearly demarcates the rebuilt beach sediments through littoral sediment transport. The role of wave refraction in foreshore deposits was understood by grain size and depositional environment analysis. The presence of fine grains with the mixed population, during the NE monsoon reveals that the high energy wave condition and sediments were derived from beach and river environment. Conversely, the presence of medium grains with uniform population, during SW and non-monsoon attested less turbulence and sediments were derived from prolong propagation of onshore-offshore wave process.These upshots are apparently correlated with the in situ beach condition. On the whole, from this study it is understood that beaches underwent erosion during the NE monsoon and restored its original condition during the SW and non-monsoon seasons that exposed the stability of the beach and nearshore condition.
文摘The Ouladine lagoon has an irregular bottom lined with different substrates. The lithological characteristics make it possible to observe sediments ranging from silts to sands and mixed sediments of variable color. These different fractions have varying proportions. The coarse fraction (>63 μm) has percentages ranging from 0 to 77% and the fine fraction ( μm) from 22.46 to 100% in the different sediments collected. The minority fraction of fine sands occupies the northern banks where the greatest depths of the section parallel to the coastal strip are observed. On the other hand, the sandy fractions occupy the southern shore up to the vicinity of the Azuretti mangrove island. This sandy fraction is also present on almost the entire section from the Comoé-Ebrié lagoon confluence to the closed mouth. The grain size characters of the sediments, such as the diagram of the classification coefficient So and the mean Mz, show well-classified sands. These sediments are deposited in a slightly agitated environment coming mainly from dunes and rivers. The sands of the estuarine complex were emplaced by saltation for most samples and by rotation.
