Article

A kinetic model to explain the grainsize and organic matter content dependence of magnetic susceptibility in transitional marine environments: A case study in Ría de Muros (NW Iberia)

Article

A kinetic model to explain the grainsize and organic matter content dependence of magnetic susceptibility in transitional marine environments: A case study in Ría de Muros (NW Iberia)

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Abstract

Magnetic minerals in marine sediments are sensitive indicators of processes such as provenance changes, climatic controls, pollution, and postdepositional geochemical changes. Magnetic susceptibility is the bulk property of the sediments most commonly used to understand the magnetic characteristics of sediments. Before conclusions can be drawn from changes in this parameter, it is important to understand what factors and to what extent control changes in magnetic susceptibility. The magnetic susceptibility of surficial sediments in the Galician Rias Baixas, in NW Spain, has been shown to covary with sediment texture and organic matter content. Downcore, the magnetic properties of these sediments experience drastic changes as a result of strong dissolution caused by early diagenesis. In this paper, we further explore the relationship between these factors and formalize the observed covariations as the result of a simple second-order kinetic model dependent on the content of organic matter in surficial sediments in the Ria de Muros. The reanalysis of previously reported data from the Rias de Vigo and Pontevedra confirmed the validity of this model and suggested further controls such as wave climate and water depth in the rates at which magnetic susceptibility changes are controlled by organic matter content.

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... Bulk sediment magnetic signal in marine sediment is strongly affected by dilution with paramagnetic and diamagnetic minerals (Mohamed et al., 2017). The distinct drop in concentration dependent magnetic parameters in MTD-rich sediment intervals below 12 mbsf (Z-II, Z-III, Z-IV) could be either due to intense sediment mixing and reworking triggering by sliding/slumping activities (Ramprasad et al., 2011), or dilution caused by increased terrigenous (diamagnetic) inputs or due to different sediment provenance and age. ...
... We proposed that distinct drop in χ lf within the MTD-rich sediment intervals (below 12 mbsf) could be due to the dilution of ferromagnetic minerals caused by increase in the concentration of diamagnetic and paramagnetic minerals like quartz and clay. Our interpretation is similar to the observations reported in sediments from Galician Rias Baixas (Mohamed et al., 2017), and Ria de Pontevedra, NW Spain (Rey et al., 2005). ...
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We reviewed the factors influencing organic carbon and carbonate preservation in marine sediments. The application and problems of these two biogenic components as paleoproductivity proxies are exemplified by comparison of two sediment cores: one from the high productivity upwelling region off Angola, and the other from the low productivity area off North Brazil. Unlike the upwelling site, sedimentary organic carbon in the low productivity area is problematic as a paleoproductivity indicator. There, calcium carbonate, the predominant biogenic material of the pelagic ocean, serves as an alternative estimator for paleoproductivity. During the last 300,000 years, high and variable paleoproductivity in the eastern Atlantic contrasts with low and relatively constant values in the West. Beyond this, a countercyclicity of paleoproductivity variations between the eastern and the western tropical Atlantic is observed. During cold climatic substages, paleoproductivity was at maximum in the East, whereas minimum values were recorded in the West. These inverse relationships are attributed to a lowered nutrient concentration of glacial intermediate waters which are the nutrient source of open ocean new production. At the same time, the supply of nutrients was enhanced in the eastern Atlantic due to intensified wind-driven upwelling. Moreover, the increased zonal wind stress may have caused a deepening of the nutricline in the West coupled with a synchronous shallowing in the East. The sharp Glacial-to-Holocene decrease in paleoproductivity in the upwelling areas (dominated by opal producers), occurred contemporaneously with an increase in the oligotrophic open ocean (dominated by carbonate producers). This should have resulted in a decrease of the carbon rain ratio (Corg /CCaCO3), possibly contributing to the observed Glacial-to-Holocene increase in atmospheric pCO2
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December 2004 Indian Ocean Tsunami (IOT) had a major impact on the geomorphology and sedimentology of the east coast of India. Estimation of the magnitude of the tsunami from its deposits is a challenging topic to be developed in studies on tsunami hazard assessment. Two core sediments (C1 and C2) from Nagapattinam, southeast coast of India were subjected into textural, mineral, geochemical and rock-magnetic measurements. In both cores, three zones (noted zone I, II and II) have been distinguished based on mineralogical, geochemical and magnetic data. Zone II is featured by peculiar rock-magnetic, textural, mineralogical and geochemical signatures in both sediment cores that we interpret to correspond to the 2004 IOT deposit. Textural, mineralogical, geochemical and rock-magnetic investigations showed that the tsunami deposit is featured by relative enrichment in sand, quartz, feldspar, carbonate, SiO2, TiO2, K2O and CaO and by a depletion in clay and iron oxides. These results point to a dilution of reworked ferromagnetic particles into huge volume of paramagnetic materials, similarly to what has been described in other nearshore tsunami deposit (Font et al., 2010). Correlation analysis elucidated the relationships among the textural, mineral, geochemical and magnetic parameters, and suggests that most of the quartz-rich coarse sediments have been transported offshore by the tsunami wave. These results are well agreed with the previously published numerical model of tsunami induced sediment transport off southeast coast of India and can be used for future comparative studies on tsunami deposits.
Article
Storm- and tsunami-deposits are generated by similar depositional mechanisms making their discrimination hard to establish using classic sedimentologic methods. Here we propose an original approach to identify tsunami-induced deposits by combining numerical simulation and rock magnetism. To test our method, we investigate the tsunami deposit of the Boca do Rio estuary generated by the 1755 earthquake in Lisbon which is well described in the literature. We first test the 1755 tsunami scenario using a numerical inundation model to provide physical parameters for the tsunami wave. Then we use concentration (MS, SIRM) and grain size (χARM, ARM, B1/2, ARM/SIRM) sensitive magnetic proxies coupled with SEM microscopy to unravel the magnetic mineralogy of the tsunami-induced deposit and its associated depositional mechanisms. In order to study the connection between the tsunami deposit and the different sedimentologic units present in the estuary, magnetic data were processed by multivariate statistical analyses. Our numerical simulation show a large inundation of the estuary with flow depths varying from 0.5 to 6m and run up of ∼7m. Magnetic data show a dominance of paramagnetic minerals (quartz) mixed with lesser amount of ferromagnetic minerals, namely titanomagnetite and titanohematite both of a detrital origin and reworked from the underlying units. Multivariate statistical analyses indicate a better connection between the tsunami-induced deposit and a mixture of Units C and D. All these results point to a scenario where the energy released by the tsunami wave was strong enough to overtop and erode important amount of sand from the littoral dune and mixed it with reworked materials from underlying layers at least 1m in depth. The method tested here represents an original and promising tool to identify tsunami-induced deposits in similar embayed beach environments.
Article
A third-generation numerical wave model to compute random, short-crested waves in coastal regions with shallow water and ambient currents (Simulating Waves Nearshore (SWAN)) has been developed, implemented, and validated. The model is based on a Eulerian formulation of the discrete spectral balance of action density that accounts for refractive propagation over arbitrary bathymetry and current fields. It is driven by boundary conditions and local winds. As in other third-generation wave models, the processes of wind generation, whitecapping, quadruplet wave-wave interactions, and bottom dissipation are represented explicitly. In SWAN, triad wave-wave interactions and depth-induced wave breaking are added. In contrast to other third-generation wave models, the numerical propagation scheme is implicit, which implies that the computations are more economic in shallow water. The model results agree well with analytical solutions, laboratory observations, and (generalized) field observations.
Article
This chapter explains the geomorphology and sedimentology of estuaries. Geomorphology is concerned with the study of earth-surface forms and with their evolution in time and space because of the physicochemical and biological factors acting on them. Most of the evolution is the product of a cyclic process based on erosion transport-deposition of sediment particles. In particular, the coastal environments are subjected to the most energetic conditions on the earth surface. Estuaries are one of the most important coastal features subject to strong processes that fully cover the space-temporal scale. Nevertheless spatial and time scales may range from few seconds and centimeters to centuries and thousands of kilometers. Although the number of examples of estuaries observed in the geological record is small, there are increasing evidences that these estuaries were a common feature of the planet. It is only a matter of common sense to accept this concept, because river and sea have interacted from the Precambrian period to the present. Nevertheless, within the estuaries the dynamical processes are rather strong and impose a remarkable stress over the biota, either permanent or temporary, the morphology, and the civil works.
Article
Interpretations of magnetic susceptibility variations in circum-Saharan marine sediments have suggested a close relationship with Saharan dust supply, which assumes that dust dominates over the potential contributions from a variety of other sources and processes. To evaluate the importance of Saharan dust supply versus that of other potential sources of variability in magnetic susceptibility, we compile magnetic susceptibility data from eastern Mediterranean Plio-Pleistocene sequences at Ocean Drilling Program (ODP) sites 964, 966, 967 and 969, for comparison with other paleoclimatic and paleoceanographic proxy data for the same intervals. Our results demonstrate that magnetic susceptibility variations are linked to the supply of Saharan dust through some parts of the studied intervals, but seem to be predominantly controlled by the discharge of suspended matter from Eurasian rivers and the Nile. Depositional and diagenetic processes in the stratigraphic vicinity of ash layers and sapropels also affect magnetic susceptibility values. We conclude that magnetic susceptibility records can only be used as a proxy for Saharan dust supply in eastern Mediterranean sediments, and likely also in other peri-Saharan marine sediments, when this has been demonstrated by further analyses to be the only (or predominant) source of magnetic susceptibility variability.
Article
In the Ría de Muros, the northernmost of the four large coastal embayments on the NW coast of the Iberian Peninsula known as Rías Baixas, river discharges, winds and tides are the main agents driving the circulation. Both river discharges and winds present a high degree of seasonality: river flows are typically low in summer and high in winter, and the direction of prevailing winds is N–NE in spring–summer and S–SW in fall–winter. This seasonality may be expected to affect the circulation in the ría. To investigate this, a 3D, baroclinic model is implemented with an unconventional mixed boundary condition at the open (ocean) boundary. Once validated by comparing simulated and observed data of water level, current velocity and salinity, the model is applied to computing the circulation in four cases representative of typical summer and winter scenarios. In each case the model is forced by a specific combination of driving agents, including river runoff, tide and, in some cases, wind. A two-layer circulation pattern with bottom inflow and surface outflow (positive estuarine circulation) exists in the summer cases as well as in the winter case without wind, but its intensity varies greatly. It is weak in typical summer conditions in the absence of wind, but very strong in typical winter conditions also in the absence of wind due to the increase of baroclinic effects brought about by the high river discharges. Moreover, the winds characteristic of summer (N–NE) and winter (S–SW) have markedly different effects when added to the hydrodynamic forcing characteristic of the respective season. While the N–NE wind strengthens the summer no-wind circulation, the S–SW wind transforms the winter no-wind circulation into a three-layer pattern—previously undescribed in the Rías Baixas—in which the surface layer is mostly at rest, outflow resumes immediately underneath, and inflow continues at lower levels. The fact that the S–SW wind is incapable of triggering a negative estuarine circulation in the face of winter average river flows is indicative of the fundamental importance of baroclinic effects in the Ría de Muros. In sum, the seasonal variability of river discharges and winds is found to have a substantial effect on the circulation in the ría.
Article
The circulation in the Ría de Muros, a large coastal embayment in the Rías Baixas region (NW Spain), is studied for the first time using a numerical model—a baroclinic model in two horizontal dimensions (2DH) driven by the tide, wind, and river inflows. The model grid covers the whole ría, including the alternately drying and flooding areas of the inner ría. In situ data of the current velocity and direction, temperature and salinity, river discharges, and wind velocity and direction are gathered for this purpose. The numerical results agree well with measurements from an Acoustic Doppler Current Profiler (ADCP); e.g. the correlation coefficient is 0.71 for the velocity component along the main axis of the ría. This indicates that the tide, wind, and river inflows are the most relevant factors driving ría circulation on a time scale of days to weeks. The model is then applied to an analysis of flood and ebb circulation patterns in two cases of interest: (1) a NNE wind, and (2) a WSW wind. The first is a typical summer condition in the Ría de Muros. The second, although characteristic of winter conditions, also occurred in July 2007, which is very atypical from a meteorological standpoint and was likely due to the Azores High not occupying its usual summer position to the NE of the eponymous islands. The strong similarities between the circulation patterns in both cases indicate that the tide is the main driving factor of ría hydrodynamics. Nonetheless, a more detailed analysis reveals that wind also plays a relevant role, especially in certain areas of the middle and outer ría.
Article
The present paper reviews the current state of knowledge regarding the geology of the Rias Baixas (Galicia, northwest Iberian Peninsula), focusing specifically on characterisation, geometry, and evolution of the sedimentary bodies; physical and geological description; drainage patterns; and advances in palaeoceanography and palaeoecology.
Article
Diagenetic Fe and Mn oxyhydroxides were isolated in situ by vertically inserting inert collectors into the sediments of two geochemically different lakes located near Sudbury, Ontario. X-ray diffraction and electron microscopic analyses indicated that the Fe-rich material collected was predominantly ferrihydrite and poorly crystallized lepidocrocite, while the Mn-rich material was a mixture of poorly crystallized Mn oxyhydroxides. Conditional adsorption constants (KF-M and KMn-M) were calculated using the concentrations of metals (Ca, Cd, Cu, Mg, Ni, Pb, Zn) associated with the Fe- and Mn-rich material and the measured dissolved concentrations of these metals. Comparison of these in situ derived KFe-M and KMn-M values were made with: (1) the hydrolysis constants of the metals; (2) laboratory-derived intrinsic surface complexation constants obtained for adsorption of these metals on well-characterized Fe and Mn oxyhydroxides, and (3) predicted KFe-M and KMn-M values determined using the surface complexation model under the geochemical conditions observed in the lakes. Complexation of these metals with adsorbed natural organic matter was also compared to metal complexation with dissolved natural organic matter. The results are consistent with the scenario that trace metals bind directly to the OH groups of the Fe and Mn oxyhydroxides in circumneutral McFarlane Lake and to the functional groups of organic matter adsorbed on Fe oxyhydroxides in the more acidic (pH = 4.8) Clearwater Lake. Alkaline earth metals Ca and Mg bind, presumably as outer-sphere complexes, to the organic coatings. Our results provide support for the argument that laboratory-derived adsorption datasets may be useful for predicting metal adsorption in the field.
Article
The residual circulation of the Ría de Muros, a large coastal embayment in NW Spain, are studied using a three-dimensional baroclinic finite-difference model. The driving forces considered by the model include the tide, winds, river inflows and density forcing at the open boundary. In situ data of current velocity and direction, water level, wind velocity and direction, river discharge, and temperature and salinity are used for model validation. Simulated and observed time series of water level and current velocity are in good agreement. Once validated, the model is applied to compute the residual circulation induced by the relevant agents of the ría hydrodynamics—the tide, an upwelling-favourable wind characteristic of spring and summer, a downwelling-favourable wind typical of winter, and freshwater inflows associated with high river runoff. The resulting residual circulation differ notably. The tide does not generate significant residual flows except in the inner ría. By contrast, winds and river discharges induce important residual flows throughout; in the middle and outer ría they generate a 3D residual circulation pattern which renders the conventional two-layer scheme of estuarine circulation too simplistic in this case. Thus, this first application of a 3D numerical model to the Ría de Muros sheds new light on its fundamental hydrodynamics.
Article
Magnetic screening in the area of Baia Mare (Romania) was carried out in June 2000 in order to detect the degree of environmental pollution and to test the applicability of this method in this area. With a long tradition of mining activities, a gradual pollution of soil, air and rivers took place continuously in addition to smaller accidents in this area until the dam breakage on the 30.1.2000. During this accident, about 100,000 m3 of mud containing cyanide and heavy metals leaked out and moved over fields and through a village into the river system of Lapûs, Someş, Tisza and Danube.Initial magnetic monitoring carried out during the translocation of the polluted waters along the Bulgarian part of the Danube revealed the effectiveness of the method for a proper and fast identification of pollution both in time and space even at remote distances from the source. For the later pilot project magnetic (χ) screening was performed using a portable Bartington MS2 kappameter with a D-loop sensor. In addition fine-grained material (
Article
This paper presents results of geochemical investigations conducted on three gravity cores recovered along an E-W transect (3 degrees-5 degrees N) in the equatorial Atlantic. Considering the high terrigenous content of the sediments (approximately 12-74 wt%), Al and Ti concentrations are predominantly associated with the input of lithogenous phases. The terrigenous fraction of western equatorial Atlantic sediments is more influenced by material derived from the Amazon River than by deposition of African dust particles. As a possible route of transport, the North Equatorial Countercurrent is considered. Fluctuations in Al/Ti records generally reflect changes in the low-latitude insolation cycle (19-23 kyr) and thus indicate a close coupling to variations of the trade-wind systems and continental climate changes. However, characteristics of the terrigenous signals in the eastern and western equatorial Atlantic differ significantly. While the precessional signal in the Al/Ti record and low latitude portion in the delta(18)O record are in phase in the eastern equatorial Atlantic, variations in the terrigenous fraction westward of the Mid-Atlantic Ridge precede the marine signal by 2-3 kyr, which we ascribe to a shift between trade-wind systems of the Northern and Southern Hemispheres.
Article
Changes in the sources, properties and fluxes of mineral aerosol (‘dust’) have significance as both indicators and agents of climate change, through radiative, cloud condensation and ocean biogeochemical effects. Quaternary aeolian sediments, worldwide in distribution, can comprise high-resolution archives of past climatic and environmental change, by incorporating chronological, physico-chemical and magnetic information.The magnetic record for a sediment sequence may reflect changes in sediment source, and diagenetic (post-depositional) loss and/or transformation and/or gain of magnetic minerals. Each potential pathway requires careful evaluation, to achieve robust understanding of the palaeo-environmental and/or palaeoclimatic information carried by sediment magnetic properties.The most important minerals for studies of aeolian dusts are those carrying a magnetic remanence at room temperature. For the arid zone, the weakly but very magnetically stable minerals, haematite and goethite, form key magnetic tracers for aeolian transport through space and time. Elsewhere, the strongly magnetic ferrimagnets, magnetite and maghemite, arising from lithogenic and/or in situ sources, can dominate sediment magnetic properties. Magnetic measurements, sensitive even to trace concentrations of these iron minerals, can readily discriminate between different magnetic mineral assemblages, and are also relatively rapid, non sample-destructive, and cost-effective. Combined with robust chronological control, magnetic measurements are a powerful means of identifying palaeoclimatic and palaeoenvironmental change from palaeo-dust records. In the case of the classic loess/palaeosol sequences of East Asia, it has been possible to obtain quantitative magnetic climofunctions, enabling spatially- and temporally-dense reconstructions of palaeoprecipitation.
Article
A variety of measures of organic matter concentration and quality were made on samples collected from the top few mm of intertidal mudflat sediment over the course of a year, in order to assess the relative importance of biological and sedimentological influences on sedimentary organic matter. Winter and summer were times of relatively fine-grained sediment accumulation, caused by biological deposition or stabilization processes and resulting in higher organic matter concentrations. Stable carbon isotope and Br:C ratios indicated a planktonic source of bulk organic matter. Ratios of organic carbon to specific surface area of the sediments were consistent with an organic monolayer coverage of sediment grains. Correction for changing grain size during the year showed no change in the organic concentration per unit surface area, in spite of organic matter inputs by in situ primary production, buildup of heterotroph biomass and mucus coatings, and biodeposition of organic-rich seston. There were also no indications of changes in bulk organic quality, measured as hydrolyzable carbohydrates and amino acids, in response to these biological processes. It is concluded that biological processes on a seasonal time scale affect the bulk organic matter of these sediments via a modulation of grain size rather than creation or decay of organic matter.
Article
The effects of the short-term resuspension of a contaminated anoxic estuarine sediment on solid-phase metal speciation have been studied. Preliminary experiments investigated the oxidation rates of model metal sulfide phases to provide mechanistic information for interpreting the observations on the natural sediment. FeS and MnS model phases were particularly labile and oxidized rapidly in aerated waters. In contrast, CdS, CuS, PbS, and ZnS model phases were kinetically stable over periods of several hours. The oxidation rate of free sulfide (HS-) was significantly slower than that of FeS and MnS. Upon sediment resuspension, the rapid decrease in acid volatile sulfide (AVS) could be accounted for by the oxidation of iron monosulfide phases. Over prolonged resuspension periods (>300 min), AVS decreased to values lower than the simultaneously extracted metals [SEM = ∑Cd, Cu, Ni, Pb, Zn (1 M HCl extraction, 30 min)] concentration, indicating that a significant fraction of trace metal sulfide phases may be oxidized during resuspension events. During 8-h sediment resuspension experiments, SEM(Cu) increased from 0.1 to ca. 2 μmol/g while the SEM measured for the other metals remained constant. The increase in SEM(Cu) was shown to be an artifact of the AVS/SEM analytical procedure. Fe(OH)3, formed through the oxidation of FeS, dissolved upon acidification to produce Fe3+(aq), which subsequently oxidized acid-insoluble copper sulfide mineral phases in the sediment. The implications of these observations for natural systems and for the assessment of metal toxicity using AVS/SEM procedures are discussed.
Article
This paper considers the magnetic properties of a range of recent and contemporary sediments from the north eastern part of the Irish Sea. Principal component ordinations of the results show a close link between magnetic property variations and particle size. The magnetic properties of a subset of samples, particles sized by a combination of sieving and pipette analysis, confirm that variations in ferrimagnetic (‘magnetite’) grain size parallel those in particle size, despite the fact that the magnetic grains in the fine grades have diameters 1–2 orders of magnitude smaller than those of the particle size fraction in which they occur. This is best explained by postulating that the fine magnetic grains occur in the clay fraction but are present in declining concentrations in the coarser grades up to 4ø as an artefact of the pipette method. Most samples have a biomodal distribution of magnetic minerals, with a coarse mode associated with heavy minerals in the sands or coarse silts, and a fine mode in the clays. Magnetic susceptibility (x) and saturation isothermal remanent magnetization (SIRM) largely pick out the coarse mode where present; anhysteretic remanent magnetization (ARM) largely picks out the fine mode. The results open up the possibility of normalizing samples from these environments for particle size and, more specifically, clay content, by means of ARM or ARM/x values. The most likely source for the uniform and almost exclusive stable single domain magnetite, which dominates the magnetic properties of the clays, is thought to be bacterial magnetosomes. The measurements as a whole do not appear to hold much promise for discriminating sediment source types.
Article
A detailed magnetic study of mineral dissolution has been carried out in order to better characterise the sedimentary environment in the Ría de Arousa, an estuarine-like system in western Spain. There the large number (>3000) of mussel rafts has resulted in a high influx of organic matter causing a change of the original chemical environment. Magnetic measurements of sediment cores (reaching 4.1 m depth) combined with electron microscopy show that there is a distinctive depth trend for the concentration of magnetic minerals. The different iron oxides dissolve with increasing time and depth and at different rates, so that their relative proportions change. At the same time, pyrite is forming, replacing the iron oxides at shallow depths. The magnetic properties of the sediments indicate a high dissolution rate of magnetite (half-life ⩽5 year) and other iron oxides in a strongly reducing environment. Additionally, goethite and hematite in the studied system seem to be less reactive than magnetite.
Article
The rias of NW Spain are coastal ecosystems of high biological productivity and great economic importance. They are intensively exploited by man for fish and shellfish. There are a number of important centres of population and industrial activity along their margins, which serve as sources of contamination. In this context, it is desirable to achieve the best possible understanding of the physico-chemical processes that control spatial and temporal variations in the geochemical, mineralogical and sedimentological characteristics of near-surface sediments in the Ria de Pontevedra and, in particular, the distribution and mobility of heavy metal contaminants. Thus, adequate environmental planning can be achieved for this site and understanding gained for comparable contexts. Core samples were examined from the inner, middle and outer parts of the ria. Grain-size distributions reflect the presence of two main populations, one dominated by silt and clay, derived mainly from terrestrial sources, and the other by fine sand to coarse silt, which is derived mainly from continental shelf and ria mouth sources. Mineralogical analysis shows an abundance of terrestrial intensive-weathering products near the ria head, a dominance of shelf-derived sediment towards the mouth and the presence of several diagenetic minerals whose nature varies with location within the ria. In the inner ria, the near-surface sediments are slightly enriched in Pb, Cu and Zn from anthropogenic sources. These sediments are fine grained and have a high organic content; hence, they have a higher potential to sorb contaminants than the coarser grained, less organic-rich sediments of the mid and outer ria. The estimated sedimentation rates for the fine-grained organic-rich sediments from the inner part of the ria are about 1 mm year–1. The dominant authigenic minerals in the inner ria are iron sulphides, whereas in the mid and outer ria, iron silicates and oxyhydroxides are more important. These differences in authigenic iron mineralogy are clearly reflected by the magnetic properties of the sediments.
Article
In environmental magnetism, the properties of magnetic minerals are used as proxy parameters for many purposes. Examples are paleoclimate analysis, paleoceanographic studies, provenance studies of sediments, studies of anthropogenically-induced pollution, and archeological investigations. Mineral-magnetic techniques are sensitive, require little sample preparation, are rapid, often grain-size indicative, and usually non-destructive. These techniques involve bulk properties which makes them complementary to geochemical micro-analytical techniques. Measurements include the field- and temperature-dependence of various types of induced and remanent magnetizations. Mineral-magnetic methods are continuously being improved. The underlying causal relations between observed mineral-magnetic properties and the processes that led to those properties, are becoming increasingly better understood, and the extended use of such properties as proxy parameters for many processes is foreseen. The following environmental magnetic applications are reviewed: the analysis of paleoclimatic variations in loess and other sediment types, the untangling of sedimentary features in piston cores, and the interpretation of the anthropogenic impact on the environment, in archeological studies and in studies of present-day pollution. The pathway between the provenance area and depositional site is shown to have a crucial impact on the magnetic properties.
Article
The subtidal sediments of four coastal environments (beach, berm, surf zone and nearshore sea floor) of Kuala Terengganu have been studied in terms of their textural characteristics and depositional process. Sampling and statistical analyses of the grain size distributions of beach, surf zone and shallow sea-floor sediments at various locations along the coastline show that they varied in their mean grain size as well as values of sorting and skewness. The statistical parameters of grain size distributions thus allowed recognition of distinct sub-environments. The size distribution of such sediments suggests that the various processes that are responsible for their transportation and deposition are wave, current and wind action. The different energy conditions and the morphology of each coastal environment seem to be reflected in the characteristics of the sediments in each environment.