Environmental geochemistry of core sediments from Serthalaikkadu creek,East coast of India

The Serthalaikkadu creek in Muthupet mangroves region is the only E–W trending coastal strip in the SE coast of India and it also acts as a barrier to natural disasters. Natural, anthropogenic signals and accumulation of elements were studied by collecting sediments from two cores. Textural parameters were studied in detail and carbonates (CaCO₃), organic carbon (OC), major (Si, Al, Fe, Na, K, Ca, Mg, P) and trace elements (Mn, Cr, Cu, Ni, Co, Pb, Zn) were determined. Textural parameters, CaCO₃, OC and Al-normalized pattern of elements indicate depositional events in core samples that can be directly related to natural events during the last decade. The calculated enrichment, anthropogenic factors and comparison of data indicate that the observed trace metals (especially Pb, Co) are enriched mainly due to the anthropogenic activities in the land as well as in the coastal zone (Palk Strait).     

The geochemistry of iodine in oxidised and reduced recent marine sediments

Surface sediments from the South West Africa shelf and the Gulf of California have been analysed for iodine and organic carbon. The iodine contents range from 96 to 1990 ppm. While iodine and organic carbon show certain anomalies on the South West Africa shelf, the trend of the $\text{I}\text{C}$ ratios is smooth and decreases from the shelf edge, an area of oxidising surface sediment, shorewards to reducing sediments, formed as a result of intense water upwelling. In the Gulf of California, a similar distribution of $\text{I}\text{C}$ ratios with surface sediment type occurs; lowest values occur in the reduced sediments and highest in oxidised sediments. Values of the $\text{I}\text{C}\text{(× 10}{}^4\text{)}$ ratio of the oxidised sediments (~250) are more than an order of magnitude higher than in reduced sediments, and are similar to some other surface oxidised sediments.The high I content of oxidised sediments is mostly due to uptake of I on to plankton seston on the seabed. In reduced sediments, I contained in planktonic matter originating in surface waters forms the bulk of iodine in the sediment.With sediment burial, oxidised sediments lose most of the iodine through degradation of unspecified organic constituents. This does not happen to the same extent in reduced sediments. The geological implications of these reactions are briefly discussed.     

The influence of rivers on the geochemistry of shelf sediments, southwestern coast of India

Geochemical and magnetic susceptibility studies of shelf sediments off Mangalore were carried out to understand the influence of rivers on sediment geochemistry, to study the elemental distribution patterns, and to evaluate the importance of the shelf as a source/sink for base metals. The contents of Cu, Pb, Mn, Fe and Al in the surficial sediments are lower by factors of 1.6–5.6, except Ca which is higher by a factor of 3.4 in relation to riverine suspended particulate matter (SPM). This is due to the seaward decrease of terrigenous influx which is reflected in the offshore protrusion of contours of Al, Fe, Cu, Zn, Ni and magnetic susceptibility values, particularly off Netravati and Gurpur rivers. Lower Mn content is also due to its remobilization from the anoxic-sulphidic shelf sediments. In contrast to the elements mentioned above, Ca increases seaward, suggesting that it is biogenic. The enrichment factor (EF) indicates that the surficial sediments are depleted in Cu, Zn and Mn compared to average shale and other anoxic sediments, and marginally enriched with Ni, Co, and Pb in relation to the average shale. However, a comparison between the EF of SPM of Netravati-Gurpur rivers in the hinterland and surficial sediments indicates that the latter are depleted in Mn and Co, but enriched with Ni, Pb, and Fe, thereby suggesting a source and a sink for the former and latter elements, respectively, to the Arabian Sea.     

The influence of humic substances on the geochemistry of iodine in nearshore and hemipelagic marine sediments

Iodine is characteristically enriched at the surface of hemipelagic and nearshore sediments deposited under oxygenated conditions. In such sediments, bulk I/C_org ratios usually decrease with depth to values which are characteristic of anoxic sediments, reflecting a preferential release of I during early diagenesis. There is some debate as to whether sedimentary I is associated with the iron oxyhydroxide phase or with the organic fraction, and whether the decrease in I/C_org with depth is due to the dissolution of the iron oxyhydroxides or the decomposition of labile organic matter.It is shown that in a surficial hemipelagic sediment sample and in a nearshore sediment core I is mainly associated with the organic fraction and, moreover, that humic substances are involved in the surficial iodine enrichment. Laboratory experiments on the uptake and release of I by and from sedimentary humic substances also suggest a mechanism whereby humic materials reduce iodate at the sediment/water interface to an electrophilic I species which further reacts with the organic matter to produce iodinated organic molecules. During burial, this excess I could be displaced from the organic matrix by nucleophiles such as sulphide ions or thiosulphate, thus providing a possible explanation for the decrease in I/C_org ratio with depth observed in many nearshore and hemipelagic sediments.     

Determination of organochlorine compounds in coastal marine sediments from the southern west of the Mediterranean Sea

Recent evidence suggests that polychlorinated biphenyls might also have adverse reproductive, developmental and endocrine effects. Although, the use of polychlorobiphenyls in Algeria has been banned for more than two decades, large quantities of these compounds containing products remain disseminated, mainly stored in obsolete or damaged equipments. This research describes a study to assess polychlorinated biphenyls distribution in marine sediments collected from the seaside of Tamentfoust touristic resort located in the eastern side of Algiers Bay. After microwave-assisted extraction and purification with both concentrated sulphuric acid and activated silica gel, the extracts were analyzed by gas chromatography with an electron capture detector. Relatively high contamination levels of polychlorinated biphenyls were found in samples collected from the port of Tamentfoust (15 to 70 ng/g d.w.), while the concentrations were lower in the stations located outside the port (0 to 26 ng/g d.w.). Compared with data previously reported by some other researchers, the polychlorobiphenyls concentrations found in this work showed an environmental persistence, but a decrease of approximately 5 times in 30 year i.e since the ban of the use of polychlorinated biphenyls. The predominant polychlorinated biphenyls congeners in all sediment samples were polychlorinated biphenyls138, 153, 180 and 187. This composition was similar to industrial mixture (Aroclor 1260). This probably indicated that the contamination originated from the port and has a continental source.     

Nature and geochemistry of surface sediments of the mangrove environment along the Egyptian Red Sea coast

Grain size and geochemical analyses have been carried out on 58 samples collected from different areas of mangrove environment of the Egyptian Red Sea coast. The texture characteristics of mangrove sediments show that the mean size decreases in sediments of coastal areas while increase in island sediments and the sediment type generally changes from sand to slightly gravelly muddy sand. The sediments are composed mainly of poorly sorted, negatively nearly symmetrical and leptokurtic fine sands. Cluster analysis showed that, distribution of gravel, sand and mud fractions is related to bottom facies and type of sediment source. Generally, sand fraction is the main category among the three constituents. Geochemically the factor controlling the carbonate content of studied sediments includes material supply of biogenic and terrigenous components. Therefore, sediments of Hamata area, km 17 south Safaga, Wadi El-Gemal Island and Abu-Minqar Island are terrigenous sediments, while sediments of km 37 north Quseir are highly carbonates. In general organic matter is higher in the mangrove sediments relative to adjacent areas. The high organic matter in the mangrove sediments is primarily due to the high supply from primary productivity, terrestrial and reworked sediments. Texture is the main controlling factor for the organic matter enrichment. Spatial variations in the phosphorus content in the different studied localities are related to the sources of phosphorus to the area. In comparison, cluster analysis indicates that phosphorus might be transported from terrestrial source to the sea through wadis draining the excavated Upper Cretaceous phosphate rocks. Also, the abundance of phosphorus content may be attributed to phosphatization of calcareous skeletons. Our observations provide knowledge on the physico-chemical effects and will be useful in the management and suitable development of the areas under study. In addition it represent database in the future.     

Luminescence dating of well-sorted marine terrace sediments on the southeastern coast of Korea

Along the southeastern coastline of the Korean peninsula, well-developed marine terraces are found at various elevations. The ages of these terraces, and the time of deposition of the terrace sediments are important to our understanding of the geological history of this area during the Quaternary period, and represent a unique record of the regional tectonic activity. Previous efforts to establish a chronology using optically stimulated luminescence (OSL) methods have produced controversial results, particularly because of stratigraphic inconsistency and poor reproducibility. In this paper, the application of OSL dating based on the single-aliquot regenerative-dose (SAR) protocol for quartz is investigated. The dependence of equivalent dose on the preheat and cut-heat temperatures (thermal treatment of the regeneration and test-doses, respectively) are examined. Linearly modulated luminescence signals from chemically cleaned quartz samples are used to identify the presence of a thermally unstable component with a large optical cross-section (component A′), which in part affects the ability to correct for sensitivity changes during measurements, and thus the reliability of the equivalent dose estimates. In some samples, a higher heat treatment after the test-dose is shown to improve our ability to measure a dose given in the laboratory before any heat treatment (dose recovery test). This higher temperature treatment effectively removes component A′, and hence improves sensitivity correction. Furthermore, the samples were broadly divided into poorly sorted and well-sorted, based on field evidence. The poorly sorted samples contain friable, weathered gravel clasts, which is a likely post-depositional source of quartz grains. In general, these grains will not have been zeroed prior to deposition, and so the poorly sorted samples are rejected from further age studies. Results obtained from the well-sorted samples are reproducible at each sampling location, and give ages grouping broadly into 50–70 and 110–120 ka, but laterally discontinuous on a scale of tens of km. Our OSL results for the younger group are supported by radiocarbon ages from overlying terrestrial deposits. It is concluded that these results point to considerable tectonic activity in the southeast of Korea during the Late Pleistocene.     

A geochemical and statistical approach for assessing heavy metal pollution in sediments from the southern Caspian coast

The nearshore marine environment of the Caspian sea is a major repository for toxic metals originating from various sources. Since the persistent toxic metals pose serious health risks this research concentrated on investigating the concentrations and spatial distribution of metals in the nearshore sediments along the Iranian coast of the Caspian sea. Fourteen sampling sites were selected along the coast and approximately 400 g of surficial sediments were obtained. Samples were sieved and three grain size fractions from each sample plus fourteen bulk samples were selected for the analysis of metals. Laboratory analysis of the samples utilized the Cold Acetic protocol, followed by Inductively coupled plasma optical emission spectroscopy. The statistical techniques were used to analyze all obtained data. Linear regression analysis demonstrated that grain size of the sediments was not a major factor controlling the concentrations and spatial distributions of heavy metals. Box and Whisker plots emphasized that metal concentrations were not homogeneously distributed. Discriminant analysis was also proved to be useful in identifying geographic areas where heavy metal concentrations occur along the coast.     

Texture and geochemistry of the sediments of a tropical mangrove ecosystem,southwest coast of India

The textural and geochemical aspects of the sediments of a tropical mangrove ecosystem have been studied and discussed. The sediments are characterized by the abundance of silt and sand with minor amounts of clay. The mean size of the sediment ranges from 0.205 mm to 0.098 mm (fine to very fine grained sand). The sediments are very poorly sorted, negatively to very negatively skewed, and platy to extremely leptokurtic in nature. The organic carbon content of the sediments ranges from 0,33% to 4.93%, which is controlled by the particle size of the sediments. The CaCO₃ content is five times the enrichment of organic carbon. This enhanced CaCO₃ content of the mangrove sediments might be a result of the abundance of shell fragments in the sediments. The shell mining activities in the estuarine bed adjoining the Kumarakam mangroves also contribute a substantial amount of lime muds to the mangrove area, which in turn add CaCO₃ to the sediments. The relative concentrations of heavy metals are Fe > Mn > Cr > Zn > Ni > Cu. All heavy metals other than Fe show an increase in concentration compared to the other parts of the estuarine bed. Cluster analysis indicates that the contents of organic C, Fe and Mn have a marked bearing on the Cr, Zn, Ni, and Cu levels of the mangrove sediments.     

Lignin geochemistry of sediments from the Narragansett Bay Estuary

Cupric oxide oxidation has been employed to characterize the lignin geochemistry of Narragansett Bay sediments. Lignin concentrations throughout the estuary are low when expressed on a carbon-normalized basis, but can be characterized as enriched when expressed on a mass-normalized basis. This implies substantial dilution of the sedimentary lignin by inputs of lignin-poor carbon. Lignin concentrations do not correlate with the ¹³C isotopic composition of the sedimentary organic matter. These results are consistent with a sediment lignin component consisting of varying amounts of vascular plant debris and lignin-depleted organic matter, the latter originating from both marine (planktonic) and terrestrial (uncharacterized) sources. Compositional plots of lignin-derived phenols show that sediments in the upper estuary are influenced to a greater extent by gymnosperm lignin sources than those in the mid-and lower estuary. Given the extent to which the upper estuary is affected by pollution sources, inputs from anthropogenic discharges are the most likely cause of these compositional differences. However, an evaluation of processed paper products as an “anthropogenic” lignin source indicates that the lignin content of these materials is insufficient to account for the levels found in the sediments. Subsurface lignin compositions at an upper estuary site reveal that lignin originating from the inferred anthropogenic sources disappears at a depth shallower than that which would be expected based on the distribution of other trace organic pollutants (hydrocarbons and several synthetic organic compounds). We speculate that differences in either the depositional history or the degree of preservation of these two compound classes are responsible for the observed trends.     

Geochemistry of Jizan shelf sediments, southern Red Sea coast of Saudi Arabia

Surface sediments from the Jizan shelf, southern Red Sea, were analysed for grain size and mineralogical and elemental composition in order to establish their geochemical characteristics. Texturally, sediments are classified into sand and mud; the latter dominates the shelf. Grain size variability and mineralogical assemblages present in the sediments largely control the abundance and distribution of CaCO₃, organic carbon content (OC) and the major and trace elements. Sand sediments are composed of carbonate material of marine origin and contain high concentrations of Ca, Mg and Sr. Mud sediments are relatively rich in OC and are characterised by high concentrations of Al, Fe, Ti, Mn, Cu, Cr, Co, Ni, V and Ba. Unlike the sand, Mg concentration in the mud sediments seems to be controlled by stronger contribution from non-carbonate material. Factor analysis is applied to identify the variables accounting for most of the variance in the mud sediment samples. Three factors are found to describe about 78% of the variance. The first factor which accounts for 41% of the total variance is the Fe and Mn oxides that reach the area through episodic flooding. The second and third factors are the mud (22%) and the mineralogy (15%) of the sediments, respectively.     

Uranium geochemistry in groundwater from tertiary sediments

Dissolved U concentrations and activity ratios (ARs) of the U isotopes in the ²³⁸U decay series were measured in ground and surface waters as part of an investigation to delineate the water quality in a proposed uranium mining area of northwest Nebraska. In oxidizing groundwaters from 67 wells completed in the Tertiary sediments, increasing U concentrations in the direction of groundwater flow generally were associated with a maturation of the formation water as evidenced by evolutionary trends in major ion character. The increased U levels probably are associated with leaching as shown by the positive correlation between U concentrations and total dissolved solids (TDS) (r = +0.83). The inverse relationships between TDS and U ARs (r = ?0.73) and U levels and ARs (r = 0.72) indicate that the decay of excess U-234 is related to maturation of the formation water and to sediment leaching along the flowpath. The data are described by a model which incorporates etching, decay and recoil and suggests that aquifer residence time can be estimated from the TDS level.The levels of soluble U in a reducing uraniferous hydrogeologic unit near Crawford, Nebraska are affected by the proximity of the sample collection to ore. In groundwater samples having similar chemistries (Na-SO₄ + Cl type), similar Ehs, and collected from a close-knit pattern, U concentrations ranged from 0.01 to 2,037 μg l^?1 and ARs ranged from 0.75 to 12.6. This high variability in U levels and ARs is indicative of uranium ore in small areal studies where low ARs almost always are associated with high U concentrations.     

Earthquake-induced burial of archaeological sites along the southern Washington coast about A.D. 1700

Although inhabited by thousands of people when first reached by Europeans, the Pacific coast of southern Washington has little recognized evidence of prehistoric human occupation. This apparent contradiction may be explained partly by geologic evidence for coastal submergence during prehistoric earthquakes on the Cascadia subduction zone. Recently discovered archaeological sites, exposed in the banks of two tidal streams, show evidence for earthquake-induced submergence and consequent burial by intertidal mud about A.D. 1700. We surmise that, because of prehistoric earthquakes, other archaeological sites may now lie hidden beneath the surfaces of modern tidelands. Such burial of archaeological sites raises questions about the estimation of prehistoric human population densities along coasts subject to earthquake-induced submergence. © 1996 John Wiley & Sons, Inc.     

Albeluvisol development with time in loamy marine sediments of southern Norway

This paper reports a study on soil development in loamy marine sediments on both sides of the Oslofjord (Vestfold, Østfold). This region has been subject to steady glacio-isostatic uplift during the whole Holocene. Hence, land surface age continuously increases from the coast inland. Several sea level curves, based on radiocarbon datings, enable estimation of land surface age for all locations. Clay illuviation starts in less than 1650 years. E horizons become lighter with age, but their lower boundary stays around 40 cm for more than 10 000 years. Albeluvic tongues develop between 4600 and 6200 years. Initially, they form along intersections of cracks. As preferential flow and leaching along the cracks continues, the tongues increase in length and width, progressively consuming the prisms between the cracks in the upper Bt horizon. The Fe_d/Fe_t ratios (weighted means of the upper meter) show a clear linear increase with soil age and may be used for “pedo-dating”, i.e. for estimating the ages of non-dated land surfaces covered with similar sediments. In contrast, the logarithmic decrease of base saturation and pH, with rapid changes in the first time but only very slight changes between 2000 and 10 000 years, makes these parameters unsuitable for “pedo-dating”.     

Surface carbonate and land-derived clastic marine sediments from southern Chile: mineralogical and geochemical investigation

Surface carbonate and land-derived deposits in the sea off southern Chile were investigated for their mineralogical and geochemical composition. The data were related to environmental features and compared with those of similar temperate and polar carbonate deposits from Tasmania, New Zealand, Arctica, and Antarctica. The mineralogy of the siliciclastic fraction is typical of cold areas and is mainly composed of chlorite, mica, quartz, feldspars and amphibole. The CaCO₃ content varies from 30 to 90%; carbonate mineralogy is made up of low-Mg calcite, high-Mg calcite and minor amounts of aragonite. The Ca, Mg, Sr, Fe, and Mn contents of bulk carbonates and some selected skeletal hard parts are comparable to those of carbonates from Tasmania. The elemental composition is mainly related to carbonate mineralogy, skeletal components, and seawater conditions. The δ¹³C and δ¹⁸O values of carbonates are positive, and their field falls between the “seafloor diagenesis” and “upwelling water” trend lines, because the sediments are likely to be in equilibrium with waters of Antarctic origin. The mineralogical, elemental, and isotopic compositions of carbonates from southern Chile show better similarities with the “temperate” carbonates from Tasmania and New Zealand than with the “polar” carbonates from Arctica and Antarctica. Carbonate deposition is allowed by the low terrigenous input, the low SPM concentration and, probably, the upwelling of seawater from Antarctica.     

The aquatic geochemistry of arsenic in volcanic groundwaters from southern Italy

This paper discusses the abundance, speciation and mobility of As in groundwater systems from active volcanic areas in Italy. Using literature data and new additional determinations, the main geochemical processes controlling the fate of As during gas–water–rock interaction in these systems are examined. Arsenic concentrations in the fluids range from 0.1 to 6940 μg/l, with wide differences observed among the different volcanoes and within each area. The dependence of As content on water temperature, pH, redox potential and major ions is investigated. Results demonstrate that As concentrations are highest where active hydrothermal circulation takes place at shallow levels, i.e. at Vulcano Island and the Phlegrean Fields. In both areas the dissolution of As-bearing sulphides is likely to be the main source of As. Mature Cl-rich groundwaters, representative of the discharge from the deep thermal reservoirs, are typically enriched in As with respect to SO₄-rich “steam heated groundwaters”. In the HCO₃⁻ groundwaters recovered at Vesuvius and Etna, aqueous As cycling is limited by the absence of high-temperature interactions and by high-Fe content of the host rocks, resulting in oxidative As adsorption. Thermodynamic modelling suggests that reducing H₂S-rich groundwaters are in equilibrium with realgar, whereas in oxidising environments over-saturation with respect to Fe oxy-hydroxides is indicated. Under these oxidising conditions, As solubility decreases controlled by As co-precipitation with, or adsorption on, Fe oxy-hydroxides. Consistent with thermodynamic considerations, As mobility in the studied areas is enhanced in intermediate redox environments, where both sulphides and Fe hydroxides are unstable.     

Heavy metal pollution assessment in marine sediments in the Northwest coast of Sabah,Malaysia

Heavy metal contents along the Northwest coast of Sabah were determined to interpret the pollution level in the marine sediment. The metal abundance is regulated by the physico-chemical properties such as the average sediment pH(7.82, 9.00 and 8.99), organic matter(0.62%, 1.60%, and 2.27%), moisture content(25.00%, 29.70%, and 15.00%) and sandy texture in Kota Belud, Kudat and Mantanani Island,respectively. The major elements show Ca>Fe>Mg>Al>Mn for all study sites, while the heavy m...